Characteristics of Short Wavelength Compressional Alfven Eigenmodes
Fredrickson, E D; Podesta, M; Bortolon, A; Crocker, N A; Gerhardt, S P; Bell, R E; Diallo, A; LeBlanc, B; Levinton, F M
2012-12-19
Most Alfvenic activity in the frequency range between Toroidal Alfven Eigenmodes and roughly one half of the ion cyclotron frequency on NSTX [M. Ono, et al., Nucl. Fusion 40 (2000) 557], that is, approximately 0.3 MHz up to ≈ 1.2 MHz, are modes propagating counter to the neutral beam ions. These have been modeled as Compressional and Global Alfven Eigenmodes (CAE and GAE) and are excited through a Doppler-shifted cyclotron resonance with the beam ions. There is also a class of co-propagating modes at higher frequency than the counter-propagating CAE and GAE. These modes have been identified as CAE, and are seen mostly in the company of a low frequency, n=1 kink-like mode. In this paper we present measurements of the spectrum of these high frequency CAE (hfCAE), and their mode structure. We compare those measurements to a simple model of CAE and present evidence of a curious non-linear coupling of the hfCAE and the low frequency kink-like mode.
Theory and Observations of High Frequency Alfven Eigenmodes in Low Aspect Ratio Plasma
N.N. Gorelenkov; E. Fredrickson; E. Belova; C.Z. Cheng; D. Gates; S. Kaye; R. White
2003-06-27
New observations of sub-cyclotron frequency instability in low aspect ratio plasma in National Spherical Torus Experiments (NSTX) are reported. The frequencies of observed instabilities correlate with the characteristic Alfven velocity of the plasma. A theory of localized Compressional Alfven Eigenmodes (CAE) and Global shear Alfven Eigenmodes (GAE) in low aspect ratio plasma is presented to explain the observed high frequency instabilities. CAE's/GAE's are driven by the velocity space gradient of energetic super-Alfvenic beam ions via Doppler shifted cyclotron resonances. One of the main damping mechanisms of GAE's, the continuum damping, is treated perturbatively within the framework of ideal MHD. Properties of these cyclotron instabilities ions are presented.
Toroidal Alfven eigenmode-induced ripple trapping
White, R.B.; Fredrickson, E.; Darrow, D.; Zarnstorff, M.; Wilson, R.; Zweben, S.; Hill, K.; Chen, Y.; Fu, G.
1995-08-01
Toroidal Alfven eigenmodes are shown to be capable of inducing ripple trapping of high-energy particles in tokamaks, causing intense localized particle loss. The effect has been observed in TFTR [R. Hawryluk, Plasma Phys. Controlled Fusion {bold 33}, 1509 (1991)]. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Continuum damping of ideal toroidal Alfven eigenmodes
Zhang, X.D.; Zhang, Y.Z.; Mahajan, S.M.
1993-08-01
A perturbation theory based on the two dimensional (2D) ballooning transform is systematically developed for ideal toroidal Alfven eigenmodes (TAEs). A formula, similar to the Fermi golden rule for decaying systems in quantum mechanics, is derived for the continuum damping rate of the TAE; the decay (damping) rate is expressed explicitly in terms of the coupling of the TAE to the continuum spectrum. Numerical results are compared with previous calculations. It is found that in some narrow intervals of the parameter m{cflx {epsilon}} the damping rate varies very rapidly. These regions correspond precisely to the root missing intervals of the numerical solution by Rosenbluth et al.
Alfven Continuum and Alfven Eigenmodes in the National Compact Stellarator Experiment
Fesenyuk, O. P.; Kolesnichenko, Ya. I.; Lutsenko, V. V.; White, R. B.; Yakovenko, Yu. V.
2004-09-17
The Alfven continuum (AC) in the National Compact Stellarator Experiment (NCSX) is investigated with the AC code COBRA. The resonant interaction of Alfven eigenmodes and the fast ions produced by neutral beam injection is analyzed. Alfven eigenmodes residing in one of the widest gaps of the NCSX AC, the ellipticity-induced gap, are studied with the code BOA-E.
Kinetic Alfven eigenmodes in JET and DIII-D
Jaun, A.; Hellsten, T.; Heidbrink, W.W.; Carolipio, E.
1996-12-31
Kinetic effects are studied for global Alfven eigenmodes in realistic tokamak equilibria with finite aspect ratio and plasmas, comparing calculations from the full wave code PENN with experimental measurements. The kinetic plasma model is based on a Larmor radius expansion in toroidal geometry and takes into account the gradients in the equilibrium density and temperatures. It allows for a consistent description of the mode conversion to the kinetic Alfven wave (KAW) and the effect of diamagnetic drifts on electromagnetic waves. Comparisons axe first carried out for a JET discharge, showing that multiple peeks measured in the low frequency Alfven spectrum are the signature of kinetic Alfven eigenmodes (KAE) induced through coupling between a global ellipticity Alfven eigenmode (EAE) and the KAW. In general, series of modes appear in the proximity of global fluid modes, some with a regular spacing in frequency and a very weak Landau damping of {vert_bar}{gamma}/{omega}{vert_bar} {approx_equal} 0.0007. A kinetic analysis of a DIII-D discharge shows that TAE mode wavefields reach the plasma core through electromagnetic drift waves which propagate because of finite temperature gradients in the regions of small k{sub {parallel}}. They can lead to particle diffusion and may explain the large losses of beam ions observed during the TAE instabilities. Comparisons of frequency and eigenmode structure axe carried out for resistive and kinetic models, between the theoretical calculations using the PENN code and the experimental measurements from magnetic probes.
Conventional and nonconventional global Alfven eigenmodes in stellarators
Kolesnichenko, Ya. I.; Lutsenko, V. V.; Weller, A.; Werner, A.; Yakovenko, Yu. V.; Geiger, J.; Fesenyuk, O. P.
2007-10-15
Conditions of the existence of the Global Alfven Eigenmodes (GAE) and Nonconventional Global Alfven Eigenmodes (NGAE) predicted for stellarators by Ya. I. Kolesnichenko et al. [Phys. Rev. Lett. 94, 165004 (2005)] have been obtained. It is found that they depend on the nature of the rotational transform and that conditions for NGAE can be most easily satisfied in currentless stellarators. It is shown that the plasma compressibility may play an important role for the modes with the frequency about or less than that of the Toroidicity-induced Alfven Eigenmodes. It is found that features of the Alfven continuum in the vicinity of the k{sub parallel}=0 radius (k{sub parallel}) is the longitudinal wave number) can be very different, depending on a parameter which we refer to as 'the sound parameter'. Specific calculations modeling low-frequency Alfven instabilities in the stellarator Wendelstein 7-AS [A. Weller et al., Phys. Plasmas 8, 931 (2001)] are carried out, which are in reasonable agreement with the observations. It is emphasized that experimental data on low-frequency Alfvenic activity can be used for the reconstruction of the profile of the rotational transform. The mentioned results are obtained with the use of the equations derived in this paper for the GAE/NGAE modes and of the codes COBRAS and BOA-fe.
Finite Pressure Effects on Reversed Shear Alfven Eigenmodes
G.J. Kramer; N.N. Gorelenkov; R. Nazikian; C.Z. Cheng
2004-09-03
The inclusion of finite pressure in ideal-magnetohydrodynamic (MHD) theory can explain the Reversed magnetic Shear Alfven Eigenmodes (RSAE) (or Alfven cascades) that have been observed in several large tokamaks without the need to invoke the energetic particle mechanism for the existence of these modes. The chirping of the RSAEs is cased by changes in the minimum of the magnetic safety factor, q(sub)min, while finite pressure effects explains the observed non-zero minimum frequency of the RSAE when qmin has a rational value. Finite pressure effects also play a dominant role in the existence of the downward chirping RSAE branch.
Spectroscopic determination of kinetic parameters for frequency sweeping Alfven eigenmodes
Lesur, M.; Idomura, Y.; Shinohara, K.; Garbet, X.
2010-12-15
A method for analyzing fundamental kinetic plasma parameters, such as linear drive and external damping rate, based on experimental observations of chirping Alfven eigenmodes, is presented. The method, which relies on new semiempirical laws for nonlinear chirping characteristics, consists of fitting procedures between the so-called Berk-Breizman model and the experiment in a quasiperiodic chirping regime. This approach is applied to the toroidicity induced Alfven eigenmode (TAE) on JT-60 Upgrade (JT-60U) [N. Oyama et al., Nucl. Fusion 49, 104007 (2009)], which yields an estimation of the kinetic parameters and suggests the existence of TAEs far from marginal stability. Two collision models are considered, and it is shown that dynamical friction and velocity-space diffusion are essential to reproduce nonlinear features observed in experiments. The results are validated by recovering measured growth and decay of perturbation amplitude and by estimating collision frequencies from experimental equilibrium data.
Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes
N.N. Gorelenkov, G.J. Kramer, and R. Nazikian
2011-05-23
A theory of Reversed Shear Alfven Eigenmodes (RSAEs) is developed for reversed magnetic field shear plasmas when the safety factor minimum, qmin, is at or above a rational value. The modes we study are known sometimes as either the bottom of the frequency sweep or the down sweeping RSAEs. We show that the ideal MHD theory is not compatible with the eigenmode solution in the reversed shear plasma with qmin above integer values. Corrected by special analytic FLR condition MHD dispersion of these modes nevertheless can be developed. Large radial scale part of the analytic RSAE solution can be obtained from ideal MHD and expressed in terms of the Legendre functions. The kinetic equation with FLR effects for the eigenmode is solved numerically and agrees with the analytic solutions. Properties of RSAEs and their potential implications for plasma diagnostics are discussed.
MAGNETOSEISMOLOGY: EIGENMODES OF TORSIONAL ALFVEN WAVES IN STRATIFIED SOLAR WAVEGUIDES
Verth, G.; Goossens, M.; Erdelyi, R. E-mail: Marcel.Goossens@wis.kuleuven.b
2010-05-10
There have recently been significant claims of Alfven wave observation in the solar chromosphere and corona. We investigate how the radial and longitudinal plasma structuring affects the observational properties of torsional Alfven waves in magnetic flux tubes for the purposes of solar magnetoseismology. The governing magnetohydrodynamic equations of these waves in axisymmetric flux tubes of arbitrary radial and axial plasma structuring are derived and we study their observable properties for various equilibria in both thin and finite-width magnetic flux tubes. For thin flux tubes, it is demonstrated that observation of the eigenmodes of torsional Alfven waves can provide temperature diagnostics of both the internal and surrounding plasma. In the finite-width flux tube regime, it is shown that these waves are the ideal magnetoseismological tool for probing radial plasma inhomogeneity in solar waveguides.
Alfven continuum and Alfven eigenmodes in the National Compact Stellarator Experiment
Fesenyuk, O.P.; Kolesnichenko, Ya.I.; Lutsenko, V.V.; White, R.B.; Yakovenko, Yu.V.
2004-12-01
The Alfven continuum (AC) in the National Compact Stellarator Experiment (NCSX) [G. H. Neilson et al., in Fusion Energy 2002, 19th Conference Proceedings, Lyon, 2002 (International Atomic Energy Agency, Vienna, 2003), Report IAEA-CN-94/IC-1] is investigated with the AC code COBRA [Ya. I. Kolesnichenko et al., Phys. Plasmas 8, 491 (2001)]. The resonant interaction of Alfven eigenmodes and the fast ions produced by neutral beam injection is analyzed. Alfven eigenmodes residing in one of the widest gap of the NCSX AC, the ellipticity-induced gap, are studied with the code BOA-E [V. V. Lutsenko et al., in Fusion Energy 2002, 19th Conference Proceedings, Lyon, 2002 (International Atomic Energy Agency, Vienna, 2003), Report IAEA-CN-94-TH/P3-16].
Effect of alpha particles on Toroidal Alfven Eigenmodes
Berk, H.L.
1992-11-01
An overview is given of the analytic structure for the linear theory of the Toroidal Alfven Eigenmode (TAE), where multiple gap structures occur. A discussion is given of the alpha particle drive and the various dissipation mechanisms that can stabilize the system. A self-consistent calculation of the TAE mode, for a low-beta high-aspect-ratio plasma, indicates that though the alpha particle drive is comparable to the dissipation mechanisms, overall stability is still achieved for ignited ITER-like plasma. A brief discussion is given of the nonlinear theory for the TAE mode and how nonlinear alpha particle dynamics can be treated by mapping methods.
Kinetic theory of toroidicity and ellipticity-induced Alfven eigenmodes
NASA Astrophysics Data System (ADS)
Mett, R. R.; Mahajan, S. M.
1992-10-01
Toroidicity-induced Alfven eigenmodes (TAE) and ellipticity-induced Alfven eigenmodes (EAE) are currently of great interest because they may destroy the confinement of fast ions in a burning tokamak plasma. The present study focuses on kinetic effects, extending the non-perturbative kinetic analysis of the TAE to the EAE. One finds that the parameter which measures the kinetic character of the EAE is significantly smaller than it is for the TAE for elongated plasmas like DIII-D. The parameter is rather small for the lower mode numbers but attains values of order unity or larger for the higher mode numbers, since the parameter scales as the square of the mode number. Consequently, one expects the lower mode number EAE's to have a strongly magnetohydrodynamic (MHD) character, and to suffer only perturbative damping that depends linearly on the dissipative mechanisms. However, while the former is true, the latter is not necessarily the case. This work examines these kinetic T/EAE(KT/EAE) modes in further detail.
On Properties of Compressional Alfven Eigenmode Instability Driven by Superalfvinic Ions
N.N. Gorelenkov; C.Z. Cheng
2002-02-06
Properties of the instability of Compressional Alfven Eigenmodes (CAE) in tokamak plasmas are studied in the cold plasma approximation with an emphasis on the instability driven by the energetic minority Ion Cyclotron Resonance Heating (ICRH) ions. We apply earlier developed theory [N.N. Gorelenkov and C.Z. Cheng, Nuclear Fusion 35 (1995) 1743] to compare two cases: Ion Cyclotron Emission (ICE) driven by charged fusion products and ICRH Minority driven ICE (MICE) [J. Cottrell, Phys. Rev. Lett. (2000)] recently observed on JET [Joint European Torus]. Particularly in MICE spectrum, only instabilities with even harmonics of deuterium-cyclotron frequency at the low-field-side plasma edge were reported. Odd deuterium-cyclotron frequency harmonics of ICE spectrum between the cyclotron harmonics of protons can be driven only via the Doppler-shifted cyclotron wave-particle resonance of CAEs with fusion products, but are shown to be damped due to the electron Landau damping in experiments on MI CE. Excitation of odd harmonics of MICE with high-field-side heating is predicted. Dependencies of the instability on the electron temperature is studied and is shown to be strong. Low electron temperature is required to excite odd harmonics in MICE.
Gyrokinetic particle simulation of beta-induced Alfven eigenmode
Zhang, H. S.; Lin, Z.; Holod, I.; Xiao, Y.; Wang, X.; Zhang, W. L.
2010-11-15
The beta-induced Alfven eigenmode (BAE) in toroidal plasmas is studied using global gyrokinetic particle simulations. The BAE real frequency and damping rate measured in the initial perturbation simulation and in the antenna excitation simulation agree well with each other. The real frequency is slightly higher than the ideal magnetohydrodynamic (MHD) accumulation point frequency due to the kinetic effects of thermal ions. Simulations with energetic particle density gradient show exponential growth of BAE with a growth rate sensitive to the energetic particle temperature and density. The nonperturbative contributions by energetic particles modify the mode structure and reduce the frequency relative to the MHD theory. The finite Larmor radius effects of energetic particles reduce the BAE growth rate. Benchmarks between gyrokinetic particle simulation and hybrid MHD-gyrokinetic simulation show good agreement in BAE real frequency and mode structure.
Existence of core localized toroidicity-induced Alfven eigenmode
Fu, G.Y. )
1995-04-01
The core-localized toroidicity-induced Alfven eigenmode (TAE) is shown to exist at finite plasma pressure due to finite aspect ratio effects in tokamak plasma. The new critical beta for the existence of the TAE mode is given by [alpha][approx]3[epsilon]+2[ital s][sup 2], where [epsilon]=[ital r]/[ital R] is the inverse aspect ratio, [ital s] is the magnetic shear and [alpha]=[minus][ital Rq][sup 2][ital d][beta]/[ital dr] is the normalized pressure gradient. In contrast, previous critical [alpha] is given by [alpha][approx][ital s][sup 2]. In the limit of [ital s][much lt][radical][ital r]/[ital R], the new critical [alpha] is greatly enhanced by the finite aspect ratio effects.
Existence of core localized toroidicity-induced Alfven eigenmode
Fu, G.Y.
1995-02-01
The core-localized toroidicity-induced Alfven eigenmode (TAE) is shown to exist at finite plasma pressure due to finite aspect ratio effects in tokamak plasma. The new critical beta for the existence of the TAE mode is given by {alpha}{approx} 3{epsilon} + 2s{sup 2}, where {epsilon} = r/R is the inverse aspect ratio, s is the magnetic shear and {alpha} = -Rq{sup 2}d{beta}/dr is the normalized pressure gradient. In contrast, previous critical {alpha} is given by {alpha} {approx} s{sup 2}. In the limit of s << {radical}r/R, the new critical {alpha} is greatly enhanced by the finite aspect ratio effects.
Evolution of toroidal Alfven eigenmode instability in TFTR
Wong, K.L.; Majeski, R.; Petrov, M.
1996-07-01
The nonlinear behavior of the Toroidal Alfven Eigenmode (TAE) driven unstable by energetic ions in TFTR is studied. The evolution of instabilities can take on several scenarios: a single mode or several modes can be driven unstable at the same time, the spectrum can be steady or pulsating and there can be negligible or anomalous loss associated with the instability. This paper presents a comparison between experimental results and recently developed nonlinear theory. The authors find many features observed in experiment are compatible with the consequences of the nonlinear theory. Examples include the structure of the saturated pulse that emerges from the onset of instability of a single mode and the decrease but persistence of TAE signals when the applied rf power is reduced or shut off.
Asymmetric radiative damping of low shear toroidal Alfven eigenmodes
Nyqvist, R. M.; Sharapov, S. E.
2012-08-15
Radiative damping of toroidicity-induced Alfven eigenmodes (TAEs) in tokamaks, caused by coupling to the kinetic Alfven wave (KAW), is investigated analytically in the limit of low magnetic shear. A significant asymmetry is found between the radiative damping of the odd TAE, whose frequency lies above the central TAE gap frequency {omega}{sub 0}, and that of the even TAE, with frequency {omega}<{omega}{sub 0}. For the even TAE, which consists of a symmetric combination of neighboring poloidal harmonics (and therefore has ballooning-type mode structure), the coupling results in two non-overlapping, outgoing fluxes of KAWs that propagate radially away from each other and the TAE localization region. In contrast, the odd TAE consists of an antisymmetric combination of neighboring poloidal harmonics, resulting in anti-ballooning mode structure. For this mode, the KAWs initially propagate towards each other and form an interference pattern in the TAE localization region, resulting in a negligibly small escaping flux and a correspondingly low radiative damping rate. As a result of the up/down asymmetry in radiative damping with respect to the mode frequency, the odd TAE may be destabilized by fusion born alpha particles more easily than the usual, even TAE.
Alpha particle destabilization of the toroidicity-induced Alfven eigenmodes
Cheng, C.Z.
1990-10-01
The high frequency, low mode number toroidicity-induced Alfven eigenmodes (TAE) are shown to be driven unstable by the circulating and/or trapped {alpha}-particles through the wave-particle resonances. Satisfying the resonance condition requires that the {alpha}-particle birth speed v{sub {alpha}} {ge} v{sub A}/2{vert bar}m-nq{vert bar}, where v{sub A} is the Alfven speed, m is the poloidal model number, and n is the toroidal mode number. To destabilize the TAE modes, the inverse Landau damping associated with the {alpha}-particle pressure gradient free energy must overcome the velocity space Landau damping due to both the {alpha}-particles and the core electrons and ions. The growth rate was studied analytically with a perturbative formula derived from the quadratic dispersion relation, and numerically with the aid of the NOVA-K code. Stability criteria in terms of the {alpha}-particle beta {beta}{sub {alpha}}, {alpha}-particle pressure gradient parameter ({omega}{sub {asterisk}}/{omega}{sub A}) ({omega}{sub {asterisk}} is the {alpha}-particle diamagnetic drift frequency), and (v{sub {alpha}}/v{sub A}) parameters will be presented for TFTR, CIT, and ITER tokamaks. The volume averaged {alpha}-particle beta threshold for TAE instability also depends sensitively on the core electron and ion temperature. Typically the volume averaged {alpha}-particle beta threshold is in the order of 10{sup {minus}4}. Typical growth rates of the n=1 TAE mode can be in the order of 10{sup {minus}2}{omega}{sub A}, where {omega}{sub A}=v{sub A}/qR. Other types of global Alfven waves are stable in D-T tokamaks due to toroidal coupling effects.
Observation of Reversed-Shear Alfven Eigenmodes Excited by Energetic Ions in a Helical Plasma
Toi, K.; Tokuzawa, T.; Ida, K.; Morita, S.; Ido, T.; Shimizu, A.; Isobe, M.; Todo, Y.; Watari, T.; Ohdachi, S.; Sakakibara, S.; Narihara, K.; Osakabe, M.; Nagaoka, K.; Narushima, Y.; Watanabe, K. Y.; Funaba, H.; Goto, M.; Ikeda, K.; Kaneko, O.
2010-10-01
Reversed-shear Alfven eigenmodes were observed for the first time in a helical plasma having negative q{sub 0}{sup ''} (the curvature of the safety factor q at the zero shear layer). The frequency is swept downward and upward sequentially via the time variation in the maximum of q. The eigenmodes calculated by ideal MHD theory are consistent with the experimental data. The frequency sweeping is mainly determined by the effects of energetic ions and the bulk pressure gradient. Coupling of reversed-shear Alfven eigenmodes with energetic ion driven geodesic acoustic modes generates a multitude of frequency-sweeping modes.
Van Zeeland, Michael; Heidbrink, W.; Nazikian, Raffi; Austin, M. E.; Cheng, C Z; Chu, M. S.; Gorelenkov, Nikolai; Holcomb, C T; Hyatt, A. W.; Kramer, G.; Lohr, J.T.; Mckee, G. R.; Petty, C C.; Prater, R.; Solomon, W. M.; Spong, Donald A
2009-01-01
Neutral beam injection into reversed magnetic shear DIII-D plasmas produces a variety of Alfvenic activity including toroidicity and ellipticity induced Alfven eigenmodes (TAE/EAE, respectively) and reversed shear Alfven eigenmodes (RSAE) as well as their spatial coupling. These modes are studied during the discharge current ramp phase when incomplete current penetration results in a high central safety factor and strong drive due to multiple higher order resonances. It is found that ideal MHD modelling of eigenmode spectral evolution, coupling and structure are in excellent agreement with experimental measurements. It is also found that higher radial envelope harmonic RSAEs are clearly observed and agree with modelling. Some discrepancies with modelling such as that due to up/down eigenmode asymmetries are also pointed out. Concomitant with the Alfvenic activity, fast ion (FIDA) spectroscopy shows large reductions in the central fast ion profile, the degree of which depends on the Alfven eigenmode amplitude. Interestingly, localized electron cyclotron heating (ECH) near the mode location stabilizes RSAE activity and results in significantly improved fast ion confinement relative to discharges with ECH deposition on axis. In these discharges, RSAE activity is suppressed when ECH is deposited near the radius of the shear reversal point and enhanced with deposition near the axis. The sensitivity of this effect to deposition power and current drive phasing as well as ECH modulation are presented.
Reduced quasilinear models for energetic particles interaction with Alfvenic eigenmodes
NASA Astrophysics Data System (ADS)
Ghantous, Katy
The Line Broadened Quasilinear (LBQ) and the 1.5D reduced models are able to predict the effect of Alfvenic eigenmodes' interaction with energetic particles in burning plasmas. This interaction can result in energetic-particle losses that can damage the first wall, deteriorate the plasma performance, and even prevent ignition. The 1.5D model assumes a broad spectrum of overlapping modes and, based on analytic expressions for the growth and damping rates, calculates the pressure profiles that the energetic particles relax to upon interacting with the modes. 1.5D is validated with DIII-D experiments and predicted neutron losses consistent with observation. The model is employed to predict alpha-particle fusion-product losses in a large-scale operational parameter-space for burning plasmas. The LBQ model captures the interaction both in the regime of isolated modes as well as in the conventional regime of overlapping modes. Rules were established that allow quasilinear equations to replicate the expected steady-state saturation levels of isolated modes. The fitting formula is improved and the model is benchmarked with a Vlasov code, BOT. The saturation levels are accurately predicted and the mode evolution is well-replicated in the case of steady-state evolution where the collisions are high enough that coherent structures do not form. When the collisionality is low, oscillatory behavior can occur. LBQ can also exhibit non-steady behavior, but the onset of oscillations occurs for much higher collisional rates in BOT than in LBQ. For certain parameters of low collisionality, hole-clump creation and frequency chirping can occur which are not captured by the LBQ model. Also, there are cases of non-steady evolution without chirping which is possible for LBQ to study. However the results are inconclusive since the periods and amplitudes of the oscillations in the mode evolution are not well-replicated. If multiple modes exist, they can grow to the point of overlap which
Two-Dimensional Ballooning Transformation with Applications to Toroidal Alfven Eigenmodes.
NASA Astrophysics Data System (ADS)
Zhang, Xiao-Dong
A general formulation for high-n (n is the toroidal mode number) modes in an axisymmetric toroidal plasma is presented, based on the two dimensional (2-D) ballooning transformation. It is shown that this formulation is more general than the conventional ballooning theory, and reduces to the conventional theory in a special case. Toroidal Alfven waves are studied using the 2 -D ballooning formulation. A perturbation theory is systematically developed for the continuum damping of the toroidal Alfven eigenmode (TAE). A formula, similar to the Fermi golden rule for decaying systems in quantum mechanics, is derived for the continuum damping rate of the TAE; the decay (damping) rate is expressed explicitly in terms of the coupling of the TAE to the continuum spectrum. Numerical results are obtained and compared to previous calculations. Kinetic effects on toroidal Alfven waves are studied. Multiple -gap coupling is included automatically by the 2-D ballooning formulation. A new branch of modes, the kinetic toroidal Alfven eigenmodes (KTAE), emerges as a result of kinetic effects. This mode resides just above the toroidal shear Alfven gap, and has a structure similar to the TAE. Numerical results for the kinetic damping rates for the TAE and the KTAE are obtained, and multiple-gap coupling effects are studied by comparing with the single gap theory of Mett and Mahajan (Phys. Fluids B 4 2885 (1992)).
Plasma pressure effect on the multiple low-shear toroidal Alfven eigenmodes
Marchenko, V. S.
2009-04-15
It is shown that there is a critical thermal pressure gradient at which the polarizations of the multiple low-shear toroidal Alfven eigenmodes (TAEs) are reversed. Below the critical value, the TAE spectrum consists of two bands of the even (odd) modes located in the upper (lower) part of the toroidal Alfven gap, which is consistent with the zero-pressure limit [J. Candy, B. N. Breizman, J. W. Van Dam, and T. Ozeki, Phys. Lett. A 215, 299 (1996)]. Above the critical pressure, the odd (even) TAEs appear in the upper (lower) part of the gap.
Observations of toroidicity-induced Alfven eigenmodes in a reversed field pinch plasma
Regnoli, G.; Bergsaaker, H.; Tennfors, E.; Zonca, F.; Martines, E.; Serianni, G.; Spolaore, M.; Vianello, N.; Cecconello, M.; Antoni, V.; Cavazzana, R.; Malmberg, J.-A.
2005-04-15
High frequency peaks in the spectra of magnetic field signals have been detected at the edge of Extrap-T2R [P. R. Brunsell, H. Bergsaaker, M. Cecconello, J. R. Drake, R. M. Gravestijn, A. Hedqvist, and J.-A. Malmberg, Plasma Phys. Controlled Fusion, 43, 1457 (2001)]. The measured fluctuation is found to be mainly polarized along the toroidal direction, with high toroidal periodicity n and Alfvenic scaling (f{proportional_to}B/{radical}(m{sub i}n{sub i})). Calculations for a reversed field pinch plasma predict the existence of an edge resonant, high frequency, high-n number toroidicity-induced Alfven eigenmode with the observed frequency scaling. In addition, gas puffing experiments show that edge density fluctuations are responsible for the rapid changes of mode frequency. Finally a coupling with the electron drift turbulence is proposed as drive mechanism for the eigenmode.
Finite orbit energetic particle linear response to toroidal Alfven eigenmodes
Berk, H.L.; Ye, Huanchun . Inst. for Fusion Studies); Breizman, B.N. . Inst. Yadernoj Fiziki)
1991-07-01
The linear response of energetic particles to the TAE modes is calculated taking into account their finite orbit excursion from the flux surfaces. The general expression reproduces the previously derived theory for small banana width: when the banana width {triangle}{sub b} is much larger than the mode thickness {triangle}{sub m}, we obtain a new compact expression for the linear power transfer. When {triangle}{sub m}/{triangle}{sub b} {much lt} 1, the banana orbit effect reduces the power transfer by a factor of {triangle}{sub m}/{triangle}{sub b} from that predicted by the narrow orbit theory. A comparison is made of the contribution to the TAE growth rate of energetic particles with a slowing-down distribution arising from an isotropic source, and a balance-injected beam source when the source speed is close to the Alfven speed. For the same stored energy density, the contribution from the principal resonances ({vert bar}{upsilon}{sub {parallel}}{vert bar} = {upsilon}{sub A} is substantially enhanced in the beam case compared to the isotropic case, while the contribution at the higher sidebands ({vert bar}{upsilon}{sub {parallel}}{vert bar}) = {upsilon}{sub A}/(2{ell} {minus} 1) with {ell} {ge} 2) is substantially reduced. 10 refs.
C.Z. Cheng; G.Y.-Fu; N.N. Gorelenkov; R. Nazikian; R.V. Budny
1999-11-01
Resonant Toroidal Alfven Eigenmodes (RTAEs) [1, 2] excited by neutral beam ions are observed in the region of the internal transport barrier in enhanced reverse shear (ERS) plasmas on TFTR. These modes occur in multiples of the same toroidal mode number in the range n=2-4 and appear as highly localized structures near the minimum in the q-profile with frequency near to that expected for TAEs. Unlike regular TAEs, these modes are observed in plasmas where the birth velocity of beam ions is well below the fundamental or sideband resonance condition. Theoretical analysis indicates that the Toroidicity induced Alfven Eigenmode (TAE) does not exist in these discharges due to strong pressure gradients (of the thermal and fast ions) which moves the mode frequency down into the lower Alfven continuum. However a new non-perturbative analysis (where the energetic particles are allowed to modify the mode frequency and mode structure) indicates that RTAEs can be driven by neutral beam ions in the weak magnetic shear region of ERS plasma, consistent with observations on TFTR. The importance of such modes is that they may affect the alpha particle heating profile or enhance the loss of energetic alpha particles in an advanced tokamak reactor where large internal pressure gradients and reverse magnetic shear operation are required to sustain large bootstrap current.
Stability analysis of toroidicity-induced Alfven eigenmodes in TFTR deuterium-tritium experiments
Fu, G.Y.; Cheng, C.Z.; Budny, R.; Chang, Z.; Darrow, D.S.; Fredrickson, E.; Mazzucato, E.; Nazikian, R.; Zweben, S.
1995-09-18
The toroidicity-induced Alfven eigenmodes (TAE) are found to be stable in the Tokamak Fusion Test Reactor (TFTR) deuterium-tritium plasmas. The dominant stabilizing mechanisms are beam ion Landau damping and radiative damping. A core localized TAE mode is shown to exist near the center of the plasma at small magnetic shear and finite plasma beta, which can be destabilized by energetic alpha particles in future TFTR DT experiments. With additional instability drive from fast minority ions powered by ion cyclotron radio frequency, both the global and core localized TAE modes can be readily destabilized.
Anomalous Electron Transport Due to Multiple High Frequency Beam Ion Driven Alfven Eigenmode
Gorelenkov, N. N.; Stutman, D.; Tritz, K.; Boozer, A.; Delgardo-Aparicio, L.; Fredrickson, E.; Kaye, S.; White, R.
2010-07-13
We report on the simulations of recently observed correlations of the core electron transport with the sub-thermal ion cyclotron frequency instabilities in low aspect ratio plasmas of the National Spherical Torus Experiment (NSTX). In order to model the electron transport of the guiding center code ORBIT is employed. A spectrum of test functions of multiple core localized Global shear Alfven Eigenmode (GAE) instabilities based on a previously developed theory and experimental observations is used to examine the electron transport properties. The simulations exhibit thermal electron transport induced by electron drift orbit stochasticity in the presence of multiple core localized GAE.
Perturbative Study of Energetic Particle Redistribution by Alfven Eigenmodes in ITER
N.N. Gorelenkov and R.B. White
2012-10-29
The modification of particle distributions by magnetohydrodynamic modes is an important topic for magnetically confined plasmas. Low amplitude modes are known to be capable of producing significant modification of injected neutral beam profiles. Flattening of a distribution due to phase mixing in an island or due to portions of phase space becoming stochastic is a process extremely rapid on the time scale of an experiment. In this paper we examine the effect of toroidal Alfven eigenmodes (TAE) and reversed shear Alfven eigenmodes (RSAE) in ITER on alpha particle and injected beam distributions using theoretically predicted mode amplitudes. It is found that for the equilibrium of a hybrid scenario even at ten times the predicted saturation level the modes have negligible effect on these distributions. A strongly reversed shear (or advanced) scenario, having a spectrum of modes that are much more global, is somewhat more susceptible to induced loss due to mode resonance, with alpha particle losses of over one percent with predicted amplitudes and somewhat larger with the assistance of toroidal field ripple. The elevated q profile contributes to stronger TAE (RSAE) drive and more unstable modes. An analysis of the existing mode-particle resonances is carried out to determine which modes are responsible for the profile modification and induced loss. We find that losses are entirely due to resonance with the counter-moving and trapped particle populations, with co-moving passing particles participating in resonances only deep within the plasma and not leading to loss.
Stochastic Orbit Loss of Neutral Beam Ions From NSTX Due to Toroidal Alfven Eigenmode Avalanches
Darrow, D S; Fredrickson, E D; Gorelenkov, N N; Gorelenkova, M; Kubota, S; Medley, S S; Podesta, M; Shi, L
2012-07-11
Short toroidal Alfven eigenmode (TAE) avalanche bursts in the National Spherical Torus Experiment (NSTX) cause a drop in the neutron rate and sometimes a loss of neutral beam ions at or near the full injection energy over an extended range of pitch angles. The simultaneous loss of wide ranges of pitch angle suggests stochastic transport of the beam ions occurs. When beam ion orbits are followed with a guiding center code that incorporates plasma's magnetic equilibrium plus the measured modes, the predicted ranges of lost pitch angle are similar to those seen in the experiment, with distinct populations of trapped and passing orbits lost. These correspond to domains where the stochasticity extends in the orbit phase space from the region of beam ion deposition to the loss boundary.
Gyrokinetic particle simulation of beta-induced Alfven-acoustic eigenmode
NASA Astrophysics Data System (ADS)
Zhang, H. S.; Liu, Y. Q.; Lin, Z.; Zhang, W. L.
2016-04-01
The beta-induced Alfven-acoustic eigenmode (BAAE) in toroidal plasmas is verified and studied by global gyrokinetic particle simulations. When ion temperature is much lower than electron temperature, the existence of the weakly damped BAAE is verified in the simulations using initial perturbation, antenna excitation, and energetic particle excitation, respectively. When the ion temperature is comparable to the electron temperature, the unstable BAAE can be excited by realistic energetic particle density gradient, even though the stable BAAE (in the absence of energetic particles) is heavily damped by the thermal ions. In the simulations with reversed magnetic shear, BAAE frequency sweeping is observed and poloidal mode structure has a triangle shape with a poloidal direction similar to that observed in tokamak experiments. The triangle shape changes the poloidal direction, and no frequency sweeping is found in the simulations with normal magnetic shear.
Experimental study of toroidicity-induced Alfven eigenmode (TAE) stability at high q(0)
Batha, S.H.; Levinton, F.M.; Spong, D.A.
1995-07-01
Experiments to destabilize the Toroidicity-induced Alfven Eigenmode (TAE) by energetic alpha particles were performed on the Tokamak Fusion Test Reactor using deuterium and tritium fuel. To decrease the alpha particle pressure instability threshold, discharges with an elevated value of q(0) > 1.5 were used. By raising q(0), the radial location of the low toroidal-mode-number TAE gaps moves toward the magnetic axis and into alignment with the region of maximum alpha pressure gradient, thereby (in theory) lowering the value of {beta}{sub {alpha}}(0) required for instability. No TAE activity was observed when the central alpha particle {beta}{sub {alpha}} reached 0.08% in a discharge with fusion power of 2.4 MW. Calculations show that the fusion power is within a factor of 1.5 to 3 of the instability threshold.
Effects of ICRH on the Dynamics of Fast Particle Excited Alfven Eigenmodes
Bergkvist, T.; Hellsten, T.; Holmstroem, K.
2007-09-28
ICRH is often used in experiments to simulate destabilization of Alfven eigenmodes by thermonuclear {alpha}-particles. Whereas the slowing down distribution of {alpha}-particles is nearly isotropic, the ICRH creates an anisotropic distribution function with non-standard orbits. The ICRH does not only build up gradients in phase space, which destabilizes the AEs, but it also provides a strong phase decorrelation mechanism between ions and AEs. Renewal of the distribution function by thermonuclear reactions and losses of {alpha}-particles to the wall lead to a continuous drive of the AEs. Simulations of the non-linear dynamics of AEs and the impact they have on the heating profile due to particle redistribution are presented.
Gyrokinetic particle simulations of reversed shear Alfven eigenmode excited by antenna and fast ions
Deng Wenjun; Holod, Ihor; Xiao Yong; Lin Zhihong; Wang Xin; Zhang Wenlu
2010-11-15
Global gyrokinetic particle simulations of reversed shear Alfven eigenmode (RSAE) have been successfully performed and verified. We have excited the RSAE by initial perturbation, by external antenna, and by energetic ions. The RSAE excitation by antenna provides verifications of the mode structure, the frequency, and the damping rate. When the kinetic effects of the background plasma are artificially suppressed, the mode amplitude shows a near-linear growth. With kinetic thermal ions, the mode amplitude eventually saturates due to the thermal ion damping. The damping rates measured from the antenna excitation and from the initial perturbation simulation agree very well. The RSAE excited by fast ions shows an exponential growth. The finite Larmor radius effects of the fast ions are found to significantly reduce the growth rate. With kinetic thermal ions and electron pressure, the mode frequency increases due to the elevation of the Alfven continuum by the geodesic compressibility. The nonperturbative contributions from the fast ions and kinetic thermal ions modify the mode structure relative to the ideal magnetohydrodynamic (MHD) theory. The gyrokinetic simulations have been benchmarked with extended hybrid MHD-gyrokinetic simulations.
Beam Anisotropy Effect on Alfven Eigenmode Stability in ITER-like Plasma
N.N. Gorelenkov; H.L. Berk; R.V. Budny
2004-08-18
This work studies the stability of the toroidicity-induced Alfven Eigenmodes (TAE) in the proposed ITER burning plasma experiment, which can be driven unstable by two groups of energetic particles, the 3.5-MeV {alpha}-particle fusion products and the tangentially injected 1-MeV beam ions. Both species are super-Alfvenic but they have different pitch-angle distributions and the drive for the same pressure gradients is typically stronger from co-injected beam ions as compared with the isotropically distributed {alpha}-particles. This study includes the effect of anisotropy of the beam-ion distribution function on TAE growth rate directly via the additional velocity space drive and indirectly in terms of the enhanced effect of the resonant particle phase space density. For near parallel injection, TAEs are marginally unstable if the injection aims at the plasma center where the ion Landau damping is strong, whereas with the off-axis neutral-beam injection the instability is stronger with the growth rate near 0.5% of TAE mode frequency. In contrast, for perpendicular beam injection TAEs are predicted to be stabilized in nominal ITER discharges. In addition, the effect of TAEs on the fast-ion beta profiles is evaluated on the bases of a quasi-linear diffusion model which makes use of analytic expressions for the local growth and damping rates. These results illustrate the parameter window that is available for plasma burn when TAE modes are excited.
Bass, E. M.; Waltz, R. E.
2013-01-15
The unstable spectrum of Alfven eigenmodes (AEs) driven by neutral beam-sourced energetic particles (EPs) in a benchmark DIII-D discharge (142111) is calculated in a fully gyrokinetic model using the GYRO code's massively parallel linear eigenvalue solver. One cycle of the slow (equilibrium scale) frequency sweep of the reverse shear Alfven eigenmode (RSAE) at toroidal mode number n=3 is mapped. The RSAE second harmonic and an unstable beta-induced Alfven eigenmode (BAE) are simultaneously tracked alongside the primary RSAE. An observed twist in the eigenmode pattern, caused mostly by shear in the driving EP profile, is shown through artificially varying the E Multiplication-Sign B rotational velocity shear to depend generally on shear in the local wave phase velocity. Coupling to the BAE and to the toroidal Alfven eigenmode limit the RSAE frequency sweeps at the lower and upper end, respectively. While the present fully gyrokinetic model (including thermal ions and electrons) constitutes the best treatment of compressibility physics available, the BAE frequency is overpredicted by about 20% against experiment here and is found to be sensitive to energetic beam ion pressure. The RSAE frequency is more accurately matched except when it is limited by the BAE. Simulations suggest that the experiment is very close to marginal AE stability at points of RSAE-BAE coupling. A recipe for comparing the radial profile of quasilinear transport flux from local modes to that from global modes paves the way for the development of a stiff (critical gradient) local AE transport model based on local mode stability thresholds.
Observations of fast ion losses due to toroidal Alfven eigenmodes in TFTR
Darrow, D.S.; Zweben, S.J.; Chang, Z.
1993-08-01
In a tokamak, knowledge of the rate of fast ion loss is of importance in determining the energy balance of the discharge. Heating of the discharge may be diminished if losses are significant, since neutral beam ions, ICRF heating tail ions, and alpha particles all heat the plasma and may all be lost through processes which expel fast ions. In addition, a loss of fast ions which is sufficiently intense and localized may damage plasma facing components in the vacuum vessel. For these reasons, knowledge of the fast ion loss mechanisms is desirable. Loss processes for fast ions in a tokamak fit into two broad categories: single particle and collective. Single particle losses are those, such as first orbit loss, which are independent of the number of fast ions present. These have been seen in numerous instances on TFIR with DD fusion products, and are reported elsewhere. Collective losses arise when the fast ion density is sufficient to drive instabilities which then cause loss. The drive can come from {partial_derivative}f{sub fi}/{partial_derivative}{psi} (where f{sub fi} is the fast ion distribution function), {partial_derivative}f{sub fi}/{partial_derivative}E, and resonances. Examples of collective instabilities include the toroidal Alfven eigenmode (TAE), the kinetic ballooning mode, alpha driven sawteeth, alpha driven fishbones, Alfven waves, and ion cyclotron waves. This paper limits itself to the presentation of observations made during what are believed to be TAEs which were excited under two conditions in TFTR: at low field (1.5 T), with neutral beam ions driving the mode, and at intermediate field (3.4 T) with the hydrogen minority ICRF tail ions driving the mode.
NASA Astrophysics Data System (ADS)
Sears, Stephanie; Anderson, Jay; Capecchi, William; Bonofiglo, Phillip; Kim, Jungha
2015-11-01
Alfven wave dissipation is an important mechanism behind anomalous ion heating, both in astrophysical and reversed-field pinch (RFP) plasma systems. Additionally, the damping rate has implications for the stability of energetic particle driven modes (EPMs) and their associated nonlinear dynamics and fast ion transport, which are crucial topics for any burning plasma reactor. With a 1 MW neutral beam injector on the MST RFP, a controlled set of EPMs and Alfvenic eigenmodes can be driven in this never-before-probed region of strong magnetic shear and weak externally applied magnetic field. The decay time of the average of 100s of reproducible bursts is computed for different equilibrium profiles. In this work, we report initial measurements of Alfvenic damping rates with varied RFP equilibria (including magnetic shear and flow shear) and the effects on fast ion transport. This research is supported by DOE and NSF.
Fredrickson, E. D.; Bell, R. E.; Darrow, D. S.; Gorelenkov, N. N.; Kramer, G. J.; Medley, S. S.; White, R. B.; Crocker, N. A.; Kubota, S.; Levinton, F. M.; Yuh, H.; Liu, D.; Podesta, M.; Tritz, K.
2009-12-15
Experiments on the National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 40, 557 (2000)] found strong bursts of toroidal Alfven eigenmode (TAE) activity correlated with abrupt drops in the neutron rate. A fairly complete data set offers the opportunity to benchmark the NOVA[C. Z. Cheng, Phys. Rep. 211, 1 (1992)] and ORBIT[R. B. White and M. S. Chance, Phys. Fluids 27, 2455 (1984)] codes in the low aspect ratio tokamak (ST) geometry. The internal structure of TAE was modeled with NOVA and good agreement is found with measurements made with an array of five fixed-frequency reflectometers. The fast-ion transport resulting from these bursts of multiple TAE was then modeled with the ORBIT code. The simulations are reasonably consistent with the observed drop in neutron rate, however, further refinements in both the simulation of the TAE structure and in the modeling of the fast-ion transport are needed. Benchmarking stability codes against present experiments is an important step in developing the predictive capability needed to plan future experiments.
Podesta, M; Crocker, N A; Fredrickson, E D; Gorelenkov, N N; Heidbrink, W W; Kubota, S; LeBlanc, B P
2011-04-26
The National Spherical Torus Experiment (NSTX, [M. Ono et al., Nucl. Fusion 40, 557 (2000)]) routinely operates with neutral beam injection as the primary system for heating and current drive. The resulting fast ion population is super-Alfv enic, with velocities 1 < vfast=vAlfven < 5. This provides a strong drive for toroidicity-induced Alfv en eigenmodes (TAEs). As the discharge evolves, the fast ion population builds up and TAEs exhibit increasing bursts in amplitude and down-chirps in frequency, which eventually lead to a so-called TAE avalanche. Avalanches cause large (≤ 30%) fast ion losses over ~ 1 ms, as inferred from the neutron rate. The increased fast ion losses correlate with a stronger activity in the TAE band. In addition, it is shown that a n = 1 mode with frequency well below the TAE gap appears in the Fourier spectrum of magnetic fluctuations as a result of non-linear mode coupling between TAEs during avalanche events. The non-linear coupling between modes, which leads to enhanced fast ion transport during avalanches, is investigated.
NASA Astrophysics Data System (ADS)
Wang, Ge; Berk, H. L.
2011-10-01
The frequency chirping signal arising from spontaneous a toroidial Alfven eigenmode (TAE) excited by energetic particles is studied for both numerical and analytic models. The time-dependent numerical model is based on the 1D Vlasov equation. We use a sophisticated tracking method to lock onto the resonant structure to enable the chirping frequency to be nearly constant in the calculation frame. The accuracy of the adiabatic approximation is tested during the simulation which justifies the appropriateness of our analytic model. The analytic model uses the adiabatic approximation which allows us to solve the wave evolution equation in frequency space. Then, the resonant interactions between energetic particles and TAE yield predictions for the chirping rate, wave frequency and amplitudes vs. time. Here, an adiabatic invariant J is defined on the separatrix of a chirping mode to determine the region of confinement of the wave trapped distribution function. We examine the asymptotic behavior of the chirping signal for its long time evolution and find agreement in essential features with the results of the simulation. Work supported by Department of Energy contract DE-FC02-08ER54988.
Experimental Studies of Alfven Eigenmode Stability in JET D-T Plasmas
NASA Astrophysics Data System (ADS)
Fasoli, A.; Heeter, R.; Borba, D.; Gormezano, C.; Sharapov, S.; Jaun, A.
1997-11-01
Systematic studies of Alfven Eigenmodes (AE) are performed at JET, based on the excitation via resonant interaction with fast particles generated by additional heating and by fusion reactions, and via external antennas, providing a direct measurement of the mode damping rate. Similar damping rates are observed in D-D and D-T plasmas with similar configurations. In both cases the formation of an X-point provides a strong stabilising effect on low-n TAE. The fast particle drive is detected as a reduction in the measured damping rate as the fast particle pressure is increased. For ICRH power levels above the experimentally established marginal stability limit, 3 MW < P_thres < 6 MW, the magnetic fluctuation spectra indicate the destabilisation of different families of AE (TAE, EAE, kTAE, NAE). In 50:50 D-T plasmas characterised by moderate fusion power (P_fusion< 2 MW), alpha particle pressure is observed to destabilise TAE in the afterglow of the NBI and ICRH heating phase. The diagnostic potential of AE will be discussed along with the implications for the AE stability in ignited plasmas.
Geometrical and profile effects on toroidicity and ellipticity induced Alfven eigenmodes
NASA Astrophysics Data System (ADS)
Villard, L.; Fu, G. Y.
1992-10-01
The wave structures, eigenfrequencies and damping rates of toroidicity and ellipticity induced Alfven eigenmodes (TAEs, EAEs) of low toroidal mode numbers (n) are calculated for various axisymmetric ideal MHD equilibria with the global wave finite element code LION. The importance of the safety factor (q) and density (ρ) profiles on the continuum damping rates is analysed. For realistic profiles, several continuum gaps, exist in the plasma discharge. Frequency misalignment of these gaps yields continuum damping rates γ/ω of the order of a few per cent. Finite poloidal beta lowers the TAE eigenfrequency. For beta values below the Troyon limit, the TAE enters the continuum and can thus be stabilized. Finite elongation allows the EAE to exist, but triangularity can have a stabilizing effect through coupling with the continuum. The localization of TAE and EAE eigenfunctions is found to increase with the shear and with n. Therefore, large shear, through enhanced Landau and collisional damping, is a stabilizing factor for TAEs and EAEs
Gorelenkov, N. N.; Darrow, D.; Fredrickson, E.; Fu, G.-Y.; Menard, J.; Nazikian, R.; Van Zeeland, M. A.; Berk, H. L.; Crocker, N. A.; Heidbrink, W. W.
2009-05-15
Kinetic theory and experimental observations of a special class of energetic particle driven instabilities called here beta-induced Alfven-acoustic eigenmodes (BAAEs) are reported confirming, previous results [N. N. Gorelenkov et al., Plasma Phys. Controlled Fusion 49, B371 (2007)]. The kinetic theory is based on the ballooning dispersion relation where the drift frequency effects are retained. BAAE gaps are recovered in kinetic theory. It is shown that the observed certain low-frequency instabilities on DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] and National Spherical Torus Experiment [M. Ono, S. M. Kaye, Y.-K. M. Peng et al., Nucl. Fusion 40, 557 (2000)] are consistent with their identification as BAAEs. BAAEs deteriorate the fast ion confinement in DIII-D and can have a similar effect in next-step fusion plasmas, especially if excited together with multiple global toroidicity-induced shear Alfven eigenmode instabilities. BAAEs can also be used to diagnose safety factor profiles, a technique known as magnetohydrodynamic spectroscopy.
Beta-induced Alfven-acousti Eigenmodes in NSTX and DIII-D Driven by Beam Ions
Gorelenkov, N. N.; Van Zeeland, M. A.; Berk, H. L.; Crocker, N. A.; Darrow, D.; Fredrickson, E.; Fu, G. Y.; Heidbrink, W. W.; Menard, J.; Nazikian, R.
2009-03-06
Kinetic theory and experimental observations of a special class of energetic particle driven instabilities called here Beta-induced Alfven-Acoustic Eigenmodes (BAAE) are reported confirming previous results [N.N. Gorelenkov H.L. Berk, N.A. Crocker et. al. Plasma Phys. Control. Fusion 49 B371 (2007)] The kinetic theory is based on the ballooning dispersion relation where the drift frequency effects are retained. BAAE gaps are recovered in kinetic theory. It is shown that the observed certain low-frequency instabilities on DIII-D [J.L. Luxon, Nucl. Fusion 42 614 (2002)] and National Spherical Torus Experiment [M. Ono, S.M. Kaye, Y.-K M. Peng et. al., Nucl. Fusion 40 3Y 557 (2000)] are consistent with their identification as BAAEs. BAAEs deteriorated the fast ion confinement in DIII-D and can have a similar effect in next-step fusion plasmas, especially if excited together with multiple global Toroidicity-induced shear Alfven Eigenmode (TAE) instabilities. BAAEs can also be used to diagnose safety factor profiles, a technique known as magnetohydrodynamic spectroscopy.
Reversed shear Alfv'en Eigenmodes in the frequency range of the triangularity induced gap on JET
NASA Astrophysics Data System (ADS)
Kramer, G. J.; Fu, G. Y.; Nazikian, R.; Budny, R. V.; Gorelenkov, N. N.; Cheng, C. Z.; Alper, B.; Pinches, S. D.; Rimini, F.; Sharapov, S. E.; de Vries, P.; Zastrow, K.-D.; Zoita, V.
2007-11-01
In reversed magnetic shear plasmas a class of Alfv'en eigenmodes (AE) can exist, the Reversed shear Alfv'en eigen modes (RSAE). They are often observed in Tokamaks and are located just above the local maximum of the lower TAE continuum gap at the shear reversal point. Similar maxima exist in the higher order Alfv'en gaps such as the EAE and NAE gap. In this presentation we will show from ideal MHD simulations and analytical theory that modes similar to the RSAE can exist under certain conditions in those higher order gaps. In burning plasmas modes in the AE gaps can be harmful for the confinement of fusion born alpha particles which can get lost before they thermalize thereby reducing the efficiency of a fusion reactor. We will show experimental evidence for RSAEs in the NAE gap in JET discharges. The JET NAE-RSAEs are identified from state of the art MHD simulations with the NOVA code in which the experimentally observed equilibrium parameters were used.
Ito, T.; Toi, K.; Isobe, M.; Nagaoka, K.; Takeuchi, M.; Akiyama, T.; Matsuoka, K.; Minami, T.; Nishimura, S.; Okamura, S.; Shimizu, A.; Suzuki, C.; Yoshimura, Y.; Takahashi, C.; Matsunaga, G.
2009-09-15
Stable toroidicity-induced Alfven eigenmodes (TAEs) with low toroidal mode number (n=1 and n=2) were excited by application of alternating magnetic field perturbations generated with a set of electrodes inserted into the edge region of neutral beam injection heated plasmas on the Compact Helical System [K. Nishimura, K. Matsuoka, M. Fujiwara et al., Fusion Technol. 17, 86 (1990)]. The gap locations of TAEs excited by the electrodes are in the plasma peripheral region of {rho}>0.7 ({rho} is the normalized minor radius) where energetic ion drive is negligibly small, while some AEs are excited by energetic ions in the plasma core region of {rho}<0.4. The damping rate of these stable TAEs derived from plasma responses to applied perturbations is fairly large, that is, {approx}9% to {approx}12% of the angular eigenfrequency. This large damping rate is thought to be dominantly caused by continuum damping and radiative damping.
Podesta, M; Fredrickson, E D; Gorelenkov, N N; LeBlanc, B P; Heidbrink, W W; Crocker, N A; Kubota, S
2010-08-19
The effects of a sheared toroidal rotation on the dynamics of bursting Toroidicity-induced Alfven eigenmodes are investigated in neutral beam heated plasmas on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40 557 (2000)]. The modes have a global character, extending over most of the minor radius. A toroidal rotation shear layer is measured at the location of maximum drive for the modes. Contrary to results from other devices, no clear evidence of increased damping is found. Instead, experiments with simultaneous neutral beam and radio-frequency auxiliary heating show a strong correlation between the dynamics of the modes and the instability drive. It is argued that kinetic effects involving changes in the mode drive and damping mechanisms other than rotation shear, such as continuum damping, are mostly responsible for the bursting dynamics of the modes.
Podesta, M.; Bell, R. E.; Fredrickson, E. D.; Gorelenkov, N. N.; LeBlanc, B. P.; Heidbrink, W. W.; Crocker, N. A.; Kubota, S.; Yuh, H.
2010-12-15
The effects of a sheared toroidal rotation on the dynamics of bursting toroidicity-induced Alfven eigenmodes are investigated in neutral beam heated plasmas on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)]. The modes have a global character, extending over most of the minor radius. A toroidal rotation shear layer is measured at the location of maximum drive for the modes. Contrary to results from other devices, no clear evidence of decorrelation of the modes by the sheared rotation is found. Instead, experiments with simultaneous neutral beam and radio-frequency auxiliary heating show a strong correlation between the dynamics of the modes and the instability drive. It is argued that kinetic effects involving changes in the mode drive and damping mechanisms other than rotation shear, such as continuum damping, are mostly responsible for the bursting dynamics of the modes on NSTX.
Edlund, E. M.; Porkolab, M.; Kramer, G. J.; Lin, L.; Lin, Y.; Tsuji, N.; Wukitch, S. J.
2010-08-27
Experiments conducted in the Alcator C-Mod tokamak at MIT have explored the physics of reversed shear Alfven eigenmodes (RSAEs) during the current ramp. The frequency evolution of the RSAEs throughout the current ramp provides a constraint on the evolution of qmin, a result which is important in transport modeling and for comparison with other diagnostics which directly measure the magnetic field line structure. Additionally, a scaling of the RSAE minimum frequency with the sound speed is used to derive a measure of the adiabatic index, a measure of the plasma compressibility. This scaling bounds the adiabatic index at 1.40 ± 0:15 used in MHD models and supports the kinetic calculation of separate electron and ion compressibilities with an ion adiabatic index close to 7~4.
Mikhailovskii, A.B.; Kovalishen, E.A.; Tsypin, V.S.; Galvao, R.M.O.
2005-04-15
A unified theory of the Mercier-ballooning and the compensating-electron Alfven eigenmodes (CEAEs) in positive-shear tokamaks with large-orbit energetic ions is developed. It is shown that the cross-field drift effect of electrons compensating the electric charge of energetic ions (the compensating-electron effect) leads to rotation of the Mercier-ballooning modes. If the Mercier stability criterion is satisfied, the ballooning modes rotate in the direction of compensating-electron frequency, while in violation of this stability criterion the unstable modes rotate against this frequency. The compensating-electron effect also results in decreasing the growth rate of ballooning modes, though their instability condition is unchanged. The Mercier and ballooning effects influence both rotation and decay rate of the CEAEs, the ballooning effect being smaller than the Mercier effect. As a result, rotation and damping of CEAEs increases/decreases in the case of magnetic well/hill.
Kramer, G.J.; Nazikian, R.; Alper, B.
2006-05-15
Reversed shear Alfven eigenmodes (RSAE) that were observed in the Joint European Torus (JET) [P. H. Rebut and B. E. Keen, Fusion Technol.11, 13 (1987)] and DIII-D [J. L. Luxon, Nucl. Fusion42, 614 (2002)] are studied with the ideal magnetohydrodynamic code NOVA-K [C. Z. Cheng, Phys. Rep.211, 1 (1992)]. It was found that the frequency behavior of the RSAEs can be described accurately by the NOVA-K code when plasma compressibility effects and toroidal plasma rotation are taken into account. For the mode activity on JET, the calculated drive exceeds the mode damping rate, consistent with experimental observations, while on DIII-D the growth rate from neutral beam ions for modes with high toroidal mode numbers is insufficient to account for the excitation of the modes and a major part of the drive comes from the background plasma.
Stability analysis of toroidicity-induced Alfven eigenmodes in TFTR DT experiments
Fu, G.Y.; Cheng, C.Z.; Budny, R.; Chang, Z.; Darrow, D.S.; Fredrickson, E.; Mazzucato, E.; Nazikian, R.; Zweben, S.
1995-05-15
The toroidicity-induced Alfvin eigenmodes (TAE) with radially extended structure are found to be stable in the Tokamak Fusion Test Reactor Deuterium-Tritium plasmas. A core localized TAE mode is shown to exist near the center of the plasma at small magnetic shear and finite plasma beta, which can be destabilized by energetic alpha particles on TFTR. With additional instability drive from fast minority ions powered by ICRH, both the global and the core localized TAE modes can be readily destabilized.
NASA Astrophysics Data System (ADS)
Bass, E. M.; Waltz, R. E.
2012-10-01
In ITER, convection of fusion-produced alpha particles by energetic particle (EP)-driven Alfv'en eigenmodes (AEs) risks wall damage and loss of alpha heating needed for ignition. We examine beam-excited AEs and induced quasilinear transport in a DIII-D AE experiment using the gyrokinetic code GYRO [1]. Global, linear eigenvalue simulations show reverse-shear AEs (RSAEs), toroidal AEs, and beta-induced AEs interacting over one (equilibrium time scale) RSAE frequency sweep. Eigenfunction modifications over MHD, including a poloidal twist and broad AE footprint observed in electron cyclotron emission imaging [2], show the value of a kinetic approach. Under a simple quasilinear saturation assumption, a sequence of comparatively inexpensive local simulations quantitatively recreates some global features, notably the quasilinear transport footprint. Accordingly, we present here a stiff EP transport model where AEs limit the EP density gradient to the local stability threshold, and a TGLF-driven quasilinear model elsewhere. The model gives some``worst case'' predictions of the AE-limited alpha profile in ITER.[4pt] [1] J. Candy and R.E. Waltz, Phys. Rev. Lett. 91, 045001 (2003). [2] B.J. Tobias, et al., Phys. Rev. Lett. 106, 075003 (2011).
1.5D quasilinear model and its application on beams interacting with Alfven eigenmodes in DIII-D
Ghantous, K.; Gorelenkov, N. N.; Berk, H. L.; Heidbrink, W. W.; Van Zeeland, M. A.
2012-09-15
We propose a model, denoted here by 1.5D, to study energetic particle (EP) interaction with toroidal Alfvenic eigenmodes (TAE) in the case where the local EP drive for TAE exceeds the stability limit. Based on quasilinear theory, the proposed 1.5D model assumes that the particles diffuse in phase space, flattening the pressure profile until its gradient reaches a critical value where the modes stabilize. Using local theories and NOVA-K simulations of TAE damping and growth rates, the 1.5D model calculates the critical gradient and reconstructs the relaxed EP pressure profile. Local theory is improved from previous study by including more sophisticated damping and drive mechanisms such as the numerical computation of the effect of the EP finite orbit width on the growth rate. The 1.5D model is applied on the well-diagnosed DIII-D discharges no. 142111 [M. A. Van Zeeland et al., Phys. Plasmas 18, 135001 (2011)] and no. 127112 [W. W. Heidbrink et al., Nucl. Fusion. 48, 084001 (2008)]. We achieved a very satisfactory agreement with the experimental results on the EP pressure profiles redistribution and measured losses. This agreement of the 1.5D model with experimental results allows the use of this code as a guide for ITER plasma operation where it is desired to have no more than 5% loss of fusion alpha particles as limited by the design.
Properties of Alfven Eigenmodes in the TAE range on the National Spherical Torus Experiment-Upgrade
2013-04-24
A second Neutral Beam (NB) injection line is being installed on the NSTX Upgrade device, resulting in six NB sources with di erent tangency radii that will be available for heating and current drive. This work explores the properties of instabilities in the frequency range of the Toroidal Alfv en Eigenmode (TAE) for NSTX-U scenarios with various NB injection geometries, from more perpendicular to more tangential, and with increased toroidal magnetic eld with respect to previous NSTX scenarios. Predictions are based on analysis through the ideal MHD code NOVA-K. For the scenarios considered in this work, modi cations of the Alfv en continuum result in a frequency upshift and a broadening of the radial mode structure. The latter e ect may have consequences for fast ion transport and loss. Preliminary stability considerations indicate that TAEs are potentially unstable, with ion Landau damping representing the dominant damping mechanism
New Digital Control System for the JET Alfv'en Eigenmode Active Spectroscopy Diagnostic
NASA Astrophysics Data System (ADS)
Woskov, P. P.; Stillerman, J.; Porkolab, M.; Fasoli, A.; Testa, D.; Galvao, R.; Pires Dos Resis, A.; Pires de Sa, W.; Ruchko, L.; Blanchard, P.; Figueiredo, J.; Dorling, S.; Farthing, J.; Graham, M.; Dowson, S.; Yu, L.; Concezzi, S.
2012-10-01
The state-of-the-art JET Alfv'en active spectroscopy diagnostic with eight internal inductive antennas is being upgraded from a single 5 kW tube amplifier to eight parallel, 10 -- 1000 kHz, 4 kW solid state class D power switching amplifiers. A new digital control system has been designed with arbitrary constant phase controlled frequency sweeps for traveling mode studies, amplifier gain control through a feedback loop referenced to programmed antenna current profiles, and integration with CODAS for synchronization, triggering, gating, and fault tripping. A combination of National Instruments Real Time LabView software and FPGA circuits is used to achieve the multiple control requirements with better than 1 ms response. System specifications and digital-analog design trade offs for sweep rates, response times, frequency resolution, and voltage levels will be presented.
Spong, D. A.; Bass, E. M.; Deng, W.; Heidbrink, W. W.; Lin, Z.; Tobias, B.; Van Zeeland, M. A.; Austin, M. E.; Domier, C. W.; Luhmann, N. C. Jr.
2012-08-15
A verification and validation study is carried out for a sequence of reversed shear Alfven instability time slices. The mode frequency increases in time as the minimum (q{sub min}) in the safety factor profile decreases. Profiles and equilibria are based upon reconstructions of DIII-D discharge (no. 142111) in which many such frequency up-sweeping modes were observed. Calculations of the frequency and mode structure evolution from two gyrokinetic codes, GTC and GYRO, and a gyro-Landau fluid code TAEFL are compared. The experimental mode structure of the instability was measured using time-resolved two-dimensional electron cyclotron emission imaging. The three models reproduce the frequency upsweep event within {+-}10% of each other, and the average of the code predictions is within {+-}8% of the measurements; growth rates are predicted that are consistent with the observed spectral line widths. The mode structures qualitatively agree with respect to radial location and width, dominant poloidal mode number, ballooning structure, and the up-down asymmetry, with some remaining differences in the details. Such similarities and differences between the predictions of the different models and the experimental results are a valuable part of the verification/validation process and help to guide future development of the modeling efforts.
Fu, G.Y.; Cheng, C.Z.
1992-07-01
The stability of high-n toroidicity-induced shear Alfven eigenmodes (TAE) in the presence of fusion alpha particles or energetic ions in tokamaks is investigated. The TAE modes are discrete in nature and thus can easily tap the free energy associated with energetic particle pressure gradient through wave particle resonant interaction. A quadratic form is derived for the high-n TAE modes using gyro-kinetic equation. The kinetic effects of energetic particles are calculated perturbatively using the ideal MHD solution as the lowest order eigenfunction. The finite Larmor radius (FLR) effects and the finite drift orbit width (FDW) effects are included for both circulating and trapped energetic particles. It is shown that, for circulating particles, FLR and FDW effects have two opposite influences on the stability of the high-n TAE modes. First, they have the usual stabilizing effects by reducing the wave particle interaction strength. Second, they also have destabilizing effects by allowing more particles to resonate with the TAE modes. It is found that the growth rate induced by the circulating alpha particles increase linearly with toroidal mode number n for small {kappa}{sub {theta}}{rho}{sub {alpha}}, and decreases as 1/n for {kappa}{sub {theta}}{rho}{sub {alpha}} {much_gt} 1. The maximum growth rate is obtained at {kappa}{sub {theta}}{rho}{sub {alpha}} on the order of unity and is nearly constant for the range of 0.7 < {upsilon}{sub {alpha}}/{upsilon}{sub A} < 2.5. On the other hand, the trapped particle response is dominated by the precessional drift resonance. The bounce resonant contribution is negligible. The growth rate peaks sharply at the value of {kappa}{sub {theta}}{rho}{sub {alpha}} such that the precessional drift resonance occurs for the most energetic trapped particles. The maximum growth rate due to the energetic trapped particles is comparable to that of circulating particles.
Fu, G.Y.; Cheng, C.Z.
1992-07-01
The stability of high-n toroidicity-induced shear Alfven eigenmodes (TAE) in the presence of fusion alpha particles or energetic ions in tokamaks is investigated. The TAE modes are discrete in nature and thus can easily tap the free energy associated with energetic particle pressure gradient through wave particle resonant interaction. A quadratic form is derived for the high-n TAE modes using gyro-kinetic equation. The kinetic effects of energetic particles are calculated perturbatively using the ideal MHD solution as the lowest order eigenfunction. The finite Larmor radius (FLR) effects and the finite drift orbit width (FDW) effects are included for both circulating and trapped energetic particles. It is shown that, for circulating particles, FLR and FDW effects have two opposite influences on the stability of the high-n TAE modes. First, they have the usual stabilizing effects by reducing the wave particle interaction strength. Second, they also have destabilizing effects by allowing more particles to resonate with the TAE modes. It is found that the growth rate induced by the circulating alpha particles increase linearly with toroidal mode number n for small {kappa}{sub {theta}}{rho}{sub {alpha}}, and decreases as 1/n for {kappa}{sub {theta}}{rho}{sub {alpha}} {much gt} 1. The maximum growth rate is obtained at {kappa}{sub {theta}}{rho}{sub {alpha}} on the order of unity and is nearly constant for the range of 0.7 < {upsilon}{sub {alpha}}/{upsilon}{sub A} < 2.5. On the other hand, the trapped particle response is dominated by the precessional drift resonance. The bounce resonant contribution is negligible. The growth rate peaks sharply at the value of {kappa}{sub {theta}}{rho}{sub {alpha}} such that the precessional drift resonance occurs for the most energetic trapped particles. The maximum growth rate due to the energetic trapped particles is comparable to that of circulating particles.
G.J. Kramer; S.E. Sharapov; R. Nazikian; N.N. Gorelenkov; R. Budny; JET-EFDA contributors
2003-01-15
Experimental evidence is presented for the existence of the theoretically predicted odd Torodicity-induced Alfven Eigenmode (TAEs) from the simultaneous appearance of odd and even TAEs in a normal shear discharge. The modes are observed in low central magnetic shear plasmas created by injecting lower hybrid current drive. A fast ion population was created by applying ion cyclotron heating at the high field side to excite the TAEs in the weak magnetic shear region. The odd TAEs were identified from their frequency, mode number, and timing relative to the even TAEs.
E.D. Fredrickson; N. Gorelenkov; C.Z. Cheng; R. Bell; D. Darrow; D. Johnson; S. Kaye; B. LeBlanc; J. Menard; S. Kubota; W. Peebles
2001-10-03
Neutral-beam-driven compressional Alfven eigenmodes (CAE) at frequencies below the ion cyclotron frequency have been observed and identified for the first time in the National Spherical Torus Experiment (NSTX). The modes are observed as a broad spectrum of nearly equally spaced peaks in the frequency range from approximately 0.2 to approximately 1.2 omega(subscript ''ci''). The frequency has a scaling with toroidal field and plasma density consistent with Alfven waves. The modes have been observed with high bandwidth magnetic pick-up coils and with a reflectometer.
Budny, R.; Chang, Z.; Fu, G.Y.; Nazikian, R.
1998-07-09
The toroidal Alfvén eigenmodes (TAE) in the Tokamak Fusion Test Reactor [K. Young, et al., Plasma Phys. Controlled Fusion 26, 11 (1984)]deuterium-tritium plasmas are analyzed using the NOVA-K code [C.Z. Cheng, Phys. Reports 211, 1 (1992)]. The theoretical results are compared with the experimental measurements in detail. In most cases, the theory agrees with the observations in terms of mode frequency, mode structure, and mode stability. However, one mode with toroidal mode number n = 2 is observed to be poloidally localized on the high field side of the magnetic axis with a mode frequency substantially below the TAE frequency.
Taylor, J.P.H.; Walker, A.D.M. )
1987-09-01
When the azimuthal wave number is large, the equations describing standing hydromagnetic waves in the magnetosphere can be written as a set of coupled equations describing the couples magnetosonic and Alfven waves. These equations are decoupled when the filed lines are straight. The eigenfrequencies of the decoupled oscillations are computed. For typical conditions in the outer magnetosphere these give periods in the Pc 4-5 band or above. The longitudinal magnetosonic wave consists of oscillations in the plasma pressure, the longitudinal plasma drift velocity and the compressional magnetic field. Higher harmonics of the standing waves have nodes quite near the equator. These higher harmonics have larger fractional pressure perturbations at high latitudes. The compressional magnetic field for all modes, however, is substantially attenuated at higher latitudes, and the theory predicts that compressional oscillations of B are only likely to be seen near the equator. Conditions can be favorable for resonance to occur between the magnetosonic mode and the transverse Alfven mode. The computed results show periods of the right order of magnitude to explain observations of compressional pulsations. The theory has the potential to explain the polarization when coupling is fully taken into account.
NASA Astrophysics Data System (ADS)
Waltz, R. E.; Bass, E. M.; Heidbrink, W. W.; VanZeeland, M. A.
2015-11-01
Recent experiments with the DIII-D tilted neutral beam injection (NBI) varying the beam energetic particle (EP) source profiles have provided strong evidence that unstable Alfven eigenmodes (AE) drive stiff EP transport at a critical EP density gradient [Heidbrink et al 2013 Nucl. Fusion 53 093006]. Here the critical gradient is identified by the local AE growth rate being equal to the local ITG/TEM growth rate at the same low toroidal mode number. The growth rates are taken from the gyrokinetic code GYRO. Simulation show that the slowing down beam-like EP distribution has a slightly lower critical gradient than the Maxwellian. The ALPHA EP density transport code [Waltz and Bass 2014 Nucl. Fusion 54 104006], used to validate the model, combines the low-n stiff EP critical density gradient AE mid-core transport with the Angioni et al (2009 Nucl. Fusion 49 055013) energy independent high-n ITG/TEM density transport model controling the central core EP density profile. For the on-axis NBI heated DIII-D shot 146102, while the net loss to the edge is small, about half the birth fast ions are transported from the central core r/a < 0.5 and the central density is about half the slowing down density. These results are in good agreement with experimental fast ion pressure profiles inferred from MSE constrained EFIT equilibria.
Toroidal Alfven wave stability in ignited tokamaks
Cheng, C.Z.; Fu, G.Y.; Van Dam, J.W.
1989-01-01
The effects of fusion-product alpha particles on the stability of global-type shear Alfven waves in an ignited tokamak plasma are investigated in toroidal geometry. Finite toroidicity can lead to stabilization of the global Alfven eigenmodes, but it induces a new global shear Alfven eigenmodes, which is strongly destabilized via transit resonance with alpha particles. 8 refs., 2 figs.
Low-n shear Alfven spectra in axisymmetric toroidal plasmas
Cheng, C.Z.; Chance, M.S.
1985-11-01
In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes coupling of different poloidal harmonics. It is shown both analytically and numerically that the toroidicity not only breaks up the shear Alfven continuous spectrum, but also creates new, discrete, toroidicity-induced shear Alfven eigenmodes with frequencies inside the continuum gaps. Potential applications of the low-n toroidicity-induced shear Alfven eigenmodes on plasma heating and instabilities are addressed. 17 refs., 4 figs.
Global Alfven modes: Theory and experiment
Turnbull, A.D.; Strait, E.J.; Heidbrink, W.W.; Chu, M.S.; Duong, H.H.; Greene, J.M.; Lao, L.L.; Taylor, T.S.; Thompson, S.J. )
1993-07-01
It is shown that the theoretical predictions and experimental observations of toroidicity-induced Alfven eigenmodes (TAE's) are now in good agreement, with particularly detailed agreement in the mode frequencies. Calculations of the driving and damping rates predict the importance of continuum damping for low toroidal mode numbers and this is confirmed experimentally. However, theoretical calculations in finite-[beta], shaped discharges predict the existence of other global Alfven modes, in particular the ellipticity-induced Alfven eigenmode (EAE) and a new mode, the beta-induced Alfven eigenmode (BAE). The BAE mode is calculated to be in or below the same frequency range as the TAE mode and may contribute to the experimental observations at high [beta]. Experimental evidence and complementary analyses are presented confirming the presence of the EAE mode at higher frequencies.
Decay of magnetic helicity producing polarized Alfven waves
Yoshida, Z.; Mahajan, S.M.
1994-02-01
When a super-Alfvenic electron beam propagates along an ambient magnetic field, the left-hand circularly polarized Alfven wave is Cherenkov-emitted (two stream instability). This instability results in a spontaneous conversion of the background plasma helicity to the wave helicity. The background helicity induces a frequency (energy) shift in the eigenmodes, which changes the critical velocity for Cherenkov emission, and it becomes possible for a sub-Alfvenic electron beam to excite a nonsingular Alfven mode.
Compressional Alfvin Eigenmode Dispersion in Low Aspect Ratio Plasmas
N.N. Gorelenkov; C.Z. Cheng; E. Fredrickson
2002-01-29
Recent observations of new fast ion beam driven instabilities in MHz frequency range in National Spherical Torus experiments (NSTX) are suggested to be Compressional Alfvin Eigenmodes (CAEs). A new theory of CAEs applicable to low aspect ratio toroidal plasmas is developed based on the ballooning representation for the poloidal dependence of the perturbed quantities. In agreement with observations, the analytical theory predicts that CAEs are discrete modes with frequencies correlated with the characteristic Alfvin velocity of the plasma. Plasma equilibrium structure is essential to determine accurately the dispersion of CAEs. The mode structure is localized in both the minor radius and the poloidal directions on the low magnetic field side.
Beam Distribution Modification By Alfven Modes
White, R. B.; Gorelenkov, N.; Heidbrink, W. W.; Van Zeeland, M. A.
2010-01-25
Modification of a deuterium beam distribution in the presence of low amplitude Toroidal Alfven (TAE) eigenmodes and Reversed Shear Alfven (RSAE) eigenmodes in a toroidal magnetic confinement device is examined. Comparison with experimental data shows that multiple low amplitude modes can account for significant modification of high energy beam particle distributions. It is found that there is a stochastic threshold for beam transport, and that the experimental amplitudes are only slightly above this threshold. The modes produce a substantial central flattening of the beam distribution.
Beam Distribution Modification by Alfven Modes
White, R. B.; Gorelenkov, N.; Heidbrink, W. W.; Van Zeeland, M. A.
2010-04-03
Modification of a deuterium beam distribution in the presence of low amplitude Toroidal Alfven (TAE) eigenmodes and Reversed Shear Alfven (RSAE) eigenmodes in a toroidal magnetic confinement device is examined. Comparison with experimental data shows that multiple low amplitude modes can account for significant modification of high energy beam particle distributions. It is found that there is a stochastic threshold for beam transport, and that the experimental amplitudes are only slightly above this threshold. The modes produce a substantial central flattening of the beam distribution.
Kinetic effects on global Alfven waves
Betti, R.
1992-01-01
A theoretical investigation is carried out on the effects of the kinetic particle response on global type shear-Alfven waves in tokamaks. Two kinds of wave-particle interactions have been identified: (1) resonant interaction between energetic circulating particles and high frequency Alfven waves, (2) nonresonant interaction between trapped particles and low frequency modes. The author focuses on gap modes which are discrete modes whose real frequency lies in gas of the Alfven continuum induced by geometrical effects. A new gap mode, the Ellipticity Induced Alfven Eigenmode (EAE), is induced by the ellipticity of the plasma cross section that couples the m and m + 2 poloidal harmonics. This mode is of the general class as the Toroidicity Induced Alfven Eigenmode (TAE). In configurations with finite ellipticity, the EAE (n; m, m + 2) has a global structure centered about the q = (m + 1)/n surface. In the presence of an energetic ion species any Alfven wave can be destabilized via transit resonance with circulating particles. A sufficient stability criterion is derived for energetic particle-Alfven mode. To include the stabilizing effects of the electron and ion Landau damping a general treatment using a newly derived drift kinetic description of each species is carried out. The analysis has been restricted to Alfven gap modes. Low frequency modes have been investigated using the new drift kinetic model. Focusing on the internal kink mode, the main kinetic contributions arises from trapped particles which process in the toroidal direction. The trapped bulk ions can destabilize the high frequency branch of the internal kink. The numerical solution of the dispersion relation shows that a sharp threshold in [beta][sub p] exists for the instability to grow and that stabilizing effects come from the trapped electron response.
Global particle-in-cell simulations of Alfvenic modes
Mishchenko, A.; Koenies, A.; Hatzky, R.
2008-11-01
Global linear gyro-kinetic particle-in-cell (PIC) simulations of electromagnetic modes in pinch and tokamak geometries are reported. The Toroidal Alfven Eigenmode and the Kinetic Ballooning Mode have been simulated. All plasma species have been treated kinetically (i.e. no hybrid fluid-kinetic or reduced-kinetic model has been applied). The main intention of the paper is to demonstrate that the global Alfven modes can be treated with the gyro-kinetic PIC method.
Garcia-Munoz, M.; Hicks, N.; Bilato, R.; Bobkov, V.; Bruedgam, M.; Fahrbach, H.-U.; Igochine, V.; Maraschek, M.; Sassenberg, K.; Voornveld, R. van; Classen, I. G. J.; Jaemsae, S.
2010-05-07
We present here the first phase-space characterization of convective and diffusive energetic particle losses induced by shear Alfven waves in a magnetically confined fusion plasma. While single toroidal Alfven eigenmodes (TAE) and Alfven cascades (AC) eject resonant fast ions in a convective process, an overlapping of AC and TAE spatial structures leads to a large fast-ion diffusion and loss. Diffusive fast-ion losses have been observed with a single TAE above a certain threshold in the fluctuation amplitude.
Destabilization of the shear Alfven mode by alpha particles and other high energy ions
NASA Astrophysics Data System (ADS)
Belikov, V. S.; Kolesnichenko, Ya. I.; Silivra, O. A.
1992-08-01
Toroidal Alfven eigenmode (TAE) and elliptical Alfven eigenmode (EAE) instabilities in plasmas with high energy ions are considered in the context of local theory. The instability growth rate is found for cases when waves are excited by alpha particles or by ions produced as a result of neutral injection or RF heating. Electron and ion Landau damping due to the toroidal sideband wave-particle interaction is also calculated. The electron damping rate is shown to be much lower than the generally accepted value. The TAE instability observed in the experiment with neutral beam injection on TFTR is analysed and the principal experimental features of TAE instability are explained
The interaction of Io's Alfven waves with the Jovian magnetosphere
NASA Astrophysics Data System (ADS)
Wright, A. N.
1987-09-01
A numerical solution for the propagation of the Alfven waves produced by Io is presented. The waves are shown to interact strongly with the torus and magnetic-field inhomogeneities. Substantial reflection occurs from the magnetospheric medium, and only about a quarter of the wave power will reach the ionosphere on its first pass. It is concluded that both WKB and ray-tracing arguments are inappropriate, contrary to previous studies. A more realistic picture may be that of a whole field line or L shell resonating in an eigenmode. The Alfven structure behind Io and some possible features that it may exhibit are discussed. In particular, it may be possible to produce decametric arcs that are more closely spaced than ray tracing permits by exciting higher-harmonic eigenmodes of Io's L shell.
Evolution of the alpha particle driven toroidicity induced Alfven mode
Wu, Y.; White, R.B.; Cheng, C.Z.
1994-04-01
The interaction of alpha particles with a toroidicity induced Alfven eigenmode is investigated self-consistently by using a kinetic dispersion relation. All important poloidal harmonics and their radial mode profiles are included. A Hamiltonian guiding center code is used to simulate the alpha particle motion. The simulations include particle orbit width, nonlinear particle dynamics and the effects of the modes on the particles. Modification of the particle distribution leading to mode saturation is observed. There is no significant alpha particle loss.
Kortny Rolston
2011-10-01
The Center for Advanced Energy Studies was created to lead research programs important to the nation, attract students and faculty to the Idaho universities and act as a catalyst for technology-based economic development. CAES is striving to meet those goals by continuing to develop its infrastructure and equipment capabilities, expand its research portfolio and bolster Idaho's energy workforce. This Annual Report details the progress CAES made in FY 2011 toward fulfilling its research, education and economic development missions.
Belova, E V; Gorelenkov, N N; Fredrickson, E D; Tritz, K; Crocker, N A
2015-07-01
An energy-channeling mechanism is proposed to explain flattening of the electron temperature profiles at a high beam power in the beam-heated National Spherical Torus Experiment (NSTX). Results of self-consistent simulations of neutral-beam-driven compressional Alfvén eigenmodes (CAEs) in NSTX are presented that demonstrate strong coupling of CAEs to kinetic Alfvén waves at the Alfvén resonance location. It is suggested that CAEs can channel energy from the beam ions to the location of the resonant mode conversion at the edge of the beam density profile, modifying the energy deposition profile. PMID:26182100
Evolution of Eigenmodes of the Mhd-Waveguide in the Outer Magnetosphere
NASA Astrophysics Data System (ADS)
Chuiko, Daniil
EVOLUTION OF EIGENMODES OF THE MHD-WAVEGUIDE IN THE OUTER MAGNETOSPHERE Mazur V.A., Chuiko D.A. Institute of Solar-Terrestrial Physics, Irkutsk, Russia. Geomagnetic field and plasma inhomogeneties in the outer equatorial part of the magnetosphere al-lows for existence of a channel with low Alfven speeds, which spans from the nose to the far flanks of the magnetosphere, in the morning as well as in the evening sectors. This channel plays a role of a waveguide for fast magnetosonic waves. When an eigenmode travels along the waveguide (i.e. in the azimuthal direction) it undergoes certain evolution. The parameters of the waveguide are changing along the way of wave’s propagation and the eigenmode “adapts” to these parameters. Conditions of the Kelvin-Helmholtz instability are changing due to the increment in the solar wind speed along the magnetopause. The conditions of the solar wind hydromagnetic waves penetration to the magnetosphere are changing due to the same increment. As such, the process of the penetration turns to overreflection regime, which abruptly increases the pump level of the magnetospheric waveguide. There is an Alfven resonance deep within the magnetosphere, which corresponds to the propagation of the fast mode along the waveguide. Oscillation energy dissipation takes place in the vicinity of the Alfven resonance. Alfven resonance is a standing Alfven wave along the magnetic field lines, so it reaches the ionosphere and the Earth surface, when the fast modes of the waveguide, localized in the low Alfven speed channel cannot be observed on Earth. The evolution of the waveguide oscillation propagating from the nose to the far tail is theoretically investigated in this work with consideration of all aforementioned effects. The spatial structure var-iation character, spectral composition and amplitude along the waveguide are found.
NASA Astrophysics Data System (ADS)
Gelly, B.
Starting from a well-known phenomenon -the 5 mn solar oscillations-, this text describes the process which allows to produce the very few numbers used to infer the internal structure and rotation of the Sun with an unsurpassed accuracy. We shall describe for one part the instrumental principles, the raw data processing, and all things happening prior to the spectra computation, and for another part the techniques to obtain and validate the eigenmodes parameters. Finally we shall discuss the topic of the amplification of the oscillations by solar limb, upon which is based the helioseismology program of the PICARD space mission.
Stability of Alfven gap modes in burning plasmas
Betti, R.; Freidberg, J.P. )
1992-06-01
A stability analysis is carried out for energetic particle-Alfven gap modes. Three modes have been identified: the toroidicity, ellipticity, and noncircular triangularity induced Alfven eigenmodes (TAE, EAE, and NAE). In highly elongated plasma cross sections with {kappa}{minus}1{similar to}1, the EAE may be a more robust mode than the TAE and NAE. It is found that electron Landau damping in highly elongated plasmas has a strong stabilizing influence on the {ital n}=1 EAE, while ion Landau damping stabilizes the {ital n}=1 TAE in high-density regimes. Furthermore, the NAE turns out to be stable for all currently proposed ignition experiments. The stability analysis of a typical burning plasma device, Burning Plasma Experiment (BPX) (Phys. Scr. {bold T16}, 89 (1987)) shows that {ital n}{gt}1 gap modes can pose a serious threat to the achievement of ignition conditions.
Potential underground risks associated with CAES.
Kirk, Matthew F.; Webb, Stephen Walter; Broome, Scott Thomas; Pfeifle, Thomas W.; Grubelich, Mark Charles; Bauer, Stephen J.
2010-10-01
CAES in geologic media has been proposed to help 'firm' renewable energy sources (wind and solar) by providing a means to store energy when excess energy was available, and to provide an energy source during non-productive renewable energy time periods. Such a storage media may experience hourly (perhaps small) pressure swings. Salt caverns represent the only proven underground storage used for CAES, but not in a mode where renewable energy sources are supported. Reservoirs, both depleted natural gas and aquifers represent other potential underground storage vessels for CAES, however, neither has yet to be demonstrated as a functional/operational storage media for CAES.
Fredrickson, E. D.; Gorelenkov, N.; Cheng, C. Z.; Bell, R.; Darrow, D.; Johnson, D.; Kaye, S.; LeBlanc, B.; Menard, J.; Kubota, S.
2001-10-01
Neutral-beam-driven compressional Alfven eigenmodes at frequencies below the ion cyclotron frequency have been observed and identified for the first time in the National Spherical Torus Experiment. The modes are observed as a broad spectrum of nearly equally spaced peaks in the frequency range from {approx}0.2{omega}{sub ci} to {approx}1.2{omega}{sub ci} . The frequency has a scaling with toroidal field and plasma density consistent with Alfven waves. The modes have been observed with high bandwidth magnetic pickup coils and with a reflectometer.
Observation of modes at frequencies near the second Alfven gap in TFTR
Fredrickson, E.; Van Dam, J.W.; Budny, R.V.; Darrow, D.; Fu, G.Y.; Hosea, J.; Phillips, C.K.; Wilson, J.R.
2000-04-26
Modes have been observed near the frequency of the second Alfven gap during off-axis H-minority heating experiments in the circular cross-section Tokamak Fusion Test Reactor. The observation of these modes is surprising in that the second gap, which is generally opened with ellipticity, is expected to be small, of order (r/R){sup 2}. A model is proposed in which the second gap is opened by the fast ion beta, which is shown to be able to introduce mode coupling, much as toroidal effects introduce mode coupling for Toroidal Alfven Eigenmodes (TAE). The modes are seen with and without accompanying TAE mode activity.
Hybrid MHD/particle simulation study of sub-cyclotron Alfvén Eigenmodes in NSTX
NASA Astrophysics Data System (ADS)
Lestz, Jeff; Belova, Elena; Gorelenkov, N. N.
2015-11-01
Low toroidal mode number, high frequency compressional (CAE) and global (GAE) Alfvén Eigenmodes are often driven unstable by super-Alfvénic beam ions in NSTX. These modes have been identified as part of an energy channeling mechanism that may explain observed anomalous electron temperature profile flattening in beam-heated NSTX discharges. 3D hybrid simulations using the HYM code are conducted to study the excitation and stability properties of such CAE and GAE modes in NSTX and NSTX-like plasmas. HYM allows for the self-consistent simulation of these modes with a delta-f particle treatment of the energetic beam ions coupled to a single fluid resistive MHD model of the thermal plasma. Particular attention is paid to the sensitivity of CAE/GAE excitation on parametric changes in the equilibrium beam ion distribution function, among other factors.
Eigenmode analysis of compressional waves in the magnetosphere
Cheng, C.Z.; Lin, C.S.
1987-04-01
A field-aligned eigenode analysis of compressional Alfven instabilities has been performed for a two component anisotropic plasma in a dipole magnetic field. The eigenmode equations are derived from the gyrokinetic equations in the long wavelength (k rho < 1) and low frequency (..omega.. < ..omega../sub b/) limits, where rho is the hot particle gyroradius and ..omega../sub b/ is the hot particle bounce frequency. Two types of compressional instabilities are identified. One is the drift mirror mode which has an odd parity compressional magnetic component with respect to the magnetic equator. The other is the drift compressional mode with an even parity compressional magnetic component. For typical storm time plasma parameters neargeosynchronous orbit, the drift mirror mode is most unstable and the drift compressional mode is stable. The storm time compressional Pc 5 waves, observed by multiple satellites during November 14-15, 1979 (Takahashi et al., 1987), can be explained by the drift mirror instability.
Quasi-modes as dissipative MHD eigenmodes : results for 1-dimensional equilibrium states
NASA Astrophysics Data System (ADS)
Tirry, W. J.; Goossens, M.
1996-05-01
Quasi-modes which are important for understanding the MHD wave behavior of solar and astrophysical magnetic plasmas are computed as eigenmodes of the linear dissipative MHD equations. This eigenmode computation is carried out with a simple numerical scheme which is based on analytical solutions to the dissipative MHD equations in the quasi-singular resonance layer. Non-uniformity in magnetic field and plasma density gives rise to a continuous spectrum of resonant frequencies. Global discrete eigenmodes with characteristic frequencies lying within the range of the continuous spectrum may couple to localised resonant Alfven waves. In ideal MHD these modes are not eigenmodes of the Hermitian ideal MHD operator, but are found as a temporal dominant global exponentially decaying response to an initial perturbation. In dissipative MHD they are really eigenmodes with damping becoming independent of the dissipation mechanism in the limit of vanishing dissipation. An analytical solution of these global modes is found in the dissipative layer around the resonant Alfvenic position. Using the analytical solution to cross the quasi-singular resonance layer the required numerical effort of the eigenvalue scheme is limited to the integration of the ideal MHD equations in regions away from any singularity. The presented scheme allows for a straightforward parametric study. The method is checked with known ideal quasi-mode frequencies found for a 1-D box model for the Earth's magnetosphere (Zhu & Kivelson 1988). The agreement is excellent. The dependence of the oscillation frequency on the wavenumbers for a 1-D slab model for coronal loops found by Ofman, Davila, & Steinolfson (1995) is also easily recovered.
Nature of monster sawteeth and their relationship to Alfven instabilities in tokamaks
Bernabei; Bell; Budny; Fredrickson; Gorelenkov; Hosea; Majeski; Mazzucato; Phillips; Schilling; Wilson
2000-02-01
A correlation is explored between the presence of energetic particle modes (EPM) and long-period sawtooth oscillations in tokamak plasmas heated by rf waves. The eventual crash of these sawteeth is explained in terms of the loss of the stabilizing fast particles due to the EPM. The absence of long-period sawteeth in high q(a) discharges is explained in terms of ion loss due to toroidal Alfven eigenmodes. PMID:11017481
Analysis and gyrokinetic simulation of MHD Alfven wave interactions
NASA Astrophysics Data System (ADS)
Nielson, Kevin Derek
The study of low-frequency turbulence in magnetized plasmas is a difficult problem due to both the enormous range of scales involved and the variety of physics encompassed over this range. Much of the progress that has been made in turbulence theory is based upon a result from incompressible magnetohydrodynamics (MHD), in which energy is only transferred from large scales to small via the collision of Alfven waves propagating oppositely along the mean magnetic field. Improvements in laboratory devices and satellite measurements have demonstrated that, while theories based on this premise are useful over inertial ranges, describing turbulence at scales that approach particle gyroscales requires new theory. In this thesis, we examine the limits of incompressible MHD theory in describing collisions between pairs of Alfven waves. This interaction represents the fundamental unit of plasma turbulence. To study this interaction, we develop an analytic theory describing the nonlinear evolution of interacting Alfven waves and compare this theory to simulations performed using the gyrokinetic code AstroGK. Gyrokinetics captures a much richer set of physics than that described by incompressible MHD, and is well-suited to describing Alfvenic turbulence around the ion gyroscale. We demonstrate that AstroGK is well suited to the study of physical Alfven waves by reproducing laboratory Alfven dispersion data collected using the LAPD. Additionally, we have developed an initialization alogrithm for use with AstroGK that allows exact Alfven eigenmodes to be initialized with user specified amplitudes and phases. We demonstrate that our analytic theory based upon incompressible MHD gives excellent agreement with gyrokinetic simulations for weakly turbulent collisions in the limit that k⊥rho i << 1. In this limit, agreement is observed in the time evolution of nonlinear products, and in the strength of nonlinear interaction with respect to polarization and scale. We also examine the
Anisotropic Alfven-ballooning modes in the Earth's magnetosphere
Chan, A.A. . Dept. of Physics and Astronomy); Xia, Mengfen . Dept. of Physics); Chen, Liu . Plasma Physics Lab.)
1993-05-01
We have carried out a theoretical analysis of the stability and parallel structure of coupled shear-Alfven and slow-magnetosonic waves in the Earth's inner magnetosphere including effects of finite anisotropic plasma pressure. Multiscale perturbation analysis of the anisotropic Grad-Shafranov equation yields an approximate self-consistent magnetohydrodynamic (MHD) equilibrium. This MHD equilibrium is used in the numerical solution of a set of eigenmode equations which describe the field line eigenfrequency, linear stability, and parallel eigenmode structure. We call these modes anisotropic Alfven-ballooning modes. The main results are: The field line eigenfrequency can be significantly lowered by finite pressure effects. The parallel mode structure of the transverse wave components is fairly insensitive to changes in the plasma pressure but the compressional magnetic component can become highly peaked near the magnetic equator due to increased pressure, especially when P[perpendicular] > P[parallel]. For the isotropic case ballooning instability can occur when the ratio of the plasma pressure to the magnetic pressure, exceeds a critical value [beta][sub o][sup B] [approx] 3.5 at the equator. Compared to the isotropic case the critical beta value is lowered by anisotropy, either due to decreased field-line-bending stabilization when P[parallel] > P[perpendicular], or due to increased ballooning-mirror destabilization when P[perpendicular] > P[parallel]. We use a [beta]-6 stability diagram'' to display the regions of instability with respect to the equatorial values of the parameters [bar [beta
High-n ideal and resistive shear Alfven waves in tokamaks
Cheng, C.Z.; Chen, L.; Chance, M.S.
1984-05-01
Ideal and resistive MHD equations for the shear Alfven waves are studied in a low-..beta.. toroidal model by employing the high-n ballooning formalism. The ion sound effects are neglected. For an infinite shear slab, the ideal MHD model gives rise to a continuous spectrum of real frequencies and discrete eigenmodes (Alfven-Landau modes) with complex frequencies. With toroidal coupling effects due to nonuniform toroidal magnetic field, the continuum is broken up into small continuum bands and new discrete toroidal eigenmodes can exist inside the continuum gaps. Unstable ballooning eigenmodes are also introduced by the bad curvature when ..beta.. > ..beta../sub c/. The resistivity (n) can be considered perturbatively for the ideal modes. In addition, four branches of resistive modes are induced by the resistivity: (1) Resistive entropy modes which are stable (..delta..' < 0) with frequencies approaching zero as n/sup 3/5/, (3) Resistive periodic shear Alfven waves which approach the finite frequency end points of the continuum bands and n/sup 1/2, and (4) Resistive ballooning modes which are purely growing with growth rate proportional to eta/sup 1/3/..beta../sup 2/3/ as eta ..-->.. O and ..beta.. ..-->.. O.
Experimental aspects of effects of high-energy particles on Alfven modes
Heidbrink, W.W.
1994-10-01
Global Alfven modes are observed in a number of tokamaks, including DIII-D and TFTR. Instabilities occur during neutral-beam injection and during fast-wave ICRF heating, and may recently have been observed during alpha-particle heating. Identification of toroidicity-induced Alfven eigenmodes (TAE) is based primarily on the scaling of the real frequency of the mode. Other modes, including the beta-induced Alfven eigenmode (BAE), are also observed. The stability threshold of TAE modes agree (to within a factor of two) with theoretical predictions. Toroidal mode numbers of n = 2-6 are usually most unstable, as theoretically expected. Measurements of the poloidal and radial mode structure are consistent with theoretical predictions, but the uncertainties are large. Both TAE and BAE modes can cause large, concentrated losses of fast ions. Phenomenologically, beam-driven Alfven modes usually {open_quotes}saturate{close_quotes} through bursts that expel beam ions, while modes observed during ICPF heating approach a steady saturation amplitude.
Mitigation of Alfvenic activity by 3D magnetic perturbations on NSTX
Kramer, G. J.; Bortolon, A.; Ferraro, N. M.; Spong, D. A.; Crocker, N. A.; Darrow, D. S.; Fredrickson, E. D.; Kubota, S.; Park, J. -K.; Podesta, M.; et al
2016-07-05
Observations on the National Spherical Torus eXperiment (NSTX) indicate that externally applied non-axisymmetric magnetic perturbations (MP) can reduce the amplitude of Toroidal Alfven Eigenmodes (TAE) and Global Alfven Eigenmodes (GAE) in response to pulsed n=3 non-resonant fields. From full-orbit following Monte Carlo simulations with the 1- and 2-fluid resistive MHD plasma response to the magnetic perturbation included, it was found that in response to MP pulses the fast-ion losses increased and the fast-ion drive for the GAEs was reduced. The MP did not affect the fast-ion drive for the TAEs significantly but the Alfven continuum at the plasma edge wasmore » found to be altered due to the toroidal symmetry breaking which leads to coupling of different toroidal harmonics. The TAE gap was reduced at the edge creating enhanced continuum damping of the global TAEs, which is consistent with the observations. Furthermore, the results suggest that optimized non-axisymmetric MP might be exploited to control and mitigate Alfven instabilities by tailoring the fast-ion distribution function and/or continuum structure.« less
Energy channeling from trapped to passing fast ions mediated by GAE/CAE activity in NSTX
NASA Astrophysics Data System (ADS)
Medley, S. S.; Belova, E.; Kramer, G.; Podesta, M.; Liu, D.
2013-10-01
In the National Spherical Torus Experiment, an increased charge exchange neutral flux localized at the neutral beam full injection energy is measured by the E||B Neutral Particle Analyzer. Termed the High-Energy Feature (HEF), it appears on the beam-injected energetic ion spectrum in discharges where NTM or kink modes (f < 10 kHz) are absent, TAE activity (f ~ 10-150 kHz) is weak and CAE/GAE activity (f ~ 400 - 1200 kHz) is robust. The HEF exhibits a growth time of t ~ 20-80 ms and develops a slowing down distribution that continues to evolve over periods > 100 ms. HEFs are observed only in H-mode discharges with NB power Pb >= 4 MW and in the pitch range v||/v ~ 0.7 - 0.9. The HEF appears to be caused by a CAE/GAE wave-particle interaction that modifies the fast ion distribution, fi(E,v||/v,r). This mechanism was studied using the SPIRAL code that evolves an initial TRANSP-calculated fi(E,v||/v,r) distribution in the presence of background plasma profiles under drive from wave-particle resonances with CAE/GAE Alfvén eigenmodes. Supported by U.S. Department of Energy under Contract No. DE-AC02-09CH11466.
Quark eigenmodes and lattice QCD
NASA Astrophysics Data System (ADS)
Liu, Guofeng
In this thesis, we study a number of topics in lattice QCD through the low-lying quark eigenmodes in the domain wall fermion (DWF) formulation in the quenched approximation. Specifically, we present results for the chiral condensate measured from these eigenmodes; we investigate the QCD vacuum structure by looking at the correlation between the magnitude of the chirality density, |psi†(x)gamma5psi( x)|, and the normal density, psi†( x)psi(x), for these states; we study the behavior of DWF formulation at large quark masses by investigating the mass dependence of the eigenvalues of the physical four dimensional-states as well as the bulk, five-dimensional states.
Seneca Compressed Air Energy Storage (CAES) Project
2012-11-30
This document provides specifications for the process air compressor for a compressed air storage project, requests a budgetary quote, and provides supporting information, including compressor data, site specific data, water analysis, and Seneca CAES value drivers.
Next Generation CAD/CAM/CAE Systems
NASA Technical Reports Server (NTRS)
Noor, Ahmed K. (Compiler); Malone, John B. (Compiler)
1997-01-01
This document contains presentations from the joint UVA/NASA Workshop on Next Generation CAD/CAM/CAE Systems held at NASA Langley Research Center in Hampton, Virginia on March 18-19, 1997. The presentations focused on current capabilities and future directions of CAD/CAM/CAE systems, aerospace industry projects, and university activities related to simulation-based design. Workshop attendees represented NASA, commercial software developers, the aerospace industry, government labs, and academia. The workshop objectives were to assess the potential of emerging CAD/CAM/CAE technology for use in intelligent simulation-based design and to provide guidelines for focused future research leading to effective use of CAE systems for simulating the entire life cycle of aerospace systems.
Nonlinear interaction of fast particles with Alfven waves in toroidal plasmas
Candy, J.; Borba, D.; Huysmans, G.T.A.; Kerner, W.; Berk, H.L.
1996-12-17
A numerical algorithm to study the nonlinear, resonant interaction of fast particles with Alfven waves in tokamak geometry has been developed. The scope of the formalism is wide enough to describe the nonlinear evolution of fishbone modes, toroidicity-induced Alfven eigenmodes and ellipticity-induced Alfven eigenmodes, driven by both passing and trapped fast ions. When the instability is sufficiently weak, it is known that the wave-particle trapping nonlinearity will lead to mode saturation before wave-wave nonlinearities are appreciable. The spectrum of linear modes can thus be calculated using a magnetohydrodynamic normal-mode code, then nonlinearly evolved in time in an efficient way according to a two-time-scale Lagrangian dynamical wave model. The fast particle kinetic equation, including the effect of orbit nonlinearity arising from the mode perturbation, is simultaneously solved of the deviation, {delta}f = f {minus} f{sub 0}, from an initial analytic distribution f{sub 0}. High statistical resolution allows linear growth rates, frequency shifts, resonance broadening effects, and nonlinear saturation to be calculated quickly and precisely. The results have been applied to an ITER instability scenario. Results show that weakly-damped core-localized modes alone cause negligible alpha transport in ITER-like plasmas--even with growth rates one order of magnitude higher than expected values. However, the possibility of significant transport in reactor-type plasmas due to weakly unstable global modes remains an open question.
Basic physics of Alfven instabilities driven by energetic particles in toroidally confined plasmas
Heidbrink, W. W.
2008-05-15
Superthermal energetic particles (EP) often drive shear Alfven waves unstable in magnetically confined plasmas. These instabilities constitute a fascinating nonlinear system where fluid and kinetic nonlinearities can appear on an equal footing. In addition to basic science, Alfven instabilities are of practical importance, as the expulsion of energetic particles can damage the walls of a confinement device. Because of rapid dispersion, shear Alfven waves that are part of the continuous spectrum are rarely destabilized. However, because the index of refraction is periodic in toroidally confined plasmas, gaps appear in the continuous spectrum. At spatial locations where the radial group velocity vanishes, weakly damped discrete modes appear in these gaps. These eigenmodes are of two types. One type is associated with frequency crossings of counterpropagating waves; the toroidal Alfven eigenmode is a prominent example. The second type is associated with an extremum of the continuous spectrum; the reversed shear Alfven eigenmode is an example of this type. In addition to these normal modes of the background plasma, when the energetic particle pressure is very large, energetic particle modes that adopt the frequency of the energetic particle population occur. Alfven instabilities of all three types occur in every toroidal magnetic confinement device with an intense energetic particle population. The energetic particles are most conveniently described by their constants of motion. Resonances occur between the orbital frequencies of the energetic particles and the wave phase velocity. If the wave resonance with the energetic particle population occurs where the gradient with respect to a constant of motion is inverted, the particles transfer energy to the wave, promoting instability. In a tokamak, the spatial gradient drive associated with inversion of the toroidal canonical angular momentum P{sub {zeta}} is most important. Once a mode is driven unstable, a wide variety
Skew chicane based betatron eigenmode exchange module
Douglas, David
2010-12-28
A skewed chicane eigenmode exchange module (SCEEM) that combines in a single beamline segment the separate functionalities of a skew quad eigenmode exchange module and a magnetic chicane. This module allows the exchange of independent betatron eigenmodes, alters electron beam orbit geometry, and provides longitudinal parameter control with dispersion management in a single beamline segment with stable betatron behavior. It thus reduces the spatial requirements for multiple beam dynamic functions, reduces required component counts and thus reduces costs, and allows the use of more compact accelerator configurations than prior art design methods.
Seneca Compressed Air Energy Storage (CAES) Project
None, None
2012-11-30
Compressed Air Energy Storage (CAES) is a hybrid energy storage and generation concept that has many potential benefits especially in a location with increasing percentages of intermittent wind energy generation. The objectives of the NYSEG Seneca CAES Project included: for Phase 1, development of a Front End Engineering Design for a 130MW to 210 MW utility-owned facility including capital costs; project financials based on the engineering design and forecasts of energy market revenues; design of the salt cavern to be used for air storage; draft environmental permit filings; and draft NYISO interconnection filing; for Phase 2, objectives included plant construction with a target in-service date of mid-2016; and for Phase 3, objectives included commercial demonstration, testing, and two-years of performance reporting. This Final Report is presented now at the end of Phase 1 because NYSEG has concluded that the economics of the project are not favorable for development in the current economic environment in New York State. The proposed site is located in NYSEG’s service territory in the Town of Reading, New York, at the southern end of Seneca Lake, in New York State’s Finger Lakes region. The landowner of the proposed site is Inergy, a company that owns the salt solution mining facility at this property. Inergy would have developed a new air storage cavern facility to be designed for NYSEG specifically for the Seneca CAES project. A large volume, natural gas storage facility owned and operated by Inergy is also located near this site and would have provided a source of high pressure pipeline quality natural gas for use in the CAES plant. The site has an electrical take-away capability of 210 MW via two NYSEG 115 kV circuits located approximately one half mile from the plant site. Cooling tower make-up water would have been supplied from Seneca Lake. NYSEG’s engineering consultant WorleyParsons Group thoroughly evaluated three CAES designs and concluded that any
Investigation of an ion-ion hybrid Alfven wave resonator
Vincena, S. T.; Farmer, W. A.; Maggs, J. E.; Morales, G. J.
2013-01-15
A theoretical and experimental investigation is made of a wave resonator based on the concept of wave reflection along the confinement magnetic field at a spatial location where the wave frequency matches the local value of the ion-ion hybrid frequency. Such a situation can be realized by shear Alfven waves in a magnetized plasma with two ion species because this mode has zero parallel group velocity and experiences a cut-off at the ion-ion hybrid frequency. Since the ion-ion hybrid frequency is proportional to the magnetic field, it is expected that a magnetic well configuration in a two-ion plasma can result in an Alfven wave resonator. Such a concept has been proposed in various space plasma studies and could have relevance to mirror and tokamak fusion devices. This study demonstrates such a resonator in a controlled laboratory experiment using a H{sup +}-He{sup +} mixture. The resonator response is investigated by launching monochromatic waves and impulses from a magnetic loop antenna. The observed frequency spectra are found to agree with predictions of a theoretical model of trapped eigenmodes.
Electron Signatures and Alfven Waves
NASA Technical Reports Server (NTRS)
Andersson, Laila; Ivchenko, N.; Clemmons, J.; Namgaladze, A. A.; Gustavsson, B.; Wahlund, J.-E.; Eliasson, L.; Yurik, R. Y.
2000-01-01
The electron signatures which appear together with Alfven waves observed by the Freja satellite in the auroral region are reported. Precipitating electrons are detected both with and just before the wave. The observed Alfven waves must therefore be capable of accelerating electrons to higher energies than the local phase velocity of these waves in order for the electrons to move in advance of the wave. The characteristics of such electrons suggest electrons moving infront of the wave have characteristics of origin from warmer and lower density plasma while the electrons moving with the wave have characteristics of cooler and denser plasma. The pitch angle distribution of the electrons moving with the wave indicates that there is continuous acceleration of new particles by the wave, i.e. a propagating Alfven wave is the source of these electrons . A simple model of a propagating source is made to model the electrons that are moving in advance of the wave. Depending on whether accelerated electrons leave the wave above or below the altitude where the Alfven wave has the highest phase velocity, the detected electron signatures will be different; electron dispersion or potential drop like, respectively. It is shown that the Alfven wave acceleration can create electron signatures similar to inverted-V structures.
Alfven solitons in the solar wind
NASA Technical Reports Server (NTRS)
Ovenden, C.; Schwartz, S. J.
1983-01-01
A nonlinear Alfven soliton solution of the MHD equations is presented. This solution represents the final state of modulationally unstable Alfven waves. A model of the expected turbulent spectrum due to a collection of such solitons is briefly described.
Observation of modes at frequencies near the second Alfven gap in TFTR
Fredrickson, E.; Van Dam, J. W.; Budny, R. V.; Darrow, D.; Fu, G. Y.; Hosea, J.; Phillips, C. K.; Wilson, J. R.
1999-09-20
Modes have been observed near the frequency of the second Alfven gap during off-axis H-minority heating experiments on TFTR. The observation of these modes is surprising in that the second gap, which is generally opened with ellipticity, is expected to be small, of order (r/R){sup 2}, since TFTR plasmas are circular in cross-section. A model is proposed in which the second gap is opened by the fast ion beta, which is shown to be able to introduce mode coupling, much as toroidal effects introduce mode coupling for Toroidal Alfven Eigenmodes (TAE). The modes are seen with and without accompanying TAE mode activity. (c) 1999 American Institute of Physics.
Formation of quasiparallel Alfven solitons
NASA Technical Reports Server (NTRS)
Hamilton, R. L.; Kennel, C. F.; Mjolhus, E.
1992-01-01
The formation of quasi-parallel Alfven solitons is investigated through the inverse scattering transformation (IST) for the derivative nonlinear Schroedinger (DNLS) equation. The DNLS has a rich complement of soliton solutions consisting of a two-parameter soliton family and a one-parameter bright/dark soliton family. In this paper, the physical roles and origins of these soliton families are inferred through an analytic study of the scattering data generated by the IST for a set of initial profiles. The DNLS equation has as limiting forms the nonlinear Schroedinger (NLS), Korteweg-de-Vries (KdV) and modified Korteweg-de-Vries (MKdV) equations. Each of these limits is briefly reviewed in the physical context of quasi-parallel Alfven waves. The existence of these limiting forms serves as a natural framework for discussing the formation of Alfven solitons.
Seneca Compressed Air Energy Storage (CAES) Project
2012-11-30
This report provides a review and an analysis of potential environmental justice areas that could be affected by the New York State Electric & Gas (NYSEG) compress air energy storage (CAES) project and identifies existing environmental burden conditions on the area and evaluates additional burden of any significant adverse environmental impact. The review assesses the socioeconomic and demographic conditions of the area surrounding the proposed CAES facility in Schuyler County, New York. Schuyler County is one of 62 counties in New York. Schuyler County’s 2010 population of 18,343 makes it one of the least populated counties in the State (U.S. Census Bureau, 2010). This report was prepared for WorleyParsons by ERM and describes the study area investigated, methods and criteria used to evaluate this area, and the findings and conclusions from the evaluation.
Kinetic Alfven waves on auroral field lines
NASA Technical Reports Server (NTRS)
Goertz, C. K.
1984-01-01
It is suggested on the basis of several observations of Alfven waves near auroral arcs that kinetic Alfven waves play a significant role in the process of particle acceleration. The characteristic properties of kinetic Alfven waves are summarized according to the theoretical classifications provided by Hasegawa and Mima (1979). The resonant coupling of large-scale surface waves to kinetic Alfven waves is also discussed. It is shown that kinetic Alfven waves can explain observations of what have previously been known as 'electrostatic' shocks.
Electrodynamic eigenmodes in cellular morphology.
Cifra, M
2012-09-01
Eigenmodes of the spherical and ellipsoidal dielectric electromagnetic resonator have been analysed. The sizes and shape of the resonators have been chosen to represent the shape of the interphase and dividing animal cell. Electromagnetic modes that have shape exactly suitable for positioning of the sufficiently large organelles in cell (centrosome, nucleus) have been identified. We analysed direction and magnitude of dielectrophoretic force exerted on large organelles by electric field of the modes. We found that the TM(1m1) mode in spherical resonator acts by centripetal force which drags the large organelles which have higher permittivity than the cytosol to the center of the cell. TM-kind of mode in the ellipsoidal resonator acts by force on large polarizable organelles in a direction that corresponds to the movement of the centrosomes (also nucleus) observed during the cell division, i.e. to the foci of the ellipsoidal cell. Minimal required force (10(-16) N), gradient of squared electric field and corresponding energy (10(-16) J) of the mode have been calculated to have biological significance within the periods on the order of time required for cell division. Minimal required energy of the mode, in order to have biological significance, can be lower in the case of resonance of organelle with the field of the cellular resonator mode. In case of sufficient energy in the biologically relevant mode, electromagnetic field of the mode will act as a positioning or steering mechanism for centrosome and nucleus in the cell, thus contribute to the spatial and dynamical self-organization in biological systems. PMID:22750075
NASA Astrophysics Data System (ADS)
Crocker, N. A.; Tritz, K.; White, R. B.; Fredrickson, E. D.; Gorelenkov, N. N.; NSTX-U Team
2015-11-01
New simulation results demonstrate that high frequency compressional (CAE) and global (GAE) Alfvén eigenmodes cause radial convection of electrons, with implications for particle and energy confinement, as well as electric field formation in NSTX-U. Simulations of electron orbits in the presence of multiple experimentally determined CAEs and GAEs, using the gyro-center code ORBIT, have revealed substantial convective transport, in addition to the expected diffusion via orbit stochastization. These results advance understanding of anomalous core energy transport expected in high performance, beam-heated NSTX-U plasmas. The simulations make use of experimentally determined density perturbation (δn) amplitudes and mode structures obtained by inverting measurements from 16 a channel reflectometer array using a synthetic diagnostic. Combined with experimentally determined mode polarizations (i.e. CAE or GAE), the δn are used to estimate the ExB displacements for use in ORBIT. Preliminary comparison of the simulation results with transport modeling by TRANSP indicate that the convection is currently underestimated. Supported by US DOE Contracts DE-SC0011810, DE-FG02-99ER54527 & DE-AC02-09CH11466.
CAE: A Tool for the Engineer--A Dilemma for the Academic.
ERIC Educational Resources Information Center
McCafferty, Ray
1986-01-01
Discusses the impact of Computer Aided Engineering (CAE) on traditional engineering teaching philosophy and methodology. Describes a new instructional approach based on CAE. Includes selected examples of problem situations which can be simulated through the use of CAE. (TW)
Mazur, V. A. Chuiko, D. A.
2013-06-15
Oscillations of the 'magnetosphere-solar wind' system are studied analytically in the framework of a plane-stratified model of the medium. The properties of oscillations are determined by three phenomena: Kelvin-Helmholtz instability on the tangential discontinuity (magnetopause) separating the magnetosphere and the solar wind, the presence of a waveguide for fast magnetosonic waves in the magnetosphere, and the Alfven resonance-a sharp increase in the amplitude of oscillations having the properties of Alfven waves-in the inner magnetosphere. The oscillations of the system form a discrete spectrum of eigenmodes. Analytical expressions are obtained for the frequency and growth rate of instability of each mode, as well as for the functions describing the spatial structure of these modes. All these characteristics of the eigenmodes are shown to depend on the velocity of the solar wind as a parameter. The dependences of the main mode characteristics (such as the instability thresholds, the points of the maximum and minimum growth rate, and the spatial distributions of the oscillation energy) on this parameter are determined for each eigenmode.
Stellarator Turbulence: Subdominant Eigenmodes and Quasilinear Modeling
NASA Astrophysics Data System (ADS)
Pueschel, M. J.; Faber, B. J.; Citrin, J.; Hegna, C. C.; Terry, P. W.; Hatch, D. R.
2016-02-01
Owing to complex geometry, gyrokinetic simulations in stellarator geometry produce large numbers of subdominant unstable and stable, near-orthogonal eigenmodes. Here, results based on the full eigenmode spectrum in stellarator geometry are presented for the first time. In the nonlinear state of a low-magnetic-shear ion-temperature-gradient-driven case, a multitude of these modes are active and imprint the system. Turbulent frequency spectra are broadband as a consequence, in addition to a nonlinear, narrow signature at electron frequencies. It is shown that successful quasilinear, mixing-length transport modeling is possible in stellarators, where it is essential to account for all subdominant unstable modes.
James Clerk Maxwell Prize for Plasma Physics Talk: On Nonlinear Physics of Shear Alfv'en Waves
NASA Astrophysics Data System (ADS)
Chen, Liu
2012-10-01
Shear Alfv'en Waves (SAW) are electromagnetic oscillations prevalent in laboratory and nature magnetized plasmas. Due to its anisotropic propagation property, it is well known that the linear wave propagation and dispersiveness of SAW are fundamentally affected by plasma nonuniformities and magnetic field geometries; for example, the existence of continuous spectrum, spectral gaps, and discrete eigenmodes in toroidal plasmas. This talk will discuss the crucial roles that nonuniformity and geometry could also play in the physics of nonlinear SAW interactions. More specifically, the focus will be on the Alfv'enic state and its breaking up by finite compressibility, non-ideal kinetic effects, and geometry. In the case of compressibility, finite ion-Larmor-radius effects are shown to qualitatively and quantitatively modify the three-wave parametric decays via the ion-sound perturbations. In the case of geometry, the spontaneous excitation of zonal structures by toroidal Alfv'en eigenmodes is investigated; demonstrating that, for realistic tokamak geometries, zonal current dominates over zonal flow. [4pt] Present address: Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou, China.
Highly Alfvenic Slow Solar Wind
NASA Technical Reports Server (NTRS)
Roberts, D. Aaron
2010-01-01
It is commonly thought that fast solar wind tends to be highly Alfvenic, with strong correlations between velocity and magnetic fluctuations, but examples have been known for over 20 years in which slow wind is both Alfvenic and has many other properties more typically expected of fast solar wind. This paper will present a search for examples of such flows from more recent data, and will begin to characterize the general characteristics of them. A very preliminary search suggests that such intervals are more common in the rising phase of the solar cycle. These intervals are important for providing constraints on models of solar wind acceleration, and in particular the role waves might or might not play in that process.
Do interplanetary Alfven waves cause auroral activity?
NASA Technical Reports Server (NTRS)
Roberts, D. Aaron; Goldstein, Melvyn L.
1990-01-01
A recent theory holds that high-intensity, long-duration, continuous auroral activity (HILDCAA) is caused by interplanetary Alfven waves propagating outward from the sun. A survey of Alfvenic intervals in over a year of ISEE 3 data shows that while Alfvenic intervals often accompany HILDCAAs, the reverse is often not true. There are many Alfvenic intervals during which auroral activity (measured by high values of the AE index) is very low, as well as times of high auroral activity that are not highly Alfvenic. This analysis supports the common conclusion that large AE values are associated with a southward interplanetary field of sufficient strength and duration. This field configuration is independent of the presence of Alfven waves (whether solar generated or not) and is expected to occur at random intervals in the large-amplitude stochastic fluctuations in the solar wind.
A Shift in Emphasis: Comments on CAE's New Mission Statement
ERIC Educational Resources Information Center
Anderson-Levitt, Kathryn M.
2007-01-01
In a presidential address prepared for the 2006 Council on Anthropology and Education (CAE) meeting, I argue that the new mission statement for CAE represents not a new direction for the organization, but simply a shift in emphasis, albeit an important and timely shift.
Anisotropic Alfven-ballooning modes in Earth's magnetosphere
NASA Technical Reports Server (NTRS)
Chan, Anthony A.; Xia, Mengfen; Chen, Liu
1994-01-01
We have carried out a theoretical analysis of the stability and parallel structure of coupled shear Alfven and slow magnetosonic waves in Earth's inner magnetopause (i.e., at equatorial distances between about five and ten Earth radii) including effects of finite anisotropic Grad-Shafranov equation yields an approximate self-consistent magnetohydrodynamic (MHD) equilibrium. This MHD equilibrium is used in the numerical solution of a set of eigenmode equations which describe the field line eigenfrequency, linear stability, and parallel eigenmode structure. We call these modes anisotropic Alfven-ballooning modes. The main results are: (1) The field line eigenfrequency can be significantly lowered by finite pressure effects. (2) The parallel mode structure of the transverse wave components is fairly insensitive to changes in the plasma pressure, but the compressional magnetic component can become highly peaked near the magnetic equator as a result of increased pressure, especially when P(sub perpendicular to) is greater than P(sub parallel) (here P(sub perpendicular to) and P(sub parallel) are the perpendicular and parallel plasma pressure). (3) For the isotropic (P(sub parallel) = P(sub perpendicular to) = P) case ballooning instability can occur when the ratio of the plasma presure to the magnetic pressure, beta = P/(B squared/8 pi), exceeds a critical value beta(sup B)(sub 0) is approximately equal to 3.5 at the equator. (4) Compared to the isotropic case the critical beta value is lowered by anisotropy, either due to decreased field line bending stabilization when P(sub parallel) is greater than P(sub perpendicular to) or due to increased ballooning-mirror destabilization when P(sub perpendicular to) is greater than P(sub parallel). (5) We use a beta-delta stability diagram to display the regions of instability with respect to the equatorial values of the parameters bar beta and delta, where bar beta = (1/3)(beta(sub parallel) + 2 beta(sub perpendicular to)) is an
Podesta, M.; Heidbrink, W. W.; Liu, D.; Ruskov, E.; Bell, R. E.; Darrow, D. S.; Fredrickson, E. D.; Gorelenkov, N. N.; Kramer, G. J.; LeBlanc, B. P.; Medley, S. S.; Roquemore, A. L.; Crocker, N. A.; Kubota, S.; Yuh, H.
2009-05-15
Fast-ion transport induced by Alfven eigenmodes (AEs) is studied in beam-heated plasmas on the National Spherical Torus Experiment [Ono et al., Nucl. Fusion 40, 557 (2000)] through space, time, and energy resolved measurements of the fast-ion population. Fast-ion losses associated with multiple toroidicity-induced AEs (TAEs), which interact nonlinearly and terminate in avalanches, are characterized. A depletion of the energy range >20 keV, leading to sudden drops of up to 40% in the neutron rate over 1 ms, is observed over a broad spatial range. It is shown that avalanches lead to a relaxation of the fast-ion profile, which in turn reduces the drive for the instabilities. The measured radial eigenmode structure and frequency of TAEs are compared with the predictions from a linear magnetohydrodynamics stability code. The partial disagreement suggests that nonlinearities may compromise a direct comparison between experiment and linear theory.
Nonlinear inertial Alfven wave in dusty plasmas
Mahmood, S.; Saleem, H.
2011-11-29
Solitary inertial Alfven wave in the presence of positively and negatively charged dust particles is studied. It is found that electron density dips are formed in the super Alfvenic region and wave amplitude is increased for the case of negatively charged dust particles in comparison with positively charged dust particles in electron-ion plasmas.
Solitary kinetic Alfven waves in dusty plasmas
Li Yangfang; Wu, D. J.; Morfill, G. E.
2008-08-15
Solitary kinetic Alfven waves in dusty plasmas are studied by considering the dust charge variation. The effect of the dust charge-to-mass ratio on the soliton solution is discussed. The Sagdeev potential is derived analytically with constant dust charge and then calculated numerically by taking the dust charge variation into account. We show that the dust charge-to-mass ratio plays an important role in the soliton properties. The soliton solutions are comprised of two branches. One branch is sub-Alfvenic and the soliton velocity is obviously smaller than the Alfven speed. The other branch is super-Alfvenic and the soliton velocity is very close to or greater than the Alfven speed. Both compressive and rarefactive solitons can exist. For the sub-Alfvenic branch, the rarefactive soliton is bell-shaped and it is much narrower than the compressive one. However, for the super-Alfvenic branch, the compressive soliton is bell-shaped and narrower, and the rarefactive one is broadened. When the charge-to-mass ratio of the dust grains is sufficiently high, the width of the rarefactive soliton, in the super-Alfvenic branch, will broaden extremely and a electron depletion will be observed. It is also shown that the bell-shaped soliton can transition to a cusped structure when the velocity is sufficiently high.
Investigation of IGES for CAD/CAE data transfer
NASA Technical Reports Server (NTRS)
Zobrist, George W.
1989-01-01
In a CAD/CAE facility there is always the possibility that one may want to transfer the design graphics database from the native system to a non-native system. This may occur because of dissimilar systems within an organization or a new CAD/CAE system is to be purchased. The Initial Graphics Exchange Specification (IGES) was developed in an attempt to solve this scenario. IGES is a neutral database format into which the CAD/CAE native database format can be translated to and from. Translating the native design database format to IGES requires a pre-processor and transling from IGES to the native database format requires a post-processor. IGES is an artifice to represent CAD/CAE product data in a neutral environment to allow interfacing applications, archive the database, interchange of product data between dissimilar CAD/CAE systems, and other applications. The intent here is to present test data on translating design product data from a CAD/CAE system to itself and to translate data initially prepared in IGES format to various native design formats. This information can be utilized in planning potential procurement and developing a design discipline within the CAD/CAE community.
CAE applications in a thermoforming mould design
NASA Astrophysics Data System (ADS)
Marjuki, AR; Mohd Ghazali, FA; Ismail, N. M.; Sulaiman, S.; Mohd Khairuddin, I.; Majeed, Anwar P. P. A.; Jaafar, AA; Mustapha, F.; Basri, S.
2016-02-01
Preparation of honeycomb layer is a critical step for successful fabrications of thermoformed based sandwiched structures. This paper deals with an initial investigation on the rapid manufacturing process of corrugated sheet with 120° dihedral angles. Time history of local displacements and thickness, assuming viscous dominated material model for a 1mm thick thermoformable material, was computed by using ANSYS® Polyflow solver. The quality of formed surfaces was evaluated for selection of mould geometry and assessment of two common variants of thermoforming process. Inadequate mesh refinement of a membrane elements produces satisfactorily detailing and incomplete forming. A perfectly uniform material distribution was predicted using drape forming process. However, the geometrical properties of vacuum formed part are poorly distributed and difficult to control with increasing inflation volumes. Details of the discrepancies and the contributions of the CAE tool to complement traditional trial and error methodology in the process and design development are discussed.
Improving radiation survey data using CADD/CAE
Palau, G.L.; Tarpinian, J.E.
1987-01-01
A new application of computer-aided design and drafting (CADD) and computer-aided engineering (CAE) at the Three Mile Island Unit 2 (TMI-2) cleanup is improving the quality of radiation survey data taken in the plant. The use of CADD/CAE-generated survey maps has increased both the accuracy of survey data and the capability to perform analyses with these data. In addition, health physics technician man hours and radiation exposure can be reduced in situations where the CADD/CAE-generated drawings are used for survey mapping.
SURFACE ALFVEN WAVES IN SOLAR FLUX TUBES
Goossens, M.; Andries, J.; Soler, R.; Van Doorsselaere, T.; Arregui, I.; Terradas, J.
2012-07-10
Magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. Alfven waves and magneto-sonic waves are particular classes of MHD waves. These wave modes are clearly different and have pure properties in uniform plasmas of infinite extent only. Due to plasma non-uniformity, MHD waves have mixed properties and cannot be classified as pure Alfven or magneto-sonic waves. However, vorticity is a quantity unequivocally related to Alfven waves as compression is for magneto-sonic waves. Here, we investigate MHD waves superimposed on a one-dimensional non-uniform straight cylinder with constant magnetic field. For a piecewise constant density profile, we find that the fundamental radial modes of the non-axisymmetric waves have the same properties as surface Alfven waves at a true discontinuity in density. Contrary to the classic Alfven waves in a uniform plasma of infinite extent, vorticity is zero everywhere except at the cylinder boundary. If the discontinuity in density is replaced with a continuous variation of density, vorticity is spread out over the whole interval with non-uniform density. The fundamental radial modes of the non-axisymmetric waves do not need compression to exist unlike the radial overtones. In thin magnetic cylinders, the fundamental radial modes of the non-axisymmetric waves with phase velocities between the internal and the external Alfven velocities can be considered as surface Alfven waves. On the contrary, the radial overtones can be related to fast-like magneto-sonic modes.
Alfven Wave Propagation in Inhomogeneous Plasmas
NASA Astrophysics Data System (ADS)
Sears, Stephanie
Damping of Alfven waves is one of the most likely mechanisms for ion heating in the solar corona. Density gradients have significant but poorly-understood effects on energy transfer and Alfven wave propagation in partially ionized plasmas, such as those found in the solar chromosphere. Reflection of Alfven waves at density and magnetic field gradients can give rise to turbulence which sustains particle heating. The density profile in the Hot hELIcon eXperiment (HELIX) varies strongly with radius, giving access to a wide range of Alfven dynamics across the plasma column and providing an ideal environment to observe Alfven wave-driven particle heating. A new internal wave-launching antenna, situated at the edge of the high-density core and the density-gradient region of HELIX has been used to excite low-frequency waves in argon plasma. The propagation behavior of the launched waves was measured with a small-scale (smaller than the ion gyroradius) magnetic sense coil at multiple radial locations across the plasma column (from the high-density core through the density gradient region). Time-resolved laser induced fluorescence (LIF) and Langmuir probe measurements also yield insight into the plasma response to the perturbation. This dissertation presents cross-spectral and wavelet analysis of low-frequency waves in a helicon plasma with a strong density gradient. Building on the work of Houshmandyar, shear Alfven waves were launched in a helicon plasma source with a strong density gradient. Alfven wave turbulence is suggested from phase angle and wavelet analysis of magnetic sense coil probe measurements. The perturbation wavelength derived from phase angle measurements is consistent with predictions from the full Alfven wave dispersion relation (taking electron Landua damping, electron-ion collisions, and finite frequency effects into account). Time-resolved LIF measurements across the plasma column suggest ion heating where the turbulence is strongest. Time
Center for Advanced Energy Studies (CAES) Strategic Plan
Kevin Kostelnik; Keith Perry
2007-07-01
Twenty-first century energy challenges include demand growth, national energy security, and global climate protection. The Center for Advanced Energy Studies (CAES) is a public/private partnership between the State of Idaho and its academic research institutions, the federal government through the U.S. Department of Energy (DOE) and the Idaho National Laboratory (INL) managed by the Battelle Energy Alliance (BEA). CAES serves to advance energy security for our nation by expanding the educational opportunities at the Idaho universities in energy-related areas, creating new capabilities within its member institutions, and delivering technological innovations leading to technology-based economic development for the intermountain region. CAES has developed this strategic plan based on the Balanced Scorecard approach. A Strategy Map (Section 7) summarizes the CAES vision, mission, customers, and strategic objectives. Identified strategic objectives encompass specific outcomes related to three main areas: Research, Education, and Policy. Technical capabilities and critical enablers needed to support these objectives are also identified. This CAES strategic plan aligns with and supports the strategic objectives of the four CAES institutions. Implementation actions are also presented which will be used to monitor progress towards fulfilling these objectives.
Alfven Wave Tomography for Cold MHD Plasmas
I.Y. Dodin; N.J. Fisch
2001-09-07
Alfven waves propagation in slightly nonuniform cold plasmas is studied by means of ideal magnetohydrodynamics (MHD) nonlinear equations. The evolution of the MHD spectrum is shown to be governed by a matrix linear differential equation with constant coefficients determined by the spectrum of quasi-static plasma density perturbations. The Alfven waves are shown not to affect the plasma density inhomogeneities, as they scatter off of them. The application of the MHD spectrum evolution equation to the inverse scattering problem allows tomographic measurements of the plasma density profile by scanning the plasma volume with Alfven radiation.
Generation of strong MHD Alfvenic turbulence
NASA Technical Reports Server (NTRS)
Akimoto, K.; Winske, D.
1990-01-01
Strong Alfvenic turbulence containing a number of solitonlike structures propagating at super-Alfvenic speeds is generated self-consistently and studied by means of computer simulation. A one-dimensional hybrid (kinetic ions, fluid electrons) code is used to investigate the nonlinear evolution of an electromagnetic ion-beam instability that generates low-frequency Alfven-like waves. As the instability develops, the field-aligned hydromagnetic waves steepen, forming a soliton that bifurcates several times, leading to a fully turbulent state.
The effect of microscale random Alfven waves on the propagation of large-scale Alfven waves
NASA Astrophysics Data System (ADS)
Namikawa, T.; Hamabata, H.
1983-04-01
The ponderomotive force generated by random Alfven waves in a collisionless plasma is evaluated taking into account mean magnetic and velocity shear and is expressed as a series involving spatial derivatives of mean magnetic and velocity fields whose coefficients are associated with the helicity spectrum function of random velocity field. The effect of microscale random Alfven waves through ponderomotive and mean electromotive forces generated by them on the propagation of large-scale Alfven waves is also investigated.
Chaos in driven Alfven systems
NASA Technical Reports Server (NTRS)
Hada, T.; Kennel, C. F.; Buti, B.; Mjolhus, E.
1990-01-01
The chaos in a one-dimensional system, which would be nonlinear stationary Alfven waves in the absence of an external driver, is characterized. The evolution equations are numerically integrated for the transverse wave magnetic field amplitude and phase using the derivative nonlinear Schroedinger equation (DNLS), including resistive wave damping and a long-wavelength monochromatic, circularly polarized driver. A Poincare map analysis shows that, for the nondissipative (Hamiltonian) case, the solutions near the phase space (soliton) separatrices of this system become chaotic as the driver amplitude increases, and 'strong' chaos appears when the driver amplitude is large. The dissipative system exhibits a wealth of dynamical behavior, including quasiperiodic orbits, period-doubling bifurcations leading to chaos, sudden transitions to chaos, and several types of strange attractors.
Saturation of Gyrokinetic Turbulence through Damped Eigenmodes
Hatch, D. R.; Terry, P. W.; Jenko, F.; Merz, F.; Nevins, W. M.
2011-03-18
In the context of toroidal gyrokinetic simulations, it is shown that a hierarchy of damped modes is excited in the nonlinear turbulent state. These modes exist at the same spatial scales as the unstable eigenmodes that drive the turbulence. The larger amplitude subdominant modes are weakly damped and exhibit smooth, large-scale structure in velocity space and in the direction parallel to the magnetic field. Modes with increasingly fine-scale structure are excited to decreasing amplitudes. In aggregate, damped modes define a potent energy sink. This leads to an overlap of the spatial scales of energy injection and peak dissipation, a feature that is in contrast with more traditional turbulent systems.
Stellar winds driven by Alfven waves
NASA Technical Reports Server (NTRS)
Belcher, J. W.; Olbert, S.
1973-01-01
Models of stellar winds were considered in which the dynamic expansion of a corona is driven by Alfven waves propagating outward along radial magnetic field lines. In the presence of Alfven waves, a coronal expansion can exist for a broad range of reference conditions which would, in the absence of waves, lead to static configurations. Wind models in which the acceleration mechanism is due to Alfven waves alone and exhibit lower mass fluxes and higher energies per particle are compared to wind models in which the acceleration is due to thermal processes. For example, winds driven by Alfven waves exhibit streaming velocities at infinity which may vary between the escape velocity at the coronal base and the geometrical mean of the escape velocity and the speed of light. Upper and lower limits were derived for the allowed energy fluxes and mass fluxes associated with these winds.
Fast particles-wave interaction in the Alfven frequency range on the Joint European Torus tokamak
Fasoli, A.; Borba, D.; Association EURATOM Breizman, B.; Gormezano, C.; Heeter, R. F.; Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543 ; Juan, A.; Mantsinen, M.; Sharapov, S.; Testa, D.
2000-05-01
Wave-particle interaction phenomena in the Alfven Eigenmode (AE) frequency range are investigated at the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)] using active and passive diagnostic methods. Fast particles are generated by neutral beam injection, ion cyclotron resonance heating, and fusion reactions. External antennas are used to excite stable AEs and measure fast particle drive and damping separately. Comparisons with numerical calculations lead to an identification of the different damping mechanisms. The use of the active AE diagnostic system to generate control signals based on the proximity to marginal stability limits for AE and low-frequency magnetohydrodynamic (MHD) modes is explored. Signatures of the different nonlinear regimes of fast particle driven AE instabilities predicted by theory are found in the measured spectra. The diagnostic use of AE measurements to get information both on the plasma bulk and the fast particle distribution is assessed. (c) 2000 American Institute of Physics.
Alfven wave. DOE Critical Review Series
Hasegawa, A.; Uberoi, C.
1982-01-01
This monograph deals with the properties of Alfven waves and with their application to fusion. The book is divided into 7 chapters dealing with linear properties in homogeneous and inhomogeneous plasmas. Absorption is treated by means of kinetic theory. Instabilities and nonlinear processes are treated in Chapters 1 to 6, and the closing chapter is devoted to theory and experiments in plasma heating by Alfven waves. (MOW)
Anisotropic Alfven-ballooning modes in the Earth`s magnetosphere
Chan, A.A.; Xia, Mengfen; Chen, Liu
1993-05-01
We have carried out a theoretical analysis of the stability and parallel structure of coupled shear-Alfven and slow-magnetosonic waves in the Earth`s inner magnetosphere including effects of finite anisotropic plasma pressure. Multiscale perturbation analysis of the anisotropic Grad-Shafranov equation yields an approximate self-consistent magnetohydrodynamic (MHD) equilibrium. This MHD equilibrium is used in the numerical solution of a set of eigenmode equations which describe the field line eigenfrequency, linear stability, and parallel eigenmode structure. We call these modes anisotropic Alfven-ballooning modes. The main results are: The field line eigenfrequency can be significantly lowered by finite pressure effects. The parallel mode structure of the transverse wave components is fairly insensitive to changes in the plasma pressure but the compressional magnetic component can become highly peaked near the magnetic equator due to increased pressure, especially when P{perpendicular} > P{parallel}. For the isotropic case ballooning instability can occur when the ratio of the plasma pressure to the magnetic pressure, exceeds a critical value {beta}{sub o}{sup B} {approx} 3.5 at the equator. Compared to the isotropic case the critical beta value is lowered by anisotropy, either due to decreased field-line-bending stabilization when P{parallel} > P{perpendicular}, or due to increased ballooning-mirror destabilization when P{perpendicular} > P{parallel}. We use a ``{beta}-6 stability diagram`` to display the regions of instability with respect to the equatorial values of the parameters {bar {beta}} and {delta}, where {bar {beta}} = (1/3)({beta}{sub {parallel}} + 2 {beta}{perpendicular}) is an average beta value and {delta} = 1 - P{parallel}/P{perpendicular} is a measure of the plasma anisotropy.
Ultra-high Q even eigenmode resonance in terahertz metamaterials
Al-Naib, Ibraheem Dignam, Marc M.; Yang, Yuping; Zhang, Weili; Singh, Ranjan
2015-01-05
We report the simultaneous excitation of the odd and the even eigenmode resonances in a periodic array of square split-ring resonators, with four resonators per unit cell. When the electric field is parallel to their gaps, only the two well-studied odd eigenmodes are excited. As the resonators are rotated relative to one another, we observe the emergence and excitation of an extremely sharp even eigenmode. In uncoupled split-ring resonators, this even eigenmode is typically radiative in nature with a broad resonance linewidth and low Q-factor. However, in our coupled system, for specific range of rotation angles, our simulations revealed a remarkably high quality factor (Q ∼ 100) for this eigenmode, which has sub-radiant characteristics. This type of quad-supercell metamaterial offers the advantage of enabling access to all the three distinct resonance features of the split-ring resonator, which consists of two odd eigenmodes in addition to the high-Q even eigenmode, which could be exploited for high performance multiband filters and absorbers. The high Q even eigenmode could find applications in designing label free bio-sensors and for studying the enhanced light matter interaction effects.
Calibration of higher eigenmodes of cantilevers
NASA Astrophysics Data System (ADS)
Labuda, Aleksander; Kocun, Marta; Lysy, Martin; Walsh, Tim; Meinhold, Jieh; Proksch, Tania; Meinhold, Waiman; Anderson, Caleb; Proksch, Roger
2016-07-01
A method is presented for calibrating the higher eigenmodes (resonant modes) of atomic force microscopy cantilevers that can be performed prior to any tip-sample interaction. The method leverages recent efforts in accurately calibrating the first eigenmode by providing the higher-mode stiffness as a ratio to the first mode stiffness. A one-time calibration routine must be performed for every cantilever type to determine a power-law relationship between stiffness and frequency, which is then stored for future use on similar cantilevers. Then, future calibrations only require a measurement of the ratio of resonant frequencies and the stiffness of the first mode. This method is verified through stiffness measurements using three independent approaches: interferometric measurement, AC approach-curve calibration, and finite element analysis simulation. Power-law values for calibrating higher-mode stiffnesses are reported for several cantilever models. Once the higher-mode stiffnesses are known, the amplitude of each mode can also be calibrated from the thermal spectrum by application of the equipartition theorem.
Calibration of higher eigenmodes of cantilevers.
Labuda, Aleksander; Kocun, Marta; Lysy, Martin; Walsh, Tim; Meinhold, Jieh; Proksch, Tania; Meinhold, Waiman; Anderson, Caleb; Proksch, Roger
2016-07-01
A method is presented for calibrating the higher eigenmodes (resonant modes) of atomic force microscopy cantilevers that can be performed prior to any tip-sample interaction. The method leverages recent efforts in accurately calibrating the first eigenmode by providing the higher-mode stiffness as a ratio to the first mode stiffness. A one-time calibration routine must be performed for every cantilever type to determine a power-law relationship between stiffness and frequency, which is then stored for future use on similar cantilevers. Then, future calibrations only require a measurement of the ratio of resonant frequencies and the stiffness of the first mode. This method is verified through stiffness measurements using three independent approaches: interferometric measurement, AC approach-curve calibration, and finite element analysis simulation. Power-law values for calibrating higher-mode stiffnesses are reported for several cantilever models. Once the higher-mode stiffnesses are known, the amplitude of each mode can also be calibrated from the thermal spectrum by application of the equipartition theorem. PMID:27475563
Fully electromagnetic gyrokinetic eigenmode analysis of high-beta shaped plasmas
Belli, E. A.; Candy, J.
2010-11-15
A new, more efficient method to compute unstable linear gyrokinetic eigenvalues and eigenvectors has been developed for drift-wave analysis of plasmas with arbitrary flux-surface shape, including both transverse and compressional magnetic perturbations. In high-beta, strongly shaped plasmas like in the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)], numerous branches of closely spaced unstable eigenmodes exist. These modes are difficult and time-consuming to adequately resolve with the existing linear initial-value solvers, which are further limited to the most unstable eigenmode. The new method is based on an eigenvalue approach and is an extension of the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)], reusing the existing discretization schemes in both real and velocity-space. Unlike recent methods, which use an iterative solver to compute eigenvalues of the relatively large gyrokinetic response matrix, the present scheme computes the zeros of the much smaller Maxwell dispersion matrix using a direct method. In the present work, the new eigensolver is applied to gyrokinetic stability analysis of a high-beta, NSTX-like plasma. We illustrate the smooth transformation from ion-temperature-gradient (ITG)-like to kinetic-ballooning (KBM)-like modes, and the formation of hybrid ITG/KBM modes, and further demonstrate the existence of high-k Alfvenic drift-wave 'cascades' for which the most unstable mode is a higher excited state along the field line. A new compressional electron drift wave, which is driven by a combination of strong beta and pressure gradient, is also identified for the first time. Overall, we find that accurate calculation of stability boundaries and growth rates cannot, in general, ignore the compressional component {delta}B{sub ||} of the perturbation.
Eigenmode characteristics of the double tearing mode in the presence of shear flows
Mao Aohua; Li Jiquan; Kishimoto, Y.; Liu Jinyuan
2013-02-15
The double tearing mode (DTM) is characterized by two eigen states with antisymmetric or symmetric magnetic island structure, referred to as the even or odd DTM. In this work, we systematically revisit the DTM instabilities in the presence of an antisymmetric shear flow with a focus on eigenmode characteristics as well as the stabilization or destabilization mechanism in a wide parameter region. Both initial value simulation and eigenvalue analysis are performed based on reduced resistive MHD model in slab geometry. A degenerated eigen state is found at a critical flow amplitude v{sub c}. The even (or odd) DTM is stabilized (or destabilized) by weak shear flow below v{sub c} through the distortion of magnetic islands mainly due to the global effect of shear flow rather than the local flow shear. The distortion can be quantified by the phase angles of the perturbed flux, showing a perfect correspondence to the growth rates. As the shear flow increases above v{sub c}, the degenerated eigen state bifurcates into two eigen modes with the same growth rate but opposite propagating direction, resulting in an oscillatory growth of fluctuation energy. It is identified that two eigen modes show the single tearing mode structure due to the Alfven resonance (AR) occurring on one current sheet. Most importantly, the AR can destabilize the DTMs through enhancing the plasma flow exerting on the remaining island. Meanwhile, the local flow shear plays a remarkable stabilizing role in this region. In addition, the eigenmode characteristic of the electromagnetic Kelvin-Helmholtz instability is also discussed.
PULSED ALFVEN WAVES IN THE SOLAR WIND
Gosling, J. T.; Tian, H.; Phan, T. D.
2011-08-20
Using 3 s plasma and magnetic field data from the Wind spacecraft located in the solar wind well upstream from Earth, we report observations of isolated, pulse-like Alfvenic disturbances in the solar wind. These isolated events are characterized by roughly plane-polarized rotations in the solar wind magnetic field and velocity vectors away from the directions of the underlying field and velocity and then back again. They pass over Wind on timescales ranging from seconds to several minutes. These isolated, pulsed Alfven waves are pervasive; we have identified 175 such events over the full range of solar wind speeds (320-550 km s{sup -1}) observed in a randomly chosen 10 day interval. The large majority of these events are propagating away from the Sun in the solar wind rest frame. Maximum field rotations in the interval studied ranged from 6 Degree-Sign to 109 Degree-Sign . Similar to most Alfvenic fluctuations in the solar wind at 1 AU, the observed changes in velocity are typically less than that predicted for pure Alfven waves (Alfvenicity ranged from 0.28 to 0.93). Most of the events are associated with small enhancements or depressions in magnetic field strength and small changes in proton number density and/or temperature. The pulse-like and roughly symmetric nature of the magnetic field and velocity rotations in these events suggests that these Alfvenic disturbances are not evolving when observed. They thus appear to be, and probably are, solitary waves. It is presently uncertain how these waves originate, although they may evolve out of Alfvenic turbulence.
Alfvenic waves in solar spicules
NASA Astrophysics Data System (ADS)
Ebadi, Hossein
2016-07-01
We analyzed O VI (1031.93 A) and O VI (1037.61 A line profiles from the time series of SOHO/SUMER data. The wavelet analysis is used to determine the fundamental mode and its first harmonic periods and their ratio. The period ratio, P_1/P_2 is obtained as 2.1 based on our calculations. To model the spicule oscillations, we consider an equilibrium configuration in the form of an expanding straight magnetic flux tube with varying density along tube. We used cylindrical coordinates r, phi, and z with the z-axis along tube axis. Standing Alfvenic waves with steady flows are studied. More realistic background magnetic field, plasma density, and spicule radios inferred from the actual magnetoseismology of observations are used. It is found that the oscillation periods and their ratio are shifted because of the steady flows. The observational values are reached in P_1/P_2, when the steady flows are 0.2-0.3, the values which are reported for classical spicules.
Saturation of gyrokinetic turbulence through damped eigenmodes.
Hatch, D R; Terry, P W; Jenko, F; Merz, F; Nevins, W M
2011-03-18
In the context of toroidal gyrokinetic simulations, it is shown that a hierarchy of damped modes is excited in the nonlinear turbulent state. These modes exist at the same spatial scales as the unstable eigenmodes that drive the turbulence. The larger amplitude subdominant modes are weakly damped and exhibit smooth, large-scale structure in velocity space and in the direction parallel to the magnetic field. Modes with increasingly fine-scale structure are excited to decreasing amplitudes. In aggregate, damped modes define a potent energy sink. This leads to an overlap of the spatial scales of energy injection and peak dissipation, a feature that is in contrast with more traditional turbulent systems. PMID:21469869
Experimental Investigation of Driven Alfven Wave Resonances on the Pretext Tokamak.
NASA Astrophysics Data System (ADS)
Booth, William David
The results of the recent Alfven wave experiments conducted on the PRETEXT tokamak are presented. Two quarter -turn toroidal antennas were used to drive 2.1 MHz Alfven waves in the PRETEXT plasma. Three different Global Alfven Eigenmodes were identified. The resonance frequency for each of the three observed modes was compared to the value predicted by calculation.^{dagger } The value of the antenna loading associated with each global resonance was measured and also compared to values predicted by a kinetic model.^ {ddagger} Additionally, the radial profile of the RF magnetic field was measured to a depth of five centimeters past the limiter in the plasma and these magnetic fields were compared to predicted values. Generally good agreement was found between measured and predicted values. The resonance frequencies of the global modes agreed quite well and the value of the antenna loading agreed to within about 20%. The width of the measured resonances was much wider than the width of the calculated resonances. This difference is attributed principally to losses in the antenna impedance matching system but may be due partially to loss mechanisms in the plasma which are not included in the code model. The magnetic fields displayed good agreement at the edge of the plasma, but showed some divergence from predicted values at the deeper radial positions. The general shape of the magnetic fields is consistent with the prediction of broad distribution of the fields across the plasma for a global mode. ftn ^daggerS. M. Mahajan, Phys. Fluids 27, 2238 (1984). ^ddaggerD. W. Ross, G. L. Chen, and S. M. Mahajan, Phys. Fluids 25, 652 (1982).
NESD CAE facility minimal implementation plan (June 1982)
Ames, H. S.
1983-08-04
In conjunction with other divisions in the EE Department, the Nuclear Energy Systems Division is developing a Computer-Aided Engineering (CAE) capability. Some of our needs in areas such as drafting, PC design, and IC design can be satisfied with existing turnkey systems. Many of our other needs, including modeling, analysis, document management and communication, software development, project management, and project communication will require the gradual development of an expanded computing environment. The purpose of this document is to describe our initial plans to implement a CAE facility.
Study of Thermonuclear Alfven Instabilities in Next Step Burning Plasma Experiments
N.N. Gorelenkov; H.L. Berk; R. Budny; C.Z. Cheng; G.-Y. Fu; W.W. Heidbrink; G. Kramer; D. Meade; and R. Nazikian
2002-07-02
A study is presented for the stability of alpha-particle driven shear Alfven Eigenmodes (AE) for the normal parameters of the three major burning plasma proposals, ITER (International Thermonuclear Experimental Reactor), FIRE (Fusion Ignition Research Experiment), and IGNITOR (Ignited Torus). A study of the JET (Joint European Torus) plasma, where fusion alphas were generated in tritium experiments, is also included to attempt experimental validation of the numerical predictions. An analytic assessment of Toroidal AE (TAE) stability is first presented, where the alpha particle beta due to the fusion reaction rate and electron drag is simply and accurately estimated in 7-20 keV plasma temperature regime. In this assessment the hot particle drive is balanced against ion-Landau damping of the background deuterons and electron collision effects and stability boundaries are determined. Then two numerical studies of AE instability are presented. In one the High-n stability code HINST is used . This code is capable of predicting instabilities of low and moderately high frequency Alfven modes. HINST computes the non-perturbative solution of the Alfven eigenmodes including effects of ion finite Larmor radius, orbit width, trapped electrons etc. The stability calculations are repeated using the global code NOVAK. We show that for these tokamaks the spectrum of the least stable AE modes are TAE that appear at medium-/high-n numbers. In HINST TAEs are locally unstable due to the alphas pressure gradient in all the devices under the consideration except IGNITOR. However, NOVAK calculations show that the global mode structure enhances the damping mechanisms and produces stability in all configurations considered here. A serious question remains whether the perturbation theory used in NOVAK overestimates the stability predictions, so that it is premature to conclude that the nominal operation of all three proposals are stable to AEs. In addition NBI ions produce a strong
Cascade properties of shear Alfven wave turbulence
NASA Technical Reports Server (NTRS)
Bondeson, A.
1985-01-01
Nonlinear three-wave interactions of linear normal modes are investigated for two-dimensional incompressible magnetohydrodynamics and the weakly three-dimensional Strauss equations in the case where a strong uniform background field B0 is present. In both systems the only resonant interaction affecting Alfven waves is caused by the shear of the background field plus the zero frequency components of the perturbation. It is shown that the Alfven waves are cascaded in wavenumber space by a mechanism equivalent to the resonant absorption at the Alfven resonance. For large wavenumbers perpendicular to B0, the cascade is described by Hamilton's ray equations, dk/dt = -(first-order) partial derivative of omega with respect to vector r, where omega includes the effects of the zero frequency perturbations.
Macroscale particle simulation of kinetic Alfven waves
NASA Technical Reports Server (NTRS)
Tanaka, Motohiko; Sato, Tetsuya; Hasegawa, Akira
1987-01-01
Two types of simulations of the kinetic Alfven wave are presented using a macroscale particle simulation code (Tanaka and Sato, 1986) which enables individual particle dynamics to be followed in the MHD scales. In this code, low frequency electromagnetic fields are solved by eliminating high frequency oscillations such as the light modes, and the scalar potential electric field is solved by eliminating Lagrangian oscillations. The dependences of the frequency and the Landau damping on the perpendicular wavenumber were studied, and good agreement was found between simulation and theoretical predictions. Some fundamental nonlinear interactions of the kinetic Alfven wave with the particles (parallel acceleration of the electrons) were also noted.
Nonlinear evolution of astrophysical Alfven waves
Spangler, S.R.
1984-11-01
Nonlinear Alfven waves were studied using the derivative nonlinear Schrodinger equation as a model. The evolution of initial conditions, such as envelope solitons, amplitude-modulated waves, and band-limited noise was investigated. The last two furnish models for naturally occurring Alfven waves in an astrophysical plasma. A collapse instability in which a wave packet becomes more intense and of smaller spatial extent was analyzed. It is argued that this instability leads to enhanced plasma heating. In studies in which the waves are amplified by an electron beam, the instability tends to modestly inhibit wave growth. (ESA)
Nonlinear evolution of astrophysical Alfven waves
NASA Technical Reports Server (NTRS)
Spangler, S. R.
1984-01-01
Nonlinear Alfven waves were studied using the derivative nonlinear Schrodinger equation as a model. The evolution of initial conditions, such as envelope solitons, amplitude-modulated waves, and band-limited noise was investigated. The last two furnish models for naturally occurring Alfven waves in an astrophysical plasma. A collapse instability in which a wave packet becomes more intense and of smaller spatial extent was analyzed. It is argued that this instability leads to enhanced plasma heating. In studies in which the waves are amplified by an electron beam, the instability tends to modestly inhibit wave growth.
Identification of emerging designer needs and high payoff CAE tools
Nevill, G.E. Jr.; Patterson, R.W.; Adams, L.T. Jr.
1984-03-01
CAE tools clearly offer the potential for dramatic enhancement of human performance. In the near term, principal CAE payoffs will come from further improvements in existing tools, based on continuing rapid computer hardware performance/cost improvements, from wider availability of tools, from new tools such as 3D solid modeling and voice I/O, and from networking and shared data bases to provide integration of the entire engineering endeavor. In the longe term, a new generation of intelligent CAE tools is expected, based on results emerging from the field of Artificial Intelligence. These intelligent CAE tools will, in the next decade, focus around the concept of the Expert System in which human expert knowledge is acquired, organized, and made available to others. These new tools will also begin to change in a fundamental way the relations between computers and humans, and as they increasingly become colleagues and members of project teams, they may fundamentally change the relations between the people themselves. Therein lies the promise and the danger.
Performance of a simple closed aquatic ecosystem (CAES) in space
NASA Astrophysics Data System (ADS)
Wang, G.-H.; Li, G.-B.; Hu, C.-X.; Liu, Y.-D.; Song, L.-R.; Tong, G.-H.; Liu, X.-M.; Cheng, E.-T.
2004-01-01
A simple Closed Aquatic Ecosystem (CAES) consisting of single-celled green algae ( Chlorella pyrenoidosa, producer), a spiral snail ( Bulinus australianus, consumer) and a data acquisition and control unit was flown on the Chinese Spacecraft SHENZHOU-II in January 2001 for 7 days. In order to study the effect of microgravity on the operation of CAES, a 1 g centrifuge reference group in space, a ground 1 g reference group and a ground 1 g centrifuge reference group (1.4 g group) were run concurrently. Real-time data about algae biomass (calculated from transmission light intensity), temperature, light and centrifugation of the CAES were logged at minute intervals. It was found that algae biomass of both the microgravity group and the ground 1 g centrifuge reference group (1.4 g) fluctuated during the experiment, but the algae biomass of the 1 g centrifuge reference group in space and the ground 1 g reference group increased during the experiment. The results may be attributable to influences of microgravity and 1.4 g gravity on the algae and snails metabolisms. Microgravity is the main factor to affect the operation of CAES in space and the contribution of microgravity to the effect was also estimated. These data may be valuable for the establishment of a complex CELSS in the future.
Radial Eigenmodes for a Toroidal Waveguide with Rectangular Cross Section
Rui Li
2012-07-01
In applying mode expansion to solve the CSR impedance for a section of toroidal vacuum chamber with rectangular cross section, we identify the eigenvalue problem for the radial eigenmodes which is different from that for cylindrical structures. In this paper, we present the general expressions of the radial eigenmodes, and discuss the properties of the eigenvalues on the basis of the Sturm-Liouville theory.
ALFVEN SIMPLE WAVES: EULER POTENTIALS AND MAGNETIC HELICITY
Webb, G. M.; Hu, Q.; Dasgupta, B.; Zank, G. P.; Roberts, D. A.
2010-12-20
The magnetic helicity characteristics of fully nonlinear, multi-dimensional Alfven simple waves are investigated, by using relative helicity formulae and also by using an approach involving poloidal and toroidal decomposition of the magnetic field and magnetic vector potential. Different methods to calculate the magnetic vector potential are used, including the homotopy and Biot-Savart formulae. Two basic Alfven modes are identified: (1) the plane one-dimensional Alfven simple wave given in standard texts, in which the Alfven wave propagates along the z-axis with wave phase {psi} = k{sub 0}(z - {lambda}t), where k{sub 0} is the wave number and {lambda} is the group velocity of the wave and (2) the generalized Barnes simple Alfven wave in which the wave normal n moves in a circle in the xy-plane perpendicular to the mean field, which is directed along the z-axis. The plane Alfven wave (1) is analogous to the slab Alfven mode and the generalized Barnes solution (2) is analogous to the two-dimensional mode in Alfvenic, incompressible turbulence. The helicity characteristics of these two basic Alfven modes are distinct. The helicity characteristics of more general multi-dimensional simple Alfven waves are also investigated. Applications to nonlinear Alfvenic fluctuations and structures observed in the solar wind are discussed.
Stability of sub-Alfvenic plasma expansions
NASA Technical Reports Server (NTRS)
Huba, J. D.; Hassam, A. B.; Winske, D.
1990-01-01
A theoretical treatment of the linear stability of sub-Alfvenic plasma expansion is developed. The theory is fully kinetic and includes finite-beta effects, collisional effects, and neutral gas flow. A variety of results are obtained, and are applied to the the AMPTE magnetotail release, the NRL laser experiment, and the upcoming CRRES GTO releases.
Nonlinear Evolution of Alfvenic Wave Packets
NASA Technical Reports Server (NTRS)
Buti, B.; Jayanti, V.; Vinas, A. F.; Ghosh, S.; Goldstein, M. L.; Roberts, D. A.; Lakhina, G. S.; Tsurutani, B. T.
1998-01-01
Alfven waves are a ubiquitous feature of the solar wind. One approach to studying the evolution of such waves has been to study exact solutions to approximate evolution equations. Here we compare soliton solutions of the Derivative Nonlinear Schrodinger evolution equation (DNLS) to solutions of the compressible MHD equations.
Electron acceleration by inertial Alfven waves
Thompson, B.J.; Lysak, R.L.
1996-03-01
Alfven waves reflected by the ionosphere and by inhomogeneities in the Alfven speed can develop an oscillating parallel electric field when electron inertial effects are included. These waves, which have wavelengths of the order of an Earth radius, can develop a coherent structure spanning distances of several Earth radii along geomagnetic field lines. This system has characteristic frequencies in the range of 1 Hz and can exhibit electric fields capable of accelerating electrons in several senses: via Landua resonance, bounce or transit time resonance as discussed by Andre and Eliasson or through the effective potential drop which appears when the transit time of the electrons is much smaller than the wave period, so that the electric fields appear effectively static. A time-dependent model of wave propagation is developed which represents inertial Alfven wave propagation along auroral field lines. The disturbance is modeled as it travels earthward, experiences partial reflections in regions of rapid variation, and finally reflects off a conducting ionosphere to continue propagating antiearthward. The wave experiences partial trapping by the ionospheric and the Alfven speed peaks discussed earlier by Polyakov and Rapoport and Trakhtengerts and Feldstein and later by Lysak. Results of the wave simulation and an accompanying test particle simulation are presented, which indicate that inertial Alfven waves are a possible mechanism for generating electron conic distributions and field-aligned particle precipitation. The model incorporates conservation of energy by allowing electrons to affect the wave via Landau damping, which appears to enhance the effect of the interactions which heat electron populations. 22 refs., 14 figs.
The eigenmode perspective of NMR spin relaxation in proteins
NASA Astrophysics Data System (ADS)
Shapiro, Yury E.; Meirovitch, Eva
2013-12-01
We developed in recent years the two-body (protein and probe) coupled-rotator slowly relaxing local structure (SRLS) approach for elucidating protein dynamics from NMR spin relaxation. So far we used as descriptors the set of physical parameters that enter the SRLS model. They include the global (protein-related) diffusion tensor, D1, the local (probe-related) diffusion tensor, D2, and the local coupling/ordering potential, u. As common in analyzes based on mesoscopic dynamic models, these parameters have been determined with data-fitting techniques. In this study, we describe structural dynamics in terms of the eigenmodes comprising the SRLS time correlation functions (TCFs) generated by using the best-fit parameters as input to the Smoluchowski equation. An eigenmode is a weighted exponential with decay constant given by an eigenvalue of the Smoluchowski operator, and weighting factor determined by the corresponding eigenvector. Obviously, both quantities depend on the SRLS parameters as determined by the SRLS model. Unlike the set of best-fit parameters, the eigenmodes represent patterns of motion of the probe-protein system. The following new information is obtained for the typical probe, the 15N-1H bond. Two eigenmodes, associated with the protein and the probe, dominate when the time scale separation is large (i.e., D2 ≫ D1), the tensorial properties are simple, and the local potential is either very strong or very weak. When the potential exceeds these limits while the remaining conditions are preserved, new eigenmodes arise. The multi-exponentiality of the TCFs is associated in this case with the restricted nature of the local motion. When the time scale separation is no longer large, the rotational degrees of freedom of the protein and the probe become statistically dependent (coupled dynamically). The multi-exponentiality of the TCFs is associated in this case with the restricted nature of both the local and the global motion. The effects of local
The eigenmode perspective of NMR spin relaxation in proteins
Shapiro, Yury E. E-mail: eva.meirovitch@biu.ac.il; Meirovitch, Eva E-mail: eva.meirovitch@biu.ac.il
2013-12-14
We developed in recent years the two-body (protein and probe) coupled-rotator slowly relaxing local structure (SRLS) approach for elucidating protein dynamics from NMR spin relaxation. So far we used as descriptors the set of physical parameters that enter the SRLS model. They include the global (protein-related) diffusion tensor, D{sub 1}, the local (probe-related) diffusion tensor, D{sub 2}, and the local coupling/ordering potential, u. As common in analyzes based on mesoscopic dynamic models, these parameters have been determined with data-fitting techniques. In this study, we describe structural dynamics in terms of the eigenmodes comprising the SRLS time correlation functions (TCFs) generated by using the best-fit parameters as input to the Smoluchowski equation. An eigenmode is a weighted exponential with decay constant given by an eigenvalue of the Smoluchowski operator, and weighting factor determined by the corresponding eigenvector. Obviously, both quantities depend on the SRLS parameters as determined by the SRLS model. Unlike the set of best-fit parameters, the eigenmodes represent patterns of motion of the probe-protein system. The following new information is obtained for the typical probe, the {sup 15}N−{sup 1}H bond. Two eigenmodes, associated with the protein and the probe, dominate when the time scale separation is large (i.e., D{sub 2} ≫ D{sub 1}), the tensorial properties are simple, and the local potential is either very strong or very weak. When the potential exceeds these limits while the remaining conditions are preserved, new eigenmodes arise. The multi-exponentiality of the TCFs is associated in this case with the restricted nature of the local motion. When the time scale separation is no longer large, the rotational degrees of freedom of the protein and the probe become statistically dependent (coupled dynamically). The multi-exponentiality of the TCFs is associated in this case with the restricted nature of both the local and the
Productivity increase through implementation of CAD/CAE workstation
NASA Technical Reports Server (NTRS)
Bromley, L. K.
1985-01-01
The tracking and communication division computer aided design/computer aided engineering system is now operational. The system is utilized in an effort to automate certain tasks that were previously performed manually. These tasks include detailed test configuration diagrams of systems under certification test in the ESTL, floorplan layouts of future planned laboratory reconfigurations, and other graphical documentation of division activities. The significant time savings achieved with this CAD/CAE system are examined: (1) input of drawings and diagrams; (2) editing of initial drawings; (3) accessibility of the data; and (4) added versatility. It is shown that the Applicon CAD/CAE system, with its ease of input and editing, the accessibility of data, and its added versatility, has made more efficient many of the necessary but often time-consuming tasks associated with engineering design and testing.
A SINDA thermal model using CAD/CAE technologies
NASA Technical Reports Server (NTRS)
Rodriguez, Jose A.; Spencer, Steve
1992-01-01
The approach to thermal analysis described by this paper is a technique that incorporates Computer Aided Design (CAD) and Computer Aided Engineering (CAE) to develop a thermal model that has the advantages of Finite Element Methods (FEM) without abandoning the unique advantages of Finite Difference Methods (FDM) in the analysis of thermal systems. The incorporation of existing CAD geometry, the powerful use of a pre and post processor and the ability to do interdisciplinary analysis, will be described.
Numerical measurement of turbulent responses in drift-Alfven turbulence
Fernandez, E.; Terry, P.W.
1997-07-01
A drift-Alfven magnetoturbulence model that augments reduced magnetohydrodynamics with evolution of electron density under parallel compression and fluid advection has been studied numerically. In the Alfvenic regime, measurement of spectral transfer rates, frequency spectra, energy partitions, and the ensemble-averaged turbulent response reveals both Alfvenic and hydrodynamic characteristics. The rms turbulent frequency is Alfvenic, the energies are equipartitioned, and there is a fast, Alfven-time scale relaxation in the turbulent response. The mean frequency is hydrodynamic, with diamagnetic and eddy straining signatures, and there is an eddy straining decorrelation appearing as a distinct, long time scale branch in the turbulent response. The decay rates and relative fluctuation strengths associated with fast and slow time scale decorrelation are in good agreement with theoretical predictions that posit a Kolmogorov spectrum in the Alfvenic regime. {copyright} {ital 1997 American Institute of Physics.}
An Alfven wave maser in the laboratory
Maggs, J.E.; Morales, G.J.; Carter, T.A.
2005-01-01
A frequency selective Alfven wave resonator results from the application of a locally nonuniform magnetic field to a plasma source region between the cathode and anode in a large laboratory device. When a threshold in the plasma discharge current is exceeded, selective amplification produces a highly coherent ({delta}{omega}/{omega}<5x10{sup -3}), large amplitude shear Alfven wave that propagates out of the resonator, through a semitransparent mesh anode, into the adjacent plasma column where the magnetic field is uniform. This phenomenon is similar to that encountered in the operation of masers/lasers at microwave and optical frequencies. The current threshold for maser action is found to depend upon the confinement magnetic field strength B{sub 0}. Its scaling is consistent with the condition for matching the drift speed of the bulk plasma electrons with the phase velocity of the mode in the resonator. The largest spontaneously amplified signals are obtained at low B{sub 0} and large plasma currents. The magnetic fluctuations {delta}B associated with the Alfven maser can be as large as {delta}B/B{sub 0}{approx_equal}1.5% and are observed to affect the plasma current. Steady-state behavior leading to coherent signals lasting until the discharge is terminated can be achieved when the growth conditions are well-above threshold. The maser is observed to evolve in time from an initial m=0 mode to an m=1 mode structure in the transition to the late steady state. The laboratory phenomenon reported is analogous to the Alfven wave maser proposed to exist in naturally occurring, near-earth plasmas.
Stationary nonlinear Alfven waves and solitons
NASA Technical Reports Server (NTRS)
Hada, T.; Kennel, C. F.; Buti, B.
1989-01-01
Stationary solutions of the derivative nonlinear Schroedinger equation are discussed and classified by using a pseudopotential formulation. The solutions consist of a rich family of nonlinear Alfven waves and solitons with parallel and oblique propagation directions. Expressions for the envelope and the phase of nonlinear waves with periodic envelope modulation, and 'hyperbolic' and 'algebraic' solitons are given. The propagation angle for the slightly modulated elliptic, periodic waves and for oblique solitons is evaluated.
Adiabatic trapping in coupled kinetic Alfven-acoustic waves
Shah, H. A.; Ali, Z.; Masood, W.
2013-03-15
In the present work, we have discussed the effects of adiabatic trapping of electrons on obliquely propagating Alfven waves in a low {beta} plasma. Using the two potential theory and employing the Sagdeev potential approach, we have investigated the existence of arbitrary amplitude coupled kinetic Alfven-acoustic solitary waves in both the sub and super Alfvenic cases. The results obtained have been analyzed and presented graphically and can be applied to regions of space where the low {beta} assumption holds true.
Spin wave eigenmodes in transversely magnetized thin film ferromagnetic wires
NASA Astrophysics Data System (ADS)
Duan, Zheng; Krivorotov, Ilya N.; Arias, Rodrigo E.; Reckers, Nathalie; Stienen, Sven; Lindner, Jürgen
2015-09-01
We report experimental and theoretical studies of spin wave eigenmodes in transversely magnetized thin film Permalloy wires. Using broadband ferromagnetic resonance technique, we measure the spectrum of spin wave eigenmodes in individual wires as a function of magnetic field and wire width. Comparison of the experimental data to our analytical model and micromagnetic simulations shows that the intrinsic dipolar edge pinning of spin waves is negligible in transversely magnetized wires. Our data also quantify the degree of extrinsic edge pinning in Permalloy wires. This work establishes the boundary conditions for dynamic magnetization in transversely magnetized thin film wires for the range of wire widths and thicknesses studied, and provides a quantitative description of the spin wave eigenmode frequencies and spatial profiles in this system as a function of the wire width.
Effect of Dust Grains on Solitary Kinetic Alfven Wave
Li Yangfang; Wu, D. J.; Morfill, G. E.
2008-09-07
Solitary kinetic Alfven wave has been studied in dusty plasmas. The effect of the dust charge-to-mass ratio is considered. We derive the Sagdeev potential for the soliton solutions based on the hydrodynamic equations. A singularity in the Sagdeev potential is found and this singularity results in a bell-shaped soliton. The soliton solutions comprise two branches. One branch is sub-Alfvenic and the soliton velocities are much smaller than the Alfven speed. The other branch is super-Alfvenic and the soliton velocities are very close to or greater than the Alfven speed. Both compressive and rarefactive solitons can exist in each branch. For the sub-Alfvenic branch, the rarefactive soliton is a bell shape curve which is much narrower than the compressive one. In the super-Alfvenic branch, however, the compressive soliton is bell-shaped and the rarefactive one is broadened. We also found that the super-Alfvenic solitons can develop to other structures. When the charge-to-mass ratio of the dust grains is sufficiently high, the width of the rarefactive soliton will increase extremely and an electron density depletion will be observed. When the velocity is much higher than the Alfven speed, the bell-shaped soliton will transit to a cusped structure.
Eigenmode expansion of the polarization for a spherical sample of two-level atoms
NASA Astrophysics Data System (ADS)
Friedberg, Richard; Manassah, Jamal T.
2009-12-01
We derive pseudo-orthogonality relations for both the magnetic and electric eigenmodes of a system of two-level atoms in a sphere configuration. We verify numerically that an arbitrary vector field can be reconstructed to a great accuracy from these eigenmode expansions. We apply this eigenmode analysis to explore superradiance from a sphere with initially uniform polarization.
NUMERICAL SIMULATIONS OF CONVERSION TO ALFVEN WAVES IN SUNSPOTS
Khomenko, E.; Cally, P. S. E-mail: paul.cally@monash.edu
2012-02-10
We study the conversion of fast magnetoacoustic waves to Alfven waves by means of 2.5D numerical simulations in a sunspot-like magnetic configuration. A fast, essentially acoustic, wave of a given frequency and wave number is generated below the surface and propagates upward through the Alfven/acoustic equipartition layer where it splits into upgoing slow (acoustic) and fast (magnetic) waves. The fast wave quickly reflects off the steep Alfven speed gradient, but around and above this reflection height it partially converts to Alfven waves, depending on the local relative inclinations of the background magnetic field and the wavevector. To measure the efficiency of this conversion to Alfven waves we calculate acoustic and magnetic energy fluxes. The particular amplitude and phase relations between the magnetic field and velocity oscillations help us to demonstrate that the waves produced are indeed Alfven waves. We find that the conversion to Alfven waves is particularly important for strongly inclined fields like those existing in sunspot penumbrae. Equally important is the magnetic field orientation with respect to the vertical plane of wave propagation, which we refer to as 'field azimuth'. For a field azimuth less than 90 Degree-Sign the generated Alfven waves continue upward, but above 90 Degree-Sign downgoing Alfven waves are preferentially produced. This yields negative Alfven energy flux for azimuths between 90 Degree-Sign and 180 Degree-Sign . Alfven energy fluxes may be comparable to or exceed acoustic fluxes, depending upon geometry, though computational exigencies limit their magnitude in our simulations.
The parametric decay of Alfven waves into shear Alfven waves and dust lower hybrid waves
Jamil, M.; Shah, H. A.; Zubia, K.; Zeba, I.; Uzma, Ch.; Salimullah, M.
2010-07-15
The parametric decay instability of Alfven wave into low-frequency electrostatic dust-lower-hybrid and electromagnetic shear Alfven waves has been investigated in detail in a dusty plasma in the presence of external/ambient uniform magnetic field. Magnetohydrodynamic fluid equations of plasmas have been employed to find the linear and nonlinear response of the plasma particles for this three-wave nonlinear coupling in a dusty magnetoplasma. Here, relatively high frequency electromagnetic Alfven wave has been taken as the pump wave. It couples with other two low-frequency internal possible modes of the dusty magnetoplasma, viz., the dust-lower-hybrid and shear Alfven waves. The nonlinear dispersion relation of the dust-lower-hybrid wave has been solved to obtain the growth rate of the parametric decay instability. The growth rate is maximum for small value of external magnetic field B{sub s}. It is noticed that the growth rate is proportional to the unperturbed electron number density n{sub oe}.
Automated knowledge base development from CAD/CAE databases
NASA Technical Reports Server (NTRS)
Wright, R. Glenn; Blanchard, Mary
1988-01-01
Knowledge base development requires a substantial investment in time, money, and resources in order to capture the knowledge and information necessary for anything other than trivial applications. This paper addresses a means to integrate the design and knowledge base development process through automated knowledge base development from CAD/CAE databases and files. Benefits of this approach include the development of a more efficient means of knowledge engineering, resulting in the timely creation of large knowledge based systems that are inherently free of error.
CAD/CAE Integration Enhanced by New CAD Services Standard
NASA Technical Reports Server (NTRS)
Claus, Russell W.
2002-01-01
A Government-industry team led by the NASA Glenn Research Center has developed a computer interface standard for accessing data from computer-aided design (CAD) systems. The Object Management Group, an international computer standards organization, has adopted this CAD services standard. The new standard allows software (e.g., computer-aided engineering (CAE) and computer-aided manufacturing software to access multiple CAD systems through one programming interface. The interface is built on top of a distributed computing system called the Common Object Request Broker Architecture (CORBA). CORBA allows the CAD services software to operate in a distributed, heterogeneous computing environment.
Ulysses Observations of Alfven and Magnetosonic Waves at High Latitude
NASA Technical Reports Server (NTRS)
Smith, Edward J.
1997-01-01
Ulysses observations provide a unique opportunity to study diverse problems related to Alfven and magnetosonic waves. The large amplitude of the Alfven waves influences the distribution functions of the spiral angle, the azimuthal field component and, possibly, the radial component such that their averages are not equal to their most probable values.
Nonlinear waves in an Alfven waveguide
Dmitrienko, I.S.
1992-06-01
A nonlinear Schroedinger equation is derived for the envelopes of weakly nonlinear quasilongitudinal (k{sub 1}<{radical}{omega}/{omega}{sub i}k{sub {parallel}}) Alfven waves in a waveguide, the existence of which is ensured by the presence of ion inertia (m{sub i}{ne}0) in a plasma with a transverse density gradient. It is shown that the nonlinear properties of such waves are associated with the presence of transverse structure in the waveguide modes. Estimates show that weakly nonlinear processes can have a significant effect on the dynamics of Pc 1 geomagnetic pulsations. 7 refs.
Nonlinear standing Alfven wave current system at Io - Theory
NASA Astrophysics Data System (ADS)
Neubauer, F. M.
1980-03-01
A nonlinear analytical model is presented of the Alfven current tubes continuing the currents through Io generated by the unipolar inductor effect due to Io's motion relative to the magnetospheric plasma. It was shown that: (1) the portion of the currents needing Io is aligned with the Alfven characteristics at a specific angle to the magnetic field for the special case of perpendicular flow; (2) the Alfven tubes act like an external conductance; (3) the Alfven tubes may be reflected from the torus boundary or the Jovian atmosphere; and (4) from the point of view of the electrodynamic interaction, Io is unique among the Jovian satellites because of its ionosphere arising from ionized volcanic gases and a high external Alfvenic conductance.
Double Gap Alfvén Eigenmodes: Revisiting Eigenmodes Interaction with the Alfvén Continuum
N.N. Gorelenkov
2005-12-01
A new type of global shear Alfvén Eigenmode is found in tokamak plasmas where the mode localization is in the region intersecting the Alfvén continuum. The eigenmode is formed by the coupling of two solutions from two adjacent gaps (akin to potential wells) in the shear Alfvén continuum. For tokamak plasmas with reversed magnetic shear it is shown that the toroidiciy-induced solution tunnels through the continuum to match the ellipticity-induced Alfvén eigenmode (TAE and EAE, respectively) so that the resulting solution is continuous at the point of resonance with the continuum. The existence of these Double Gap Alfvén Eigenmodes (DGAEs) allows for potentially new ways of coupling edge fields to the plasma core in conditions where the core region is conventionally considered inaccessible. Implications include new approaches to heating and current drive in fusion plasmas as well as its possible use as core diagnostic in burning plasmas.
Nonlinear standing Alfven wave current system at Io: Theory
Neubauer, F.M.
1980-03-01
We present a nonlinear analytical model of the Alfven current tubes continuing the currents through Io (or rather its ionosphere) generated by the unipolar inductor effect due to Io's motion relative to the magnetospheric plasma. We thereby extend the linear work by Drell et al. (1965) to the fully nonlinear, sub-Alfvenic situation also including flow which is not perpendicular to the background magnetic field. The following principal results have been obtained: (1) The portion of the currents feeding Io is aligned with the Alfven characteristics at an angle theta/sub A/ is the Alfven Mach number. (2) The Alfven tubes act like an external conductance ..sigma../sub A/=1/(..mu../sub 0/V/sub A/(1+M/sub A//sup 2/+2M/sub A/ sin theta)/sup 1/2/ where V/sub A/ is the Alfven wave propagation. Hence the Jovian ionospheric conductivity is not necessary for current closure. (3) In addition, the Alfven tubes may be reflected from either the torus boundary or the Jovian ionosphere. The efficiency of the resulting interaction with these boundaries varies with Io position. The interaction is particularly strong at extreme magnetic latitudes, thereby suggesting a mechanism for the Io control of decametric emissions. (4) The reflected Alfven waves may heat both the torus plasma and the Jovian ionosphere as well as produce increased diffusion of high-energy particles in the torus. (5) From the point of view of the electrodynamic interaction, Io is unique among the Jovian satellites for several reasons: these include its ionosphere arising from ionized volcanic gases, a high external Alfvenic conductance ..sigma../sub A/, and a high corotational voltage in addition to the interaction phenomenon with a boundary. (6) We find that Amalthea is probably strongly coupled to Jupiter's ionosphere while the outer Galilean satellites may occasionally experience super-Alfvenic conditions.
Coherent control of plasmonic nanoantennas using optical eigenmodes
Kosmeier, Sebastian; De Luca, Anna Chiara; Zolotovskaya, Svetlana; Di Falco, Andrea; Dholakia, Kishan; Mazilu, Michael
2013-01-01
The last decade has seen subwavelength focusing of the electromagnetic field in the proximity of nanoplasmonic structures with various designs. However, a shared issue is the spatial confinement of the field, which is mostly inflexible and limited to fixed locations determined by the geometry of the nanostructures, which hampers many applications. Here, we coherently address numerically and experimentally single and multiple plasmonic nanostructures chosen from a given array, resorting to the principle of optical eigenmodes. By decomposing the light field into optical eigenmodes, specifically tailored to the nanostructure, we create a subwavelength, selective and dynamic control of the incident light. The coherent control of plasmonic nanoantennas using this approach shows an almost zero crosstalk. This approach is applicable even in the presence of large transmission aberrations, such as present in holographic diffusers and multimode fibres. The method presents a paradigm shift for the addressing of plasmonic nanostructures by light. PMID:23657743
On apparent temperature in low-frequency Alfvenic turbulence
Nariyuki, Yasuhiro
2012-08-15
Low-frequency, parallel propagating Alfvenic turbulence in collisionless plasmas is theoretically studied. Alfvenic turbulence is derived as an equilibrium state (Beltrami field) in the magnetohydrodynamic equations with the pressure anisotropy and multi-species of ions. It is shown that the conservation of the total 'apparent temperature' corresponds to the Bernoulli law. A simple model of the radially expanding solar wind including Alfvenic turbulence is also discussed. The conversion of the wave energy in the 'apparent temperature' into the 'real temperature' is facilitated with increasing radial distance.
Cusp Dynamics-Particle Acceleration by Alfven Waves
NASA Technical Reports Server (NTRS)
Ergun, Robert E.; Parker, Scott A.
2005-01-01
Successful results were obtained from this research project. This investigation answered and/or made progresses on each of the four important questions that were proposed: (1) How do Alfven waves propagate on dayside open field lines? (2) How are precipitating electrons influenced by propagating Alfven waves? (3) How are various cusp electron distributions generated? (4) How are Alfven waves modified by electrons? During the first year of this investigation, the input parameters, such as density and temperature altitude profiles, of the gyrofluid code on the cusp field lines were constructed based on 3-point satellite observations. The initial gyrofluid result was presented at the GEM meeting by Dr. Samuel Jones.
Radio-Frequency Tank Eigenmode Sensor for Propellant Quantity Gauging
NASA Technical Reports Server (NTRS)
Zimmerli, Gregory A.; Buchanan, David A.; Follo, Jeffrey C.; Vaden, Karl R.; Wagner, James D.; Asipauskas, Marius; Herlacher, Michael D.
2010-01-01
Although there are several methods for determining liquid level in a tank, there are no proven methods to quickly gauge the amount of propellant in a tank while it is in low gravity or under low-settling thrust conditions where propellant sloshing is an issue. Having the ability to quickly and accurately gauge propellant tanks in low-gravity is an enabling technology that would allow a spacecraft crew or mission control to always know the amount of propellant onboard, thus increasing the chances for a successful mission. The Radio Frequency Mass Gauge (RFMG) technique measures the electromagnetic eigenmodes, or natural resonant frequencies, of a tank containing a dielectric fluid. The essential hardware components consist of an RF network analyzer that measures the reflected power from an antenna probe mounted internal to the tank. At a resonant frequency, there is a drop in the reflected power, and these inverted peaks in the reflected power spectrum are identified as the tank eigenmode frequencies using a peak-detection software algorithm. This information is passed to a pattern-matching algorithm, which compares the measured eigenmode frequencies with a database of simulated eigenmode frequencies at various fill levels. A best match between the simulated and measured frequency values occurs at some fill level, which is then reported as the gauged fill level. The database of simulated eigenmode frequencies is created by using RF simulation software to calculate the tank eigenmodes at various fill levels. The input to the simulations consists of a fairly high-fidelity tank model with proper dimensions and including internal tank hardware, the dielectric properties of the fluid, and a defined liquid/vapor interface. Because of small discrepancies between the model and actual hardware, the measured empty tank spectra and simulations are used to create a set of correction factors for each mode (typically in the range of 0.999 1.001), which effectively accounts for
CAD and CAE Analysis for Siphon Jet Toilet
NASA Astrophysics Data System (ADS)
Wang, Yuhua; Xiu, Guoji; Tan, Haishu
The high precision 3D laser scanner with the dual CCD technology was used to measure the original design sample of a siphon jet toilet. The digital toilet model was constructed from the cloud data measured with the curve and surface fitting technology and the CAD/CAE systems. The Realizable k - ɛ double equation model of the turbulence viscosity coefficient method and the VOF multiphase flow model were used to simulate the flushing flow in the toilet digital model. Through simulating and analyzing the distribution of the flushing flow's total pressure, the flow speed at the toilet-basin surface and the siphoning bent tube, the toilet performance can be evaluated efficiently and conveniently. The method of "establishing digital model, flushing flow simulating, performances evaluating, function shape modifying" would provide a high efficiency approach to develop new water-saving toilets.
Possible evidence for coronal Alfven waves
NASA Technical Reports Server (NTRS)
Hollweg, J. V.; Bird, M. K.; Volland, H.; Edenhofer, P.; Stelzried, C. T.; Seidel, B. L.
1982-01-01
A statistical ray analysis is used to analyze observed electron content and Faraday rotation fluctuations in the 2.29 GHz S band carrier signals of the two Helios spacecraft probing the magnetic and density structures of the solar corona inside 0.05 AU. It is found that (1) the observed Faraday rotation fluctuations cannot be due only to electron density fluctuations in the corona, unless the coronal magnetic field is about five times stronger than suggested by current estimates; and (2) the observed Faraday rotation fluctuations are consistent with the hypothesis that the sun radiates Alfven waves whose energies are great enough to heat and accelerate high-speed solar wind streams.
Ground observations of kinetic Alfven waves
Kloecker, N.; Luehr, H.; Robert, P.; Korth, A.
1985-01-01
Ground-based observations with the EISCAT magnetometer of locally confined intense drifting current systems and Geos-2 measurements during four events in November and December 1982 are examined. In the ground-based measurements near the Harang discontinuity, the events are characterized by strong pulsations with amplitudes in the horizontal component up to 1000 nT and periods of about 300 s and longer. They occur in the evening hours adjacent to the poleward side of the discontinuity with the onset of a substorm; at the same time, the inner edge of the plasma sheet passes the Geos-2 position, magnetically conjugate to ground stations. It is shown that the events can be explained in terms of kinetic Alfven waves. 8 references.
Nonlinear, dispersive, elliptically polarized Alfven wavaes
NASA Technical Reports Server (NTRS)
Kennel, C. F.; Buti, B.; Hada, T.; Pellat, R.
1988-01-01
The derivative nonlinear Schroedinger (DNLS) equation is derived by an efficient means that employs Lagrangian variables. An expression for the stationary wave solutions of the DNLS that contains vanishing and nonvanishing and modulated and nonmodulated boundary conditions as subcases is then obtained. The solitary wave solutions for elliptically polarized quasiparallel Alfven waves in the magnetohydrodynamic limit (nonvanishing, unmodulated boundary conditions) are obtained. These converge to the Korteweg-de Vries and the modified Korteweg-de Vries solitons obtained previously for oblique propagation, but are more general. It is shown that there are no envelope solitary waves if the point at infinity is unstable to the modulational instability. The periodic solutions of the DNLS are characterized.
Ducted kinetic Alfven waves in plasma with steep density gradients
Houshmandyar, Saeid; Scime, Earl E.
2011-11-15
Given their high plasma density (n {approx} 10{sup 13} cm{sup -3}), it is theoretically possible to excite Alfven waves in a conventional, moderate length (L {approx} 2 m) helicon plasma source. However, helicon plasmas are decidedly inhomogeneous, having a steep radial density gradient, and typically have a significant background neutral pressure. The inhomogeneity introduces regions of kinetic and inertial Alfven wave propagation. Ion-neutral and electron-neutral collisions alter the Alfven wave dispersion characteristics. Here, we present the measurements of propagating kinetic Alfven waves in helium helicon plasma. The measured wave dispersion is well fit with a kinetic model that includes the effects of ion-neutral damping and that assumes the high density plasma core defines the radial extent of the wave propagation region. The measured wave amplitude versus plasma radius is consistent with the pile up of wave magnetic energy at the boundary between the kinetic and inertial regime regions.
The Source of Alfven Waves That Heat the Solar Corona
NASA Technical Reports Server (NTRS)
Ruzmaikin, A.; Berger, M. A.
1998-01-01
We suggest a source for high-frequency Alfven waves invoked in coronal heating and acceleration of the solar wind. The source is associated with small-scale magnetic loops in the chromospheric network.
Study of Aspect Ratio Effects on Kinetic MHD Instabilities in NSTX and DIII-D
E.D. Fredrickson; W.W. Heidbrink; C.Z. Cheng; N.N. Gorelenkov; E. Belova; A.W. Hyatt; G.J. Kramer; J. Manickam; J. Menard; R. Nazikian; T.L. Rhodes; E. Ruskov
2004-10-21
We report general observations of kinetic instabilities on the low aspect-ratio National Spherical Torus Experiment (NSTX) and describe explicit aspect ratio scaling studies of kinetic instabilities using both the NSTX and the DIII-D tokamak. The NSTX and the DIII-D tokamak are nearly ideal for such experiments, having a factor of two difference in major radius but otherwise similar parameters. We also introduce new theoretical work on the physics of kinetic ballooning modes (KBM), toroidal Alfven eigenmodes (TAE), and compressional Alfven eigenmodes (CAE) with applications to NSTX.
Emission of radiation induced by pervading Alfven waves
Zhao, G. Q.; Wu, C. S.
2013-03-15
It is shown that under certain conditions, propagating Alfven waves can energize electrons so that consequently a new cyclotron maser instability is born. The necessary condition is that the plasma frequency is lower than electron gyrofrequency. This condition implies high Alfven speed, which can pitch-angle scatter electrons effectively and therefore the electrons are able to acquire free energy which are needed for the instability.
Theory of semicollisional kinetic Alfven modes in sheared magnetic fields
Hahm, T.S.; Chen, L.
1985-02-01
The spectra of the semicollisional kinetic Alfven modes in a sheared slab geometry are investigated, including the effects of finite ion Larmor radius and diamagnetic drift frequencies. The eigenfrequencies of the damped modes are derived analytically via asymptotic analyses. In particular, as one reduces the resistivity, we find that, due to finite ion Larmor radius effects, the damped mode frequencies asymptotically approach finite real values corresponding to the end points of the kinetic Alfven continuum.
Noncircular Triangularity and Ellipticity-Induced Alfvén Eigenmodes Observed in JT-60U
NASA Astrophysics Data System (ADS)
Kramer, G. J.; Saigusa, M.; Ozeki, T.; Kusama, Y.; Kimura, H.; Oikawa, T.; Tobita, K.; Fu, G. Y.; Cheng, C. Z.
1998-03-01
For the first time noncircular triangularity induced Alfvén eigenmodes (NAE) were observed in combined ion cyclotron resonance frequency and neutral beam injection heated plasmas. Ellipticity induced Alfvén eigenmodes (EAE) and toroidicity-induced Alfvén eigenmodes (TAE) were also observed in those plasmas. The threshold beta of the energetic ions for exciting the NAE modes was found to be similar to that for exciting TAE modes.
Heating and acceleration of ions in nonresonant Alfvenic turbulence
Nariyuki, Y.; Hada, T.; Tsubouchi, K.
2010-07-15
Nonlinear scattering of protons and alpha particles during the dissipation of the finite amplitude, low-frequency Alfvenic turbulence is studied. The process discussed here is not the coherent scattering and acceleration, as those often treated in the past studies, but is an incoherent process in which it is essential that the Alfvenic turbulence has a broadband spectrum. The presence of such an Alfvenic turbulence is widely recognized observationally both in the solar corona and in the solar wind. Numerical results suggest that, although there is no apparent sign of the occurrence of any parametric instabilities, the ions are heated efficiently by the nonlinear Landau damping, i.e., trapping and phase mixing by Alfven wave packets which are generated by beating of finite amplitude Alfven waves. The heating occurs both in the parallel and in the perpendicular directions, and the ion distribution function which is asymmetric with respect to the parallel velocity is produced. Eventual perpendicular energy of ions is much influenced by the spectrum and polarization of the given Alfvenic turbulence since the turbulence initially possess transverse energy as specified by Walen's relation.
NASA Astrophysics Data System (ADS)
Mathijssen, R. W.; Aartman, L. J.; Manders, P. J. H. M.; Slot, H.
1991-01-01
The NLR Infrastructure for Computer Aided Engineering (CAE) of Electronics (NICE) was introduced to solve problems due to the fact that CAE tools generally do not match mutually, with a view to the development of information systems for aerospace applications in which advanced electronics play an important role. CAE is used more and more to improve quality and reduce development time. Because most CAE tools generally do not match mutually, it is difficult to manage the design information present in the various tools and to exchange this information. NICE is based on an integrated set of local area networks, connected to the NLR computer network facilities. This is a basis for adding new tools for circuit simulation and analysis. Improved access to the tools and to the design information leads toward shorter development cycles of advanced electronics.
Performance evaluation of the NASA/KSC CAD/CAE and office automation LAN's
NASA Technical Reports Server (NTRS)
Zobrist, George W.
1994-01-01
This study's objective is the performance evaluation of the existing CAD/CAE (Computer Aided Design/Computer Aided Engineering) network at NASA/KSC. This evaluation also includes a similar study of the Office Automation network, since it is being planned to integrate this network into the CAD/CAE network. The Microsoft mail facility which is presently on the CAD/CAE network was monitored to determine its present usage. This performance evaluation of the various networks will aid the NASA/KSC network managers in planning for the integration of future workload requirements into the CAD/CAE network and determining the effectiveness of the planned FDDI (Fiber Distributed Data Interface) migration.
Bradshaw, D.T.; Brewer, J.E. )
1992-01-01
The Tennessee Valley Authority is currently looking at compressed air energy storage (CAES), a new but mature technology, as a new capacity option. The technology is mature because all pieces/components have been in existence and use for over 50 years. The compressors are standard components for the gas industry, and the turbo expander and motor generator are standard components in the utility business. The newness of the CAES technology is due to the integration of these components and the use of underground storage of air in porous media or possibly in abandoned mines. Although the integration of these components is new to the Untied States, they have been demonstrated in Germany for over 10 years in the 290 MWe CAES unit located in a salt cavern near Huntorf, Germany. The CAES unit has been very successful, operating with a 99% start-up reliability, and has been operated remotely.
Compressed air energy storage (CAES) environmental control concerns and program plan
Beckwith, M.A.; Boehm, D.W.
1980-06-01
This report assesses the required environmental research and recommends a program plan to assist DOD's Environmental Control Technology Division (ECT) in performing its mission of ensuring that the procedures, processes, systems, and strategies necessary to minimize any adverse environmental impacts of compressed air energy storage (CAES) are developed in a timely manner so as not to delay implementation of the technology. To do so, CAES technology and the expected major environmental concerns of the technology are described. Second, ongoing or planned research in related programs and the applicability of results from these programs to CAES environmental research are discussed. Third, the additional research and development required to provide the necessary environmental data base and resolve concerns in CAES are outlined. Finally, a program plan to carry out this research and development effort is presented.
On reflection of Alfven waves in the solar wind
NASA Technical Reports Server (NTRS)
Krogulec, M.; Musielak, Z. E.; Suess, S. T.; Moore, R. L.; Nerney, S. F.
1993-01-01
We have revisited the problem of propagation of toroidal and linear Alfven waves formulated by Heinemann and Olbert (1980) to compare WKB and non-WKB waves and their effects on the solar wind. They considered two solar wind models and showed that reflection is important for Alfven waves with periods of the order of one day and longer, and that non-WKB Alfven waves are no more effective in accelerating the solar wind than WKB waves. There are several recently published papers which seem to indicate that Alfven waves with periods of the order of several minutes should be treated as non-WKB waves and that these non-WKB waves exert a stronger acceleration force than WKB waves. The purpose of this paper is to study the origin of these discrepancies by performing parametric studies of the behavior of the waves under a variety of different conditions. In addition, we want to investigate two problems that have not been addressed by Heinemann and Olbert, namely, calculate the efficiency of Alfven wave reflection by using the reflection coefficient and identify the region of strongest wave reflection in different wind models. To achieve these goals, we investigated the influence of temperature, electron density distribution, wind velocity and magnetic field strength on the waves. The obtained results clearly demonstrate that Alfven wave reflection is strongly model dependent and that the strongest reflection can be expected in models with the base temperatures higher than 10(exp 6) K and with the base densities lower than 7 x 10(exp 7) cm(exp -3). In these models as well as in the models with lower temperatures and higher densities, Alfven waves with periods as short as several minutes have negligible reflection so that they can be treated as WKB waves; however, for Alfven waves with periods of the order of one hour or longer reflection is significant, requiring a non-WKB treatment. We also show that non-WKB, linear Alfven waves are always less effective in accelerating the
Free-boundary toroidal Alfvén eigenmodes
NASA Astrophysics Data System (ADS)
Chen, Eugene Y.; Berk, H. L.; Breizman, B.; Zheng, L. J.
2011-05-01
A numerical study is presented for the n = 1 free-boundary toroidal Alfvén eigenmodes (TAE) in tokamaks, which shows that there is considerable sensitivity of n = 1 modes to the position of the conducting wall. An additional branch of the TAE is shown to emerge from the upper continuum as the ratio of conducting wall radius to plasma radius increases. Such phenomena arise in plasma equilibria with both circular and shaped cross sections, where the shaped profile studied here is similar to that found in Alcator C-Mod.
Observation of odd toroidal Alfvén eigenmodes.
Kramer, G J; Sharapov, S E; Nazikian, R; Gorelenkov, N N; Budny, R V
2004-01-01
Experimental evidence is presented for the existence of the theoretically predicted odd toroidicity induced Alfvén eigenmode (TAE) from the simultaneous appearance of odd and even TAEs in a normal shear discharge of the joint European torus. The modes are observed in low central magnetic shear plasmas created by injecting lower hybrid current drive. A fast ion population was created by applying ion cyclotron heating at the high-field side to excite the TAEs. The odd TAEs were identified from their frequency, mode number, and timing relative to the even TAEs. PMID:14753994
The single photon superradiance from the eigenmode analysis
NASA Astrophysics Data System (ADS)
Manassah, Jamal T.
2009-11-01
Using the eigenmode analysis of the scalar photon theory, I compute the probability of the atoms remaining excited and the probability for the atoms remaining in the initial quantum state of a system of two-level atoms cloud in a sphere initially prepared to radiate in the forward direction, i.e., the single photon superradiance problem. The convergence in the results obtained for increasingly larger radii for the sphere suggests that the asymptotic limits for these quantities are obtained for a sphere with a radius equal to six times the resonant wavelength. I predict the maximal value of the probability of secondary excited states from large spheres at 17.1%.
Optical Control of Fluorescence through plasmonic eigenmode extinction
Xu, Xiaoying; Lin, Shih-Che; Li, Quanshui; Zhang, Zhili; Ivanov, Ilia N.; Li, Yuan; Wang, Wenbin; Gu, Baohua; Zhang, Zhenyu; Hsueh, C. H.; et al
2015-04-30
We introduce the concept of optical control of the fluorescence yield of CdSe quantum dots through plasmon-induced structural changes in random semicontinuous nanostructured gold films. We demonstrate that the wavelength- and polarization dependent coupling between quantum dots and the semicontinuous films, and thus the fluorescent emission spectrum, can be controlled and significantly increased through the optical extinction of a selective band of eigenmodes in the films. This optical method of effecting controlled changes in the metal nanostructure allows for versatile functionality in a single sample and opens a pathway to in situ control over the fluorescence spectrum.
Optical Control of Fluorescence through Plasmonic Eigenmode Extinction
NASA Astrophysics Data System (ADS)
Xu, Xiaoying; Lin, Shih-Che; Li, Quanshui; Zhang, Zhili; Ivanov, Ilia N.; Li, Yuan; Wang, Wenbin; Gu, Baohua; Zhang, Zhenyu; Hsueh, Chun-Hway; Snijders, Paul C.; Seal, Katyayani
2015-04-01
We introduce the concept of optical control of the fluorescence yield of CdSe quantum dots through plasmon-induced structural changes in random semicontinuous nanostructured gold films. We demonstrate that the wavelength- and polarization dependent coupling between quantum dots and the semicontinuous films, and thus the fluorescent emission spectrum, can be controlled and significantly increased through the optical extinction of a selective band of eigenmodes in the films. This optical method of effecting controlled changes in the metal nanostructure allows for versatile functionality in a single sample and opens a pathway to in situ control over the fluorescence spectrum.
Polyakov loop fluctuations in the Dirac eigenmode expansion
NASA Astrophysics Data System (ADS)
Doi, Takahiro M.; Redlich, Krzysztof; Sasaki, Chihiro; Suganuma, Hideo
2015-11-01
We investigate correlations of the Polyakov loop fluctuations with eigenmodes of the lattice Dirac operator. Their analytic relations are derived on the temporally odd-number size lattice with the normal nontwisted periodic boundary condition for the link variables. We find that the low-lying Dirac modes yield negligible contributions to the Polyakov loop fluctuations. This property is confirmed to be valid in confined and deconfined phases by numerical simulations in SU(3) quenched QCD. These results indicate that there is no direct, one-to-one correspondence between confinement and chiral symmetry breaking in QCD in the context of different properties of the Polyakov loop fluctuation ratios.
Alfven wave filamentation and dispersive phase mixing
Sulem, P. L.; Passot, T.; Laveder, D.; Borgogno, D.
2009-11-10
The formation of three-dimensional magnetic structures from quasi-monochromatic left-hand polarized dispersive Alfven waves, under the effect of transverse collapse and/or the lensing effect of density channels aligned with the ambient magnetic field is discussed, both in the context of the usual Hall-MHD and using a fluid model retaining linear Landau damping and finite Larmor radius corrections. It is in particular shown that in a small-{beta} plasma (that is stable relatively to the filamentation instability in the absence of inhomogeneities), a moderate density enhancement leads the wave energy to concentrate into a filament whose transverse size is prescribed by the dimension of the channel, while for a strong density perturbation, this structure later on evolves to thin helical ribbons where the strong gradients permit dissipation processes to become efficient and heat the plasma. The outcome of this 'dispersive phase mixing' that leads to small-scale formation on relatively extended regions contrasts with the more localized oblique shocks formed in the absence of dispersion. Preliminary results on the effect of weak collisions that lead to an increase of the transverse ion temperature are also briefly mentioned.
Toroidal Effects on the Alfven Resonance in the Phaedrus-T Tokamak.
NASA Astrophysics Data System (ADS)
Vukovic, Mirko
1995-01-01
Toroidal effects on the Alfven resonance (AR) in the Phaedrus-T tokamak (R_{m}=92cm, r_{a}=25.5cm) are examined for plasma parameters B_{T}=0.6 {-}0.7 T, q_{a}~eq 3.5, n_{e0}~eq 1.2times10 ^{13}cm^{-3}, and hydrogen plasma. Experiments were performed with a low field side, two-strap fast wave antenna at frequencies below omega_{cH} (f ~ 7 MHz, P_{RF}~eq 0.3MW, poloidal extent: {+/- }30^circ, strap separation: {~}15cm). In this regime, the ratio of the antenna to ion cyclotron frequency omega/omega_{cH} is {~eq}0.7 and toroidal mode number is ngg 1.. The two-dimensional cold plasma code L scION predicts that the continuum AR absorption lies close to the plasma edge (r > 0.8r_{a}). Due to toroidicity effects, L scION predicts that Global Alfven Eigenmodes (GAEs) damp at the AR at 0.5 < r/r_ {a} < 0.7. Damping at the AR reduces the quality factor Q of the eigenmodes considerably, facilitating antenna coupling to them. The AR radius of the GAEs is found to depend on omega/omega_ {cH} and plasma impurity concentration. The proximity of the S = 0 surface to the plasma core (S is the Stix dielectric tensor element) extinguishes the GAEs. Variation of the radius of absorption of GAEs versus B_{T} compared reasonably well with the prediction of the infinite medium AR condition (S=n_sp{parallel }{2}equiv c^2k_sp{ parallel}{2}/omega^2), where k_parallel~ 1/R is the wavenumber parallel to the magnetic field, R is the major radius, and S is evaluated for local plasma parameters. This is a consequence of the large toroidal mode numbers of the GAEs. A microwave reflectometer was used to observe the radial profile of the RF induced density fluctuations at the AR. The relative radial location of power deposition is also extracted from the analysis of the time behavior of the loop voltage signal; it compared reasonably well with the reflectometer data. Analysis of B_{T} and the deuterium (D_2) puff rate scans in a hydrogen plasma show behavior consistent with the predictions of L sc
Bass, E. M.; Waltz, R. E.
2010-11-15
Energetic particle (EP) transport from local high-n toroidal Alfven eigenmodes (TAEs) and energetic particle modes (EPMs) is simulated with a gyrokinetic code. Linear and nonlinear simulations have identified a parameter range where the longwave TAE and EPM are unstable alongside the well-known ion-temperature-gradient (ITG) and trapped-electron-mode (TEM) instabilities. A new eigenvalue solver in GYRO facilitates this mode identification. States of nonlinearly saturated local TAE/EPM turbulent intensity are identified, showing a 'soft' transport threshold for enhanced energetic particle transport against the TAE/EPM drive from the EP pressure gradient. The very long-wavelength (mesoscale) TAE/EPM transport is saturated partially by nonlinear interaction with microturbulent ITG/TEM-driven zonal flows. Fixed-gradient-length, nonlinearly saturated states are accessible over a relatively narrow range of EP pressure gradient. Within this range, and in the local limit employed, TAE/EPM-driven transport more closely resembles drift-wave microturbulent transport than 'stiff' ideal MHD transport with a clamped critical total pressure gradient. At a higher, critical EP pressure gradient, fixed-gradient nonlinear saturation fails: EP transport increases without limit and background transport decreases. Presumably saturation is then obtained by relaxation of the EP pressure gradient to near this critical EP pressure gradient. If the background plasma gradients driving the ITG/TEM turbulence and zonal flows are weakened, the critical gradient collapses to the TAE/EPM linear stability threshold. Even at the critical EP pressure gradient there is no evidence that TAE/EPM instability significantly increases transport in the background plasma channels.
Kinetic Alfven Wave Electron Acceleration on Auroral Field Lines
NASA Technical Reports Server (NTRS)
Kletzing, Craig A.
2001-01-01
Major results of the S3-3 Langmuir sweep study are published. Studies show statistics and average density and temperature variation on auroral field lines up to 8000 km altitude. Alfven wave papers were published. Our model of Alfven wave propagation on auroral field lines was successfully extended to handle varying density and magnetic field for the inertial mode. The study showed that Alfven wave can create time-dispersed electron signatures. A study was undertaken to extend Langmuir sweep I-V curves to handle the case of an kappa electron distribution as well as Maxwellian. The manuscript is in preparation. Participated in International Space Science Institute study of Alfvenic structures which resulted in a group review paper. The proposed work was to develop an extended model of Alfven wave propagation along auroral field lines to study electron acceleration. As part of this work, a major task was to characterize density and temperature along auroral field lines by using spacecraft Langmuir sweep data. The work that was completed under this funding was successful at both tasks. Three papers have been published as part of this work and a fourth manuscript is in preparation.
Tuan, P H; Wen, C P; Yu, Y T; Liang, H C; Huang, K F; Chen, Y F
2014-02-01
Experimentally resonant modes are commonly presumed to correspond to eigenmodes in the same bounded domain. However, the one-to-one correspondence between theoretical eigenmodes and experimental observations is never reached. Theoretically, eigenmodes in numerous classical and quantum systems are the solutions of the homogeneous Helmholtz equation, whereas resonant modes should be solved from the inhomogeneous Helmholtz equation. In the present paper we employ the eigenmode expansion method to derive the wave functions for manifesting the distinction between eigenmodes and resonant modes. The derived wave functions are successfully used to reconstruct a variety of experimental results including Chladni figures generated from the vibrating plate, resonant patterns excited from microwave cavities, and lasing modes emitted from the vertical cavity. PMID:25353549
NASA Technical Reports Server (NTRS)
Tanaka, Motohiko; Sato, Tetsuya; Hasegawa, A.
1989-01-01
The excitation of the kinetic Alfven wave by resonant mode conversion and longitudinal heating of the plasma by the kinetic Alfven wave were demonstrated on the basis of a macroscale particle simulation. The longitudinal electron current was shown to be cancelled by the ions. The kinetic Alfven wave produced an ordered motion of the plasma particles in the wave propagation direction. The electrons were pushed forward along the ambient magnetic field by absorbing the kinetic Alfven wave through the Landau resonance.
NASA Astrophysics Data System (ADS)
Prokopenko, Yu. V.; Filippov, Yu. F.; Shipilova, I. A.
2007-09-01
A semicylindrical dielectric resonator with a thin cylindrical inhomogeneity in the region of the field antinode of a whispering gallery eigenmode has been studied. Characteristic equations determining the complex eigenfrequencies of such resonators with axially homogeneous eigenmodes are obtained. It is shown that the presence of a dielectric or conducting inhomogeneity leads to a frequency shift and causes additional energy losses of the eigenmode.
Magnetospheric filter effect for Pc 3 Alfven mode waves
NASA Technical Reports Server (NTRS)
Zhang, X.; Comfort, R. H.; Gallagher, D. L.; Green, J. L.; Musielak, Z. E.; Moore, T. E.
1995-01-01
We present a ray-tracing study of the propagation of Pc 3 Alfven mode waves originating at the dayside magnetopause. This study reveals interesting features of magnetospheric filter effect for these waves. Pc 3 Alfven mode waves cannot penetrate to low Earth altitudes unless the wave frequency is below approximately 30 mHz. Configurations of the dispersion curves and the refractive index show that the gyroresonance and pseudo-cutoff introduced by the heavy ion O(+) block the waves. When the O(+) concentration is removed from the plasma composition, the barriers caused by the O(+) no longer exist, and waves with much higher frequencies than 30 mHz can penetrate to low altitudes. The result that the 30 mHz or lower frequency Alfven waves can be guided to low altitudes agrees with ground-based power spectrum observation at high altitudes.
Magnetospheric filter effect for Pc 3 Alfven mode waves
NASA Technical Reports Server (NTRS)
Zhang, X.; Comfort, R. H.; Gallagher, D. L.; Green, J. L.; Musielak, Z. E.; Moore, T. E.
1994-01-01
We present a ray-tracing study of the propagation of Pc 3 Alfven mode waves originating at the dayside magnetopause. This study reveals interesting features of a magnetospheric filter effect for these waves. Pc 3 Alfven mode waves cannot penetrate to low Earth altitudes unless the wave frequency is below approximately 30 mHz. Configurations of the dispersion curves and the refractive index show that the gyroresonance and pseudo-cutoff introduced by the heavy ion O(+) block the waves. When the O(+) concentration is removed from the plasma composition, the barriers caused by the O(+) no longer exist, and waves with much higher frequencies than 30 mHz can penetrate to low altitudes. The result that the 30 mHz or lower frequency Alfven waves can be guided to low altitudes agrees with ground-based power spectrum observations at high latitudes.
Radiation from accelerated Alfven solitons in inhomogeneous plasmas
NASA Technical Reports Server (NTRS)
Lakhina, G. S.; Buti, B.; Tsintsadze, N. L.
1990-01-01
In a weakly inhomogeneous plasma, the large-amplitude Alfven waves propagating parallel to the ambient magnetic field are shown to evolve into accelerated Alfven solitons. Nonlinear interaction of the accelerated Alfven solitons with the Langmuir waves results in the emission of coherent radiations. Analytical expression for the power radiated per unit solid angle from a soliton is derived for two inhomogeneity profiles, namely the linear profile and the parabolic profile. For the case of uniform plasmas, the emission occurs via a decay-type process or resonant modes. In the presence of inhomogeneity, nonresonant modes provide a new channel for the emission of radiation. The power radiated per unit solid angle is computed for the parameters relevant to Comet Halley's plasma environment. For the nonresonant modes it is found to be several orders of magnitude higher than that for the case of resonant modes.
Resonant wave-particle interactions modified by intrinsic Alfvenic turbulence
Wu, C. S.; Lee, K. H.; Wang, C. B.; Wu, D. J.
2012-08-15
The concept of wave-particle interactions via resonance is well discussed in plasma physics. This paper shows that intrinsic Alfven waves can qualitatively modify the physics discussed in conventional linear plasma kinetic theories. It turns out that preexisting Alfven waves can affect particle motion along the ambient magnetic field and, moreover, the ensuing force field is periodic in time. As a result, the meaning of the usual Landau and cyclotron resonance conditions becomes questionable. It turns out that this effect leads us to find a new electromagnetic instability. In such a process intrinsic Alfven waves not only modify the unperturbed distribution function but also result in a different type of cyclotron resonance which is affected by the level of turbulence. This instability might enable us to better our understanding of the observed radio emission processes in the solar atmosphere.
Analytical theory of interchange and compressional Alfven instabilities in EBT
Cheng, C.Z.; Tsang, K.T.
1981-07-01
The local stability of the EBT plasma is analyzed for the long wavelength perturbations in the frequency regime, ..omega.. approx. less than or equal to ..cap omega../sub i/(..cap omega../sub i/ is ion cyclotron frequency). In addition to the low frequency interchange instability, the plasma can be unstable to the compressional Alfven wave. Contrary to the previously obtained quadratic dispersion relation in ..omega.. for the interchange mode, our dispersion relations for both types of instabilities are cubic in ..omega... New stability boundaries are found, for the hot electron interchange mode, to relate to the enhanced compressibility of the core plasma in the presence of hot electrons. The compressional Alfven instability is driven due to the coupling of hot electron magnetic drifts and diamagnetic drift with the compressional Alfven wave. The stability conditions of these two types of instabilities are opposite to each other.
NASA Technical Reports Server (NTRS)
Moore, R. L.; Hammer, R.; Musielak, Z. E.; Suess, S. T.; An, C.-H.
1992-01-01
In our recent analysis of Alfven wave reflection in solar coronal holes, we found evidence that coronal holes are heated by reflected Alfven waves. This result suggests that the reflection is inherent to the process that dissipates these Alfven waves into heat. We propose a novel dissipation process that is driven by the reflection, and that plausibly dominates the heating in coronal holes.
THE ROLE OF TORSIONAL ALFVEN WAVES IN CORONAL HEATING
Antolin, P.; Shibata, K. E-mail: shibata@kwasan.kyoto-u.ac.j
2010-03-20
In the context of coronal heating, among the zoo of magnetohydrodynamic (MHD) waves that exist in the solar atmosphere, Alfven waves receive special attention. Indeed, these waves constitute an attractive heating agent due to their ability to carry over the many different layers of the solar atmosphere sufficient energy to heat and maintain a corona. However, due to their incompressible nature these waves need a mechanism such as mode conversion (leading to shock heating), phase mixing, resonant absorption, or turbulent cascade in order to heat the plasma. Furthermore, their incompressibility makes their detection in the solar atmosphere very difficult. New observations with polarimetric, spectroscopic, and imaging instruments such as those on board the Japanese satellite Hinode, or the Crisp spectropolarimeter of the Swedish Solar Telescope or the Coronal Multi-channel Polarimeter, are bringing strong evidence for the existence of energetic Alfven waves in the solar corona. In order to assess the role of Alfven waves in coronal heating, in this work we model a magnetic flux tube being subject to Alfven wave heating through the mode conversion mechanism. Using a 1.5 dimensional MHD code, we carry out a parameter survey varying the magnetic flux tube geometry (length and expansion), the photospheric magnetic field, the photospheric velocity amplitudes, and the nature of the waves (monochromatic or white-noise spectrum). The regimes under which Alfven wave heating produces hot and stable coronae are found to be rather narrow. Independently of the photospheric wave amplitude and magnetic field, a corona can be produced and maintained only for long (>80 Mm) and thick (area ratio between the photosphere and corona >500) loops. Above a critical value of the photospheric velocity amplitude (generally a few km s{sup -1}) the corona can no longer be maintained over extended periods of time and collapses due to the large momentum of the waves. These results establish several
Ion temperature in plasmas with intrinsic Alfven waves
NASA Astrophysics Data System (ADS)
Wu, C. S.; Yoon, P. H.; Wang, C. B.
2014-10-01
This Brief Communication clarifies the physics of non-resonant heating of protons by low-frequency Alfvenic turbulence. On the basis of general definition for wave energy density in plasmas, it is shown that the wave magnetic field energy is equivalent to the kinetic energy density of the ions, whose motion is induced by the wave magnetic field, thus providing a self-consistent description of the non-resonant heating by Alfvenic turbulence. Although the study is motivated by the research on the solar corona, the present discussion is only concerned with the plasma physics of the heating process.
First Results of PIC Modeling of Kinetic Alfven Wave Dissipation
NASA Technical Reports Server (NTRS)
Chulaki, Anna; Hesse, Michael; Zenitani, Seiji
2007-01-01
We present first results of an investigation of the kinetic damping of Alfven wave turbulence. The methodology is based on a fully electromagnetic, three-dimensional, particle in cell code. The calculation is initialized by an Alfven wave spectrum. Subsequently, a cascade develops, and damping by coupling to both ions and electrons is observed. We discuss results of these calculations, and present first estimates of damping rates and of the effects of energy transfer on ion and electron distributions. The results pertain to solar wind heating and acceleration.
Global structures of Alfven-ballooning modes in magnetospheric plasmas
Vetoulis, G.; Chen, Liu
1994-03-01
The authors show that a steep plasma pressure gradient can lead to radially localized Alfven modes, which are damped through coupling to filed line resonances. These have been called drift Alfven balloning modes (DABM) and are the prime candidates to explain Pc4-Pc5 geomagnetic pulsations observed during storms. A strong dependence of the damping rate on the azimuthal wave number m is established, as well as on the equilibrium profile. A minimum azimuthal mode number can be found for the DABM to be radially trapped. The authors find that higher m DABMs are better localized, which is consistent with high-m observations.
A sub-Alfvenic solar wind - Interplanetary and magnetosheath observations
NASA Technical Reports Server (NTRS)
Gosling, J. T.; Asbridge, J. R.; Bame, S. J.; Feldman, W. C.; Zwickl, R. D.; Paschmann, G.; Sckopke, N.; Russell, C. T.
1982-01-01
During much of an approximately 5-hour period on November 22, 1979, plasma and field instruments on ISEE 3 measured a solar wind flow that was simultaneously supersonic and sub-Alfvenic (about 320 km/s) due to an abnormally low ion density (about 0.07 per cu cm). The nature of the disturbed flow adjacent to the magnetosphere is examined. This examination suggests that the earth's bow wave retained its shock-like character when the solar wind flow was sub-Alfvenic.
Resonant Alfven wave instabilities driven by streaming fast particles
Zachary, A.
1987-05-08
A plasma simulation code is used to study the resonant interactions between streaming ions and Alfven waves. The medium which supports the Alfven waves is treated as a single, one-dimensional, ideal MHD fluid, while the ions are treated as kinetic particles. The code is used to study three ion distributions: a cold beam; a monoenergetic shell; and a drifting distribution with a power-law dependence on momentum. These distributions represent: the field-aligned beams upstream of the earth's bow shock; the diffuse ions upstream of the bow shock; and the cosmic ray distribution function near a supernova remnant shock. 92 refs., 31 figs., 12 tabs.
Ion temperature in plasmas with intrinsic Alfven waves
Wu, C. S.; Yoon, P. H.; Wang, C. B.
2014-10-15
This Brief Communication clarifies the physics of non-resonant heating of protons by low-frequency Alfvenic turbulence. On the basis of general definition for wave energy density in plasmas, it is shown that the wave magnetic field energy is equivalent to the kinetic energy density of the ions, whose motion is induced by the wave magnetic field, thus providing a self-consistent description of the non-resonant heating by Alfvenic turbulence. Although the study is motivated by the research on the solar corona, the present discussion is only concerned with the plasma physics of the heating process.
The transmission of Alfven waves through the Io plasma torus
NASA Astrophysics Data System (ADS)
Wright, A. N.; Schwartz, S. J.
1989-04-01
The nature of Alfven wave propagation through the Io plasma torus was investigated using a one-dimensional model with uniform magnetic field and an exponential density decrease to a constant value. The solution was interpreted in terms of a wave that is incident upon the torus, a reflected wave, and a wave that is transmitted through the torus. The results obtained indicate that Io's Alfven waves may not propagate completely through the plasma torus, and, thus, the WKB theory and ray tracing may not provide meaningful estimates of the energy transport.
Eigenmodes of quasi-static magnetic islands in current sheet
Li Yi; Cai Xiaohui; Chai Lihui; Wang Shui; Zheng Huinan; Shen Chao
2011-12-15
As observation have shown, magnetic islands often appear before and/or after the onset of magnetic reconnections in the current sheets, and they also appear in the current sheets in the solar corona, Earth's magnetotail, and Earth's magnetopause. Thus, the existence of magnetic islands can affect the initial conditions in magnetic reconnection. In this paper, we propose a model of quasi-static magnetic island eigenmodes in the current sheet. This model analytically describes the magnetic field structures in the quasi-static case, which will provide a possible approach to reconstructing the magnetic structures in the current sheet via observation data. This model is self-consistent in the kinetic theory. Also, the distribution function of charged particles in the magnetic island can be calculated.
Subthreshold optical parametric oscillator with nonorthogonal polarization eigenmodes
Aiello, A.; Nienhuis, G.; Woerdman, J.P.
2003-04-01
We study the behavior of a type-II degenerate parametric amplifier in a cavity with nonorthogonal polarization eigenmodes. The mode nonorthogonality is achieved by introducing circular birefringence and linear dichroism. We use a scattering matrix formalism to investigate the role of excess quantum noise in such a device. Since only two modes are involved we are able to derive an analytical expression for the twin-photon generation rate measured outside the cavity as a function of the degree of mode nonorthogonality. Contrary to recent claims we conclude that there is no evidence of excess quantum noise for a parametric amplifier working so far below threshold that spontaneous processes dominate. Using the same scattering matrix formalism we also investigate the output spectrum of the amplifier near the threshold of parametric oscillation. We find optical band structures very similar to those known for passive ring cavities. These optical band structures are studied as a function of mode nonorthogonality and mirror reflectivity.
Schuh, Andreas; Bozchalooi, Iman Soltani; Rangelow, Ivo W; Youcef-Toumi, Kamal
2015-06-12
High speed imaging and mapping of nanomechanical properties in atomic force microscopy (AFM) allows the observation and characterization of dynamic sample processes. Recent developments involve several cantilever frequencies in a multifrequency approach. One method actuates the first eigenmode for topography imaging and records the excited higher harmonics to map nanomechanical properties of the sample. To enhance the higher frequencies' response two or more eigenmodes are actuated simultaneously, where the higher eigenmode(s) are used to quantify the nanomechanics. In this paper, we combine each imaging methodology with a novel control approach. It modifies the Q factor and resonance frequency of each eigenmode independently to enhance the force sensitivity and imaging bandwidth. It allows us to satisfy the different requirements for the first and higher eigenmode. The presented compensator is compatible with existing AFMs and can be simply attached with minimal modifications. Different samples are used to demonstrate the improvement in nanomechanical contrast mapping and imaging speed of tapping mode AFM in air. The experiments indicate most enhanced nanomechanical contrast with low Q factors of the first and high Q factors of the higher eigenmode. In this scenario, the cantilever topography imaging rate can also be easily improved by a factor of 10. PMID:25994333
Radionuclide Emission Estimation for the Center for Advanced Energy Studies (CAES)
Bradley J Schrader
2010-02-01
An Radiological Safety Analysis Computer Program (RSAC)-7 model dose assessment was performed to evaluate maximum Center for Advanced Energy Studies (CAES) boundary effective dose equivalent (EDE, in mrem/yr) for potential individual releases of radionuclides from the facility. The CAES is a public/private partnership between the State of Idaho and its academic research institutions, the federal government through the U.S. Department of Energy (DOE), and the Idaho National Laboratory (INL) managed by the Battelle Energy Alliance (BEA). CAES serves to advance energy security for our nation by expanding educational opportunities at Idaho universities in energy-related areas, creating new capabilities within its member institutions, and delivering technological innovations leading to technology-based economic development for the intermountain region. CAES has developed a strategic plan (INL/EXT-07-12950) based on the balanced scorecard approach. At the present time it is unknown exactly what processes will be used in the facility in support of this strategic plan. What is known is that the Idaho State University (ISU) Radioactive Materials License (Nuclear Regulatory Commission [NRC] license 11-27380-01) is the basis for handling radioactive material in the facility. The material in this license is shared between the ISU campus and the CAES facility. There currently are no agreements in place to limit the amount of radioactive material at the CAES facility or what is done to the material in the facility. The scope of this analysis is a summary look at the basis dose for each radionuclide included under the license at a distance of 100, 500, and 1,000 m. Inhalation, ingestion and ground surface dose was evaluated using the NRC design basis guidelines. The results can be used to determine a sum of the fractions approach to facility safety. This sum of the fractions allows a facility threshold value (TV) to be established and potential activities to be evaluated against
Numerical study of Alfvén eigenmodes in the Experimental Advanced Superconducting Tokamak
Hu, Youjun; Li, Guoqiang; Yang, Wenjun; Zhou, Deng; Ren, Qilong; Gorelenkov, N. N.; Cai, Huishan
2014-05-15
Alfvén eigenmodes in up-down asymmetric tokamak equilibria are studied by a new magnetohydrodynamic eigenvalue code. The code is verified with the NOVA code for the Solovév equilibrium and then is used to study Alfvén eigenmodes in a up-down asymmetric equilibrium of the Experimental Advanced Superconducting Tokamak. The frequency and mode structure of toroidicity-induced Alfvén eigenmodes are calculated. It is demonstrated numerically that up-down asymmetry induces phase variation in the eigenfunction across the major radius on the midplane.
NASA Astrophysics Data System (ADS)
Kanto, Y.; Kawasumi, T.
2010-06-01
With the rapid progress of the computational mechanics, CAE software, such as FEM programs, are having many functions and become more complicated. Because the development shouldn't be stopped, every CAE program should consider future functionality expansions. It is difficult, however, to forecast what types of expansions are required from the future researches. Object-oriented approach appears a promising technique to develop complicated and flexible software. Especially adoption of design patterns fits the purpose. In this paper, a combination of Decorator pattern and Visitor pattern, or Option pattern is discussed and its application to the FEM program of structural problems is demonstrated.
ALFVEN WAVES IN A PARTIALLY IONIZED TWO-FLUID PLASMA
Soler, R.; Ballester, J. L.; Terradas, J.; Carbonell, M. E-mail: joseluis.ballester@uib.es E-mail: marc.carbonell@uib.es
2013-04-20
Alfven waves are a particular class of magnetohydrodynamic waves relevant in many astrophysical and laboratory plasmas. In partially ionized plasmas the dynamics of Alfven waves is affected by the interaction between ionized and neutral species. Here we study Alfven waves in a partially ionized plasma from the theoretical point of view using the two-fluid description. We consider that the plasma is composed of an ion-electron fluid and a neutral fluid, which interact by means of particle collisions. To keep our investigation as general as possible, we take the neutral-ion collision frequency and the ionization degree as free parameters. First, we perform a normal mode analysis. We find the modification due to neutral-ion collisions of the wave frequencies and study the temporal and spatial attenuation of the waves. In addition, we discuss the presence of cutoff values of the wavelength that constrain the existence of oscillatory standing waves in weakly ionized plasmas. Later, we go beyond the normal mode approach and solve the initial-value problem in order to study the time-dependent evolution of the wave perturbations in the two fluids. An application to Alfven waves in the low solar atmospheric plasma is performed and the implication of partial ionization for the energy flux is discussed.
Quantum effects on compressional Alfven waves in compensated semiconductors
Amin, M. R.
2015-03-15
Amplitude modulation of a compressional Alfven wave in compensated electron-hole semiconductor plasmas is considered in the quantum magnetohydrodynamic regime in this paper. The important ingredients of this study are the inclusion of the particle degeneracy pressure, exchange-correlation potential, and the quantum diffraction effects via the Bohm potential in the momentum balance equations of the charge carriers. A modified nonlinear Schrödinger equation is derived for the evolution of the slowly varying amplitude of the compressional Alfven wave by employing the standard reductive perturbation technique. Typical values of the parameters for GaAs, GaSb, and GaN semiconductors are considered in analyzing the linear and nonlinear dispersions of the compressional Alfven wave. Detailed analysis of the modulation instability in the long-wavelength regime is presented. For typical parameter ranges of the semiconductor plasmas and at the long-wavelength regime, it is found that the wave is modulationally unstable above a certain critical wavenumber. Effects of the exchange-correlation potential and the Bohm potential in the wave dynamics are also studied. It is found that the effect of the Bohm potential may be neglected in comparison with the effect of the exchange-correlation potential in the linear and nonlinear dispersions of the compressional Alfven wave.
Reflection of Alfven waves from boundaries with different conductivities
Leneman, D.
2007-12-15
The reflection of Alfven waves from the ionosphere plays a crucial role because the reflected wave can reduce or enhance the electric field pattern of the incident wave. The ionosphere is typically treated as a conducting surface, which has a height integrated Pederson conductivity. This approximation is appropriate in considering the reflection of Alfven waves because the wavelengths along the magnetic field are large compared to the height of the ionosphere. Shear Alfven wave reflection experiments have been performed in the large plasma device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. of Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles. A single frequency wave is launched from an antenna and reflects from a large plate inserted into the plasma column. By alternatively using a conducting and an insulating plate, the two extremes of conductivity relative to the Alfven conductivity, 1/({mu}{sub o}v{sub A}) are tested. The data are compared with the expected theoretical behavior of the interference pattern of incident and reflected waves. Perhaps due to experimental effects, the conducting reflector is found to behave in much the same fashion as the insulator.
On the kinetic dispersion for shear Alfven waves
Lysak, R.L.; Lotko, W.
1996-03-01
Kinetic Alfven waves have been invoked is association with auroral currents and particle acceleration since the pioneering work of Hasegawa. However, to date, no work has considered the dispersion relation including the full kinetic effects for both electrons and ions. Results from such a calculation are presented, with emphasis on the role of Landua damping in dissipating Alfven waves which propogate from the warm plasma of the outer magnetosphere to the cold plasma present in the ionosphere. It is found that the Landua damping is not important when the perpendicular wavelength is larger than the ion acoustic gyroradius and the electron inertial length. In addition, ion gyroradius effects lead to a reduction in the Landua damping by raising the parallel phase velocity of the wave above the electron thermal speed in the short perpendicular wavelength regime. These results indicate that low-frequency Alfven waves with perpendicular wavelengths greater than the order of 10 km when mapped to the ionosphere will not be significantly affected by Landau damping. While these results based on the local dispersion relation, are strictly valid only for short parallel wavelength Alfven waves, they do give an indication of the importance of Landua damping for longer parallel wavelength waves such as field line resonances. 26 refs., 5 fig.
Theory of Alfven wave heating in general toroidal geometry
Tataronis, J.A.; Salat, A.
1981-09-01
A general treatment of Alfven wave heating based on the linearized equations of ideal magnetohydrodynamics (MHD) is given. The conclusion of this study is that the geometry of the plasma equilium could play an important role on the effectiveness of this heating mechanism, and for certain geometries the fundamental equations may not possess solutions which satisfy prescribed boundary conditions.
COUPLED ALFVEN AND KINK OSCILLATIONS IN CORONAL LOOPS
Pascoe, D. J.; Wright, A. N.; De Moortel, I.
2010-03-10
Observations have revealed ubiquitous transverse velocity perturbation waves propagating in the solar corona. However, there is ongoing discussion regarding their interpretation as kink or Alfven waves. To investigate the nature of transverse waves propagating in the solar corona and their potential for use as a coronal diagnostic in MHD seismology, we perform three-dimensional numerical simulations of footpoint-driven transverse waves propagating in a low beta plasma. We consider the cases of both a uniform medium and one with loop-like density structure and perform a parametric study for our structuring parameters. When density structuring is present, resonant absorption in inhomogeneous layers leads to the coupling of the kink mode to the Alfven mode. The decay of the propagating kink wave as energy is transferred to the local Alfven mode is in good agreement with a modified interpretation of the analysis of Ruderman and Roberts for standing kink modes. Numerical simulations support the most general interpretation of the observed loop oscillations as a coupling of the kink and Alfven modes. This coupling may account for the observed predominance of outward wave power in longer coronal loops since the observed damping length is comparable to our estimate based on an assumption of resonant absorption as the damping mechanism.
1.5D quasilinear model and its application on beams interacting with Alfvén eigenmodes in DIII-D
NASA Astrophysics Data System (ADS)
Ghantous, K.; Gorelenkov, N. N.; Berk, H. L.; Heidbrink, W. W.; Van Zeeland, M. A.
2012-09-01
We propose a model, denoted here by 1.5D, to study energetic particle (EP) interaction with toroidal Alfvenic eigenmodes (TAE) in the case where the local EP drive for TAE exceeds the stability limit. Based on quasilinear theory, the proposed 1.5D model assumes that the particles diffuse in phase space, flattening the pressure profile until its gradient reaches a critical value where the modes stabilize. Using local theories and NOVA-K simulations of TAE damping and growth rates, the 1.5D model calculates the critical gradient and reconstructs the relaxed EP pressure profile. Local theory is improved from previous study by including more sophisticated damping and drive mechanisms such as the numerical computation of the effect of the EP finite orbit width on the growth rate. The 1.5D model is applied on the well-diagnosed DIII-D discharges #142111 [M. A. Van Zeeland et al., Phys. Plasmas 18, 135001 (2011)] and #127112 [W. W. Heidbrink et al., Nucl. Fusion. 48, 084001 (2008)]. We achieved a very satisfactory agreement with the experimental results on the EP pressure profiles redistribution and measured losses. This agreement of the 1.5D model with experimental results allows the use of this code as a guide for ITER plasma operation where it is desired to have no more than 5% loss of fusion alpha particles as limited by the design.
Identification of eigenmodes of volume piezoelectric resonators in resonant ultrasound spectroscopy
NASA Astrophysics Data System (ADS)
Myasnikov, D. V.; Konyashkin, A. V.; Ryabushkin, O. A.
2010-07-01
Eigenmodes of volume piezoelectric resonators used in resonant ultrasound spectroscopy (RUS) are considered. A novel method for the identification of these modes is proposed, which is based on the measurement of a temperature shift of the resonance frequency. A good coincidence of the measured and calculated eigenmode spectra is demonstrated for a quartz crystal. In comparison to the other methods of identification, the proposed approach is simple to implement and provides reliable results in solving RUS problems.
A Personal Memoir of Policy Failure: The Failed Merger of ANU and the Canberra CAE
ERIC Educational Resources Information Center
Scott, Roger
2004-01-01
The more immediate context of the events the author describes in this article is needed in order to identify the policy framework within which the Australian National University (ANU)-Canberra CAE (CCAE) merger was placed as a component of a wider public policy initiative undertaken by John Dawkins. There were four major components in that wider…
CAES 2014 Chemical Analyses of Thermal Wells and Springs in Southeastern Idaho
Baum, Jeffrey
2014-03-10
This dataset contains chemical analyses for thermal wells and springs in Southeastern Idaho. Data includes all major cations, major anions, pH, collection temperature, and some trace metals, These samples were collected in 2014 by the Center for Advanced Energy Studies (CAES), and are part of a continuous effort to analyze the geothermal potential of Southeastern Idaho.
Alfvén eigenmode experiments in tokamaks and stellarators
NASA Astrophysics Data System (ADS)
Fasoli, A.; Borba, D.; Gormezano, C.; Heeter, R.; Jaun, A.; Jacquinot, J.; Kerner, W.; King, Q.; Lister, J. B.; Sharapov, S.; Start, D.; Villard, L.
1997-12-01
In tokamaks and stellarators, measurements of electromagnetic fluctuations in the presence of resonant particle drive, including fusion-produced 0741-3335/39/12B/022/img17, reveal the excitation of Alfvén eigenmodes (AE), related under certain conditions to a degradation in the fast-particle confinement. The balance between the drive and the background damping is investigated using active diagnostic systems to excite and measure the AE spectrum in terms of frequencies and damping rates. At JET, saddle-coil antennae drive low toroidal mode number (n<4) AE in the range 30 - 500 kHz, including toroidal AE, kinetic AE, elliptical AE and global AE. Conditions for weak damping 0741-3335/39/12B/022/img18 are identified. Low-n AE appear to be strongly damped 0741-3335/39/12B/022/img19 during the creation of the magnetic X-point. In the presence of resonant fast particles, information on the instability drive is obtained: low-n modes are found to be stable in the presence of NBI with 0741-3335/39/12B/022/img20. Fast ions generated by ICRH are observed to produce a drive for 0741-3335/39/12B/022/img21, with 0741-3335/39/12B/022/img22 under these conditions, intrinsically driven TAE and EAE are clearly observed in the magnetic fluctuation spectra, with no measurable effect on the plasma performance.
Projective filtering of the fundamental eigenmode from spatially multimode radiation
NASA Astrophysics Data System (ADS)
Pérez, A. M.; Sharapova, P. R.; Straupe, S. S.; Miatto, F. M.; Tikhonova, O. V.; Leuchs, G.; Chekhova, M. V.
2015-11-01
Lossless filtering of a single coherent (Schmidt) mode from spatially multimode radiation is a problem crucial for optics in general and for quantum optics in particular. It becomes especially important in the case of nonclassical light that is fragile to optical losses. An example is bright squeezed vacuum generated via high-gain parametric down conversion or four-wave mixing. Its highly multiphoton and multimode structure offers a huge increase in the information capacity provided that each mode can be addressed separately. However, the nonclassical signature of bright squeezed vacuum, photon-number correlations, are highly susceptible to losses. Here we demonstrate lossless filtering of a single spatial Schmidt mode by projecting the spatial spectrum of bright squeezed vacuum on the eigenmode of a single-mode fiber. Moreover, we show that the first Schmidt mode can be captured by simply maximizing the fiber-coupled intensity. Importantly, the projection operation does not affect the targeted mode and leaves it usable for further applications.
The NASA Center for Astronomy Education (CAE): 2007 College Astronomy Teaching Excellence Workshops
NASA Astrophysics Data System (ADS)
Brissenden, Gina; Prather, E. E.; Slater, T. F.; Greene, W. M.; Thaller, M.
2006-12-01
Since 2003 the NASA Center for Astronomy Education (CAE) has been devoted to the professional development of introductory college astronomy faculty with a special focus on faculty teaching at community colleges. As part of our efforts CAE conducts 2-day and 3-day Teaching Excellence Workshops. In Tier I (introductory) Workshops, the overarching goal is for participants to become familiar with learner-centered teaching and assessment materials, as well as how to implement them in their college introductory astronomy courses. To accomplish this goal, participants learn how to create productive learning environments by reviewing research on the nature of teaching and learning; setting course goals and objectives; and using interactive lectures, peer instruction, engaging demonstrations, collaborative groups, tutorials, and ranking tasks. Participants also learn how to create more effective multiple-choice tests. In Tier II (advanced) Workshops, the overarching goal is to help past workshop participants with their obstacles to implementing a learner-centered introductory college astronomy course. Workshop participants work to understand how students learn while engaged in learner-centered activities and what the role of the instructor is in the learner-centered class. CAE regional workshops are held at community colleges around the country, NASA Research Centers, and in conjunction with professional society meetings, such as the American Astronomical Society and the American Association of Physics Teachers, and also through the infrastructure of the National Science Foundation's Summer Chautauqua Workshop program. The NASA Center for Astronomy Education (CAE) is a partnership with the Univ. of Arizona Conceptual Astronomy & Physics Education Research (CAPER) Team. CAE is supported by NASA JPL's Navigator Public Engagement program (consisting of several space telescopes--including SIM PlanetQuest, the Terrestrial Planet Finder, the Keck Interferometer, and the Large
Wang Chuantao
2005-08-05
In the past decade, sheet metal forming and die development has been transformed to a science-based and technology-driven engineering and manufacturing enterprise from a tryout-based craft. Stamping CAE, especially the sheet metal forming simulation, as one of the core components in digital die making and digital stamping, has played a key role in this historical transition. The stamping simulation technology and its industrial applications have greatly impacted automotive sheet metal product design, die developments, die construction and tryout, and production stamping. The stamping CAE community has successfully resolved the traditional formability problems such as splits and wrinkles. The evolution of the stamping CAE technology and business demands opens even greater opportunities and challenges to stamping CAE community in the areas of (1) continuously improving simulation accuracy, drastically reducing simulation time-in-system, and improving operationalability (friendliness) (2) resolving those historically difficult-to-resolve problems such as dimensional quality problems (springback and twist) and surface quality problems (distortion and skid/impact lines) (3) resolving total manufacturability problems in line die operations including blanking, draw/redraw, trim/piercing, and flanging, and (4) overcoming new problems in forming new sheet materials with new forming techniques. In this article, the author first provides an overview of the stamping CAE technology adventures and achievements, and industrial applications in the past decade. Then the author presents a summary of increasing manufacturability needs from the formability to total quality and total manufacturability of sheet metal stampings. Finally, the paper outlines the new needs and trends for continuous improvements and innovations to meet increasing challenges in line die formability and quality requirements in automotive stamping.
NASA Astrophysics Data System (ADS)
Wang, Chuantao (C. T.)
2005-08-01
In the past decade, sheet metal forming and die development has been transformed to a science-based and technology-driven engineering and manufacturing enterprise from a tryout-based craft. Stamping CAE, especially the sheet metal forming simulation, as one of the core components in digital die making and digital stamping, has played a key role in this historical transition. The stamping simulation technology and its industrial applications have greatly impacted automotive sheet metal product design, die developments, die construction and tryout, and production stamping. The stamping CAE community has successfully resolved the traditional formability problems such as splits and wrinkles. The evolution of the stamping CAE technology and business demands opens even greater opportunities and challenges to stamping CAE community in the areas of (1) continuously improving simulation accuracy, drastically reducing simulation time-in-system, and improving operationalability (friendliness), (2) resolving those historically difficult-to-resolve problems such as dimensional quality problems (springback and twist) and surface quality problems (distortion and skid/impact lines), (3) resolving total manufacturability problems in line die operations including blanking, draw/redraw, trim/piercing, and flanging, and (4) overcoming new problems in forming new sheet materials with new forming techniques. In this article, the author first provides an overview of the stamping CAE technology adventures and achievements, and industrial applications in the past decade. Then the author presents a summary of increasing manufacturability needs from the formability to total quality and total manufacturability of sheet metal stampings. Finally, the paper outlines the new needs and trends for continuous improvements and innovations to meet increasing challenges in line die formability and quality requirements in automotive stamping.
Weakening of magnetohydrodynamic interchange instabilities by Alfven waves
Benilov, E. S.; Hassam, A. B.
2008-02-15
Alfven waves, made to propagate along an ambient magnetic field and polarized transverse to a gravitational field g, with wave amplitude stratified along g, are shown to reduce the growth rate of interchange instability by increasing the effective inertia by a factor of 1+(B{sub y}{sup '}/B{sub z}k{sub z}){sup 2}, where B{sub z} is the ambient magnetic field, k{sub z} is the wavenumber, and B{sub y}{sup '} is the wave amplitude shear. Appropriately placed Alfven wave power could thus be used to enhance the stability of interchange and ballooning modes in tokamaks and other interchange-limited magnetically confined plasmas.
Effects of unequal particle number densities on Alfven waves
NASA Technical Reports Server (NTRS)
Cairns, I. H.
1989-01-01
Analytic plasma theory and numerical solutions of the dispersion equation are used to show that the assumption that the linear properties of the waves are determined by a charge-neutral plasma in the absence of the nonthermal particles, while the nonthermal particles cause growth or additional damping superposed onto the background, is seriously flawed even for stable plasmas. Even when the nonthermal particles do not contribute significantly to the dispersion equation, unequal thermal electron and ion number densities (due to the presence of the nonthermal particles) may cause fundamental low wave number modifications to the Alfven modes, including the creation of a new resonance and severely modified dispersion. These results are found for both cold and warm plasmas. Previous work on Alfven waves should be reevaluated in view of these results.
Laboratory study of magnetic reconnection generated Alfven waves. Final report
Watts, Christopher
2002-02-08
This grant was funded through the Department of Energy, Office of Fusion Energy Junior Faculty Development Program. The grant funded the construction and start-up of the Articulated Large-area Plasma Helicon Array (alpha) experiment, and initial studies of Alfven wave propagation in helicon generated plasmas. The three year grant contract with Auburn University was terminated early (after two years) due to PI'S acceptance of a faculty position at New Mexico Tech. The project continues at New Mexico Tech under a different grant contract. The project met all of the second-year goals outlined in the proposal, and made progress toward meeting some of the third-year goals. The alpha facility was completed and multi-helicon operation was demonstrated. We have made initial measurements of Alfven waves in a helicon plasma source.
Global structures of Alfven-ballooning modes in magnetospheric plasmas
Vetoulis, G.; Chen, L.
1994-09-15
The authors show that a steep plasma pressure gradient can lead to radially localized Alfven modes, which are damped through coupling to field line resonances. These have been called drift Alfven ballooning modes (DABM) and are the prime candidates to explain Pc4-Pc5 geomagnetic pulsations observed during the recovery phase of geomagnetic storms. A strong dependence of the damping rate on the azimuthal wave number m is established, as well as on the equilibrium profile. A minimum azimuthal mode number can be found for the DABM to be radially trapped. The authors find that higher m DABMs are better localized, which is consistent with high-m observations. 7 refs., 3 figs.
Palau, G.L.; Tarpinian, J.E.
1987-01-01
A new application of computer-aided design and drafting (CADD) and computer-aided engineering (CAE) at the Three Mile Island Unit 2 (TMI-2) cleanup is improving the quality of radiation survey data taken in the plant. The use of CADD/CAE-generated survey maps has increased both the accuracy of survey data and the capability to perform analyses with these data. In addition, health physics technician manhours and radiation exposure can be reduced in situations where the CADD/CAE-generated drawings are used for survey mapping.
Enhanced damping of Alfven waves in the solar corona by a turbulent wave spectrum
NASA Technical Reports Server (NTRS)
Kleva, Robert G.; Drake, J. F.
1992-01-01
The effect of a background spectrum of Alfven waves on the rate of dissipation of a test shear Alfven wave is numerically calculated. The results demonstrate that as the classical resistivity eta and classical viscosity mu become small, the damping rate of the Alfven wave remains large and depends only on the amplitude for the scalar potential of the wave spectrum and the wavenumber of the Alfven wave. The damping rate is virtually independent of eta and mu. The wave spectrum need not be turbulent or stochastic to affect the damping rate. The dissipation rate is nonlinear enhanced by nonstochastic spectra as well as by stochastic spectra if two conditions are met. First, the perpendicular magnetic field associated with Alfven wave spectrum must exceed a certain collision-frequency threshold and second, for nonstochastic spectra only, the magnetic field must exceed a threshold proportional to the parallel wavenumber of the shear Alfven wave. These conditions can be easily satisfied in the solar corona.
Compressibility and cyclotron damping in the oblique Alfven wave
Harmon, J.K. )
1989-11-01
Compressibility, magnetic compressibility, and damping rate are calculated for the obliquely propagating Alfven shear wave in high- and low-beta Vlasov plasmas. There is an overall increase in compressibility as beta is reduced from {beta} = 1 to {beta}{much lt}1. For high obliquity {theta} and low frequency ({omega} {much lt} {Omega}{sub p}) the compressibility C follows a k{sup 2} wave number dependence; for high {theta} and low {beta} the approximation C(k) {approx} k{sub n}{sup 2} {identical to} (kV{sub A}/{Omega}{sub p}){sup 2} holds for wave numbers up to the proton cyclotron resonance, where {Omega}{sub p} is the proton cyclotron frequency and V{sub A} is the Alfven velocity. Strong proton cyclotron damping sets in at k{sub n} of the order of unity; the precise k{sub n} position of the damping cutoff increases with decreasing {beta} and increasing {theta}. Hence compressibility can exceed unity near the damping cutoff for high-{theta} waves in a low-{beta} plasma. The magnetic compressibility of the oblique Alfven wave also has a k{sup 2} dependence and can reach a maximum value of the order of 10% at high wave number. It is shown that Alfven compressibility could be the dominant contributor to the near-Sun solar wind density fluctuation spectrum for k>10{sup {minus}2} km{sup {minus}1} and hence might cause some of the flattening at high wave number seen in radio scintillation measurements. This would also be consistent with the notion that the observed density spectrum inner scale is a signature of cyclotron damping.
Alfven soliton and multisoliton dynamics perturbed by nonlinear Landau damping
Sanchez-Arriaga, G.
2010-08-15
The evolution of weakly dispersive nonlinear Alfven waves propagating either parallel or oblique to the ambient magnetic field is investigated through the derivative nonlinear Schroedinger equation (DNLS) perturbed by nonlinear Landau damping. The dynamics is analyzed with the aid of a numeric algorithm based on the inverse scattering transform (IST) and an adiabatic model that takes advantages of the perturbed DNLS invariants. Both techniques are applied to five types of DNLS soliton and multisoliton solutions: (i) the parallel Alfven soliton, (ii) the bright and dark one-parameter oblique, (iii) the breather two-parameter oblique, (iv) two parallel Alfven solitons, and (v) the combination of a dark and a bright oblique solitons. For the parallel solitons, the adiabatic model describes correctly the dynamics and it also recovers the well-known result given by the perturbed IST. Due to the radiation emission and the formation of dark solitons, the behavior of oblique solitons is more complicated and multisoliton solutions are required in the adiabatic model. The analysis shows that parallel solitons develop into the normal regime, whereas the oblique waves leads to the formation of dark solitons and breathers with a wavepacket form.
Reconstruction of a Broadband Spectrum of Alfvenic Fluctuations
NASA Technical Reports Server (NTRS)
Vinas, Adolfo F.; Fuentes, Pablo S. M.; Araneda, Jaime A.; Maneva, Yana G.
2014-01-01
Alfvenic fluctuations in the solar wind exhibit a high degree of velocities and magnetic field correlations consistent with Alfven waves propagating away and toward the Sun. Two remarkable properties of these fluctuations are the tendencies to have either positive or negative magnetic helicity (-1 less than or equal to sigma(sub m) less than or equal to +1) associated with either left- or right- topological handedness of the fluctuations and to have a constant magnetic field magnitude. This paper provides, for the first time, a theoretical framework for reconstructing both the magnetic and velocity field fluctuations with a divergence-free magnetic field, with any specified power spectral index and normalized magnetic- and cross-helicity spectrum field fluctuations for any plasma species. The spectrum is constructed in the Fourier domain by imposing two conditions-a divergence-free magnetic field and the preservation of the sense of magnetic helicity in both spaces-as well as using Parseval's theorem for the conservation of energy between configuration and Fourier spaces. Applications to the one-dimensional spatial Alfvenic propagation are presented. The theoretical construction is in agreement with typical time series and power spectra properties observed in the solar wind. The theoretical ideas presented in this spectral reconstruction provide a foundation for more realistic simulations of plasma waves, solar wind turbulence, and the propagation of energetic particles in such fluctuating fields.
Alfven Waves in the Solar Wind, Magnetosheath, and Outer Magnetosphere
NASA Technical Reports Server (NTRS)
Sibeck, D. G.
2007-01-01
Alfven waves Propagating outward from the Sun are ubiquitous in the solar wind and play a major role in the solar wind-magnetosphere interaction. The passage of the waves generally occurs in the form of a series of discrete steepened discontinuities, each of which results in an abrupt change in the interplanetary magnetic field direction. Some orientations of the magnetic field permit particles energized at the Earth's bow shock to gain access to the foreshock region immediately upstream from the Earth's bow shock. The thermal pressure associated with these particles can greatly perturb solar wind plasma and magnetic field parameters shortly prior to their interaction with the Earth's bow shock and magnetosphere. The corresponding dynamic pressure variations batter the magnetosphere, driving magnetopause motion and transient compressions of the magnetospheric magnetic field. Alfven waves transmit information concerning the dynamic pressure variations applied to the magnetosphere to the ionosphere, where they generate the traveling convection vortices (TCVs) seen in high-latitude ground magnetograms. Finally, the sense of Alfvenic perturbations transmitted into the magnetosheath reverses across local noon because magnetosheath magnetic field lines drape against the magnetopause. The corresponding change in velocity perturbations must apply a weak torque to the Earth's magnetosphere.
Transport of parallel momentum by drift-Alfven turbulence
McDevitt, C. J.; Diamond, P. H.
2009-01-15
An electromagnetic gyrokinetic formulation is utilized to calculate the turbulent radial flux of parallel momentum for a strongly magnetized plasma in the large aspect ratio limit. For low-{beta} plasmas, excluding regions of steep density gradients, the level of momentum transport induced by microturbulence is found to be well described within the electrostatic approximation. However, near regions of steep equilibrium profile gradients, strong electromagnetic contributions to the momentum flux are predicted. In particular, for sufficiently steep density gradient, the magnitude of transport induced by the off-diagonal residual stress component of the momentum flux induced by drift wave turbulence can be quenched. This quenching mechanism, which results from shielding of the parallel electric field by the inductive term, is distinct from ExB shear decorrelation, since it allows for the level of off-diagonal turbulent transport to be strongly reduced without extinguishing the underlying microturbulence. In contrast, the level of transport induced by a given Alfvenic branch of the drift-Alfven dispersion relationship typically increases as the density gradient steepens, allowing an alternate channel for momentum transport. A calculation of the momentum transport induced by Alfvenic turbulence in a homogeneous medium suggests that an imbalance in Elsasser populations is required in order to introduce a finite level of off-diagonal momentum transport for the case of the simplified geometry considered.
On field line resonances of hydromagnetic Alfven waves in dipole magnetic field
Chen, Liu; Cowley, S.C. )
1989-08-01
Using the dipole magnetic field model, the authors have developed the theory of field line resonances of hydromagnetic Alfven waves in general magnetic field geometries. In this model, the Alfven speed thus varies both perpendicular and parallel to the magnetic field. Specifically, it is found that field line resonances do persist in the dipole model. The corresponding singular solutions near the resonant field lines as well as the natural definition of standing shear Alfven eigenfunctions have also been systematically derived.
On field line resonances of hydromagnetic Alfven waves in dipole magnetic field
Chen, Liu; Cowley, S.C.
1989-07-01
Using the dipole magnetic field model, we have developed the theory of field line resonances of hydromagnetic Alfven waves in general magnetic field geometries. In this model, the Alfven speed thus varies both perpendicular and parallel to the magnetic field. Specifically, it is found that field line resonances do persist in the dipole model. The corresponding singular solutions near the resonant field lines as well as the natural definition of standing shear Alfven eigenfunctions have also been systematically derived. 11 refs.
Using eigenmodes to perform the inverse problem associated with resonant ultrasound spectroscopy
David Hurley; Farhad Farzbod
2012-11-01
In principle, resonant ultrasonic spectroscopy (RUS) can be used to characterize any parameter that influences the mechanical resonant response of a sample. Examples include the elastic constants, sample dimensions, and crystal orientation. Extracting the parameter of interest involves performing the inverse problem, which typically entails an iterative routine that compares calculated and measured eigenfrequencies. Here, we propose an alternative method based on laser-based resonant ultrasound spectroscopy (LRUS) that uses the eigenmodes. LRUS uses a pulsed laser to thermoelastically excite ultrasound and an interferometer to detect out-of-plane displacement associated with ultrasonic resonances. By raster scanning the probe along the sample surface, an image of the out-ofplane displacement pattern (i.e., eigenmode) is obtained. As an example of this method, we describe a technique to calculate the crystallographic orientation of a single-crystal high-purity copper sample. The crystallographic orientation is computed by comparing theoretical and experimental eigenmodes. The computed angle is shown to be in very good agreement with the angle obtained using electron backscatter diffraction. In addition, a comparison is made using eigenfrequencies and eigenmodes to calculate the crystallographic orientation. It is found for this particular application, the eigenmode method has superior sensitivity to crystal orientation.
Not Available
1982-01-01
A method used for siting a compressed air energy storage (CAES) system using geotechnical and environmental criteria is explained using the siting of a proposed 220 MW water-compensated CAES plant in Illinois as an example. Information is included on the identification and comparative ranking of 28 geotechnically and environmental sites in Illinois, the examination of fatal flaws, e.g., mitigation, intensive studies, costly studies, permit denials, at 7 sites; and the selection of 3 sites for further geological surveying. (LCL)
Performance evaluation of NASA/KSC CAD/CAE graphics local area network
NASA Technical Reports Server (NTRS)
Zobrist, George
1988-01-01
This study had as an objective the performance evaluation of the existing CAD/CAE graphics network at NASA/KSC. This evaluation will also aid in projecting planned expansions, such as the Space Station project on the existing CAD/CAE network. The objectives were achieved by collecting packet traffic on the various integrated sub-networks. This included items, such as total number of packets on the various subnetworks, source/destination of packets, percent utilization of network capacity, peak traffic rates, and packet size distribution. The NASA/KSC LAN was stressed to determine the useable bandwidth of the Ethernet network and an average design station workload was used to project the increased traffic on the existing network and the planned T1 link. This performance evaluation of the network will aid the NASA/KSC network managers in planning for the integration of future workload requirements into the existing network.
The impact of software and CAE tools on SEU in field programmable gate arrays
Katz, R.; Wang, J.; McCollum, J.; Cronquist, B.
1999-12-01
Field programmable gate array (FPGA) devices, heavily used in spacecraft electronics, have grown substantially in size over the past few years, causing designers to work at a higher conceptual level, with computer aided engineering (CAE) tools synthesizing and optimizing the logic from a description. It is shown that the use of commercial-off-the-shelf (COTS) CAE tools can produce unreliable circuit designs when the device is used in a radiation environment and a flip-flop is upset. At a lower level, software can be used to improve the SEU performance of a flip-flop, exploiting the configurable nature of FPGA technology and on-chip delay, parasitic resistive, and capacitive circuit elements.
FAST Modular Wind Turbine CAE Tool: Nonmatching Spatial and Temporal Meshes: Preprint
Sprague, M. A.; Jonkman, J. M.; Jonkman, B. J.
2014-01-01
In this paper we propose and examine numerical algorithms for coupling time-dependent multi-physics modules relevant to computer-aided engineering (CAE) of wind turbines. In particular, we examine algorithms for coupling modules where spatial grids are non- matching at interfaces and module solutions are time advanced with different time increments and different time integrators. Sharing of data between modules is accomplished with a predictor-corrector approach, which allows for either implicit or explicit time integration within each module. Algorithms are presented in a general framework, but are applied to simple problems that are representative of the systems found in a whole-turbine analysis. Numerical experiments are used to explore the stability, accuracy, and efficiency of the proposed algorithms. This work is motivated by an in-progress major revision of FAST, the National Renewable Energy Laboratory's (NREL's) premier aero-elastic CAE simulation tool. The algorithms described here will greatly increase the flexibility and efficiency of FAST.
Utilization of CAD/CAE for concurrent design of structural aircraft components
NASA Technical Reports Server (NTRS)
Kahn, William C.
1993-01-01
The feasibility of installing the Stratospheric Observatory for Infrared Astronomy telescope (named SOFIA) into an aircraft for NASA astronomy studies is investigated using CAD/CAE equipment to either design or supply data for every facet of design engineering. The aircraft selected for the platform was a Boeing 747, chosen on the basis of its ability to meet the flight profiles required for the given mission and payload. CAD models of the fuselage of two of the aircraft models studied (747-200 and 747 SP) were developed, and models for the component parts of the telescope and subsystems were developed by the various concurrent engineering groups of the SOFIA program, to determine the requirements for the cavity opening and for design configuration. It is noted that, by developing a plan to use CAD/CAE for concurrent engineering at the beginning of the study, it was possible to produce results in about two-thirds of the time required using traditional methods.
Tests of US rock salt for long-term stability of CAES reservoirs
Gehle, R.M.; Thoms, R.L.
1986-01-01
This is a report on laboratory tests to assess the effects of compressed air energy storage (CAES) on rock salt within the US. The project included a conventional laboratory test phase, with triaxial test machines, and a bench-scale test phase performed in salt mines in southern Louisiana. Limited numerical modeling also was performed to serve as a guide in selecting test layouts and for interpreting test data.
Scaling of Kinetic Instability Induced Fast Ion Losses in NSTX
E.D. Fredrickson; D. Darrow; S. Medley; J. Menard; H. Park; L. Roquemore; D. Stutman; K. Tritz; S. Kubota; K.C. Lee
2005-06-24
During neutral beam injection (NBI) in the National Spherical Torus Experiment (NSTX), a wide variety of fast ion driven instabilities is excited by the large ratio of fast ion velocity to Alfven velocity, together with the relatively high fast ion beta, beta(sub)f. The fast ion instabilities have frequencies ranging from a few kilohertz to the ion cyclotron frequency. The modes can be divided roughly into three categories, starting with Energetic Particle Modes (EPM) in the lowest frequency range (0 to 120 kHz), the Toroidal Alfven Eigenmodes (TAE) in the intermediate frequency range (50 to 200 kHz) and the Compressional and Global Alfven Eigenmodes (CAE and GAE, respectively) from approximately equal to 300 kHz up to the ion cyclotron frequency. Each of these categories of modes exhibits a wide range of behavior, including quasi-continuous oscillation, bursting, chirping and, except for the lower frequency range, turbulence.
NASA Astrophysics Data System (ADS)
Cossu, Guido; Hashimoto, Shoji
2016-06-01
We investigate the properties of the background gauge field configurations that act as disorder for the Anderson localization mechanism in the Dirac spectrum of QCD at high temperatures. We compute the eigenmodes of the Möbius domain-wall fermion operator on configurations generated for the SU(3) gauge theory with two flavors of fermions, in the temperature range [0.9, 1.9]T c . We identify the source of localization of the eigenmodes with gauge configurations that are self-dual and support negative fluctuations of the Polyakov loop P L , in the high temperature sea of P L ˜ 1. The dependence of these observations on the boundary conditions of the valence operator is studied. We also investigate the spatial overlap of the left-handed and right-handed projected eigenmodes in correlation with the localization and the corresponding eigenvalue. We discuss an interpretation of the results in terms of monopole-instanton structures.
NASA Technical Reports Server (NTRS)
Arnold, Steven M.; Bednarcyk, Brett A.; Hussain, Aquila; Katiyar, Vivek
2010-01-01
A unified framework is presented that enables coupled multiscale analysis of composite structures and associated graphical pre- and postprocessing within the Abaqus/CAE environment. The recently developed, free, Finite Element Analysis--Micromechanics Analysis Code (FEAMAC) software couples NASA's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) with Abaqus/Standard and Abaqus/Explicit to perform micromechanics based FEA such that the nonlinear composite material response at each integration point is modeled at each increment by MAC/GMC. The Graphical User Interfaces (FEAMAC-Pre and FEAMAC-Post), developed through collaboration between SIMULIA Erie and the NASA Glenn Research Center, enable users to employ a new FEAMAC module within Abaqus/CAE that provides access to the composite microscale. FEA IAC-Pre is used to define and store constituent material properties, set-up and store composite repeating unit cells, and assign composite materials as sections with all data being stored within the CAE database. Likewise FEAMAC-Post enables multiscale field quantity visualization (contour plots, X-Y plots), with point and click access to the microscale i.e., fiber and matrix fields).
MF-CAE: A Novel Lab on a Chip Simulation Tool
NASA Astrophysics Data System (ADS)
Zeng, Yi; Mastrangelo, C. H.; Sun, Li
The design of microfluidic systems with a large number of dynamic 011-chip components poses a challenge because today it is difficult to simulate time dependent transport of solvent and solutes through complex chips inclusive of dispersion and convection with low time-cost. Present approaches based on 3D C'FD tools are inadequate for system-level simulation. To address these needs, we propose a novel general simulation method for the approximate solution of linear and nonlinear, static and time-dependent solute and solvent transport in large chips with no need for analytical solution. Some design, modeling, and simulation features of a computer aided engineering tool for microfluidic systems called MF-CAE (Microfluidic CAE) are presented. The features include: an extensible modeling framework for computationally efficient lumped models; a flexible SPICE-like netlist language for microfluidic system design; a user friendly graphical user interface that allows users to quickly configure complex system; and a compact toolkit integrating design, simulation and data displaying. In this paper MF-CAE's architecture, reduced order modeling technique and design methodology are described. A comparison of behavior of microfluidic dilution networks indicates that the simulation results are in good agreement with the model simulations.
Surface Alfven Wave Contribution to Coronal Heating in a Wave-Driven Solar Wind Model
NASA Astrophysics Data System (ADS)
Evans, Rebekah M.; Opher, M.; Oran, R.; Sokolov, I. V.
2010-05-01
We present results from the development of a solar wind model driven by Alfven waves with realistic damping mechanisms. We investigate the contribution of surface Alfven wave damping to the heating of the corona and acceleration of the solar wind. These waves are present and damp in regions of strong gradients in density or magnetic field (e.g., the border between open and closed magnetic fields). Recently Oran et al. (2009) implemented a first principle solar wind model driven by a spectrum of Alfven waves into the Space Weather Modeling Framework. The wave transport equation, including wave advection and dissipation, is coupled to the MHD equations for the wind. The waves contribute to the momentum and energy of the wind through the action of wave pressure. Here we extend this model to include surface Alfven wave damping as a dissipation mechanism, considering waves with frequencies lower than those damped in the chromosphere and on the order of those dominating the heliosphere (0.0001 to 100 Hz.) We demonstrate the influence of the damping by quantifying the differences between a solution that includes surface Alfven wave damping and one driven solely by Alfven wave pressure. We relate to possible observational signatures of heat transfer by surface Alfven wave damping. This work is the first to study surface Alfven waves self-consistently as an energy driven for the solar wind in a 4D (three in space and one in frequency) environment. This work is supported by the NSF CAREER Grant.
Arc-Polarized, Nonlinear Alfven Waves and Rotational Discontinuities: Directions of Propogation?
NASA Technical Reports Server (NTRS)
Tsurutani, B. T.; Ho, C. M.; Sakurai, R.; Arballo, J. K.; Riley, P.; Balogh, A.
1996-01-01
Large amplitude, noncompressive Alfven waves and rotational discontinuities are shown to be arc-polarized. The slowly rotating Alfven wave portion plus the fast rotating discontinuity comprise 360(deg) in phase rotation. The magnetic field vector perturbation lies in a plane. There are two (or more) possible interpretations to the observations.
Time dependent simulation of cosmic-ray shocks including Alfven transport
NASA Technical Reports Server (NTRS)
Jones, T. W.
1993-01-01
Time evolution of plane, cosmic-ray modified shocks was simulated numerically for the case with parallel magnetic fields. Computations were done in a 'three-fluid' dynamical model incorporating cosmic-ray and Alfven wave energy transport equations. Nonlinear feedback from the cosmic-rays and Alfven waves is included in the equation of motion for the underlying plasma, as is the finite propagation speed and energy dissipation of the Alfven waves. Exploratory results confirm earlier, steady state analyses that found these Alfven transport effects to be potentially important when the upstream Alfven speed and gas sound speeds are comparable. As noted earlier Alfven transport effects tend to reduce the transfer of energy through a shock from gas to energetic particles. These studies show as well that the time scale for modification of the shock is altered in nonlinear ways. It is clear, however, that the consequences of Alfven transport are strongly model dependent and that both advection of cosmic-rays by the waves and dissipation of wave energy in the plasma will be important to model correctly when quantitative results are needed. Comparison is made between simulations based on a constant diffusion coefficient and more realistic diffusion models allowing the diffusion coefficient to vary in response to changes in Alfven wave intensity. No really substantive differences were found between them.
NASA Technical Reports Server (NTRS)
Fetterman, Timothy L.; Noor, Ahmed K.
1987-01-01
Computational procedures are presented for evaluating the sensitivity derivatives of the vibration frequencies and eigenmodes of framed structures. Both a displacement and a mixed formulation are used. The two key elements of the computational procedure are: (a) Use of dynamic reduction techniques to substantially reduce the number of degrees of freedom; and (b) Application of iterative techniques to improve the accuracy of the derivatives of the eigenmodes. The two reduction techniques considered are the static condensation and a generalized dynamic reduction technique. Error norms are introduced to assess the accuracy of the eigenvalue and eigenvector derivatives obtained by the reduction techniques. The effectiveness of the methods presented is demonstrated by three numerical examples.
Drift and geodesic effects on the ion sound eigenmode in tokamak plasmas
NASA Astrophysics Data System (ADS)
Elfimov, A. G.; Smolyakov, A. I.; Melnikov, A. V.; Galvão, R. M. O.
2016-05-01
A kinetic treatment of geodesic acoustic modes (GAMs), taking into account ion parallel dynamics, drift and the second poloidal harmonic effects is presented. It is shown that first and second harmonics of the ion sound modes, which have respectively positive and negative radial dispersion, can be coupled due to the geodesic and drift effects. This coupling results in the drift geodesic ion sound eigenmode with a frequency below the standard GAM continuum frequency. Such eigenmode may be able to explain the split modes observed in some experiments.
Multiplicity of low-shear toroidal Alfvén eigenmodes
NASA Astrophysics Data System (ADS)
Candy, J.; Breizman, B. N.; Van Dam, J. W.; Ozeki, T.
1996-02-01
An enlarged spectrum of ideal toroidal Alfvén eigenmodes is demonstrated to exist within a toroidicity-induced Alfvén gap when the inverse aspect ratio is comparable to or larger than the value of the magnetic shear. This limit is appropriate for the low-shear region in most tokamaks, especially those with low aspect ratio. The new modes may be destabilized by fusion-product alpha particles more easily than the standard toroidal Alfvén eigenmodes.
Accuracy of an approximate static structural analysis technique based on stiffness matrix eigenmodes
NASA Technical Reports Server (NTRS)
Sobieszczanski-Sobieski, J.; Hajela, P.
1979-01-01
Use of the stiffness matrix eigenmodes, instead of the vibration eigenmodes, as generalized coordinates is proposed for condensation of static load deflection equations in finite element stiffness method. The modes are selected by strain energy criteria and the resulting fast, approximate analysis technique is evaluated by applications to idealized built-up wings and a fuselage segment. The best results obtained are a two-order of magnitude reduction of the number of degrees of freedom in a high aspect ratio wing associated with less than one percent error in prediction of the largest displacement.
NASA Technical Reports Server (NTRS)
Black, Carrie; Germaschewski, Kai; Bhattacharjee, Amitava; Ng, C. S.
2013-01-01
It has been demonstrated that in the presence of weak collisions, described by the Lenard-Bernstein collision operator, the Landau-damped solutions become true eigenmodes of the system and constitute a complete set. We present numerical results from an Eulerian Vlasov code that incorporates the Lenard-Bernstein collision operator. The effect of the collisions on the numerical recursion phenomenon seen in Vlasov codes is discussed. The code is benchmarked against exact linear eigenmode solutions in the presence of weak collisions, and a spectrum of Landau-damped solutions is determined within the limits of numerical resolution. Tests of the orthogonality and the completeness relation are presented.
Observations of High Frequency Harmonics of the Ionospheric Alfven Resonator
NASA Astrophysics Data System (ADS)
Mann, Ian; Usanova, Maria; Bortnik, Jacob; Milling, David; Kale, Andy; Shao, Leo; Miles, David; Rae, I. Jonathan
We present observations of high frequency harmonics of the ionospheric Alfven Resonator (IAR). These are seen in the form of spectral resonance structures (SRS) recorded by a ground-based search coil magnetometer sampling at 100 samples/s at the Ministik Lake station at L=4.2 within the expanded CARISMA magnetometer array. Previous observational studies have indicated that such SRS are typically confined to frequencies <~5 Hz with only several SRS harmonics being observed. We report the first observations of clear and discrete SRS, which we believe are harmonics of the IAR, and which extend to around 20 Hz in at least 10-12 clear SRS harmonics. We additionally demonstrate the utility of the Bortnik et al. (2007) auto-detection algorithm, designed for Pc1 wavepackets, for characterising the properties of the IAR. Our results also indicate that the cavity supporting SRS in the IAR at this time must be structured to support and trap much higher frequency IAR harmonics than previously assumed. This impacts the potential importance of the IAR for magnetosphere-ionosphere coupling, especially in relation to the impacts of incident Alfven waves on the ionosphere including Alfvenic aurora. Our observations also highlight the potential value of IAR observations for diagnosing the structure of the topside ionosphere, not least using the observed structure of the SRS. These are the first mid-latitude observations demonstrating that the IAR can extend to frequencies beyond those of the lowest few harmonics of the Schumann resonances - significantly suggesting the possibility that the Schumann resonance modes and the IAR may be coupled. The in-situ structure of the IAR is also examined by combining satellite data with conjugate measurements from the ground, and the impacts of the IAR for magnetosphere-ionosphere-thermosphere coupling examined.
Nonlinear absorption of Alfven wave in dissipative plasma
Taiurskii, A. A. Gavrikov, M. B.
2015-10-28
We propose a method for studying absorption of Alfven wave propagation in a homogeneous non-isothermal plasma along a constant magnetic field, and relaxation of electron and ion temperatures in the A-wave. The absorption of a A-wave by the plasma arises due to dissipative effects - magnetic and hydrodynamic viscosities of electrons and ions and their elastic interaction. The method is based on the exact solution of two-fluid electromagnetic hydrodynamics of the plasma, which for A-wave, as shown in the work, are reduced to a nonlinear system of ordinary differential equations.
Theoretical Studies of Drift-Alfven and Energetic Particle Physics
CHEN, L.
2014-05-14
The research program supported by this DOE grant has been rather successful and productive in terms of both scientific investigations as well as human resources development; as demonstrated by the large number (60) of journal articles, 6 doctoral degrees, and 3 postdocs. This PI is particularly grateful to the generous support and flexible management of the DOE–SC-OFES Program. He has received three award/prize (APS Excellence in Plasma Physics Research Award, 2004; EPS Alfven Prize, 2008; APS Maxwell Prize, 2012) as the results of research accomplishments supported by this grant.
On the stability of shear-Alfven vortices
Jovanovic, D.; Horton, W.
1993-08-01
Linear stability of shear-Alfven vortices is studied analytically using the Lyapunov method. Instability is demonstrated for vortices belonging to the drift mode, which is a generalization of the standard Hasegawa-Mima vortex to the case of large parallel phase velocities. In the case of the convective-cell mode, short perpendicular-wavelength perturbations are stable for a broad class of vortices. Eventually, instability of convective-cell vortices may occur on the perpendicular scale comparable with the vortex size, but it is followed by a simultaneous excitation of coherent structures with better localization than the original vortex.
Parallel inhomogeneity and the Alfven resonance. 1: Open field lines
NASA Technical Reports Server (NTRS)
Hansen, P. J.; Harrold, B. G.
1994-01-01
In light of a recent demonstration of the general nonexistence of a singularity at the Alfven resonance in cold, ideal, linearized magnetohydrodynamics, we examine the effect of a small density gradient parallel to uniform, open ambient magnetic field lines. To lowest order, energy deposition is quantitatively unaffected but occurs continuously over a thickened layer. This effect is illustrated in a numerical analysis of a plasma sheet boundary layer model with perfectly absorbing boundary conditions. Consequences of the results are discussed, both for the open field line approximation and for the ensuing closed field line analysis.
The Jupiter-Io connection - an Alfven engine in space
NASA Astrophysics Data System (ADS)
Belcher, J. W.
1987-10-01
Much has been learned about the electromagnetic interaction between Jupiter and its satellite Io from in situ observations. Io, in its motion through the Io plasma torus at Jupiter, continuously generates an Alfven wing that carries two billion kilowatts of power into the jovian ionosphere. Concurrently, Io is acted upon by a J x B force tending to propel it out of the jovian system. The energy source for these processes is the rotation of Jupiter. This unusual planet-satellite coupling serves as an archetype for the interaction of a large moving conductor with a magnetized plasma, a problem of general space and astrophysical interest.
The Jupiter-Io connection - An Alfven engine in space
NASA Technical Reports Server (NTRS)
Belcher, John W.
1987-01-01
Much has been learned about the electromagnetic interaction between Jupiter and its satellite Io from in situ observations. Io, in its motion through the Io plasma torus at Jupiter, continuously generates an Alfven wing that carries two billion kilowatts of power into the jovian ionosphere. Concurrently, Io is acted upon by a J x B force tending to propel it out of the jovian system. The energy source for these processes is the rotation of Jupiter. This unusual planet-satellite coupling serves as an archetype for the interaction of a large moving conductor with a magnetized plasma, a problem of general space and astrophysical interest.
Damping of long-wavelength kinetic alfven fluctuations: linear theory
Gary, S Peter; Borovsky, Joseph E
2008-01-01
The full electromagnetic linear dispersion equation for kinetic Alfven fluctuations in a homogeneous, isotropic, Maxwellian electron-proton plasma is solved numerically in the long wavelength limit. The solutions are summarized by an analytic expression for the damping rate of such modes at propagation sufficiently oblique to the background magnetic field B{sub o} which scales as k{sub {perpendicular}}{sup 2} k{sub {parallel}} where the subscripts denote directions relative to B{sub o}. This damping progressively (although not monotonically) increases with increasing electron {beta}, corresponding to four distinct damping regimes: nonresonant, electron Landau, proton Landau, and proton transit-time damping.
Heating of ions by low-frequency Alfven waves in partially ionized plasmas
Dong Chuanfei; Paty, Carol S.
2011-03-15
In the solar atmosphere, the chromospheric and coronal plasmas are much hotter than the visible photosphere. The heating of the solar atmosphere, including the partially ionized chromosphere and corona, remains largely unknown. In this letter, we demonstrate that the ions can be substantially heated by Alfven waves with very low frequencies in partially ionized low-beta plasmas. This differs from other Alfven wave related heating mechanisms such as ion-neutral collisional damping of Alfven waves and heating described by previous work on resonant Alfven wave heating. We find that the nonresonant Alfven wave heating is less efficient in partially ionized plasmas than when there are no ion-neutral collisions, and the heating efficiency depends on the ratio of the ion-neutral collision frequency to the ion gyrofrequency.
Nonlinear astrophysical Alfven waves - Onset and outcome of the modulational instability
NASA Technical Reports Server (NTRS)
Spangler, S. R.
1985-01-01
The nonlinear development of Alfven waves is numerically studied, with applications to Alfven waves in astrophysical plasmas. It is found that amplitude-modulated Alfven wave packets undergo a collapse instability in which the wave packets become more intense and of smaller spatial extent. The wave packet steepening is eventually halted in a process most aptly described as soliton formation. A simple analytic model based on the method of characteristics can account for many of the results of the numerical calculations. The instability probably cannot prevent particle pitch angle isotropization due to self-generated Alfven waves. Nonlinear effects of the collapse may modify the process by which energetic electrons are reaccelerated by plasma turbulence. The model calculations can semiquantitatively account for properties of shock-associated Alfven waves in the solar system.
PROPAGATING COUPLED ALFVEN AND KINK OSCILLATIONS IN AN ARBITRARY INHOMOGENEOUS CORONA
Pascoe, D. J.; Wright, A. N.; De Moortel, I.
2011-04-10
Observations have revealed ubiquitous transverse velocity perturbation waves propagating in the solar corona. We perform three-dimensional numerical simulations of footpoint-driven transverse waves propagating in a low {beta} plasma. We consider the cases of distorted cylindrical flux tubes and a randomly generated inhomogeneous medium. When density structuring is present, mode coupling in inhomogeneous regions leads to the coupling of the kink mode to the Alfven mode. The decay of the propagating kink wave is observed as energy is transferred to the local Alfven mode. In all cases considered, modest changes in density were capable of efficiently converting energy from the driving footpoint motion to localized Alfven modes. We have demonstrated that mode coupling efficiently couples propagating kink perturbations to Alfven modes in an arbitrary inhomogeneous medium. This has the consequence that transverse footpoint motions at the base of the corona will deposit energy to Alfven modes in the corona.
ACCELERATION OF THE SOLAR WIND BY ALFVEN WAVE PACKETS
Galinsky, V. L.; Shevchenko, V. I.
2013-01-20
A scale separation kinetic model of the solar wind acceleration is presented. The model assumes an isotropic Maxwellian distribution of protons and a constant influx of outward propagating Alfven waves with a single exponent Kolmogorov-type spectrum at the base of a coronal acceleration region ({approx}2 R {sub Sun }). Our results indicate that nonlinear cyclotron resonant interaction taking energy from Alfven waves and depositing it into mostly perpendicular heating of protons in initially weakly expanding plasma in a spherically non-uniform magnetic field is able to produce the typical fast solar wind velocities for the typical plasma and wave conditions after expansion to about 5-10 solar radii R {sub Sun }. The acceleration model takes into account the gravity force and the ambipolar electric field, as well as the mirror force, which plays the most important role in driving the solar wind acceleration. Contrary to the recent claims of Isenberg, the cold plasma dispersion only slightly slows down the acceleration and actually helps in obtaining the more realistic fast solar wind speeds.
Role of Alfven instabilities in energetic ion transport
Bernabei, S.; Gorelenkov, N. N.; Budny, R.; Fredrickson, E. D.; Hosea, J. C.; Majeski, R.; Phillips, C. K.; Wilson, J. R.
1999-09-20
Experiments with plasma heating by waves at the ion cyclotron resonance of a minority species have shown that the heating efficiency degrades above a certain power threshold. It is found that this threshold is due to the destabilization of shear Alfven waves, which causes loss of fast ions. There are two distinct regimes characterized by low q{sub a} and high q{sub a}. In the first case, the fast ion distribution created by ICRF, lies entirely inside r{sub q=1}, away from the location of global TAE. This situation leads to the formation of a very strong fast ion population which stabilizes the sawteeth, but also excites Energetic Particle Modes (EPM), which transport fast ions outside r{sub q=1} causing the giant crash. At higher q{sub a}, the widening of the Alfven gap due to the steeper q profile, brings the global TAE ''in contact'' with the fast ion distribution. This results in an immediate and continuous depletion of fast ions from the core, which prevents the formation of the monster sawtooth and the excitation of EPM. (c) 1999 American Institute of Physics.
Emission of Alfven Waves by Planets in Close Orbits
NASA Astrophysics Data System (ADS)
MacGregor, Keith B.; Pinsonneault, M. H.
2011-01-01
We examine the electrodynamics of a conducting planet orbiting within a magnetized wind that emanates from its parent star. When the orbital motion differs from corotation with the star, an electric field exists in the rest frame of the planet, inducing a charge separation in its ionosphere. Because the planet is immersed in a plasma, this charge can flow away from it along the stellar magnetic field lines it successively contacts in its orbit. For sufficiently rapid orbital motion, a current system can be formed that is closed by Alfvenic disturbances that propagate along field lines away from the planet. Using a simple model for the wind from a Sun-like star, we survey the conditions under which Alfven wave emission can occur, and estimate the power radiated in the form of linear waves for a range of stellar, planetary, and wind properties. For a Jupiter-like planet in a close (a < 0.10 AU) orbit about a solar-type star, the emitted wave power can be as large as 1027 erg/s. While only a small influence on the planet's orbit, a wave power of this magnitude may have consequences for wind dynamics and localized heating of the stellar atmosphere. NCAR is sponsored by the NSF.
Plasma transport induced by kinetic Alfven wave turbulence
Izutsu, T.; Hasegawa, H.; Fujimoto, M.; Nakamura, T. K. M.
2012-10-15
At the Earth's magnetopause that separates the hot-tenuous magnetospheric plasma from the cold dense solar wind plasma, often seen is a boundary layer where plasmas of both origins coexist. Plasma diffusions of various forms have been considered as the cause of this plasma mixing. Here, we investigate the plasma transport induced by wave-particle interaction in kinetic Alfven wave (KAW) turbulence, which is one of the candidate processes. We clarify that the physical origin of the KAW-induced cross-field diffusion is the drift motions of those particles that are in Cerenkov resonance with the wave: E Multiplication-Sign B-like drift that emerges in the presence of non-zero parallel electric field component and grad-B drift due to compressional magnetic fluctuations. We find that KAW turbulence, which has a spectral breakpoint at which an MHD inertial range transits to a dissipation range, causes selective transport for particles whose parallel velocities are specified by the local Alfven velocity and the parallel phase velocity at the spectral breakpoint. This finding leads us to propose a new data analysis method for identifying whether or not a mixed plasma in the boundary layer is a consequence of KAW-induced transport across the magnetopause. The method refers to the velocity space distribution function data obtained by a spacecraft that performs in situ observations and, in principle, is applicable to currently available dataset such as that provided by the NASA's THEMIS mission.
Gravitational damping of Alfven waves in stellar atmospheres and winds
NASA Technical Reports Server (NTRS)
Khabibrakhmanov, I. K.; Mullan, D. J.
1994-01-01
We consider how gravity affects the propagation of Alfven waves in a stellar atmosphere. We show that when the ion gyrofrequency exceeds the collision rate, the waves are absorbed at a rate proportional to the gravitational acceleration g. Estimates show that this mechanism can readily account for the observed energy losses in the solar chromosphere. The mechanism predicts that the pressure at the top of the chromosphere P(sub Tc) should scale with g as P(sub Tc) proportional to g(exp delta), where delta approximately equals 2/3; this is close to empirical results which suggest delta approximately equals 0.6. Gravitational damping leads to deposition of energy at a rate proportional to the mass of the particles. Hence, heavier ion are heated more effectively than protons. This is consistent with the observed proportionality between ion temperature and mass in the solar wind. Gravitational damping causes the local g to be effectively decreased by an amount proportional to the wave energy. This feature affects the acceleration of the solar wind. Gravitational damping may also lead to self-regulation of the damping of Alfven waves in stellar winds: this is relevant in the context of slow massive winds in cool giants.
Experiment to Study Alfven Wave Propagation in Plasma Loops
NASA Astrophysics Data System (ADS)
Kendall, Mark; Bellan, Paul
2010-11-01
Arched plasma-filled twisted magnetic flux tubes are generated in the laboratory using pulsed power techniques (J.F. Hansen, S.K.P. Tripathi, P.M. Bellan, 2004). Their structure and time evolution exhibit similarities with both solar coronal loops and spheromaks. We are now developing a method to excite propagating torsional Alfven wave modes in such plasma loops by superposing a ˜10kA, ˜100ns current pulse upon the ˜50kA, 10μs main discharge current that flows along the ˜20cm long, 2cm diameter arched flux tube. To achieve this high power 100ns pulse, a magnetic pulse compression technique based on saturable reactors is employed. A low power prototype has been successfully tested, and design and construction of a full-power device is nearing completion. The full-power device will compress an initial 2μs pulse by a factor of nearly 20; the final stage utilizes a water-filled transmission line with ultra-low inductance to attain the final timescale. This new pulse device will subsequently be used to investigate interactions between Alfven waves and the larger-scale loop evolution; one goal will be to directly image the wave using high-speed photography. Attention will be paid to wave propagation including dispersion and reflection, as well as dissipation mechanisms and possible energetic particle generation.
Motion of ions influenced by enhanced Alfven waves
Wu, C.S.; Yoon, P.H.; Chao, J.K.
1997-03-01
In this paper we discuss the dynamics of an ion interacting with large-amplitude Alfven waves. The objective of the present analysis is to attain an in-depth understanding of the ion-pickup process which has been extensively studied in the literature by means of both quasilinear theory and numerical simulations. In general, results from self-consistent simulations provide a more complete picture of the ion pickup process, but details of the pickup process are not easily comprehended on the basis of these results. For this reason, the present study is carried out in which a test particle approach is used. It is found that for moderately large-amplitude Alfven waves, an approximate analytical solution for the ion equation of motion can be obtained. This solution clarifies a number of basic issues such as (1) whether the cyclotron resonance is a necessary condition for the pickup to occur, (2) what is the role of initial ion phase space position on subsequent pitch angle scattering, and (3) how the wave amplitude affects the maximum velocity that an ion can gain along the direction of the ambient magnetic field during the pickup process. {copyright} {ital 1997 American Institute of Physics.}
Coupling of axial plasma jets to compressional Alfven waves
NASA Astrophysics Data System (ADS)
Vincena, Stephen; Gekelman, Walter
2009-11-01
The coupling of mass, energy, and momentum from a localized, dense, and rapidly expanding plasma into a large-scale magnetized background plasma is central to understanding many physical processes; these include galactic jets, coronal mass ejections, tokamak pellet fueling, high-altitude nuclear detonations, chemical releases in the ionosphere, and supernovae. The large-scale magnetized plasmas are capable of supporting Alfv'en waves, which mediate the flow of currents and associated changes of magnetic topology on the largest size scales of the external system. We present initial results from a laboratory experiment wherein a fast-moving, laser-produced plasma (LPP) is allowed to propagate along the magnetic field lines of a pre-existing plasma column (17m long by 60 cm diameter). The LPP is generated using a 1J, 8ns Nd:YAG laser fired at a graphite target. The laser is pulsed along with the background plasma at 1Hz. This work focuses on the coupling of the LPP to compressional Alfv'en waves in the background plasma. The experiments are conducted at UCLA's Basic Plasma Science Facility in the Large Plasma Device.
Effects of pressure gradient on global Alfvén eigenmodes in reversed field pinch
Cai, Huishan; Fu, Guoyong; Lin, Liang; Ding, Weixing; Brower, D. L.; Liu, D. Y.; Hu, Y. J.
2014-02-15
The effects of pressure gradient on the existence of global Alfvén eigenmodes (GAE) in Reversed Field Pinch are studied by numerical calculation. It is found that GAEs near the plasma core can exist when pressure gradient is sufficiently large. The calculated mode frequency and structure are consistent with the experimental results in the Madison Symmetric Torus.
Kiracofe, Daniel; Raman, Arvind
2010-02-15
The effect of hydrodynamic loading on the eigenmode shapes, modal stiffnesses, and optical lever sensitivities of atomic force microscope (AFM) microcantilevers is investigated by measuring the vibrations of such microcantilevers in air and water using a scanning laser Doppler vibrometer. It is found that for rectangular tipless microcantilevers, the measured fundamental and higher eigenmodes and their equivalent stiffnesses are nearly identical in air and in water. However, for microcantilevers with a tip mass or for picket shaped cantilevers, there is a marked difference in the second (and higher) eigenmode shapes between air and water that leads to a large decrease in their modal stiffness in water as compared to air as well as a decrease in their optical lever sensitivity. These results are explained in terms of hydrodynamic interactions of microcantilevers with nonuniform mass distribution. The results clearly demonstrate that tip mass and hydrodynamic loading must be taken into account in stiffness calibration and optical lever sensitivity calibration while using higher-order eigenmodes in dynamic AFM.
Ions lost on their first orbit can impact Alfvén eigenmode stability
Heidbrink, W. W.; Fu, Guo-Yong; Van Zeeland, M. A.
2015-08-15
Some neutral-beam ions are deflected onto loss orbits by Alfvén eigenmodes on their first bounce orbit. The resonance condition for these ions differs from the usual resonance condition for a confined fast ion. Estimates indicate that particles on single-pass loss orbits transfer enough energy to the wave to alter mode stability.
Maruta, Kazuki; Iwakuni, Tatsuhiko; Ohta, Atsushi; Arai, Takuto; Shirato, Yushi; Kurosaki, Satoshi; Iizuka, Masataka
2016-01-01
Drastic improvements in transmission rate and system capacity are required towards 5th generation mobile communications (5G). One promising approach, utilizing the millimeter wave band for its rich spectrum resources, suffers area coverage shortfalls due to its large propagation loss. Fortunately, massive multiple-input multiple-output (MIMO) can offset this shortfall as well as offer high order spatial multiplexing gain. Multiuser MIMO is also effective in further enhancing system capacity by multiplexing spatially de-correlated users. However, the transmission performance of multiuser MIMO is strongly degraded by channel time variation, which causes inter-user interference since null steering must be performed at the transmitter. This paper first addresses the effectiveness of multiuser massive MIMO transmission that exploits the first eigenmode for each user. In Line-of-Sight (LoS) dominant channel environments, the first eigenmode is chiefly formed by the LoS component, which is highly correlated with user movement. Therefore, the first eigenmode provided by a large antenna array can improve the robustness against the channel time variation. In addition, we propose a simplified beamforming scheme based on high efficient channel state information (CSI) estimation that extracts the LoS component. We also show that this approximate beamforming can achieve throughput performance comparable to that of the rigorous first eigenmode transmission. Our proposed multiuser massive MIMO scheme can open the door for practical millimeter wave communication with enhanced system capacity. PMID:27399715
Maruta, Kazuki; Iwakuni, Tatsuhiko; Ohta, Atsushi; Arai, Takuto; Shirato, Yushi; Kurosaki, Satoshi; Iizuka, Masataka
2016-01-01
Drastic improvements in transmission rate and system capacity are required towards 5th generation mobile communications (5G). One promising approach, utilizing the millimeter wave band for its rich spectrum resources, suffers area coverage shortfalls due to its large propagation loss. Fortunately, massive multiple-input multiple-output (MIMO) can offset this shortfall as well as offer high order spatial multiplexing gain. Multiuser MIMO is also effective in further enhancing system capacity by multiplexing spatially de-correlated users. However, the transmission performance of multiuser MIMO is strongly degraded by channel time variation, which causes inter-user interference since null steering must be performed at the transmitter. This paper first addresses the effectiveness of multiuser massive MIMO transmission that exploits the first eigenmode for each user. In Line-of-Sight (LoS) dominant channel environments, the first eigenmode is chiefly formed by the LoS component, which is highly correlated with user movement. Therefore, the first eigenmode provided by a large antenna array can improve the robustness against the channel time variation. In addition, we propose a simplified beamforming scheme based on high efficient channel state information (CSI) estimation that extracts the LoS component. We also show that this approximate beamforming can achieve throughput performance comparable to that of the rigorous first eigenmode transmission. Our proposed multiuser massive MIMO scheme can open the door for practical millimeter wave communication with enhanced system capacity. PMID:27399715
Spiral eigenmodes triggered by grooves in the phase space of disc galaxies
NASA Astrophysics Data System (ADS)
De Rijcke, S.; Voulis, I.
2016-02-01
We use linear perturbation theory to investigate how a groove in the phase space of a disc galaxy changes the stellar disc's stability properties. Such a groove is a narrow trough around a fixed angular momentum from which most stars have been removed, rendering part of the disc unresponsive to spiral waves. We find that a groove can dramatically alter a disc's eigenmode spectrum by giving rise to a set of vigorously growing eigenmodes. These eigenmodes are particular to the grooved disc and are absent from the original ungrooved disc's mode spectrum. We discuss the properties and possible origin of the different families of new modes. By the very nature of our technique, we prove that a narrow phase-space groove can be a source of rapidly growing spiral patterns that are true eigenmodes of the grooved disc and that no non-linear processes need to be invoked to explain their presence in N-body simulations of disc galaxies. Our results lend support to the idea that spiral structure can be a recurrent phenomenon, in which one generation of spiral modes alters a disc galaxy's phase space in such a way that a following generation of modes is destabilized.
BENCHMARKING FAST-TO-ALFVEN MODE CONVERSION IN A COLD MAGNETOHYDRODYNAMIC PLASMA
Cally, Paul S.; Hansen, Shelley C. E-mail: shelley.hansen@monash.edu
2011-09-10
Alfven waves may be generated via mode conversion from fast magnetoacoustic waves near their reflection level in the solar atmosphere, with implications both for coronal oscillations and for active region helioseismology. In active regions this reflection typically occurs high enough that the Alfven speed a greatly exceeds the sound speed c, well above the a = c level where the fast and slow modes interact. In order to focus on the fundamental characteristics of fast/Alfven conversion, stripped of unnecessary detail, it is therefore useful to freeze out the slow mode by adopting the gravitationally stratified cold magnetohydrodynamic model c {yields} 0. This provides a benchmark for fast-to-Alfven mode conversion in more complex atmospheres. Assuming a uniform inclined magnetic field and an exponential Alfven speed profile with density scale height h, the Alfven conversion coefficient depends on three variables only: the dimensionless transverse-to-the-stratification wavenumber {kappa} = kh, the magnetic field inclination from the stratification direction {theta}, and the polarization angle {phi} of the wavevector relative to the plane containing the stratification and magnetic field directions. We present an extensive exploration of mode conversion in this parameter space and conclude that near-total conversion to outward-propagating Alfven waves typically occurs for small {theta} and large {phi} (80{sup 0}-90{sup 0}), though it is absent entirely when {theta} is exactly zero (vertical field). For wavenumbers of helioseismic interest, the conversion region is broad enough to encompass the whole chromosphere.
NASA Astrophysics Data System (ADS)
He, J.; Pei, Z. T.; Wang, L.; Tu, C. Y.; Marsch, E.; Yao, S.
2014-12-01
It is believed that MHD turbulence cascading is mainly caused by the collisions between Alfven waves, which propagate oppositely and are polarized perpendicularly to each other. Nonlinear interaction will vanish if the counter-propagating Alfven waves have their polarization aligned with each other. However, the Alfven waves satisfying these collision criteria have not yet been found in the solar wind observations. Here we report the existence of Alfven waves with opposite propagation and non-aligned polarization in the solar wind. In one case of anti-sunward magnetic sector, with RTN as the coordinates, the magnetic fluctuations in T-component (BT) are anti-correlated with the velocity fluctuations in T-component (VT), while BR and BN fluctuations are in positive correlation with VR and VN fluctuations, respectively. These features suggest a possible nonlinear interaction between outward propagating Alfven wave with polarization in T-direction and inward propagating Alfven wave with polarization in R&N-directions. Moreover, the associated proton kinetics shows the existence of field-aligned sunward beam rather than anti-sunward beam, which may indicate a parallel Landau heating by sunward kinetic Alfven waves. A statistical study including more cases is also conducted.
Hobson, M. J.
1981-11-01
The objective of this study was to perform a conceptual engineering design and evaluation study and to develop a design for an adiabatic CAES system using water-compensated hard rock caverns for compressed air storage. The conceptual plant design was to feature underground containment for thermal energy storage and water-compensated hard rock caverns for high pressure air storage. Other design constraints included the selection of turbomachinery designs that would require little development and would therefore be available for near-term plant construction and demonstration. The design was to be based upon the DOE/EPRI/PEPCO-funded 231 MW/unit conventional CAES plant design prepared for a site in Maryland. This report summarizes the project, its findings, and the recommendations of the study team; presents the development and optimization of the plant heat cycle and the selection and thermal design of the thermal energy storage system; discusses the selection of turbomachinery and estimated plant performance and operational capability; describes the control system concept; and presents the conceptual design of the adiabatic CAES plant, the cost estimates and economic evaluation, and an assessment of technical and economic feasibility. Particular areas in the plant design requiring further development or investigation are discussed. It is concluded that the adiabatic concept appears to be the most attractive candidate for utility application in the near future. It is operationally viable, economically attractive compared with competing concerns, and will require relatively little development before the construction of a plant can be undertaken. It is estimated that a utility could start the design of a demonstration plant in 2 to 3 years if research regarding TES system design is undertaken in a timely manner. (LCL)
Parametric instabilities of parallel propagating incoherent Alfven waves in a finite ion beta plasma
Nariyuki, Y.; Hada, T.; Tsubouchi, K.
2007-12-15
Large amplitude, low-frequency Alfven waves constitute one of the most essential elements of magnetohydrodynamic (MHD) turbulence in the fast solar wind. Due to small collisionless dissipation rates, the waves can propagate long distances and efficiently convey such macroscopic quantities as momentum, energy, and helicity. Since loading of such quantities is completed when the waves damp away, it is important to examine how the waves can dissipate in the solar wind. Among various possible dissipation processes of the Alfven waves, parametric instabilities have been believed to be important. In this paper, we numerically discuss the parametric instabilities of coherent/incoherent Alfven waves in a finite ion beta plasma using a one-dimensional hybrid (superparticle ions plus an electron massless fluid) simulation, in order to explain local production of sunward propagating Alfven waves, as suggested by Helios/Ulysses observation results. Parameter studies clarify the dependence of parametric instabilities of coherent/incoherent Alfven waves on the ion and electron beta ratio. Parametric instabilities of coherent Alfven waves in a finite ion beta plasma are vastly different from those in the cold ions (i.e., MHD and/or Hall-MHD systems), even if the collisionless damping of the Alfven waves are neglected. Further, ''nonlinearly driven'' modulational instability is important for the dissipation of incoherent Alfven waves in a finite ion beta plasma regardless of their polarization, since the ion kinetic effects let both the right-hand and left-hand polarized waves become unstable to the modulational instability. The present results suggest that, although the antisunward propagating dispersive Alfven waves are efficiently dissipated through the parametric instabilities in a finite ion beta plasma, these instabilities hardly produce the sunward propagating waves.
NASA Astrophysics Data System (ADS)
Goloshumova, V. N.; Kortenko, V. V.; Pokhoriler, V. L.; Kultyshev, A. Yu.; Ivanovskii, A. A.
2008-08-01
We describe the experience ZAO Ural Turbine Works specialists gained from mastering the series of CAD/CAE/CAM/PDM technologies, which are modern software tools of computer-aided engineering. We also present the results obtained from mathematical simulation of the process through which high-and intermediate-pressure rotors are heated for revealing the most thermally stressed zones, as well as the results from mathematical simulation of a new design of turbine cylinder shells for improving the maneuverability of these turbines.
Parametric Instabilities of Alfven Waves in the Solar Wind.
NASA Astrophysics Data System (ADS)
Jayanti, Venku Babu
1995-01-01
We consider the stability of a circularly-polarized Alfven wave (the pump wave) propagating along a uniform ambient magnetic field B_{rm O}. The system is linearly perturbed to study the stability of the Alfven wave. The perturbations are also assumed to propagate along the ambient field. Four different problems are addressed relating to the stability of the Alfven wave. The first involves using Floquet's theorem to obtain a dispersion relation for studying the stability. The result is a hierarchy of dispersion relations. However, all the dispersion relations are found to be equivalent. This technique showed that some results of other workers are incorrect. This method is very useful to obtain a dispersion relation for obliquely propagating perturbations. The second problem is to obtain analytical approximations to the dispersion relation using A = (Delta B/BO)^2 as a small expansion parameter; DeltaB is the pump amplitude. The analysis shows the crucial role played by plasma beta ( beta) in determining the behavior of the parametric instabilities of the pump. Expressions for the growth rates are presented for four ranges of beta. The polarizations are also computed to give some physical insight into the properties of the daughter waves (the modes generated as a result of the instability are called daughter waves). The third problem is to study the effects of streaming He ^{++}. The growth rates for new instabilities due to streaming He^{++ } are presented as a function of plasma beta, pump wave frequency, and DeltaB. The studies show that these new instabilities could compete with the well known decay instability. The final problem is to develop a methodology to study kinetic effects on the instabilities. This was done by breaking the plasma into beams, and treating each beam as a fluid. The nonlinear fluid equations are solved iteratively to obtain the perturbed densities and velocities. These are then used to derive the kinetic dispersion relation for the decay
Alfven wave transport effects in the time evolution of parallel cosmic-ray modified shocks
NASA Technical Reports Server (NTRS)
Jones, T. W.
1993-01-01
Some of the issues associated with a more complete treatment of Alfven transport in cosmic ray shocks are explored qualitatively. The treatment is simplified in some important respects, but some new issues are examined and for the first time a nonlinear, time dependent study of plane cosmic ray mediated shocks with both the entropy producing effects of wave dissipation and effects due to the Alfven wave advection of the cosmic ray relative to the gas is included. Examination of the direct consequences of including the pressure and energy of the Alfven waves in the formalism began.
NASA Technical Reports Server (NTRS)
Similon, Philippe L.; Sudan, R. N.
1989-01-01
The importance of field line geometry for shear Alfven wave dissipation in coronal arches is demonstrated. An eikonal formulation makes it possible to account for the complicated magnetic geometry typical in coronal loops. An interpretation of Alfven wave resonance is given in terms of gradient steepening, and dissipation efficiencies are studied for two configurations: the well-known slab model with a straight magnetic field, and a new model with stochastic field lines. It is shown that a large fraction of the Alfven wave energy flux can be effectively dissipated in the corona.
Borysov, Stanislav S.; Forchheimer, Daniel; Haviland, David B.
2014-10-29
Here we present a theoretical framework for the dynamic calibration of the higher eigenmode parameters (stiffness and optical lever inverse responsivity) of a cantilever. The method is based on the tip–surface force reconstruction technique and does not require any prior knowledge of the eigenmode shape or the particular form of the tip–surface interaction. The calibration method proposed requires a single-point force measurement by using a multimodal drive and its accuracy is independent of the unknown physical amplitude of a higher eigenmode.
Influence of radial electric field on Alfven-type instabilities
Hahm, T.S.; Tang, W.M.
1994-03-01
The influence of the large scale radial electric field, E{sub r}{sup (0)} on the frequency of shear-Alfven-type instability is analyzed. A frozen-in-flux constraint and the moderate-{beta} ion gyrokinetic equation are used in the derivation. The analysis indicates that the frequency predicted by a theory with E{sub r}{sup (0)} effect should be Doppler-shifted by k {center_dot} V{sub E} for comparison to the experimentally observed frequency. A specific example of the practical relevance of the result is given regarding possible identification of the edge-localized-mode-associated magnetic activity recently observed in PBX-M tokamak experiment.
Nonlinear evolution of Alfven waves in a finite beta plasma
Som, B.K. ); Dasgupta, B.; Patel, V.L. ); Gupta, M.R. )
1989-12-01
A general form of the derivative nonlinear Schroedinger (DNLS) equation, describing the nonlinear evolution of Alfven waves propagating parallel to the magnetic field, is derived by using two-fluid equations with electron and ion pressure tensors obtained from Braginskii (in {ital Reviews} {ital of} {ital Plasma Physics} (Consultants Bureau, New York, 1965), Vol. 1, p. 218). This equation is a mixed version of the nonlinear Schroedinger (NLS) equation and the DNLS, as it contains an additional cubic nonlinear term that is of the same order as the derivative of the nonlinear terms, a term containing the product of a quadratic term, and a first-order derivative. It incorporates the effects of finite beta, which is an important characteristic of space and laboratory plasmas.
Radial evolution of power spectra of interplanetary Alfvenic turbulence
NASA Technical Reports Server (NTRS)
Bavassano, B.; Dobrowolny, M.; Mariani, F.; Ness, N. F.
1981-01-01
The radial evolution of the power spectra of the MHD turbulence within the trailing edge of high speed streams in the solar wind was investigated with the magnetic field data of Helios 1 and 2 for heliocentric distance between 0.3 and 0.9 AU. In the analyzed frequency range (.00028 Hz to .0083 Hz) the computed spectra have, near the Earth, values of the spectral index close to that predicted for an incompressible hydromagnetic turbulence in a stationary state. Approaching the Sun the spectral slope remains unchanged for frequencies f or approximately .00 Hz, whereas at lower frequencies, a clear evolution toward a less steep fall off with frequency is found. The radial gradient of the power in Alfvenic fluctuations depends on frequency and it increases upon increasing frequency. For frequencies f or approximately .00 Hz, however, the radial gradient remains approximately the same. Possible theoretical implications of the observational features are discussed.
KINETIC ALFVEN TURBULENCE AND PARALLEL ELECTRIC FIELDS IN FLARE LOOPS
Zhao, J. S.; Wu, D. J.; Lu, J. Y.
2013-04-20
This study investigates the spectral structure of the kinetic Alfven turbulence in the low-beta plasmas. We consider a strong turbulence resulting from collisions between counterpropagating wavepackets with equal energy. Our results show that (1) the spectra of the magnetic and electric field fluctuations display a transition at the electron inertial length scale, (2) the turbulence cascades mainly toward the magnetic field direction as the cascade scale is smaller than the electron inertial length, and (3) the parallel electric field increases as the turbulent scale decreases. We also show that the parallel electric field in the solar flare loops can be 10{sup 2}-10{sup 4} times the Dreicer field as the turbulence reaches the electron inertial length scale.
Alfven waves and associated energetic ions downstream from Uranus
Zhang, Ming; Belcher, J.W.; Richardson, J.D. ); Smith, C.W. )
1991-02-01
The authors report the observation of low-frequency waves in the solar wind downstream from Uranus. These waves are observed by the Voyager spacecraft for more than 2 weeks after the encounter with Uranus and are present during this period whenever the interplanetary magnetic field is oriented such that the field lines intersect the Uranian bow shock. The magnetic field and velocity components transverse to the background field are strongly correlated, consistent with the interpretation that these waves are Alfvenic and/or fast-mode waves. The waves have a spacecraft frame frequency of about 10{sup {minus}3} Hz, and when first observed near the bow shock have an amplitude comparable to the background field. As the spacecraft moves farther from Uranus, the amplitude decays. The waves appear to propagate along the magnetic field lines outward from Uranus and are right-hand polarized. Theory suggests that these waves are generated in the upstream region by a resonant instability with a proton beam streaming along the magnetic field lines. The solar wind subsequently carries these waves downstream to the spacecraft location. These waves are associated with the presence of energetic (> 28 keV) ions observed by the low-energy charged particle instrument. These ions appear two days after the start of the wave activity and occur thereafter whenever the Alfven waves occur, increasing in intensity away from Uranus. The ions are argued to originate in the Uranian magnetosphere, but pitch-angle scattering in the upstream region is required to bring them downstream to the spacecraft location.
Correction to the Alfven-Lawson criterion for relativistic electron beams
Dodin, I. Y.; Fisch, N. J.
2006-10-15
The Alfven-Lawson criterion for relativistic electron beams is revised. The parameter range is found, in which a stationary beam can carry arbitrarily large current, regardless of its transverse structure.
NASA Technical Reports Server (NTRS)
Parker, E. N.
1974-01-01
It had been pointed out by Parker (1974) that the basic cause of the sunspot phenomenon is the enhanced heat transport in the magnetic field of the sunspot. The enhanced transport occurs through convective overstability which operates as a heat engine generating Alfven waves. The characteristics of the convective forces present are investigated along with questions concerning overstability and convectively driven Alfven waves. Relations regarding instability and convectively driven surface waves are discussed and attention is given to individual overstable Alfven modes. It is found that the form of an Alfven wave in the absence of convective forces is entirely arbitrary, so that waves with any arbitrary profile can be fitted into a vertical column of the field without disturbing the fluid outside. With the introduction of convective forces the situation changes so that the presence of lateral boundaries alters the form of the basic wave modes.
Generation of Alfven waves by deceleration of magnetospheric convection and broadband Pi pulsations
NASA Technical Reports Server (NTRS)
Kan, J. R.; Lee, L. C.; Longenecker, D. U.; Chiu, Y. T.
1982-01-01
The generation of Alfven waves by the deceleration of magnetospheric convection caused by ionospheric loading effects in the magnetospheric dynamo is considered. A one-dimensional model of that region of the plasma sheet where convection is decelerated due to the dynamo process in the magnetosphere-ionosphere coupling is formulated, and the stability of the region is analyzed in order to derive the growth rate of unstable Alfven waves. The effects of ionospheric damping on unstable Alfven wave packets bounding between hemispheres are estimated. It is found that the overall growth rate is proportional to the height-integrated Pedersen conductivity and the convection speed in the dynamic region, but changes into a damping rate when the Pedersen conductivity is reduced below a specific threshold. The unstable Alfven waves thus generated are also found to contribute to both burstlike and relatively continuous Pi pulsations observed during substorms.
Ion beam generation at the plasma sheet boundary layer by kinetic Alfven waves
NASA Technical Reports Server (NTRS)
Moghaddam-Taaheri, E.; Goertz, C. K.; Smith, R. A.
1989-01-01
A two-dimensional quasi-linear numerical code was developed for studying ion beam generation at the plasma sheet boundary layer by kinetic Alfven waves. The model assumes that the central plasma sheet is the particle source, and that the last magnetic field lines on which kinetic Alfven waves exist and diffusion occurs can be either open or closed. As the possible source for the excitement of the kinetic Alfven waves responsible for ion diffusion, the resonant mode conversion of the surface waves to kinetic Alfven waves is considered. It is shown that, depending on the topology of the magnetic field at the lobe side of the simulation system, i.e., on whether field lines are open or closed, the ion distribution function may or may not reach a steady state.
Hybrid Alfven resonant mode generation in the magnetosphere-ionosphere coupling system
Hiraki, Yasutaka; Watanabe, Tomo-Hiko
2012-10-15
Feedback unstable Alfven waves involving global field-line oscillations and the ionospheric Alfven resonator (IAR) were comprehensively studied to clarify their properties of frequency dispersion, growth rate, and eigenfunctions. It is discovered that a new mode called here the hybrid Alfven resonant (HAR) mode can be destabilized in the magnetosphere-ionosphere coupling system with a realistic Alfven velocity profile. The HAR mode found in a high frequency range over 0.3 Hz is caused by coupling of IAR modes with strong dispersion and magnetospheric cavity resonances. The harmonic relation of HAR eigenfrequencies is characterized by a constant frequency shift from those of IAR modes. The three modes are robustly found even if effects of two-fluid process and ionospheric collision are taken into account and thus are anticipated to be detected by magnetic field observations in a frequency range of 0.3-1 Hz in auroral and polar-cap regions.
Bisle, Stephanie; Klingenbeck, Leonie; Borges, Vítor; Sobotta, Katharina; Schulze-Luehrmann, Jan; Menge, Christian; Heydel, Carsten; Gomes, João Paulo; Lührmann, Anja
2016-05-18
ABSRTACT Coxiella burnetii is an obligate intracellular bacterium that causes Query (Q) fever, a zoonotic disease. It requires a functional type IV secretion system (T4SS) which translocate bacterial effector proteins into the host cell cytoplasm and thereby facilitates bacterial replication. To date, more than 130 effector proteins have been identified, but their functions remain largely unknown. Recently, we demonstrated that one of these proteins, CaeA (CBU1524) localized to the host cell nucleus and inhibited intrinsic apoptosis of HEK293 or CHO cells. In the present study we addressed the question whether CaeA also affects the extrinsic apoptosis pathway. Ectopic expression of CaeA reduced extrinsic apoptosis and prevented the cleavage of the executioner caspase 7, but did not impair the activation of initiator caspase 9. CaeA expression resulted in an up-regulation of survivin (an inhibitor of activated caspases), which, however, was not causal for the anti-apoptotic effect of CaeA. Comparing the sequence of CaeA from 25 different C. burnetii isolates we identified an EK (glutamic acid/ lysine) repetition motif as a site of high genetic variability. The EK motif of CaeA was essential for the anti-apoptotic activity of CaeA. From these data, we conclude that the C. burnetii effector protein CaeA interferes with the intrinsic and extrinsic apoptosis pathway. The process requires the EK repetition motif of CaeA, but is independent of the upregulated expression of survivin. PMID:26760129
Brandt, C; Thakur, S C; Light, A D; Negrete, J; Tynan, G R
2014-12-31
Spatiotemporal splitting events of drift wave (DW) eigenmodes due to nonlinear coupling are investigated in a cylindrical helicon plasma device. DW eigenmodes in the radial-azimuthal cross section have been experimentally observed to split at radial locations and recombine into the global eigenmode with a time shorter than the typical DW period (t≪fDW(-1)). The number of splits correlates with the increase of turbulence. The observed dynamics can be theoretically reproduced by a Kuramoto-type model of a network of radially coupled azimuthal eigenmodes. Coupling by E×B-vortex convection cell dynamics and ion gyro radii motion leads to cross-field synchronization and occasional mode splitting events. PMID:25615346
Generation of magnetoacoustic zonal flows by Alfven waves in a rotating plasma
Mikhailovskii, A. B.; Lominadze, J. G.; Churikov, A. P.; Erokhin, N. N.; Tsypin, V. S.; Smolyakov, A. I.; Galvao, R. M. O.
2007-08-15
Analytical theory of nonlinear generation of magnetoacoustic zonal flows in a rotating plasma is developed. As the primary modes causing such a generation, a totality of the Alfven waves are considered, along with the kinetic, inertial, and rotational. It is shown that in all these cases of the Alfven waves the generation is possible if the double plasma rotation frequency exceeds the zonal flow frequency.
Super-alfvenic propagation of cosmic rays: The role of streaming modes
NASA Technical Reports Server (NTRS)
Morrison, P. J.; Scott, J. S.; Holman, G. D.; Ionson, J. A.
1980-01-01
Numerous cosmic ray propagation and acceleration problems require knowledge of the propagation speed of relativistic particles through an ambient plasma. Previous calculations indicated that self-generated turbulence scatters relativistic particles and reduces their bulk streaming velocity to the Alfven speed. This result was incorporated into all currently prominent theories of cosmic ray acceleration and propagation. It is demonstrated that super-Alfvenic propagation is indeed possible for a wide range of physical parameters. This fact dramatically affects the predictions of these models.
A Unique Self-Sensing, Self-Actuating AFM Probe at Higher Eigenmodes
Wu, Zhichao; Guo, Tong; Tao, Ran; Liu, Leihua; Chen, Jinping; Fu, Xing; Hu, Xiaotang
2015-01-01
With its unique structure, the Akiyama probe is a type of tuning fork atomic force microscope probe. The long, soft cantilever makes it possible to measure soft samples in tapping mode. In this article, some characteristics of the probe at its second eigenmode are revealed by use of finite element analysis (FEA) and experiments in a standard atmosphere. Although the signal-to-noise ratio in this environment is not good enough, the 2 nm resolution and 0.09 Hz/nm sensitivity prove that the Akiyama probe can be used at its second eigenmode under FM non-contact mode or low amplitude FM tapping mode, which means that it is easy to change the measuring method from normal tapping to small amplitude tapping or non-contact mode with the same probe and equipment. PMID:26580619
Kinetic toroidal Alfv{acute e}n eigenmodes in finite-{beta} tokamak plasmas
Zheng, L.-.; Chen, L.
1998-04-01
Kinetic toroidal Alfv{acute e}n eigenmodes (KTAEs) in finite-{beta} circular tokamak plasmas are investigated. Here, {beta} is the ratio between plasma and magnetic pressures, and, formally, {beta}{approximately}scr(O)(r/Rq{sup 2}), with q being the safety factor, r and R denoting, respectively, minor and major radii. A new effect associated with finite parallel electric field effect due to the ion magnetic drift (IMD) is discovered, which is of the same order as that due to the well-known effect associated with the finite ion Larmor radii. The IMD-induced parallel electric field effect is shown to contribute to potential wells for the eigenmodes. Therefore, the IMD-induced parallel electric field effect can discretize the lower Alfv{acute e}n continuum along the real eigenfrequency. Subsequently, this new branch of KTAEs could be readily destabilized by the energetic ions. {copyright} {ital 1998 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Miriţoiu, C. M.; Stănescu, M. M.; Burada, C. O.; Bolcu, D.; Roşca, V.
2015-11-01
For modal identification, the single-point excitation method has been widely used in modal tests and it consists in applying a force in a given point and recording the vibratory structure response in all interest points, including the excitation point. There will be presented the experimental recordings for the studied bars (with Kevlar-carbon or carbon fibers), the frequency response function in Cartesian and polar coordinates. By using the frequency response functions we determine the eigenparameters for each bar. We present the final panel of the eigenmodes (with the damping factors, eigenfrequencies and critical damping) for each considered bar. Using the eigenfrequency of the first determined eigenmode, the bars stiffness has been determined. The presented bars can be used in practical engineering for: car or bus body parts, planes body parts, bullet-proof vests, reinforcements for sandwich beams, and so on.
Black, Carrie; Ng, C. S.
2013-01-15
It has been demonstrated that in the presence of weak collisions, described by the Lenard-Bernstein (LB) collision operator, the Landau-damped solutions become true eigenmodes of the system and constitute a complete set [C.-S. Ng et al., Phys. Rev. Lett. 83, 1974 (1999) and C. S. Ng et al., Phys. Rev. Lett. 96, 065002 (2004)]. We present numerical results from an Eulerian Vlasov code that incorporates the Lenard-Bernstein collision operator [A. Lenard and I. B. Bernstein, Phys. Rev. 112, 1456 (1958)]. The effect of collisions on the numerical recursion phenomenon seen in Vlasov codes is discussed. The code is benchmarked against exact linear eigenmode solutions in the presence of weak collisions, and a spectrum of Landau-damped solutions is determined within the limits of numerical resolution. Tests of the orthogonality and the completeness relation are presented.
Alfven wave transport effects in the time evolution of parallel cosmic-ray-modified shocks
NASA Technical Reports Server (NTRS)
Jones, T. W.
1993-01-01
This paper presents a numerical study of the time evolution of plane, cosmic-ray modified shocks with magnetic field parallel to the shock normal, based on the diffusive shock acceleration formalism and including the effects from the finite propagation speed and energy of Alfven waves responsible for controlling the transport of the cosmic rays. The simulations discussed are based on a three-fluid model for the dynamics, but a more complete formalism is laid out for future work. The results of the simulations confirm earlier steady state analyses that found these Alfven transport effects to be potentially important when the upstream Alfven speed and the gas sound speed are comparable, i.e., when the plasma and magnetic pressures are similar. It is also clear, however, that the impact of Alfven transport effects, which tend to slow shock evolution and reduce the time asymptotic cosmic-ray pressure in the shock, is strongly dependent upon uncertain details in the transport models. Both cosmic-ray advection tied to streaming Alfven waves and dissipation of wave energy are important to include in the models. Further, Alfven transport properties on both sides of the shock are also influential.
LARGE-AMPLITUDE ALFVEN WAVE IN INTERPLANETARY SPACE: THE WIND SPACECRAFT OBSERVATIONS
Wang Xin; He Jiansen; Tu Chuanyi; Zhang Lei; Marsch, Eckart; Chao, Jih-Kwin
2012-02-20
We present, for the first time, measurements of arc-polarized velocity variations together with magnetic field variations associated with a large-amplitude Alfven wave as observed by the Wind satellite. The module of the magnetic field variance is larger than the magnitude of the average magnetic field, indicating the large amplitude of these fluctuations. When converting to the deHoffman-Teller frame, we find that the magnetic field and velocity vector components, in the plane perpendicular to the minimum-variance direction of the magnetic field, are arc-polarized, and their tips almost lie on the same circle. We also find that the normalized cross helicity and Alfven ratio of the wave are both nearly equal to unity, a result which has not been reported in previous studies at 1 AU. It is worthy to stress here that pure Alfven waves can also exist in the solar wind even near the Earth at 1 AU, but not only near 0.3 AU. Further study could be done to help us know more about the properties of pure Alfven wave at 1 AU that could not be figured out easily before because of the contaminations (e.g., Alfven waves propagating in different directions, magnetic structures, and other compressional waves) on previously reported Alfven wave cases.
Winds from Luminous Late-Type Stars: II. Broadband Frequency Distribution of Alfven Waves
NASA Technical Reports Server (NTRS)
Airapetian, V.; Carpenter, K. G.; Ofman, L.
2010-01-01
We present the numerical simulations of winds from evolved giant stars using a fully non-linear, time dependent 2.5-dimensional magnetohydrodynamic (MHD) code. This study extends our previous fully non-linear MHD wind simulations to include a broadband frequency spectrum of Alfven waves that drive winds from red giant stars. We calculated four Alfven wind models that cover the whole range of Alfven wave frequency spectrum to characterize the role of freely propagated and reflected Alfven waves in the gravitationally stratified atmosphere of a late-type giant star. Our simulations demonstrate that, unlike linear Alfven wave-driven wind models, a stellar wind model based on plasma acceleration due to broadband non-linear Alfven waves, can consistently reproduce the wide range of observed radial velocity profiles of the winds, their terminal velocities and the observed mass loss rates. Comparison of the calculated mass loss rates with the empirically determined mass loss rate for alpha Tau suggests an anisotropic and time-dependent nature of stellar winds from evolved giants.
WINDS FROM LUMINOUS LATE-TYPE STARS. II. BROADBAND FREQUENCY DISTRIBUTION OF ALFVEN WAVES
Airapetian, V.; Ofman, L.; Carpenter, K. G.
2010-11-10
We present the numerical simulations of winds from evolved giant stars using a fully nonlinear, time-dependent 2.5-dimensional magnetohydrodynamic (MHD) code. This study extends our previous fully nonlinear MHD wind simulations to include a broadband frequency spectrum of Alfven waves that drive winds from red giant stars. We calculated four Alfven wind models that cover the whole range of the Alfven wave frequency spectrum to characterize the role of freely propagated and reflected Alfven waves in the gravitationally stratified atmosphere of a late-type giant star. Our simulations demonstrate that, unlike linear Alfven wave-driven wind models, a stellar wind model based on plasma acceleration due to broadband nonlinear Alfven waves can consistently reproduce the wide range of observed radial velocity profiles of the winds, their terminal velocities, and the observed mass-loss rates. Comparison of the calculated mass-loss rates with the empirically determined mass-loss rate for {alpha} Tau suggests an anisotropic and time-dependent nature of stellar winds from evolved giants.
FMS and Alfven from the initial disturbance in the FMS waveguide
NASA Astrophysics Data System (ADS)
Dmitrienko, Irina
A description of the evolution of the initial disturbance in the fast magnetosonic (FMS) waveguide in transversely inhomogeneous plasma, given a weak coupling between FMS and Alfven modes, is made. It is shown that the Fourier transform of the FMS waveguide disturbance with respect to the coordinates along which plasma is homogeneous can be presented as a superposition of collective modes of the leading approximation with respect to the weak FMS-Alfven wave coupling from the initial instant of time. Frequencies of such collective modes and dependence of their structures on the coordinate along the inhomogeneity are found without taking the FMS-Alfven resonance into consideration, and the mode decrements are calculated using the perturbation technique. On the basis of such a representation of the FMS waveguide disturbance, the evolution of Alfven waves generating with waveguide mode packets produced by the initial disturbance of an arbitrary longitudinal structure is described. It is shown that the longitudinal structure of the Alfven disturbance generated by the collective mode packet is determined by the ratio between longitudinal scales of the initial disturbance and scales specified by resonance conditions (the resonance longitudinal wave number and the width of the range of the resonance longitudinal wave numbers). The structures of Alfven disturbances for the cases of such different ratios are described.
THREE-DIMENSIONAL NUMERICAL SIMULATIONS OF FAST-TO-ALFVEN CONVERSION IN SUNSPOTS
Felipe, T.
2012-10-20
The conversion of fast waves to the Alfven mode in a realistic sunspot atmosphere is studied through three-dimensional numerical simulations. An upward propagating fast acoustic wave is excited in the high-{beta} region of the model. The new wave modes generated at the conversion layer are analyzed from the projections of the velocity and magnetic field in their characteristic directions, and the computation of their wave energy and fluxes. The analysis reveals that the maximum efficiency of the conversion to the slow mode is obtained for inclinations of 25 Degree-Sign and low azimuths, while the Alfven wave conversions peak at high inclinations and azimuths between 50 Degree-Sign and 120 Degree-Sign . Downward propagating Alfven waves appear at the regions of the sunspot where the orientation of the magnetic field is in the direction opposite to the wave propagation, since at these locations the Alfven wave couples better with the downgoing fast magnetic wave which is reflected due to the gradients of the Alfven speed. The simulations show that the Alfven energy at the chromosphere is comparable to the acoustic energy of the slow mode, being even higher at high inclined magnetic fields.
Omega3P: A Parallel Finite-Element Eigenmode Analysis Code for Accelerator Cavities
Lee, Lie-Quan; Li, Zenghai; Ng, Cho; Ko, Kwok; /SLAC
2009-03-04
Omega3P is a parallel eigenmode calculation code for accelerator cavities in frequency domain analysis using finite-element methods. In this report, we will present detailed finite-element formulations and resulting eigenvalue problems for lossless cavities, cavities with lossy materials, cavities with imperfectly conducting surfaces, and cavities with waveguide coupling. We will discuss the parallel algorithms for solving those eigenvalue problems and demonstrate modeling of accelerator cavities through different examples.
Stable ellipticity-induced Alfv{acute e}n eigenmodes in the Joint European Torus
Heidbrink, W.W.; Fasoli, A.; Borba, D.; Jaun, A.
1997-10-01
An external antenna excites stable eigenmodes in elongated Ohmically heated plasmas in the Joint European Torus (JET) [P.-H. Rebut, R. J. Bickerton, and B. E. Keen, Nucl. Fusion {bold 25}, 1011 (1985)]. The frequency of the modes (240{minus}290 kHz) falls in the gap in the magnetohydrodynamic (MHD) continuum that is produced by ellipticity. Some modes are very weakly damped ({gamma}/{omega}{lt}10{sup {minus}3}). {copyright} {ital 1997 American Institute of Physics.}
Identification of an Island-induced Alfvén Eigenmode in MST plasmas
NASA Astrophysics Data System (ADS)
Anderson, J. K.; Cook, C. R.; Hegna, C. C.; Boguski, J.; Feng, R.; McCollam, K. M.; Sears, S. H.; Spong, D. A.; Hirshman, S. P.
2015-11-01
Recent theoretical work analytically computes the effect of a magnetic island on the shear Alfvén continuum and may explain unresolved Alfvénic activity observed in neutral beam-heated MST plasmas. Consideration of the previously-ignored core-localized n=5 island leads to theoretical Alfvén continua that provide a gap in which the observed n=4 Alfvénic bursts reside. Numerical simulations using the STELLGAP/AE3D codes, as well as a new code called SIESTAlfvén have identified the bursts as the first observation of an Island-induced Alfvén Eigenmode (IAE). The IAE arises from a helical coupling of mode numbers, similar to the helicity-induced Alfvén eigenmode, but occurs in the core of an island. The observed frequency of bursting n=4 Alfvénic modes fall within the island-induced gap over a wide range of MST operating parameters. Characteristics such as mode frequency, width and damping rate are measured as a function of experimentally-varied magnetic island width. Coincident bursts with toroidal mode number n=1 may exhibit frequency scaling of an Alfvénic eigenmode; the possibility of an island induced extremum mode is explored as an explanation. Work supported by US DoE under grants DE-FG02-99ER54546, DE-SC0006103 and DE-FC02-05ER54814.
Full Wave Modeling of Wave -- Plasma Interactions in NSTX.
NASA Astrophysics Data System (ADS)
Phillips, C. K.; Bernabei, S.; Fredrickson, E.; Gorelenkov, N.; Hosea, J. C.; Leblanc, B.; Valeo, E. J.; Wilson, J. R.; Bonoli, P. T.; Wright, J. C.; Ryan, P. M.; Wilgen, J. B.
2006-10-01
Wave plasma interactions play an important role in the dynamics of NSTX plasmas in a wide range of frequencies. High harmonic fast waves (HHFW), with frequencies significantly above the fundamental ion cyclotron frequency, are used to heat and drive noninductive currents in NSTX plasmas. Fast ions from neutral beam injection can excite compressional and / or global Alfven eigenmodes (CAE/GAE) with frequencies near the fundamental ion cyclotron frequency. Simulations of power deposition profiles obtained with the full wave code, TORIC, will be compared to the observations from recent HHFW experiments that show that the wave propagation and absorption depend strongly on the antenna phasing and plasma conditions [i]. The issue of mode conversion of the HHFWs to shorter wavelength modes will be revisited. Initial simulations of driven eigenmodes in the CAE / GAE frequency range will also be discussed. [i] See contributed Oral Talk by J. C. Hosea et al this conference
Rutqvist, J.; Kim, H. -M.; Ryu, D. -W.; Synn, J. -H.; Song, W. -K.
2012-02-01
We applied coupled nonisothermal, multiphase fluid flow and geomechanical numerical modeling to study the coupled thermodynamic and geomechanical performance of underground compressed air energy storage (CAES) in concrete-lined rock caverns. The paper focuses on CAES in lined caverns at relatively shallow depth (e.g., 100 m depth) in which a typical CAES operational pressure of 5 to 8 MPa is significantly higher than both ambient fluid pressure and in situ stress. We simulated a storage operation that included cyclic compression and decompression of air in the cavern, and investigated how pressure, temperature and stress evolve over several months of operation. We analyzed two different lining options, both with a 50 cm thick low permeability concrete lining, but in one case with an internal synthetic seal such as steel or rubber. For our simulated CAES system, the thermodynamic analysis showed that 96.7% of the energy injected during compression could be recovered during subsequent decompression, while 3.3% of the energy was lost by heat conduction to the surrounding media. Our geomechanical analysis showed that tensile effective stresses as high as 8 MPa could develop in the lining as a result of the air pressure exerted on the inner surface of the lining, whereas thermal stresses were relatively smaller and compressive. With the option of an internal synthetic seal, the maximum effective tensile stress was reduced from 8 to 5 MPa, but was still in substantial tension. We performed one simulation in which the tensile tangential stresses resulted in radial cracks and air leakage though the lining. This air leakage, however, was minor (about 0.16% of the air mass loss from one daily compression) in terms of CAES operational efficiency, and did not significantly impact the overall energy balance of the system. However, despite being minor in terms of energy balance, the air leakage resulted in a distinct pressure increase in the surrounding rock that could be
Design and development of a quad copter (UMAASK) using CAD/CAM/CAE
NASA Astrophysics Data System (ADS)
Manarvi, Irfan Anjum; Aqib, Muhammad; Ajmal, Muhammad; Usman, Muhammad; Khurshid, Saqib; Sikandar, Usman
Micro flying vehicles1 (MFV) have become a popular area of research due to economy of production, flexibility of launch and variety of applications. A large number of techniques from pencil sketching to computer based software are being used for designing specific geometries and selection of materials to arrive at novel designs for specific requirements. Present research was focused on development of suitable design configuration using CAD/CAM/CAE tools and techniques. A number of designs were reviewed for this purpose. Finally, rotary wing Quadcopter flying vehicle design was considered appropriate for this research. Performance requirements were planned as approximately 10 meters ceiling, weight less than 500grams and ability to take videos and pictures. Parts were designed using Finite Element Analysis, manufactured using CNC machines and assembled to arrive at final design named as UMAASK. Flight tests were carried out which confirmed the design requirements.
Modulational instability of finite-amplitude, circularly polarized Alfven waves
NASA Technical Reports Server (NTRS)
Derby, N. F., Jr.
1978-01-01
The simple theory of the decay instability of Alfven waves is strictly applicable only to a small-amplitude parent wave in a low-beta plasma, but, if the parent wave is circularly polarized, it is possible to analyze the situation without either of these restrictions. Results show that a large-amplitude circularly polarized wave is unstable with respect to decay into three waves, one longitudinal and one transverse wave propagating parallel to the parent wave and one transverse wave propagating antiparallel. The transverse decay products appear at frequencies which are the sum and difference of the frequencies of the parent wave and the longitudinal wave. The decay products are not familiar MHD modes except in the limit of small beta and small amplitude of the parent wave, in which case the decay products are a forward-propagating sound wave and a backward-propagating circularly polarized wave. In this limit the other transverse wave disappears. The effect of finite beta is to reduce the linear growth rate of the instability from the value suggested by the simple theory. Possible applications of these results to the theory of the solar wind are briefly touched upon.
Ionospheric Ion Upflows Associated with the Alfven Wave Heating
NASA Astrophysics Data System (ADS)
Song, P.; Tu, J.
2014-12-01
In this study we present the simulation results from a self-consistent inductive-dynamic ionosphere-thermosphere model. In a 2-D numerical simulation (noon-midnight meridian plane), we solve the continuity, momentum, and energy equations for multiple species of ions and neutrals and Maxwell's equations. In particular, the model retains Faraday's law, inertial term in the ion momentum equations and photochemistry. The code is based on an implicit algorithm and simulates a region from 80 km to 5000 km above the Earth. The system is driven by an antisunward motion at the upper boundary of the dayside cusp latitude in both hemispheres. We show that the frictional heating, which can produce upflows of the light (H+ and He+) and heave (O+) ions, is driven by the Alfven wave-induced ion motion relative to the neutrals. The variations of the upflows along a noon-midnight magnetic meridian are examined in association with given driving conditions imposed by the magnetosphere convection.
Oxygen Ion Heat Rate within Alfvenic Turbulence in the Cusp
NASA Technical Reports Server (NTRS)
Coffey, Victoria N.; Singh, Nagendra; Chandler, Michael O.
2009-01-01
The role that the cleft/cusp has in ionosphere-magnetosphere coupling makes it a dynamic and important region. It is directly exposed to the solar wind, making it possible for the entry of electromagnetic energy and precipitating electrons and ions from dayside reconnection and other dayside events. It is also a significant source of ionospheric plasma, contributing largely to the mass loading of the magnetosphere with large fluxes of outflowing ions. Crossing the cusp/cleft near 5100 km, the Polar instruments observe the common correlation of downward Poynting flux, ion energization, soft electron precipitation, broadband extremely low-frequency (BB-ELF) emissions, and density depletions. The dominant power in the BB-ELF emissions is now identified to be from spatially broad, low frequency Alfv nic structures. For a cusp crossing, we determine using the Electric Field Investigation (EFI), that the electric and magnetic field fluctuations are Alfv nic and the electric field gradients satisfy the inequality for stochastic acceleration. With all the Polar 1996 horizontal crossings of the cusp, we determine the O+ heating rate using the Thermal Ion Dynamics Experiment (TIDE) and Plasma Wave Investigation (PWI). We then compare this heating rate to other heating rates assuming the electric field gradient criteria exceeds the limit for stochastic acceleration for the remaining crossings. The comparison suggests that a stochastic acceleration mechanism is operational and the heating is controlled by the transverse spatial scale of the Alfvenic waves.
POLARIZATION AND COMPRESSIBILITY OF OBLIQUE KINETIC ALFVEN WAVES
Hunana, P.; Goldstein, M. L.; Passot, T.; Sulem, P. L.; Laveder, D.; Zank, G. P.
2013-04-01
It is well known that a complete description of the solar wind requires a kinetic description and that, particularly at sub-proton scales, kinetic effects cannot be ignored. It is nevertheless usually assumed that at scales significantly larger than the proton gyroscale r{sub L} , magnetohydrodynamics or its extensions, such as Hall-MHD and two-fluid models with isotropic pressures, provide a satisfactory description of the solar wind. Here we calculate the polarization and magnetic compressibility of oblique kinetic Alfven waves and show that, compared with linear kinetic theory, the isotropic two-fluid description is very compressible, with the largest discrepancy occurring at scales larger than the proton gyroscale. In contrast, introducing anisotropic pressure fluctuations with the usual double-adiabatic (or CGL) equations of state yields compressibility values which are unrealistically low. We also show that both of these classes of fluid models incorrectly describe the electric field polarization. To incorporate linear kinetic effects, we use two versions of the Landau fluid model that include linear Landau damping and finite Larmor radius (FLR) corrections. We show that Landau damping is crucial for correct modeling of magnetic compressibility, and that the anisotropy of pressure fluctuations should not be introduced without taking into account the Landau damping through appropriate heat flux equations. We also show that FLR corrections to all the retained fluid moments appear to be necessary to yield the correct polarization. We conclude that kinetic effects cannot be ignored even for kr{sub L} << 1.
Particle energization and current sheets in Alfvenic plasma turbulence
NASA Astrophysics Data System (ADS)
Makwana, Kirit; Li, Hui; Guo, Fan; Daughton, William; Cattaneo, Fausto
2015-11-01
Plasma turbulence is driven by injecting energy at large scales through stirring or instabilities. This energy cascades forward to smaller scales by nonlinear interactions, described by magnetohydrodynamics (MHD) at scales larger than the ion gyroradius. At smaller scales, the fluid description of MHD breaks down and kinetic mechanisms convert turbulent energy into particle energy. We investigate this entire process by simulating the cascade of strongly interacting Alfven waves using MHD and particle-in-cell (PIC) simulations. The plasma beta is varied and particle heating is analyzed. Anisotropic heating of particles is observed. We calculate the fraction of injected energy converted into non-thermal energy. At low beta we obtain a significant non-thermal component to the particle energy distribution function. We investigate the mechanisms behind this acceleration. The velocity distribution function is correlated with the sites of turbulent current sheets. The different dissipative terms due to curvature drift, gradB drift, polarization drifts, and parallel current density are also calculated. This has applications for understanding particle energization in turbulent space plasmas.
Standing Alfven wave current system at Io - Voyager 1 observations
NASA Astrophysics Data System (ADS)
Acuna, M. H.; Neubauer, F. M.; Ness, N. F.
1981-09-01
The enigmatic control of the occurrence frequency of Jupiter's decametric emissions by the satellite Io has been explained theoretically on the basis of its strong electrodynamic interaction with the corotating Jovian magnetosphere leading to field-aligned currents connecting Io with the Jovian ionosphere. Direct measurements of the perturbation magnetic fields due to this current system were obtained by the Goddard Space Flight Center magnetic field experiment on Voyager 1 on March 5, 1979, when it passed within 20,500 km south of Io. An interpretation in the framework of Alfven waves radiated by Io leads to current estimates of 2.8 x 10 to the 6th A. A mass density of 7400-13,600 proton mass units/cu cm is derived, which compares very favorably with independent observations of the torus composition characterized by 7-9 proton mass units per electron for a local electron density of 1050-1500/cu cm. The power dissipated in the current system may be important for heating the Io heavy ion torus, inner magnetosphere, Jovian ionosphere, and possibly the ionosphere or even the interior of Io.
Generation of Alfvenic Waves and Turbulence in Magnetic Reconnection Jets
NASA Astrophysics Data System (ADS)
Hoshino, M.
2014-12-01
The magneto-hydro-dynamic (MHD) linear stability for the plasma sheet with a localized bulk plasma flow parallel to the neutral sheet is investigated. We find three different unstable modes propagating parallel to the anti-parallel magnetic field line, and we call them as "streaming tearing'', "streaming sausage'', and "streaming kink'' mode. The streaming tearing and sausage modes have the tearing mode-like structure with symmetric density fluctuation to the neutral sheet, and the streaming kink mode has the asymmetric fluctuation. The growth rate of the streaming tearing mode decreases with increasing the magnetic Reynolds number, while those of the streaming sausage and kink modes do not strongly depend on the Reynolds number. The wavelengths of these unstable modes are of the order of the thickness of plasma sheet, which behavior is almost same as the standard tearing mode with no bulk flow. Roughly speaking the growth rates of three modes become faster than the standard tearing mode. The situation of the plasma sheet with the bulk flow can be realized in the reconnection exhaust with the Alfvenic reconnection jet, and the unstable modes may be regarded as one of the generation processes of Alfvenic turbulence in the plasma sheet during magnetic reconnection.
Growing 'Alfvenic' modes in the upstream region of Saturn
NASA Technical Reports Server (NTRS)
Orlowski, D. S.; Russell, C. T.; Krauss-Varban, D.; Omidi, N.
1994-01-01
Recent studies of low-frequency electromagnetic waves upstream of the Saturn bow shock have shown that these waves, in contrast to those at Earth, are observed not in one, but in at least two, distinct frequency bands. The results of wave mode identification based on the Hall-magnetohydrodynamic (MHD) model of plasma and observed wave polarization suggested that these waves propagate in the high beta intermediate mode. However, the underlying instability was not unambiguously determined. In the present paper we use the full electromagnetic dispersion relation derived from linear Vlasov theory in order to examine which of the plasma modes, with observed properties, are unstable in an isotropic Maxwellian plasma in the presence of backstreaming proton beams consistent with Voyager 2 observations at Saturn. As a result we find that the unstable 'Alfvenic' beam mode, as well as resonant and non-resonant fast magnetosonic modes have properties consistent with the data. Moreover, we find that in contrast to the Earth's upstream waves, at Saturn no 'kinetic' normal mode can account for the observed magnetic polarization.
Podestà, M.; Gorelenkov, N. N.; White, R. B.; Fredrickson, E. D.; Gerhardt, S. P.; Kramer, G. J.
2013-08-15
A second Neutral Beam (NB) injection line is being installed on the NSTX Upgrade device, resulting in six NB sources with different tangency radii that will be available for heating and current drive. This work explores the properties of instabilities in the frequency range of the Toroidal Alfvén Eigenmode (TAE) for NSTX-U scenarios with various NB injection geometries, from more perpendicular to more tangential, and with increased toroidal magnetic field with respect to previous NSTX scenarios. Predictions are based on analysis through the ideal MHD code NOVA-K. For the scenarios considered in this work, modifications of the Alfvén continuum result in a frequency up-shift and a broadening of the radial mode structure. The latter effect may have consequences for fast ion transport and loss. Preliminary stability considerations indicate that TAEs are potentially unstable with ion Landau damping representing the dominant damping mechanism.
Alfven wave-driving mechanism of late-type stellar wind
NASA Astrophysics Data System (ADS)
Yong, Zheng; Li, Xiao-Qing
1990-05-01
Because late-type stellar wind has low temperature, massive outflow, and high terminal velocity, theoretical models of thermal pressure or radiation pressure cannot explain the acceleration of late-type stellar wind. Energy damping of Alfven wave in stellar winds is small, and Alfven wave is perhaps the driving force of late-type stellar wind if the wave energy-flux is large enough. After theoretical analysis and numerical calculation, various velocity distributions are obtained by taking various wave energy-fluxes in reliable range, the terminal velocities accord with observations. If late-type stellar winds are driven by thermal pressure, the temperature is higher that acceptable. The results of Alfven wave driving winds also indicate that massive stellar winds need large energy flux and acceleration is closely related with gravity. In discussion, it is thought that Alfven wave accelerating late-type stellar winds is feasible and the initial energy-flux, damping of Alfven wave in stellar winds need further study.
Energy Budget of Alfven Wave Interactions with the Auroral Acceleration Region
NASA Astrophysics Data System (ADS)
Pilipenko, V.; Fedorov, E.; Engebretson, M. J.
2003-12-01
Recent Polar satellite observations of intense Alfven ULF bursts over auroral arcs prompted researchers to suggest that ULF wave activity does provide energy to the auroral arc intensification. However, to provide physical grounds for this suggestion, it is important to know possible bounds on the rate of the ULF wave energy transfer into electron acceleration. To estimate the power dissipated in the ionosphere and that transferred into electron acceleration, we consider the interaction of magnetospheric Alfven waves with the auroral ionosphere, comprising the auroral acceleration region (AAR). The AAR is characterized by a mirror resistance to the field-aligned upward current that can provide the potential drop and the acceleration of electrons. Analytical treatment of the interaction of Alfven waves with the combined magnetosphere-AAR-topside ionosphere-E-layer system has been made within the "thin" AAR approximation, which is valid for small-scale disturbances. The input of Alfven waves into the energy balance of the AAR depends critically on their transverse scale. Only waves with scales comparable to the Alfven transit scale, that is kperpendicular to λ A ˜= 1, will provide energy into electron acceleration. This process is expected to be more effective above a conductive ionosphere. These theoretical predictions could be verified with the multi-satellite measurements in the Cluster-2 mission.
Transmission of Alfven waves through the earth's bow shock - Theory and observation
NASA Technical Reports Server (NTRS)
Hassam, A. B.
1978-01-01
From both theoretical and experimental bases, the transmission of Alfven waves through the bow shock is investigated. The theory of Alfven wave transmission through fast MHD shocks is extended to all cases of incident wave vectors. Particular consideration is given to Alfven waves propagating parallel to the ambient magnetic field with field perturbations polarized in the plane formed by the ambient magnetic field and the shock normal. An analysis is also made of magnetic field and plasma data from Explorer-35 in the vicinity of the bow shock. It is suggested that hydromagnetic waves are present in all of the 14 shock crossings studied, and that in upstream regions of at least 6 crossings, predominantly Alfvenic fluctuations exist. Average amplitudes of these fluctuations are measured on either side of the shock and the enhancement is measured by comparing their levels. Theoretical and experimental findings are compared and the apparent discrepancy in amplification factors may be explained by the strong damping of any transmitted magnetoacoustic modes downstream with relatively little damping of any transmitted Alfven waves.
Stellar winds with non-WKB Alfven waves 1: Wind models for solar coronal conditions
NASA Astrophysics Data System (ADS)
MacGregor, K. B.; Charbonneau, P.
1994-07-01
We have constructed numerical models for stationary, wind-type outflows that include treatment of the force produced by propagating Alfven waves. We make no assumptions regarding the relative sizes of the wavelengths of such disturbances and the scale lengths that characterize the variation of the physical properties of the expanding stellar atmosphere. Consequently, our models take account the process of Alfven wave reflection, and provide for dynamical effects arising from the simultaneous presence of outward and inward traveling waves in the wind. For physical conditions like those prevailing in the outer solar corona and wind, we find that even relatively high frequency, short wavelength waves can suffer some reflection from the gradient in Alfven speed at the vase of the flow. Among the consequences of the interaction between outward and inward directed perturbations in the sub-Alfvenic portion of the wind is a reduction in the magnitude of the time-averaged wave force relative to its value in the Wentzel-Kramer-Brillouin (WKB) (i.e., short-wavelenght) limit. As a result, the flow velocities of our models interior to the Alfven radius are smaller than those of corresponding WKB models. For models containing very low frequency, long wavelength waves, a substantial amount of wave reflection can also take place in the super-Alvenic portion of the wind. The resulting modifications to the spatial dependences of the eave magnetic and velocity amplitudes can lead to a wave force whose magnitude at large distances exceeds that of an equivalent WKB solution.
NASA Technical Reports Server (NTRS)
Choueiri, E. Y.; Kelly, A. J.; Jahn, R. G.
1985-01-01
The role of Alfven's critical ionization velocity in the performance of the self-field MPD thruster has been investigated. The existence of a well defined characteristic velocity can be attributed to an ionization process involving the production of a population of suprathermal electrons by an electrostatic instability. It is shown that for the MPD thruster plasma, suprathermalization of electrons via this electrostatic instability can only happen if ions are initially accelerated to velocities larger than the Alfven critical ionization velocity. When this occurs the mechanism will be initiated and the ions decelerated to velocities near the critical velocity. This mechanism ceases to be limiting when all neutrals are ionized. A model of MPD thruster terminal behavior, incorporating Alfven's hypothesis, is presented. Experiments with three different propellants reveal that operation at values of the current squared to total mass flow ratio corresponding to the Alfven critical velocity is marked by a transition wherein low frequency voltage oscillations and a notable change in the voltage-current dependence occurs. One major result of this study is the demonstration that the Alfven critical velocity is not a fundamental limitation on MPD exhaust velocity.
ION HEATING BY A SPECTRUM OF OBLIQUELY PROPAGATING LOW-FREQUENCY ALFVEN WAVES
Lu Quanming; Chen Liu
2009-10-10
Ion stochastic heating by a monochromatic Alfven wave, which propagates obliquely to the background magnetic field, has been studied by Chen et al. It is shown that ions can be resonantly heated at frequencies a fraction of the ion cyclotron frequency when the wave amplitude is sufficiently large. In this paper, the monochromatic wave is extended to a spectrum of left-hand polarized Alfven waves. When the amplitude of the waves is small, the components of the ion velocity have several distinct frequencies, and their motions are quasi-periodic. However, when the amplitude of the waves is sufficiently large, the components of the ion velocity have a spectrum of continuous frequencies near the ion cyclotron frequency due to the nonlinear coupling between the Alfven waves and the ion gyromotion, and the ion motions are stochastic. Compared with the case of a monochromatic Alfven wave, the threshold of the ion stochastic heating by a spectrum of Alfven waves is much lower. Even when their frequencies are only several percent of the ion cyclotron frequency, the ions can also be stochastically heated. The relevance of this heating mechanism to solar corona is also discussed.
HEATING OF THE SOLAR CHROMOSPHERE AND CORONA BY ALFVEN WAVE TURBULENCE
Van Ballegooijen, A. A.; Cranmer, S. R.; DeLuca, E. E.; Asgari-Targhi, M.
2011-07-20
A three-dimensional magnetohydrodynamic (MHD) model for the propagation and dissipation of Alfven waves in a coronal loop is developed. The model includes the lower atmospheres at the two ends of the loop. The waves originate on small spatial scales (less than 100 km) inside the kilogauss flux elements in the photosphere. The model describes the nonlinear interactions between Alfven waves using the reduced MHD approximation. The increase of Alfven speed with height in the chromosphere and transition region (TR) causes strong wave reflection, which leads to counter-propagating waves and turbulence in the photospheric and chromospheric parts of the flux tube. Part of the wave energy is transmitted through the TR and produces turbulence in the corona. We find that the hot coronal loops typically found in active regions can be explained in terms of Alfven wave turbulence, provided that the small-scale footpoint motions have velocities of 1-2 km s{sup -1} and timescales of 60-200 s. The heating rate per unit volume in the chromosphere is two to three orders of magnitude larger than that in the corona. We construct a series of models with different values of the model parameters, and find that the coronal heating rate increases with coronal field strength and decreases with loop length. We conclude that coronal loops and the underlying chromosphere may both be heated by Alfvenic turbulence.
Li, Dong; Bi, Chao; Zhao, Jianlin
2016-04-20
We present the evolution of the eigenmode frequency spectrum in a nonplanar ring resonator based on the Jones matrix and the Fresnel-Kirchhoff diffraction integral. Taking the modes TEM_{(q+1)01} and TEM_{q10} with different polarization states as examples, we numerically derive the frequency difference between them versus the folding angles of the resonator by considering the polarization and the light field distribution of the eigenmodes synchronously. It can be found that the extreme values of frequency difference between TEM_{(q+1)01} and TEM_{q10} are particularly affected by the polarization states of the eigenmode, and the locations of these consecutive extreme values correspond to the total image rotation angle with values of the integer multiple of 90°. Moreover, the influence of the resonator structure on the frequency difference of eigenmodes with the identical polarization state is also analyzed. The results prove that the frequency difference between the fundamental mode and higher order modes declines with the increase of the spherical mirrors' radius of curvature but increases with the augmentation of the resonator's total length. These interesting findings are important for the mode selection in high-accuracy ring laser gyroscopes with nonplanar structure by modulating the polarization states and the light field distribution of the eigenmodes to control the frequency difference between them. PMID:27140100
NASA Astrophysics Data System (ADS)
Van Zeeland, M. A.; Heidbrink, W. W.; Nazikian, R.; Austin, M. E.; Cheng, C. Z.; Chu, M. S.; Gorelenkov, N. N.; Holcomb, C. T.; Hyatt, A. W.; Kramer, G. J.; Lohr, J.; McKee, G. R.; Petty, C. C.; Prater, R.; Solomon, W. M.; Spong, D. A.
2009-06-01
Neutral beam injection into reversed magnetic shear DIII-D plasmas produces a variety of Alfvénic activity including toroidicity and ellipticity induced Alfvén eigenmodes (TAE/EAE, respectively) and reversed shear Alfvén eigenmodes (RSAE) as well as their spatial coupling. These modes are studied during the discharge current ramp phase when incomplete current penetration results in a high central safety factor and strong drive due to multiple higher order resonances. It is found that ideal MHD modelling of eigenmode spectral evolution, coupling and structure are in excellent agreement with experimental measurements. It is also found that higher radial envelope harmonic RSAEs are clearly observed and agree with modelling. Some discrepancies with modelling such as that due to up/down eigenmode asymmetries are also pointed out. Concomitant with the Alfvénic activity, fast ion (FIDA) spectroscopy shows large reductions in the central fast ion profile, the degree of which depends on the Alfvén eigenmode amplitude. Interestingly, localized electron cyclotron heating (ECH) near the mode location stabilizes RSAE activity and results in significantly improved fast ion confinement relative to discharges with ECH deposition on axis. In these discharges, RSAE activity is suppressed when ECH is deposited near the radius of the shear reversal point and enhanced with deposition near the axis. The sensitivity of this effect to deposition power and current drive phasing as well as ECH modulation are presented.
Calculation of continuum damping of Alfvén eigenmodes in tokamak and stellarator equilibria
NASA Astrophysics Data System (ADS)
Bowden, G. W.; Hole, M. J.; Könies, A.
2015-09-01
In an ideal magnetohydrodynamic (MHD) plasma, shear Alfvén eigenmodes may experience dissipationless damping due to resonant interaction with the shear Alfvén continuum. This continuum damping can make a significant contribution to the overall growth/decay rate of shear Alfvén eigenmodes, with consequent implications for fast ion transport. One method for calculating continuum damping is to solve the MHD eigenvalue problem over a suitable contour in the complex plane, thereby satisfying the causality condition. Such an approach can be implemented in three-dimensional ideal MHD codes which use the Galerkin method. Analytic functions can be fitted to numerical data for equilibrium quantities in order to determine the value of these quantities along the complex contour. This approach requires less resolution than the established technique of calculating damping as resistivity vanishes and is thus more computationally efficient. The complex contour method has been applied to the three-dimensional finite element ideal MHD Code for Kinetic Alfvén waves. In this paper, we discuss the application of the complex contour technique to calculate the continuum damping of global modes in tokamak as well as torsatron, W7-X and H-1NF stellarator cases. To the authors' knowledge, these stellarator calculations represent the first calculation of continuum damping for eigenmodes in fully three-dimensional equilibria. The continuum damping of global modes in W7-X and H-1NF stellarator configurations investigated is found to depend sensitively on coupling to numerous poloidal and toroidal harmonics.
Calculation of continuum damping of Alfvén eigenmodes in tokamak and stellarator equilibria
Bowden, G. W.; Hole, M. J.; Könies, A.
2015-09-15
In an ideal magnetohydrodynamic (MHD) plasma, shear Alfvén eigenmodes may experience dissipationless damping due to resonant interaction with the shear Alfvén continuum. This continuum damping can make a significant contribution to the overall growth/decay rate of shear Alfvén eigenmodes, with consequent implications for fast ion transport. One method for calculating continuum damping is to solve the MHD eigenvalue problem over a suitable contour in the complex plane, thereby satisfying the causality condition. Such an approach can be implemented in three-dimensional ideal MHD codes which use the Galerkin method. Analytic functions can be fitted to numerical data for equilibrium quantities in order to determine the value of these quantities along the complex contour. This approach requires less resolution than the established technique of calculating damping as resistivity vanishes and is thus more computationally efficient. The complex contour method has been applied to the three-dimensional finite element ideal MHD Code for Kinetic Alfvén waves. In this paper, we discuss the application of the complex contour technique to calculate the continuum damping of global modes in tokamak as well as torsatron, W7-X and H-1NF stellarator cases. To the authors' knowledge, these stellarator calculations represent the first calculation of continuum damping for eigenmodes in fully three-dimensional equilibria. The continuum damping of global modes in W7-X and H-1NF stellarator configurations investigated is found to depend sensitively on coupling to numerous poloidal and toroidal harmonics.
Gyrokinetic particle simulation of fast-electron driven beta-induced Aflvén eigenmode
NASA Astrophysics Data System (ADS)
Cheng, Junyi; Zhang, Wenlu; Lin, Zhihong; Holod, Ihor; Li, Ding; Chen, Yang; Cao, Jintao
2016-05-01
The fast-electron driven beta-induced Alfvén eigenmode (e-BAE) in toroidal plasmas is investigated for the first time using global gyrokinetic particle simulations, where the fast electron is described by the drift kinetic equation. The simulation shows that the e-BAE propagates in the fast electron diamagnetic direction and its polarization is close to an ideal MHD mode. The phase space structure shows that only the fast electron processional resonance is responsible for the e-BAE excitations while fast-ion driven BAE can be excited through all the channels, including transit, bounce, and processional resonance.
NASA Astrophysics Data System (ADS)
Chardon, Gilles; Daudet, Laurent
2013-11-01
This paper extends the method of particular solutions (MPS) to the computation of eigenfrequencies and eigenmodes of thin plates, in the framework of the Kirchhoff-Love plate theory. Specific approximation schemes are developed, with plane waves (MPS-PW) or Fourier-Bessel functions (MPS-FB). This framework also requires a suitable formulation of the boundary conditions. Numerical tests, on two plates with various boundary conditions, demonstrate that the proposed approach provides competitive results with standard numerical schemes such as the finite element method, at reduced complexity, and with large flexibility in the implementation choices.
Pukhova, Valentina; Banfi, Francesco; Ferrini, Gabriele
2015-05-01
The transient eigenmode structure of an interacting cantilever during a single impact on different surfaces evidences the excitation of higher flexural modes and low frequency oscillations. The frequency shift of the fundamental mode after the tip comes into contact with the sample surface allows calculating the tip-sample interaction stiffness and evidences the role of capillary condensation and surface wettability on the cantilever dynamics. Wavelet transforms are used to trace the origin of spectral features in the cantilever spectra and calculate force gradients of the tip-sample interaction. PMID:25837684
Low-Lying Dirac Eigenmodes, Topological Charge Fluctuations and the Instanton Liquid Model
I. Horvath; S.J. Dong; T. Draper; F.X. Lee; H.B. Thacker; J.B. Zhang
2002-05-01
The local structure of low-lying eigenmodes of the overlap Dirac operator is studied. It is found that these modes cannot be described as linear combinations of 't Hooft ''would-be'' zeromodes associated with instanton excitations that underly the Instanton Liquid Model. This implies that the instanton liquid scenario for spontaneous chiral symmetry breaking in QCD is not accurate. More generally, our data suggests that the vacuum fluctuations of topological charge are not effectively dominated by localized lumps of unit charge with which the topological ''would-be'' zeromodes could be associated.
Nonlinear dynamics of beta-induced Alfvén eigenmode driven by energetic particles.
Wang, X; Briguglio, S; Chen, L; Di Troia, C; Fogaccia, G; Vlad, G; Zonca, F
2012-10-01
Nonlinear saturation of a beta-induced Alfvén eigenmode, driven by slowing down energetic particles via transit resonance, is investigated by the nonlinear hybrid magnetohyrodynamic gyrokinetic code. Saturation is characterized by frequency chirping and symmetry breaking between co- and counter-passing particles, which can be understood as the evidence of resonance detuning. The scaling of the saturation amplitude with the growth rate is also demonstrated to be consistent with radial resonance detuning due to the radial nonuniformity and mode structure. PMID:23214643
Eigenmode Analysis of Boundary Conditions for One-Dimensional Preconditioned Euler Equations
NASA Technical Reports Server (NTRS)
Darmofal, David L.
1998-01-01
An analysis of the effect of local preconditioning on boundary conditions for the subsonic, one-dimensional Euler equations is presented. Decay rates for the eigenmodes of the initial boundary value problem are determined for different boundary conditions. Riemann invariant boundary conditions based on the unpreconditioned Euler equations are shown to be reflective with preconditioning, and, at low Mach numbers, disturbances do not decay. Other boundary conditions are investigated which are non-reflective with preconditioning and numerical results are presented confirming the analysis.
Phase slips and dissipation of Alfvenic intermediate shocks and solitons
Laveder, D.; Passot, T.; Sulem, P. L.
2012-09-15
The time evolution of a rotational discontinuity, characterized by a change of the magnetic-field direction by an angle {Delta}{theta} such that {pi}<|{Delta}{theta}|<2{pi} and no amplitude variation, is considered in the framework of asymptotic models that, through reductive perturbative expansions, isolate the dynamics of parallel or quasi-parallel Alfven waves. In the presence of viscous and Ohmic dissipation, and for a zero or sufficiently weak dispersion (originating from the Hall effect), an intermediate shock rapidly forms, steepens and undergoes reconnection through a quasi gradient collapse, leading to a reduction of |{Delta}{theta}| by an amount of 2{pi}, which can be viewed as the breaking of a topological constraint. Afterwards, as |{Delta}{theta}|<{pi}, the intermediate shock broadens and slowly dissipates. In the case of a phase jump |{Delta}{theta}|>3{pi}, which corresponds to a wave train limited on both sides by uniform fields, a sequence of such reconnection processes takes place. Differently, in the presence of a strong enough dispersion, the rotational discontinuity evolves, depending on the sign of {Delta}{theta}, to a dark or bright soliton displaying a 2{pi} phase variation. The latter is then eliminated, directly by reconnection in the case of a dark soliton, or through a more complex process involving a quasi amplitude collapse in that of a bright soliton. Afterwards, the resulting structure is progressively damped. For a prescribed initial rotational discontinuity, both quasi gradient and amplitude collapses lead to a sizeable energy decay that in the collisional regime is independent of the diffusion coefficient {eta} but requires a time scaling like 1/{eta}. In the non-collisional regime where dissipation originates from Landau resonance, the amount of dissipated energy during the event is independent of the plasma {beta}, but the process becomes slower for smaller {beta}.
NASA Astrophysics Data System (ADS)
Safaei Mohamadabadi, Hossein
Increasing electrification of the economy while decarbonizing the electricity supply is among the most effective strategies for cutting greenhouse gas (GHG) emissions in order to abate climate change. This thesis offers insights into the role of bulk energy storage (BES) systems to cut GHG emissions from the electricity sector. Wind and solar energies can supply large volumes of low-carbon electricity. Nevertheless, large penetration of these resources poses serious reliability concerns to the grid, mainly because of their intermittency. This thesis evaluates the performance of BES systems - especially compressed air energy storage (CAES) technology - for integration of wind energy from engineering and economic aspects. Analytical thermodynamic analysis of Distributed CAES (D-CAES) and Adiabatic CAES (A-CAES) suggest high roundtrip storage efficiencies ( 80% and 70%) compared to conventional CAES ( 50%). Using hydrogen to fuel CAES plants - instead of natural gas - yields a low overall efficiency ( 35%), despite its negligible GHG emissions. The techno-economic study of D-CAES shows that exporting compression heat to low-temperature loads (e.g. space heating) can enhance both the economic and emissions performance of compressed air storage plants. A case study for Alberta, Canada reveals that the abatement cost of replacing a conventional CAES with D-CAES plant practicing electricity arbitrage can be negative (-$40 per tCO2e, when the heat load is 50 km away from the air storage site). A green-field simulation finds that reducing the capital cost of BES - even drastically below current levels - does not substantially impact the cost of low-carbon electricity. At a 70% reduction in the GHG emissions intensity of the grid, gas turbines remain three times more cost-efficient in managing the wind variability compared to BES (in the best case and with a 15-minute resolution). Wind and solar thus, do not need to wait for availability of cheap BES systems to cost
Energetic particle destabilization of shear Alfven waves in stellarators and tokamaks
Spong, D.A.; Carreras, B.A.; Hedrick, C.L.; Leboeuf, J.N.; Weller, A.
1994-12-31
An important issue for ignited devices is the resonant destabilization of shear Alfven waves by energetic populations. These instabilities have been observed in a variety of toroidal plasma experiments in recent years, including: beam-destabilized toroidal Alfven instabilities (TAE) in low magnetic field tokamaks, ICRF destabilized TAE`s in higher field tokamaks, and global Alfven instabilities (GAE) in low shear stellarators. In addition, excitation and study of these modes is a significant goal of the TFIR-DT program and a component of the ITER physics tasks. The authors have developed a gyrofluid model which includes the wave-particle resonances necessary to excite such instabilities. The TAE linear mode structure is calculated nonperturbatively, including many of the relevant damping mechanisms, such as: continuum damping, non-ideal effects (ion FLR and electron collisionality), and ion/electron Landau damping. This model has been applied to both linear and nonlinear regimes for a range of experimental cases using measured profiles.
NASA Technical Reports Server (NTRS)
Hollweg, Joseph V.; Esser, R.; Jayanti, V.
1993-01-01
The parametric instability of a circularly polarized Alfven wave propagating along the background magnetic field are considered, with emphasis on the effects of a second ion species, He(2+), which drifts relative to the protons. Even though its abundance is small, the He(2+) modifies the dispersion relation of the 'pump' Alfven wave and introduces a new sound wave (alpha sound) in addition to the usual sound wave carried primarily by the electrons and protons. Instabilities which are close to the He(2+) gyroresonance are found. This may provide a means of directly transferring Alfven wave energy to the alpha particles, if the alphas are able to resonantly extract energy from the unstable waves without quenching the instability altogether. Instabilities which are close to the alpha particle sound speed are also found.
Klein-Gordon equation and reflection of Alfven waves in nonuniform media
NASA Technical Reports Server (NTRS)
Musielak, Z. E.; Fontenla, J. M.; Moore, R. L.
1992-01-01
A new analytical approach is presented for assessing the reflection of linear Alfven waves in smoothly nonuniform media. The general one-dimensional case in Cartesian coordinates is treated. It is shown that the wave equations, upon transformation into the form of the Klein-Gordon equation, display a local critical frequency for reflection. At any location in the medium, reflection becomes strong as the wave frequency descends past this characteristic frequency set by the local nonuniformity of the medium. This critical frequecy is given by the transformation as an explicit function of the Alfven velocity and its first and second derivatives, and hence as an explicit spatial function. The transformation thus directly yields, without solution of the wave equations, the location in the medium at which an Alfven wave of any given frequency becomes strongly reflected and has its propagation practically cut off.
Electromagnetic fluctuation spectrum associated with the drift Alfven-cyclotron instability
Rha, Kicheol; Ryu, Chang-Mo; Yoon, Peter H.
2012-07-15
The present paper investigates the electromagnetic fluctuation spectrum associated with the drift Alfven-cyclotron instability by means of a two-dimensional particle-in-cell simulation, which may be plausibly associated with a current disruption event. The current disruption event shows localized high-amplitude electromagnetic fluctuations. In recent theories, these fluctuation characteristics are shown to correspond to the drift Alfven-cyclotron instability. A simulation is carried out to clarify this instability. The simulation shows that the drift Alfven-cyclotron instabilities are excited in two frequency regimes, a relatively low frequency mode propagating in a quasi-perpendicular direction while the second high-frequency branch propagating in a predominantly parallel propagation direction, consistent with observations as well as with a recent theory.
NASA Astrophysics Data System (ADS)
Hamabata, Hiromitsu; Namikawa, Tomikazu
1988-02-01
Using first-order smoothing theory, Fourier analysis and perturbation methods, a new equation is derived governing the evolution of the spectrum tensor (including the energy and helicity spectrum functions) of the random velocity field as well as the ponderomotive and mean electromotive forces generated by random Alfven waves in a plasma with weak magnetic diffusion. The ponderomotive and mean electromotive forces are expressed as series involving spatial derivatives of mean magnetic and velocity fields whose coefficients are associated with the helicity spectrum function of the random velocity field. The effect of microscale random Alfven waves, through ponderomotive and mean electromotive forces generated by them, on the propagation of large-scale Alfven waves is also investigated by solving the mean-field equations, including the transport equation of the helicity spectrum function.
NASA Technical Reports Server (NTRS)
Lichtenstein, B. R.; Sonett, C. P.
1979-01-01
The paper shows that the experimentally observed close alignment of magnetic field minimum variance direction with the average magnetic field for Alfven waves in the solar wind is consistent with theoretically predicted properties of plane large amplitude Alfven waves in the MHD approximation. The theoretical properties of these Alfven waves constrain the time averaged magnetic field to cluster around the direction of minimum variance, which is aligned with the wave normal. Thus, spacecraft magnetometer observations in the solar wind of minimum variance directions strongly peaked about the average magnetic field direction are consistent with plane large amplitude Alfven waves which have wave normals aligned with the directions of minimum variance. This does not imply that geometrical hydromagnetic calculations for Alfven wave propagation direction in the solar wind are incorrect, but there is a discrepancy between geometrical hydromagnetics theory and observations that IMF minimum variance directions tend to be aligned with the ideal Parker spiral instead of the radial direction.
The effect of random Alfven waves on the propagation of hydromagnetic waves in a finite-beta plasma
NASA Technical Reports Server (NTRS)
Hamabata, Hiromitsu; Namikawa, Tomikazu
1990-01-01
Using first-order smoothing theory, Fourier analysis and perturbation methods, the evolution equation of the wave spectrum as well as the nonlinear forces generated by random Alfven waves in a finite-beta plasma with phenomenological Landau-damping effects are obtained. The effect of microscale random Alfven waves on the propagation of large-scale hydromagnetic waves is also investigated by solving the mean-field equations. It is shown that parallel-propagating random Alfven waves are modulationally stable and that obliquely propagating random Alfven waves can be modulationally unstable when the energy of random waves is converted to slow magnetoacoustic waves that can be Landau-damped, providing a dissipation mechanism for the Alfven waves.
Generation of Alfven waves by high power pulse at the electron plasma frequency
NASA Astrophysics Data System (ADS)
van Compernolle, Bart Gilbert
The physics of the interaction between plasmas and high power waves with frequencies in the electron plasma frequency range is of importance in many areas of space and plasma physics. A great deal of laboratory research has been done on the interaction of microwaves in a density gradient when o = ope in unmagnetized plasmas. [SWK74, WS78, KSW74]. Extensive studies of HF-ionospheric modifications have been performed [Fej79] as evidenced by experiments at Arecibo [HMD92, BHK86, CDF92, FGI85], at the HAARP facility [RKK98] in Alaska, at the EISCAT observatory in Norway [IHR99], and at SURA in Russia [FKS99]. This dissertation focusses on the interaction with a fully magnetized plasma, capable of supporting Alfven waves. The experiment is performed in the upgraded LArge Plasma Device (LAPD) at UCLA [GPL91] (Helium, n = 1012 cm-3, B = 1 kG - 2.5 kG). A number of experiments have been done at LAPD using antennas, skin depth scale currents and laser produced plasmas to generate Alfven waves [LGM99, GVL97a, GVL97b, VGV01]. In this work a high power pulse 6th, frequency in the electron plasma frequency range is launched into the radial density gradient, perpendicular to the background magnetic field. The microwave pulses last on the order of one ion gyro period and has a maximum power of |E|2/ nT ≃ .5 in the afterglow. The absorption of these waves leads to a pulse of field aligned suprathermal electrons. This electron current pulse then launches with Alfven wave with o ≤ o ci. The experiment was performed bath in ordinary node (O-mode) and extraordinary (X-mode), for different background magnetic fields B0, different temperatures (afterglow vs discharge) and different power levels of the incoming microwaves. It was found that the Alfven wave generation can be explained by Cherenkov radiation of Alfven waves by the suprathermal electron pulse. Theoretical solutions for the perturbed magnetic field due to a pulse of field aligned electrons were obtained, and shown to be
Arbitrary amplitude double layers in warm dust kinetic Alfven wave plasmas
Gogoi, Runmoni; Devi, Nirupama
2008-07-15
Large amplitude electrostatic structures associated with low-frequency dust kinetic Alfvenic waves are investigated under the pressure (temperature) gradient indicative of dust dynamics. The set of equations governing the dust dynamics, Boltzmann electrons, ions and Maxwell's equation have been reduced to a single equation known as the Sagdeev potential equation. Parameter ranges for the existence of arbitrary amplitude double layers are observed. Exact analytical expressions for the energy integral is obtained and computed numerically through which sub-Alfvenic arbitrary amplitude rarefactive double layers are found to exist.
Method of description of the Alfven and magnetosonic branches of inhomogeneous plasma oscillations
Klimushkin, D.Yu.
1994-12-31
A method of description of the Alfven and magnetosonic branches of the 3-D inhomogeneous plasma oscillations is proposed. In the absence of kinetic effects, the electric field of the MHD-wave is two-dimensional and can be split into potential and eddy components. The first component is identified with the Alfven wave, and the second one with the FMS-wave. It was shown that this approach can be applied to analyze the Earth`s magnetosphere oscillations (geomagnetic pulsations). 21 refs.
Global particle-in-cell simulations of plasma pressure effects on Alfvenic modes
Mishchenko, Alexey; Koenies, Axel; Hatzky, Roman
2011-01-15
Global linear gyrokinetic particle-in-cell simulations of electromagnetic modes in realistic tokamak geometry are reported. The effect of plasma pressure on Alfvenic modes is studied. It is shown that the fast-particle pressure can considerably affect the shear Alfven wave continuum structure and hence the toroidicity-induced gap in the continuum. It is also found that the energetic ions can substantially reduce the growth rate of the ballooning modes (and perhaps completely stabilize them in a certain parameter range). Ballooning modes are found to be the dominant instabilities if the bulk-plasma pressure gradient is large enough.
Computer simulation of Alfven resonance in a cylindrical, axially bounded flux tube
NASA Technical Reports Server (NTRS)
Strauss, H. R.; Lawson, William S.
1989-01-01
The resonant absorption of Alfven waves in an axially bounded cylindrical flux tube is investigated in a dissipative MHD simulation. It is found that in an axially bounded flux tube, in contrast to an infinite periodic model, the resonant frequency is nearly independent of the poloidal component of the magnetic field. This is a consequence of the 'ballooning' structure of the resonant Alfven waves. The scaling with resistivity and viscosity of the width of the resonance layer, the dissipation rate, and the time for steady state absorption to occur, are all in agreement with theory.
The soliton transform and a possible application to nonlinear Alfven waves in space
NASA Technical Reports Server (NTRS)
Hada, T.; Hamilton, R. L.; Kennel, C. F.
1993-01-01
The inverse scattering transform (IST) based on the derivative nonlinear Schroedinger (DNLS) equation is applied to a complex time series of nonlinear Alfven wave data generated by numerical simulation. The IST describes the long-time evolution of quasi-parallel Alfven waves more efficiently than the Fourier transform, which is adapted to linear rather than nonlinear problems. When dissipation is added, so the conditions for the validity of the DNLS are not strictly satisfied, the IST continues to provide a compact description of the wavefield in terms of a small number of decaying envelope solitons.
A self-consistent theory of collective alpha particle losses induced by Alfvenic turbulence
Biglari, H.; Diamond, P.H.
1992-01-01
The nonlinear dynamics of kinetic Alfven waves, resonantly excited by energetic ions/alpha particles, is investigated. It is shown that {alpha}-particles govern both linear instability and nonlinear saturation dynamics, while the background MHD turbulence results only in a nonlinear real frequency shift. The most efficient saturation mechanism is found to be self-induced profile modification. Expressions for the fluctuation amplitudes and the {alpha}-particle radial flux are self-consistently derived. The work represents the first self-consistent, turbulent treatment of collective {alpha}-particle losses by Alfvenic fluctuations.
Basic principles approach for studying nonlinear Alfven wave-alpha particle dynamics
Berk, H.L.; Breizman, B.N.; Pekker, M.
1994-01-01
An analytical model and a numerical procedure are presented which give a kinetic nonlinear description of the Alfven-wave instabilities driven by the source of energetic particles in a plasma. The steady-state and bursting nonlinear scenarios predicted by the analytical theory are verified in the test numerical simulation of the bump-on-tail instability. A mathematical similarity between the bump-on-tail problem for plasma waves and the Alfven wave problem gives a guideline for the interpretation of the bursts in the wave energy and fast particle losses observed in the tokamak experiments with neutral beam injection.
Increasing productivity of the McAuto CAD/CAE system by user-specific applications programming
NASA Technical Reports Server (NTRS)
Plotrowski, S. M.; Vu, T. H.
1985-01-01
Significant improvements in the productivity of the McAuto Computer-Aided Design/Computer-Aided Engineering (CAD/CAE) system were achieved by applications programming using the system's own Graphics Interactive Programming language (GRIP) and the interface capabilities with the main computer on which the system resides. The GRIP programs for creating springs, bar charts, finite element model representations and aiding management planning are presented as examples.
NASA Astrophysics Data System (ADS)
Perov, D. V.; Rinkevich, A. B.; Demokritov, S. O.
2016-02-01
Ferromagnetic resonance (FMR) and spin-wave resonances (SWRs) have been studied in transmission of an electromagnetic wave through the plate of ferromagnetic metal and in reflection from the plate. The method of calculation of the resonance phenomena has been developed which allows one to study the influence of spin pinning conditions on the amplitudes of eigenmodes. The spatial distribution of eigenmodes is investigated under FMR, SWR and magnetic antiresonance conditions. The transmission coefficient of Fe19Ni81 permalloy films measured as a function of the magnetic field agrees well with the calculated values.
From micro- to nanomagnetic dots: evolution of the eigenmode spectrum on reducing the lateral size
NASA Astrophysics Data System (ADS)
Carlotti, G.; Gubbiotti, G.; Madami, M.; Tacchi, S.; Hartmann, F.; Emmerling, M.; Kamp, M.; Worschech, L.
2014-07-01
Brillouin light scattering experiments and micromagnetic simulations have been exploited to investigate the spectrum of thermally excited magnetic eigenmodes in 10 nm-thick elliptical Permalloy dots, when the longer axis D is scaled down from about 1000 to 100 nm. It is shown that for D larger than about 200 nm the characteristics of the spin-wave eigenmodes are dominated by dipolar energy, while for D in the range of about 100 to 200 nm exchange energy effects cause qualitative and quantitative differences in the spin-wave spectrum. In this ‘mesoscopic’ regime, the usual classification scheme, involving one fundamental mode with large average magnetization and many other modes collected in families with specific symmetries, no longer holds. Rather, one finds the simultaneous presence of two modes with ‘fundamental’ character, i.e. with a significant and comparable value of the average dynamical magnetization: the former is at larger frequency and has its maximum amplitude at the dot's centre, while the latter occurs at lower frequency and is localized at the dot's edges. Interestingly, the maximum intensity swaps from the higher frequency mode to the lower frequency one, just when the dot size is reduced from about 200 to 100 nm. This is relevant in view of the exploitation of nanodots for the design of nanomagnetic devices with lateral dimensions in the above interval, such as memory cells, logic gates, reading heads and spin-torque oscillators.
Hybrid simulation of toroidal Alfvén eigenmode on the National Spherical Torus Experiment
Liu, D.; Fu, G. Y.; Podestà, M.; Breslau, J. A.; Fredrickson, E. D.; Crocker, N. A.; Kubota, S.
2015-04-15
Energetic particle modes and Alfvén eigenmodes driven by super-Alfvénic fast ions are routinely observed in neutral beam heated plasmas on the National Spherical Torus eXperiment (NSTX). These modes can significantly impact fast ion transport and thus cause fast ion redistribution or loss. Self-consistent linear simulations of Toroidal Alfvén Eigenmodes (TAEs) in NSTX plasmas have been carried out with the kinetic/magnetohydrodynamic hybrid code M3D-K using experimental plasma parameters and profiles including plasma toroidal rotation. The simulations show that unstable TAEs with n=3,4, or 5 can be excited by the fast ions from neutral beam injection. The simulated mode frequency, mode radial structure, and phase shift are consistent with measurements from a multi-channel microwave reflectometer diagnostic. A sensitivity study on plasma toroidal rotation, safety factor q profile, and initial fast ion distribution is performed. The simulations show that rotation can have a significant destabilizing effect when the rotation is comparable or larger than the experimental level. The mode growth rate is sensitive to q profile and fast ion distribution. Although mode structure and peak position depend somewhat on q profile and plasma rotation, the variation of synthetic reflectometer response is within experimental uncertainty and it is not sensitive enough to see the difference clearly.
Nonlinear magnetohydrodynamic effects on Alfvén eigenmode evolution and zonal flow generation
NASA Astrophysics Data System (ADS)
Todo, Y.; Berk, H. L.; Breizman, B. N.
2010-08-01
Nonlinear magnetohydrodynamic (MHD) effects on Alfvén eigenmode evolution were investigated via hybrid simulations of an MHD fluid interacting with energetic particles. The investigation focused on the evolution of an n = 4 toroidal Alfvén eigenmode (TAE) which is destabilized by energetic particles in a tokamak. In addition to fully nonlinear code, a linear-MHD code was used for comparison. The only nonlinearity in that linear code is from the energetic-particle dynamics. No significant difference was found in the results of the two codes for low saturation levels, δB/B ~ 10-3. In contrast, when the TAE saturation level predicted by the linear code is δB/B ~ 10-2, the saturation amplitude in the fully nonlinear simulation was reduced by a factor of 2 due to the generation of zonal (n = 0) and higher-n (n >= 8) modes. This reduction is attributed to the increased dissipation arising from the nonlinearly generated modes. The fully nonlinear simulations also show that geodesic acoustic mode is excited by the MHD nonlinearity after the TAE mode saturation.
A simple apparatus for recording the eigenmodes in a microwave cavity
NASA Astrophysics Data System (ADS)
Schultz, K. D.; Koch, P. M.; Zelazny, S. A.
2000-06-01
Maier and Slaterfootnote L.C. Maier, Jr. and J.C. Slater, J. App. Phys. 23, 68 (1952) showed how to record the spatial distribution of cavity eigenmodes by measuring resonant frequency shifts caused by a small metal or dielectric bead. Using equipment available around a physics or EE department or that can be bought relatively cheaply, we have developed a simple ``bead-pull" apparatus suitable for student research projects or classroom demonstrations. We describe its use for azimuthally symmetric TM eigenmodes in a 2D cavity resonator. These are in the set of solutions of a scalar Helmholtz equation mathematically equivalent to the 2D Schrödinger equation. Therefore, the cavity corresponds to a quantal billiard, of interest for quantum chaos studies. We begin with an empty 2D circular cavity, which is easily solved analytically and used to test the method. Next we place inside a disk that partially fills the cavity radially and vertically. We compare measurements along a diameter to the results of calculations with public domain software (Superfish). Our apparatus exposes students to a variety of experimental techniques as well as research topics of high interest in contemporary physics.
Active and fast particle driven Alfvén eigenmodes in Alcator C-Moda)
NASA Astrophysics Data System (ADS)
Snipes, J. A.; Basse, N.; Boswell, C.; Edlund, E.; Fasoli, A.; Gorelenkov, N. N.; Granetz, R. S.; Lin, L.; Lin, Y.; Parker, R.; Porkolab, M.; Sears, J.; Sharapov, S.; Tang, V.; Wukitch, S.
2005-05-01
Alfvén eigenmodes (AEs) are studied to assess their stability in high density reactor relevant regimes where Ti≈Te and as a diagnostic tool. Stable AEs are excited with active magnetohydrodynamics antennas in the range of the expected AE frequency. Toroidal Alfvén eigenmode (TAE) damping rates between 0.5%<γ/ω<4.5% have been observed in diverted and limited Ohmic plasmas. Unstable AEs are excited with a fast ion tail driven by H minority ion cyclotron radio frequency (ICRF) heating with electron densities in the range of n¯e=0.5-2×1020m-3. Energetic particle modes or TAEs have been observed to decrease in frequency and mode number with time up to a large sawtooth collapse, indicating the role fast particles play in stabilizing sawteeth. In the current rise phase, unstable modes with frequencies that increase rapidly with time are observed with magnetic pick-up coils at the wall and phase contrast imaging density fluctuation measurements in the core. Modeling of these modes constrains the calculated safety factor profile to be very flat or with slightly reversed shear. AEs are found to be more stable for an inboard than for central or outboard ICRF resonances in qualitative agreement with modeling.
Itasse, Maxime Brazier, Jean-Philippe Léon, Olivier Casalis, Grégoire
2015-08-15
Nonlinear evolution of disturbances in an axisymmetric, high subsonic, high Reynolds number hot jet with forced eigenmodes is studied using the Parabolized Stability Equations (PSE) approach to understand how modes interact with one another. Both frequency and azimuthal harmonic interactions are analyzed by setting up one or two modes at higher initial amplitudes and various phases. While single mode excitation leads to harmonic growth and jet noise amplification, controlling the evolution of a specific mode has been made possible by forcing two modes (m{sub 1}, n{sub 1}), (m{sub 2}, n{sub 2}), such that the difference in azimuth and in frequency matches the desired “target” mode (m{sub 1} − m{sub 2}, n{sub 1} − n{sub 2}). A careful setup of the initial amplitudes and phases of the forced modes, defined as the “killer” modes, has allowed the minimizing of the initially dominant instability in the near pressure field, as well as its estimated radiated noise with a 15 dB loss. Although an increase of the overall sound pressure has been found in the range of azimuth and frequency analyzed, the present paper reveals the possibility to make the initially dominant instability ineffective acoustically using nonlinear interactions with forced eigenmodes.
Holographic modal analysis for the separation of narrow-spaced eigenmodes
NASA Astrophysics Data System (ADS)
Klingele, Hermann; Steinbichler, Hans; Freymann, Raymond; Honsberg, Wolfram; Haberstok, Carsten
1996-08-01
The automotive industry has particular interest in obtaining modal models of panel-like structures in the higher frequency range where the accuracy of FE-models normally is not longer sufficient to predict the dynamic response of a car body structure to a given operational excitation. Experimental modal analysis can fill this gap. However, the sensors which are currently used for the acquisition of vibrational data (accelerometers, laser vibrometer) are limited in spatial resolution and therefore higher-order panel modes are hard to be investigated. Holographic interferometry is widely used for qualitative and quantitative measurements of the mode shapes of dynamic systems, where its high spatial resolution outperforms any other kind of vibrational dynamic sensor. The limitations of holography with respect to the sampling rate can be overcome in the context of modal analysis by using stepped sine testing. A large number of holograms is then automatically recorded and evaluated. First results on a test structure which exhibits narrow-spaced eigenmodes are shown using this kind of measurement setup with a high frequency resolution. The dense vibration data enables the modal analysis software to separate the eigenmodes.
Spin wave eigenmodes in single and coupled sub-150 nm rectangular permalloy dots
Carlotti, G. Madami, M.; Tacchi, S.; Gubbiotti, G.; Dey, H.; Csaba, G.; Porod, W.
2015-05-07
We present the results of a Brillouin light scattering investigation of thermally excited spin wave eigenmodes in square arrays of either isolated rectangular dots of permalloy or twins of dipolarly coupled elements, placed side-by-side or head-to-tail. The nanodots, fabricated by e-beam lithography and lift-off, are 20 nm thick and have the major size D in the range between 90 nm and 150 nm. The experimental spectra show the presence of two main peaks, corresponding to modes localized either at the edges or in the center of the dots. Their frequency dependence on the dot size and on the interaction with adjacent elements has been measured and successfully interpreted on the basis of dynamical micromagnetic simulations. The latter enabled us also to describe the spatial profile of the eigenmodes, putting in evidence the effects induced by the dipolar interaction between coupled dots. In particular, in twinned dots the demagnetizing field is appreciably modified in proximity of the “internal edges” if compared to the “external” ones, leading to a splitting of the edge mode. These results can be relevant for the exploitation of sub-150 nm magnetic dots in new applications, such as magnonic metamaterials, bit-patterned storage media, and nano-magnetic logic devices.
Embedded monopoles in quark eigenmodes in SU(2) Yang-Mills theory
Chernodub, M. N.; Morozov, S. M.
2006-09-01
We study the embedded QCD monopoles ('quark monopoles') using low-lying eigenmodes of the overlap Dirac operator in zero- and finite-temperature SU(2) Yang-Mills theory on the lattice. These monopoles correspond to the gauge-invariant hedgehogs in the quark-antiquark condensates. The monopoles were suggested to be agents of the chiral symmetry restoration since their cores should suppress the chiral condensate. We study numerically the scalar, axial, and chirally invariant definitions of the embedded monopoles and show that the monopole densities are in fact globally anticorrelated with the density of the Dirac eigenmodes. We observe that the embedded monopoles corresponding to low-lying Dirac eigenvalues are dense in the chirally invariant (high temperature) phase and dilute in the chirally broken (low-temperature) phase. We find that the scaling of the scalar and axial monopole densities towards the continuum limit is similar to the scaling of the stringlike objects while the chirally invariant monopoles scale as membranes. The excess of gluon energy at monopole positions reveals that the embedded QCD monopole possesses a gluonic core which is, however, empty at the very center of the monopole.
Embedded monopoles in quark eigenmodes in SU(2) Yang-Mills theory
NASA Astrophysics Data System (ADS)
Chernodub, M. N.; Morozov, S. M.
2006-09-01
We study the embedded QCD monopoles (“quark monopoles”) using low-lying eigenmodes of the overlap Dirac operator in zero- and finite-temperature SU(2) Yang-Mills theory on the lattice. These monopoles correspond to the gauge-invariant hedgehogs in the quark-antiquark condensates. The monopoles were suggested to be agents of the chiral symmetry restoration since their cores should suppress the chiral condensate. We study numerically the scalar, axial, and chirally invariant definitions of the embedded monopoles and show that the monopole densities are in fact globally anticorrelated with the density of the Dirac eigenmodes. We observe that the embedded monopoles corresponding to low-lying Dirac eigenvalues are dense in the chirally invariant (high temperature) phase and dilute in the chirally broken (low-temperature) phase. We find that the scaling of the scalar and axial monopole densities towards the continuum limit is similar to the scaling of the stringlike objects while the chirally invariant monopoles scale as membranes. The excess of gluon energy at monopole positions reveals that the embedded QCD monopole possesses a gluonic core which is, however, empty at the very center of the monopole.
Nonlinear electromagnetic plasma eigenmodes and their stability to stimulated Raman scattering
Pathak, Vishwa Bandhu; Tripathi, V. K.
2006-08-15
Transverse mode structure of nonlinear laser eigenmodes in underdense and overdense plasmas has been obtained by numerically solving the wave equation under relativistic and ponderomotive nonlinearities. The mode structure closely resembles a Lorentzian with half width scaling inversely as the axial intensity of the laser. The threshold condition for laser penetration in an overdense plasma turns out to be {gamma}{sub 0}{identical_to}(1+a{sub 0}{sup 2}/2){sup 1/2}{>=}2n{sub 0}/n{sub cr}-1, where n{sub 0} is the equilibrium electron density, n{sub cr} is the critical density at laser frequency, and {gamma}{sub 0} is the electron Lorentz factor due to the laser of normalized axial intensity a{sub 0}{sup 2}. The nonlinear laser eigenmode, in a low density plasma, is unstable to stimulated Raman backscattering off a copropagating space charge reactive quasimode. The growth rate increases with laser intensity as a{sub 0} rises up to a{sub 0}{approx}1. Beyond this value, growth rate decreases with a{sub 0}, due to the enhancement of electron mass and depletion of electrons from the axial region. Geometrical effects also reduce the growth rate.
Hansen, Shelley C.; Cally, Paul S. E-mail: paul.cally@monash.edu
2012-05-20
Alfven waves may be difficult to excite at the photosphere due to low-ionization fraction and suffer near-total reflection at the transition region (TR). Yet they are ubiquitous in the corona and heliosphere. To overcome these difficulties, we show that they may instead be generated high in the chromosphere by conversion from reflecting fast magnetohydrodynamic waves, and that Alfvenic TR reflection is greatly reduced if the fast reflection point is within a few scale heights of the TR. The influence of mode conversion on the phase of the reflected fast wave is also explored. This phase can potentially be misinterpreted as a travel speed perturbation with implications for the practical seismic probing of active regions.
A circumbinary planet in orbit around the short-period white dwarf eclipsing binary RR Cae
NASA Astrophysics Data System (ADS)
Qian, S.-B.; Liu, L.; Zhu, L.-Y.; Dai, Z.-B.; Fernández Lajús, E.; Baume, G. L.
2012-05-01
By using six newly determined mid-eclipse times together with those collected from the literature, we have found that the observed minus calculated (O-C) curve of RR Cae shows a cyclic change with a period of 11.9 yr and an amplitude of 14.3 s while it undergoes an upward parabolic variation [revealing a long-term period increase at a rate of ?]. The cyclic change was analysed for the light-travel-time effect that arises from the gravitational influence of a third companion. The mass of the third body was determined to be M3sin i'= 4.2(± 0.4) MJup, suggesting that it is a circumbinary giant planet when its orbital inclination is larger than 17?6. The orbital separation of the circumbinary planet from the central eclipsing binary is about 5.3(± 0.6) au. The period increase is opposite to the changes caused by angular momentum loss via magnetic braking or/and gravitational radiation; and it cannot be explained by the mass transfer between both components because of its detached configuration. These indicate that the observed upward parabolic change is only a part of a long-period (longer than 26.3 yr) cyclic variation, which may reveal the presence of another giant circumbinary planet in a wide orbit.
Simulating the dynamic behavior of chain drive systems by advanced CAE programs
Ross, J.; Meyer, J.
1996-09-01
Due to the increased requirements for chain drive systems of 4-stroke internal combustion engines CAE-tools are necessary to design the optimum dynamic system. In comparison to models used din the past the advantage of the new model CDD (Chain Drive Dynamics) is the capability of simulating the trajectory of each chain link around the drive system. Each chain link is represented by a mass with two degrees of freedom and is coupled to the next by a spring-damper element. The drive sprocket can be moved with a constant or non-constant speed. As in reality the other sprockets are driven by the running chain and can be excited by torques. Due to these unique model features it is possible to calculate all vibration types of the chain, polygon effects and radial or angular vibrations of the sprockets very accurately. The model includes the detailed simulation of a mechanical or a hydraulic tensioner as well. The method is ready to be coupled to other detailed calculation models (e.g. valve train systems, crankshaft, etc.). The high efficiency of the tool predicting the dynamic and acoustic behavior of a chain drive system will be demonstrated in comparison to measurements.
Emerging CAE technologies and their role in Future Ambient Intelligence Environments
NASA Astrophysics Data System (ADS)
Noor, Ahmed
2011-03-01
Dramatic improvements are on the horizon in Computer Aided Engineering (CAE) and various simulation technologies. The improvements are due, in part, to the developments in a number of leading-edge technologies and their synergistic combinations/convergence. The technologies include ubiquitous, cloud, and petascale computing; ultra high-bandwidth networks, pervasive wireless communication; knowledge based engineering; networked immersive virtual environments and virtual worlds; novel human-computer interfaces; and powerful game engines and facilities. This paper describes the frontiers and emerging simulation technologies, and their role in the future virtual product creation and learning/training environments. The environments will be ambient intelligence environments, incorporating a synergistic combination of novel agent-supported visual simulations (with cognitive learning and understanding abilities); immersive 3D virtual world facilities; development chain management systems and facilities (incorporating a synergistic combination of intelligent engineering and management tools); nontraditional methods; intelligent, multimodal and human-like interfaces; and mobile wireless devices. The Virtual product creation environment will significantly enhance the productivity and will stimulate creativity and innovation in future global virtual collaborative enterprises. The facilities in the learning/training environment will provide timely, engaging, personalized/collaborative and tailored visual learning.
NASA Astrophysics Data System (ADS)
Koepke, Mark
2008-11-01
A small, off-axis mesh anode electrode at one plasma-column end is used to create a paraxial channel of both electron current and depleted density in the Large Plasma Device Upgrade (LAPD-U) at UCLA. It is shown that the on-axis, larger, surrounding-plasma column rotates about its cylindrical axis because a radial electric field is imposed by a multiple-segmented-disk termination electrode on the same end as the mesh-anode electrode. The radial profile of azimuthal velocity is shown to be consistent with rigid-body rotation. Launched inertial Alfven waves are shown to concentrate in the off-axis channel of electron current and depleted plasma density. In the absence of launched waves, time varying boundary conditions, or spatially structured boundary conditions, we demonstrate that a non-fluctuating, non-traveling pattern in the plasma density arises spontaneously in the channel, but only in the combined presence of electron current, density depletion, and cross-field convection (i.e., rotation). The experimental verification of stationary inertial Alfven waves is based on these results and the predictions from a model of finite-collisionality, finite-pressure stationary Alfven waves that links laboratory and auroral plasma regimes. Ground-based optical observations will be shown that indicate the need for a quasi- static theory of structured electron acceleration within auroral arcs. The properties of the stationary inertial Alfven wave suggest it as promising candidate.
Parametric instability of a monochromatic Alfven wave: Perpendicular decay in low beta plasma
NASA Astrophysics Data System (ADS)
Gao, Xinliang; Lu, Quanming; Li, Xing; Shan, Lican; Wang, Shui
2013-07-01
Two-dimensional hybrid simulations are performed to investigate the parametric decay of a monochromatic Alfven wave in low beta plasma. Both the linearly and left-hand polarized pump Alfven waves are considered in the paper. For the linearly polarized pump Alfven wave, either a parallel or obliquely propagating wave can lead to the decay along the perpendicular direction. Initially, the parametric decay takes place along the propagating direction of the pump wave, and then the decay occurs in the perpendicular direction. With the increase of the amplitude and the propagating angle of the pump wave (the angle between the propagating direction of the pump wave and the ambient magnetic field), the spectral range of the excited waves becomes broad in the perpendicular direction. But the effects of the plasma beta on the spectral range of the excited waves in perpendicular direction are negligible. However, for the left-hand polarized pump Alfven wave, when the pump wave propagates along the ambient magnetic field, the parametric decay occurs nearly along the ambient magnetic field, and there is no obvious decay in the perpendicular direction. Significant decay in the perpendicular direction can only be found when the pump wave propagates obliquely.
Arbitrary amplitude kinetic Alfven solitary waves in two temperature electron superthermal plasma
NASA Astrophysics Data System (ADS)
Singh, Manpreet; Singh Saini, Nareshpal; Ghai, Yashika
2016-07-01
Through various satellite missions it is observed that superthermal velocity distribution for particles is more appropriate for describing space and astrophysical plasmas. So it is appropriate to use superthermal distribution, which in the limiting case when spectral index κ is very large ( i.e. κ→∞), shifts to Maxwellian distribution. Two temperature electron plasmas have been observed in auroral regions by FAST satellite mission, and also by GEOTAIL and POLAR satellite in the magnetosphere. Kinetic Alfven waves arise when finite Larmor radius effect modifies the dispersion relation or characteristic perpendicular wavelength is comparable to electron inertial length. We have studied the kinetic Alfven waves (KAWs) in a plasma comprising of positively charged ions, superthermal hot electrons and Maxwellian distributed cold electrons. Sagdeev pseudo-potential has been employed to derive an energy balance equation. The critical Mach number has been determined from the expression of Sagdeev pseudo-potential to see the existence of solitary structures. It is observed that sub-Alfvenic compressive solitons and super-Alfvenic rarefactive solitons exist in this plasma model. It is also observed that various parameters such as superthermality of hot electrons, relative concentration of cold and hot electron species, Mach number, plasma beta, ion to cold electron temperature ratio and ion to hot electron temperature ratio have significant effect on the amplitude and width of the KAWs. Findings of this investigation may be useful to understand the dynamics of coherent non-linear structures (i.e. KAWs) in space and astrophysical plasmas.
Alfvenic modes in a bi-Maxwellian electron-ion plasma
Bashir, M. F.; Iqbal, Z.; Aslam, I.; Murtaza, G.
2010-10-15
Employing linearized Vlasov-Maxwell system, we derive a generalized dielectric tensor for a magnetized nonrelativistic bi-Maxwellian electron-ion plasma. Assuming low frequency waves in a low {beta} plasma, a new dispersion relation describing oblique propagation of the Alfvenic modes is determined, incorporating the temperature anisotropies of both the electrons and ions and their finite Larmor radii effects. From the resulting dispersion relation for kinetic Alfven waves, analytical expressions are determined for both the kinetic (v{sub t||}){sub i}<<{omega}/k{sub ||}<
NASA Technical Reports Server (NTRS)
Bavassano, B.; Mariani, F.
1983-01-01
Magnetic field data from HELIOS 1 and 2 are used to test a stochastic model for Alfvenic fluctuations recently proposed. A reasonable matching between observations and predictions is found. A rough estimate of the correlation length of the observed fluctuations is inferred.
Weng, C. J.; Lee, L. C.; Kuo, C. L.; Wang, C. B.
2013-03-15
Alfven waves are low-frequency transverse waves propagating in a magnetized plasma. We define the Alfven frequency {omega}{sub 0} as {omega}{sub 0}=kV{sub A}cos{theta}, where k is the wave number, V{sub A} is the Alfven speed, and {theta} is the angle between the wave vector and the ambient magnetic field. There are partially ionized plasmas in laboratory, space, and astrophysical plasma systems, such as in the solar chromosphere, interstellar clouds, and the earth ionosphere. The presence of neutral particles may modify the wave frequency and cause damping of Alfven waves. The effects on Alfven waves depend on two parameters: (1) {alpha}=n{sub n}/n{sub i}, the ratio of neutral density (n{sub n}), and ion density (n{sub i}); (2) {beta}={nu}{sub ni}/{omega}{sub 0}, the ratio of neutral collisional frequency by ions {nu}{sub ni} to the Alfven frequency {omega}{sub 0}. Most of the previous studies examined only the limiting case with a relatively large neutral collisional frequency or {beta} Much-Greater-Than 1. In the present paper, the dispersion relation for Alfven waves is solved for all values of {alpha} and {beta}. Approximate solutions in the limit {beta} Much-Greater-Than 1 as well as {beta} Much-Less-Than 1 are obtained. It is found for the first time that there is a 'forbidden zone (FZ)' in the {alpha}-{beta} parameter space, where the real frequency of Alfven waves becomes zero. We also solve the wavenumber k from the dispersion equation for a fixed frequency and find the existence of a 'heavy damping zone (HDZ).' We then examine the presence of FZ and HDZ for Alfven waves in the ionosphere and in the solar chromosphere.
Mechanisms for the Dissipation of Alfven Waves in Near-Earth Space Plasma
NASA Technical Reports Server (NTRS)
Singh, Nagendra; Khazanov, George; Krivorutsky, E. N.; Davis, John M. (Technical Monitor)
2002-01-01
Alfven waves are a major mechanism for the transport of electromagnetic energy from the distant part of the magnetosphere to the near-Earth space. This is especially true for the auroral and polar regions of the Earth. However, the mechanisms for their dissipation have remained illusive. One of the mechanisms is the formation of double layers when the current associated with Alfven waves in the inertial regime interact with density cavities, which either are generated nonlinearly by the waves themselves or are a part of the ambient plasma turbulence. Depending on the strength of the cavities, weak and strong double layers could form. Such double layers are transient; their lifetimes depend on that of the cavities. Thus they impulsively accelerate ions and electrons. Another mechanism is the resonant absorption of broadband Alfven- wave noise by the ions at the ion cyclotron frequencies. But this resonant absorption may not be possible for the very low frequency waves, and it may be more suited for electromagnetic ion cyclotron waves. A third mechanism is the excitation of secondary waves by the drifts of electrons and ions in the Alfven wave fields. It is found that under suitable conditions, the relative drifts between different ion species and/or between electrons and ions are large enough to drive lower hybrid waves, which could cause transverse accelerations of ions and parallel accelerations of electrons. This mechanism is being further studied by means of kinetic simulations using 2.5- and 3-D particle-in-cell codes. The ongoing modeling efforts on space weather require quantitative estimates of energy inputs of various kinds, including the electromagnetic energy. Our studies described here contribute to the methods of determining the estimates of the input from ubiquitous Alfven waves.
NASA Astrophysics Data System (ADS)
Song, Y.; Lysak, R. L.
2013-12-01
The nonlinear interaction of incident and reflected Alfven wave packets in auroral acceleration regions can create non-propagating electromagnetic-plasma structures, such as transverse Alfvenic double layers and charge holes. These dynamical structures are often characterized by localized strong electrostatic electric fields, localized density cavities and enhanced magnetic or mechanical stresses, and are responsible for auroral particle acceleration and the formation of both Alfvenic and quasi-static inverted-V discrete auroras. Similar electromagnetic-plasma structures should also be generated in other cosmic plasmas, and would constitute effective high energy accelerators of charged particles in cosmic plasmas.
NASA Astrophysics Data System (ADS)
Todo, Y.; Berk, H. L.; Breizman, B. N.
2012-03-01
A hybrid simulation code for nonlinear magnetohydrodynamics (MHD) and energetic-particle dynamics has been extended to simulate recurrent bursts of Alfvén eigenmodes by implementing the energetic-particle source, collisions and losses. The Alfvén eigenmode bursts with synchronization of multiple modes and beam ion losses at each burst are successfully simulated with nonlinear MHD effects for the physics condition similar to a reduced simulation for a TFTR experiment (Wong et al 1991 Phys. Rev. Lett. 66 1874, Todo et al 2003 Phys. Plasmas 10 2888). It is demonstrated with a comparison between nonlinear MHD and linear MHD simulation results that the nonlinear MHD effects significantly reduce both the saturation amplitude of the Alfvén eigenmodes and the beam ion losses. Two types of time evolution are found depending on the MHD dissipation coefficients, namely viscosity, resistivity and diffusivity. The Alfvén eigenmode bursts take place for higher dissipation coefficients with roughly 10% drop in stored beam energy and the maximum amplitude of the dominant magnetic fluctuation harmonic δBm/n/B ~ 5 × 10-3 at the mode peak location inside the plasma. Quadratic dependence of beam ion loss rate on magnetic fluctuation amplitude is found for the bursting evolution in the nonlinear MHD simulation. For lower dissipation coefficients, the amplitude of the Alfvén eigenmodes is at steady levels δBm/n/B ~ 2 × 10-3 and the beam ion losses take place continuously. The beam ion pressure profiles are similar among the different dissipation coefficients, and the stored beam energy is higher for higher dissipation coefficients.
Nonlinear dynamics of toroidal Alfvén eigenmodes driven by energetic particles
Zhu, J.; Ma, Z. W.; Fu, G. Y.
2013-07-15
A kinetic simulation code based on a reduced model is developed to study dynamic evolutions of a single toroidicity-induced shear Alfvén eigenmode driven by energetic particles. For zero background damping, it is found that the wave amplitude in nonlinear phase can either saturate for weak energetic particle drives or slowly increase for strong drives. This slow nonlinear growth in strong drive cases is found to be associated with broadening and overlapping of resonances between the wave and trapped particles. For the near-marginal-stability case with a large background damping, the mode nonlinear evolution exhibits strong upward and downward frequency chirping in multiple branches. A hole/clump formation is observed clearly in the corresponding evolution of energetic particle distribution.
Properties of toroidal Alfvén eigenmode in DIII-D plasma
Wang, Zhixuan; Lin, Zhihong Holod, Ihor; Heidbrink, W. W.; Deng, Wenjun; Xiao, Y.; Zhang, H.; Zhang, W.; Van Zeeland, M.
2015-02-15
Linear properties of the toroidal Alfvén eigenmode (TAE) excited by energetic particles (EP) in a DIII-D tokamak experiment have been studied in global gyrokinetic particle simulations treating self-consistently kinetic effects of EP, thermal ions, and electrons. Simulation results of the TAE frequency and mode structure agree very well with the experimental measurements. The non-perturbative EP contribution induces a radial localization of the TAE mode structure, a break-down of mode radial symmetry, as well as a frequency dependence on the toroidal mode number. The simulations further demonstrate the dependence of the growth rate and mode structure on EP pressure gradients. The in-out asymmetry of the mode structure and the experimental identification of the poloidal harmonics have also been clarified.
Identification of island-induced Alfvén eigenmodes in a reversed field pinch
NASA Astrophysics Data System (ADS)
Cook, C. R.; Hegna, C. C.; Anderson, J. K.; McCollam, K. J.; Boguski, J.; Feng, R.; Koliner, J. J.; Spong, D. A.; Hirshman, S. P.
2016-05-01
The modification of the shear Alfvén spectrum due to a core resonant magnetic island is used to explain the Alfvénic activity observed on the Madison symmetric torus (MST) reversed-field pinch during neutral beam injection. Theoretical studies show that the Alfvén continua in the core of the island provide a gap in which the observed Alfvénic bursts reside. Numerical simulations using a new code called SIESTAlfvén have identified the bursts as the first observation of an island-induced Alfvén eigenmode (IAE) in an RFP. The IAE arises from a helical coupling of harmonics due to the magnetic island.
Parallel equilibrium current effect on existence of reversed shear Alfvén eigenmodes
Xie, Hua-sheng Xiao, Yong
2015-02-15
A new fast global eigenvalue code, where the terms are segregated according to their physics contents, is developed to study Alfvén modes in tokamak plasmas, particularly, the reversed shear Alfvén eigenmode (RSAE). Numerical calculations show that the parallel equilibrium current corresponding to the kink term is strongly unfavorable for the existence of the RSAE. An improved criterion for the RSAE existence is given for with and without the parallel equilibrium current. In the limits of ideal magnetohydrodynamics (MHD) and zero-pressure, the toroidicity effect is the main possible favorable factor for the existence of the RSAE, which is however usually small. This suggests that it is necessary to include additional physics such as kinetic term in the MHD model to overcome the strong unfavorable effect of the parallel current in order to enable the existence of RSAE.
Spontaneous excitation of geodesic acoustic mode by toroidal Alfvén eigenmodes
NASA Astrophysics Data System (ADS)
Qiu, Zhiyong; Chen, Liu; Zonca, Fulvio
2013-02-01
Spontaneous nonlinear excitation of geodesic acoustic mode (GAM) by toroidal Alfvén eigenmodes (TAE) is studied within the framework of gyrokinetic theory. The dispersion relation for the parametric decays of a pump TAE mode into a TAE lower sideband and a GAM is derived. It is shown that, in the ideal MHD first stability region, the condition for spontaneous excitation of GAM by TAEs is ω20 > V2A/(4q2R20), in which, ω0 is the pump TAE real frequency, V A is the Alfvén speed, q is the safety factor and R0 is the torus major radius. The corresponding threshold condition is also derived and suggests the decay process as an effective saturation mechanism for TAE.
A singular finite element technique for calculating continuum damping of Alfvén eigenmodes
Bowden, G. W.; Hole, M. J.
2015-02-15
Damping due to continuum resonances can be calculated using dissipation-less ideal magnetohydrodynamics provided that the poles due to these resonances are properly treated. We describe a singular finite element technique for calculating the continuum damping of Alfvén waves. A Frobenius expansion is used to determine appropriate finite element basis functions on an inner region surrounding a pole due to the continuum resonance. The location of the pole due to the continuum resonance and mode frequency is calculated iteratively using a Galerkin method. This method is used to find the complex frequency and mode structure of a toroidicity-induced Alfvén eigenmode in a large aspect ratio circular tokamak and is shown to agree closely with a complex contour technique.
Fully electromagnetic gyrokinetic eigenmode analysis of high-beta shaped plasmas
NASA Astrophysics Data System (ADS)
Belli, E. A.; Candy, J.
2010-11-01
A new, more efficient method to compute unstable linear gyrokinetic eigenvalues and eigenvectors has been developed for drift-wave analysis of plasmas with arbitrary flux-surface shape, including both transverse and compressional magnetic perturbations. In high-beta, strongly shaped plasmas like in the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)], numerous branches of closely spaced unstable eigenmodes exist. These modes are difficult and time-consuming to adequately resolve with the existing linear initial-value solvers, which are further limited to the most unstable eigenmode. The new method is based on an eigenvalue approach and is an extension of the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)], reusing the existing discretization schemes in both real and velocity-space. Unlike recent methods, which use an iterative solver to compute eigenvalues of the relatively large gyrokinetic response matrix, the present scheme computes the zeros of the much smaller Maxwell dispersion matrix using a direct method. In the present work, the new eigensolver is applied to gyrokinetic stability analysis of a high-beta, NSTX-like plasma. We illustrate the smooth transformation from ion-temperature-gradient (ITG)-like to kinetic-ballooning (KBM)-like modes, and the formation of hybrid ITG/KBM modes, and further demonstrate the existence of high-k Alfvénic drift-wave "cascades" for which the most unstable mode is a higher excited state along the field line. A new compressional electron drift wave, which is driven by a combination of strong beta and pressure gradient, is also identified for the first time. Overall, we find that accurate calculation of stability boundaries and growth rates cannot, in general, ignore the compressional component δB∥ of the perturbation.
Transient evolution of eigenmodes in dynamic cavities and time-varying media
NASA Astrophysics Data System (ADS)
Gradoni, Gabriele; Arnaut, Luk R.
2015-12-01
In this paper, we investigate the perturbation of natural eigenmodes of dynamic cavities with boundaries moving at quasi-static speeds relative to the wave velocity. For an arbitrarily shaped source-free cavity, the amplitude of the irrotational mode is modeled as a damped harmonic oscillator with time-varying eigenfrequency, i.e., a parametric oscillator. It is found that the effect of the pure Doppler shift of the resonance frequencies of the eigenmodes is small at nonrelativistic speeds. However, it is known that any spectrum of eigenenergies that is perturbed by a space- and/or time-fluctuating medium can develop frequency shifts of arbitrary magnitude. By using a linear dynamic (time-dependent) shift for the cavity broad resonances, we find that Doppler-like large shifts result in a mere frequency modulation of the total (resultant) field amplitude, while nonuniform red or blue shift can create a hybrid amplitude and frequency modulation. Interestingly, the combined action of red and blue shifts of uniform magnitude can also create a hybrid modulation. If the angle between modal wave vector and stirrer speed is accounted for in the static (time-independent) shift, the resulting red and blue shifts lead to irregular hybrid modulations. This can occur even for regular perturbations in regular cavities. In addition, owing to the stochastic nature of mode-stirred cavities, the effect of random Doppler-like shifts is also investigated, leading to a Fokker-Planck equation whose diffusion coefficient shows quadratic dependence on the mode amplitude. Thus, the analysis of random perturbations offers an effective framework for observed instantaneous Doppler effects in closed electromagnetic environments. The mathematical framework obtained in terms of stochastic differential equations is useful to predict the nonstationary response of dynamic cavities with complicated or unknown boundary geometry.
Application of CAD/CAE class systems to aerodynamic analysis of electric race cars
NASA Astrophysics Data System (ADS)
Grabowski, L.; Baier, A.; Buchacz, A.; Majzner, M.; Sobek, M.
2015-11-01
Aerodynamics is one of the most important factors which influence on every aspect of a design of a car and car driving parameters. The biggest influence aerodynamics has on design of a shape of a race car body, especially when the main objective of the race is the longest distance driven in period of time, which can not be achieved without low energy consumption and low drag of a car. Designing shape of the vehicle body that must generate the lowest possible drag force, without compromising the other parameters of the drive. In the article entitled „Application of CAD/CAE class systems to aerodynamic analysis of electric race cars” are being presented problems solved by computer analysis of cars aerodynamics and free form modelling. Analysis have been subjected to existing race car of a Silesian Greenpower Race Team. On a basis of results of analysis of existence of Kammback aerodynamic effect innovative car body were modeled. Afterwards aerodynamic analysis were performed to verify existence of aerodynamic effect for innovative shape and to recognize aerodynamics parameters of the shape. Analysis results in the values of coefficients and aerodynamic drag forces. The resulting drag forces Fx, drag coefficients Cx(Cd) and aerodynamic factors Cx*A allowed to compare all of the shapes to each other. Pressure distribution, air velocities and streams courses were useful in determining aerodynamic features of analyzed shape. For aerodynamic tests was used Ansys Fluent CFD software. In a paper the ways of surface modeling with usage of Realize Shape module and classic surface modeling were presented. For shapes modeling Siemens NX 9.0 software was used. Obtained results were used to estimation of existing shapes and to make appropriate conclusions.
Hostetler, D.D.; Childs, S.W.; Phillips, S.J.
1983-03-01
This subsurface-instrumentation design has been developed for the first Compressed Air Energy Storage (CAES) field experiment to be performed in porous media. Energy storage will be accomplished by alternating the injection and withdrawal of compressed air in a confined sandstone aquifer near Pittsfield, Illinois. The overall experiment objective is to characterize the reservoir's geochemical and thermohydraulic response to imposed CAES conditions. Specific experiment objectives require monitoring: air-bubble development; thermal development; cyclic pressure response; reservoir dehydration; and water coning. Supporting these objectives, four parameters will be continuously monitored at depth in the reservoir. They are: temperature; pressure; pore-air relative humidity; and pore-water content. Reservoir temperatures and pressures will range to maximum values approaching 200/sup 0/C and 300 psi, respectively. Both pore-air relative humidity and pore-water content will range from approx. 0 to 100%. This report discusses: instrumentation design; sensor and sensor system calibration; field installation and testing; and instrument-system operation. No comprehensive off-the-shelf instrument package exists to adequately monitor CAES reservoir parameters at depth. The best available sensors were selected and adapted for use under expected ranges of reservoir conditions. The instrumentation design criteria required: suitable sensor accuracy; continuous monitoring capability; redundancy; maximum sensor integrity; contingency planning; and minimum cost-information ratio. Three wells will be instrumented: the injection/withdrawal (I/W) well and the two instrument wells. Sensors will be deployed by wireline suspension in both open and backfilled (with sand) wellbores. The sensors deployed in the I/W well will be retrievable; the instrument-well sensors will not.
Verwichte, E.; Foullon, C.; White, R. S.; Van Doorsselaere, T.
2013-04-10
Two transversely oscillating coronal loops are investigated in detail during a flare on the 2011 September 6 using data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We compare two independent methods to determine the Alfven speed inside these loops. Through the period of oscillation and loop length, information about the Alfven speed inside each loop is deduced seismologically. This is compared with the Alfven speed profiles deduced from magnetic extrapolation and spectral methods using AIA bandpass. We find that for both loops the two methods are consistent. Also, we find that the average Alfven speed based on loop travel time is not necessarily a good measure to compare with the seismological result, which explains earlier reported discrepancies. Instead, the effect of density and magnetic stratification on the wave mode has to be taken into account. We discuss the implications of combining seismological, extrapolation, and spectral methods in deducing the physical properties of coronal loops.
Damiani, R.; Jonkman, J.; Robertson, A.; Song, H.
2013-03-01
Design and analysis of wind turbines are performed using aero-servo-elastic tools that account for the nonlinear coupling between aerodynamics, controls, and structural response. The NREL-developed computer-aided engineering (CAE) tool FAST also resolves the hydrodynamics of fixed-bottom structures and floating platforms for offshore wind applications. This paper outlines the implementation of a structural-dynamics module (SubDyn) for offshore wind turbines with space-frame substructures into the current FAST framework, and focuses on the initial assessment of the importance of structural nonlinearities. Nonlinear effects include: large displacements, axial shortening due to bending, cross-sectional transverse shear effects, etc.
Parametric instabilities of parallel-propagating Alfven waves: Some analytical results
NASA Technical Reports Server (NTRS)
Jayanti, V.; Hollweg, Joseph V.
1993-01-01
We consider the stability of a circularly polarized Alfven wave (the pump wave) which propagates parallel to the ambient magnetic field. Only parallel-propagating perturbations are considered, and we ignore dispersive effects due to the ion cyclotron frequency. The dissipationless MHD equations are used throughout; thus possibibly important effects arising from Landau and transit time damping are omitted. We derive a series of analytical approximations to the dispersion relation using A = (Delta B/B(sub O))(exp 2) as a small expansion parameter; Delta B is the pump amplitude, and B(sub O) is the ambient magnetic field strength. We find that the plasma beta (the square of the ratio of the sound speed to the Alfven speed) plays a crucial role in determining the behavior of the parametric instabilities of the pump. If 0 less than beta less than 1 we find the familiar result that the pump decays into a forward propagating sound wave and a backward propagating Alfven wave with maximum growth rate gamma(sub max) varies A(sup 1/2), but beta cannot be too close to 0 or to 1. If beta approx. 1, we find gamma(sub max) varies A(sup 3/4), if beta greater than 1, we find gamma(sub max) varies A(sup 3/2), while if beta approx. 0, we obtain gamma(sub max) varies A(sup 1/3); moreover, if beta approx. 0 there is a nearly purely growing instability. In constrast to the familiar decay instability, for which the backward propagating Alfven wave has lower frequency and wavenumber than the pump, we find that if beta greater than or approx. equal to 1 the instability is really a beat instability which is dominated by a transverse wave which is forward propagating and has frequency and wavenumber which are nearly twice the pump values. Only the decay instability for 0 less than beta less than 1 can be regarded as producing two recognizable normal modes, namely, a sound wave and an Alfven wave. We discuss how the different characteristics of the instabilities may affect the evolution of
Energy densities of Alfven waves between 0.7 and 1.6 AU. [in interplanetary medium
NASA Technical Reports Server (NTRS)
Belcher, J. W.; Burchsted, R.
1974-01-01
Plasma and field data from Mariner 4 and 5 between 0.7 and 1.6 AU are used to study the radial dependence of the levels of microscale fluctuation associated with interplanetary Alfven waves. The observed decrease of these levels with increasing distance from the sun is consistent with little or no local generation or damping of the ambient Alfven waves over this range of radial distance.
NASA Astrophysics Data System (ADS)
Mukaitani, Ichiroh; Hayashi, Koji; Shimoura, Ichiro; Takemasa, Arihiko; Takahashi, Isamu; Tsubakino, Harushige
software " Solid Works" and computer aided engineering (CAE) software " ANSYS" with corrosion elongation transformed into thermal elongation. We established a current collector corrosion elongation forecast and found that the microstructure controlled the Pb-Ca-Sn alloy; thus newly designed VRLA batteries (MU-series [A. Takemasa, I. Mukaitani, Y. Yoshiyama, K. Fukui, T. Sakamoto, T. Kuwano, M. Fukuda, H. Misaki, K. Uwatari, Shin-Kobe Technical Report 9 (1999) 11] for telecommunication and LL-series [H. Takabayashi, T. Shibahara, Y. Mastuda, K. Fukui, S. Hazui, Y. Matsumura, S. Kondo, Shin-Kobe Tech. Rep. 11 (2001) 35] for electric energy storage) which are lightweight and have long life are introduced here.
High-resolution sounding rocket observations of large-amplitude Alfven waves
NASA Technical Reports Server (NTRS)
Boehm, M. H.; Carlson, C. W.; Mcfadden, J. P.; Clemmons, J. H.; Mozer, F. S.
1990-01-01
Shear Alfven waves with amplitudes greater than 100 mV/m were observed on two recent sounding rocket flights. The largest waveforms are best described as a series of step functions, rather than as broadband noise or as single frequency waves. Complete two-dimensional E and B measurements at 4-ms time resolution were made, showing a downward propagation direction and implying insignificant reflection from the ionosphere at frequencies greater than 1 Hz. Intense, field-aligned, low-energy electron fluxes accompany the waves. Acceleration of these electrons by the Alfven waves is shown to be feasible. The waves in at least one case have a sufficently large ponderomotive potential to generate the observed density fluctuations of order one.
Wave merging mechanism: formation of low-frequency Alfven and magnetosonic waves in cosmic plasmas
Tishchenko, V N; Shaikhislamov, I F
2014-02-28
We investigate the merging mechanism for the waves produced by a pulsating cosmic plasma source. A model with a separate background/source description is used in our calculations. The mechanism was shown to operate both for strong and weak source – background interactions. We revealed the effect of merging of individual Alfven waves into a narrow low-frequency wave, whose amplitude is maximal for a plasma expansion velocity equal to 0.5 – 1 of the Alfven Mach number. This wave is followed along the field by a narrow low-frequency magnetosonic wave, which contains the bulk of source energy. For low expansion velocities the wave contains background and source particles, but for high velocities it contains only the background particles. The wave lengths are much greater than their transverse dimension. (letters)
Some wave-particle effects on large-scale Alfven wave propagation and damping
NASA Technical Reports Server (NTRS)
Siregar, E.; Goldstein, M. L.
1995-01-01
Phase mixing can reduce greatly the torsional Alfven wave's dissipation length for propagation in complex magnetic field-line geometries. This phase mixing causes significant energy transfers from large to small scales where a conversion from ordered wave energy into a particle kinetic form occurs. This conversion during its initial stages is an entropy conserving process well described by Vlasov theory, Nonlinear stages of wave-particle resonance, particle trapping, and collisional resistivity are often invoked as processes eventually responsible for converting ordered wave motions into random thermal motion. Strictly speaking, this entropy producing phase cannot be described within Vlasov theory, and the large-scale effects of these microscopic events resides at the difficult frontier between generalized fluid and kinetic theories. We attempt to describe certain aspects of such resonances within the framework of fluid theory focusing on torsional Alfven wave energy transport and deposition within flux tubes.
Ruchko, L. F.; Elfimov, A. G.; Teixeira, C. M.; Elizondo, J. I.; Sanada, E.; Galvao, R. M. O.; Manso, M. E.; Silva, A.
2011-02-15
A frequency scanning O-mode reflectometer was used for studies of plasma density oscillations during local Alfven wave (LAW) excitation in the Tokamak Chauffage Alfven Bresilien (TCABR) at the frequency f{sub A}= 5 MHz. It was found that the spectrum of the reflectometer output signal, which consists mainly of the ''beat'' frequency f{sub B}, is modified by the LAW excitation, and two additional frequency peaks appear, which are symmetrical in relation to the LAW excitation frequency f=f{sub A}{+-}f{sub B}. This result opens the possibility to improve the efficiency of studying the LAW induced density oscillations. The symmetry of these frequency peaks yields the possibility of finding the microwave frequency at which the reflectometer cutoff layer coincides with radial position of the LAW resonance zone in the TCABR tokamak.
Panwar, Anuraj; Rizvi, H.; Ryu, C. M.
2013-11-15
Sagdeev’s technique is used to study the large amplitude compressional Alfvenic double layers in a magnetohydrodynamic plasma taking into account the small plasma β and small values of kinematic viscosity. Dispersive effect raised by non-ideal electron inertia currents perpendicular to the ambient magnetic field. The range of allowed values of the soliton speed, M (Mach number), plasma β (ratio of the plasma thermal pressure to the pressure in the confining magnetic field), and viscosity coefficient, wherein double layer may exist, are determined. In the absence of collisions, viscous dissipation modifies the Sagdeev potential and results in large amplitude compressional Alfvenic double layers. The depth of Sagdeev potential increases with the increasing Mach number and plasma β, however, decreases with the increasing viscosity. The double layer structure increases with the increasing plasma β, but decreases with increasing viscous dissipation μ(tilde sign)
Nonlinear evolution of a large-amplitude circularly polarized Alfven wave: High beta
NASA Technical Reports Server (NTRS)
Ghosh, S.; Vinas, A. F.; Goldstein, M. L.
1994-01-01
The nonlinear dynamics following saturation of the parametric instabilities of a monochromatic field-aligned large-amplitude circularly polarized Alfven wave is investigated via direct numerical simulation in the case of high plasma beta and no wave dispersion. The magnetohydrodynamic (MHD) code permits nonlinear couplings in the parallel direction to the ambient magnetic field and one perpendicular direction. Compressibility is included in the form of a polytropic equation of state. Turbulent cascades develop after saturation of two coupled oblique three-wave parametric instabilities; one of which is an oblique filamentationlike instability reported earlier. Remnants of the parametric processes, as well as of the original Alfven pump wave, persist during late nonlinear times. Nearly incompressible MHD features such as spectral anisotropies appear as well.
Phenomenology of non-Alfvenic turbulence in a uniformly expanding medium
NASA Technical Reports Server (NTRS)
Matthaeus, W. H.; Zank, G. P.
1995-01-01
Transport and decay of magnetohydrodynamic (MHD) turbulence in a weakly inhomogeneous uniformly expanding medium involves a fairly complex formalism, even for the case where no spectral information is required. Here we argue that the phenomenology for decay simplifies greatly if: (1) the cross helicity (Alfvenicity) is small, (2) the dynamical influence of the large scale magnetic field is negligible either because of spectral anisotropy or because the expansion speed is much greater than the corresponding Alfven speed, and (3) the ratio of kinetic energy to magnetic energy for the fluctuations is either unity or some other constant. These conditions are acceptable as an approximation to solar wind turbulence in the outer heliosphere. In these circumstances a reasonable MHD energy-containing phenomenology is essentially that of locally homogeneous Kolmogoroff turbulence in a uniformly expanding medium. Analytical solutions for this model are presented for both undriven and driven cases.
Modification and damping of Alfven waves in a magnetized dusty plasma
NASA Astrophysics Data System (ADS)
Salimullah, M.; Dasgupta, B.; Watanabe, K.; Sato, T.
1994-10-01
The dispersion characteristics of the circularly polarized electromagnetic waves along a homogeneous magnetic field in a dusty plasma have been investigated theoretically. The Vlasov equation has been employed to find the response of the magnetized plasma particles where the dust grains form a static background of highly charged and massive centers having certain correlations. It is found that in addition to the unusual Landau damping, which is negligible in the low temperature approximation, a novel mechanism of damping of the Alfven waves due to the dust comes into play. The modification and damping of the Alfven waves depend on the dust perturbation parameters, unequal densities of plasma particles, the average correlation length of the dust grains, temperature of the plasma and the magnetic field.
Is the Alfven-wave propagation effect important for energy decay in homogeneous MHD turbulence?
Hossain, Murshed; Gray, Perry C.; Pontius, Duane H. Jr.; Matthaeus, William H.; Oughton, Sean
1996-07-20
We investigate the role of three-point decorrelation due to Alfven wave propagation in three-dimensional incompressible homogeneous MHD turbulence. By comparing numerical simulations with theoretical expectations, we have studied how this effect influences the decay of turbulent energy caused by both an external mean magnetic field and the fluctuating turbulent field. Decay is initially suppressed by a mean magnetic field, as expected, but the effect soon saturates. The decay rate does not scale with mean magnetic field for higher values. The disagreement with theoretical predictions can be accounted for by anisotropic spectral transfer. Thus, phenomenological models for energy decay that include decorrelation due to Alfvenic propagation are not substantiated. This work complements our detailed study of various models of energy decay in homogeneous MHD [Hossain et al., 1995].
Kinetic Alfven waves in a homogeneous dusty magnetoplasma with dust charge fluctuation effects
Zubia, K.; Rubab, N.; Shah, H. A.; Salimullah, M.; Murtaza, G.
2007-03-15
Kinetic Alfven waves with finite Larmor radius effects have been examined rigorously in a uniform dusty plasma in the presence of an external/ambient magnetic field. Two-potential theory has been applied for these electromagnetic waves and the dispersion relation is derived which shows a cutoff frequency at the dust-lower-hybrid frequency due to the hybrid motion of magnetized ions and cold and unmagnetized dust dynamics. The dust charge fluctuation effect was analyzed for finding the damping of the electromagnetic kinetic Alfven waves, which arises on account of the electrostatic parallel component of the waves. The dust charge fluctuation damping is seen to be contributed dominantly by the perpendicular motion of electrons and ions in the dusty magnetoplasma.
NASA Astrophysics Data System (ADS)
Zhang, Xianmei; Chen, Wei; Yu, Limin; Sheng, Zheng-Mao; Xue, Erbing
2016-09-01
The reserved shear Alfvén eigenmodes (RSAEs) whose frequencies sweep down have been observed in HL-2A plasmas at qmin ˜ 1 during current ramp-up and NBI+ECRH recently. The kinetic Alfvén eigenmode code (KAEC), which is a non-perturbative kinetic/magnetohydrodynamic eigenvalue code for calculating kinetic damping of shear Alfvén eigenmodes, is used to investigate the modes according to the experimental data. It is found that the kinetic reversed shear Alfvén eigenmodes (KRSAEs) with downsweeping frequency and localized radial structure would appear, which are consistent with the observations. The theoretical analysis for the existence of the mode and the scaling of the mode width are provided. It is shown that the mode width of KRSAEs is proportional to the square root of thermal ion Larmor radius.
A PARALLEL-PROPAGATING ALFVENIC ION-BEAM INSTABILITY IN THE HIGH-BETA SOLAR WIND
Verscharen, Daniel; Bourouaine, Sofiane; Chandran, Benjamin D. G.; Maruca, Bennett A. E-mail: s.bourouaine@unh.edu E-mail: bmaruca@ssl.berkeley.edu
2013-08-10
We investigate the conditions under which parallel-propagating Alfven/ion-cyclotron waves are driven unstable by an isotropic (T{sub {alpha}} = T{sub Parallel-To {alpha}}) population of alpha particles drifting parallel to the magnetic field at an average speed U{sub {alpha}} with respect to the protons. We derive an approximate analytic condition for the minimum value of U{sub {alpha}} needed to excite this instability and refine this result using numerical solutions to the hot-plasma dispersion relation. When the alpha-particle number density is {approx_equal} 5% of the proton number density and the two species have similar thermal speeds, the instability requires that {beta}{sub p} {approx}> 1, where {beta}{sub p} is the ratio of the proton pressure to the magnetic pressure. For 1 {approx}< {beta}{sub p} {approx}< 12, the minimum U{sub {alpha}} needed to excite this instability ranges from 0.7v{sub A} to 0.9v{sub A}, where v{sub A} is the Alfven speed. This threshold is smaller than the threshold of {approx_equal} 1.2v{sub A} for the parallel magnetosonic instability, which was previously thought to have the lowest threshold of the alpha-particle beam instabilities at {beta}{sub p} {approx}> 0.5. We discuss the role of the parallel Alfvenic drift instability for the evolution of the alpha-particle drift speed in the solar wind. We also analyze measurements from the Wind spacecraft's Faraday cups and show that the U{sub {alpha}} values measured in solar-wind streams with T{sub {alpha}} Almost-Equal-To T{sub Parallel-To {alpha}} are approximately bounded from above by the threshold of the parallel Alfvenic instability.
Study of Nonlinear Interaction and Turbulence of Alfven Waves in LAPD Experiments
Boldyrev, Stanislav; Perez, Jean Carlos
2013-11-29
The complete project had two major goals — investigate MHD turbulence generated by counterpropagating Alfven modes, and study such processes in the LAPD device. In order to study MHD turbulence in numerical simulations, two codes have been used: full MHD, and reduced MHD developed specialy for this project. Quantitative numerical results are obtained through high-resolution simulations of strong MHD turbulence, performed through the 2010 DOE INCITE allocation. We addressed the questions of the spectrum of turbulence, its universality, and the value of the so-called Kolmogorov constant (the normalization coefficient of the spectrum). In these simulations we measured with unprecedented accuracy the energy spectra of magnetic and velocity fluctuations. We also studied the so-called residual energy, that is, the difference between kinetic and magnetic energies in turbulent fluctuations. In our analytic work we explained generation of residual energy in weak MHD turbulence, in the process of random collisions of counterpropagating Alfven waves. We then generalized these results for the case of strong MHD turbulence. The developed model explained generation of residual energy is strong MHD turbulence, and verified the results in numerical simulations. We then analyzed the imbalanced case, where more Alfven waves propagate in one direction. We found that spectral properties of the residual energy are similar for both balanced and imbalanced cases. We then compared strong MHD turbulence observed in the solar wind with turbulence generated in numerical simulations. Nonlinear interaction of Alfv´en waves has been studied in the upgraded Large Plasma Device (LAPD). We have simulated the collision of the Alfven modes in the settings close to the experiment. We have created a train of wave packets with the apltitudes closed to those observed n the experiment, and allowed them to collide. We then saw the generation of the second harmonic, resembling that observed in the
The making of an Alfvenic fluctuation: The resolution of a second-order analysis
NASA Technical Reports Server (NTRS)
Vasquez, Bernard J.; Hollweg, Joseph V.
1995-01-01
Ulysses observations of the high speed polar streams show that they are largely occupied by very large amplitude Alfvenic fluctuations accompanied by many rotational discontinuities. These fluctuations have a nearly constant magnetic intensity or amplitude, and the magnetic field direction per wave cycle sweeps only through a limited arc, much as a car wiperblade would do. Barnes and Hollweg (JGR, 79, 2302, 1974) suggested that this unusual waveform could arise from an obliquely propagating and linearly polarized Alfven wave of finite amplitude. From a second-order analysis, they showed that the existence of a particular solution with a constant amplitude but could not resolve the outcome of the homogeneous solution which consisted of fast waves. They suggested that Landau damping of these fast waves may be needed to get the observed waveform. We present a 1 1/2 D hybrid simulation which is fully nonlinear and correctly describes the ion kinetics for an initially monochromatic and linearly polarized Alfven wave propagating obliquely to the background magnetic field. The wave has a large amplitude and a wavelength so long that it can be considered dispersionless for simulation times. At early times, the second harmonic in density and in magnetic field transverse to the initial wave magnetic field are generated and have more power than other harmonics. Steepening is observed with a weak fast shock emerging, but no rotational discontinuity is left behind, and instead a constant amplitude and an arc-shaped waveform is made. The compressional component which develops after the shocks have dissipated is to zeroth order better described as a pure acoustic wave than as a fast wave. This might be explained by the relaxing of the Alfven wave to a state where its ponderomotive force vanishes so that the compressional component can travel almost independently of it.
Measurements of Inertial Limit Alfven Wave Dispersion for Finite Perpendicular Wave Number
Kletzing, C. A.; Thuecks, D. J.; Skiff, F.; Bounds, S. R.; Vincena, S.
2010-03-05
Measurements of the dispersion relation for shear Alfven waves as a function of perpendicular wave number are reported for the inertial regime for which V{sub A}>V{sub Te}. The parallel phase velocity and damping are determined as k{sub perpendicular} varies and the measurements are compared to theoretical predictions. The comparison shows that the best agreement between theory and experiment is achieved for a fully complex plasma dispersion relation which includes the effects of electron collisions.
Linear and non-linear numerical simulations of poloidal Alfven waves
NASA Astrophysics Data System (ADS)
Ribeiro, A.
2013-05-01
Among the many of numerical simulations of MHD turbulence, few studies had been made of Alfven waves interacting with realistic boundaries. Thus, we have developed a novel hybrid spectral/finite element code, which is capable of simulate properly realistic boundaries properties. Our model is based on a Fourier decompositions of all variables in the azimuthal direction and on a finite element projection in the meridian plan. In order to simulate realistic boundary conditions for the magnetic field we solve the induction equation enforcing continuity of the magnetic field H at the interface with the external insulating medium through a Interior Penalty Galerkin method (IPG) [1]. I will present the results of our investigation of Alfven waves propagating in a cylinder filled of liquid metal submitted to an axial magnetic field. Poloidal Alfven waves are excited magnetically by imposing an azimuthal current pulse at the bottom of the cylinder. In the linear axisymmetric model we find a good agreement with previous experiments in liquid metals by Lundquist and by Lenhert and more recently by Alboussiere et al [2]. This axisymmetric study is extended to the non linear regime, where the amplitudes of the perturbations are comparable to the external applied magnetic field,in this conditions a complex response is found due to waves waves interactions. [1] J. L. Guermond, J.L Leorat, F. Luddens, C. Nore, A. Ribeiro. Effects of discontinuous magnetic permeability on magnetodynamic problems, Journal of Computational Physics Volume 230, Issue 16, 10 July 2011, Pages 6299 -- 6319. [2] T. Alboussiere, P. Cardin, F. Debray, H. C. Nataf, F. Plunian, A. Ribeiro, D. Schmitt, Experimental evidence of Alfven wave propagation in a Gallium alloy, Physics of fluids, 2011, vol. 23, nb 9.
Magnetosphere--Ionosphere Coupling: Effects of Plasma Alfven Wave Relative Motion
NASA Astrophysics Data System (ADS)
Christiansen, P. J.; Dum, C. T.
1989-06-01
The introduction of relative perpendicular motion between a flux-tube supporting shear Alfven wave activity and the background plasma is studied in the context of the coupling of a wave generating region with a distant ionosphere. The results of a representative simulation, using an extended version of the code developed by Lysak & Dum (J. geophys. Res. 88, 365 (1983)), are used as a basis for interpreting some aspects of recent satellite observations.
Gasmi, A.; Sprague, M. A.; Jonkman, J. M.; Jones, W. B.
2013-02-01
In this paper we examine the stability and accuracy of numerical algorithms for coupling time-dependent multi-physics modules relevant to computer-aided engineering (CAE) of wind turbines. This work is motivated by an in-progress major revision of FAST, the National Renewable Energy Laboratory's (NREL's) premier aero-elastic CAE simulation tool. We employ two simple examples as test systems, while algorithm descriptions are kept general. Coupled-system governing equations are framed in monolithic and partitioned representations as differential-algebraic equations. Explicit and implicit loose partition coupling is examined. In explicit coupling, partitions are advanced in time from known information. In implicit coupling, there is dependence on other-partition data at the next time step; coupling is accomplished through a predictor-corrector (PC) approach. Numerical time integration of coupled ordinary-differential equations (ODEs) is accomplished with one of three, fourth-order fixed-time-increment methods: Runge-Kutta (RK), Adams-Bashforth (AB), and Adams-Bashforth-Moulton (ABM). Through numerical experiments it is shown that explicit coupling can be dramatically less stable and less accurate than simulations performed with the monolithic system. However, PC implicit coupling restored stability and fourth-order accuracy for ABM; only second-order accuracy was achieved with RK integration. For systems without constraints, explicit time integration with AB and explicit loose coupling exhibited desired accuracy and stability.
Cherenkov radiation of shear Alfven waves in plasmas with two ion species
Farmer, W. A.; Morales, G. J.
2012-09-15
A calculation is presented of the radiation pattern of shear Alfven waves generated by a burst of charged particles in a charge-neutral plasma with two-ions of differing charge-to-mass ratios. The wake pattern is obtained for the inertial and kinetic regimes of wave propagation. Due to the presence of two ion-species, the Alfven waves propagate within two different frequency bands separated by a gap. One band is restricted to frequencies below the cyclotron frequency of the heavier species and the other to frequencies between the ion-ion hybrid frequency and the cyclotron frequency of the lighter species. The radiation pattern in the lower frequency band is found to exhibit essentially the same properties reported in a previous study [Van Compernolle et al., Phys. Plasmas 15, 082101 (2008)] of a single species plasma. However, the upper frequency band differs from the lower one in that it always allows for the Cherenkov radiation condition to be met. The methodology is extended to examine the Alfvenic wake of point-charges in the inertial and adiabatic regimes. The adiabatic regime is illustrated for conditions applicable to fusion-born alpha particles in ITER.
Alfven Wave Reflection Model of Field-Aligned Currents at Mercury
NASA Technical Reports Server (NTRS)
Lyatsky, Wladislaw; Khazanov, George V.; Slavin, James
2010-01-01
An Alfven Wave Reflection (AWR) model is proposed that provides closure for strong field-aligned currents (FACs) driven by the magnetopause reconnection in the magnetospheres of planets having no significant ionospheric and surface electrical conductance. The model is based on properties of the Alfven waves, generated at high altitudes and reflected from the low-conductivity surface of the planet. When magnetospheric convection is very slow, the incident and reflected Alfven waves propagate along approximately the same path. In this case, the net field-aligned currents will be small. However, as the convection speed increases. the reflected wave is displaced relatively to the incident wave so that the incident and reflected waves no longer compensate each other. In this case, the net field-aligned current may be large despite the lack of significant ionospheric and surface conductivity. Our estimate shows that for typical solar wind conditions at Mercury, the magnitude of Region 1-type FACs in Mercury's magnetosphere may reach hundreds of kilo-Amperes. This AWR model of field-aligned currents may provide a solution to the long-standing problem of the closure of FACs in the Mercury's magnetosphere. c2009 Elsevier Inc. All rights reserved.
Generation of field-aligned currents and Alfven waves by 3D magnetic reconnection
Ma, Z.W.; Lee, L.C.; Otto, A.
1995-07-01
The authors have carried out a three-dimensional compressible MHD simulation to study the generation of field-aligned currents (FAC`s) and Alfven waves by magnetic reconnection for locally antiparallel magnetic fields across the current sheet. Reconnection is triggered by a localized resistivity. The results indicate that both FAC`s and Alfven waves are generated by the three-dimensional reconnection process. Two pairs of FAC`s are generated on each side of current sheet. The polarities of the resulting FAC pair in the leading bulge region are opposite to those of a FAC pair in the trailing quasi-steady region. It is further found that a large portion of the FAC`s ({approximately}40%) is located in the closed field line region. They examine the Walen relation between FAC and parallel vorticity and find that Alfven waves are generated and propagate away from the reconnection site. They discuss the relevance of the results to the observed Region 1 FAC`s at noon. 15 refs., 4 figs.
Kinetic Alfven wave in the presence of kappa distribution function in plasma sheet boundary layer
Shrivastava, G. Ahirwar, G.; Shrivastava, J.
2015-07-31
The particle aspect approach is adopted to investigate the trajectories of charged particles in the electromagnetic field of kinetic Alfven wave. Expressions are found for the dispersion relation, damping/growth rate and associated currents in the presence of kappa distribution function. Kinetic effect of electrons and ions are included to study kinetic Alfven wave because both are important in the transition region. It is found that the ratio β of electron thermal energy density to magnetic field energy density and the ratio of ion to electron thermal temperature (T{sub i}/T{sub e}), and kappa distribution function affect the dispersion relation, damping/growth rate and associated currents in both cases(warm and cold electron limit).The treatment of kinetic Alfven wave instability is based on assumption that the plasma consist of resonant and non resonant particles. The resonant particles participate in an energy exchange process, whereas the non resonant particles support the oscillatory motion of the wave.
Supergranulation-driven Alfven waves in the solar chromosphere and related phenomena.
NASA Technical Reports Server (NTRS)
Hollweg, J. V.
1972-01-01
It has recently been recognized that Alfven waves frequently dominate the microstructure of the solar wind at the orbit of the earth. We seek a solar source for these waves, and consider here their excitation by the supergranular motions. The wave equation is solved in a horizontally stratified, bi-exponential solar atmosphere. The interaction of Alfven wave motions associated with adjacent supergranules is discussed qualitatively. The Alfven wave effectively conveys the supergranular motions to great heights in the chromosphere. These motions are oppositely directed above intersupergranule boundaries, and compress the magnetic field there. A naive calculation of the compression, based on balancing dynamic and magnetic pressures, leads to adequate agreement with observations of the chromospheric network. We find that the magnetic field is appreciably compressed only below about 1500 km, and on this basis we reject theories of spicule formation which require large vertical magnetic fields at the heights reached by spicules. We advance a theory for spicule formation, in which spicules form as a result of matter being squeezed upward, out of the compression region between adjacent supergranules.
Small scales formation via Alfven wave propagation in compressible nonuniform media
NASA Technical Reports Server (NTRS)
Malara, F.; Primavera, L.; Veltri, P.
1995-01-01
In weakly dissipative media governed by the magnetohydrodynamics (MHD) equations, any efficient mechanism of energy dissipation requires the formation of small scales. The possibility to produce small scales has been studied by Malara et al. in the case of MHD disturbances propagating in an incompressible and inhomogeneous medium, for a strictly 2D geometry. We extend the work of Malara et al. to include both compressibility and the third component for vector quantities. Using numerical simulations we show that, when an Alfven wave propagates in a compressible nonuniform medium, the two dynamical effects responsible for the small scales formation in the incompressible case are still at work: energy pinching and phase-mixing. Moreover, the interaction between the initial Alfven wave and the inhomogeneity gives rise to the formation of compressible perturbations (fast and slow waves or a static entropy wave). Some of these compressive fluctuations are subject to the steepening of the wave front and become shock waves, which are extremely efficient in dissipating their energy, their dissipation being independent of the Reynolds number. A rough estimate of the typical times which the various dynamical processes take to produce small scales and then to dissipate the energy show that these times are consistent with those required to dissipate inside the solar corona the energy of Alfven waves of photospheric origin.
Star of Lima - Overview and optical diagnostics of a barium Alfven critical velocity experiment
NASA Technical Reports Server (NTRS)
Wescott, E. M.; Stenbaek-Nielsen, H. C.; Hallinan, T.; Foeppl, H.; Valenzuela, A.
1986-01-01
The Alfven critical velocity mechanism for ionization of a neutral gas streaming across the magnetic field has been demonstrated in laboratory experiments. In March 1983, two rocket-borne experiments with Ba and Sr tested the effect in the wall-less laboratory of space from Punto Lobos, Peru, near 430 km altitude. 'Star of Lima' used a conical Ba shaped charge aimed at an instrument payload about 2 km away. Because of rocket overperformance the detonation occurred in partial sunlight, so that less than 21.6 percent of the ionizing UV was present. Particle and field measurements indicate the production of hot electrons and waves in the energy and frequency range that are respectively predicted to produce a cascade of ionization by the Alfven mechanism. However, the ionization fluxes and wave energy density did not reach cascade levels, and optical observations indicate that only 2.5 to 5 x 10 to the 20th Ba ions were produced. A substantial portion and perhaps all of the ionization could have been produced by solar UV. The failure of the Alfven process in this experiment is not well understood.
Eigenmode analysis of a high-gain free-electron laser based on a transverse gradient undulator
NASA Astrophysics Data System (ADS)
Baxevanis, Panagiotis; Huang, Zhirong; Ruth, Ronald; Schroeder, Carl B.
2015-01-01
The use of a transverse gradient undulator (TGU) is viewed as an attractive option for free-electron lasers (FELs) driven by beams with a large energy spread. By suitably dispersing the electron beam and tilting the undulator poles, the energy spread effect can be substantially mitigated. However, adding the dispersion typically leads to electron beams with large aspect ratios. As a result, the presence of higher-order modes in the FEL radiation can become significant. To investigate this effect, we study the eigenmode properties of a TGU-based, high-gain FEL, using both an analytically-solvable model and a variational technique. Our analysis, which includes the fundamental and the higher-order FEL eigenmodes, can provide an estimate of the mode content for the output radiation. This formalism also enables us to study the trade-off between FEL gain and transverse coherence. Numerical results are presented for a representative soft X-ray, TGU FEL example.
Soft iron and axisymetric eigenmodes in the von-Karman-Sodium dynamo
NASA Astrophysics Data System (ADS)
Giesecke, A.; Stefani, F.; Gerbeth, G.
2012-04-01
In the Cadarache von-Karman-Sodium (VKS) dynamo experiment magnetic field excitation is generated by a turbulent flow of liquid sodium. In the experiment this so called von-Karman-like flow is driven by two counter-rotating impellers that are located close to the end-caps of a cylindrical vessel. Despite of extensive numerical and experimental efforts the very nature of the VKS dynamo and its surprising properties still remain unclear. Firstly, dynamo action is obtained only when (at least one of) the flow driving impellers are made of soft iron with a relative permeability around 65. Moreover, and in apparent contradiction with Cowling's anti-dynamo theorem, the geometric structure of the observed magnetic field is dominated by an axisymmetric field. Our kinematic simulations of an axisymmetric model of the Cadarache dynamo show a close connection between the exclusive occurrence of dynamo action with soft iron impellers and the axisymmetry of the magnetic field. We observe two distinct classes of axisymmetric eigenmodes, a purely toroidal mode that is amplified by paramagnetic pumping at the fluid-disk interface and a mixed mode consisting of a poloidal and a toroidal contribution that is rather insensitive to the disk permeability. In the limit of large permeability, the purely toroidal mode is close to the onset of dynamo action with a growth-rate that is rather independent of the flow field. This mode is located near to and in the high permeability disks and becomes the leading mode when the disk permeability exceeds a critical value. However, since in our axisymmetric configuration the purely toroidal mode is decoupled from any poloidal field component no dynamo action can be expected from this mode. The purely toroidal mode and its strong amplification by paramagnetic pumping at the fluid-disks interface can be obtained only by explicitly considering the internal permeability distribution. This mode does not exist in case of highly conducting disks or in
Evidence of kinetic Alfvén eigenmode in the near-Earth magnetotail during substorm expansion phase
NASA Astrophysics Data System (ADS)
Duan, S. P.; Dai, Lei; Wang, Chi; Liang, J.; Lui, A. T. Y.; Chen, L. J.; He, Z. H.; Zhang, Y. C.; Angelopoulos, V.
2016-05-01
Unipolar pulses of kinetic Alfvén waves (KAW) are first observed in the near-Earth plasma sheet (NEPS) associated with dipolarizations during substorm expansion phases. Two similar events are studied with Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations during substorms on 3 February 2008 and 7 February 2008. The unipolar pulses were located at a trough-like Alfvén speed profile in the northern plasma sheet at a distance of 10-11 RE from Earth. The dominant wave components consist of a southward δEz toward the neutral plane and a +δBy toward the dusk. The |δEz|/|δBy| ratio was in the range of a few times the local Alfvén speed, a strong indication of KAW nature. The wave Poynting flux was earthward and nearly parallel to the background magnetic field. The pulse was associated with an earthward field-aligned current carried by electrons. These observational facts strongly indicate a KAW eigenmode that is confined by the plasma sheet but propagates earthward along the field line. The KAW eigenmode was accompanied by short timescale (1 min) dipolarizations likely generated by transient magnetotail reconnection. The observed polarity of the KAW field/current is consistent with that of the Hall field/current in magnetic reconnection, supporting the scenario that the Hall fields/current propagate out from reconnection site as KAW eigenmodes. Aurora images on the footprint of THEMIS spacecraft suggest that KAW eigenmode may power aurora brightening during substorm expansion phase.
Gyrokinetic particle-in-cell simulations of Alfvén eigenmodes in presence of continuum effects
Mishchenko, Alexey Könies, Axel; Hatzky, Roman
2014-05-15
First-principle gyrokinetic particle-in-cell simulations of a global Toroidal Alfvén Eigenmode (TAE) are undertaken in the presence of a strong coupling with the continuum. Effects of the bulk plasma temperature on the interplay between the TAE and Kinetic Alfvén Waves (KAWs) are investigated. A global TAE-KAW structure is identified which appears to be more unstable with respect to the fast ions than a simple (fluid-like) TAE mode.
Wang, G.; Peebles, W. A.; Rhodes, T. L.; Doyle, E. J.; Hillesheim, J. C.; Schmitz, L.; Zeng, L.; Austin, M. E.; Yan, Z.; McKee, G. R.; La Haye, R. J.; Burrell, K. H.; Lanctot, M. J.; Petty, C. C.; Smith, S.; Strait, E. J.; Van Zeeland, M.; Nazikian, R.
2013-09-15
The geodesic acoustic mode (GAM), a coherent form of the zonal flow, plays a critical role in turbulence regulation and cross-magnetic-field transport. In the DIII-D tokamak, unique information on multi-field characteristics and radial structure of eigenmode GAMs has been measured. Two simultaneous and distinct, radially overlapping eigenmode GAMs (i.e., constant frequency vs. radius) have been observed in the poloidal E×B flow in L-mode plasmas. As the plasma transitions from an L-mode to an Ohmic regime, one of these eigenmode GAMs becomes a continuum GAM (frequency responds to local parameters), while the second decays below the noise level. The eigenmode GAMs occupy a radial range of ρ = 0.6–0.8 and 0.75–0.95, respectively. In addition, oscillations at the GAM frequency are observed for the first time in multiple plasma parameters, including n{sub e}, T{sub e}, and B{sub θ}. The magnitude of T(tilde sign){sub e}/T{sub e} at the GAM frequency (the magnitude is similar to that of ñ{sub e}/n{sub e}) and measured n{sub e}–T{sub e} cross-phase (∼140° at the GAM frequency) together indicate that the GAM pressure perturbation is not determined solely by ñ{sub e}. The magnetic GAM behavior, a feature only rarely reported, is significantly stronger (×18) on the high-field side of the tokamak, suggesting an anti-ballooning nature. Finally, the GAM is also observed to directly modify intermediate-wavenumber ñ{sub e} levels (kρ{sub s} ∼ 1.1). The simultaneous temperature, density, flow fluctuations, density-temperature cross-phase, and magnetic behavior present a new perspective on the underlying physics of the GAM.
NASA Astrophysics Data System (ADS)
Figueiredo, A. C. A.; Rodrigues, P.; Borba, D.; Coelho, R.; Fazendeiro, L.; Ferreira, J.; Loureiro, N. F.; Nabais, F.; Pinches, S. D.; Polevoi, A. R.; Sharapov, S. E.
2016-07-01
The linear stability of Alfvén eigenmodes in the presence of fusion-born alpha particles is thoroughly assessed for two variants of an ITER baseline scenario, which differ significantly in their core and pedestal temperatures. A systematic approach based on CASTOR-K (Borba and Kerner 1999 J. Comput. Phys. 153 101; Nabais et al 2015 Plasma Sci. Technol. 17 89) is used that considers all possible eigenmodes for a given magnetic equilibrium and determines their growth rates due to alpha-particle drive and Landau damping on fuel ions, helium ashes and electrons. It is found that the fastest growing instabilities in the aforementioned ITER scenario are core-localized, low-shear toroidal Alfvén eigenmodes. The largest growth-rates occur in the scenario variant with higher core temperatures, which has the highest alpha-particle density and density gradient, for eigenmodes with toroidal mode numbers n≈ 30 . Although these eigenmodes suffer significant radiative damping, which is also evaluated, their growth rates remain larger than those of the most unstable eigenmodes found in the variant of the ITER baseline scenario with lower core temperatures, which have n≈ 15 and are not affected by radiative damping.
Local and global kinetic stability analysis of Alfvén eigenmodes in the 15 MA ITER scenario
NASA Astrophysics Data System (ADS)
Lauber, Ph
2015-05-01
The linear gyrokinetic spectral code LIGKA (Lauber et al 2007 J. Comput. Phys. 226 447-65) is used to examine the Alfvén eigenmode stability properties of the ITER 15 MA scenario. It is shown that a kinetic multi-species treatment i.e. deuterium (D), tritium (T), helium ash (He), beryllium (Be), energetic α-particles and neutral beam deuterium is indispensable for an accurate estimate of linear Alfvén mode properties. Comparisons to analytical expressions are carried out and several frequency ranges and modes such as the geodesic-acoustic/beta-induced Alfvén mode (GAM/BAE), the toroidal Alfvén eigenmode (TAE) and the ellipticity-induced Alfvén eigenmode (EAE) are discussed. A scan for the damping of TAEs (including radiative damping, continuum damping, ion and electron Landau damping) with the toroidal mode numbers n = 1-35 is performed. Finally, the instability threshold as a function of the energetic particle β is investigated for one example.
Diaz, Alfredo J.; Eslami, Babak; López-Guerra, Enrique A.; Solares, Santiago D.
2014-09-14
This paper explores the effect of the amplitude ratio of the higher to the fundamental eigenmode in bimodal atomic force microscopy (AFM) on the phase contrast and the dissipated power contrast of the higher eigenmode. We explore the optimization of the amplitude ratio in order to maximize the type of contrast that is most relevant to the particular study. Specifically, we show that the trends in the contrast range behave differently for different quantities, especially the dissipated power and the phase, with the former being more meaningful than the latter (a similar analysis can be carried out using the virial, for which we also provide a brief example). Our work is based on numerical simulations using two different conservative-dissipative tip-sample models, including the standard linear solid and the combination of a dissipation coefficient with a conservative model, as well as experimental images of thin film Nafion{sup ®} proton exchange polymers. We focus on the original bimodal AFM method, where the higher eigenmode is driven with constant amplitude and frequency (i.e., in “open loop”).
NASA Astrophysics Data System (ADS)
Christov, Ivan C.; Ottino, Julio M.; Lueptow, Richard M.
2011-10-01
Through a combined computational-experimental study of flow in a slowly rotating quasi-two-dimensional container, we show several new aspects related to the kinematics of granular mixing. In the Lagrangian frame, for small numbers of revolutions, the mixing pattern is captured by a model termed "streamline jumping." This minimal model, arising at the limit of a vanishingly thin surface flowing layer, possesses no intrinsic stretching or streamline crossing in the usual sense, yet it can lead to complex particle trajectories. Meanwhile, for intermediate numbers of revolutions, we show the presence of naturally persistent granular mixing patterns, i.e., "strange" eigenmodes of the advection-diffusion operator governing the mixing process in Eulerian frame. Through a comparative analysis of the structure of eigenmodes and the corresponding Poincaré section and finite-time Lyapunov exponent field of the flow, the relationship between the Eulerian and Lagrangian descriptions of mixing is highlighted. Finally, we show how the mapping method for scalar transport can be modified to include diffusion. This allows us to examine (for the first time in a granular flow) the change in shape, lifespan, and eventual decay of eigenmodes due to diffusive effects at larger numbers of revolutions.
Eigenmodes of Three-dimensional Magnetic Arcades in the Sun’s Corona
NASA Astrophysics Data System (ADS)
Hindman, Bradley W.; Jain, Rekha
2015-12-01
We develop a model of coronal-loop oscillations that treats the observed bright loops as an integral part of a larger three-dimensional (3D) magnetic structure comprised of the entire magnetic arcade. We demonstrate that magnetic arcades within the solar corona can trap MHD fast waves in a 3D waveguide. This is accomplished through the construction of a cylindrically symmetric model of a magnetic arcade with a potential magnetic field. For a magnetically dominated plasma, we derive a governing equation for MHD fast waves and from this equation we show that the magnetic arcade forms a 3D waveguide if the Alfvén speed increases monotonically beyond a fiducial radius. Both magnetic pressure and tension act as restoring forces, instead of just tension as is generally assumed in 1D models. Since magnetic pressure plays an important role, the eigenmodes involve propagation both parallel and transverse to the magnetic field. Using an analytic solution, we derive the specific eigenfrequencies and eigenfunctions for an arcade possessing a discontinuous density profile. The discontinuity separates a diffuse cylindrical cavity and an overlying shell of denser plasma that corresponds to the bright loops. We emphasize that all of the eigenfunctions have a discontinuous axial velocity at the density interface; hence, the interface can give rise to the Kelvin-Helmholtz instability. Further, we find that all modes have elliptical polarization with the degree of polarization changing with height. However, depending on the line of sight, only one polarization may be clearly visible.
Toroidal Alfv{acute e}n eigenmodes in TFTR deuterium{endash}tritium plasmas
Nazikian, R.; Fu, G.Y.; Chang, Z.; Batha, S.H.; Berk, H.; Budny, R.V.; Chen, Y.; Cheng, C.Z.; Darrow, D.S.; Gorelenkov, N.N.; Levinton, F.M.; Medley, S.; Petrov, M.P.; Redi, M.; Ruskov, E.; Spong, D.A.; White, R.B.; Zweben, S.J.
1998-05-01
Purely alpha-particle-driven toroidal Alfv{acute e}n eigenmodes (TAEs) with toroidal mode numbers n=1{endash}6 have been observed in deuterium{endash}tritium (D{endash}T) plasmas on the tokamak fusion test reactor [D. J. Grove and D. M. Meade, Nucl. Fusion {bold 25}, 1167 (1985)]. The appearance of mode activity following termination of neutral beam injection in plasmas with q(0){gt}1 is generally consistent with theoretical predictions of TAE stability [G. Y. Fu {ital et al.} Phys. Plasmas {bold 3}, 4036 (1996)]. Internal reflectometer measurements of TAE activity is compared with theoretical calculations of the radial mode structure. Core localization of the modes to the region of reduced central magnetic shear is confirmed, however the mode structure can deviate significantly from theoretical estimates. The peak measured TAE amplitude of {delta}n/n{approximately}10{sup {minus}4} at r/a{approximately}0.3{minus}0.4 corresponds to {delta}B/B{approximately}10{sup {minus}5}, while {delta}B/B{approximately}10{sup {minus}8} is measured at the plasma edge. Enhanced alpha particle loss associated with TAE activity has not been observed. {copyright} {ital 1998 American Institute of Physics.}
Eigenmode expansion methods for simulation of optical propagation in photonics: pros and cons
NASA Astrophysics Data System (ADS)
Gallagher, Dominic F. G.; Felici, Thomas P.
2003-06-01
With the rapid growth of the telecommunications industry over the last 5 to 10 years has come the need to solve ever more complex electromagnetic problems and to solve them more precisely than ever before. The basic EME (EigenMode Expansion) technique is a powerful method for calculation of electromagnetic propagation which has been well known amongst academic environments and also in microwave fields, representing the electromagnetic fields everywhere in terms of a basis set of local modes. It is at the same time a rigorous solution of Maxwell's Equations and is able to deal with very long structures. We discuss here progress that the authors and others have made recently in applying and extending it to integrated, fibre, and diffractive optics - including development of efficient ways of modelling tapers and other smoothly varying structures, new more efficient boundary conditions and improved mode finders. We outline the advantages it has over other techniques and also its limitations. We illustrate its application with a variety of real life examples, including diffractive elements, directional couplers, tapers, MMI's, bend modelling, periodic structures and others.
Toroidal Alfvén Eigenmodes in TFTR Deuterium-Tritium Plasmas
G.Y. Fu; H. Berk; R. Nazikian; S.H. Batha; Z. Chang; et al
1998-01-01
Purely alpha-particle-driven Toroidal Alfvén Eigenmodes (TAEs) with toroidal mode numbers n=1-6 have been observed in Deuterium-Tritium (D-T) plasmas on the Tokamak Fusion Test Reactor [D.J. Grove and D.M. Meade, Nucl. Fusion 25, 1167 (1985)]. The appearance of mode activity following termination of neutral beam injection in plasmas with q(0)>1 is generally consistent with theoretical predictions of TAE stability [G.Y. Fu et al., Phys. Plasmas 3, 4036 (1996]. Internal reflectometer measurements of TAE activity is compared with theoretical calculations of the radial mode structure. Core localization of the modes to the region of reduced central magnetic shear is confirmed, however the mode structure can deviate significantly from theoretical estimates. The peak measured TAE amplitude of delta n/n~10(superscript -4) at r/a~0.3-0.4 corresponds to delta B/B~10-5, while dB/B~10(superscript -8) is measured at the plasma edge. Enhanced alpha particle loss associated with TAE activity has not been observed.
Externally driven global Alfvén eigenmodes applied for effective mass number measurement on TCABR
Puglia, P. G. P. P.; Elfimov, A. G.; Ruchko, L. F.; Galvão, R. M. O.; Guimarães-Filho, Z.; Ronchi, G.
2014-12-15
The excitation and detection of Global Alfvén Eigenmodes on TCABR for diagnostic purposes are presented. The modes can be excited with one or two in-vessel antennae, with up to 15 A of current in each, in the frequency range from 2 to 4 MHz. This scheme allows the estimation of the effective mass number at the plasma center, which value is affected by impurity concentration in the core. An amplifier based on MOSFETs is used to excite the waves driven by low power, in order to not change the basic plasma parameters. The variation of the GAE with density is verified and the location of the mode resonance at the plasma center is confirmed by the sawtooth beating, so that the correspondingly beating phase inversion improves the precision on the resonant condition determination. The toroidal parity of the modes N = 1,2 is determined by use of two opposite located antennae with different phase of the RF current. Knowledge of toroidal mode number is important as it identifies GAE location and defines the estimated effective mass value. The estimated value for A{sub eff} is ∼1.4–1.5, corresponding to 5–7% of carbon impurity concentration. The measured value of A{sub eff} is used to estimate Z{sub eff}, which is compared to older TCA experiments and the value obtained by the Spitzer conductivity.
Saturation of a toroidal Alfvén eigenmode due to enhanced damping of nonlinear sidebands
NASA Astrophysics Data System (ADS)
Todo, Y.; Berk, H. L.; Breizman, B. N.
2012-09-01
This paper examines nonlinear magneto-hydrodynamic effects on the energetic particle driven toroidal Alfvén eigenmode (TAE) for lower dissipation coefficients and with higher numerical resolution than in the previous simulations (Todo et al 2010 Nucl. Fusion 50 084016). The investigation is focused on a TAE mode with toroidal mode number n = 4. It is demonstrated that the mechanism of mode saturation involves generation of zonal (n = 0) and higher-n (n ⩾ 8) sidebands, and that the sidebands effectively increase the mode damping rate via continuum damping. The n = 0 sideband includes the zonal flow peaks at the TAE gap locations. It is also found that the n = 0 poloidal flow represents a balance between the nonlinear driving force from the n = 4 components and the equilibrium plasma response to the n = 0 fluctuations. The spatial profile of the n = 8 sideband peaks at the n = 8 Alfvén continuum, indicating enhanced dissipation due to continuum damping.
Stability of the non-radial eigenmodes of a uniformly charged elastic globe
NASA Astrophysics Data System (ADS)
Bastrukov, Sergey; Podgainy, Dmitry
1998-04-01
The eigenmotions of an electrically charged isotropic elastic material are modeled by self-consistent system of elastodynamic equations (comprising the continuity equation for the density, the Euler equation for the velocity field of elastic displacements coupled with equation for the stress tensor governing evolution of elastic distortions) and Poisson’s equation of electrostatics. To elucidate the question of how the elastodynamic features of bulk elastic substance can be traced in a spherical sample of finite size, the low-frequency electromagnetic response of the sample is studied in the homogeneous model of a uniformly charged elastic globe. The response is described in terms of long wavelength, essentially non-radial, spheroidal (S-mode) and torsional (T-mode) electro-elastic vibrations. The restoring force is presumed to be dominated by the surface cohesive stresses and the volume disruptive stresses of electric origin acting destructively. It is shown that the continuum model in question leads to explicit form for the frequency of the non-radial eigenmodes. The emphasis is placed on the onset of vibrational instability originating from conflicting tendency of the above surface and volume elastic stresses. The elastodynamic criteria of instability for both spheroidal and torsional vibrations are established in analytic form.
ERIC Educational Resources Information Center
Zhang, Yujie; Terai, Asuka; Nakagawa, Masanori
2013-01-01
Inductive reasoning under risk conditions is an important thinking process not only for sciences but also in our daily life. From this viewpoint, it is very useful for language learning to construct computational models of inductive reasoning which realize the CAE for foreign languages. This study proposes the comparison of inductive reasoning…
Espinosa-Luna, Graciela; Sánchez-Otero, María Guadalupe; Quintana-Castro, Rodolfo; Matus-Toledo, Rodrigo Eloir; Oliart-Ros, Rosa María
2016-01-01
A gene encoding a carboxylesterase produced by Geobacillus thermoleovoras CCR11 was cloned in the pET-3b cloning vector, sequenced and expressed in Escherichia coli BL21(DE3). Gene sequence analysis revealed an open reading frame of 750 bp that encodes a polypeptide of 250 amino acid residues (27.3 kDa) named CaesCCR11. The enzyme showed its maximum activity at 50 °C and pH 5-8, with preference for C4 substrates, confirming its esterase nature. It displayed good resistance to temperature, pH, and the presence of organic solvents and detergents, that makes this enzyme biotechnologically applicable in the industries such as fine and oleo-chemicals, cosmetics, pharmaceuticals, organic synthesis, biodiesel production, detergents, and food industries. A 3D model of CaesCCR11 was predicted using the Bacillus sp. monoacyl glycerol lipase bMGL H-257 structure as template (PBD code 3RM3, 99 % residue identity with CaesCCR11). Based on its canonical α/β hydrolase fold composed of 7 β-strands and 6 α-helices, the α/β architecture of the cap domain, the GLSTG pentapeptide, and the formation of distinctive salt bridges, we are proposing CaesCCR11 as a new member of family XV of lipolytic enzymes. PMID:26603441
Matsumoto, Takuma; Shibata, Kazunari
2010-02-20
We have performed MHD simulations of Alfven wave propagation along an open flux tube in the solar atmosphere. In our numerical model, Alfven waves are generated by the photospheric granular motion. As the wave generator, we used a derived temporal spectrum of the photospheric granular motion from G-band movies of Hinode/Solar Optical Telescope. It is shown that the total energy flux at the corona becomes larger and the transition region's height becomes higher in the case when we use the observed spectrum rather than the white/pink noise spectrum as the wave generator. This difference can be explained by the Alfven wave resonance between the photosphere and the transition region. After performing Fourier analysis on our numerical results, we have found that the region between the photosphere and the transition region becomes an Alfven wave resonant cavity. We have confirmed that there are at least three resonant frequencies, 1, 3, and 5 mHz, in our numerical model. Alfven wave resonance is one of the most effective mechanisms to explain the dynamics of the spicules and the sufficient energy flux to heat the corona.
Huysmans, G.T.A.; Kerner, W.; Borba, D.; Holties, H.A.; Goedbloed, J.P.
1995-05-01
The active excitation of global Alfven modes using the saddle coils in the Joint European Torus (JET) [{ital Plasma} {ital Physics} {ital and} {ital Controlled} {ital Nuclear} {ital Fusion} {ital Research} 1984, Proceedings of the 10th International Conference, London (International Atomic Energy Agency, Vienna, 1985), Vol. 1, p. 11] as the external antenna, will provide information on the damping of global modes without the need to drive the modes unstable. For the modeling of the Alfven mode excitation, the toroidal resistive magnetohydrodynamics (MHD) code CASTOR (Complex Alfven Spectrum in TORoidal geometry) [18{ital th} {ital EPS} {ital Conference} {ital On} {ital Controlled} {ital Fusion} {ital and} {ital Plasma} {ital Physics}, Berlin, 1991, edited by P. Bachmann and D. C. Robinson (The European Physical Society, Petit-Lancy, 1991), Vol. 15, Part IV, p. 89] has been extended to calculate the response to an external antenna. The excitation of a high-performance, high beta JET discharge is studied numerically. In particular, the influence of a finite pressure is investigated. Weakly damped low-{ital n} global modes do exist in the gaps in the continuous spectrum at high beta. A pressure-driven global mode is found due to the interaction of Alfven and slow modes. Its frequency scales solely with the plasma temperature, not like a pure Alfven mode with a density and magnetic field.
NASA Astrophysics Data System (ADS)
Zhang, Guimin; Li, Yinping; Daemen, Jaak J. K.; Yang, Chunhe; Wu, Yu; Zhang, Kai; Chen, Yanlong
2015-09-01
The lower reaches of the Yangtze River is one of the most developed regions in China. It is desirable to build compressed air energy storage (CAES) power plants in this area to ensure the safety, stability, and economic operation of the power network. Geotechnical feasibility analysis was carried out for CAES in impure bedded salt formations in Huai'an City, China, located in this region. First, geological investigation revealed that the salt groups in the Zhangxing Block meet the basic geological conditions for CAES storage, even though the possible unfavorable characteristics of the salt formations include bedding and different percentages of impurities. Second, mechanical tests were carried out to determine the mechanical characteristics of the bedded salt formations. It is encouraging that the samples did not fail even when they had undergone large creep deformation. Finally, numerical simulation was performed to evaluate the stability and volume shrinkage of the CAES under the following conditions: the shape of a single cavern is that of a pear; the width of the pillar is adopted as two times the largest diameter; three regular operating patterns were adopted for two operating caverns (internal pressure 9-10.5 MPa, 10-11.5 MPa, and 11-12.5 MPa), while the other two were kept at high pressure (internal pressure 10.5, 11.5, and 12.5 MPa) as backups; an emergency operating pattern in which two operating caverns were kept at atmospheric pressure (0.1 MPa) for emergency while the backups were under operation (9-10.5 MPa), simulated for 12 months at the beginning of the 5th year. The results of the analysis for the plastic zone, displacement, and volume shrinkage support the feasibility of the construction of an underground CAES power station.
Analysis of the Hexapod Work Space using integration of a CAD/CAE system and the LabVIEW software
NASA Astrophysics Data System (ADS)
Herbuś, K.; Ociepka, P.
2015-11-01
The paper presents the problems related to the integration of a CAD/CAE system with the LabVIEW software. The purpose of the integration is to determine the workspace of a hexapod model basing on a mathematical model describing it motion. In the first stage of the work concerning the integration task the 3D model to simulate movements of a hexapod was elaborated. This phase of the work was done in the “Motion Simulation” module of the CAD/CAE/CAM Siemens NX system. The first step was to define the components of the 3D model in the form of “links”. Individual links were defined according to the nature of the hexapod elements action. In the model prepared for movement simulation were created links corresponding to such elements as: electric actuator, top plate, bottom plate, ball-and-socket joint, toggle joint Phillips. Then were defined the constraints of the “joint” type (e.g.: revolute joint, slider joint, spherical joint) between the created component of the “link” type, so that the computer simulation corresponds to the operation of a real hexapod. The next stage of work included implementing the mathematical model describing the functioning of a hexapod in the LabVIEW software. At this stage, particular attention was paid to determining procedures for integrating the virtual 3D hexapod model with the results of calculations performed in the LabVIEW. The results relate to specific values of the jump of electric actuators depending on the position of the car on the hexapod. The use of integration made it possible to determine the safe operating space of a stationary hexapod taking into consideration the security of a person in the driving simulator designed for the disabled.
Resonant-state-expansion Born approximation with a correct eigen-mode normalisation
NASA Astrophysics Data System (ADS)
Doost, M. B.
2016-08-01
The Born approximation (Born 1926 Z. Phys. 38 802) is a fundamental result in physics, it allows the calculation of weak scattering via the Fourier transform of the scattering potential. As was done by previous authors (Ge et al 2014 New J. Phys. 16 113048) the Born approximation is extended by including in the formula the resonant-states (RSs) of the scatterer. However in this study unlike previous studies the included eigen-modes are correctly normalised with dramatic positive consequences for the accuracy of the method. The normalisation of RSs used in the previous RS expansion Born approximation or resonant-state expansion (RSE) Born approximation made in Ge et al (2014 New J. Phys. 16 113048) has been shown to be numerically unstable in Muljarov et al (2014 arXiv:1409.6877) and by analytics here. The RSs of the system can be calculated using my recently discovered RSE perturbation theory for dispersive electrodynamic scatterers (Muljarov et al 2010 Europhys. Lett. 92 50010; Doost et al 2012 Phys. Rev. A 85 023835; Doost et al 2013 Phys. Rev. A 87 043827; Armitage et al 2014 Phys. Rev. A 89; Doost et al 2014 Phys. Rev. A 90 013834) and normalised correctly to appear in spectral Green's functions and hence the RSE Born approximation via the flux-volume normalisation which I recently rigorously derived in Armitage et al (2014 Phys. Rev. A 89), Doost et al (2014 Phys. Rev. A 90 013834), Doost (2016 Phys. Rev. A 93 023835). In the case of effectively one-dimensional systems I find a RSE Born approximation alternative to the scattering matrix method.
NASA Astrophysics Data System (ADS)
Gordeyev, S. V.; Thomas, F. O.
2002-06-01
The topology of the large-scale structure in the similarity region of a turbulent planar jet is investigated experimentally. The large-scale structure is reconstructed in physical space by projection of measured proper orthogonal decomposition eigenmodes onto instantaneous flow-field realizations. The instantaneous flow-field realizations are obtained by a spanwise aligned triple X-wire rake arrangement which is used in conjunction with the linear stochastic estimation technique. Instantaneous realizations are also acquired via a second triple rake arrangement which provides an assessment of the effect of spatial aliasing on the resulting structural topology. Results indicate that the self-similar large-scale structure in the planar jet consists of a dominant planar component consisting of two lines of large-scale spanwise vortices arranged approximately asymmetrically with respect to the jet centreline. This planar component of the structure resembles the classic Kármán vortex street. There is a strong interaction between structures on opposite sides of the jet in the form of nearly two-dimensional lateral streaming motions that extend well across the flow. In addition, results indicate that the effect of the nonplanar spanwise modes is to both tilt and bend the primary spanwise vortex tubes and thereby redistribute large-scale vorticity. The bending occurs primarily in the streamwise direction. The degree to which the spanwise vortices are distorted varies greatly; in some cases they are nearly streamwise oriented and in others only slight distortion of a spanwise vortex is noted. Based upon the experimental results, prospects for low-order modelling of the jet large-scale structure are discussed.
Propagation and Damping of Kinetic Alfven Waves Generated During Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Sharma, P.; Shay, M. A.; Haggerty, C. C.; Parashar, T.
2015-12-01
Magnetospheric waves have the potential to convert to Kinetic Alfven Waves (KAW) at scales close to the ion larmor radius and the electron inertial length. At this length scale, it is observed that KAW generated at reconnection propagates super-Alfvenically and the wave is responsible for the parallel propagation of the Hall magnetic field near the separatrice from the magnetotial region. The pointing flux associated with this Hall magnetic field is also consistent with observed Cluster data observations [1]. An important question is whether this KAW energy will be able to propagate all the way to the Earth, creating aurora associated with a substorm. If this KAW propagation can be well understood, then this will provide valuable insight as to the relative timing of substorm onset versus reconnection onset in the magnetotail. The difficulty currently is that the nonlinear damping of KAW is not well understood even in a homogenous system, let alone more realistic magnetotail geometries including changes to density, magnetic field strength, and magnetic orientation. We study the propagation, dispersion, and damping of these KAWs using P3D, a kinetic particle-in-cell (PIC) simulation code. Travelling waves are initialized based on a fluid model and allowed to propagate for substantial time periods. Damping of the waves are compared with Landau damping predictions. The waves are simulated in both homogenous and varying equilibrium meant to determine the effect on propagation. Implications for energetic electron production and Poynting flux input into the ionosphere are discussed. [1] Shay, M. A., J. F. Drake, J. P. Eastwood, and T. D. Phan, Super-Alfvenic propagation of substorm reconnection signatures and Poynting flux,, Physics Review Letters, Vol. 107, 065001, 2011.
Detection of Ionospheric Alfven Resonator Signatures Onboard C/NOFS: Implications for IRI Modeling
NASA Technical Reports Server (NTRS)
Simoes, F.; Klenzing, J.; Ivanov, S.; Pfaff, R.; Rowland, D.; Bilitza, D.
2011-01-01
The 2008-2009 long-lasting solar minimum activity has been the one of its kind since the dawn of space age, offering exceptional conditions for investigating space weather in the near-Earth environment. First ever detection of Ionospheric Alfven Resonator (IAR) signatures in orbit offers new means for investigating ionospheric electrodynamics, namely MHD (MagnetoHydroDynamics) wave propagation, aeronomy processes, ionospheric dynamics, and Sun-Earth connection mechanisms at a local scale. Local and global plasma density heterogeneities in the ionosphere and magnetosphere allow for formation of waveguides and resonators where magnetosonic and shear Alfven waves propagate. The ionospheric magnetosonic waveguide results from complete magnetosonic wave reflection about the ionospheric F-region peak, where the Alfven index of refraction presents a maximum. MHD waves can also be partially trapped in the vertical direction between the lower boundary of the ionosphere and the magnetosphere, a resonance mechanism known as IAR. In this work we present C/NOFS (Communications/Navigation Outage Forecasting System) Extremely Low Frequency (ELF) electric field measurements related to IAR signatures, discuss the resonance and wave propagation mechanisms in the ionosphere, and address the electromagnetic inverse problem from which electron/ion distributions can be derived. These peculiar IAR electric field measurements provide new, complementary methodologies for inferring ionospheric electron and ion density profiles, and also contribute for the investigation of ionosphere dynamics and space weather monitoring. Specifically, IAR spectral signatures measured by C/NOFS contribute for improving the International Reference Ionosphere (IRI) model, namely electron density and ion composition.
A DATA-DRIVEN, TWO-TEMPERATURE SOLAR WIND MODEL WITH ALFVEN WAVES
Van der Holst, B.; Manchester, W. B.; Frazin, R. A.; Toth, G.; Gombosi, T. I.; Vasquez, A. M.
2010-12-10
We have developed a new three-dimensional magnetohydrodynamic (MHD) solar wind model coupled to the Space Weather Modeling Framework (SWMF) that solves for the different electron and proton temperatures. The collisions between the electrons and protons are taken into account as well as the anisotropic thermal heat conduction of the electrons. The solar wind is assumed to be accelerated by the Alfven waves. In this paper, we do not consider the heating of closed magnetic loops and helmet streamers but do address the heating of the protons by the Kolmogorov dissipation of the Alfven waves in open field-line regions. The inner boundary conditions for this solar wind model are obtained from observations and an empirical model. The Wang-Sheeley-Arge model is used to determine the Alfven wave energy density at the inner boundary. The electron density and temperature at the inner boundary are obtained from the differential emission measure tomography applied to the extreme-ultraviolet images of the STEREO A and B spacecraft. This new solar wind model is validated for solar minimum Carrington rotation 2077 (2008 November 20 through December 17). Due to the very low activity during this rotation, this time period is suitable for comparing the simulated corotating interaction regions (CIRs) with in situ ACE/WIND data. Although we do not capture all MHD variables perfectly, we do find that the time of occurrence and the density of CIRs are better predicted than by our previous semi-empirical wind model in the SWMF that was based on a spatially reduced adiabatic index to account for the plasma heating.
Saito, S.; Umeda, T.
2011-07-20
Shock drift acceleration is one of the important mechanisms for electron acceleration associated with magnetic mirror reflection along the magnetic field in a quasi-perpendicular collisionless shock. We study the influence of a rippled shock surface in the in-plane magnetic field on the magnetic mirror reflection of electrons. Simulation results show that the number of reflected electrons reduces after generation of the rippled shock surface. Electric and magnetic wavenumber spectra of the generated fluctuations in the shock transition region indicate the existence of kinetic Alfven turbulence. The kinetic Alfven turbulence decreases the electron pitch angle by parallel scattering, which reduces the magnetic mirror force acting on the electrons. These results suggest that the shock-generated kinetic Alfven turbulence suppresses the magnetic mirror reflection of electrons during the shock drift acceleration.
Observations of neutral beam and ICRF tail ion losses due to Alfven modes in TFTR
Darrow, D.S.; Zweben, S.J.; Chang, Z.
1996-04-01
Fast ion losses resulting from MHD modes at the Alfven frequency, such as the TAE, have been observed in TFTR. The modes have been driven both by neutral beam ions, at low B{sub T}, and by H-minority ICRF tail ions at higher B{sub T}. The measurements indicate that the loss rate varies linearly with the mode amplitude, and that the fast ion losses during the mode activity can be significant, e.g. up to 10% of the input power is lost in the worst case.
Anomalous perturbative transport in tokamaks due to drift-Alfven-wave turbulence
Thoul, A.A. ); Similon, P.L. ); Sudan, R.N. )
1994-03-01
The method developed in Thoul, Similon, and Sudan [Phys. Plasmas [bold 1], 579 (1994)] is used to calculate the transport due to drift-Alfven-wave turbulence, in which electromagnetic effects such as the fluttering of the magnetic field lines are important. Explicit expressions are obtained for all coefficients of the anomalous transport matrix relating particle and heat fluxes to density and temperature gradients in the plasma. Although the magnetic terms leave the transport by trapped electrons unaffected, they are important for the transport by circulating electrons.
Parametric instabilities of large amplitude Alfven waves with obliquely propagating sidebands
NASA Technical Reports Server (NTRS)
Vinas, A. F.; Goldstein, M. L.
1992-01-01
This paper presents a brief report on properties of the parametric decay and modulational, filamentation, and magnetoacoustic instabilities of a large amplitude, circularly polarized Alfven wave. We allow the daughter and sideband waves to propagate at an arbitrary angle to the background magnetic field so that the electrostatic and electromagnetic characteristics of these waves are coupled. We investigate the dependance of these instabilities on dispersion, plasma/beta, pump wave amplitude, and propagation angle. Analytical and numerical results are compared with numerical simulations to investigate the full nonlinear evolution of these instabilities.
Alfven's critical ionization velocity observed in high power impulse magnetron sputtering discharges
Brenning, N.; Lundin, D.
2012-09-15
Azimuthally rotating dense plasma structures, spokes, have recently been detected in several high power impulse magnetron sputtering (HiPIMS) devices used for thin film deposition and surface treatment, and are thought to be important for plasma buildup, energizing of electrons, as well as cross-B transport of charged particles. In this work, the drift velocities of these spokes are shown to be strongly correlated with the critical ionization velocity, CIV, proposed by Alfven. It is proposed as the most promising approach in combining the CIV and HiPIMS research fields is to focus on the role of spokes in the process of electron energization.
Schulze-Berge, S.; Crowley, S.; Chen, Liu.
1991-05-01
We have analyzed field line resonances of Alfven waves in a rectangular box model with a straight uniform magnetic field but three dimensionally varying density. Field line resonances are shown to exist even with this three-dimensional nonuniformity. For a given wave frequency, we can construct the surface on which the resonance occurs and derive the local form of the singular solution. Magnetic perturbations are found to lie predominantly in the resonant surface. In the presence of azimuthal inhomogeneities, the present theory could explain why some satellite measurements show geomagnetic pulsations of comparable magnitude in radial and azimuthal components. 5 refs.
Schulze-Berge, S.; Cowley, S.; Liu Chen )
1992-03-01
The authors have analyzed field line resonances of Alfven waves in a rectangular box model with a straight uniform magnetic field but three-dimensionally varying density. Field line resonances are shown to exist even with this three-dimensional uniformity. For a given wave frequency they can construct the surface on which the resonance occurs and derive the local form of the singular solution. Magnetic perturbations are found to lie predominantly in the resonant surface. In the presence of azimuthal inhomogeneous the present theory could explain why some satellite measurements show geomagnetic pulsations of comparable magnitude in radial and azimuthal components.
Flow shear suppression of turbulence using externally driven ion Bernstein and Alfven waves
Biglari, H.; Ono, M. . Plasma Physics Lab.); Diamond, P.H. . Dept. of Physics); Craddock, G.G. )
1991-01-01
The utilization of externally-launched radio-frequency waves as a means of active confinement control through the generation of sheared poloidal flows is explored. For low-frequency waves, kinetic Alfven waves are proposed, and are shown to drive sheared E {times} B flows as a result of the radial variation in the electromagnetic Reynolds stress. In the high frequency regime, ion Bernstein waves are considered, and shown to generate sheared poloidal rotation through the ponderomotive force. In either case, it is shown that modest amounts of absorbed power ({approximately} few 100 kW) are required to suppress turbulence in a region of several cm radial width. 9 refs.
NASA Astrophysics Data System (ADS)
Prokopov, Pavel; Zaharov, Yuriy; Tishchenko, Vladimir; Boyarintsev, Eduard; Melehov, Aleksandr; Ponomarenko, Arnold; Posuh, Vitaliy; Shayhislamov, Ildar
2016-03-01
The paper deals with generation of Alfven plasma disturbances in magnetic flux tubes through exploding laser plasma in magnetized background plasma. Processes with similar effect of excitation of torsion-type waves seem to provide energy transfer from the solar photosphere to corona. The studies were carried out at experimental stand KI-1 represented a high-vacuum chamber of 1.2 m diameter, 5 m long, external magnetic field up to 500 Gs along the chamber axis, and up to 2×10^-6 Torr pressure in operating mode. Laser plasma was produced when focusing the CO2 laser pulse on a flat polyethylene target, and then the laser plasma propagated in θ-pinch background hydrogen (or helium) plasma. As a result, the magnetic flux tube of 15-20 cm radius was experimentally simulated along the chamber axis and the external magnetic field direction. Also, the plasma density distribution in the tube was measured. Alfven wave propagation along the magnetic field was registered from disturbance of the magnetic field transverse component B_ψ and field-aligned current J_z. The disturbances propagate at near-Alfven velocity of 70-90 km/s and they are of left-hand circular polarization of the transverse component of magnetic field. Presumably, Alfven wave is generated by the magnetic laminar mechanism of collisionless interaction between laser plasma cloud and background. The right-hand polarized high-frequency whistler predictor was registered which have been propagating before Alfven wave at 300 km/s velocity. The polarization direction changed with Alfven wave coming. Features of a slow magnetosonic wave as a sudden change in background plasma concentration along with simultaneous displacement of the external magnetic field were found. The disturbance propagates at ~20-30 km/s velocity, which is close to that of ion sound at low plasma beta value. From preliminary estimates, the disturbance transfers about 10 % of the original energy of laser plasma.
Wave Driven Fast Ion Loss in the National Spherical Torus Experiment
E.D. Fredrickson; C.Z. Cheng; D. Darrow; G. Fu; N.N. Gorelenkov; G. Kramer; S.S. Medley; J. Menard; L. Roquemore; D. Stutman; R.B. White
2003-08-05
The study of fast ion instabilities in conventional aspect ratio tokamaks is motivated in large part by their potential to negatively impact the ignition threshold in fusion reactors by causing fast ion losses. Spherical tokamak's (ST), with intrinsically low magnetic fields, are particularly susceptible to fast ion driven instabilities. The 3.5 MeV alpha's from the D-T [deuterium-tritium] fusion reaction in proposed ST reactors will have velocities much higher than the Alfven speed. The Larmor radius of the fusion alphas, normalized to the plasma size, will also be larger than for conventional aspect ratio tokamak reactors. The resulting longer wavelengths of the *AE instabilities will be more effective in driving fast ion loss. The change in magnetic topology also influences the mode structure, as in the case of the Compressional Alfven Eigenmodes (CAE) seen on NSTX.
NASA Technical Reports Server (NTRS)
Neugebauer, M.; Buti, B.
1990-01-01
Results are presented of a study designed to confirm the suspected relation between Alfven solitons (steepened Afven waves) and rotational discontinuities (RDs) in the solar wind. The ISEE 3 data were used to search for the predicted correlations between the beta value of plasma, the sense of polarization of the discontinuity, and changes of the magnetic field strength and plasma density across the discontinuity. No statistically significant evidence was found for the evolution of RDs from Alfven solitons. A possibility is suggested that the observations made could have been far from the regions in which the RDs were formed.
NASA Technical Reports Server (NTRS)
Bhattacharjee, A.; Hasegawa, A.
1990-01-01
The Final Technical Report on linear and non-linear studies of Alfven waves in space is presented. Areas of research included relaxation of magnetotail plasmas with field-aligned currents; the equilibrium dayside magnetosphere; macroscale particle simulation of kinetic Alfven wave physics; ballooning stability of plasmas with sheared equilibrium flows; theory of the drift-mirror instability; collisionless tearing instability in magnetotail plasmas; and nonadiabatic behavior of the magnetic moment of a charged particle in a dipole magnetic field and the development of stochastic webs.
NASA Astrophysics Data System (ADS)
Edlund, E. M.; Porkolab, M.; Kramer, G. J.; Lin, L.; Lin, Y.; Wukitch, S. J.
2009-04-01
Groups of frequency chirping modes observed between sawtooth crashes in the Alcator C-Mod tokamak are interpreted as reversed shear Alfvén eigenmodes near the q=1 surface. These modes indicate that a reversed shear q profile is generated during the relaxation phase of the sawtooth cycle. Two important parameters, qmin and its radial position, are deduced from comparisons of measured density fluctuations with calculations from the ideal MHD code NOVA. These studies provide valuable constraints for further modeling of the sawtooth cycle.
Evolution of large amplitude Alfven waves in solar wind plasmas: Kinetic-fluid models
NASA Astrophysics Data System (ADS)
Nariyuki, Y.
2014-12-01
Large amplitude Alfven waves are ubiquitously observed in solar wind plasmas. Mjolhus(JPP, 1976) and Mio et al(JPSJ, 1976) found that nonlinear evolution of the uni-directional, parallel propagating Alfven waves can be described by the derivative nonlinear Schrodinger equation (DNLS). Later, the multi-dimensional extension (Mjolhus and Wyller, JPP, 1988; Passot and Sulem, POP, 1993; Gazol et al, POP, 1999) and ion kinetic modification (Mjolhus and Wyller, JPP, 1988; Spangler, POP, 1989; Medvedev and Diamond, POP, 1996; Nariyuki et al, POP, 2013) of DNLS have been reported. Recently, Nariyuki derived multi-dimensional DNLS from an expanding box model of the Hall-MHD system (Nariyuki, submitted). The set of equations including the nonlinear evolution of compressional wave modes (TDNLS) was derived by Hada(GRL, 1993). DNLS can be derived from TDNLS by rescaling of the variables (Mjolhus, Phys. Scr., 2006). Nariyuki and Hada(JPSJ, 2007) derived a kinetically modified TDNLS by using a simple Landau closure (Hammet and Perkins, PRL, 1990; Medvedev and Diamond, POP, 1996). In the present study, we revisit the ion kinetic modification of multi-dimensional TDNLS through more rigorous derivations, which is consistent with the past kinetic modification of DNLS. Although the original TDNLS was derived in the multi-dimensional form, the evolution of waves with finite propagation angles in TDNLS has not been paid much attention. Applicability of the resultant models to solar wind turbulence is discussed.
Effect of two ion species on the propagation of shear Alfven waves of small transverse scale
Vincena, S. T.; Morales, G. J.; Maggs, J. E.
2010-05-15
The results of a theoretical modeling study and experimental investigation of the propagation properties of shear Alfven waves of small transverse scale in a plasma with two ion species are reported. In the two ion plasma, depending on the mass of the heavier species, ion kinetic effects can become prominent, and significant parallel electric fields result in electron acceleration. The theory predicts the appearance of frequency propagation gaps at the ion-ion hybrid frequency and between harmonics of the lower cyclotron frequency. Within these frequency bands spatial structures arise that mix the cone-propagation characteristics of Alfven waves with radially expanding ion Bernstein modes. The experiments, performed at the Basic Plasma Science Facility (BaPSF) at UCLA, consist of the spatial mapping of shear waves launched by a loop antenna. Although a variety of two ion-species combinations were explored, only results from a helium-neon mix are reported. A clear signature of a shear wave propagation gap, as well as propagation between multiple harmonics, is found for this gas combination. The evanescence of shear waves beyond the reflection point at the ion-ion hybrid frequency in the presence of an axial magnetic field gradient is also documented.
Alfvenic phenomena triggered by resonant absorption of an O-mode pulse
Tsung, F. S.; Morales, G. J.; Tonge, J.
2007-04-15
A simulation and modeling study is made of the nonlinear interaction of an electromagnetic pulse, in the O-mode polarization, with a magnetized plasma having a cross-field density gradient. For small amplitudes, the pulse propagates up to the cutoff layer where an Airy pattern develops. Beyond a certain power level, the ponderomotive force produced by the standing electromagnetic fields carves density cavities. The excess density piled up on the side of the cavities causes secondary, field-aligned plasma resonances to arise. Strong electron acceleration occurs due to the short scale of the secondary resonant fields. The fast electrons exiting the new resonant layers induce a return current system in the background plasma. This generates a packet of shear Alfven waves of small transverse scale and increasing frequency. The results provide insight into microscopic processes associated with a recent laboratory investigation in which large-amplitude Alfven waves have been generated upon application of high-power microwaves [B. Van Compernolle et al., Phys. Plasmas 13, 092112 (2006)].
Simulation of amplitude-modulated circularly polarized Alfven waves for beta less than one
NASA Technical Reports Server (NTRS)
Machida, S.; Spangler, S. R.; Goertz, C. K.
1987-01-01
The nonlinear properties of the amplitude-modulated circularly polarized Alfven wave are studied for beta less than one. The temporal behavior of the wave packet of the electromagnetic hybrid simulation is compared with a numerical solution of the derivative nonlinear Schroedinger (DNLS) equation. It is shown that the left-hand-polarized mode evolves into a shocklike structure due to the modulational instability. However, both cyclotron damping and a snowplow effect near the steepened wave packet suppress its further steepening, contrary to the predictions of the DNLS equation. For the right-hand mode, formation of the shock does not take place, and the initial time development is well described by the DNLS equation. The daughter Alfven wave and ion acoustic waves are excited due to the decay instability at a later time. Heating or acceleration of the particles takes place for both left- and right-hand waves. Energy transfer from the wave to the particles occurs effectively when substantial modulation in the wave amplitude is present.