Progress Toward Steady State Tokamak Operation Exploiting the high bootstrap current fraction regime
NASA Astrophysics Data System (ADS)
Ren, Q.
2015-11-01
Recent DIII-D experiments have advanced the normalized fusion performance of the high bootstrap current fraction tokamak regime toward reactor-relevant steady state operation. The experiments, conducted by a joint team of researchers from the DIII-D and EAST tokamaks, developed a fully noninductive scenario that could be extended on EAST to a demonstration of long pulse steady-state tokamak operation. Fully noninductive plasmas with extremely high values of the poloidal beta, βp >= 4 , have been sustained at βT >= 2 % for long durations with excellent energy confinement quality (H98y,2 >= 1 . 5) and internal transport barriers (ITBs) generated at large minor radius (>= 0 . 6) in all channels (Te, Ti, ne, VTf). Large bootstrap fraction (fBS ~ 80 %) has been obtained with high βp. ITBs have been shown to be compatible with steady state operation. Because of the unusually large ITB radius, normalized pressure is not limited to low βN values by internal ITB-driven modes. βN up to ~4.3 has been obtained by optimizing the plasma-wall distance. The scenario is robust against several variations, including replacing some on-axis with off-axis neutral beam injection (NBI), adding electron cyclotron (EC) heating, and reducing the NBI torque by a factor of 2. This latter observation is particularly promising for extension of the scenario to EAST, where maximum power is obtained with balanced NBI injection, and to a reactor, expected to have low rotation. However, modeling of this regime has provided new challenges to state-of-the-art modeling capabilities: quasilinear models can dramatically underpredict the electron transport, and the Sauter bootstrap current can be insufficient. The analysis shows first-principle NEO is in good agreement with experiments for the bootstrap current calculation and ETG modes with a larger saturated amplitude or EM modes may provide the missing electron transport. Work supported in part by the US DOE under DE-FC02-04ER54698, DE-AC52-07NA
Limitations of bootstrap current models
NASA Astrophysics Data System (ADS)
Belli, E. A.; Candy, J.; Meneghini, O.; Osborne, T. H.
2014-04-01
We assess the accuracy and limitations of two analytic models of the tokamak bootstrap current: (1) the well-known Sauter model (1999 Phys. Plasmas 6 2834, 2002 Phys. Plasmas 9 5140) and (2) a recent modification of the Sauter model by Koh et al (2012 Phys. Plasmas 19 072505). For this study, we use simulations from the first-principles kinetic code NEO as the baseline to which the models are compared. Tests are performed using both theoretical parameter scans as well as core-to-edge scans of real DIII-D and NSTX plasma profiles. The effects of extreme aspect ratio, large impurity fraction, energetic particles, and high collisionality are studied. In particular, the error in neglecting cross-species collisional coupling—an approximation inherent to both analytic models—is quantified. Furthermore, the implications of the corrections from kinetic NEO simulations on MHD equilibrium reconstructions is studied via integrated modeling with kinetic EFIT.
Progress toward steady-state tokamak operation exploiting the high bootstrap current fraction regime
NASA Astrophysics Data System (ADS)
Ren, Q. L.; Garofalo, A. M.; Gong, X. Z.; Holcomb, C. T.; Lao, L. L.; McKee, G. R.; Meneghini, O.; Staebler, G. M.; Grierson, B. A.; Qian, J. P.; Solomon, W. M.; Turnbull, A. D.; Holland, C.; Guo, W. F.; Ding, S. Y.; Pan, C. K.; Xu, G. S.; Wan, B. N.
2016-06-01
Recent DIII-D experiments have increased the normalized fusion performance of the high bootstrap current fraction tokamak regime toward reactor-relevant steady state operation. The experiments, conducted by a joint team of researchers from the DIII-D and EAST tokamaks, developed a fully noninductive scenario that could be extended on EAST to a demonstration of long pulse steady-state tokamak operation. Improved understanding of scenario stability has led to the achievement of very high values of βp and βN , despite strong internal transport barriers. Good confinement has been achieved with reduced toroidal rotation. These high βp plasmas challenge the energy transport understanding, especially in the electron energy channel. A new turbulent transport model, named TGLF-SAT1, has been developed which improves the transport prediction. Experiments extending results to long pulse on EAST, based on the physics basis developed at DIII-D, have been conducted. More investigations will be carried out on EAST with more additional auxiliary power to come online in the near term.
Bootstrapped tokamak with oscillating field current drive
Weening, R.H. )
1993-07-01
A magnetic helicity conserving mean-field Ohm's law is used to study bootstrapped tokamaks with oscillating field current drive. The Ohm's law leads to the conclusion that the tokamak bootstrap effect can convert the largely alternating current of oscillating field current drive into a direct toroidal plasma current. This plasma current rectification is due to the intrinsically nonlinear nature of the tokamak bootstrap effect, and suggests that it may be possible to maintain the toroidal current of a tokamak reactor by supplementing the bootstrap current with oscillating field current drive. Steady-state tokamak fusion reactors operating with oscillating field current drive could provide an alternative to tokamak reactors operating with external current drive.
NASA Astrophysics Data System (ADS)
Ferron, J. E.; Luce, T. C.; Politzer, P. A.; Deboo, J. C.; Petrie, T. W.; Petty, C. C.; La Haye, R. J.; Holcomb, C. T.; White, A. E.; Turco, F.; Doyle, E. J.; Rhodes, T. L.; Zeng, L.
2009-11-01
A systematic scan of the safety factor (q) profile has been used to study the optimum for steady-state operation, which requires the maximum possible beta and bootstrap current fraction (fBS) and good alignment between the total current density and the bootstrap current density (JBS). The ne, Te, and Ti profiles at constant βN= 2.7 were measured in a scan of the minimum q (1.1
Control of bootstrap current in the pedestal region of tokamaks
Shaing, K. C.; Lai, A. L.
2013-12-15
The high confinement mode (H-mode) plasmas in the pedestal region of tokamaks are characterized by steep gradient of the radial electric field, and sonic poloidal U{sub p,m} flow that consists of poloidal components of the E×B flow and the plasma flow velocity that is parallel to the magnetic field B. Here, E is the electric field. The bootstrap current that is important for the equilibrium, and stability of the pedestal of H-mode plasmas is shown to have an expression different from that in the conventional theory. In the limit where ‖U{sub p,m}‖≫ 1, the bootstrap current is driven by the electron temperature gradient and inductive electric field fundamentally different from that in the conventional theory. The bootstrap current in the pedestal region can be controlled through manipulating U{sub p,m} and the gradient of the radial electric. This, in turn, can control plasma stability such as edge-localized modes. Quantitative evaluations of various coefficients are shown to illustrate that the bootstrap current remains finite when ‖U{sub p,m}‖ approaches infinite and to provide indications how to control the bootstrap current. Approximate analytic expressions for viscous coefficients that join results in the banana and plateau-Pfirsch-Schluter regimes are presented to facilitate bootstrap and neoclassical transport simulations in the pedestal region.
Control of bootstrap current in the pedestal region of tokamaks
NASA Astrophysics Data System (ADS)
Shaing, K. C.; Lai, A. L.
2013-12-01
The high confinement mode (H-mode) plasmas in the pedestal region of tokamaks are characterized by steep gradient of the radial electric field, and sonic poloidal Up ,m flow that consists of poloidal components of the E ×B flow and the plasma flow velocity that is parallel to the magnetic field B. Here, E is the electric field. The bootstrap current that is important for the equilibrium, and stability of the pedestal of H-mode plasmas is shown to have an expression different from that in the conventional theory. In the limit where |Up ,m| ≫ 1, the bootstrap current is driven by the electron temperature gradient and inductive electric field fundamentally different from that in the conventional theory. The bootstrap current in the pedestal region can be controlled through manipulating Up ,m and the gradient of the radial electric. This, in turn, can control plasma stability such as edge-localized modes. Quantitative evaluations of various coefficients are shown to illustrate that the bootstrap current remains finite when |Up ,m| approaches infinite and to provide indications how to control the bootstrap current. Approximate analytic expressions for viscous coefficients that join results in the banana and plateau-Pfirsch-Schluter regimes are presented to facilitate bootstrap and neoclassical transport simulations in the pedestal region.
ITER equilibrium with bootstrap currents, lower hybrid current drive and fast wave current drive
Ehst, D.A.
1989-03-01
A current drive system is proposed for the technology phase of ITER which relies on rf power and bootstrap currents. The rf/bootstrap system permits operation at high safety factor, and we consider the axial value to be q/sub a/ approx. = 1.9, which minimizes the need for seed current near the magnetic axis. Lower hybrid power (/approximately/30 MW) provides current density near the surface, ICRF (/approximately/65 MHz, /approximately/30 MW) fast waves generate current near the axis, and high frequency fast waves (/approximately/250 MHz, /approximately/74 MW) supply the remaining current density. The system is not yet optimized but appears to offer great flexibility (ion heating for ignition, current rampup, etc.) with relatively inexpensive and well developed technology. 29 refs., 16 figs., 1 tab.
Magnetic island induced bootstrap current on island dynamics in tokamaks
Shaing, K.C.; Spong, D.A.
2006-02-15
When a magnetic island is embedded in toroidally symmetric tokamaks, the toroidal symmetry in |B| is broken [K. C. Shaing, Phys. Rev. Lett. 87, 245003 (2001)]. Here, B is the magnetic field. This broken symmetry induces an additional bootstrap current density in the vicinity of the island. It is illustrated that this island induced bootstrap current density modifies the island evolution equation and imposes a lower limit on the absolute value of the tearing mode stability parameter {delta}{sup '} for the island to be unstable. This lower limit depends on the local poloidal plasma beta {beta}{sub p}, the ratio of the plasma pressure to the poloidal magnetic field pressure. If {beta}{sub p} is high enough, the magnetic island is stable. This mechanism provides an alternative route to stabilize the island.
Magnetic Island Induced Bootstrap Current on Island Dynamics in Tokamaks
Spong, Donald A; Shaing, K. C.
2006-02-01
When a magnetic island is embedded in toroidally symmetric tokamaks, the toroidal symmetry in |B| is broken [K. C. Shaing, Phys. Rev. Lett. 87, 245003 (2001)] . Here, B is the magnetic field. This broken symmetry induces an additional bootstrap current density in the vicinity of the island. It is illustrated that this island induced bootstrap current density modifies the island evolution equation and imposes a lower limit on the absolute value of the tearing mode stability parameter |{Delta}{prime}| for the island to be unstable. This lower limit depends on the local poloidal plasma beta {beta}{sub p}, the ratio of the plasma pressure to the poloidal magnetic field pressure. If {beta}{sub p} is high enough, the magnetic island is stable. This mechanism provides an alternative route to stabilize the island.
Enhancement of the Bootstrap Current in a Tokamak Pedestal
Kagan, Grigory; Catto, Peter J.
2010-07-23
The strong radial electric field in a subsonic tokamak pedestal modifies the neoclassical ion parallel flow velocity, as well as the radial ion heat flux. Existing experimental evidence of the resulting alteration in the poloidal flow of a trace impurity is discussed. We then demonstrate that the modified parallel ion flow can noticeably enhance the pedestal bootstrap current when the background ions are in the banana regime. Only the coefficient of the ion temperature gradient drive term is affected. The revised expression for the pedestal bootstrap current is presented. The prescription for inserting the modification into any existing banana regime bootstrap current expression is given.
An improved bootstrap current formula for edge pedestal plasma
NASA Astrophysics Data System (ADS)
Hager, Robert; Chang, C.-S.
2014-10-01
An improved version of a bootstrap current formula based on the results of the neoclassical guiding-center particle-in-cell code XGC0 is presented. The original formula improved the accuracy of the predicted bootstrap current in the edge pedestal, where the ion orbit width can be comparable to the pressure gradient scale length, the passing particle region is narrow, and the ions experience orbit loss. We improved two aspects of this formula. We corrected the asymptotic behavior of the bootstrap current coefficients at higher collisionality from what was inherited from the Sauter formula. We also improved the jumpy aspect-ratio dependence of the transition between an enhanced (NSTX) and reduced (DIII-D) bootstrap current regime found by Koh et al. In addition, we elucidate the physical origins of the improvement and of the difference from a local analysis that includes the importance of finite ion orbit excursion effects on the electron current in the edge pedestal.
The bootstrap current in small rotating magnetic islands
Bergmann, A.; Poli, E.; Peeters, A. G.
2009-09-15
The bootstrap current in small magnetic islands of neoclassical tearing modes is studied with guiding center particle simulations including pitch angle scattering. A model for a rotating island and its electric field is used and a new approximation to the electric potential in small islands is derived. Islands with sizes of the order of the ion banana orbit width are studied by means of a two-step model, which allows to treat both ions and electrons kinetically. The bootstrap current in such small islands is found to depend strongly on the direction of rotation of the island. The bootstrap current in small islands rotating in the ion diamagnetic direction is strongly diminished, similarly to what happens in big islands. In small islands rotating in the electron diamagnetic direction, on the contrary, the bootstrap current is almost completely preserved, implying a reduced neoclassical drive of the island growth.
Simulations of the bootstrap current in small rotating magnetic islands
Bergmann, A.; Poli, E.; Peeters, A. G.
2008-11-01
The bootstrap current in small magnetic islands of neoclassical tearing modes is studied in numerical simulations whith the guiding center particle code HAGIS. The contributions of both, electrons and ions, are included, as well as the island rotation and its electric field. The case of islands that are smaller than the ion banana orbit width is studied. We find that the size of the bootstrap current in small islands depends strongly on the rotation frequency of the island.
Bootstrap current close to magnetic axis in tokamaks
Shaing, K.C.; Hazeltine, R.D.
1996-12-01
It is shown that the bootstrap current density close to the magnetic axis in tokamaks does not vanish in simple electron-ion plasmas because the fraction of the trapped particles is finite. The magnitude of the current density could be comparable to that in the outer core region. This may reduce or even eliminate the need of the seed current.
NASA Astrophysics Data System (ADS)
Saarelma, S.; Günter, S.; Kurki-Suonio, T.; Zehrfeld, H.-P.
2000-05-01
An ELMy ASDEX Upgrade plasma equilibrium is reconstructed taking into account the bootstrap current. The peeling mode stability of the equilibrium is numerically analysed using the GATO [1] code, and it is found that the bootstrap current can drive the plasma peeling mode unstable. A high-n ballooning mode stability analysis of the equilibria revealed that, while destabilizing the peeling modes, the bootstrap current has a stabilizing effect on the ballooning modes. A combination of these two instabilities is a possible explanation for the type I ELM phenomenon. A triangularity scan showed that increasing triangularity stabilizes the peeling modes and can produce ELM-free periods observed in the experiments.
MHD stability of ITER H-mode confinement with pedestal bootstrap current effects taken into account
NASA Astrophysics Data System (ADS)
Zheng, L. J.; Kotschenreuther, M. T.; Valanju, P.; Mahajan, S. M.; Hatch, D.; Liu, X.
2015-11-01
We have shown that the bootstrap current can have significant effects both on tokamak equilibrium and stability (Nucl. Fusion 53, 063009 (2013)). For ITER H-mode discharges pedestal density is low and consequently bootstrap current is large. We reconstruct numerically ITER equilibria with bootstrap current taken into account. Especially, we have considered a more realistic scenario in which density and temperature profiles can be different. The direct consequence of bootstrap current effects on equilibrium is the modification of local safety factor profile at pedestal. This results in a dramatic change of MHD mode behavior. The stability of ITER numerical equilibria is investigated with AEGIS code. Both low-n and peeling-ballooning modes are investigated. Note that pressure gradient at pedestal is steep. High resolution computation is needed. Since AEGIS code is an adaptive code, it can well handle this problem. Also, the analytical continuation technique based on the Cauchy-Riemann condition of dispersion relation is applied, so that the marginal stability conditions can be determined. Both numerical scheme and results will be presented. The effects of different density and temperature profiles on ITER H-mode discharges will be discussed. This research is supported by U. S. Department of Energy, Office of Fusion Energy Science: Grant No. DE-FG02-04ER-54742.
EBW-Bootstrap Current Synergy in the National Spherical Torus Experiment (NSTX)
R.W. Harvey; G. Taylor
2005-02-02
Current driven by electron Bernstein waves (EBW) and by the electron bootstrap effect are calculated separately and concurrently with a kinetic code, to determine the degree of synergy between them. A target {beta} = 40% NSTX plasma is examined. A simple bootstrap model in the CQL3D Fokker-Planck code is used in these studies: the transiting electron distributions are connected in velocity-space at the trapped-passing boundary to trapped-electron distributions which are displaced radially by a half-banana width outwards/inwards for the co-/counter-passing regions. This model agrees well with standard bootstrap current calculations, over the outer 60% of the plasma radius. Relatively small synergy net bootstrap current is obtained for EBW power up to 4 MW. Locally, bootstrap current density increases in proportion to increased plasma pressure, and this effect can significantly affect the radial profile of driven current.
Computation of lower hybrid, neutral beam and bootstrap currents in consistent MHD equilibria
Devoto, R.S.; Blackfield, D.T.; Fenstermacher, M.E.; Bonoli, P.T.; Porkolab, M.
1989-02-01
A possible scenario for steady state current drive in large, high- temperature tokamaks includes current driven by lower hybrid (LH) waves in the outer region with high-energy neutral beams (NB) used for current drive in the core. In addition, provided the poloidal beta is sufficiently high, there can be substantial bootstrap (BS) current, as observed in the TFTR and JET experiments. In work reported previously, a computer code, ACCOME, was written to obtain a solution to the MHD equations which is consistent with current driven by neutral beams, electric fields, and neoclassical (bootstrap) effects. For the computation of the solution to the Grad-Shafranov equation, the SELENE code is used. Iteration is necessary between SELENE and the current-drive computations to obtain a consistent solution. In this paper we describe modifications to ACCOME to enable the computation of LH current in addition to the NB, BS, and OH currents. The next section describes the models used and then the final section presents an application to ITER. 4 refs., 4 figs.
Bootstrap current for the edge pedestal plasma in a diverted tokamak geometry
Koh, S.; Choe, W.; Chang, C. S.; Ku, S.; Menard, J. E.; Weitzner, H.
2012-07-15
The edge bootstrap current plays a critical role in the equilibrium and stability of the steep edge pedestal plasma. The pedestal plasma has an unconventional and difficult neoclassical property, as compared with the core plasma. It has a narrow passing particle region in velocity space that can be easily modified or destroyed by Coulomb collisions. At the same time, the edge pedestal plasma has steep pressure and electrostatic potential gradients whose scale-lengths are comparable with the ion banana width, and includes a magnetic separatrix surface, across which the topological properties of the magnetic field and particle orbits change abruptly. A drift-kinetic particle code XGC0, equipped with a mass-momentum-energy conserving collision operator, is used to study the edge bootstrap current in a realistic diverted magnetic field geometry with a self-consistent radial electric field. When the edge electrons are in the weakly collisional banana regime, surprisingly, the present kinetic simulation confirms that the existing analytic expressions [represented by O. Sauter et al., Phys. Plasmas 6, 2834 (1999)] are still valid in this unconventional region, except in a thin radial layer in contact with the magnetic separatrix. The agreement arises from the dominance of the electron contribution to the bootstrap current compared with ion contribution and from a reasonable separation of the trapped-passing dynamics without a strong collisional mixing. However, when the pedestal electrons are in plateau-collisional regime, there is significant deviation of numerical results from the existing analytic formulas, mainly due to large effective collisionality of the passing and the boundary layer trapped particles in edge region. In a conventional aspect ratio tokamak, the edge bootstrap current from kinetic simulation can be significantly less than that from the Sauter formula if the electron collisionality is high. On the other hand, when the aspect ratio is close to unity
Bootstrap Current for the Edge Pedestal Plasma in a Diverted Tokamak Geometry
Koh, S.; Chang, C. S.; Ku, S.; Menard, J. E.; Weitzner, H.; Choe, W.
2012-08-10
The edge bootstrap current plays a critical role in the equilibrium and stability of the steep edge pedestal plasma. The pedestal plasma has an unconventional and difficult neoclassical property, as compared with the core plasma. It has a narrow passing particle region in velocity space that can be easily modified or destroyed by Coulomb collisions. At the same time, the edge pedestal plasma has steep pressure and electrostatic potential gradients whose scale-lengths are comparable with the ion banana width, and includes a magnetic separatrix surface, across which the topological properties of the magnetic field and particle orbits change abruptly. A driftkinetic particle code XGC0, equipped with a mass-momentum-energy conserving collision operator, is used to study the edge bootstrap current in a realistic diverted magnetic field geometry with a self-consistent radial electric field. When the edge electrons are in the weakly collisional banana regime, surprisingly, the present kinetic simulation confirms that the existing analytic expressions [represented by O. Sauter et al. , Phys. Plasmas 6 , 2834 (1999)] are still valid in this unconventional region, except in a thin radial layer in contact with the magnetic separatrix. The agreement arises from the dominance of the electron contribution to the bootstrap current compared with ion contribution and from a reasonable separation of the trapped-passing dynamics without a strong collisional mixing. However, when the pedestal electrons are in plateau-collisional regime, there is significant deviation of numerical results from the existing analytic formulas, mainly due to large effective collisionality of the passing and the boundary layer trapped particles in edge region. In a conventional aspect ratio tokamak, the edge bootstrap current from kinetic simulation can be significantly less than that from the Sauter formula if the electron collisionality is high. On the other hand, when the aspect ratio is close to unity
Ion-Banana-Orbit-Width Effect on Bootstrap Current for Small Magnetic Islands
NASA Astrophysics Data System (ADS)
Qu, Hongpeng
2013-09-01
A simple and direct theoretical method has been proposed to investigate the so-called ion-banana-orbit-width (IBW) effect on the bootstrap current in the region of magnetic islands generated by the neoclassical tearing mode (NTM). The result shows that, when the IBW approaches the island width, the (ion) bootstrap current can be partly restored inside the island while the pressure profile is flattened. This can lead to the reduction of the bootstrap current drive on the NTM. The strength of the IBW effect on the NTM is related to the safety factor and the inverse aspect ratio on the rational surface.
Island-induced bootstrap current on the saturation of a thin magnetic island in tokamaks
Shaing, K. C.
2007-04-15
It is shown that island-induced bootstrap current density, which results from the symmetry breaking of the vertical bar B vertical bar when an island is embedded in the equilibrium magnetic field B, modifies the evolution equation and the saturation level for a thin magnetic island in tokamaks. This modification is independent of the fraction of the equilibrium bootstrap current density. It is found that island-induced bootstrap current density increases the saturation level for modes with positive values of {delta}{sup '}. Here, {delta}{sup '} is the stability parameter for the linear tearing modes.
Reduction of bootstrap current in the Modular Helias-like Heliac stellarator
NASA Astrophysics Data System (ADS)
Garabedian, P. R.; Gardner, H. J.
1995-06-01
A geometric estimate for the size of the bootstrap current has been implemented in a plasma equilibrium code and applied to the Modular Helias-like Heliac (MHH) stellarator [Nucl. Fusion 34, 881 (1994)]. The predicted change in the rotational transform of the MHH due to the bootstrap current has been brought down to an acceptable level, and this has resulted in one of the smallest stellarator reactor candidates to be discovered so far.
On Current Drive and Wave Induced Bootstrap Current in Toroidal Plasmas
Hellsten, T.; Johnson, T.
2008-11-01
A comprehensive treatment of wave-particle interactions in toroidal plasmas including collisional relaxation, applicable to heating or anomalous wave induced transport, has been obtained by using Monte Carlo operators satisfying quasi-neutrality. This approach enables a self-consistent treatment of wave-particle interactions applicable to the banana regime in the neoclassical theory. It allows an extension into a regime with large temperature and density gradients, losses and transport of particles by wave-particle interactions making the method applicable to transport barriers. It is found that at large gradients the relationship between radial electric field, parallel velocity, temperature and density gradient in the neoclassical theory is modified such that coefficient in front of the logarithmic ion temperature gradient, which in the standard neoclassical theory is small and counteracts the electric field caused by the density gradient, now changes sign and contributes to the built up of the radial electric field. The possibility to drive current by absorbing the waves on trapped particles has been studied and how the wave-particle interactions affect the bootstrap current. Two new current drive mechanisms are studied: current drive by wave induced bootstrap current and selective detrapping into passing orbits by directed waves.
Impurities in a non-axisymmetric plasma. Transport and effect on bootstrap current
Mollén, A.; Landreman, M.; Smith, H. M.; Braun, S.; Helander, P.
2015-11-20
Impurities cause radiation losses and plasma dilution, and in stellarator plasmas the neoclassical ambipolar radial electric field is often unfavorable for avoiding strong impurity peaking. In this work we use a new continuum drift-kinetic solver, the SFINCS code (the Stellarator Fokker-Planck Iterative Neoclassical Conservative Solver) [M. Landreman et al., Phys. Plasmas 21 (2014) 042503] which employs the full linearized Fokker-Planck-Landau operator, to calculate neoclassical impurity transport coefficients for a Wendelstein 7-X (W7-X) magnetic configuration. We compare SFINCS calculations with theoretical asymptotes in the high collisionality limit. We observe and explain a 1/nu-scaling of the inter-species radial transport coefficient at lowmore » collisionality, arising due to the field term in the inter-species collision operator, and which is not found with simplified collision models even when momentum correction is applied. However, this type of scaling disappears if a radial electric field is present. We use SFINCS to analyze how the impurity content affects the neoclassical impurity dynamics and the bootstrap current. We show that a change in plasma effective charge Zeff of order unity can affect the bootstrap current enough to cause a deviation in the divertor strike point locations.« less
Impurities in a non-axisymmetric plasma: Transport and effect on bootstrap current
Mollén, A.; Landreman, M.; Smith, H. M.; Helander, P.; Braun, S.
2015-11-15
Impurities cause radiation losses and plasma dilution, and in stellarator plasmas the neoclassical ambipolar radial electric field is often unfavorable for avoiding strong impurity peaking. In this work we use a new continuum drift-kinetic solver, the SFINCS code (the Stellarator Fokker-Planck Iterative Neoclassical Conservative Solver) [M. Landreman et al., Phys. Plasmas 21, 042503 (2014)] which employs the full linearized Fokker-Planck-Landau operator, to calculate neoclassical impurity transport coefficients for a Wendelstein 7-X (W7-X) magnetic configuration. We compare SFINCS calculations with theoretical asymptotes in the high collisionality limit. We observe and explain a 1/ν-scaling of the inter-species radial transport coefficient at low collisionality, arising due to the field term in the inter-species collision operator, and which is not found with simplified collision models even when momentum correction is applied. However, this type of scaling disappears if a radial electric field is present. We also use SFINCS to analyze how the impurity content affects the neoclassical impurity dynamics and the bootstrap current. We show that a change in plasma effective charge Z{sub eff} of order unity can affect the bootstrap current enough to cause a deviation in the divertor strike point locations.
Impurities in a non-axisymmetric plasma. Transport and effect on bootstrap current
Mollén, A.; Landreman, M.; Smith, H. M.; Braun, S.; Helander, P.
2015-11-20
Impurities cause radiation losses and plasma dilution, and in stellarator plasmas the neoclassical ambipolar radial electric field is often unfavorable for avoiding strong impurity peaking. In this work we use a new continuum drift-kinetic solver, the SFINCS code (the Stellarator Fokker-Planck Iterative Neoclassical Conservative Solver) [M. Landreman et al., Phys. Plasmas 21 (2014) 042503] which employs the full linearized Fokker-Planck-Landau operator, to calculate neoclassical impurity transport coefficients for a Wendelstein 7-X (W7-X) magnetic configuration. We compare SFINCS calculations with theoretical asymptotes in the high collisionality limit. We observe and explain a 1/nu-scaling of the inter-species radial transport coefficient at low collisionality, arising due to the field term in the inter-species collision operator, and which is not found with simplified collision models even when momentum correction is applied. However, this type of scaling disappears if a radial electric field is present. We use SFINCS to analyze how the impurity content affects the neoclassical impurity dynamics and the bootstrap current. We show that a change in plasma effective charge Z_{eff} of order unity can affect the bootstrap current enough to cause a deviation in the divertor strike point locations.
Electron Bernstein wave-bootstrap current synergy in the National Spherical Torus Experiment
Harvey, R.W.; Taylor, G.
2005-05-15
Current driven by electron Bernstein waves (EBW) and by the electron bootstrap effect are calculated separately and concurrently with a kinetic code to determine the degree of synergy between them. A target {beta}=40% NSTX [M. Ono, S. Kaye, M. Peng et al., Proceedings of the 17th IAEA Fusion Energy Conference, edited by M. Spak (IAEA, Vienna, Austria, 1999), Vol. 3, p. 1135] plasma is examined. A simple bootstrap model in the collisional-quasilinear CQL3D Fokker-Planck code (National Technical Information Service document No. DE93002962) is used in these studies: the transiting electron distributions are connected in velocity space at the trapped-passing boundary to trapped-electron distributions that are displaced radially by a half-banana-width outwards/inwards for the co-passing/counter-passing regions. This model agrees well with standard bootstrap current calculations over the outer 60% of the plasma radius. Relatively small synergy net bootstrap current is obtained for EBW power up to 4 MW. Locally, bootstrap current density increases in proportion to increased plasma pressure, and this effect can significantly affect the radial profile of driven current.
Coope, Wilfred Anthony; Ferrando i Margalet, Sergi; Allfrey, Simon J.; Kisslinger, Johann; Wobig, Horst F.G.; Narushima, Yoshiro; Okamura, Shoichi; Suzuki, Chihiro; Watanabe, Kiyomasa Y.; Yamazaki, Kozo; Isaev, Maxim Yu
2004-09-15
The impact of the bootstrap current is investigated on the equilibrium properties of a two-period quasi-axisymmetric stellarator reactor with free boundary and on the corresponding ideal magnetohydrodynamic stability properties. Although the magnetic field strength B spectrum is dominated by a m/n = 1/0 component, the discrete filamentary coils trigger some small-amplitude symmetry-breaking components that can disturb the quasi-symmetry of B. Finite {beta} causes the plasma column to shift outward in the absence of bootstrap current. With a self-consistent bootstrap current in the 1/{nu} regime, the plasma becomes more elongated and more distorted in the horizontally elongated up-down symmetric cross section. At {beta} (approximately equal to) 3.25%, the plasma can be restored to its near-vacuum shape with the application of a vertical field with coil currents 20% of those of the modular coils, but at the expense of a significant mirror component in the B-field spectrum. The bootstrap current causes the rotational transform {iota} profile to increase above the critical resonant value ({iota}{sub c} = 1/2 for {beta} {>=}1.1%) and combines with the Pfirsch-Schlueter current to destabilize a m/n = 2/1 external kink mode for {beta} {>=}1.8%.
Effects of orbit squeezing on poloidal mass flow and bootstrap current in tokamak plasmas
Shaing, K.C. ); Hsu, C.T. ); Hazeltine, R.D. )
1994-10-01
It is shown, by solving the drift kinetic equation, that the asymptotic values of the poloidal mass flow and the bootstrap current in the banana regime of large-aspect-ratio tokamak plasmas are not affected by orbit squeezing. However, because the definition of ion collisionality [upsilon][sub *[ital i
NASA Astrophysics Data System (ADS)
Holcomb, C. T.; Ferron, J. R.; Luce, T. C.; Politzer, P. A.; Deboo, J. C.; Petrie, T. W.; Petty, C. C.; La Haye, R. J.; White, A. E.; Turco, F.; Doyle, E. J.; Rhodes, T. L.; Zeng, L.
2009-11-01
A high beta, high gain steady state tokamak scenario with large bootstrap current fraction will have strong coupling between the current density and the pressure gradient through turbulent transport and the bootstrap current. To address this coupling experimentally, a scan of the safety factor minimum (qmin, from 1.1 to over 2) and edge value (q95, from 4.5 to 6.5) was performed. The bootstrap current fraction increases with qmin and q95 by virtue of increasing density gradients. Compared to lower qmin, qmin>2 has lower n=1 stability limits, enhanced drift wave growth rates, higher low-k density fluctuations, and lower confinement. At qmin>2 and q95=4.5 the unsustainable condition JBS> JTotal occurs near the axis. These considerations suggest intermediate q is the optimal operating point.
Schmitt, J. C.; Talmadge, J. N.; Anderson, D. T.; Hanson, J. D.
2014-09-15
The bootstrap current for three electron cyclotron resonance heated plasma scenarios in a quasihelically symmetric stellarator (the Helically Symmetric Experiment) are analyzed and compared to a neoclassical transport code PENTA. The three conditions correspond to 50 kW input power with a resonance that is off-axis, 50 kW on-axis heating and 100 kW on-axis heating. When the heating location was moved from off-axis to on-axis with 50 kW heating power, the stored energy and the extrapolated steady-state current were both observed to increase. When the on-axis heating power was increased from 50 kW to 100 kW, the stored energy continued to increase while the bootstrap current slightly decreased. This trend is qualitatively in agreement with the calculations which indicate that a large positive electric field for the 100 kW case was driving the current negative in a small region close to the magnetic axis and accounting for the decrease in the total integrated current. This trend in the calculations is only observed to occur when momentum conservation between particle species is included. Without momentum conservation, the calculated bootstrap current increases monotonically. We show that the magnitude of the bootstrap current as calculated by PENTA agrees better with the experiment when momentum conservation between plasma species is included in the calculation. The total current was observed in all cases to flow in a direction to unwind the transform, unlike in a tokamak in which the bootstrap current adds to the transform. The 3-D inductive response of the plasma is simulated to predict the evolution of the current profile during the discharge. The 3-D equilibrium reconstruction code V3FIT is used to reconstruct profiles of the plasma pressure and current constrained by measurements with a set of magnetic diagnostics. The reconstructed profiles are consistent with the measured plasma pressure profile and the simulated current profile when the
Simulation of bootstrap current in 2D and 3D ideal magnetic fields in tokamaks
NASA Astrophysics Data System (ADS)
Raghunathan, M.; Graves, J. P.; Cooper, W. A.; Pedro, M.; Sauter, O.
2016-09-01
We aim to simulate the bootstrap current for a MAST-like spherical tokamak using two approaches for magnetic equilibria including externally caused 3D effects such as resonant magnetic perturbations (RMPs), the effect of toroidal ripple, and intrinsic 3D effects such as non-resonant internal kink modes. The first approach relies on known neoclassical coefficients in ideal MHD equilibria, using the Sauter (Sauter et al 1999 Phys. Plasmas 6 2834) expression valid for all collisionalities in axisymmetry, and the second approach being the quasi-analytic Shaing–Callen (Shaing and Callen 1983 Phys. Fluids 26 3315) model in the collisionless regime for 3D. Using the ideal free-boundary magnetohydrodynamic code VMEC, we compute the flux-surface averaged bootstrap current density, with the Sauter and Shaing–Callen expressions for 2D and 3D ideal MHD equilibria including an edge pressure barrier with the application of resonant magnetic perturbations, and equilibria possessing a saturated non-resonant 1/1 internal kink mode with a weak internal pressure barrier. We compare the applicability of the self-consistent iterative model on the 3D applications and discuss the limitations and advantages of each bootstrap current model for each type of equilibrium.
D.A. Gates, for the NSTX National Research Team
2003-02-26
Long-pulse, high-beta scenarios have been established on the National Spherical Torus Experiment (NSTX). Beta(sub)t(always equal to 2{mu}(sub)0{center_dot}
/B{sup 2}(sub)t0) {approx} 35% has been achieved during transient discharges. The machine improvements that lead to these results, including error field reduction and high-temperature bakeout of plasma-facing components are described. The highest Beta(sub)t plasmas have high triangularity (delta = 0.8) and elongation (k = 2.0) at low-aspect ratio A always equal to R/a = 1.4. The strong shaping permits large values of normalized current, I(sub)N(always equal to I(sub)p /(aB(sub)t0)) approximately equal to 6 while maintaining moderate values of q(sub)95 = 4. Long-pulse discharges up to 1 sec in duration have been achieved with substantial bootstrap current. The total noninductive current drive can be as high as 60%, comprised of 50% bootstrap current and {approx}10% neutral-beam current drive. The confinement enhancement factor H89P is in excess of 2.7. Beta(sub)N * H(sub)89P approximately or greater than 15 has been maintained for 8 * tau(sub)E {approx} 1.6 * tau(sub)CR, where tau(sub)CR is the relaxation time of the first radial moment of the toroidal current density. The ion temperature for these plasmas is significantly higher than that predicted by neoclassical theory.
NASA Technical Reports Server (NTRS)
Pfiffner, H. J.
1969-01-01
Circuit can sample a number of transducers in sequence without drawing from them. This bootstrap unloader uses a differential amplifier with one input connected to a circuit which is the equivalent of the circuit to be unloaded, and the other input delivering the proper unloading currents.
Cohen-Adad, J.; Descoteaux, M.; Wald, L.L.
2011-01-01
Purpose To develop a bootstrap method to assess the quality of High Angular Resolution Diffusion Imaging (HARDI) data using Q-Ball imaging (QBI) reconstruction. Materials and Methods HARDI data were re-shuffled using regular bootstrap with jackknife sampling. For each bootstrap dataset, the diffusion orientation distribution function (ODF) was estimated voxel-wise using QBI reconstruction based on spherical harmonics functions. The reproducibility of the ODF was assessed using the Jensen-Shannon divergence (JSD) and the angular confidence interval was derived for the first and the second ODF maxima. The sensitivity of the bootstrap method was evaluated on a human subject by adding synthetic noise to the data, by acquiring a map of image signal-to-noise ratio (SNR) and by varying the echo time and the b-value. Results The JSD was directly linked to the image SNR. The impact of echo times and b-values was reflected by both the JSD and the angular confidence interval, proving the usefulness of the bootstrap method to evaluate specific features of HARDI data. Conclusion The bootstrap method can effectively assess the quality of HARDI data and can be used to evaluate new hardware and pulse sequences, perform multi-fiber probabilistic tractography, and provide reliability metrics to support clinical studies. PMID:21509879
Observation of non-classical radial current diffusion in a fully bootstrap current driven tokamak
Hwang, Y.S.; Forest, C.B.; Ono, M.
1996-02-01
Reconstruction and modeling of the plasma current profiles in a fully pressure-driven tokamak have been performed in the Current Drive Experiment-Upgrade (CDX-U). The reconstructed experimental current profile has a significant deviation from that of the calculated neoclassical currents. Satisfactory agreement between the measured and calculated model profiles was obtained by including a helicity conserving current diffusion term in the modeling which created the required self-generated `seed` current.
NASA Astrophysics Data System (ADS)
Hager, Robert; Chang, C. S.
2016-04-01
As a follow-up on the drift-kinetic study of the non-local bootstrap current in the steep edge pedestal of tokamak plasma by Koh et al. [Phys. Plasmas 19, 072505 (2012)], a gyrokinetic neoclassical study is performed with gyrokinetic ions and drift-kinetic electrons. Besides the gyrokinetic improvement of ion physics from the drift-kinetic treatment, a fully non-linear Fokker-Planck collision operator—that conserves mass, momentum, and energy—is used instead of Koh et al.'s linearized collision operator in consideration of the possibility that the ion distribution function is non-Maxwellian in the steep pedestal. An inaccuracy in Koh et al.'s result is found in the steep edge pedestal that originated from a small error in the collisional momentum conservation. The present study concludes that (1) the bootstrap current in the steep edge pedestal is generally smaller than what has been predicted from the small banana-width (local) approximation [e.g., Sauter et al., Phys. Plasmas 6, 2834 (1999) and Belli et al., Plasma Phys. Controlled Fusion 50, 095010 (2008)], (2) the plasma flow evaluated from the local approximation can significantly deviate from the non-local results, and (3) the bootstrap current in the edge pedestal, where the passing particle region is small, can be dominantly carried by the trapped particles in a broad trapped boundary layer. A new analytic formula based on numerous gyrokinetic simulations using various magnetic equilibria and plasma profiles with self-consistent Grad-Shafranov solutions is constructed.
Hager, Robert; Chang, C. S.
2016-04-08
As a follow-up on the drift-kinetic study of the non-local bootstrap current in the steep edge pedestal of tokamak plasma by Koh et al. [Phys. Plasmas 19, 072505 (2012)], a gyrokinetic neoclassical study is performed with gyrokinetic ions and drift-kinetic electrons. Besides the gyrokinetic improvement of ion physics from the drift-kinetic treatment, a fully non-linear Fokker-Planck collision operator—that conserves mass, momentum, and energy—is used instead of Koh et al.'s linearized collision operator in consideration of the possibility that the ion distribution function is non-Maxwellian in the steep pedestal. An inaccuracy in Koh et al.'s result is found in the steepmore » edge pedestal that originated from a small error in the collisional momentum conservation. The present study concludes that (1) the bootstrap current in the steep edge pedestal is generally smaller than what has been predicted from the small banana-width (local) approximation [e.g., Sauter et al., Phys. Plasmas 6, 2834 (1999) and Belli et al., Plasma Phys. Controlled Fusion 50, 095010 (2008)], (2) the plasma flow evaluated from the local approximation can significantly deviate from the non-local results, and (3) the bootstrap current in the edge pedestal, where the passing particle region is small, can be dominantly carried by the trapped particles in a broad trapped boundary layer. In conclusion, a new analytic formula based on numerous gyrokinetic simulations using various magnetic equilibria and plasma profiles with self-consistent Grad-Shafranov solutions is constructed.« less
The Bootstrap Fraction in TFTR
Hoang, G. T.
1997-04-15
The TRANSP plasma analysis code is used to calculate the bootstrap current generated during neutral-beam injection and ion cyclotron resonance frequency heating for a wide variety of TFTR discharges. An empirical scaling relation is given for the bootstrap current fraction using the ratio of the peakedness of the thermal pressure and the total current density.
A bootstrapped, low-noise, and high-gain photodetector for shot noise measurement
Zhou, Haijun; Yang, Wenhai; Li, Zhixiu; Li, Xuefeng; Zheng, Yaohui
2014-01-15
We presented a low-noise, high-gain photodetector based on the bootstrap structure and the L-C (inductance and capacitance) combination. Electronic characteristics of the photodetector, including electronic noise, gain and frequency response, and dynamic range, were verified through a single-frequency Nd:YVO{sub 4} laser at 1064 nm with coherent output. The measured shot noise of 50 μW laser was 13 dB above the electronic noise at the analysis frequency of 2 MHz, and 10 dB at 3 MHz. And a maximum clearance of 28 dB at 2 MHz was achieved when 1.52 mW laser was illuminated. In addition, the photodetector showed excellent linearities for both DC and AC amplifications in the laser power range between 12.5 μW and 1.52 mW.
Temperature Corrected Bootstrap Algorithm
NASA Technical Reports Server (NTRS)
Comiso, Joey C.; Zwally, H. Jay
1997-01-01
A temperature corrected Bootstrap Algorithm has been developed using Nimbus-7 Scanning Multichannel Microwave Radiometer data in preparation to the upcoming AMSR instrument aboard ADEOS and EOS-PM. The procedure first calculates the effective surface emissivity using emissivities of ice and water at 6 GHz and a mixing formulation that utilizes ice concentrations derived using the current Bootstrap algorithm but using brightness temperatures from 6 GHz and 37 GHz channels. These effective emissivities are then used to calculate surface ice which in turn are used to convert the 18 GHz and 37 GHz brightness temperatures to emissivities. Ice concentrations are then derived using the same technique as with the Bootstrap algorithm but using emissivities instead of brightness temperatures. The results show significant improvement in the area where ice temperature is expected to vary considerably such as near the continental areas in the Antarctic, where the ice temperature is colder than average, and in marginal ice zones.
Completely bootstrapped tokamak
Weening, R.H. ); Boozer, A.H. )
1992-01-01
Numerical simulations of the evolution of large-scale magnetic fields have been developed using a mean-field Ohm's law. The Ohm's law is coupled to a {Delta}{prime} stabilty analysis and a magnetic island growth equation in order to simulate the behavior of tokamak plasmas that are subject to tearing modes. In one set of calculations, the magnetohydrodynamic (MHD)-stable regime of the tokamak is examined via the construction of an {ital l}{sub {ital i}} -{ital q}{sub {ital a}} diagram. The results confirm previous calculations that show that tearing modes introduce a stability boundary into the {ital l}{sub {ital i}} -{ital q}{sub {ital a}} space. In another series of simulations, the interaction between tearing modes and the bootstrap current is investigated. The results indicate that a completely bootstrapped tokamak may be possible, even in the absence of any externally applied loop voltage or current drive.
Moran, Stuart L.; Hutcherson, R. Kenneth
1990-03-27
A triggerable, high voltage, high current, spark gap switch for use in pu power systems. The device comprises a pair of electrodes in a high pressure hydrogen environment that is triggered by introducing an arc between one electrode and a trigger pin. Unusually high repetition rates may be obtained by undervolting the switch, i.e., operating the trigger at voltages much below the self-breakdown voltage of the device.
Bootstrapping structured page segmentation
NASA Astrophysics Data System (ADS)
Ma, Huanfeng; Doermann, David S.
2003-01-01
In this paper, we present an approach to the bootstrap learning of a page segmentation model. The idea evolves from attempts to segment dictionaries that often have a consistent page structure, and is extended to the segmentation of more general structured documents. In cases of highly regular structure, the layout can be learned from examples of only a few pages. The system is first trained using a small number of samples, and a larger test set is processed based on the training result. After making corrections to a selected subset of the test set, these corrected samples are combined with the original training samples to generate bootstrap samples. The newly created samples are used to retrain the system, refine the learned features and resegment the test samples. This procedure is applied iteratively until the learned parameters are stable. Using this approach, we do not need to initially provide a large set of training samples. We have applied this segmentation to many structured documents such as dictionaries, phone books, spoken language transcripts, and obtained satisfying segmentation performance.
NASA Astrophysics Data System (ADS)
Garofalo, A. M.; Gong, X.; Grierson, B. A.; Ren, Q.; Solomon, W. M.; Strait, E. J.; Van Zeeland, M. A.; Holcomb, C. T.; Meneghini, O.; Smith, S. P.; Staebler, G. M.; Wan, B.; Bravenec, R.; Budny, R. V.; Ding, S.; Hanson, J. M.; Heidbrink, W. W.; Lao, L. L.; Li, G.; Pan, C.; Petty, C. C.; Qian, J.; Paz-Soldan, C.; Xu, G.
2015-11-01
Recent EAST/DIII-D joint experiments on the high poloidal beta tokamak regime in DIII-D have demonstrated fully noninductive operation with an internal transport barrier (ITB) at large minor radius, at normalized fusion performance increased by ⩾30% relative to earlier work (Politzer et al 2005 Nucl. Fusion 45 417). The advancement was enabled by improved understanding of the ‘relaxation oscillations’, previously attributed to repetitive ITB collapses, and of the fast ion behavior in this regime. It was found that the ‘relaxation oscillations’ are coupled core-edge modes amenable to wall-stabilization, and that fast ion losses which previously dictated a large plasma-wall separation to avoid wall over-heating, can be reduced to classical levels with sufficient plasma density. By using optimized waveforms of the plasma-wall separation and plasma density, fully noninductive plasmas have been sustained for long durations with excellent energy confinement quality, bootstrap fraction ⩾80%, {β\\text{N}}≤slant 4 , {β\\text{P}}≥slant 3 , and {β\\text{T}}≥slant 2% . These results bolster the applicability of the high poloidal beta tokamak regime toward the realization of a steady-state fusion reactor.
High temperature current mirror amplifier
Patterson, III, Raymond B.
1984-05-22
A high temperature current mirror amplifier having biasing means in the transdiode connection of the input transistor for producing a voltage to maintain the base-collector junction reversed-biased and a current means for maintaining a current through the biasing means at high temperatures so that the base-collector junction of the input transistor remained reversed-biased. For accuracy, a second current mirror is provided with a biasing means and current means on the input leg.
Interpretation of bootstrap values in phylogenetic analysis.
Wiesemüller, Bernhard; Rothe, Hartmut
2006-06-01
Bootstrap Analysis is a common tool in cladistics, and consequently many authors tend to believe that it could be close to a test of monophyly. In fact, it is only a procedure to calculate the redundancy of a certain character pattern among taxa. To demonstrate this, we set up a study with questionable data: Four skulls of great apes and humans were digitally photographed, and the pixels' brightness values were simply transformed to a one-zero-matrix, which was then used to calculate a Wagner tree with PHYLIP. As a rule, the higher the resolution of the photos is, the higher are the bootstrap values of supported taxa (and the lower are the bootstrap values of non-supported data). Redundancy of intertaxic information might indeed be an indicator of phylogenetic relationship, but can also be due to other reasons, like functional-adaptive needs in morphology, or semantic needs in a DNA-code. As a result, we tend to believe that high bootstrap values are actually less important than low ones. It is safer, based on a low bootstrap value, to claim that a certain taxon is not well supported by certain data. Therefore, we recommend discussions of low bootstrap values in future publications. PMID:16850767
NASA Astrophysics Data System (ADS)
Rejon-Barrera, Fernando; Robbins, Daniel
2016-01-01
We work out all of the details required for implementation of the conformal bootstrap program applied to the four-point function of two scalars and two vectors in an abstract conformal field theory in arbitrary dimension. This includes a review of which tensor structures make appearances, a construction of the projectors onto the required mixed symmetry representations, and a computation of the conformal blocks for all possible operators which can be exchanged. These blocks are presented as differential operators acting upon the previously known scalar conformal blocks. Finally, we set up the bootstrap equations which implement crossing symmetry. Special attention is given to the case of conserved vectors, where several simplifications occur.
Bootstrapping the O( N) archipelago
NASA Astrophysics Data System (ADS)
Kos, Filip; Poland, David; Simmons-Duffin, David; Vichi, Alessandro
2015-11-01
We study 3d CFTs with an O( N) global symmetry using the conformal bootstrap for a system of mixed correlators. Specifically, we consider all nonvanishing scalar four-point functions containing the lowest dimension O( N) vector ϕ i and the lowest dimension O( N) singlet s, assumed to be the only relevant operators in their symmetry representations. The constraints of crossing symmetry and unitarity for these four-point functions force the scaling dimensions (Δ ϕ , Δ s ) to lie inside small islands. We also make rigorous determinations of current two-point functions in the O(2) and O(3) models, with applications to transport in condensed matter systems.
High temperature current mirror amplifier
Patterson, R.B. III.
1984-05-22
Disclosed is a high temperature current mirror amplifier having biasing means in the transdiode connection of the input transistor for producing a voltage to maintain the base-collector junction reversed-biased and a current means for maintaining a current through the biasing means at high temperatures so that the base-collector junction of the input transistor remained reversed-biased. For accuracy, a second current mirror is provided with a biasing means and current means on the input leg. 2 figs.
Milestone report: Status report on high {beta}p experiments at high plasma current
Casper, T.A.; James, R.A.; Rice, B.W.; Stallard, B.W.
1995-07-01
This report summarizes LLNL`s involvement in recent high {beta}{sub p} experiments on the DIII-D tokamak at General Atomics. These experiments were done in collaboration with several members of the DIII-D physics staff from GA and from other collaborating institutions and could not have succeeded without this joint effort. In this report, the authors summary a specific, limited set of experiments to extend high {beta}{sub p} operation with enhanced core confinement to higher plasma currents. The interest in these experiments stems from the non-inductive current drive requirement for steady-state advanced tokamak regimes which can most reasonably be met by operation with a high bootstrap current fraction.
NASA Astrophysics Data System (ADS)
Poland, David; Simmons-Duffin, David
2016-06-01
The conformal bootstrap was proposed in the 1970s as a strategy for calculating the properties of second-order phase transitions. After spectacular success elucidating two-dimensional systems, little progress was made on systems in higher dimensions until a recent renaissance beginning in 2008. We report on some of the main results and ideas from this renaissance, focusing on new determinations of critical exponents and correlation functions in the three-dimensional Ising and O(N) models.
High current, high bandwidth laser diode current driver
NASA Technical Reports Server (NTRS)
Copeland, David J.; Zimmerman, Robert K., Jr.
1991-01-01
A laser diode current driver has been developed for free space laser communications. The driver provides 300 mA peak modulation current and exhibits an optical risetime of less than 400 ps. The current and optical pulses are well behaved and show minimal ringing. The driver is well suited for QPPM modulation at data rates up to 440 Mbit/s. Much previous work has championed current steering circuits; in contrast, the present driver is a single-ended on/off switch. This results in twice the power efficiency as a current steering driver. The driver electrical efficiency for QPPM data is 34 percent. The high speed switch is realized with a Ku-band GaAsFET transistor, with a suitable pre-drive circuit, on a hybrid microcircuit adjacent to the laser diode.
Murakami, M; Wade, M R; Greenfield, C M; Luce, T C; Makowski, M A; Petty, C C; DeBoo, J C; Ferron, J R; Jayakumar, R J; Lao, L L; Lohr, J; Politzer, P A; Prater, R; St John, H E
2003-06-27
Recent DIII-D experiments using off-axis electron cyclotron current drive (ECCD) have demonstrated the ability to modify the current profile in a plasma with toroidal beta near 3%. The resulting plasma simultaneously sustains the key elements required for Advanced Tokamak operation: high bootstrap current fraction, high beta, and good confinement. More than 85% of the plasma current is driven by noninductive means. ECCD is observed to produce strong negative central magnetic shear, which in turn acts to trigger confinement improvements in all transport channels in the plasma core. PMID:12857139
NASA Astrophysics Data System (ADS)
Iliesiu, Luca; Kos, Filip; Poland, David; Pufu, Silviu S.; Simmons-Duffin, David; Yacoby, Ran
2016-03-01
We study the conformal bootstrap for a 4-point function of fermions < ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge C T . We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N . We also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.
NASA Astrophysics Data System (ADS)
Chester, Shai M.; Pufu, Silviu S.
2016-08-01
We initiate the conformal bootstrap study of Quantum Electrodynamics in 2+1 space-time dimensions (QED3) with N flavors of charged fermions by focusing on the 4-point function of four monopole operators with the lowest unit of topological charge. We obtain upper bounds on the scaling dimension of the doubly-charged monopole operator, with and without assuming other gaps in the operator spectrum. Intriguingly, we find a (gap-dependent) kink in these bounds that comes reasonably close to the large N extrapolation of the scaling dimensions of the singly-charged and doubly-charged monopole operators down to N = 4 and N = 6.
The N=2 superconformal bootstrap
NASA Astrophysics Data System (ADS)
Beem, Christopher; Lemos, Madalena; Liendo, Pedro; Rastelli, Leonardo; van Rees, Balt C.
2016-03-01
In this work we initiate the conformal bootstrap program for N=2 super-conformal field theories in four dimensions. We promote an abstract operator-algebraic viewpoint in order to unify the description of Lagrangian and non-Lagrangian theories, and formulate various conjectures concerning the landscape of theories. We analyze in detail the four-point functions of flavor symmetry current multiplets and of N=2 chiral operators. For both correlation functions we review the solution of the superconformal Ward identities and describe their superconformal block decompositions. This provides the foundation for an extensive numerical analysis discussed in the second half of the paper. We find a large number of constraints for operator dimensions, OPE coefficients, and central charges that must hold for any N=2 superconformal field theory.
Cesario, R. C.; Castaldo, C.; De Angelis, R.; Smeulders, P.; Calabro, G.; Pericoli, V.; Ravera, G.
2007-09-28
LHCD has been used in JET experiments aimed at producing internal transport barriers (ITBs) in highly triangular plasmas ({delta}{approx_equal}0.4) at high {beta}{sub N} (up to 3) for steady-state application. The LHCD is a potentially valuable tool for (i) modifying the target q-profile, which can help avoid deleterious MHD modes and favour the formation of ITBs, and (ii) contributing to the non-inductive current drive required to prolong such plasma regimes. The q-profile evolution has been simulated during the current ramp-up phase for such a discharge (B{sub 0} = 2.3 T, I{sub P} = 1.5 MA) where 2 MW of LHCD has been coupled. The JETTO code was used taking measured plasma profiles, and the LHCD profile modeled by the LHstar code. The results are in agreement with MSE measurements and indicate the importance of the elevated electron temperature due to LHCD, as well as the driven current. During main heating with 18 MW of NBI and 3 MW of ICRH the bootstrap current density at the edge also becomes large, consistently with the observed reduction of the local turbulence and of the MHD activity. JETTO modelling suggests that the bootstrap current can reduce the magnetic shear (sh) at large radius, potentially affecting the MHD stability and turbulence behaviour in this region. Keywords: lower hybrid current drive (LHCD), bootstrap current, q (safety factor) and shear (sh) profile evolutions.
Explorations in Statistics: the Bootstrap
ERIC Educational Resources Information Center
Curran-Everett, Douglas
2009-01-01
Learning about statistics is a lot like learning about science: the learning is more meaningful if you can actively explore. This fourth installment of Explorations in Statistics explores the bootstrap. The bootstrap gives us an empirical approach to estimate the theoretical variability among possible values of a sample statistic such as the…
HIGH VOLTAGE, HIGH CURRENT SPARK GAP SWITCH
Dike, R.S.; Lier, D.W.; Schofield, A.E.; Tuck, J.L.
1962-04-17
A high voltage and current spark gap switch comprising two main electrodes insulatingly supported in opposed spaced relationship and a middle electrode supported medially between the main electrodes and symmetrically about the median line of the main electrodes is described. The middle electrode has a perforation aligned with the median line and an irradiation electrode insulatingly supported in the body of the middle electrode normal to the median line and protruding into the perforation. (AEC)
High-current, high-frequency capacitors
NASA Technical Reports Server (NTRS)
Renz, D. D.
1983-01-01
The NASA Lewis high-current, high-frequency capacitor development program was conducted under a contract with Maxwell Laboratories, Inc., San Diego, California. The program was started to develop power components for space power systems. One of the components lacking was a high-power, high-frequency capacitor. Some of the technology developed in this program may be directly usable in an all-electric airplane. The materials used in the capacitor included the following: the film is polypropylene, the impregnant is monoisopropyl biphenyl, the conductive epoxy is Emerson and Cuming Stycast 2850 KT, the foil is aluminum, the case is stainless steel (304), and the electrode is a modified copper-ceramic.
High current high accuracy IGBT pulse generator
Nesterov, V.V.; Donaldson, A.R.
1995-05-01
A solid state pulse generator capable of delivering high current triangular or trapezoidal pulses into an inductive load has been developed at SLAC. Energy stored in a capacitor bank of the pulse generator is switched to the load through a pair of insulated gate bipolar transistors (IGBT). The circuit can then recover the remaining energy and transfer it back to the capacitor bank without reversing the capacitor voltage. A third IGBT device is employed to control the initial charge to the capacitor bank, a command charging technique, and to compensate for pulse to pulse power losses. The rack mounted pulse generator contains a 525 {mu}F capacitor bank. It can deliver 500 A at 900V into inductive loads up to 3 mH. The current amplitude and discharge time are controlled to 0.02% accuracy by a precision controller through the SLAC central computer system. This pulse generator drives a series pair of extraction dipoles.
High current capacity electrical connector
Bettis, Edward S.; Watts, Harry L.
1976-01-13
An electrical connector is provided for coupling high current capacity electrical conductors such as copper busses or the like. The connector is arranged in a "sandwiched" configuration in which a conductor plate contacts the busses along major surfaces thereof clamped between two stainless steel backing plates. The conductor plate is provided with a plurality of contact buttons affixed therein in a spaced array such that the caps of the buttons extend above the conductor plate surface to contact the busses. When clamping bolts provided through openings in the sandwiched arrangement are tightened, Belleville springs provided under the rim of each button cap are compressed and resiliently force the caps into contact with the busses' contacting surfaces to maintain a predetermined electrical contact area provided by the button cap tops. The contact area does not change with changing thermal or mechanical stresses applied to the coupled conductors.
HIGH CURRENT COAXIAL PHOTOMULTIPLIER TUBE
Glass, N.W.
1960-01-19
A medium-gain photomultiplier tube having high current output, fast rise- time, and matched output impedance was developed. The photomultiplier tube comprises an elongated cylindrical envelope, a cylindrical anode supported at the axis of the envelope, a plurality of elongated spaced opaque areas on the envelope, and a plurality of light admitting windows. A photo-cathode is supported adjacent to each of the windows, and a plurality of secondary emissive dynodes are arranged in two types of radial arrays which are alternately positioned to fill the annular space between the anode and the envelope. The dynodes are in an array being radially staggered with respect to the dynodes in the adjacent array, the dynodes each having a portion arranged at an angle with respect to the electron path, such that electrons emitted by each cathode undergo multiplication upon impingement on a dynode and redirected flight to the next adjacent dynode.
Confidence Intervals for the Mean: To Bootstrap or Not to Bootstrap
ERIC Educational Resources Information Center
Calzada, Maria E.; Gardner, Holly
2011-01-01
The results of a simulation conducted by a research team involving undergraduate and high school students indicate that when data is symmetric the student's "t" confidence interval for a mean is superior to the studied non-parametric bootstrap confidence intervals. When data is skewed and for sample sizes n greater than or equal to 10, the results…
Bootstrapping Time Dilation Decoherence
NASA Astrophysics Data System (ADS)
Gooding, Cisco; Unruh, William G.
2015-10-01
We present a general relativistic model of a spherical shell of matter with a perfect fluid on its surface coupled to an internal oscillator, which generalizes a model recently introduced by the authors to construct a self-gravitating interferometer (Gooding and Unruh in Phys Rev D 90:044071, 2014). The internal oscillator evolution is defined with respect to the local proper time of the shell, allowing the oscillator to serve as a local clock that ticks differently depending on the shell's position and momentum. A Hamiltonian reduction is performed on the system, and an approximate quantum description is given to the reduced phase space. If we focus only on the external dynamics, we must trace out the clock degree of freedom, and this results in a form of intrinsic decoherence that shares some features with a proposed "universal" decoherence mechanism attributed to gravitational time dilation (Pikovski et al in Nat Phys, 2015). We note that the proposed decoherence remains present in the (gravity-free) limit of flat spacetime, emphasizing that the effect can be attributed entirely to proper time differences, and thus is not necessarily related to gravity. Whereas the effect described in (Pikovski et al in Nat Phys, 2015) vanishes in the absence of an external gravitational field, our approach bootstraps the gravitational contribution to the time dilation decoherence by including self-interaction, yielding a fundamentally gravitational intrinsic decoherence effect.
Ferron, J.R.; Holcomb, C T; Luce, T.C.; Politzer, P. A.; Turco, F.; DeBoo, J. C.; Doyle, E. J.; In, Y.; La Haye, R.; Murakami, Masanori; Okabayashi, M.; Park, J. M.; Petrie, T W; Petty, C C.; Reimerdes, H.
2011-01-01
In order to maintain stationary values of the stored energy and the plasma current in a tokamak discharge with all of the current driven noninductively, the sum of the alpha-heating power and the power required to provide externally driven current must be equal to the power required to maintain the pressure against transport losses. In a study of high noninductive current fraction discharges in the DIII-D tokamak, it is shown that in the case of present-day tokamaks with no alpha-heating, adjustment of the toroidal field strength (B(T)) is a tool to obtain this balance between the required current drive and heating powers with other easily modifiable discharge parameters (beta(N), q(95), discharge shape, n(e)) fixed at values chosen to satisfy specific constraints. With all of the external power sources providing both heating and current drive, and beta(N) and q(95) fixed, the fraction of externally driven current scales with B(T) with little change in the bootstrap current fraction, thus allowing the noninductive current fraction to be adjusted.
Bootstrapping a time series model
Son, M.S.
1984-01-01
The bootstrap is a methodology for estimating standard errors. The idea is to use a Monte Carlo simulation experiment based on a nonparametric estimate of the error distribution. The main objective of this dissertation was to demonstrate the use of the bootstrap to attach standard errors to coefficient estimates and multi-period forecasts in a second-order autoregressive model fitted by least squares and maximum likelihood estimation. A secondary objective of this article was to present the bootstrap in the context of two econometric equations describing the unemployment rate and individual income tax in the state of Oklahoma. As it turns out, the conventional asymptotic formulae (both the least squares and maximum likelihood estimates) for estimating standard errors appear to overestimate the true standard errors. But there are two problems: 1) the first two observations y/sub 1/ and y/sub 2/ have been fixed, and 2) the residuals have not been inflated. After these two factors are considered in the trial and bootstrap experiment, both the conventional maximum likelihood and bootstrap estimates of the standard errors appear to be performing quite well. At present, there does not seem to be a good rule of thumb for deciding when the conventional asymptotic formulae will give acceptable results.
NASA Astrophysics Data System (ADS)
Ferron, J. R.; Holcomb, C. T.; Luce, T. C.; Politzer, P. A.; Turco, F.; White, A. E.; DeBoo, J. C.; Doyle, E. J.; Hyatt, A. W.; La Haye, R. J.; Murakami, M.; Petrie, T. W.; Petty, C. C.; Rhodes, T. L.; Zeng, L.
2011-06-01
In order to assess the optimum q profile for discharges in DIII-D with 100% of the current driven noninductively (fNI = 1), the self-consistent response of the plasma profiles to changes in the q profile was studied in high fNI, high βN discharges through a scan of qmin and q95 at two values of βN. As expected, both the bootstrap current fraction, fBS, and fNI increased with q95. The temperature and density profiles were found to broaden as either qmin or βN is increased. A consequence is that fBS does not continue to increase at the highest values of qmin. A scaling function that depends on qmin, q95, and the peaking factor for the thermal pressure was found to represent well the fBS/βN inferred from the experimental profiles. The changes in the shapes of the density and temperature profiles as βN is increased modify the bootstrap current density (JBS) profile from peaked close to the axis to relatively flat in the region between the axis and the H-mode pedestal. Therefore, significant externally driven current density in the region inside the H-mode pedestal is required in addition to JBS in order to match the profiles of the noninductive current density (JNI) to the desired total current density (J). In this experiment, the additional current density was provided mostly by neutral beam current drive with the neutral-beam-driven current fraction 40-90% of fBS. The profiles of JNI and J were most similar at qmin ≈ 1.35-1.65, q95 ≈ 6.8, where fBS is also maximum, establishing this q profile as the optimal choice for fNI = 1 operation in DIII-D with the existing set of external current drive sources.
High current gain transistor laser.
Liang, Song; Qiao, Lijun; Zhu, Hongliang; Wang, Wei
2016-01-01
A transistor laser (TL), having the structure of a transistor with multi-quantum wells near its base region, bridges the functionality gap between lasers and transistors. However, light emission is produced at the expense of current gain for all the TLs reported up to now, leading to a very low current gain. We propose a novel design of TLs, which have an n-doped InP layer inserted in the emitter ridge. Numerical studies show that a current flow aperture for only holes can be formed in the center of the emitter ridge. As a result, the common emitter current gain can be as large as 143.3, which is over 15 times larger than that of a TL without the aperture. Besides, the effects of nonradiative recombination defects can be reduced greatly because the flow of holes is confined in the center region of the emitter ridge. PMID:27282466
High current gain transistor laser
NASA Astrophysics Data System (ADS)
Liang, Song; Qiao, Lijun; Zhu, Hongliang; Wang, Wei
2016-06-01
A transistor laser (TL), having the structure of a transistor with multi-quantum wells near its base region, bridges the functionality gap between lasers and transistors. However, light emission is produced at the expense of current gain for all the TLs reported up to now, leading to a very low current gain. We propose a novel design of TLs, which have an n-doped InP layer inserted in the emitter ridge. Numerical studies show that a current flow aperture for only holes can be formed in the center of the emitter ridge. As a result, the common emitter current gain can be as large as 143.3, which is over 15 times larger than that of a TL without the aperture. Besides, the effects of nonradiative recombination defects can be reduced greatly because the flow of holes is confined in the center region of the emitter ridge.
High current gain transistor laser
Liang, Song; Qiao, Lijun; Zhu, Hongliang; Wang, Wei
2016-01-01
A transistor laser (TL), having the structure of a transistor with multi-quantum wells near its base region, bridges the functionality gap between lasers and transistors. However, light emission is produced at the expense of current gain for all the TLs reported up to now, leading to a very low current gain. We propose a novel design of TLs, which have an n-doped InP layer inserted in the emitter ridge. Numerical studies show that a current flow aperture for only holes can be formed in the center of the emitter ridge. As a result, the common emitter current gain can be as large as 143.3, which is over 15 times larger than that of a TL without the aperture. Besides, the effects of nonradiative recombination defects can be reduced greatly because the flow of holes is confined in the center region of the emitter ridge. PMID:27282466
High critical current superconducting tapes
Holesinger, Terry G.; Jia, Quanxi; Foltyn, Stephen R.
2003-09-23
Improvements in critical current capacity for superconducting film structures are disclosed and include the use of a superconducting RE-BCO layer including a mixture of rare earth metals, e.g., yttrium and europium, where the ratio of yttrium to europium in the RE-BCO layer ranges from about 3 to 1 to from about 1.5 to 1.
ELECTROMIGRATION ISSUES IN HIGH CURRENT HORN.
ZHANG, S.Y.; BELLAVIA, S.; SANDBERG, J.; ET AL.
2005-05-16
The secondary particle focusing horn for the AGS neutrino experiment proposal is a high current and high current density device. The peak current of horn is 300 kA. At the smallest area of horn, the current density is near 8 kA/mm{sup 2}. At very high current density, a few kA/mm{sup 2}, the electromigration phenomena will occur. Momentum transfer between electrons and metal atoms at high current density causes electromigration. The reliability and lifetime of focusing horn can be severely reduced by electromigration. In this paper, we discuss issues such as device reliability model, incubation time of electromigration, and lifetime of horn.
Coefficient Omega Bootstrap Confidence Intervals: Nonnormal Distributions
ERIC Educational Resources Information Center
Padilla, Miguel A.; Divers, Jasmin
2013-01-01
The performance of the normal theory bootstrap (NTB), the percentile bootstrap (PB), and the bias-corrected and accelerated (BCa) bootstrap confidence intervals (CIs) for coefficient omega was assessed through a Monte Carlo simulation under conditions not previously investigated. Of particular interests were nonnormal Likert-type and binary items.…
High temperature superconductor current leads
Hull, J.R.; Poeppel, R.B.
1995-06-20
An electrical lead is disclosed having one end for connection to an apparatus in a cryogenic environment and the other end for connection to an apparatus outside the cryogenic environment. The electrical lead includes a high temperature superconductor wire and an electrically conductive material distributed therein, where the conductive material is present at the one end of the lead at a concentration in the range of from 0 to about 3% by volume, and at the other end of the lead at a concentration of less than about 20% by volume. Various embodiments are shown for groups of high temperature superconductor wires and sheaths. 9 figs.
High temperature superconductor current leads
Hull, John R.; Poeppel, Roger B.
1995-01-01
An electrical lead having one end for connection to an apparatus in a cryogenic environment and the other end for connection to an apparatus outside the cryogenic environment. The electrical lead includes a high temperature superconductor wire and an electrically conductive material distributed therein, where the conductive material is present at the one end of the lead at a concentration in the range of from 0 to about 3% by volume, and at the other end of the lead at a concentration of less than about 20% by volume. Various embodiments are shown for groups of high temperature superconductor wires and sheaths.
High temperature superconducting fault current limiter
Hull, J.R.
1997-02-04
A fault current limiter for an electrical circuit is disclosed. The fault current limiter includes a high temperature superconductor in the electrical circuit. The high temperature superconductor is cooled below its critical temperature to maintain the superconducting electrical properties during operation as the fault current limiter. 15 figs.
High temperature superconducting fault current limiter
Hull, John R.
1997-01-01
A fault current limiter (10) for an electrical circuit (14). The fault current limiter (10) includes a high temperature superconductor (12) in the electrical circuit (14). The high temperature superconductor (12) is cooled below its critical temperature to maintain the superconducting electrical properties during operation as the fault current limiter (10).
Multi-baseline bootstrapping at the Navy precision optical interferometer
NASA Astrophysics Data System (ADS)
Armstrong, J. T.; Schmitt, H. R.; Mozurkewich, D.; Jorgensen, A. M.; Muterspaugh, M. W.; Baines, E. K.; Benson, J. A.; Zavala, Robert T.; Hutter, D. J.
2014-07-01
The Navy Precision Optical Interferometer (NPOI) was designed from the beginning to support baseline boot- strapping with equally-spaced array elements. The motivation was the desire to image the surfaces of resolved stars with the maximum resolution possible with a six-element array. Bootstrapping two baselines together to track fringes on a third baseline has been used at the NPOI for many years, but the capabilities of the fringe tracking software did not permit us to bootstrap three or more baselines together. Recently, both a new backend (VISION; Tennessee State Univ.) and new hardware and firmware (AZ Embedded Systems and New Mexico Tech, respectively) for the current hybrid backend have made multi-baseline bootstrapping possible.
Apparatus for measuring high frequency currents
NASA Technical Reports Server (NTRS)
Hagmann, Mark J. (Inventor); Sutton, John F. (Inventor)
2003-01-01
An apparatus for measuring high frequency currents includes a non-ferrous core current probe that is coupled to a wide-band transimpedance amplifier. The current probe has a secondary winding with a winding resistance that is substantially smaller than the reactance of the winding. The sensitivity of the current probe is substantially flat over a wide band of frequencies. The apparatus is particularly useful for measuring exposure of humans to radio frequency currents.
Bootstrapping N=2 chiral correlators
NASA Astrophysics Data System (ADS)
Lemos, Madalena; Liendo, Pedro
2016-01-01
We apply the numerical bootstrap program to chiral operators in four-dimensional N=2 SCFTs. In the first part of this work we study four-point functions in which all fields have the same conformal dimension. We give special emphasis to bootstrapping a specific theory: the simplest Argyres-Douglas fixed point with no flavor symmetry. In the second part we generalize our setup and consider correlators of fields with unequal dimension. This is an example of a mixed correlator and allows us to probe new regions in the parameter space of N=2 SCFTs. In particular, our results put constraints on relations in the Coulomb branch chiral ring and on the curvature of the Zamolodchikov metric.
NASA Astrophysics Data System (ADS)
Horn, D.
2015-03-01
The quark model emerged from the Gell-Mann-Ne'eman flavor SU(3) symmetry. Its development, in the context of strong interactions, took place in a heuristic theoretical framework, referred to as the Bootstrap Era. Setting the background for the dominant ideas in strong interaction of the early 1960s, we outline some aspects of the constituent quark model. An independent theoretical development was the emergence of hadron duality in 1967, leading to a realization of the Bootstrap idea by relating hadron resonances (in the s-channel) with Regge pole trajectories (in t- and u-channels). The synthesis of duality with the quark-model has been achieved by duality diagrams, serving as a conceptual framework for discussing many aspects of hadron dynamics toward the end of the 1960s.
NASA Astrophysics Data System (ADS)
Horn, D.
2014-12-01
The quark model emerged from the Gell-Mann-Ne'eman flavor SU(3) symmetry. Its development, in the context of strong interactions, took place in a heuristic theoretical framework, referred to as the Bootstrap Era. Setting the background for the dominant ideas in strong interaction of the early 1960s, we outline some aspects of the constituent quark model. An independent theoretical development was the emergence of hadron duality in 1967, leading to a realization of the Bootstrap idea by relating hadron resonances (in the s-channel) with Regge pole trajectories (in t- and u-channels). The synthesis of duality with the quark-model has been achieved by duality diagrams, serving as a conceptual framework for discussing many aspects of hadron dynamics toward the end of the 1960s.
Conformal bootstrap in embedding space
NASA Astrophysics Data System (ADS)
Fortin, Jean-François; Skiba, Witold
2016-05-01
It is shown how to obtain conformal blocks from embedding space with the help of the operator product expansion. The minimal conformal block originates from scalar exchange in a four-point correlation function of four scalars. All remaining conformal blocks are simple derivatives of the minimal conformal block. With the help of the orthogonality properties of the conformal blocks, the analytic conformal bootstrap can be implemented directly in embedding space, leading to a Jacobi-like definition of conformal field theories.
Modified Bootstrap Sensitometry In Radiography
NASA Astrophysics Data System (ADS)
Bednarek, Daniel R.; Rudin, Stephen
1981-04-01
A new modified bootstrap approach to sensitometry is presented which provides H and D curves that show almost exact agreement with those obtained using conventional methods. Two bootstrap techniques are described; both involve a combination of inverse-square and stepped-wedge modulation of the radiation field and provide intensity-scale sensitometric curves as appropriate for medical radiography. H and D curves obtained with these modified techniques are compared with those obtained for screen-film combinations using inverse-square sensitometry as well as with those obtained for direct x-ray film using time-scale sensitometry. The stepped wedge of the Wisconsin X-Ray Test Cassette was used in the bootstrap approach since it provides sufficient exposure latitude to encompass the useful density range of medical x-ray film. This approach makes radiographic sensitometry quick and convenient, allowing accurate characteristic curves to be obtained for any screen-film cassette using standard diagnostic x-ray equipment.
Investigations of dipole localization accuracy in MEG using the bootstrap.
Darvas, F; Rautiainen, M; Pantazis, D; Baillet, S; Benali, H; Mosher, J C; Garnero, L; Leahy, R M
2005-04-01
We describe the use of the nonparametric bootstrap to investigate the accuracy of current dipole localization from magnetoencephalography (MEG) studies of event-related neural activity. The bootstrap is well suited to the analysis of event-related MEG data since the experiments are repeated tens or even hundreds of times and averaged to achieve acceptable signal-to-noise ratios (SNRs). The set of repetitions or epochs can be viewed as a set of independent realizations of the brain's response to the experiment. Bootstrap resamples can be generated by sampling with replacement from these epochs and averaging. In this study, we applied the bootstrap resampling technique to MEG data from somatotopic experimental and simulated data. Four fingers of the right and left hand of a healthy subject were electrically stimulated, and about 400 trials per stimulation were recorded and averaged in order to measure the somatotopic mapping of the fingers in the S1 area of the brain. Based on single-trial recordings for each finger we performed 5000 bootstrap resamples. We reconstructed dipoles from these resampled averages using the Recursively Applied and Projected (RAP)-MUSIC source localization algorithm. We also performed a simulation for two dipolar sources with overlapping time courses embedded in realistic background brain activity generated using the prestimulus segments of the somatotopic data. To find correspondences between multiple sources in each bootstrap, sample dipoles with similar time series and forward fields were assumed to represent the same source. These dipoles were then clustered by a Gaussian Mixture Model (GMM) clustering algorithm using their combined normalized time series and topographies as feature vectors. The mean and standard deviation of the dipole position and the dipole time series in each cluster were computed to provide estimates of the accuracy of the reconstructed source locations and time series. PMID:15784414
Hybrid high direct current circuit interrupter
Rockot, Joseph H.; Mikesell, Harvey E.; Jha, Kamal N.
1998-01-01
A device and a method for interrupting very high direct currents (greater than 100,000 amperes) and simultaneously blocking high voltages (greater than 600 volts). The device utilizes a mechanical switch to carry very high currents continuously with low loss and a silicon controlled rectifier (SCR) to bypass the current around the mechanical switch while its contacts are separating. A commutation circuit, connected in parallel with the SCR, turns off the SCR by utilizing a resonant circuit to divert the SCR current after the switch opens.
Hybrid high direct current circuit interrupter
Rockot, J.H.; Mikesell, H.E.; Jha, K.N.
1998-08-11
A device and a method are disclosed for interrupting very high direct currents (greater than 100,000 amperes) and simultaneously blocking high voltages (greater than 600 volts). The device utilizes a mechanical switch to carry very high currents continuously with low loss and a silicon controlled rectifier (SCR) to bypass the current around the mechanical switch while its contacts are separating. A commutation circuit, connected in parallel with the SCR, turns off the SCR by utilizing a resonant circuit to divert the SCR current after the switch opens. 7 figs.
Taylor, G.; Hosea, J.; Kessel, C. E.; LeBlanc, B; Mueller, D.; Phillips, C. K.; Valeo, E. J.; Wilson, J. R.; Ryan, Philip Michael; Bonoli, P.; Harvey, R. W.
2012-01-01
A deuterium H-mode discharge with a plasma current of 300 kA, an axial toroidal magnetic field of 0.55 T, and a calculated non-inductive plasma current fraction of 0.7 1 has been generated in the National Spherical Torus Experiment by 1.4MW of 30MHz high-harmonic fast wave (HHFW) heating and current drive. Seventy-five percent of the non-inductive current was generated inside an internal transport barrier that formed at a normalized minor radius 0.4. Three quarters of the non-inductive current was bootstrap current, and the remaining non-inductive current was generated directly by HHFW power inside a normalized minor radius 0.2. VC 2012 American Institute of Physics.
A neural network based reputation bootstrapping approach for service selection
NASA Astrophysics Data System (ADS)
Wu, Quanwang; Zhu, Qingsheng; Li, Peng
2015-10-01
With the concept of service-oriented computing becoming widely accepted in enterprise application integration, more and more computing resources are encapsulated as services and published online. Reputation mechanism has been studied to establish trust on prior unknown services. One of the limitations of current reputation mechanisms is that they cannot assess the reputation of newly deployed services as no record of their previous behaviours exists. Most of the current bootstrapping approaches merely assign default reputation values to newcomers. However, by this kind of methods, either newcomers or existing services will be favoured. In this paper, we present a novel reputation bootstrapping approach, where correlations between features and performance of existing services are learned through an artificial neural network (ANN) and they are then generalised to establish a tentative reputation when evaluating new and unknown services. Reputations of services published previously by the same provider are also incorporated for reputation bootstrapping if available. The proposed reputation bootstrapping approach is seamlessly embedded into an existing reputation model and implemented in the extended service-oriented architecture. Empirical studies of the proposed approach are shown at last.
High current ion beam transport using solenoids
Hollinger, R.; Spaedtke, P.
2008-02-15
In the framework of the future project FAIR several upgrade programs and construction of new facilities are in progress such as the U{sup 4+} upgrade for the existing high current injector and the new 70 MeV proton injector. For both injectors solenoids in the low energy beam transport section are foreseen to inject the beam into the following rf accelerator. The paper presents beam quality measurements of high current ion beams behind a solenoid using a slit-grid emittance measurement device, viewing targets, and a pepper pot measurement device at the high current test bench at GSI.
High pressure, high current, low inductance, high reliability sealed terminals
Hsu, John S [Oak Ridge, TN; McKeever, John W [Oak Ridge, TN
2010-03-23
The invention is a terminal assembly having a casing with at least one delivery tapered-cone conductor and at least one return tapered-cone conductor routed there-through. The delivery and return tapered-cone conductors are electrically isolated from each other and positioned in the annuluses of ordered concentric cones at an off-normal angle. The tapered cone conductor service can be AC phase conductors and DC link conductors. The center core has at least one service conduit of gate signal leads, diagnostic signal wires, and refrigerant tubing routed there-through. A seal material is in direct contact with the casing inner surface, the tapered-cone conductors, and the service conduits thereby hermetically filling the interstitial space in the casing interior core and center core. The assembly provides simultaneous high-current, high-pressure, low-inductance, and high-reliability service.
Taylor, G; Kessel, C E; LeBlanc, B P; Mueller, D; Phillips, D K; Valeo, E J; Wilson, J R; Ryan, P M; Bonoli, P T; Wright, J C
2012-02-13
1.4 MW of 30 MHz high-harmonic fast wave (HHFW) heating, with current drive antenna phasing, has generated a Ip = 300kA, BT (0) = 0.55T deuterium H-mode plasma in the National Spherical Torus Experiment that has a non-inductive plasma current fraction, fNI = 0.7-1. Seventy-five percent of the non-inductive current was generated inside an internal transport barrier that formed at a normalized minor radius, r/a {approx} 0.4 . Three quarters of the non-inductive current was bootstrap current and the remaining non-inductive current was generated directly by HHFW power inside r/a {approx} 0.2.
Bootstrap percolation on spatial networks
NASA Astrophysics Data System (ADS)
Gao, Jian; Zhou, Tao; Hu, Yanqing
2015-10-01
Bootstrap percolation is a general representation of some networked activation process, which has found applications in explaining many important social phenomena, such as the propagation of information. Inspired by some recent findings on spatial structure of online social networks, here we study bootstrap percolation on undirected spatial networks, with the probability density function of long-range links’ lengths being a power law with tunable exponent. Setting the size of the giant active component as the order parameter, we find a parameter-dependent critical value for the power-law exponent, above which there is a double phase transition, mixed of a second-order phase transition and a hybrid phase transition with two varying critical points, otherwise there is only a second-order phase transition. We further find a parameter-independent critical value around -1, about which the two critical points for the double phase transition are almost constant. To our surprise, this critical value -1 is just equal or very close to the values of many real online social networks, including LiveJournal, HP Labs email network, Belgian mobile phone network, etc. This work helps us in better understanding the self-organization of spatial structure of online social networks, in terms of the effective function for information spreading.
The (2, 0) superconformal bootstrap
NASA Astrophysics Data System (ADS)
Beem, Christopher; Lemos, Madalena; Rastelli, Leonardo; van Rees, Balt C.
2016-01-01
We develop the conformal bootstrap program for six-dimensional conformal field theories with (2, 0) supersymmetry, focusing on the universal four-point function of stress tensor multiplets. We review the solution of the superconformal Ward identities and describe the superconformal block decomposition of this correlator. We apply numerical bootstrap techniques to derive bounds on operator product expansion (OPE) coefficients and scaling dimensions from the constraints of crossing symmetry and unitarity. We also derive analytic results for the large spin spectrum using the light cone expansion of the crossing equation. Our principal result is strong evidence that the A1 theory realizes the minimal allowed central charge (c =25 ) for any interacting (2, 0) theory. This implies that the full stress tensor four-point function of the A1 theory is the unique unitary solution to the crossing symmetry equation at c =25 . For this theory, we estimate the scaling dimensions of the lightest unprotected operators appearing in the stress tensor operator product expansion. We also find rigorous upper bounds for dimensions and OPE coefficients for a general interacting (2, 0) theory of central charge c . For large c , our bounds appear to be saturated by the holographic predictions obtained from eleven-dimensional supergravity.
Bootstrap percolation on spatial networks
Gao, Jian; Zhou, Tao; Hu, Yanqing
2015-01-01
Bootstrap percolation is a general representation of some networked activation process, which has found applications in explaining many important social phenomena, such as the propagation of information. Inspired by some recent findings on spatial structure of online social networks, here we study bootstrap percolation on undirected spatial networks, with the probability density function of long-range links’ lengths being a power law with tunable exponent. Setting the size of the giant active component as the order parameter, we find a parameter-dependent critical value for the power-law exponent, above which there is a double phase transition, mixed of a second-order phase transition and a hybrid phase transition with two varying critical points, otherwise there is only a second-order phase transition. We further find a parameter-independent critical value around −1, about which the two critical points for the double phase transition are almost constant. To our surprise, this critical value −1 is just equal or very close to the values of many real online social networks, including LiveJournal, HP Labs email network, Belgian mobile phone network, etc. This work helps us in better understanding the self-organization of spatial structure of online social networks, in terms of the effective function for information spreading. PMID:26423347
Coefficient Alpha Bootstrap Confidence Interval under Nonnormality
ERIC Educational Resources Information Center
Padilla, Miguel A.; Divers, Jasmin; Newton, Matthew
2012-01-01
Three different bootstrap methods for estimating confidence intervals (CIs) for coefficient alpha were investigated. In addition, the bootstrap methods were compared with the most promising coefficient alpha CI estimation methods reported in the literature. The CI methods were assessed through a Monte Carlo simulation utilizing conditions…
ERIC Educational Resources Information Center
Kim, Se-Kang
2010-01-01
The aim of the current study is to validate the invariance of major profile patterns derived from multidimensional scaling (MDS) by bootstrapping. Profile Analysis via Multidimensional Scaling (PAMS) was employed to obtain profiles and bootstrapping was used to construct the sampling distributions of the profile coordinates and the empirical…
Analytic bootstrap at large spin
NASA Astrophysics Data System (ADS)
Kaviraj, Apratim; Sen, Kallol; Sinha, Aninda
2015-11-01
We use analytic conformal bootstrap methods to determine the anomalous dimensions and OPE coefficients for large spin operators in general conformal field theories in four dimensions containing a scalar operator of conformal dimension Δ ϕ . It is known that such theories will contain an infinite sequence of large spin operators with twists approaching 2Δ ϕ + 2 n for each integer n. By considering the case where such operators are separated by a twist gap from other operators at large spin, we analytically determine the n, Δ ϕ dependence of the anomalous dimensions. We find that for all n, the anomalous dimensions are negative for Δ ϕ satisfying the unitarity bound. We further compute the first subleading correction at large spin and show that it becomes universal for large twist. In the limit when n is large, we find exact agreement with the AdS/CFT prediction corresponding to the Eikonal limit of a 2-2 scattering with dominant graviton exchange.
A New High-Current Proton Accelerator
Cleland, M. R.; Galloway, R. A.; DeSanto, L.; Jongen, Y.
2009-03-10
A high-current (>20 mA) dc proton accelerator is being developed for applications such as boron neutron capture therapy (BNCT) and the detection of explosive materials by nuclear resonance absorption (NRA) of gamma radiation. The high-voltage dc accelerator (adjustable between 1.4 and 2.8 MeV) will be a single-ended industrial Dynamitron registered system equipped with a compact high-current, microwave-driven proton source. A magnetic mass analyzer inserted between the ion source and the acceleration tube will select the protons and reject heavier ions. A sorption pump near the ion source will minimize the flow of neutral hydrogen gas into the acceleration tube. For BNCT, a lithium target for generating epithermal neutrons is being developed that will be capable of dissipating the high power (>40 kW) of the proton beam. For NRA, special targets will be used to generate gamma rays with suitable energies for exciting nuclides typically present in explosive materials. Proton accelerators with such high-current and high-power capabilities in this energy range have not been developed previously.
A New High-Current Proton Accelerator
NASA Astrophysics Data System (ADS)
Cleland, M. R.; Galloway, R. A.; DeSanto, L.; Jongen, Y.
2009-03-01
A high-current (>20 mA) dc proton accelerator is being developed for applications such as boron neutron capture therapy (BNCT) and the detection of explosive materials by nuclear resonance absorption (NRA) of gamma radiation. The high-voltage dc accelerator (adjustable between 1.4 and 2.8 MeV) will be a single-ended industrial Dynamitron® system equipped with a compact high-current, microwave-driven proton source. A magnetic mass analyzer inserted between the ion source and the acceleration tube will select the protons and reject heavier ions. A sorption pump near the ion source will minimize the flow of neutral hydrogen gas into the acceleration tube. For BNCT, a lithium target for generating epithermal neutrons is being developed that will be capable of dissipating the high power (>40 kW) of the proton beam. For NRA, special targets will be used to generate gamma rays with suitable energies for exciting nuclides typically present in explosive materials. Proton accelerators with such high-current and high-power capabilities in this energy range have not been developed previously.
Conformal collider physics from the lightcone bootstrap
NASA Astrophysics Data System (ADS)
Li, Daliang; Meltzer, David; Poland, David
2016-02-01
We analytically study the lightcone limit of the conformal bootstrap equations for 4-point functions containing global symmetry currents and the stress tensor in 3d CFTs. We show that the contribution of the stress tensor to the anomalous dimensions of large spin double-twist states is negative if and only if the conformal collider physics bounds are satisfied. In the context of AdS/CFT these results indicate a relation between the attractiveness of AdS gravity and positivity of the CFT energy flux. We also study the contribution of non-Abelian conserved currents to the anomalous dimensions of double- twist operators, corresponding to the gauge binding energy of 2-particle states in AdS. We show that the representation of the double-twist state determines the sign of the gauge binding energy if and only if the coefficients appearing in the current 3-point function satisfies a similar bound, which is equivalent to an upper bound on the charge flux asymmetry of the CFT.
Ring current development during high speed streams
NASA Astrophysics Data System (ADS)
Jordanova, V. K.; Matsui, H.; Puhl-Quinn, P. A.; Thomsen, M. F.; Mursula, K.; Holappa, L.
2009-07-01
Episodes of southward (Bz<0) interplanetary magnetic field (IMF) which lead to disturbed geomagnetic conditions are associated either with coronal mass ejections (CMEs) and possess long and continuous negative IMF Bz excursions, or with high speed solar wind streams (HSS) whose geoeffectiveness is due to IMF Bz profiles fluctuating about zero with various amplitudes and duration. We simulate ring current evolution during a HSS-driven storm that occurred during 24-26 October 2002 and compare its dynamics with a CME-driven storm of similar strength during 22-23 April 2001. We use our kinetic ring current-atmosphere interactions model (RAM), and investigate the mechanisms responsible for trapping particles and for causing their loss. Ring current evolution depends on the interplay of time-dependent inflow of plasma from the magnetotail, particle acceleration and loss (mainly due to charge exchange) along adiabatic drift paths, and outflow of plasma from the dayside magnetopause; all of these processes are incorporated in our model. We compare results from simulations using a newly developed, Cluster data based, University of New Hampshire inner magnetospheric electric field (UNH-IMEF) convection model with simulations using a Volland-Stern (V-S) type convection model. We find that, first, periods of increased magnetospheric convection coinciding with enhancements of plasma sheet density are needed for strong ring current buildup. Second, during the HSS-driven storm the convection potential from UNH-IMEF model is highly variable and causes sporadic shallow injections resulting in a weak ring current. The long period of enhanced convection during the CME-driven storm causes a continuous ion injection penetrating to lower L shells and stronger ring current buildup. V-S model predicts larger ring current injection during both storms. Third, the RAM driven by either convection model underestimates the total ring current energy during the recovery phase of the HSS storm
COMPILATION OF CURRENT HIGH ENERGY PHYSICS EXPERIMENTS
Wohl, C.G.; Kelly, R.L.; Armstrong, F.E.; Horne, C.P.; Hutchinson, M.S.; Rittenberg, A.; Trippe, T.G.; Yost, G.P.; Addis, L.; Ward, C.E.W.; Baggett, N.; Goldschmidt-Clermong, Y.; Joos, P.; Gelfand, N.; Oyanagi, Y.; Grudtsin, S.N.; Ryabov, Yu.G.
1981-05-01
This is the fourth edition of our compilation of current high energy physics experiments. It is a collaborative effort of the Berkeley Particle Data Group, the SLAC library, and nine participating laboratories: Argonne (ANL), Brookhaven (BNL), CERN, DESY, Fermilab (FNAL), the Institute for Nuclear Study, Tokyo (INS), KEK, Serpukhov (SERP), and SLAC. The compilation includes summaries of all high energy physics experiments at the above laboratories that (1) were approved (and not subsequently withdrawn) before about April 1981, and (2) had not completed taking of data by 1 January 1977. We emphasize that only approved experiments are included.
Extremely High Current, High-Brightness Energy Recovery Linac
I. Ben-Zvi; D.S. Barton; D.B. Beavis; M. Blaskiewicz; J.M. Brennan; A. Burrill; R. Calaga; P. Cameron; X.Y. Chang; R. Connolly; D.M. Gassner; J.G. Grimes; H. Hahn; A. Hershcovitch; H.-C. Hseuh; P.D.J. Johnson; D. Kayran; J. Kewisch; R.F. Lambiase; V. Litvinenko; G.T. McIntyre; W. Meng; T.C.N. Nehring; T. Nicoletti; B. Oerter; D. Pate; J. Rank; T. Rao; T. Roser; T. Russo; J. Scaduto; Z. Segalov; K. Smith; N.W.W. Williams; K.-C. Wu; V. Yakimenko; K. Yip; A. Zaltsman; Y. Zhao; H. Bluem; A. Burger; M.D. Cole; A.J. Favale; D. Holmes; J. Rathke; T. Schultheiss; A.M.M. Todd; J.R. Delayen; L. W. Funk; P. Kneisel; H.L. Phillips; J.P. Preble
2005-05-16
Next generation ERL light-sources, high-energy electron coolers, high-power Free-Electron Lasers, powerful Compton X-ray sources and many other accelerators were made possible by the emerging technology of high-power, high-brightness electron beams. In order to get the anticipated performance level of ampere-class currents, many technological barriers are yet to be broken. BNL's Collider-Accelerator Department is pursuing some of these technologies for its electron cooling of RHIC application, as well as a possible future electron-hadron collider. We will describe work on CW, high-current and high-brightness electron beams. This will include a description of a superconducting, laser-photocathode RF gun and an accelerator cavity capable of producing low emittance (about 1 micron rms normalized) one nano-Coulomb bunches at currents of the order of one ampere average.
Lao, L.L.; Ferron, J.R.; Strait, E.J.
1997-06-01
One of the major goals of advanced tokamak research is to develop plasma configurations with good confinement and improved stability at high {beta}. In DIII-D, various high performance configurations with H- and VH-mode edges have been produced. These include discharges with poloidal cross sections in the forms of dee and crecent shapes, single- and double-null divertors, and with various central magnetic shear profiles and current profile peakedness. All these discharges exhibit confinement in the outer plasma region which leads to a large edge pressure gradient and a large edge bootstrap current driven by this steep pressure gradient. These edge conditions often drive an instability near the edge region which can severely degrade the discharge performance. An understanding of this edge instability is essential to sustain an enhance discharge performance.
Improving Microarray Sample Size Using Bootstrap Data Combination
Phan, John H.; Moffitt, Richard A.; Barrett, Andrea B.; Wang, May D.
2016-01-01
Microarray technology has enabled us to simultaneously measure the expression of thousands of genes. Using this high-throughput technology, we can examine subtle genetic changes between biological samples and build predictive models for clinical applications. Although microarrays have dramatically increased the rate of data collection, sample size is still a major issue when selecting features. Previous methods show that combining multiple microarray datasets improves feature selection using simple methods such as fold change. We propose a wrapper-based gene selection technique that combines bootstrap estimated classification errors for individual genes across multiple datasets and reduces the contribution of datasets with high variance. We use the bootstrap because it is an unbiased estimator of classification error that is also effective for small sample data. Coupled with data combination across multiple datasets, we show that our meta-analytic approach improves the biological relevance of gene selection using prostate and renal cancer microarray data. PMID:19164001
A Robust High Current Density Electron Gun
NASA Astrophysics Data System (ADS)
Mako, F.; Peter, W.; Shiloh, J.; Len, L. K.
1996-11-01
Proof-of-principle experiments are proposed to validate a new concept for a robust, high-current density Pierce electron gun (RPG) for use in klystrons and high brightness electron sources for accelerators. This rugged, long-life electron gun avoids the difficulties associated with plasma cathodes, thermionic emitters, and field emission cathodes. The RPG concept employs the emission of secondary electrons in a transmission mode as opposed to the conventional mode of reflection, i.e., electrons exit from the back face of a thin negative electron affinity (NEA) material, and in the same direction as the incident beam. Current amplification through one stage of a NEA material could be over 50 times. The amplification is accomplished in one or more stages consisting of one primary emitter and one or more secondary emitters. The primary emitter is a low current density robust emitter (e.g., thoriated tungsten). The secondary emitters are thin NEA electrodes which emit secondary electrons in the same direction as the incident beam. Specific application is targeted for a klystron gun to be used by SLAC with a cold cathode at 30-40 amps/cm^2 output from the secondary emission stage, a ~2 μs pulse length, and ~200 pulses/second.
Versatile high current metal ion implantation facility
Brown, I.G.; Dickinson, M.R.; Galvin, J.E.; Godechot, X.; MacGill, R.A.
1991-06-01
A metal ion implantation facility has been developed with which high current beams of practically all the solid metals of the periodic table can be produced. A multi-cathode, broad beam, metal vapor vacuum arc ion source is used to produce repetitively pulsed metal ion beams at an extraction voltage of up to 100 kV, corresponding to an ion energy of up to several hundred keV because of the ion-charge state multiplicity, and with a beam current of up to several amperes peak pulsed and several tens of mA time averaged delivered onto a downstream target. Implantation is done in a broad-beam mode, with a direct line-of-sight from ion source to target. Here we summarize some of the features of the ion source and the implantation facility that has been built up around it. 28 refs., 5 figs.
Fast high-temperature superconductor switch for high current applications
NASA Astrophysics Data System (ADS)
Solovyov, Vyacheslav F.; Li, Qiang
2013-07-01
Reversible operation of a high current superconductor switch based on the quench of high-resistance second generation high temperature superconducting wire is demonstrated. The quench is induced by a burst of an ac field generated by an inductively coupled radio-frequency coil. The switch makes a superconducting-to-normal transition within 5 ms and also has a rapid recovery to the superconducting state. The device has potential applications as an active current limiter or as a storage switch for superconducting magnetic energy storage systems. Operation in a full flux penetration/flow regime can effectively minimize the detrimental effects of the intrinsic conductor non-uniformity.
HIGH CURRENT RADIO FREQUENCY ION SOURCE
Abdelaziz, M.E.
1963-04-01
This patent relates to a high current radio frequency ion source. A cylindrical plasma container has a coil disposed around the exterior surface thereof along the longitudinal axis. Means are provided for the injection of an unionized gas into the container and for applying a radio frequency signal to the coil whereby a radio frequency field is generated within the container parallel to the longitudinal axis thereof to ionize the injected gas. Cathode and anode means are provided for extracting transverse to the radio frequency field from an area midway between the ends of the container along the longitudinal axis thereof the ions created by said radio frequency field. (AEC)
High-current SRF cavity design
NASA Astrophysics Data System (ADS)
Meidlinger, D.; Grimm, T. L.; Hartung, W.
2006-07-01
For high current applications, it is desirable for the cavity shape to have a low longitudinal loss factor and to have a high beam-breakup threshold current. This paper briefly describes three different cavities designed for this purpose: a six-cell elliptical cavity for particles traveling at the speed of light, a two-cell elliptical cavity for subluminal particle speeds, and a single cell cavity which uses the TM012 mode for acceleration. SUPERFISH simulations predict the peak fields in both of the elliptical cavities will not exceed the TeSLA values by more than 10% but both will have 28.7% larger apertures. The elliptical designs assume the bunch frequency equals the accelerating mode frequency. The beam pipe radius is chosen so that the cutoff frequency is less than twice that of the accelerating mode. Hence all of the monopole and dipole higher-order modes (HOMs) that can be driven by the beam have low loaded Q values. This simplifies the problem of HOM damping. The TM012 cavity is predicted to have much higher peak fields than a π-mode elliptical cavity, but offers potential advantages from its simplified shape; it is essentially a circular waveguide with curved end plates. This basic shape results in easier fabrication and simplified tuning.
Robust, Scalable, and Fast Bootstrap Method for Analyzing Large Scale Data
NASA Astrophysics Data System (ADS)
Basiri, Shahab; Ollila, Esa; Koivunen, Visa
2016-02-01
In this paper we address the problem of performing statistical inference for large scale data sets i.e., Big Data. The volume and dimensionality of the data may be so high that it cannot be processed or stored in a single computing node. We propose a scalable, statistically robust and computationally efficient bootstrap method, compatible with distributed processing and storage systems. Bootstrap resamples are constructed with smaller number of distinct data points on multiple disjoint subsets of data, similarly to the bag of little bootstrap method (BLB) [1]. Then significant savings in computation is achieved by avoiding the re-computation of the estimator for each bootstrap sample. Instead, a computationally efficient fixed-point estimation equation is analytically solved via a smart approximation following the Fast and Robust Bootstrap method (FRB) [2]. Our proposed bootstrap method facilitates the use of highly robust statistical methods in analyzing large scale data sets. The favorable statistical properties of the method are established analytically. Numerical examples demonstrate scalability, low complexity and robust statistical performance of the method in analyzing large data sets.
High Current Energy Recovery Linac at BNL
Vladimir N. Litvinenko; Donald Barton; D. Beavis; Ilan Ben-Zvi; Michael Blaskiewicz; J.M. Brennan; A. Burrill; R. Calaga; P. Cameron; X. Chang; Roger Connolly; D. Gassner; H. Hahn; A. Hershcovitch; H.C. Hseuh; P. Johnson; D. Kayran; J. Kewisch; R. Lambiase; G. McIntyre; W. Meng; T. C. Nehring; A. Nicoletti; D. Pate; J. Rank; T. Roser; T. Russo; J. Scaduto; K. Smith; T. Srinivasan-Rao; N. Williams; K.-C. Wu; Vitaly Yakimenko; K. Yip; A. Zaltsman; Y. Zhao; H. Bluem; A. Burger; Mike Cole; A. Favale; D. Holmes; John Rathke; Tom Schultheiss; A. Todd; J. Delayen; W. Funk; L. Phillips; Joe Preble
2004-08-01
We present the design, the parameters of a small test Energy Recovery Linac (ERL) facility, which is under construction at Collider-Accelerator Department, BNL. This R&D facility has goals to demonstrate CW operation of ERL with average beam current in the range of 0.1 - 1 ampere, combined with very high efficiency of energy recovery. A possibility for future up-grade to a two-pass ERL is considered. The heart of the facility is a 5-cell 700 MHz super-conducting RF linac with HOM damping. Flexible lattice of ERL provides a test-bed for testing issues of transverse and longitudinal instabilities and diagnostics of intense CW e-beam. ERL is also perfectly suited for a far-IR FEL. We present the status and our plans for construction and commissioning of this facility.
HIGH CURRENT ENERGY RECOVERY LINAC AT BNL.
LITVINENKO,V.N.; BEN-ZVI,I.; BARTON,D.S.; ET AL.
2005-05-16
We present the design and parameters of an energy recovery linac (ERL) facility, which is under construction in the Collider-Accelerator Department at BNL. This R&D facility has the goal of demonstrating CW operation of an ERL with an average beam current in the range of 0.1-1 ampere and with very high efficiency of energy recovery. The possibility of a future upgrade to a two-pass ERL is also being considered. The heart of the facility is a 5-cell 703.75 MHz super-conducting RF linac with strong Higher Order Mode (HOM) damping. The flexible lattice of the ERL provides a test-bed for exploring issues of transverse and longitudinal instabilities and diagnostics of intense CW electron beams. This ERL is also perfectly suited for a far-IR FEL. We present the status and plans for construction and commissioning of this facility.
The non-local bootstrap--estimation of uncertainty in diffusion MRI.
Yap, Pew-Thian; An, Hongyu; Chen, Yasheng; Shen, Dinggang
2013-01-01
Diffusion MRI is a noninvasive imaging modality that allows for the estimation and visualization of white matter connectivity patterns in the human brain. However, due to the low signal-to-noise ratio (SNR) nature of diffusion data, deriving useful statistics from the data is adversely affected by different sources of measurement noise. This is aggravated by the fact that the sampling distribution of the statistic of interest is often complex and unknown. In situations as such, the bootstrap, due to its distribution-independent nature, is an appealing tool for the estimation of the variability of almost any statistic, without relying on complicated theoretical calculations, but purely on computer simulation. In this work, we present new bootstrap strategies for variability estimation of diffusion statistics in association with noise. In contrast to the residual bootstrap, which relies on a predetermined data model, or the repetition bootstrap, which requires repeated signal measurements, our approach, called the non-local bootstrap (NLB), is non-parametric and obviates the need for time-consuming multiple acquisitions. The key assumption of NLB is that local image structures recur in the image. We exploit this self-similarity via a multivariate non-parametric kernel regression framework for bootstrap estimation of uncertainty. Evaluation of NLB using a set of high-resolution diffusion-weighted images, with lower than usual SNR due to the small voxel size, indicates that NLB is markedly more robust to noise and results in more accurate inferences. PMID:24683985
The high current experiment: First results
Seidl, Peter A.; Baca, D.; Bieniosek, F.M.; Faltens, A.; Lund, S.M.; Molvik, A.W.; Prost, L.R.; Waldron, W.L.
2002-05-26
The High Current Experiment (HCX) is being assembled at Lawrence Berkeley National Laboratory as part of the US program to explore heavy-ion beam transport at a scale representative of the low-energy end of an induction linac driver for fusion energy production. The primary mission of this experiment is to investigate aperture fill factors acceptable for the transport of space-charge dominated heavy-ion beams at high spacecharge intensity (line-charge density {approx} 0.2 {micro}C/m) over long pulse durations (>4 {micro}s). This machine will test transport issues at a driver-relevant scale resulting from nonlinear space-charge effects and collective modes, beam centroid alignment and beam steering, matching, image charges, halo, lost-particle induced electron effects, and longitudinal bunch control. We present the first experimental results carried out with the coasting K{sup +} ion beam transported through the first 10 electrostatic transport quadrupoles and associated diagnostics. Later phases of the experiment will include more electrostatic lattice periods to allow more sensitive tests of emittance growth, and also magnetic quadrupoles to explore similar issues in magnetic channels with a full driver scale beam.
The high current experiment: First results
NASA Astrophysics Data System (ADS)
Seidl, P. A.; Baca, D.; Bieniosek, F. M.; Faltens, A.; Lund, S. M.; Molvik, A. W.; Prost, L. R.; Waldron, W. L.
2002-07-01
The High Current Experiment (HCX) is being assembled at Lawrence Berkeley National Laboratory as part of the U.S. program to explore heavy ion beam transport at a scale representative of the low-energy end of an induction linac driver for fusion energy production. The primary mission of this experiment is to investigate aperture fill factors acceptable for the transport of space-charge dominated heavy ion beams at high space-charge intensity (line-charge density [similar] 0.2 [mu]C/m) over long pulse durations (>4 [mu]s). This machine will test transport issues at a driver-relevant scale resulting from nonlinear space-charge effects and collective modes, beam centroid alignment and beam steering, matching, image charges, halo, lost-particle induced electron effects, and longitudinal bunch control. We present the first experimental results carried out with the coasting K+ ion beam transported through the first 10 electrostatic transport quadrupoles and associated diagnostics. Later phases of the experiment will include more electrostatic lattice periods to allow more sensitive tests of emittance growth, and also magnetic quadrupoles to explore similar issues in magnetic channels with a full driver scale beam.
The Index of Biological Integrity and the bootstrap revisited: an example from Minnesota streams
Dolph, Christine L.; Sheshukov, Aleksey Y.; Chizinski, Christopher J.; Vondracek, Bruce C.; Wilson, Bruce
2010-01-01
Multimetric indices, such as the Index of Biological Integrity (IBI), are increasingly used by management agencies to determine whether surface water quality is impaired. However, important questions about the variability of these indices have not been thoroughly addressed in the scientific literature. In this study, we used a bootstrap approach to quantify variability associated with fish IBIs developed for streams in two Minnesota river basins. We further placed this variability into a management context by comparing it to impairment thresholds currently used in water quality determinations for Minnesota streams. We found that 95% confidence intervals ranged as high as 40 points for IBIs scored on a 0–100 point scale. However, on average, 90% of IBI scores calculated from bootstrap replicate samples for a given stream site yielded the same impairment status as the original IBI score. We suggest that sampling variability in IBI scores is related to both the number of fish and the number of rare taxa in a field collection. A comparison of the effects of different scoring methods on IBI variability indicates that a continuous scoring method may reduce the amount of bias in IBI scores.
High voltage compliance constant current ballast
NASA Technical Reports Server (NTRS)
Rosenthal, L. A.
1976-01-01
A ballast circuit employing a constant current diode and a vacuum tube that can provide a constant current over a voltage range of 1000 volts. The simple circuit can prove useful in studying voltage breakdown characteristics.
Bootstrapped models for intrinsic random functions
Campbell, K.
1987-01-01
The use of intrinsic random function stochastic models as a basis for estimation in geostatistical work requires the identification of the generalized covariance function of the underlying process, and the fact that this function has to be estimated from the data introduces an additional source of error into predictions based on the model. This paper develops the sample reuse procedure called the ''bootstrap'' in the context of intrinsic random functions to obtain realistic estimates of these errors. Simulation results support the conclusion that bootstrap distributions of functionals of the process, as well as of their ''kriging variance,'' provide a reasonable picture of the variability introduced by imperfect estimation of the generalized covariance function.
Bootstrapped models for intrinsic random functions
Campbell, K.
1988-08-01
Use of intrinsic random function stochastic models as a basis for estimation in geostatistical work requires the identification of the generalized covariance function of the underlying process. The fact that this function has to be estimated from data introduces an additional source of error into predictions based on the model. This paper develops the sample reuse procedure called the bootstrap in the context of intrinsic random functions to obtain realistic estimates of these errors. Simulation results support the conclusion that bootstrap distributions of functionals of the process, as well as their kriging variance, provide a reasonable picture of variability introduced by imperfect estimation of the generalized covariance function.
High Current Hollow Cathode Plasma Plume Measurements
NASA Technical Reports Server (NTRS)
Thomas, Robert E.; Kamhawi, Hani; Williams, George J., Jr.
2014-01-01
Plasma plume measurements are reported for a hollow cathode assembly (HCA) operated at discharge currents of 50, 70, and 100 A at xenon flow rates between 19 - 46 standard cubic centimeter per minute. The HCA was centrally mounted in the NASA-300MS Hall Thruster and was operated in the "spot" and "plume" modes with additional data taken with an applied magnetic field. Langmuir probes, retarding potential analyzers, and optical emission spectroscopy were employed to measure plasma properties near the orifice of the HCA and to assess the charge state of the near-field plasma. Electron temperatures (2-6 electron volt) and plasma potentials are consistent with probe-measured values in previous investigations. Operation with an applied-field yields higher discharge voltages, increased Xe III production, and increased signals from the 833.5 nm C I line. While operating in plume mode and with an applied field, ion energy distribution measurements yield ions with energies significantly exceeding the applied discharge voltage. These findings are correlated with high-frequency oscillations associated with each mode.
MACHINE PROTECTION FOR HIGH AVERAGE CURRENT LINACS
Jordan, Kevin; Allison, Trent; Evans, Richard; Coleman, James; Grippo, Albert
2003-05-01
A fully integrated Machine Protection System (MPS) is critical to efficient commissioning and safe operation of all high current accelerators. The Jefferson Lab FEL [1,2] has multiple electron beam paths and many different types of diagnostic insertion devices. The MPS [3] needs to monitor both the status of these devices and the magnet settings which define the beam path. The matrix of these devices and beam paths are programmed into gate arrays, the output of the matrix is an allowable maximum average power limit. This power limit is enforced by the drive laser for the photocathode gun. The Beam Loss Monitors (BLMs), RF status, and laser safety system status are also inputs to the control matrix. There are 8 Machine Modes (electron path) and 8 Beam Modes (average power limits) that define the safe operating limits for the FEL. Combinations outside of this matrix are unsafe and the beam is inhibited. The power limits range from no beam to 2 megawatts of electron beam power.
High Current Hollow Cathode Plasma Plume Measurements
NASA Technical Reports Server (NTRS)
Thomas, Robert E.; Kamhawi, Hani; Williams, George J., Jr.
2013-01-01
Plasma plume measurements are reported for a hollow cathode assembly (HCA) oper-ated at discharge currents of 50, 70, and 100 A at xenon ow rates between 19 - 46 sccm.The HCA was centrally mounted in the annulus of the NASA-300MS Hall Thruster andwas operated in the spot and plume modes with additional data taken with an appliedmagnetic eld. Langmuir probes, retarding potential analyzers, and optical emission spec-troscopy were employed to measure plasma properties near the orice of the HCA and toassess the charge state of the near-eld plasma. Electron temperatures (2-6 eV) and plasmapotentials are consistent with probe-measured values in previous investigations. Operationwith an applied-eld yields higher discharge voltages, increased Xe III production, andincreased signals from the 833.5 nm C I line. While operating in plume mode and with anapplied eld, ion energy distribution measurements yield ions with energies signicantlyexceeding the applied discharge voltage. These ndings are correlated with high-frequencyoscillations associated with each mode.
Pass the Globe: Teaching Bootstrapping without Using a Computer
ERIC Educational Resources Information Center
Beaujean, A. Alexander; Cooper-Twamley, Susan
2010-01-01
While bootstrapping is a computationally intensive procedure, teaching about the concept does not necessarily require any more technology than a simple calculator. This article describes an interactive teaching approach for introducing bootstrapping without using a statistics program or a computer.
A high-energy, high-current ion implantation system
NASA Astrophysics Data System (ADS)
Rose, Peter H.; Faretra, Ronald; Ryding, Geoffery
1985-01-01
High current (Pre-DepTM) ion implanters, operating at 80 keV, have met a need in the semiconductor industry. For certain processes, higher energies are required, either to penetrate a surface layer or to place the dopant ion at a greater depth. The Eaton/Nova Model NV10-160 Pre-DepTM Ion Implanter has been developed to meet those special needs. Beam currents as high as 10.0 mA are available at energies up to 160 keV for routine production applications. The system has also been qualified for low current, low dose operation (1011 ions cm-2) and this unique versatility provides the Process and Equipment Engineers with a powerful new tool. The Model NV10-160 also utilizes the Nova-designed, double disk interchange processing system to minimize inactive beam time so that wafer throughputs, up to 300 wafers/h, are achievable on a routine basis. DatalockTM, a computer driven implant monitoring system and AT-4, the Nova cassette-to-cassette wafer loader, are available as standard options. As a production machine, the Model NV10-160 with its high throughput capability, will reduce the implant cost per wafer significantly for doses above 10 × 1015 ions/cm2. Performance patterns are now emerging as some twenty-five systems have now been shipped. This paper summarizes the more important characteristics and reviews the major design features of the NV10-160.
Bootstrapping Methods Applied for Simulating Laboratory Works
ERIC Educational Resources Information Center
Prodan, Augustin; Campean, Remus
2005-01-01
Purpose: The aim of this work is to implement bootstrapping methods into software tools, based on Java. Design/methodology/approach: This paper presents a category of software e-tools aimed at simulating laboratory works and experiments. Findings: Both students and teaching staff use traditional statistical methods to infer the truth from sample…
Pulling Econometrics Students up by Their Bootstraps
ERIC Educational Resources Information Center
O'Hara, Michael E.
2014-01-01
Although the concept of the sampling distribution is at the core of much of what we do in econometrics, it is a concept that is often difficult for students to grasp. The thought process behind bootstrapping provides a way for students to conceptualize the sampling distribution in a way that is intuitive and visual. However, teaching students to…
A Bootstrap Procedure of Propensity Score Estimation
ERIC Educational Resources Information Center
Bai, Haiyan
2013-01-01
Propensity score estimation plays a fundamental role in propensity score matching for reducing group selection bias in observational data. To increase the accuracy of propensity score estimation, the author developed a bootstrap propensity score. The commonly used propensity score matching methods: nearest neighbor matching, caliper matching, and…
Automatic bootstrapping and tracking of object contours.
Chiverton, John; Xie, Xianghua; Mirmehdi, Majid
2012-03-01
A new fully automatic object tracking and segmentation framework is proposed. The framework consists of a motion-based bootstrapping algorithm concurrent to a shape-based active contour. The shape-based active contour uses finite shape memory that is automatically and continuously built from both the bootstrap process and the active-contour object tracker. A scheme is proposed to ensure that the finite shape memory is continuously updated but forgets unnecessary information. Two new ways of automatically extracting shape information from image data given a region of interest are also proposed. Results demonstrate that the bootstrapping stage provides important motion and shape information to the object tracker. This information is found to be essential for good (fully automatic) initialization of the active contour. Further results also demonstrate convergence properties of the content of the finite shape memory and similar object tracking performance in comparison with an object tracker with unlimited shape memory. Tests with an active contour using a fixed-shape prior also demonstrate superior performance for the proposed bootstrapped finite-shape-memory framework and similar performance when compared with a recently proposed active contour that uses an alternative online learning model. PMID:21908256
How to Bootstrap a Human Communication System
ERIC Educational Resources Information Center
Fay, Nicolas; Arbib, Michael; Garrod, Simon
2013-01-01
How might a human communication system be bootstrapped in the absence of conventional language? We argue that motivated signs play an important role (i.e., signs that are linked to meaning by structural resemblance or by natural association). An experimental study is then reported in which participants try to communicate a range of pre-specified…
Characterization of high-current, high-temperature superconductor current lead elements
Niemann, R.C.; Evans, D.J.; Fisher, B.L.; Brockenborough, W.E.; Roberts, P.R.; Rodenbush, A.J.
1996-08-01
The refrigeration loads of current leads for superconducting magnets can be significantly reduced by using high-temperature superconductor (HTS) leads. An HTS conductor type that is well suited for this application is a laminated sintered stack of HTS powder-in-tube (PIT) tapes. The superconducting elements are normally characterized by their manufacturer by measuring critical currents at 77 K in self field. Additional characterization, which correlates electrical performance at 77 K and at lower temperatures with applied magnetic fields, provides the current lead designer and conductor element manufacturer with critical information. For HTS conductor elements comprising a laminated and sintered stack of Bi-2223 PIT tapes having an alloyed Ag sheath, this characterization uses variable applied fields and operating temperatures.
Lightweight, High-Current Welding Gun
NASA Technical Reports Server (NTRS)
Starck, Thomas F.; Brennan, Andrew D.
1989-01-01
Lighweight resistance-welding, hand-held gun supplies alternating or direct current over range of 600 to 4,000 A and applies forces from 40 to 60 lb during welding. Used to weld metal sheets in multilayered stacks.
Developing high brightness and high current beams for HIF injectors
Ahle, Larry; Grote, Dave; Kwan, Joe
2002-05-24
The US Heavy Ion Fusion Virtual National Laboratory is continuing research into ion sources and injectors that simultaneously provide high current (0.5-1.0 Amps) and high brightness (normalized emittance better than 1.0 {pi}-mm-mr). The central issue of focus is whether to continue pursuing the traditional approach of large surface ionization sources or to adopt a multiaperture approach that transports many smaller ''beamlets'' separately at low energies before allowing them to merge. For the large surface source concept, the recent commissioning of the 2-MeV injector for the High Current eXperiment has increased our understanding of the beam quality limitations for these sources. We have also improved our techniques for fabricating large diameter aluminosilicate sources to improve lifetime and emission uniformity. For the multiaperture approach, we are continuing to study the feasibility of small surface sources and a RF induced plasma source in preparation for beamlet merging experiments, while continuing to run computer simulations for better understanding of this alternate concept. Experiments into both architectures will be performed on a newly commissioned ion source test stand at LLNL called STS-500. This stand test provides a platform for testing a variety of ion sources and accelerating structures with 500 kV, 17-microsecond pulses. Recent progress in these areas will be discussed as well as plans for future experiments.
A Bootstrap Approach to an Affordable Exploration Program
NASA Technical Reports Server (NTRS)
Oeftering, Richard C.
2011-01-01
This paper examines the potential to build an affordable sustainable exploration program by adopting an approach that requires investing in technologies that can be used to build a space infrastructure from very modest initial capabilities. Human exploration has had a history of flight programs that have high development and operational costs. Since Apollo, human exploration has had very constrained budgets and they are expected be constrained in the future. Due to their high operations costs it becomes necessary to consider retiring established space facilities in order to move on to the next exploration challenge. This practice may save cost in the near term but it does so by sacrificing part of the program s future architecture. Human exploration also has a history of sacrificing fully functional flight hardware to achieve mission objectives. An affordable exploration program cannot be built when it involves billions of dollars of discarded space flight hardware, instead, the program must emphasize preserving its high value space assets and building a suitable permanent infrastructure. Further this infrastructure must reduce operational and logistics cost. The paper examines the importance of achieving a high level of logistics independence by minimizing resource consumption, minimizing the dependency on external logistics, and maximizing the utility of resources available. The approach involves the development and deployment of a core suite of technologies that have minimum initial needs yet are able expand upon initial capability in an incremental bootstrap fashion. The bootstrap approach incrementally creates an infrastructure that grows and becomes self sustaining and eventually begins producing the energy, products and consumable propellants that support human exploration. The bootstrap technologies involve new methods of delivering and manipulating energy and materials. These technologies will exploit the space environment, minimize dependencies, and
Modular High Current Test Facility at LLNL
Tully, L K; Goerz, D A; Speer, R D; Ferriera, T J
2008-05-20
This paper describes the 1 MA, 225 kJ test facility in operation at Lawrence Livermore National Laboratory (LLNL). The capacitor bank is constructed from three parallel 1.5 mF modules. The modules are capable of switching simultaneously or sequentially via solid dielectric puncture switches. The bank nominally operates up to 10 kV and reaches peak current with all three cabled modules in approximately 30 {micro}s. Parallel output plates from the bank allow for cable or busbar interfacing to the load. This versatile bank is currently in use for code validation experiments, railgun related activities, switch testing, and diagnostic development.
Bootstrapping a change-point Cox model for survival data.
Xu, Gongjun; Sen, Bodhisattva; Ying, Zhiliang
2014-08-20
This paper investigates the (in)-consistency of various bootstrap methods for making inference on a change-point in time in the Cox model with right censored survival data. A criterion is established for the consistency of any bootstrap method. It is shown that the usual nonparametric bootstrap is inconsistent for the maximum partial likelihood estimation of the change-point. A new model-based bootstrap approach is proposed and its consistency established. Simulation studies are carried out to assess the performance of various bootstrap schemes. PMID:25400719
High-current ion-ring accelerator
Sudan, R.N. )
1993-03-15
An accelerator concept is outlined which enables 10[sup 15] to 10[sup 18] ions in the form of a charge neutralized ion ring to be accelerated to GeV energies. A repetition rate of 10 Hz will deliver an average current in the range of 0.1 A.
A high performance current source inverter
Joos, G.; Moschopoulos, G.; Ziogas, P.D.
1993-10-01
A recent innovation in current source inverter (CSI) drives has been the introduction of pulsewidth modulation (PWM) for the purpose of improving the quality of the load currents and voltages. However, the typical six switch CSI circuit is not compatible with all standard PWM techniques thus limiting the number of schemes that can be used. The modified CSI circuit discussed in this paper removes most of the restrictions at the ``cost`` of an extra switch. Additional advantages include faster response times through modulation index control and higher efficiency. This paper includes a detailed steady-state analysis and design procedure. The feasibility and performance of the modified CSI are verified by simulation and experimental implementation on a 5 kVA converter.
Insulator damage in high current discharges
NASA Astrophysics Data System (ADS)
Ranon, P. M.; Kristiansen, M.; Lehr, F. M.; Hatfield, L. L.
1986-11-01
The degradation of the hold-off voltage capability of several composite candidates for railgun insulators was studied experimentally. The materials examined were BN, alumina (Coor's ceramic), and two types of laminated fiberglass/epoxy (FGE I and FGE II). Sample 1 cm thick plates of the insulators were inserted into a surface discharge switch (SDS) with a gap of 1.6 in., i.e., an initial hold-off voltage of 40 kV. FGE I retained the hold-off voltage for more than 10,000 shots at a current of 1 kA maximum, but degraded significantly after 50 shots at currents over 200 kA. BN shattered when the repetition rate exceeded 1 pulse/sec.
A compact submicrosecond, high current generator
NASA Astrophysics Data System (ADS)
Kovalchuk, B. M.; Kharlov, A. V.; Zorin, V. B.; Zherlitsyn, A. A.
2009-08-01
Pulsed current generator was developed for experiments with current carrying pulsed plasma. Main parts of the generator are capacitor bank, low inductive current driving lines, and central load part. Generator consists of four identical sections, connected in parallel to one load. Capacitor bank is assembled from 24 capacitor blocks (100 kV, 80 nF), connected in parallel. It stores 9.6 kJ at 100 kV charging voltage. Each capacitor block incorporates a multigap spark switch, which is able to commute by six parallel channels. Switches operate in dry air at atmospheric pressure. The generator was tested with an inductive load and a liner load. At 17.5 nH inductive load and 100 kV of charging voltage it provides 650 kA of current amplitude with 390 ns rise time with 0.6 Ω damping resistors in discharge circuit of each capacitor block. The net generator inductance without a load was optimized to be as low as 15 nH, which results in extremely low impedance of the generator (˜0.08 Ω). It ensures effective energy coupling with a low impedance load such as Z pinch. The generator operates reliably without any adjustments in 70-100 kV range of charging voltage. Jitter in delay between output pulse and triggering pulse is less than 5 ns at 70-100 kV charging voltage. Operation and handling are very simple, because no oil or purified gases are required for the generator. The generator has dimensions 5.24×1.2×0.18 m3 and total weight about 1400 kg, thus manifesting itself as simple, robust, and cost effective apparatus.
Architecture for high critical current superconducting tapes
Jia, Quanxi; Foltyn, Stephen R.
2002-01-01
Improvements in critical current capacity for superconducting film structures are disclosed and include the use of, e.g., multilayer YBCO structures where individual YBCO layers are separated by a layer of an insulating material such as CeO.sub.2 and the like, a layer of a conducting material such as strontium ruthenium oxide and the like or by a second superconducting material such as SmBCO and the like.
High-current density coils for high-radiation environments
Harvey, A.
1981-01-01
This paper concentrates on the problems of providing normal (that is, nonsuperconducting) magnet coils for present and short-term-future requirements where significant radiation doses are involved. Projects such as 100-mA deuteron accelerators and bundle diverter coils for TOKAMAKS are typical of applications where conventional organic insulation limited to 10/sup 10/ rads makes epoxy-based systems unacceptable. Moreover, even in present-day accelerators, radiation levels can be high enough to give rise to problems with oxidation of copper conductors if water is used in direct contact with the copper. The radiolytic oxygen, being formed in situ, cannot be controlled by external deoxygenators. An acceptable insulation for such environments has been described previously, and is being employed where radiation is expected to be a problem. Being a compacted magnesium oxide powder, the insulation has advantages. Analysis of constraints on maximum current densities achievable in such a coil construction, using computer codes, leads to coil configurations that operate at higher current densities than are usually found in directly cooled coils. An example of the thermal analysis of one coil configuration is given. The problems are addressed here.
High-current plasma contactor neutralizer system
NASA Technical Reports Server (NTRS)
Beattie, J. R.; Williamson, W. S.; Matossian, J. N.; Vourgourakis, E. J.; Burch, J. L.
1989-01-01
A plasma-contactor neutralizer system is described, for the stabilizing the Orbiter's potential during flights of the Atmospheric Laboratory for Applications and Science missions. The plasma contactor neutralizer will include a Xe plasma source that can provide steady-state ion-emission currents of up to 1.5 A. The Orbiter's potential will be maintained near that of the surrounding space plasma during electron-beam accelerator firings through a combination of ion emission from the Xe plasma source and electron collection from the ambient space plasma. Configuration diagrams and block diagrams are presented along with the performance characteristics of the system.
MHD Stability Calculations of High-Beta Quasi-Axisymmetric Stellarators
C. Kessel; G.Y. Fu; L.P. Ku; M.H. Redi; N. Pomphrey; et al
1999-09-01
The MHD stability of quasi-axisymmetric compact stellarators is investigated. It is shown that bootstrap current driven external kink modes can be stabilized by a combination of edge magnetic shear and appropriate 3D plasma boundary shaping while maintaining good quasi-axisymmetry. The results demonstrate that there exists a new class of stellarators with quasi-axisymmetry, large bootstrap current, high MHD beta limit, and compact size.
Clarification of the Bootstrap Percolation Paradox
NASA Astrophysics Data System (ADS)
de Gregorio, Paolo; Lawlor, Aonghus; Bradley, Phil; Dawson, Kenneth A.
2004-07-01
We study the onset of the bootstrap percolation transition as a model of generalized dynamical arrest. Our results apply to two dimensions, but there is no significant barrier to extending them to higher dimensionality. We develop a new importance-sampling procedure in simulation, based on rare events around “holes”, that enables us to access bootstrap lengths beyond those previously studied. By framing a new theory in terms of paths or processes that lead to emptying of the lattice we are able to develop systematic corrections to the existing theory and compare them to simulations. Thereby, for the first time in the literature, it is possible to obtain credible comparisons between theory and simulation in the accessible density range.
Current Perspectives in High Energy Astrophysics
NASA Technical Reports Server (NTRS)
Ormes, Jonathan F. (Editor)
1996-01-01
High energy astrophysics is a space-age discipline that has taken a quantum leap forward in the 1990s. The observables are photons and particles that are unable to penetrate the atmosphere and can only be observed from space or very high altitude balloons. The lectures presented as chapters of this book are based on the results from the Compton Gamma-Ray Observatory (CGRO) and Advanced Satellite for Cosmology and Astrophysics (ASCA) missions to which the Laboratory for High Energy Astrophysics at NASA's Goddard Space Flight Center made significant hardware contributions. These missions study emissions from very hot plasmas, nuclear processes, and high energy particle interactions in space. Results to be discussed include gamma-ray beaming from active galactic nuclei (AGN), gamma-ray emission from pulsars, radioactive elements in the interstellar medium, X-ray emission from clusters of galaxies, and the progress being made to unravel the gamma-ray burst mystery. The recently launched X-ray Timing Explorer (XTE) and prospects for upcoming Astro-E and Advanced X-ray Astronomy Satellite (AXAF) missions are also discussed.
Accidental symmetries and the conformal bootstrap
NASA Astrophysics Data System (ADS)
Chester, Shai M.; Giombi, Simone; Iliesiu, Luca V.; Klebanov, Igor R.; Pufu, Silviu S.; Yacoby, Ran
2016-01-01
We study an N=2 supersymmetric generalization of the three-dimensional critical O( N) vector model that is described by N + 1 chiral superfields with superpotential W = g 1 X∑ i Z 1 2 + g 2 X 3. By combining the tools of the conformal bootstrap with results obtained through supersymmetric localization, we argue that this model exhibits a symmetry enhancement at the infrared superconformal fixed point due to g 2 flowing to zero. This example is special in that the existence of an infrared fixed point with g 1 , g 2 ≠ 0, which does not exhibit symmetry enhancement, does not generally lead to any obvious unitarity violations or other inconsistencies. We do show, however, that the F-theorem excludes the models with g 1 , g 2 ≠ 0 for N > 5. The conformal bootstrap provides a stronger constraint and excludes such models for N > 2. We provide evidence that the g 2 = 0 models, which have the enhanced O( N) × U(1) symmetry, come close to saturating the bootstrap bounds. We extend our analysis to fractional dimensions where we can motivate the nonexistence of the g 1 , g 2 ≠ 0 models by studying them perturbatively in the 4 - ɛ expansion.
High current density cathode for electrorefining in molten electrolyte
Li, Shelly X.
2010-06-29
A high current density cathode for electrorefining in a molten electrolyte for the continuous production and collection of loose dendritic or powdery deposits. The high current density cathode eliminates the requirement for mechanical scraping and electrochemical stripping of the deposits from the cathode in an anode/cathode module. The high current density cathode comprises a perforated electrical insulated material coating such that the current density is up to 3 A/cm.sup.2.
Bootstrap Enhanced Penalized Regression for Variable Selection with Neuroimaging Data.
Abram, Samantha V; Helwig, Nathaniel E; Moodie, Craig A; DeYoung, Colin G; MacDonald, Angus W; Waller, Niels G
2016-01-01
Recent advances in fMRI research highlight the use of multivariate methods for examining whole-brain connectivity. Complementary data-driven methods are needed for determining the subset of predictors related to individual differences. Although commonly used for this purpose, ordinary least squares (OLS) regression may not be ideal due to multi-collinearity and over-fitting issues. Penalized regression is a promising and underutilized alternative to OLS regression. In this paper, we propose a nonparametric bootstrap quantile (QNT) approach for variable selection with neuroimaging data. We use real and simulated data, as well as annotated R code, to demonstrate the benefits of our proposed method. Our results illustrate the practical potential of our proposed bootstrap QNT approach. Our real data example demonstrates how our method can be used to relate individual differences in neural network connectivity with an externalizing personality measure. Also, our simulation results reveal that the QNT method is effective under a variety of data conditions. Penalized regression yields more stable estimates and sparser models than OLS regression in situations with large numbers of highly correlated neural predictors. Our results demonstrate that penalized regression is a promising method for examining associations between neural predictors and clinically relevant traits or behaviors. These findings have important implications for the growing field of functional connectivity research, where multivariate methods produce numerous, highly correlated brain networks. PMID:27516732
Bootstrap Enhanced Penalized Regression for Variable Selection with Neuroimaging Data
Abram, Samantha V.; Helwig, Nathaniel E.; Moodie, Craig A.; DeYoung, Colin G.; MacDonald, Angus W.; Waller, Niels G.
2016-01-01
Recent advances in fMRI research highlight the use of multivariate methods for examining whole-brain connectivity. Complementary data-driven methods are needed for determining the subset of predictors related to individual differences. Although commonly used for this purpose, ordinary least squares (OLS) regression may not be ideal due to multi-collinearity and over-fitting issues. Penalized regression is a promising and underutilized alternative to OLS regression. In this paper, we propose a nonparametric bootstrap quantile (QNT) approach for variable selection with neuroimaging data. We use real and simulated data, as well as annotated R code, to demonstrate the benefits of our proposed method. Our results illustrate the practical potential of our proposed bootstrap QNT approach. Our real data example demonstrates how our method can be used to relate individual differences in neural network connectivity with an externalizing personality measure. Also, our simulation results reveal that the QNT method is effective under a variety of data conditions. Penalized regression yields more stable estimates and sparser models than OLS regression in situations with large numbers of highly correlated neural predictors. Our results demonstrate that penalized regression is a promising method for examining associations between neural predictors and clinically relevant traits or behaviors. These findings have important implications for the growing field of functional connectivity research, where multivariate methods produce numerous, highly correlated brain networks. PMID:27516732
Excitons in solids with time-dependent density-functional theory: the bootstrap kernel and beyond
NASA Astrophysics Data System (ADS)
Byun, Young-Moo; Yang, Zeng-Hui; Ullrich, Carsten
Time-dependent density-functional theory (TDDFT) is an efficient method to describe the optical properties of solids. Lately, a series of bootstrap-type exchange-correlation (xc) kernels have been reported to produce accurate excitons in solids, but different bootstrap-type kernels exist in the literature, with mixed results. In this presentation, we reveal the origin of the confusion and show a new empirical TDDFT xc kernel to compute excitonic properties of semiconductors and insulators efficiently and accurately. Our method can be used for high-throughput screening calculations and large unit cell calculations. Work supported by NSF Grant DMR-1408904.
HIGH DYNAMIC-RANGE HIGH SPEED LINAC CURRENT MEASUREMENTS
Deibele, Craig Edmond; Curry, Douglas E; Dickson, Richard W
2012-01-01
It is desired to measure the linac current of a charged particle beam with a consistent accuracy over a dynamic range of over 120 dB. Conventional current transformers suffer from droop, can be susceptible to electromagnetic interference (EMI), and can be bandwidth limited. A novel detector and electronics were designed to maximize dynamic range of about 120 dB and measure rise-times on the order of 10 nanoseconds.
Modeling of high-current devices with explosive electron emission
NASA Astrophysics Data System (ADS)
Anishchenko, S. V.; Gurinovich, A. A.
2014-01-01
Based on a detailed analysis of explosive electron emission in high-current electronic devices, we formulate a system of equations that describes the expansion of cathode plasma and the generation of high-current electron beams. The system underlies the numerical algorithm for the hybrid code which enables the simulation of the charged particles’ dynamics in high-current vircators with open resonators. Using the Gabor-Morlet transform, we perform a time-frequency analysis of vircator radiation.
Stable superconducting magnet. [high current levels below critical temperature
NASA Technical Reports Server (NTRS)
Boom, R. W. (Inventor)
1967-01-01
Operation of a superconducting magnet is considered. A method is described for; (1) obtaining a relatively high current in a superconducting magnet positioned in a bath of a gas refrigerant; (2) operating a superconducting magnet at a relatively high current level without training; and (3) operating a superconducting magnet containing a plurality of turns of a niobium zirconium wire at a relatively high current level without training.
Concept Innateness, Concept Continuity, and Bootstrapping
Carey, Susan
2011-01-01
The commentators raised issues relevant to all three important theses of The Origin of Concepts (TOOC). Some questioned the very existence of innate representational primitives, and others questioned my claims about their richness and whether they should be thought of as concepts. Some questioned the existence of conceptual discontinuity in the course of knowledge acquisition and others argued that discontinuity is much more common than portrayed in TOOC. Some raised issues with my characterization of Quinian bootstrapping, and others questioned the dual factor theory of concepts motivated by my picture of conceptual development. PMID:23264705
A bootstrap approach to bump hunting
NASA Technical Reports Server (NTRS)
Silverman, B. W.
1982-01-01
An important question in cluster analysis and pattern recognition is the determination of the number of clusters into which a given population should be divided. Frequently, particularly when certain specific clustering methods are being used, the number of clusters is taken to be equal to the number of modes, or local maxima, in the probability density function underlying the given data set. The use of kernal density estimates in mode estimation is discussed. The test statistic to be used is defined and a bootstrap technique for assessing significance is given. An illustrative application is followed by an examination of the asymptotic behavior of the test statistic.
Bootstrap position analysis for forecasting low flow frequency
Tasker, Gary D.; Dunne, P.
1997-01-01
A method of random resampling of residuals from stochastic models is used to generate a large number of 12-month-long traces of natural monthly runoff to be used in a position analysis model for a water-supply storage and delivery system. Position analysis uses the traces to forecast the likelihood of specified outcomes such as reservoir levels falling below a specified level or streamflows falling below statutory passing flows conditioned on the current reservoir levels and streamflows. The advantages of this resampling scheme, called bootstrap position analysis, are that it does not rely on the unverifiable assumption of normality, fewer parameters need to be estimated directly from the data, and accounting for parameter uncertainty is easily done. For a given set of operating rules and water-use requirements for a system, water managers can use such a model as a decision-making tool to evaluate different operating rules. ?? ASCE,.
Multipulse current source offers low power losses and high reliability
NASA Technical Reports Server (NTRS)
1967-01-01
Pulse current source uses low loss, high reliability, LC circuits to provide the necessary high impedance for magnetic memory cores, frequently used in digital computational equipment. Square-loop reactors replace the semiconductor switches previously used.
Effects of high frequency current in welding aluminum alloy 6061
NASA Technical Reports Server (NTRS)
Fish, R. E.
1968-01-01
Uncontrolled high frequency current causes cracking in the heat-affected zone of aluminum alloy 6061 weldments during tungsten inert gas ac welding. Cracking developed when an improperly adjusted superimposed high frequency current was agitating the semimolten metal in the areas of grain boundary.
Dynamics of laser-guided alternating current high voltage discharges
NASA Astrophysics Data System (ADS)
Daigle, J.-F.; Théberge, F.; Lassonde, P.; Kieffer, J.-C.; Fujii, T.; Fortin, J.; Châteauneuf, M.; Dubois, J.
2013-10-01
The dynamics of laser-guided alternating current high voltage discharges are characterized using a streak camera. Laser filaments were used to trigger and guide the discharges produced by a commercial Tesla coil. The streaking images revealed that the dynamics of the guided alternating current high voltage corona are different from that of a direct current source. The measured effective corona velocity and the absence of leader streamers confirmed that it evolves in a pure leader regime.
Confidence Intervals in Qtl Mapping by Bootstrapping
Visscher, P. M.; Thompson, R.; Haley, C. S.
1996-01-01
The determination of empirical confidence intervals for the location of quantitative trait loci (QTLs) was investigated using simulation. Empirical confidence intervals were calculated using a bootstrap resampling method for a backcross population derived from inbred lines. Sample sizes were either 200 or 500 individuals, and the QTL explained 1, 5, or 10% of the phenotypic variance. The method worked well in that the proportion of empirical confidence intervals that contained the simulated QTL was close to expectation. In general, the confidence intervals were slightly conservatively biased. Correlations between the test statistic and the width of the confidence interval were strongly negative, so that the stronger the evidence for a QTL segregating, the smaller the empirical confidence interval for its location. The size of the average confidence interval depended heavily on the population size and the effect of the QTL. Marker spacing had only a small effect on the average empirical confidence interval. The LOD drop-off method to calculate empirical support intervals gave confidence intervals that generally were too small, in particular if confidence intervals were calculated only for samples above a certain significance threshold. The bootstrap method is easy to implement and is useful in the analysis of experimental data. PMID:8725246
Efficient online bootstrapping of sensory representations.
Gepperth, Alexander
2013-05-01
This is a simulation-based contribution exploring a novel approach to the open-ended formation of multimodal representations in autonomous agents. In particular, we address the issue of transferring ("bootstrapping") feature selectivities between two modalities, from a previously learned or innate reference representation to a new induced representation. We demonstrate the potential of this algorithm by several experiments with synthetic inputs modeled after a robotics scenario where multimodal object representations are "bootstrapped" from a (reference) representation of object affordances. We focus on typical challenges in autonomous agents: absence of human supervision, changing environment statistics and limited computing power. We propose an autonomous and local neural learning algorithm termed PROPRE (projection-prediction) that updates induced representations based on predictability: competitive advantages are given to those feature-sensitive elements that are inferable from activities in the reference representation. PROPRE implements a bi-directional interaction of clustering ("projection") and inference ("prediction"), the key ingredient being an efficient online measure of predictability controlling learning in the projection step. We show that the proposed method is computationally efficient and stable, and that the multimodal transfer of feature selectivity is successful and robust under resource constraints. Furthermore, we successfully demonstrate robustness to noisy reference representations, non-stationary input statistics and uninformative inputs. PMID:23266481
A Superconducting transformer system for high current cable testing
Godeke, A.; Dietderich, D. R.; Joseph, J. M.; Lizarazo, J.; Prestemon, S. O.; Miller, G.; Weijers, H. W.
2010-02-15
This article describes the development of a direct-current (dc) superconducting transformer system for the high current test of superconducting cables. The transformer consists of a core-free 10 464 turn primary solenoid which is enclosed by a 6.5 turn secondary. The transformer is designed to deliver a 50 kA dc secondary current at a dc primary current of about 50 A. The secondary current is measured inductively using two toroidal-wound Rogowski coils. The Rogowski coil signal is digitally integrated, resulting in a voltage signal that is proportional to the secondary current. This voltage signal is used to control the secondary current using a feedback loop which automatically compensates for resistive losses in the splices to the superconducting cable samples that are connected to the secondary. The system has been commissioned up to 28 kA secondary current. The reproducibility in the secondary current measurement is better than 0.05% for the relevant current range up to 25 kA. The drift in the secondary current, which results from drift in the digital integrator, is estimated to be below 0.5 A/min. The system's performance is further demonstrated through a voltage-current measurement on a superconducting cable sample at 11 T background magnetic field. The superconducting transformer system enables fast, high resolution, economic, and safe tests of the critical current of superconducting cable samples.
A superconducting transformer system for high current cable testing.
Godeke, A; Dietderich, D R; Joseph, J M; Lizarazo, J; Prestemon, S O; Miller, G; Weijers, H W
2010-03-01
This article describes the development of a direct-current (dc) superconducting transformer system for the high current test of superconducting cables. The transformer consists of a core-free 10,464 turn primary solenoid which is enclosed by a 6.5 turn secondary. The transformer is designed to deliver a 50 kA dc secondary current at a dc primary current of about 50 A. The secondary current is measured inductively using two toroidal-wound Rogowski coils. The Rogowski coil signal is digitally integrated, resulting in a voltage signal that is proportional to the secondary current. This voltage signal is used to control the secondary current using a feedback loop which automatically compensates for resistive losses in the splices to the superconducting cable samples that are connected to the secondary. The system has been commissioned up to 28 kA secondary current. The reproducibility in the secondary current measurement is better than 0.05% for the relevant current range up to 25 kA. The drift in the secondary current, which results from drift in the digital integrator, is estimated to be below 0.5 A/min. The system's performance is further demonstrated through a voltage-current measurement on a superconducting cable sample at 11 T background magnetic field. The superconducting transformer system enables fast, high resolution, economic, and safe tests of the critical current of superconducting cable samples. PMID:20370213
Unbiased Estimates of Variance Components with Bootstrap Procedures
ERIC Educational Resources Information Center
Brennan, Robert L.
2007-01-01
This article provides general procedures for obtaining unbiased estimates of variance components for any random-model balanced design under any bootstrap sampling plan, with the focus on designs of the type typically used in generalizability theory. The results reported here are particularly helpful when the bootstrap is used to estimate standard…
Bootstrapping Confidence Intervals for Robust Measures of Association.
ERIC Educational Resources Information Center
King, Jason E.
A Monte Carlo simulation study was conducted to determine the bootstrap correction formula yielding the most accurate confidence intervals for robust measures of association. Confidence intervals were generated via the percentile, adjusted, BC, and BC(a) bootstrap procedures and applied to the Winsorized, percentage bend, and Pearson correlation…
Using Commonly Available Software for Conducting Bootstrap Analyses.
ERIC Educational Resources Information Center
Fan, Xitao
Bootstrap analysis, both for nonparametric statistical inference and for describing sample results stability and replicability, has been gaining prominence among quantitative researchers in educational and psychological research. Procedurally, however, it is often quite a challenge for quantitative researchers to implement bootstrap analysis in…
Bootstrap Estimates of Standard Errors in Generalizability Theory
ERIC Educational Resources Information Center
Tong, Ye; Brennan, Robert L.
2007-01-01
Estimating standard errors of estimated variance components has long been a challenging task in generalizability theory. Researchers have speculated about the potential applicability of the bootstrap for obtaining such estimates, but they have identified problems (especially bias) in using the bootstrap. Using Brennan's bias-correcting procedures…
Problems with Multivariate Normality: Can the Multivariate Bootstrap Help?
ERIC Educational Resources Information Center
Thompson, Bruce
Multivariate normality is required for some statistical tests. This paper explores the implications of violating the assumption of multivariate normality and illustrates a graphical procedure for evaluating multivariate normality. The logic for using the multivariate bootstrap is presented. The multivariate bootstrap can be used when distribution…
Efficient circuit triggers high-current, high-voltage pulses
NASA Technical Reports Server (NTRS)
Green, E. D.
1964-01-01
Modified circuit uses diodes to effectively disconnect the charging resistors from the circuit during the discharge cycle. Result is an efficient parallel charging, high voltage pulse modulator with low voltage rating of components.
Performance of Bootstrap MCEWMA: Study case of Sukuk Musyarakah data
NASA Astrophysics Data System (ADS)
Safiih, L. Muhamad; Hila, Z. Nurul
2014-07-01
Sukuk Musyarakah is one of several instruments of Islamic bond investment in Malaysia, where the form of this sukuk is actually based on restructuring the conventional bond to become a Syariah compliant bond. The Syariah compliant is based on prohibition of any influence of usury, benefit or fixed return. Despite of prohibition, daily returns of sukuk are non-fixed return and in statistic, the data of sukuk returns are said to be a time series data which is dependent and autocorrelation distributed. This kind of data is a crucial problem whether in statistical and financing field. Returns of sukuk can be statistically viewed by its volatility, whether it has high volatility that describing the dramatically change of price and categorized it as risky bond or else. However, this crucial problem doesn't get serious attention among researcher compared to conventional bond. In this study, MCEWMA chart in Statistical Process Control (SPC) is mainly used to monitor autocorrelated data and its application on daily returns of securities investment data has gained widespread attention among statistician. However, this chart has always been influence by inaccurate estimation, whether on base model or its limit, due to produce large error and high of probability of signalling out-of-control process for false alarm study. To overcome this problem, a bootstrap approach used in this study, by hybridise it on MCEWMA base model to construct a new chart, i.e. Bootstrap MCEWMA (BMCEWMA) chart. The hybrid model, BMCEWMA, will be applied to daily returns of sukuk Musyarakah for Rantau Abang Capital Bhd. The performance of BMCEWMA base model showed that its more effective compare to real model, MCEWMA based on smaller error estimation, shorter the confidence interval and smaller false alarm. In other word, hybrid chart reduce the variability which shown by smaller error and false alarm. It concludes that the application of BMCEWMA is better than MCEWMA.
Development of Large Current High Precision Pulse Power Supply
NASA Astrophysics Data System (ADS)
Takayanagi, Tomohiro; Koseki, Shoichiro; Kubo, Hiroshi; Katoh, Shuji; Ogawa, Shinichi
JAEA and KEK are jointly constructing a high intensity proton accelerator project J-PARC. Its main accelerator is 3GeV synchrotron. Its injection bump magnets, especially horizontal paint bump magnets, are excited by large pulse currents. Their rated currents are over 10kA and pulse widths are about 1ms. Tracking errors are required to be less than 1%. Multiple connected two-quadrant IGBT choppers are adopted for their power supplies. Their output currents are controlled by feedback control with minor loop voltage control (m-AVR). When output current of a chopper intermits at small current, its output voltage rises up and current control becomes difficult. In this paper response of m-AVR and output voltage characteristics at current intermittent region are studied and an improved control scheme is proposed. The performance is confirmed by a test.
Conformal bootstrap, universality and gravitational scattering
NASA Astrophysics Data System (ADS)
Jackson, Steven; McGough, Lauren; Verlinde, Herman
2015-12-01
We use the conformal bootstrap equations to study the non-perturbative gravitational scattering between infalling and outgoing particles in the vicinity of a black hole horizon in AdS. We focus on irrational 2D CFTs with large c and only Virasoro symmetry. The scattering process is described by the matrix element of two light operators (particles) between two heavy states (BTZ black holes). We find that the operator algebra in this regime is (i) universal and identical to that of Liouville CFT, and (ii) takes the form of an exchange algebra, specified by an R-matrix that exactly matches the scattering amplitude of 2 + 1 gravity. The R-matrix is given by a quantum 6j-symbol and the scattering phase by the volume of a hyperbolic tetrahedron. We comment on the relevance of our results to scrambling and the holographic reconstruction of the bulk physics near black hole horizons.
Infant speech perception bootstraps word learning.
Werker, Janet F; Yeung, H Henny
2005-11-01
By their first birthday, infants can understand many spoken words. Research in cognitive development has long focused on the conceptual changes that accompany word learning, but learning new words also entails perceptual sophistication. Several developmental steps are required as infants learn to segment, identify and represent the phonetic forms of spoken words, and map those word forms to different concepts. We review recent research on how infants' perceptual systems unfold in the service of word learning, from initial sensitivity for speech to the learning of language-specific sound patterns. Building on a recent theoretical framework and emerging new methodologies, we show how speech perception is crucial for word learning, and suggest that it bootstraps the development of a separate but parallel phonological system that links sound to meaning. PMID:16202639
A 'bootstrapped' Teaching/Learning Procedure
NASA Astrophysics Data System (ADS)
Odusina Odusote, Olusogo
1998-04-01
Erasing preconceived antiphysics ideas by nonscience/nonmajor physics students have elicited diverse teaching methods. Introductory general physics courses at college level have been taught by a 'bootstrap' approach. A concise treatment of the syllabus by the teacher in about 1/2 of the course duration, with brief exercises and examples. Students are then introduced to real life situations - toys, home appliances, sports, disasters, etc, and the embedded physics concepts discussed. Usually this generates a feeling of deja vu, which elicits desire for more. Each application usually encompasses topics in a broad range of the syllabus. The other half of the course is used by students to work individually/groups on assigned and graded home-works and essays, with guidance from the lecture notes and the teacher/supervisor. An end of course examination shows increase in the success rate.
Bootstrap performance profiles in stochastic algorithms assessment
Costa, Lino; Espírito Santo, Isabel A.C.P.; Oliveira, Pedro
2015-03-10
Optimization with stochastic algorithms has become a relevant research field. Due to its stochastic nature, its assessment is not straightforward and involves integrating accuracy and precision. Performance profiles for the mean do not show the trade-off between accuracy and precision, and parametric stochastic profiles require strong distributional assumptions and are limited to the mean performance for a large number of runs. In this work, bootstrap performance profiles are used to compare stochastic algorithms for different statistics. This technique allows the estimation of the sampling distribution of almost any statistic even with small samples. Multiple comparison profiles are presented for more than two algorithms. The advantages and drawbacks of each assessment methodology are discussed.
Laser diagnostic for high current H{sup {minus}} beams
Shafer, R.E.
1998-01-01
Laser photodetachment can be used on high current, high energy H{sup {minus}} beams to carry out a wide variety of beam diagnostic measurements parasitically during normal operation, without having to operate the facility at either reduced current or duty cycle. Suitable Q-switched laser systems are small, inexpensive, and can be mounted on or near the beamline. Most of the proposed laser-based diagnostics techniques have already been demonstrated.
New Pulsed Power Technology for High Current Accelerators
Caporaso, G J
2002-06-27
Recent advances in solid-state modulators now permit the design of a new class of high current accelerators. These new accelerators will be able to operate in burst mode at frequencies of several MHz with unprecedented flexibility and precision in pulse format. These new modulators can drive accelerators to high average powers that far exceed those of any other technology and can be used to enable precision beam manipulations. New insulator technology combined with novel pulse forming lines and switching may enable the construction of a new type of high gradient, high current accelerator. Recent developments in these areas will be reviewed.
Motor monitoring method and apparatus using high frequency current components
Casada, Donald A.
1996-01-01
A motor current analysis method and apparatus for monitoring electrical-motor-driven devices. The method and apparatus utilize high frequency portions of the motor current spectra to evaluate the condition of the electric motor and the device driven by the electric motor. The motor current signal produced as a result of an electric motor is monitored and the low frequency components of the signal are removed by a high-pass filter. The signal is then analyzed to determine the condition of the electrical motor and the driven device.
Motor monitoring method and apparatus using high frequency current components
Casada, D.A.
1996-05-21
A motor current analysis method and apparatus for monitoring electrical-motor-driven devices are disclosed. The method and apparatus utilize high frequency portions of the motor current spectra to evaluate the condition of the electric motor and the device driven by the electric motor. The motor current signal produced as a result of an electric motor is monitored and the low frequency components of the signal are removed by a high-pass filter. The signal is then analyzed to determine the condition of the electrical motor and the driven device. 16 figs.
NASA Astrophysics Data System (ADS)
Luo, Pandian; Li, Zhenhua; Li, Hongbin; Li, Hongfeng
2013-12-01
The calibration of the protective current transformer (CT) is of particular importance, since its accuracy at high currents is crucial to the correct operation of the subsequent relay protection devices. Conventional calibration methods have been using an electromagnetic CT which contains an iron core as the standard CT. The iron core is big and difficult to manufacture for high-current measurement, and the serious residual magnetism of the iron core at high currents can lead to excessive measurement errors. This paper proposes a calibration system based on indirect comparison of CT and Rogowski coil, i.e. using an iron-core CT to correct the error of the Rogowski coil at low currents, which may be caused by the position of the current-carrying conductor and so on, and then using the calibrated Rogowski coil as the standard transformer at high currents for its good linearity and wide dynamic range, and there is no magnetic saturation. Since the output of the Rogowski coil needs to be integrated, an improved digital integrator based on direct current (dc) negative feedback is adopted, which can effectively eliminate the influences of temperature drift, time drift and dc offset caused by the analogue circuit. The measurement errors of each part of the calibration system have also been discussed, and the test results show that the accuracy of the system can reach up to the 0.05S Class and the uncertainties are 0.038% for ratio and 0.68‧ for phase in the range 500 A to 50 kA.
Non-abelian binding energies from the lightcone bootstrap
NASA Astrophysics Data System (ADS)
Li, Daliang; Meltzer, David; Poland, David
2016-02-01
We analytically study the lightcone limit of the conformal bootstrap for 4-point functions containing scalars charged under global symmetries. We show the existence of large spin double-twist operators in various representations of the global symmetry group. We then compute their anomalous dimensions in terms of the central charge C T , current central charge C J , and the OPE coefficients of low dimension scalars. In AdS, these results correspond to the binding energy of two-particle states arising from the exchange of gravitons, gauge bosons, and light scalar fields. Using unitarity and crossing symmetry, we show that gravity is universal and attractive among different types of two-particle states, while the gauge binding energy can have either sign as determined by the representation of the two-particle state, with universal ratios fixed by the symmetry group. We apply our results to 4D {N}=1 SQCD and the 3D O( N) vector models. We also show that in a unitary CFT, if the current central charge C J stays finite when the global symmetry group becomes infinitely large, such as the N → ∞ limit of the O( N) vector model, then the theory must contain an infinite number of higher spin currents.
Integrated compact optical current sensors with high sensitivity
NASA Astrophysics Data System (ADS)
Huang, Duanni; Pintus, Paolo; Srinivasan, Sudharsanan; Bowers, John E.
2016-02-01
We demonstrate a Sagnac based fiber optic current sensor using only 10cm of terbium doped fiber with a high Verdet constant of 15.5 rad/Tm at a wavelength of 1300nm. Measurements of the fiber inside a solenoid show over 40dB of open loop dynamic range as well as a minimum detectable current of 0.1mA. In order to decrease size while increasing sensitivity even further, we consider integrated magneto-optic waveguides as the sensing element. Using silicon waveguides alongside magneto-optic material such as cerium doped yttrium iron garnet (Ce:YiG), we model the Verdet constant to be as high as 10,000 rad/Tm. This improvement by three orders of magnitude shows potential for magnetooptic waveguides to be used in ultra-high sensitivity optical magnetometers and current sensors. Finally, we propose a fully integrated optical current sensor using heterogeneous integration for silicon photonics.
High-accuracy current sensing circuit with current compensation technique for buck-boost converter
NASA Astrophysics Data System (ADS)
Rao, Yuan; Deng, Wan-Ling; Huang, Jun-Kai
2015-03-01
A novel on-chip current sensing circuit with current compensation technique suitable for buck-boost converter is presented in this article. The proposed technique can sense the full-range inductor current with high accuracy and high speed. It is mainly based on matched current mirror and does not require a large proportion of aspect ratio between the powerFET and the senseFET, thus it reduces the complexity of circuit design and the layout mismatch issue without decreasing the power efficiency. The circuit is fabricated with TSMC 0.25 µm 2P5M mixed-signal process. Simulation results show that the buck-boost converter can be operated at 200 kHz to 4 MHz switching frequency with an input voltage from 2.8 to 4.7 V. The output voltage is 3.6 V, and the maximum accuracy for both high and low side sensing current reaches 99% within the load current ranging from 200 to 600 mA.
High frequency eddy current device for near surface material characterizations
NASA Astrophysics Data System (ADS)
Hillmann, S.; Heuer, H.; Meyendorf, N.
2009-03-01
For near surface characterization a new high frequency eddy current device was been developed. By using a measurement frequency up to 100 MHz information of near surface areas can be acquired. Depending on the investigated material high resolution depth profiles can be derived. The obtained data with the new device were compared to those obtained with a high precision impedance analyser. It could be demonstrated that the new device measures the eddy current conductivity signal in the high frequencies much better than the impedance analyser. By sweeping the frequency from 100 kHz up to 100 MHz the technique delivers a depth profile of the electrical conductivity of the material. This kind of high frequency eddy current technique can be used for quality assurance, surface contamination control or near surface material characterization e.g. microstructure and cold work influences. It can be a powerful tool to obtain information for process control or a good / bad decision in mass production processes like for example rolling, coating, and surface treatments. The big advantage of the high frequency eddy current method is that it is fast und precise. This paper presents results with a new developed prototype Eddy-Current-Device for measurement frequencies up to 100 MHz which is first time suitable in rough industrial environment and makes expensive lab network analysers unnecessary for this kind of investigations.
Current Student Assessment Practices of High School Band Directors
ERIC Educational Resources Information Center
LaCognata, John P.
2010-01-01
Measurement and assessment are becoming increasingly important to all music educators. The purpose of this study was to investigate the following questions: 1) in what specific ways are current high school band directors assessing students in their ensemble classes; 2) what are high school band directors' attitudes toward the assessment process;…
Lattice Effects Due to High Currents in PEP-II
Decker, F.-J.; Smith, H.; Turner, J.L.; /SLAC
2005-05-09
The very high beam currents in the PEP-II B-Factory have caused many expected and unexpected effects: Synchrotron light fans move the beam pipe and cause dispersion; higher order modes cause excessive heating, e-clouds around the positron beam blow up its beam size. Here we describe an effect where the measured dispersion of the beam in the Low Energy Ring (LER) is different at high and at low beam currents. The dispersion was iteratively lowered by making anti-symmetric orbit bumps in many sextupole duplets, checking each time with a dispersion measurement where a dispersive kick is generated. This can be done parasitically during collisions. It was a surprise when checking the low current characterization data that there is a change. Subsequent high and low current measurements confirmed the effect. One source was believed to be located far away from any synchrotron radiation in the middle of a straight (PR12), away from sextupoles and skew quadrupoles and created a dispersion wave of about 70 mm at high current while at low current it is negligible.
Compact Tb doped fiber optic current sensor with high sensitivity.
Huang, Duanni; Srinivasan, Sudharsanan; Bowers, John E
2015-11-16
A highly sensitive fiber optic current sensor using terbium doped fiber is presented. The Verdet constant of the terbium doped fiber at 1300nm is found to be 19.5μrad/A using both a polarimetric and interferometric type sensor. Measurements on a Sagnac-loop sensor using 10cm of terbium doped fiber placed inside a solenoid show over 40dB of open loop dynamic range as well as a minimum detectable current of 0.1mA. Extrapolations of our measurements show that in a practical setup with Tb fiber wrapped around a current carrying wire, the optimal configuration is a 0.5m piece of Tb fiber with a noise limit of 22mA/√Hz. This sensor is promising for current sensing applications that require high sensitivity and small size, weight, and power. PMID:26698480
Electrical measurement techniques for pulsed high current electron beams
Struve, K.W.
1986-04-01
The advent of high current (1 to 100 kA), moderate energy (>10 MeV), short pulse (1 to 100 ns) electron accelerators used for charged particle beam research has motivated a need to complement standard diagnostics with development of new diagnostic techniques to measure electron beam parameters. A brief survey is given of the diagnostics for measuring beam current, position, size, energy, and emittance. While a broad scope of diagnostics will be discussed, this survey will emphasize diagnostics used on the Experimental Test Accelerator (ETA) and Advanced Test Accelerator (ATA). Focus is placed on diagnostics measuring beam current, position and size. Among the diagnostics discussed are resistive wall current monitors, B/sub theta/ loops, Rogowski coils, Faraday cups, and x-ray wire diagnostics. Operation at higher current levels also increases radiation and electromagnetic pulse interference. These difficulties and methods for circumventing them are also discussed.
A resonant series counterpulse technique for high current opening switches
Dijk, E. van; Gelder, P. van
1995-01-01
A counterpulse technique for the controlled interruption of very high currents in inductive storage pulsed power systems is described and analyzed, and some simulation results of its performance are presented. The accompanying circuit comprises a pre-charged capacitor bank, connected in series with the inductive load, which has to be provided with a current pulse. Upon actuation, a resonant counterpulse current is created in the opening switch, connected in parallel with the current source and the load. In this way, the opening switch is opened at low current. A separate closing switch prevents closing of the opening switch at high voltage. Operation of the opening switch, often a mechanical switch, at low current and low voltage prevents arc erosion of the contacts. The advantage of this circuit compared to other counterpulse circuits is that the capacitor bank does not experience a voltage reversal. Electrolytic capacitors, which have a high energy density, are applied. The remaining energy of the capacitor bank after opening the opening switch, is transferred to the load. The required initial voltage of the capacitor bank is only a few hundred volts, whereas it may be above a kilovolt in other circuits. Another advantage of the method described here is that the load does not experience a pre-current, causing unwanted preheating of the load, before the resonant current is activated. At the moment, work is being performed at the Pulse Physics Laboratory to develop the resonant series counterpulse circuit for use with rail accelerators, which must be supplied with current pulses in the millisecond range up to the mega-ampere level.
High temperature superconducting current leads for fusion magnet systems
NASA Astrophysics Data System (ADS)
Wu, J. L.; Dederer, J. T.; Singh, S. K.; Hull, J. R.
Superconducting magnets for fusion applications typically have very high operating currents. These currents are transmitted from the room temperature power supplies to the low temperature superconducting coils by way of helium-vapor-cooled current leads. Because of the high current magnitude and the resistive characteristics associated with the normal metallic lead conductors, a substantial amount of power is dissipated in the lead. To maintain a stable operation, a high rate of helium vapor flow, generated by the boil-off of liquid helium, is required to cool the lead conductors. This helium boil-off substantially increases both the installation capacity and the operating cost of the helium refrigerator/liquefier. The boil-off of liquid helium can be significantly reduced by employing ceramic high temperature superconductors, such as Y-Ba-Cu-O, in the low temperature part of the lead conductor structure. This concept utilizes the superconducting, as well as the low thermal conductivity properties of the superconductor materials in eliminating power dissipation in part of the current lead and in inhibiting heat conduction into the liquid helium pool, resulting in reduced helium boil-off. This design concept has been conclusively demonstrated by a 2-kA current lead test model using Y-Ba-Cu-O (123) material which, although not optimized in design, has significantly reduced the rate of helium boil-off in comparison to optimized conventional leads. There appear to be no major technological barriers for scaling up this design to higher current levels for applications in fusion magnet systems or in fusion related testing activities. The theoretical basis of the current lead concept, as well as the important design and technology issues are addressed. The potential cost saving derived from employing these leads in fusion magnets is also discussed. In addition, a design concept for a 10-kA lead is presented.
High-current, fast-switching transistor development
NASA Technical Reports Server (NTRS)
Hower, P. L.
1981-01-01
The design, wafer-processing techniques, and various measurements which include forward safe operating area, dc characteristics, and switching times are described for a larger-diameter (33) transistor. An improved base contact for equalizing the base-emitter voltage at high currents was developed along with an improved emitter contact preform which increases the silicon area available for current conduction. The electrical performance achieved is consistent with the proposed optimum design.
High current density pulsed cathode experiments at SLAC
Koontz, R.; Fant, K.; Vlieks, A.
1990-06-01
A 1.9 microperveance beam diode has been constructed to test high current density cathodes for use in klystrons. Several standard and specially coated dispenser cathodes are being tested. Results of tests to date show average cathode current densities in excess of 25 amps/cm, and maximum electric field gradients of more than 450 kV/cm for pulses of the order of 1{mu}sec. 3 refs., 11 figs.
Microstructures and critical currents in high-{Tc} superconductors
Suenaga, Masaki
1998-11-01
Microstructural defects are the primary determining factors for the values of critical-current densities in a high {Tc} superconductor after the electronic anisotropy along the a-b plane and the c-direction. A review is made to assess firstly what would be the maximum achievable critical-current density in YBa{sub 2}Cu{sub 3}O{sub 7} if nearly ideal pinning sites were introduced and secondly what types of pinning defects are currently introduced or exist in YBa{sub 2}Cu{sub 3}O{sub 7} and how effective are these in pinning vortices.
Discharge current modes of high power impulse magnetron sputtering
Wu, Zhongzhen Xiao, Shu; Ma, Zhengyong; Cui, Suihan; Ji, Shunping; Pan, Feng; Tian, Xiubo; Fu, Ricky K. Y.; Chu, Paul K.
2015-09-15
Based on the production and disappearance of ions and electrons in the high power impulse magnetron sputtering plasma near the target, the expression of the discharge current is derived. Depending on the slope, six possible modes are deduced for the discharge current and the feasibility of each mode is discussed. The discharge parameters and target properties are simplified into the discharge voltage, sputtering yield, and ionization energy which mainly affect the discharge plasma. The relationship between these factors and the discharge current modes is also investigated.
High current DyBCO-ROEBEL Assembled Coated Conductor (RACC)
NASA Astrophysics Data System (ADS)
Goldacker, W.; Nast, R.; Kotzyba, G.; Schlachter, S. I.; Frank, A.; Ringsdorf, B.; Schmidt, C.; Komarek, P.
2006-06-01
Low AC loss high transport current HTS cables (>1 kA) are required for application in transformers, generators and are considered for future generations of fusion reactors coils. 2G coated conductors are suitable candidates for high field application at quite high operation temperatures of 50-77 K, which is crucial precondition for economical cooling costs. As a feasibility study we present the first ROEBEL bar cable of approx. 35 cm length made from industrial DyBCO coated conductor (THEVA GmbH, Germany). Meander shaped ROEBEL strands of 4 mm width with a twist pitch of 180 mm were cut from 10 mm wide CC tapes using a specially designed tool. The strands carried in average 157 Amps/cm-width DC and were assembled to a subcable with 5 strands and a final cable with 16 strands. The 5 strand cable was tested and carried a transport current of >300 Amps DC at 77 K, equivalent to the sum of the individual strand transport critical currents. The 16 strand cable carried 500 A limited through heating effects and non sufficient stabilisation and current sharing. A pulse current load indicated a current carrying potential of >1 kA for the 16 strand cable.
'Bootstrap' Configuration for Multistage Pulse-Tube Coolers
NASA Technical Reports Server (NTRS)
Nguyen, Bich; Nguyen, Lauren
2008-01-01
A bootstrap configuration has been proposed for multistage pulse-tube coolers that, for instance, provide final-stage cooling to temperatures as low as 20 K. The bootstrap configuration supplants the conventional configuration, in which customarily the warm heat exchangers of all stages reject heat at ambient temperature. In the bootstrap configuration, the warm heat exchanger, the inertance tube, and the reservoir of each stage would be thermally anchored to the cold heat exchanger of the next warmer stage. The bootstrapped configuration is superior to the conventional setup, in some cases increasing the 20 K cooler's coefficient of performance two-fold over that of an otherwise equivalent conventional layout. The increased efficiency could translate into less power consumption, less cooler mass, and/or lower cost for a given amount of cooling.
Characteristics of current filamentation in high gain photoconductive semiconductor switching
Zutavern, F J; Loubriel, G M; O'Malley, M W; Helgeson, W D; McLaughlin, D L; Denison, G J
1992-01-01
Characteristics of current filamentation are reported for high gain photoconductive semiconductor switches (PCSS). Infrared photoluminescence is used to monitor carrier recombination radiation during fast initiation of high gain switching in large (1.5 cm gap) lateral GaAs PCSS. Spatial modulation of the optical trigger, a 200--300 ps pulse width laser, is examined. Effects on the location and number of current filaments, rise time, and delay to high gain switching, minimum trigger energy, and degradation of switch contacts are presented. Implications of these measurements for the theoretical understanding and practical development of these switches are discussed. Efforts to increase current density and reduce switch size and optical trigger energy requirements are described. Results from contact development and device lifetime testing are presented and the impact of these results on practical device applications is discussed.
Thyratron-choke switch for high-current nanosecond pulses
Vizir, V.A.; Chervyakov, V.V.; Laier, A.V.; Shubkin, N.G.
1986-06-01
Electric-discharge excimer lasers and high-current nanosecond accelerators, i.e., linear induction accelerators, require highcurrent nanosecond pulse (HCNP) generators with high repetition frequencies. This paper describes a design and some formulas for a thyratron-choke assembly for switching high-current nanosecond pulses, which consists of a thyratron and a single turn nonlinear choke connected in series with it; these are enclosed in a coaxial shield. The operation of a thyratronchoke assembly with a TGI1-1000/25 thyratron in switching pulses of up to 10kA with a duration of 250 nsec is studied. The current rise rate is 200 kA/usec, the pulse repetition frequency is 200 Hz, and the average switched power is 5kW.
FEL POTENTIAL OF THE HIGH CURRENT ERLs AT BNL.
KAYRAN,D.; BEN-ZVI, I.; LITVINENKO, V.; POZDEYEV, E.; MATVEENKO, A.; SHEVCHENKO, O.; VINOKUROV, N.
2007-08-26
An ampere class 20 MeV superconducting Energy Recovery Linac (ERL) is under construction at Brookhaven National Laboratory (BNL) for testing concepts for high-energy electron cooling and electron-ion colliders. This ERL prototype will be used as a test bed to study issues relevant for very high current ERLs. High average current and high performance of electron beam with some additional components make this ERL an excellent driver for high power far infrared Free Electron Laser (FEL). A possibility for future up-grade to a two-pass ERL is considered. We present the status and our plans for construction and commissioning of the ERL. We discus a FEL potential based on electron beam provided by BNL ERL.
NASA Astrophysics Data System (ADS)
Winterberg, F.
2003-11-01
Fast thermonuclear ignition with a high gain seems possible with two Marx generators feeding two nested magnetically insulated transmission lines, one delivering a high current lower voltage pulse for compression and confinement, and one delivering a high voltage lower current pulse for fast ignition. With an input energy conceivably as small as 100 kJ the gain can be as large as 10 3. The concept not only would be by orders of magnitude less expensive than laser compression and fast ignition schemes, but because of the large gain with a small yield also be more suitable for a thermonuclear reactor.
High Current Ion Sources and Injectors for Heavy Ion Fusion
Kwan, Joe W.
2005-02-15
Heavy ion beam driven inertial fusion requires short ion beam pulses with high current and high brightness. Depending on the beam current and the number of beams in the driver system, the injector can use a large diameter surface ionization source or merge an array of small beamlets from a plasma source. In this paper, we review the scaling laws that govern the injector design and the various ion source options including the contact ionizer, the aluminosilicate source, the multicusp plasma source, and the MEVVA source.
Bootstrap inference longitudinal semiparametric regression model
NASA Astrophysics Data System (ADS)
Pane, Rahmawati; Otok, Bambang Widjanarko; Zain, Ismaini; Budiantara, I. Nyoman
2016-02-01
Semiparametric regression contains two components, i.e. parametric and nonparametric component. Semiparametric regression model is represented by yt i=μ (x˜'ti,zt i)+εt i where μ (x˜'ti,zt i)=x˜'tiβ ˜+g (zt i) and yti is response variable. It is assumed to have a linear relationship with the predictor variables x˜'ti=(x1 i 1,x2 i 2,…,xT i r) . Random error εti, i = 1, …, n, t = 1, …, T is normally distributed with zero mean and variance σ2 and g(zti) is a nonparametric component. The results of this study showed that the PLS approach on longitudinal semiparametric regression models obtain estimators β˜^t=[X'H(λ)X]-1X'H(λ )y ˜ and g˜^λ(z )=M (λ )y ˜ . The result also show that bootstrap was valid on longitudinal semiparametric regression model with g^λ(b )(z ) as nonparametric component estimator.
RF Input Power Couplers for High Current SRF Applications
Khan, V. F.; Anders, W.; Burrill, Andrew; Knobloch, Jens; Kugeler, Oliver; Neumann, Axel; Wang, Haipeng
2014-12-01
High current SRF technology is being explored in present day accelerator science. The bERLinPro project is presently being built at HZB to address the challenges involved in high current SRF machines with the goal of generating and accelerating a 100 mA electron beam to 50 MeV in continuous wave (cw) mode at 1.3 GHz. One of the main challenges in this project is that of handling the high input RF power required for the photo-injector as well as booster cavities where there is no energy recovery process. A high power co-axial input power coupler is being developed to be used for the photo-injector and booster cavities at the nominal beam current. The coupler is based on the KEK–cERL design and has been modified to minimise the penetration of the coupler tip in the beam pipe without compromising on beam-power coupling (Qext ~105). Herein we report on the RF design of the high power (115 kW per coupler, dual couplers per cavity) bERLinPro (BP) coupler along with initial results on thermal calculations. We summarise the RF conditioning of the TTF-III couplers (modified for cw operation) performed in the past at BESSY/HZB. A similar conditioning is envisaged in the near future for the low current SRF photo-injector and the bERLinPro main linac cryomodule.
HIGH-CURRENT ERL-BASED ELECTRON COOLING FOR RHIC.
BEN-ZVI, I.
2005-09-18
The design of an electron cooler must take into account both electron beam dynamics issues as well as the electron cooling physics. Research towards high-energy electron cooling of RHIC is in its 3rd year at Brookhaven National Laboratory. The luminosity upgrade of RHIC calls for electron cooling of various stored ion beams, such as 100 GeV/A gold ions at collision energies. The necessary electron energy of 54 MeV is clearly out of reach for DC accelerator system of any kind. The high energy also necessitates a bunched beam, with a high electron bunch charge, low emittance and small energy spread. The Collider-Accelerator Department adopted the Energy Recovery Linac (ERL) for generating the high-current, high-energy and high-quality electron beam. The RHIC electron cooler ERL will use four Superconducting RF (SRF) 5-cell cavities, designed to operate at ampere-class average currents with high bunch charges. The electron source will be a superconducting, 705.75 MHz laser-photocathode RF gun, followed up by a superconducting Energy Recovery Linac (ERL). An R&D ERL is under construction to demonstrate the ERL at the unprecedented average current of 0.5 amperes. Beam dynamics performance and luminosity enhancement are described for the case of magnetized and non-magnetized electron cooling of RHIC.
Structure of High Latitude Currents in Magnetosphere-Ionosphere Models
NASA Astrophysics Data System (ADS)
Wiltberger, M.; Rigler, E. J.; Merkin, V.; Lyon, J. G.
2016-07-01
Using three resolutions of the Lyon-Fedder-Mobarry global magnetosphere-ionosphere model (LFM) and the Weimer 2005 empirical model we examine the structure of the high latitude field-aligned current patterns. Each resolution was run for the entire Whole Heliosphere Interval which contained two high speed solar wind streams and modest interplanetary magnetic field strengths. Average states of the field-aligned current (FAC) patterns for 8 interplanetary magnetic field clock angle directions are computed using data from these runs. Generally speaking the patterns obtained agree well with results obtained from the Weimer 2005 computing using the solar wind and IMF conditions that correspond to each bin. As the simulation resolution increases the currents become more intense and narrow. A machine learning analysis of the FAC patterns shows that the ratio of Region 1 (R1) to Region 2 (R2) currents decreases as the simulation resolution increases. This brings the simulation results into better agreement with observational predictions and the Weimer 2005 model results. The increase in R2 current strengths also results in the cross polar cap potential (CPCP) pattern being concentrated in higher latitudes. Current-voltage relationships between the R1 and CPCP are quite similar at the higher resolution indicating the simulation is converging on a common solution. We conclude that LFM simulations are capable of reproducing the statistical features of FAC patterns.
High dislocation density of tin induced by electric current
Liao, Yi-Han; Liang, Chien-Lung; Lin, Kwang-Lung; Wu, Albert T.
2015-12-15
A dislocation density of as high as 10{sup 17} /m{sup 2} in a tin strip, as revealed by high resolution transmission electron microscope, was induced by current stressing at 6.5 x 10{sup 3} A/ cm{sup 2}. The dislocations exist in terms of dislocation line, dislocation loop, and dislocation aggregates. Electron Backscattered Diffraction images reflect that the high dislocation density induced the formation of low deflection angle subgrains, high deflection angle Widmanstätten grains, and recrystallization. The recrystallization gave rise to grain refining.
A new high-precision current supply for magnets
Wisnivesky, D. |; Lira, A.C.
1995-08-01
A new, high-precision, low-ripple current power supply (CPS) for magnets, based on a combination of an SCR converter and a single transistor switched mode power supply (SMPS) is described. The load power is primarily supplied by the SCR converter. The SMPS handles only a small fraction of the load power, and also, what is more significant, a very small part of the load current. In this paper, the topology and operating principle of the new power supply is discussed. A CPS, rated at 200 A at 45 V, was constructed and tested. The power supply energizes a family of quadrupole magnets at the Brazilian Synchrotron Light Source--LNLS. Making use of the current limit modulation (CLM) control method, magnetic field variations at full current are 5 ppm, with only 8 A passing through the switching transistor. The design and performance of the power supply under different operating conditions ar described. Variations of the proposed topology, suitable for high-current and high-voltage loads, are also discussed.
High latitude equivalent current systems during extremely quiet times
NASA Technical Reports Server (NTRS)
Rostoker, G.; Chen, A. J.; Yasuhara, F.; Akasofu, S.-I.; Kawasaki, K.
1974-01-01
The magnetic perturbation patterns in the polar cap and auroral zone regions are obtained for extremely quiet days using two different techniques. It is shown that the form of the equivalent current flow pattern is extremely sensitive to the level of quietness, and that even so-called quiet days are at times disturbed by substorm activity. Certain characteristic equivalent flow not typically observed during substorms is noted in the polar cap, and this flow appears to be associated with effects of polar cap perturbations discussed by Svalgaard (1973). A region of equatorward flow at high latitudes near the dawn meridian, appears to be Hall current driven by an eastward electric field. The dayside sub-auroral zone is dominated by the Sq-current system, while the nightside shows no significant current flow in the absence of substorm activity.
Rf Gun with High-Current Density Field Emission Cathode
Jay L. Hirshfield
2005-12-19
High current-density field emission from an array of carbon nanotubes, with field-emission-transistor control, and with secondary electron channel multiplication in a ceramic facing structure, have been combined in a cold cathode for rf guns and diode guns. Electrodynamic and space-charge flow simulations were conducted to specify the cathode configuration and range of emission current density from the field emission cold cathode. Design of this cathode has been made for installation and testing in an existing S-band 2-1/2 cell rf gun. With emission control and modulation, and with current density in the range of 0.1-1 kA/cm2, this cathode could provide performance and long-life not enjoyed by other currently-available cathodes
Design considerations for high-current superconducting ion linacs
Delayen, J.R.; Bohn, C.L.; Micklich, B.J.; Roche, C.T.; Sagalovsky, L.
1993-08-01
Superconducting linacs may be a viable option for high-current applications such as fusion materials irradiation testing, spallation neutron source, transmutation of radioactive waste, tritium production, and energy production. These linacs must run reliably for many years and allow easy routine maintenance. Superconducting cavities operate efficiently with high cw gradients, properties which help to reduce operating and capital costs, respectively. However, cost-effectiveness is not the sole consideration in these applications. For example, beam impingement must be essentially eliminated to prevent unsafe radioactivation of the accelerating structures, and thus large apertures are needed through which to pass the beam. Because of their high efficiency, superconducting cavities can be designed with very large bore apertures, thereby reducing the effect of beam impingement. Key aspects of high-current cw superconducting linac designs are explored in this context.
Focusing of high-current laser-driven ion beams
NASA Astrophysics Data System (ADS)
Badziak, J.; Jabłoński, S.
2007-04-01
Using a two-dimensional relativistic hydrodynamic code, it is shown that a dense high-current ion beam driven by a short-pulse laser can be effectively focused by curving the target front surface. The focused beam parameters essentially depend on the density gradient scale length of the preplasma Ln and the surface curvature radius RT. When Ln⩽0.5λL (λL is the laser wavelength) and RT is comparable with the laser beam aperture dL, a significant fraction of the accelerated ions is focused on a spot much smaller than dL, which results in a considerable increase in the ion fluence and current density. Using high-contrast multipetawatt picosecond laser pulses of relativistic intensity (˜1020W/cm2), focused ion (proton) current densities approaching those required for fast ignition of DT fuel seem to be feasible.
High-quality lossy compression: current and future trends
NASA Astrophysics Data System (ADS)
McLaughlin, Steven W.
1995-01-01
This paper is concerned with current and future trends in the lossy compression of real sources such as imagery, video, speech and music. We put all lossy compression schemes into common framework where each can be characterized in terms of three well-defined advantages: cell shape, region shape and memory advantages. We concentrate on image compression and discuss how new entropy constrained trellis-based compressors achieve cell- shape, region-shape and memory gain resulting in high fidelity and high compression.
A design approach for superconducting high-current ion linacs
Garnett, R.W.; Wangler, T.P.
1996-09-01
An approach for designing superconducting high-current ion linacs is described. This approach takes advantage of the large velocity acceptance of high-gradient cavities with a small number of cells. It is well known that this feature leads to a linac design with great operational flexibility. Algorithms which have been incorporated into a design code and a beam dynamics code are discussed. Simulation results using these algorithms are also presented.
59. View of high voltage (4160 volts alternating current) electric ...
59. View of high voltage (4160 volts alternating current) electric load center and motor control center at mezzanine level in transmitter building no. 102. - Clear Air Force Station, Ballistic Missile Early Warning System Site II, One mile west of mile marker 293.5 on Parks Highway, 5 miles southwest of Anderson, Anderson, Denali Borough, AK
Current isolating epitaxial buffer layers for high voltage photodiode array
Morse, Jeffrey D.; Cooper, Gregory A.
2002-01-01
An array of photodiodes in series on a common semi-insulating substrate has a non-conductive buffer layer between the photodiodes and the semi-insulating substrate. The buffer layer reduces current injection leakage between the photodiodes of the array and allows optical energy to be converted to high voltage electrical energy.
A review of high beam current RFQ accelerators and funnels
Schneider, J.D.
1998-12-01
The authors review the design features of several high-current (> 20-mA) and high-power (> 1-mA average) proton or H{sup {minus}} injectors, RFQs, and funnels. They include a summary of observed performance and will mention a sampling of new designs, including the proposed incorporation of beam choppers. Different programs and organizations have chosen to build the RFQ in diverse configurations. Although the majority of RFQs are either low-current or very low duty-factor, several versions have included high-current and/or high-power designs for either protons or H{sup {minus}} ions. The challenges of cooling, handling high space-charge forces, and coupling with injectors and subsequent accelerators are significant. In all instances, beam tests were a valuable learning experience, because not always did these as-built structures perform exactly as predicted by the earlier design codes. They summarize the key operational parameters, indicate what was achieved, and highlight what was learned in these tests. Based on this generally good performance and high promise, even more challenging designs are being considered for new applications that include even higher powers, beam funnels and choppers.
NASA Astrophysics Data System (ADS)
Cummer, Steven A.; Frey, Harald U.; Mende, Stephen B.; Hsu, Rue-Ron; Su, Han-Tzong; Chen, Alfred B.; Fukunishi, Hiroshi; Takahashi, Yukihiro
2006-10-01
We report coordinated measurements of lightning and resulting sprites using ground-level magnetic field sensors (<0.1 Hz to 30 kHz bandwidth) and the ISUAL instrument on the FORMOSAT-2 satellite. These measurements demonstrate two distinct elements of the connection between the radio and optical emissions. First, the quasi-static magnetic field signature is tightly correlated with the low-altitude optical emissions from the lightning flash, indicating that this radio signature is produced by continuing lightning current. Second, in two events with strong postreturn stroke extremely low frequency (ELF) magnetic pulses, the optical emissions demonstrate that there are no observable intensifications of low-altitude optical emissions associated with those pulses. If they were produced by a lightning process, such as an M-component, the connection between optical emissions and current seen in the return stroke and the continuing current suggests they should be visible. However, as has been observed previously, the bright, high-altitude optical emissions associated with the sprite are simultaneous with the ELF pulse. This is strong evidence that these ELF pulses originate in high-altitude electric current in the sprite itself and are not produced by a low-altitude lightning process.
Current halo structures in high-current plasma experiments: {theta}-pinch
Matveev, Yu. V.
2007-03-15
Experimental data elucidating mechanisms for halo formation in {theta}-pinch discharges are presented and discussed. The experiments were performed with different gases (H{sub 2}, D{sub 2}, He, and Ar) in a theta-pinch device with a porcelain vacuum chamber and an excitation coil 15 cm in diameter and 30 cm in length. The stored energy, the current in the excitation coil, and the current half-period were W = 10 kJ, I = 400 kA, and T/2 = 14 {mu}s, respectively. It is found that the plasma rings (halos) surrounding the pinch core arise as a result of coaxial pinch stratification due to both the excitation of closed currents (inductons) inside the pinch and the radial convergence of the plasma current sheaths produced after the explosion of T-layers formed near the wall in the initial stage of the discharge. It is concluded that halo structures observed in pinches, tokamaks, and other high-current devices used in controlled fusion research have the same nature.
Status of high transport current ROEBEL assembled coated conductor cables
NASA Astrophysics Data System (ADS)
Goldacker, Wilfried; Frank, Antje; Kudymow, Andrej; Heller, Reinhard; Kling, Andrea; Terzieva, Stanimira; Schmidt, Curt
2009-03-01
Assembling coated conductors (CC) into flat ROEBEL bars (RACC cable) was introduced in 2005 by the authors as a practicable method of reaching high transport currents in a low AC loss cable, which is a cable design suited for application in windings. The transport current of 1.02 kA in self-field at 77 K achieved so far, however, is still too low for several applications in electrical machinery such as larger transformers and generators/motors. A new cable concept for further increased currents was presented just recently. The goal of the new design was primarily to demonstrate the possibility of strongly increased transport currents without changing the important cable features for low AC losses. such as, for example, the transposition length of the strands. We present detailed investigations of the properties of this progressed cable design, which has threefold layered strands, an unchanged transposition pitch of 18.8 cm and finally the application of 45 coated conductors in the cable. A 1.1 m long sample (equivalent to six transposition lengths) was prepared from commercial Cu stabilized coated conductors purchased from Superpower. The measured new record DC transport current of the cable was 2628 A at 77 K in self-field (5 µV cm-1 criterion). The use of three slightly different current carrying batches of strand material (± 10%) was a special feature of the cable, which allowed for interesting investigations of current redistribution effects in the cable, by monitoring a representative strand of each batch during the critical current measurement. Although current redistribution effects showed a complex situation, the behaviour of the cable was found to be absolutely stable under all operational conditions, even above the critical current. The high self-field degradation of the critical current reached the order of 60% at 77 K, and could be modelled satisfactory with calculations based on a proven Biot-Savart-law approach, adapted to the specific boundary
Fiber optic current monitor for high-voltage applications
Renda, G.F.
1992-04-21
A current monitor which derives its power from the conductor being measured for bidirectionally measuring the magnitude of current (from DC to above 50 khz) flowing through a conductor across which a relatively high level DC voltage is applied, includes a pair of identical transmitter modules connected in opposite polarity to one another in series with the conductor being monitored, for producing from one module a first light signal having an intensity directly proportional to the magnitude of current flowing in one direction through the conductor during one period of time, and from the other module a second light signal having an intensity directly proportional to the magnitude of current flowing in the opposite direction through the conductor during another period of time, and a receiver located in a safe area remote from the high voltage area for receiving the first and second light signals, and converting the same to first and second voltage signals having levels indicative of the magnitude of current being measured at a given time. 6 figs.
Fiber optic current monitor for high-voltage applications
Renda, George F.
1992-01-01
A current monitor which derives its power from the conductor being measured for bidirectionally measuring the magnitude of current (from DC to above 50 khz) flowing through a conductor across which a relatively high level DC voltage is applied, includes a pair of identical transmitter modules connected in opposite polarity to one another in series with the conductor being monitored, for producing from one module a first light signal having an intensity directly proportional to the magnitude of current flowing in one direction through the conductor during one period of time, and from the other module a second light signal having an intensity directly proportional to the magnitude of current flowing in the opposite direction through the conductor during another period of time, and a receiver located in a safe area remote from the high voltage area for receiving the first and second light signals, and converting the same to first and second voltage signals having levels indicative of the magnitude of current being measured at a given time.
Transient analysis and burnout of high temperature superconducting current leads
NASA Astrophysics Data System (ADS)
Seol, S. Y.; Hull, J. R.
The transient behaviour of high-temperature superconductor (HTS) current leads operated between liquid helium and liquid nitrogen temperatures is analysed for burnout conditions upon transition of the HTS into the normal state. Leads composed of HTS only and of HTS sheathed by pure silver or silver alloy are investigated numerically for temperature-dependent properties and analytically for temperature-independent properties. For lower values of shape factor (current density times length), the lead can be operated indefinitely without burnout. At higher values of shape factor, the lead reaches burnout in a finite time. With high current densities, the leads heat adiabatically. For a fixed shape factor, low current densities are desired to achieve long burnout times. To achieve a low helium boil-off rate in the superconducting state without danger of burnout, there is a preferred temperature dependence for thermal conductivity, and silver alloy sheaths are preferred to pure silver sheaths. However, for a given current density, pure silver sheaths take longer to burn out.
Bootstrapping least-squares estimates in biochemical reaction networks.
Linder, Daniel F; Rempała, Grzegorz A
2015-01-01
The paper proposes new computational methods of computing confidence bounds for the least-squares estimates (LSEs) of rate constants in mass action biochemical reaction network and stochastic epidemic models. Such LSEs are obtained by fitting the set of deterministic ordinary differential equations (ODEs), corresponding to the large-volume limit of a reaction network, to network's partially observed trajectory treated as a continuous-time, pure jump Markov process. In the large-volume limit the LSEs are asymptotically Gaussian, but their limiting covariance structure is complicated since it is described by a set of nonlinear ODEs which are often ill-conditioned and numerically unstable. The current paper considers two bootstrap Monte-Carlo procedures, based on the diffusion and linear noise approximations for pure jump processes, which allow one to avoid solving the limiting covariance ODEs. The results are illustrated with both in-silico and real data examples from the LINE 1 gene retrotranscription model and compared with those obtained using other methods. PMID:25898769
Bootstrapping Least Squares Estimates in Biochemical Reaction Networks
Linder, Daniel F.
2015-01-01
The paper proposes new computational methods of computing confidence bounds for the least squares estimates (LSEs) of rate constants in mass-action biochemical reaction network and stochastic epidemic models. Such LSEs are obtained by fitting the set of deterministic ordinary differential equations (ODEs), corresponding to the large volume limit of a reaction network, to network’s partially observed trajectory treated as a continuous-time, pure jump Markov process. In the large volume limit the LSEs are asymptotically Gaussian, but their limiting covariance structure is complicated since it is described by a set of nonlinear ODEs which are often ill-conditioned and numerically unstable. The current paper considers two bootstrap Monte-Carlo procedures, based on the diffusion and linear noise approximations for pure jump processes, which allow one to avoid solving the limiting covariance ODEs. The results are illustrated with both in-silico and real data examples from the LINE 1 gene retrotranscription model and compared with those obtained using other methods. PMID:25898769
More on analytic bootstrap for O( N) models
NASA Astrophysics Data System (ADS)
Dey, Parijat; Kaviraj, Apratim; Sen, Kallol
2016-06-01
This note is an extension of a recent work on the analytical bootstrapping of O( N) models. An additonal feature of the O( N) model is that the OPE contains trace and antisymmetric operators apart from the symmetric-traceless objects appearing in the OPE of the singlet sector. This in addition to the stress tensor ( T μν ) and the ϕ i ϕ i scalar, we also have other minimal twist operators as the spin-1 current J μ and the symmetric-traceless scalar in the case of O( N). We determine the effect of these additional objects on the anomalous dimensions of the corresponding trace, symmetric-traceless and antisymmetric operators in the large spin sector of the O( N) model, in the limit when the spin is much larger than the twist. As an observation, we also verified that the leading order results for the large spin sector from the ɛ-expansion are an exact match with our n = 0 case. A plausible holographic setup for the special case when N = 2 is also mentioned which mimics the calculation in the CFT.
Magnetohydrodynamic transport equations for high current propagation in overdense plasmas
NASA Astrophysics Data System (ADS)
Zha, Xuejun; Wang, Yan; Han, Shensheng
2008-10-01
In this paper, it is presented that the full set of magnetohydrodynamic (MHD) equations which may be used to study the transport mechanism for the high current relativistic electron beams (current intensity 100˜1000 MA, electron energy ˜ MeV) by the laser in background overdense plasma (1022-1026cm). The transport of intense relativistic electron beams (REB) has two basic characteristics: the first is that the forward current is a giga-ampere and the forward current density is about 10 14 A/cm 2 which exceeds the Alfven current limit [M. Tabak et al., Phys. Plasmas 12, 057305 (2005)]; the second is the propagation of the intense forward current in the presence of a background overdense plasma which may have very strong MHD instability. The transport problem can be solved by MHD equations that describe the dynamic, self consistent collisional and electromagnetic interaction of REB with overdense hydrogenic plasmas or arbitrary atomic-number plasmas. The full set of equations consists of the REB transport equations which are coupled to Maxwell's equations through the electromagnetic-field terms and two-fluid plasma dynamical equations for the background overdense plasma through the collision term.
Neutral current neutrino-nucleus interactions at high energies
Gay Ducati, M. B.; Machado, M. M.; Machado, M. V. T.
2009-04-01
We present a QCD analysis of the neutral current (NC) neutrino-nucleus interaction at the small-x region using the color dipole formalism. This phenomenological approach is quite successful in describing experimental results in deep inelastic ep scattering and charged current neutrino-nucleus interactions at high energies. We present theoretical predictions for the relevant structure functions and the corresponding implications for the total NC neutrino cross section. It is shown that at small x, the NC boson-nucleon cross section should exhibit the geometric scaling property that has important consequences for ultrahigh energy neutrino phenomenology.
A Bootstrap Approach to Martian Manufacturing
NASA Technical Reports Server (NTRS)
Dorais, Gregory A.
2004-01-01
In-Situ Resource Utilization (ISRU) is an essential element of any affordable strategy for a sustained human presence on Mars. Ideally, Martian habitats would be extremely massive to allow plenty of room to comfortably live and work, as well as to protect the occupants from the environment. Moreover, transportation and power generation systems would also require significant mass if affordable. For our approach to ISRU, we use the industrialization of the U.S. as a metaphor. The 19th century started with small blacksmith shops and ended with massive steel mills primarily accomplished by blacksmiths increasing their production capacity and product size to create larger shops, which produced small mills, which produced the large steel mills that industrialized the country. Most of the mass of a steel mill is comprised of steel in simple shapes, which are produced and repaired with few pieces of equipment also mostly made of steel in basic shapes. Due to this simplicity, we expect that the 19th century manufacturing growth can be repeated on Mars in the 21st century using robots as the primary labor force. We suggest a "bootstrap" approach to manufacturing on Mars that uses a "seed" manufacturing system that uses regolith to create major structural components and spare parts. The regolith would be melted, foamed, and sintered as needed to fabricate parts using casting and solid freeform fabrication techniques. Complex components, such as electronics, would be brought from Earth and integrated as needed. These parts would be assembled to create additional manufacturing systems, which can be both more capable and higher capacity. These subsequent manufacturing systems could refine vast amounts of raw materials to create large components, as well as assemble equipment, habitats, pressure vessels, cranes, pipelines, railways, trains, power generation stations, and other facilities needed to economically maintain a sustained human presence on Mars.
Assessment of bootstrap resampling performance for PET data.
Markiewicz, P J; Reader, A J; Matthews, J C
2015-01-01
Bootstrap resampling has been successfully used for estimation of statistical uncertainty of parameters such as tissue metabolism, blood flow or displacement fields for image registration. The performance of bootstrap resampling as applied to PET list-mode data of the human brain and dedicated phantoms is assessed in a novel and systematic way such that: (1) the assessment is carried out in two resampling stages: the 'real world' stage where multiple reference datasets of varying statistical level are generated and the 'bootstrap world' stage where corresponding bootstrap replicates are generated from the reference datasets. (2) All resampled datasets were reconstructed yielding images from which multiple voxel and regions of interest (ROI) values were extracted to form corresponding distributions between the two stages. (3) The difference between the distributions from both stages was quantified using the Jensen-Shannon divergence and the first four moments. It was found that the bootstrap distributions are consistently different to the real world distributions across the statistical levels. The difference was explained by a shift in the mean (up to 33% for voxels and 14% for ROIs) being proportional to the inverse square root of the statistical level (number of counts). Other moments were well replicated by the bootstrap although for very low statistical levels the estimation of the variance was poor. Therefore, the bootstrap method should be used with care when estimating systematic errors (bias) and variance when very low statistical levels are present such as in early time frames of dynamic acquisitions, when the underlying population may not be sufficiently represented. PMID:25490178
Bootstrap-based intercomparison of regional flood estimation procedures
Ouarda, T.B.M.J.; Ashkar, F.
1995-12-31
The present paper describes a methodology, based on the regional bootstrap procedure, for the intercomparison of some of the most frequently used regional flood frequency estimation models. The results of the application of this methodology, with Canadian flood data, for comparing the different regional estimation models are also presented. A regional model C{sub ij} = [DRH]{sub i} x [MER]{sub j} (i=1,...,L ; j=1,...,M) is obtained by combining a methodology for the delineation of homogeneous regions [DRH]{sub i} and a regional estimation method [MER]{sub j}. These regional models are compared with respect to their ability to provide reliable estimates of certain flood quantiles (floods with return periods of 10 and 100 years). Two types of bootstrapping have been applied within the framework of this project: the classical scalar bootstrap used in at-site estimation, and the vector (or regional) bootstrap procedure applied in the intercomparison between the different regional models. This last technique is illustrated with an example, and all the details of the procedure are presented. The performance indices that were employed for the purpose of the intercomparison are also detailed. One important feature of regional bootstrapping is that it preserves the regional dependence structure between annual flood values at the different sites of an {open_quote}homogeneous{close_quote} region. Three versions of the regional bootstrap algorithm are presented and applied to the three cases of estimation-regional estimation for ungauged sites, regional estimation for gauged sites with a short record, and at-site estimation. It will be shown how at-site estimates can be used as basis for the intercomparison between the regional models. Results of the application of the bootstrap procedure, with flood data from the Provinces of Quebec and Ontario, are presented in the final section of the paper.
Assessment of bootstrap resampling performance for PET data
NASA Astrophysics Data System (ADS)
Markiewicz, P. J.; Reader, A. J.; Matthews, J. C.
2015-01-01
Bootstrap resampling has been successfully used for estimation of statistical uncertainty of parameters such as tissue metabolism, blood flow or displacement fields for image registration. The performance of bootstrap resampling as applied to PET list-mode data of the human brain and dedicated phantoms is assessed in a novel and systematic way such that: (1) the assessment is carried out in two resampling stages: the ‘real world’ stage where multiple reference datasets of varying statistical level are generated and the ‘bootstrap world’ stage where corresponding bootstrap replicates are generated from the reference datasets. (2) All resampled datasets were reconstructed yielding images from which multiple voxel and regions of interest (ROI) values were extracted to form corresponding distributions between the two stages. (3) The difference between the distributions from both stages was quantified using the Jensen-Shannon divergence and the first four moments. It was found that the bootstrap distributions are consistently different to the real world distributions across the statistical levels. The difference was explained by a shift in the mean (up to 33% for voxels and 14% for ROIs) being proportional to the inverse square root of the statistical level (number of counts). Other moments were well replicated by the bootstrap although for very low statistical levels the estimation of the variance was poor. Therefore, the bootstrap method should be used with care when estimating systematic errors (bias) and variance when very low statistical levels are present such as in early time frames of dynamic acquisitions, when the underlying population may not be sufficiently represented.
High-Current Energy-Recovering Electron Linacs
Nikolitsa Merminga; David Douglas; Geoffrey Krafft
2003-12-01
The use of energy recovery provides a potentially powerful new paradigm for generation of the charged particle beams used in synchrotron radiation sources, high-energy electron cooling devices, electron-ion colliders, and other applications in photon science and nuclear and high-energy physics. Energy-recovering electron linear accelerators (called energy-recovering linacs, or ERLs) share many characteristics with ordinary linacs, as their six-dimensional beam phase space is largely determined by electron source properties. However, in common with classic storage rings, ERLs possess a high average-current-carrying capability enabled by the energy recovery process, and thus promise similar efficiencies. The authors discuss the concept of energy recovery and its technical challenges and describe the Jefferson Lab (JLab) Infrared Demonstration Free-Electron Laser (IR Demo FEL), originally driven by a 3548-MeV, 5-mA superconducting radiofrequency (srf) ERL, which provided the most substantial demonstration of energy recovery to date: a beam of 250 kW average power. They present an overview of envisioned ERL applications and a development path to achieving the required performance. They use experimental data obtained at the JLab IR Demo FEL and recent experimental results from CEBAF-ERL GeV-scale, comparatively low-current energy-recovery demonstration at JLab to evaluate the feasibility of the new applications of high-current ERLs, as well as ERLs' limitations and ultimate performance.
Drift distance survey in DPIS for high current beam production
Kanesue,T.; Okamura, M.; Kondo, K.; Tamura, J.; Kashiwagi, H.; Zhang, Z.
2009-09-20
In a laser ion source, plasma drift distance is one of the most important design parameters. Ion current density and beam pulse width are defined by plasma drift distance between laser target and beam extraction position. In direct plasma injection scheme (DPIS), which uses a laser ion source and Radio Frequency Quadrupole (RFQ) linac, we can apply relatively higher electric field at the beam extraction due to the unique shape of a positively biased electrode. However, when we aim at very high current acceleration like several tens of mA, we observed mismatched beam extraction conditions. We tested three different ion current at ion extraction region by changing plasma drift distance to study better extraction condition. In this experiment, C{sup 6+} beam was accelerated. We confirmed that the matching condition can be improved by controlling plasma drift distance.
TOPICAL REVIEW: Current status of high-Tc wire
NASA Astrophysics Data System (ADS)
Vase, Per; Flükiger, René; Leghissa, Martino; Glowacki, Bartek
2000-07-01
This paper is the result of the work of a SCENET (The European Network for Superconductivity) material working group's efforts on giving values for present and future expected performance of high-temperature superconducting (HTS) wires and tapes. The purpose of the work is to give input to the design of HTS applications like power cables, motors, current leads, magnets, transformers and generators. The current status performance values are supposed to be used in the design of today's prototypes and the future values for the design of fully commercial HTS applications of the future. We focus on what is expected to be the relevant parameters for HTS application design. The most successful technique by far for making HTS tapes has been on the (Bi, Pb)2Sr2Ca2Cu3Ox (Bi-2223) material by the powder-in-tube (PIT) technique and this paper therefore focuses on giving the current status and expected future performance for Bi-2223 tapes.
High current density, cryogenically cooled sliding electrical joint development
Murray, H.
1986-09-01
In the past two years, conceptual designs for fusion energy research devices have focussed on compact, high magnetic field configurations. The concept of sliding electrical joints in the large magnets allows a number of technical advantages including enhanced mechanical integrity, remote maintainability, and reduced project cost. The rationale for sliding electrical joints is presented. The conceptual configuration for this generation of experimental devices is highlghted by an approx. 20 T toroidal field magnet with a flat top conductor current of approx. 300 kA and a sliding electrical joint with a gross current density of approx. 0.6 kA/cm/sup 2/. A numerical model was used to map the conductor current distribution as a function of time and position in the conductor. A series of electrical joint arrangements were produced against the system code envelope constraints for a specific version of the Ignition Studies Project (ISP) which is designated as 1025.
MHD Modeling of Conductors at Ultra-High Current Density
ROSENTHAL,STEPHEN E.; DESJARLAIS,MICHAEL P.; SPIELMAN,RICK B.; STYGAR,WILLIAM A.; ASAY,JAMES R.; DOUGLAS,M.R.; HALL,C.A.; FRESE,M.H.; MORSE,R.L.; REISMAN,D.B.
2000-08-29
In conjunction with ongoing high-current experiments on Sandia National Laboratories' Z accelerator, the authors have revisited a problem first described in detail by Heinz Knoepfel. Unlike the 1-Tesla MITLs of pulsed power accelerators used to produce intense particle beams, Z's disc transmission line (downstream of the current addition) is in a 100--1,200 Tesla regime, so its conductors cannot be modeled simply as static infinite conductivity boundaries. Using the MHD code MACH2 they have been investigating the conductor hydrodynamics, characterizing the joule heating, magnetic field diffusion, and material deformation, pressure, and velocity over a range of current densities, current rise-times, and conductor materials. Three purposes of this work are (1) to quantify power flow losses owing to ultra-high magnetic fields, (2) to model the response of VISAR diagnostic samples in various configurations on Z, and (3) to incorporate the most appropriate equation of state and conductivity models into the MHD computations. Certain features are strongly dependent on the details of the conductivity model.
High current pulse testing for ground rod integrity
NASA Technical Reports Server (NTRS)
Walko, Lawrence C.
1991-01-01
A test technique was developed to assess various grounding system concepts used for mobile facilities. The test technique involves applying a high current pulse to the grounding system with the proper waveshape and magnitude to simulate a lightning return stroke. Of concern were the step voltages present along the ground near the point of lightning strike. Step voltage is equated to how fast the current pulse is dissipated by the grounding system. The applied current pulse was produced by a high current capacitor bank with a total energy content of 80 kilojoules. A series of pulse tests were performed on two types of mobile facility grounding systems. One system consisted of an array of four 10 foot copper clad steel ground rods connected by 1/0 gauge wire. The other system was an array of 10 inch long tapered ground rods, strung on stainless steel cable. The focus here is on the pulse test technique used and its relevance to actual lightning strike conditions.
Current collection by high voltage anodes in near ionospheric conditions
NASA Technical Reports Server (NTRS)
Antoniades, John A.; Greaves, Rod G.; Boyd, D. A.; Ellis, R.
1990-01-01
The authors experimentally identified three distinct regimes with large differences in current collection in the presence of neutrals and weak magnetic fields. In magnetic field/anode voltage space the three regions are separated by very sharp transition boundaries. The authors performed a series of laboratory experiments to study the dependence of the region boundaries on several parameters, such as the ambient neutral density, plasma density, magnetic field strength, applied anode voltage, voltage pulsewidth, chamber material, chamber size and anode radius. The three observed regimes are: classical magnetic field limited collection; stable medium current toroidal discharge; and large scale, high current space glow discharge. There is as much as several orders of magnitude of difference in the amount of collected current upon any boundary crossing, particularly if one enters the space glow regime. They measured some of the properties of the plasma generated by the breakdown that is present in regimes II and III in the vicinity of the anode including the sheath modified electrostatic potential, I-V characteristics at high voltage as well as the local plasma density.
Testing of full size high current superconductors in SULTAN III
Blau, B.; Rohleder, I.; Vecsey, G.
1994-07-01
The high field test facility SULTAN III in operation at PSI/Switzerland tests full size industrial prototype superconductors for fusion applications such as ITER. The facility provides a background field of up to 11 T over a length of 58 cm. A 50 kA superconducting transformer works as a very low noise current source which allows a criterion of 0.1 {mu}V/cm to determine the superconducting to normal transition. Three 3.6 m long cable-in-conduit conductors based on both NbTi and Nb{sub 3}Sn, developed by different manufacturers, suitable for the central solenoid and toroidal field coils of ITER, have been tested so far. This paper presents the results of extensive measurements of critical current and current sharing temperature of the Nb{sub 3}Sn conductors in the 8--11 T range for temperatures between 4.5 K and 11 K Voltage versus current curves have been analyzed with respect to the n value. The manufacturing of a high quality joint between two Nb{sub 3}Sn conductors after heat treatment is reported, together with some measurements of the joint resistance.
Dynamics of a high-current relativistic electron beam
Strelkov, P. S.; Tarakanov, V. P.; Ivanov, I. E. Shumeiko, D. V.
2015-06-15
The dynamics of a high-current relativistic electron beam is studied experimentally and by numerical simulation. The beam is formed in a magnetically insulated diode with a transverse-blade explosive-emission cathode. It is found experimentally that the radius of a 500-keV beam with a current of 2 kA and duration of 500 ns decreases with time during the beam current pulse. The same effect was observed in numerical simulations. This effect is explained by a change in the shape of the cathode plasma during the current pulse, which, according to calculations, leads to a change in the beam parameters, such as the electron pitch angle and the spread over the longitudinal electron momentum. These parameters are hard to measure experimentally; however, the time evolution of the radial profile of the beam current density, which can be measured reliably, coincides with the simulation results. This allows one to expect that the behavior of the other beam parameters also agrees with numerical simulations.
Characterization of a High Current, Long Life Hollow Cathode
NASA Technical Reports Server (NTRS)
VanNoord, Jonathan L.; Kamhawi, Hani; McEwen, Heather K.
2006-01-01
The advent of higher power spacecraft makes it desirable to use higher power electric propulsion thrusters such as ion thrusters or Hall thrusters. Higher power thrusters require cathodes that are capable of producing higher currents. One application of these higher power spacecraft is deep-space missions that require tens of thousands of hours of operation. This paper presents the approach used to design a high current, long life hollow cathode assembly for that application, along with test results from the corresponding hollow cathode. The design approach used for the candidate hollow cathode was to reduce the temperature gradient in the insert, yielding a lower peak temperature and allowing current to be produced more uniformly along the insert. The lower temperatures result in a hollow cathode with increased life. The hollow cathode designed was successfully operated at currents from 10 to 60 A with flow rates of 5 to 19 sccm with a maximum orifice temperature measured of 1100 C. Data including discharge voltage, keeper voltage, discharge current, flow rates, and orifice plate temperatures are presented.
Electron beam current in high power cylindrical diode
Roy, Amitava; Menon, R.; Mitra, S.; Sharma, Vishnu; Singh, S. K.; Nagesh, K. V.; Chakravarthy, D. P.
2010-01-15
Intense electron beam generation studies were carried out in high power cylindrical diode to investigate the effect of the accelerating gap and diode voltage on the electron beam current. The diode voltage has been varied from 130 to 356 kV, whereas the current density has been varied from 87 to 391 A/cm{sup 2} with 100 ns pulse duration. The experimentally obtained electron beam current in the cylindrical diode has been compared with the Langmuir-Blodgett law. It was found that the diode current can be explained by a model of anode and cathode plasma expanding toward each other. However, the diode voltage and current do not follow the bipolar space-charge limited flow model. It was also found that initially only a part of the cathode take part in the emission process. The plasma expands at 4.2 cm/mus for 1.7 cm anode-cathode gap and the plasma velocity decreases for smaller gaps. The electrode plasma expansion velocity of the cylindrical diode is much smaller as compared with the planar diode for the same accelerating gap and diode voltage. Therefore, much higher voltage can be obtained for the cylindrical diodes as compared with the planar diodes for the same accelerating gap.
New HOM coupler design for high current SRF cavity
Xu, W.; Ben-Zvi, I.; Belomestnykh, S.; Hahn, H.; Johnson, E.
2011-03-28
Damping higher order modes (HOMs) significantly to avoid beam instability is a challenge for the high current Energy Recovery Linac-based eRHIC at BNL. To avoid the overheating effect and high tuning sensitivity, current, a new band-stop HOM coupler is being designed at BNL. The new HOM coupler has a bandwidth of tens of MHz to reject the fundamental mode, which will avoid overheating due to fundamental frequency shifting because of cooling down. In addition, the S21 parameter of the band-pass filter is nearly flat from first higher order mode to 5 times the fundamental frequency. The simulation results showed that the new couplers effectively damp HOMs for the eRHIC cavity with enlarged beam tube diameter and 2 120{sup o} HOM couplers at each side of cavity. This paper presents the design of HOM coupler, HOM damping capacity for eRHIC cavity and prototype test results.
ULTRA-LOW-ENERGY HIGH-CURRENT ION SOURCE
Anders, Andre; Yushkov, Georgy Yu.; Baldwin, David A.
2009-11-20
The technical objective of the project was to develop an ultra-low-energy, high-intensity ion source (ULEHIIS) for materials processing in high-technology fields including semiconductors, micro-magnetics and optics/opto-electronics. In its primary application, this ion source can be incorporated into the 4Wave thin-film deposition technique called biased target ion-beam deposition (BTIBD), which is a deposition technique based on sputtering (without magnetic field, i.e., not the typical magnetron sputtering). It is a technological challenge because the laws of space charge limited current (Child-Langmuir) set strict limits of how much current can be extracted from a reservoir of ions, such as a suitable discharge plasma. The solution to the problem was an innovative dual-discharge system without the use of extraction grids.