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1

Numerical investigation of pulsed-driven DBD plasma actuator  

NASA Astrophysics Data System (ADS)

Dielectric barrier discharge (DBD) plasma actuators are promising devices for flow separation control. The operation of conventional DBDs, driven by AC or pulses+bias voltage, is based on direct induction of momentum into boundary layer by transferring momenta from charged particles to neutrals. However, the maximum DBD induced flow velocity for the conventional DBD is limited to ˜10-20 m/s, since conventional DBD operates in corona regime. The way to overcome this limitation is to use ns pulses, which transfer much more momentum to the flow during discharge propagation (forward breakdown), as driving voltage. However, on the back slope of the ns pulse, the backward breakdown induces strong negative force on the gas, significantly decreasing to effect of forward pushing. The second problem is the surface charge accumulation, which is reported to be one of the major limiting factors for pulsed DBDs. In this talk, we will present numerical simulations of both forward and backward breakdowns for DBD plasma actuators using 2D/3D hybrid plasma simulation tool VORPAL. We will also discuss potential solutions for the backward breakdown elimination.

Likhanskii, Alexandre; Shneider, Mikhail; Miles, Richard; Macheret, Sergey

2011-11-01

2

Airfoil Leading Edge Flow Separation Control using DBD Plasma Actuators driven by Nanosecond Pulses  

Microsoft Academic Search

This work continues an ongoing exploration of the use of dielectric barrier discharge plasma actuators driven by repetitive nanosecond pulses (NS-DBD hereafter) for aerodynamic flow control. The NS-DBD transfers very little momentum to the neutral air, but generates compression waves that manipulate flow instabilities similar to localized arc filament plasma actuators. Such devices which are believed to function through thermal

Jesse Little; Chris Rethmel; Keisuke Takashima; Chris Wiet; Igor Adamovich; Mo Samimy

2010-01-01

3

Characterization of nanosecond pulse driven dielectric barrier discharge plasma actuators for aerodynamic flow control  

NASA Astrophysics Data System (ADS)

Positive polarity nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuators are studied experimentally in quiescent atmosphere. Pulse energy and instantaneous pulse power (hereafter referred to as energy and power) are calculated using simultaneous voltage and current measurements. Electrical characteristics are evaluated as a function of peak voltage, pulse frequency, discharge length, and dielectric thickness. Schlieren imaging is used to provide a relative estimate of discharge energy that is coupled to the near surface gas as heat for the same parameters. Characteristics of the DBD load have a substantial effect on the individual voltage and current traces which are reflected in the energy and power values. Power is mainly dependent on actuator length which is inconsistent with schlieren data as expected. Higher per unit length energy indicates a stronger compression wave for a given actuator geometry, but this is not universally true across different actuators suggesting some constructions more efficiently couple energy to the gas. Energy and compression wave strength are linearly related. Higher pulse frequency produces higher energy but is primarily attributed to heating of the actuator and power supply components and not to an optimal discharge frequency. Both energy and wave strength increase as peak voltage to the power of approximately 3.5 over a substantial range similar to ac-DBD plasma actuators.

Dawson, Robert; Little, Jesse

2013-03-01

4

Surface discharge plasma actuator driven by a pulsed 13.56 MHz-5 kHz voltage waveform  

NASA Astrophysics Data System (ADS)

The effect of incorporating pulses of radio-frequency (rf: 13.56 MHz) voltage into the driving waveform of a surface discharge plasma actuator is investigated. Rf voltage is applied to the actuator to increase the production of ions and thereby increase the thrust that is generated by the discharge. This waveform is coupled to the powered electrode in 5 µs pulses and combined with a relatively low-frequency (LF) 5 kHz sinusoid to form a pulsed 13.56 MHz-5 kHz (rf-LF) driving voltage. Measurements of the applied voltage, rf and LF currents, effective power, and velocity field of the surrounding air are undertaken at atmospheric pressure. The thrust that is generated using the rf-LF waveform is estimated from the velocity fields using a momentum balance and is found to increase for increasing rf voltage when the LF voltage remains constant. Maximum thrust is achieved when the rf pulses are positioned at the LF voltage minima and this suggests the importance of negative ions. The efficacy of rf-LF actuation is investigated by comparing the thrust that is generated per unit increase in peak voltage with that obtained using an LF-driven discharge.

Dedrick, J.; Im, S.; Cappelli, M. A.; Boswell, R. W.; Charles, C.

2013-10-01

5

Modeling of dielectric barrier discharge plasma actuators driven by repetitive nanosecond pulses  

SciTech Connect

A detailed physical model for an asymmetric dielectric barrier discharge (DBD) in air driven by repetitive nanosecond voltage pulses is developed. In particular, modeling of DBD with high voltage repetitive negative and positive nanosecond pulses combined with positive dc bias is carried out. Operation at high voltage is compared with operation at low voltage, highlighting the advantage of high voltages, however the effect of backward-directed breakdown in the case of negative pulses results in a decrease of the integral momentum transferred to the gas. The use of positive repetitive pulses with dc bias is demonstrated to be promising for DBD performance improvement. The effects of the voltage waveform not only on force magnitude, but also on the spatial profile of the force, are shown. The crucial role of background photoionization in numerical modeling of ionization waves (streamers) in DBD plasmas is demonstrated.

Likhanskii, Alexandre V.; Shneider, Mikhail N.; Macheret, Sergey O.; Miles, Richard B. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Lockheed Martin Skunk Works, 1011 Lockheed Way, Palmdale, California 93599 (United States); Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

2007-07-15

6

On Plasma Synthetic Jet Actuators  

Microsoft Academic Search

The term plasma actuator refers to an asymmetric arrangement of two electrodes (typ- ically rectangular strips) separated by dielectric material that can be used as active flow control devices. A plasma actuator design consisting of an annular electrode array, the plasma synthetic jet actuator (PSJA), is experimentally investigated in this paper. This particular geometry creates a zero-net mass flux (or

Arvind Santhanakrishnan; Jamey D. Jacob

2006-01-01

7

Plasma actuated heat transfer  

NASA Astrophysics Data System (ADS)

We introduce plasmas for film cooling enhancement in gas turbines and other engineering applications. We identify mechanisms to actuate essentially stagnant fluid just downstream of the cooling hole by employing three-dimensional body force for different hole geometries. Such methods actively alter flow structures in the vicinity of an actuator using an electrodynamic mechanism that induces attachment of cold jet to the work surface. Numerical results are compared with published experimental data and other numerical predictions for the latest film cooling technology. An effectiveness improvement of above 100% over the standard baseline design is predicted.

Roy, Subrata; Wang, Chin-Cheng

2008-06-01

8

Optimization of Dielectric Barrier Discharge Plasma Actuators Driven By Repetitive Nanosecond Pulses  

Microsoft Academic Search

A detailed physical model for an asymmetric dielectric barrier discharge (DBD) in air driven by repetitive nanosecond voltage pulses is developed. In particular, modeling of DBD with high voltage repetitive negative and positive nanosecond pulses combined with positive dc bias is carried out. Operation at high voltage is compared with operation at low voltage, highlighting the advantage of high voltages,

A. V. Likhanskii; M. N. Shneider; S. O. Macheret; R. B. Miles

2007-01-01

9

Experimental investigation of dielectric barrier discharge plasma actuators driven by repetitive high-voltage nanosecond pulses with dc or low frequency sinusoidal bias  

SciTech Connect

Experimental studies were conducted of a flow induced in an initially quiescent room air by a single asymmetric dielectric barrier discharge driven by voltage waveforms consisting of repetitive nanosecond high-voltage pulses superimposed on dc or alternating sinusoidal or square-wave bias voltage. To characterize the pulses and to optimize their matching to the plasma, a numerical code for short pulse calculations with an arbitrary impedance load was developed. A new approach for nonintrusive diagnostics of plasma actuator induced flows in quiescent gas was proposed, consisting of three elements coupled together: the schlieren technique, burst mode of plasma actuator operation, and two-dimensional numerical fluid modeling. The force and heating rate calculated by a plasma model was used as an input to two-dimensional viscous flow solver to predict the time-dependent dielectric barrier discharge induced flow field. This approach allowed us to restore the entire two-dimensional unsteady plasma induced flow pattern as well as characteristics of the plasma induced force. Both the experiments and computations showed the same vortex flow structures induced by the actuator. Parametric studies of the vortices at different bias voltages, pulse polarities, peak pulse voltages, and pulse repetition rates were conducted experimentally. The significance of charge buildup on the dielectric surface was demonstrated. The charge buildup decreases the effective electric field in the plasma and reduces the plasma actuator performance. The accumulated surface charge can be removed by switching the bias polarity, which leads to a newly proposed voltage waveform consisting of high-voltage nanosecond repetitive pulses superimposed on a high-voltage low frequency sinusoidal voltage. Advantages of the new voltage waveform were demonstrated experimentally.

Opaits, Dmitry F.; Likhanskii, Alexandre V.; Neretti, Gabriele; Zaidi, Sohail; Shneider, Mikhail N.; Miles, Richard B. [Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Macheret, Sergey O. [Lockheed Martin Aeronautics Company, Palmdale, California 93599 (United States)

2008-08-15

10

Novel applications of plasma actuators  

NASA Astrophysics Data System (ADS)

The current study investigates the effectiveness of two different dielectric barrier discharge plasma actuator configurations, a 3-D annular geometry for use in micro thrusters and internal duct aerodynamics and a jet vectoring actuator that acts as a vortex generator and flow control device. The first configuration consists of a closed circumferential arrangement which yields a body force when a voltage difference is applied across the inner and outer electrodes separated by a dielectric. The primary flow is driven by this zero-net mass flux jet at the wall that then entrains fluid in the core of the duct. PIV experiments in both quiescent flow and freestream are conducted on tubes of different diameters while varying parameters such as the modulation frequency, duty cycle and tunnel speed. The values of the induced velocities increase with the forcing frequency and duty cycle although there is a peak value for the forcing frequency after which the velocity and thrust decrease for each thruster. The velocities and thrust increase as the inner diameter of the tubes are increased while the velocity profiles show a great difference with the (l/di) ratio; recirculation occurs after going below a critical value. Experiments in the wind tunnel illustrate that the jet exit characteristics significantly change upon actuation in freestream flow but the effect tends to diminish with increasing inner diameters and tunnel speeds. Using staged arrays of these thrusters result in higher velocities while operating at both in phase and out of phase. The jet vectoring configuration consists of a single embedded electrode separated from two exposed electrodes on either side by the dielectric. The embedded electrode is grounded while the exposed electrodes are driven with a high frequency high voltage input signal. PIV measurements of the actuator in a freestream show that vectoring the jet yields stronger vortices than a linear configuration and increasing the difference between the duty cycles of the channels increases the vortex strength. It is seen that while the vortex is barely visible at the leading edge with little strength, it grows significantly large in the streamwise direction and reaches its maximum strength around mid-chord locations while the circulation distribution shows that the bulk of the circulation is added here. The motion of the vortex along this direction illustrates a braiding phenomena that can be observed via flow visualizations. Streamwise PIV data for this configuration on a wing with a NACA 0012 airfoil is used to plot the reverse flow probability, which in turn reveals that the use of the jet vectoring actuator as a vortex generator jet does suppress separation, but the actuator tends to lose its efficacy with increasing tunnel speeds.

Ozturk, Arzu Ceren

11

Micro Jet Generation with Annular Plasma Actuators  

Microsoft Academic Search

The effectiveness of dielectric barrier discharge plasma actuators for use in micro thrusters and internal duct aerodynamics are investigated. The primary flow is driven by tha zero-net mass flux jet at the wall in a closed circumferential arrangemen that then entrains fluid in the core of the duct. This results in a unique configuration for studying impulsively started jet phenomena.

Ceren Ozturk; Jamey Jacob

2008-01-01

12

Novel applications of plasma actuators  

Microsoft Academic Search

The current study investigates the effectiveness of two different dielectric barrier discharge plasma actuator configurations, a 3-D annular geometry for use in micro thrusters and internal duct aerodynamics and a jet vectoring actuator that acts as a vortex generator and flow control device. The first configuration consists of a closed circumferential arrangement which yields a body force when a voltage

Arzu Ceren Ozturk

2009-01-01

13

Microscale plasma actuators for improved thrust density  

Microsoft Academic Search

We present a study of the dielectric barrier discharge (DBD) plasma actuators for microscale applications. Traditional macroscale DBD actuators suffer from relatively small actuation effect as characterized by small induced force density and resulting flow velocity. As a remedy we propose microscale plasma actuators that may induce orders of magnitude higher force density. We study the physics of such actuation

Chin-Cheng Wang; Subrata Roy

2009-01-01

14

Gear-Driven Turnbuckle Actuator  

NASA Technical Reports Server (NTRS)

This actuator design allows the extension and contraction of turnbuckle assemblies. It can be operated manually or remotely, and is extremely compact. It is ideal for turnbuckles that are hard to reach by conventional tools. The tool assembly design solves the problem of making accurate adjustments to the variable geometry guide vanes without having to remove and reinstall the actuator system back on the engine. The actuator does this easily by adjusting the length of the turnbuckles while they are still attached to the engine.

Rivera, Ricky N.

2010-01-01

15

Serpentine Geometry Plasma Actuators for Flow Control.  

National Technical Information Service (NTIS)

In this paper, a curved class of plasma actuator geometries is presented. The intension of this paper is to extend the versatility of a dielectric barrier discharge plasma actuator by modifying the geometry of its electrodes, so that the plasma generated ...

M. Riherd S. Roy

2013-01-01

16

Note: A novel rotary actuator driven by only one piezoelectric actuator  

NASA Astrophysics Data System (ADS)

This paper presents a novel piezo-driven rotary actuator based on the parasitic motion principle. Output performances of the rotary actuator were tested and discussed. Experiment results indicate that using only one piezoelectric actuator and simple sawtooth wave control, the rotary actuator reaches the rotation velocity of about 20 097 ?rad/s when the driving voltage is 100 V and the driving frequency is 90 Hz. The actuator can rotate stably with the minimum resolution of 0.7 ?rad. This paper verifies feasibility of the parasitic motion principle for applications of rotary actuators, providing new design ideas for precision piezoelectric rotary actuators.

Huang, Hu; Fu, Lu; Zhao, Hongwei; Shi, Chengli; Ren, Luquan; Li, Jianping; Qu, Han

2013-09-01

17

Experimental Investigation of the Plasma Aerodynamic Actuation Generated by Nanosecond-pulse Sliding Discharge  

Microsoft Academic Search

Plasma flow control, based on plasma aerodynamic actuation, has become a newly-rising research focus in international aerodynamic field. Sliding discharge is a novel approach to generate plasma aerodynamic actuation. In this paper, a three-electrode plasma sheet actuator driven by repetitive nanosecond pulses with negative DC component is used to generate sliding discharge, which can be called nanosecond-pulse sliding discharge. The

Song Huimin; Jia Min; Liang Hua; Wu Yun

2011-01-01

18

Combustion stabilization using serpentine plasma actuators  

NASA Astrophysics Data System (ADS)

This letter presents a numerical model for combustion stabilization with plasma actuators. Recently, we demonstrated that serpentine actuators induce complex neighboring flow structures due to pinching and spreading effects suitable for rapid flow mixing. Here, the influence of serpentine plasma actuator is numerically investigated on inner and outer recirculation zones of a gas turbine combustor. Beyond benchmarking with reported experimental data, we show that the swirl generated by the serpentine plasma actuators creates local low velocity regions stabilizing the flame. Such simple flow-mixing device does not need any moving parts, hence may be useful in the any combustors.

Wang, Chin-Cheng; Roy, Subrata

2011-07-01

19

Two-Dimensional Plasma Actuator Analysis Code.  

National Technical Information Service (NTIS)

A two-dimensional plasma actuator analysis code has been developed. A time-accurate Navier-Stokes CFD code was coupled with a time-dependent, phenomenological model of an alternating current, single dielectric barrier discharge plasma actuator. The accura...

S. Ellison

2006-01-01

20

Bluff Body Flow Control Using Plasma Actuators  

NASA Astrophysics Data System (ADS)

In this study, the use of single dielectric barrier discharge plasma actuators for the control of bluff body flow separation is investigated. In particular, surface mounted plasma actuators are used to reduce both drag and unsteady vortex shedding from circular cylinders in cross-flow. It is demonstrated that the plasma-induced surface blowing gives rise to a local Coanda effect that promotes the maintenance of flow attachment. Large reductions in vortex shedding and drag are demonstrated for Reynolds numbers ˜ 10^410^5. Both steady and unsteady plasma-induced surface blowing is explored. Results are presented from experiments involving both two and four surface mounted actuators.

Thomas, Flint

2005-11-01

21

Serpentine geometry plasma actuators for flow control  

NASA Astrophysics Data System (ADS)

In this paper, a curved class of plasma actuator geometries is presented. The intension of this paper is to extend the versatility of a dielectric barrier discharge plasma actuator by modifying the geometry of its electrodes, so that the plasma generated body force is able to excite a broader spectrum of flow physics than plasma actuators with a more standard geometry. Two examples of flow control are demonstrated numerically. An example of this class of actuators is shown to generate boundary layer streaks, which can be used to accelerate or delay the laminar to turbulent transition process, depending on how they are applied. Simulations of a low Reynolds number airfoil are also performed using additional examples of this class of actuators, where it is shown that this plasma actuator geometry is able to introduce energy into and excite a secondary instability mode and increase unsteady kinetic energy in the boundary layer. These two cases show that this general class of curved actuators possesses an increased versatility with respect to the standard geometry actuators.

Riherd, Mark; Roy, Subrata

2013-08-01

22

Plasma actuators for bluff body flow control  

NASA Astrophysics Data System (ADS)

The aerodynamic plasma actuators have shown to be efficient flow control devices in various applications. In this study the results of flow control experiments utilizing single dielectric barrier discharge plasma actuators to control flow separation and unsteady vortex shedding from a circular cylinder in cross-flow are reported. This work is motivated by the need to reduce landing gear noise for commercial transport aircraft via an effective streamlining created by the actuators. The experiments are performed at Re D = 20,000...164,000. Circular cylinders in cross-flow are chosen for study since they represent a generic flow geometry that is similar in all essential aspects to a landing gear oleo or strut. The minimization of the unsteady flow separation from the models and associated large-scale wake vorticity by using actuators reduces the radiated aerodynamic noise. Using either steady or unsteady actuation at ReD = 25,000, Karman shedding is totally eliminated, turbulence levels in the wake decrease significantly and near-field sound pressure levels are reduced by 13.3 dB. Unsteady actuation at an excitation frequency of St D = 1 is found to be most effective. The unsteady actuation also has the advantage that total suppression of shedding is achieved for a duty cycle of only 25%. However, since unsteady actuation is associated with an unsteady body force and produces a tone at the actuation frequency, steady actuation is more suitable for noise control applications. Two actuation strategies are used at ReD = 82,000: spanwise and streamwise oriented actuators. Near field microphone measurements in an anechoic wind tunnel and detailed study of the near wake using LDA are presented in the study. Both spanwise and streamwise actuators give nearly the same noise reduction level of 11.2 dB and 14.2 dB, respectively, and similar changes in the wake velocity profiles. The contribution of the actuator induced noise is found to be small compared to the natural shedding noise. A tandem cylinder configuration with the plasma actuation on the upstream cylinder is investigated using surface dynamic pressure sensors. As a result of the plasma actuation, the surface pressure fluctuations on the downstream cylinder are reduced by about two times at the free-stream velocity of 40 m/s (ReD = 164,000). In addition, this study presents the results of a parametric experimental investigation aimed at optimizing the body force produced by single dielectric barrier discharge (SDBD) plasma actuators used for aerodynamic flow control. A primary goal of the study is the improvement of actuator authority for flow control applications at higher Reynolds number than previously possible. The study examines the effects of dielectric material and thickness, applied voltage amplitude and frequency, voltage waveform, exposed electrode geometry, covered electrode width and multiple actuator arrays. The metric used to evaluate the performance of the actuator in each case is the measured actuator-induced thrust which is proportional to the total body force. It is demonstrated that actuators constructed with thick dielectric material of low dielectric constant and operated at low frequency AC voltage produce a body force that is an order of magnitude larger than that obtained by the Kapton-based actuators used in many previous plasma flow control studies. These actuators allow operation at much higher applied voltages without the formation of discrete streamers which lead to body force saturation.

Kozlov, Alexey V.

23

Dielectric barrier discharge plasma actuator for flow control  

NASA Astrophysics Data System (ADS)

Electrohydrodynamic (EHD) and magnetohydrodynamic phenomena are being widely studied for aerodynamic applications. The major effects of these phenomena are heating of the gas, body force generation, and enthalpy addition or extraction, [1, 2, 3]. In particular, asymmetric dielectric barrier discharge (DBD) plasma actuators are known to be effective EHD device in aerodynamic control, [4, 5]. Experiments have demonstrated their effectiveness in separation control, acoustic noise reduction, and other aeronautic applications. In contrast to conventional DBD actuators driven by sinusoidal voltages, we proposed and used a voltage profile consisting of nanosecond pulses superimposed on dc bias voltage. This produces what is essentially a non-self-sustained discharge: the plasma is generated by repetitive short pulses, and the pushing of the gas occurs primarily due to the bias voltage. The advantage of this non-self-sustained discharge is that the parameters of ionizing pulses and the driving bias voltage can be varied independently, which adds flexibility to control and optimization of the actuators performance. Experimental studies were conducted of a flow induced in a quiescent room air by a single DBD actuator. A new approach for non-intrusive diagnostics of plasma actuator induced flows in quiescent gas was proposed, consisting of three elements coupled together: the Schlieren technique, burst mode of plasma actuator operation, and 2-D numerical fluid modeling. During the experiments, it was found that DBD performance is severely limited by surface charge accumulation on the dielectric. Several ways to mitigate the surface charge were found: using a reversing DC bias potential, three-electrode configuration, slightly conductive dielectrics, and semi conductive coatings. Force balance measurements proved the effectiveness of the suggested configurations and advantages of the new voltage profile (pulses+bias) over the traditional sinusoidal one at relatively low voltages. In view of practical applications certain questions have been also addressed, such as electrodynamic effects which accompany scaling of the actuators to real size models, and environmental effects of ozone production by the plasma actuators.

Opaits, Dmitry Florievich

24

Effective Discharge Dynamics for Plasma Actuators.  

National Technical Information Service (NTIS)

Some effective control parameters for active separation mitigation using asymmetric dielectric barrier discharges is studied by considering the weakly ionized gas flow past a flat plate at angle of attack. A self-consistent plasma actuator model is employ...

D. V. Gaitonde H. Kumar K. P. Singh M. Visbal S. Roy

2006-01-01

25

Tip Clearance Control Using Plasma Actuators.  

National Technical Information Service (NTIS)

This report documents experimental results from a series of experiments using active flow control to improve the performance and efficiency of turbine tip clearance flows. The flow control was based on plasma actuators. Two experimental facilities were us...

S. C. Morris T. C. Corke

2007-01-01

26

Experimental Investigation of DBD Plasma Actuators Driven by Repetitive High Voltage Nanosecond Pulses with DC or Low-Frequency Sinusoidal Bias  

Microsoft Academic Search

Experimental studies were conducted of a flow induced in an initially quiescent room air by a single asymmetric dielectric barrier discharge driven by voltage waveforms consisting of repetitive nanosecond high-voltage pulses superimposed on DC or alternating sinusoidal or square-wave bias voltage. To characterize the pulses and to optimize their matching to the plasma, a numerical code for short pulse calculations

Dmitry F. Opaits; Gabriele Neretti; Alexandre V. Likhanskii; Sohail Zaidi; Mikhail N. Shneider; Richard B. Miles; Sergey O. Macheret

2007-01-01

27

Microscale plasma actuators for improved thrust density  

SciTech Connect

We present a study of the dielectric barrier discharge (DBD) plasma actuators for microscale applications. Traditional macroscale DBD actuators suffer from relatively small actuation effect as characterized by small induced force density and resulting flow velocity. As a remedy we propose microscale plasma actuators that may induce orders of magnitude higher force density. We study the physics of such actuation using a multiscale ionized gas flow code based on the high-fidelity finite-element procedure. First, a two-dimensional volume discharge with nitrogen as a working gas is investigated using a first-principles approach solving coupled system of hydrodynamic plasma equations and Poisson equation for ion density, electron density, and electric field distribution. The quasi-neutral plasma and the sheath regions are identified. As the gap between electrodes is reduced, the sheath structure dominates the plasma region. Second, we simulate a first generation plasma micropump. We solve multiscale plasma-gas interaction inside a two-dimensional cross section of the microscale pump geometry. The result shows that a reasonable mass flow rate can be pumped using a set of small active electrodes.

Wang, C.-C.; Roy, Subrata [Department of Mechanical and Aerospace Engineering, Computational Plasma Dynamics Laboratory and Test Facility, Applied Physics Research Group, University of Florida, Gainesville, Florida 32611 (United States)

2009-07-01

28

Hybrid transition control approach for plasma actuators  

NASA Astrophysics Data System (ADS)

This work reports on the development of a novel hybrid transition control method for single DBD plasma actuators. The experiments have been carried out on a natural laminar flow airfoil in a wind tunnel and combine two methods previously used for transition control purposes with DBD plasma actuators: boundary-layer stabilization by quasi-steady wall-parallel momentum addition, and active wave cancelation by linear superposition utilizing modulated momentum injection. For this purpose, the modulated body force is controlled using an improved extremum seeking controller based on an extended Kalman filter. Combining the two methods in a single actuator has advantages. Applied to 2-D Tollmien-Schlichting waves, the achievable transition delay in hybrid mode is significantly larger than the isolated effects, while the energy consumption remains almost unchanged compared to the case of continuous actuation. For a Reynolds number of , a transition delay of could be observed.

Kurz, A.; Goldin, N.; King, R.; Tropea, C.; Grundmann, S.

2013-11-01

29

Atmospheric Plasma Actuators for Aeroacoustic Applications  

Microsoft Academic Search

A plasma actuator operating in atmospheric air was applied to attenuate low-speed cavity flow-induced tones. It demonstrated the working effect of glow discharges for aeroacoustic applications. The details of the overall system were summarized. To improve the power efficiency, several plasma driving signals were tested on a real-time system. The corresponding results were discussed in this paper.

Xun Huang; Sammie Chan; Xin Zhang

2007-01-01

30

A Study on a Microwave-Driven Smart Material Actuator  

NASA Technical Reports Server (NTRS)

NASA s Next Generation Space Telescope (NGST) has a large deployable, fragmented optical surface (greater than or = 2 8 m in diameter) that requires autonomous correction of deployment misalignments and thermal effects. Its high and stringent resolution requirement imposes a great deal of challenge for optical correction. The threshold value for optical correction is dictated by lambda/20 (30 nm for NGST optics). Control of an adaptive optics array consisting of a large number of optical elements and smart material actuators is so complex that power distribution for activation and control of actuators must be done by other than hard-wired circuitry. The concept of microwave-driven smart actuators is envisioned as the best option to alleviate the complexity associated with hard-wiring. A microwave-driven actuator was studied to realize such a concept for future applications. Piezoelectric material was used as an actuator that shows dimensional change with high electric field. The actuators were coupled with microwave rectenna and tested to correlate the coupling effect of electromagnetic wave. In experiments, a 3x3 rectenna patch array generated more than 50 volts which is a threshold voltage for 30-nm displacement of a single piezoelectric material. Overall, the test results indicate that the microwave-driven actuator concept can be adopted for NGST applications.

Choi, Sang H.; Chu, Sang-Hyon; Kwak, M.; Cutler, A. D.

2001-01-01

31

Cylinder Flow Control Using Plasma Actuators  

NASA Astrophysics Data System (ADS)

In this study the results of flow control experiments utilizing single dielectric barrier discharge plasma actuators to control flow separation and unsteady vortex shedding from a circular cylinder in cross-flow are reported. Two optimized quartz dielectric plasma actuators mounted on the cylinder surface utilizing an improved saw-tooth waveform high-voltage generator allowed flow control at Reynolds number approaching supercritical. Using either steady or unsteady actuation, it is demonstrated that the plasma-induced surface blowing gives rise to a local Coanda effect that promotes the maintenance of flow attachment. PIV based flow fields and wake velocity profiles obtained with hot-wire anemometry show large reductions in vortex shedding, wake width and turbulence intensity.

Kozlov, Alexey; Thomas, Flint

2007-11-01

32

An arm wrestling robot driven by dielectric elastomer actuators  

NASA Astrophysics Data System (ADS)

The first arm wrestling match between a human arm and a robotic arm driven by electroactive polymers (EAP) was held at the EAPAD conference in 2005. The primary objective was to demonstrate the potential of the EAP actuator technology for applications in the field of robotics and bioengineering. The Swiss Federal Laboratories for Materials Testing and Research (Empa) was one of the three organizations participating in this competition. The robot presented by Empa was driven by a system of rolled dielectric elastomer (DE) actuators. Based on the calculated stress condition in the rolled actuator, a low number of pre-strained DE film wrappings were found to be preferential for achieving the best actuator performance. Because of the limited space inside the robot body, more than 250 rolled actuators with small diameters were arranged in two groups according to the human agonist-antagonist muscle configuration in order to achieve an arm-like bidirectional rotation movement. The robot was powered by a computer-controlled high voltage amplifier. The rotary motion of the arm was activated and deactivated electrically by corresponding actuator groups. The entire development process of the robot is presented in this paper where the design of the DE actuators is of primary interest. Although the robot lost the arm wrestling contest against the human opponent, the DE actuators have demonstrated very promising performance as artificial muscles. The scientific knowledge gained during the development process of the robot has pointed out the challenges to be addressed for future improvement in the performance of rolled dielectric elastomer actuators.

Kovacs, Gabor; Lochmatter, Patrick; Wissler, Michael

2007-04-01

33

Effective Discharge Dynamics for Plasma Actuators  

Microsoft Academic Search

Some effective control parameters for active separation mitigation using asymmetric dielectric barrier discharges is studied by considering the weakly ionized gas flow past a flat plate at angle of attack. A self- consistent plasma actuator model is employed to couple the electric force field to the momentum of the neutral gas. The equations governing the motion of electrons, ions and

Subrata Roy; K. P. Singh; Haribalan Kumar; Datta V. Gaitonde; Miguel Visbal

34

Pressure Dependence of Plasma Actuated Flow Control  

NASA Astrophysics Data System (ADS)

An experimental investigation was conducted to determine how Single Dielectric-Barrier Discharge (SDBD) plasma actuators performed under variable ambient pressure. The static pressure was varied from 0.17 to 9.0 bar. The plasma initiation voltage and static thrust were measured and compared to similar data in literature. The results showed that at a given pressure, the plasma initiation voltage scaled with the actuator capacitor per unit area. The measured thrust showed the previously observed power-law relation with voltage, but the exponent varied with pressure. These trends were evaluated against simulations from the SDBD Space-Time Lumped Element Model. Parameters in the model affected by ambient pressure (capacitance, resistance, and Debye length of the air) were then systematically investigated to determine their effects on the plasma-produced body force. The overall trends were best modeled through a pressure dependence of the Debye length.

Valerioti, Joseph; Corke, Thomas

2010-11-01

35

Dielectric Barrier Discharge Plasma Actuator for Flow Control  

NASA Technical Reports Server (NTRS)

This report is Part II of the final report of NASA Cooperative Agreement contract no. NNX07AC02A. It includes a Ph.D. dissertation. The period of performance was January 1, 2007 to December 31, 2010. Part I of the final report is the overview published as NASA/CR-2012- 217654. Asymmetric dielectric barrier discharge (DBD) plasma actuators driven by nanosecond pulses superimposed on dc bias voltage are studied experimentally. This produces non-self-sustained discharge: the plasma is generated by repetitive short pulses, and the pushing of the gas occurs primarily due to the bias voltage. The parameters of ionizing pulses and the driving bias voltage can be varied independently, which adds flexibility to control and optimization of the actuators performance. The approach consisted of three elements coupled together: the Schlieren technique, burst mode of plasma actuator operation, and 2-D numerical fluid modeling. During the experiments, it was found that DBD performance is severely limited by surface charge accumulation on the dielectric. Several ways to mitigate the surface charge were found: using a reversing DC bias potential, three-electrode configuration, slightly conductive dielectrics, and semi conductive coatings. Force balance measurements proved the effectiveness of the suggested configurations and advantages of the new voltage profile (pulses+bias) over the traditional sinusoidal one at relatively low voltages. In view of practical applications certain questions have been also addressed, such as electrodynamic effects which accompany scaling of the actuators to real size models, and environmental effects of ozone production by the plasma actuators.

Opaits, Dmitry, F.

2012-01-01

36

Scalability of Localized Arc Filament Plasma Actuators  

NASA Technical Reports Server (NTRS)

Temporal flow control of a jet has been widely studied in the past to enhance jet mixing or reduce jet noise. Most of this research, however, has been done using small diameter low Reynolds number jets that often have little resemblance to the much larger jets common in real world applications because the flow actuators available lacked either the power or bandwidth to sufficiently impact these larger higher energy jets. The Localized Arc Filament Plasma Actuators (LAFPA), developed at the Ohio State University (OSU), have demonstrated the ability to impact a small high speed jet in experiments conducted at OSU and the power to perturb a larger high Reynolds number jet in experiments conducted at the NASA Glenn Research Center. However, the response measured in the large-scale experiments was significantly reduced for the same number of actuators compared to the jet response found in the small-scale experiments. A computational study has been initiated to simulate the LAFPA system with additional actuators on a large-scale jet to determine the number of actuators required to achieve the same desired response for a given jet diameter. Central to this computational study is a model for the LAFPA that both accurately represents the physics of the actuator and can be implemented into a computational fluid dynamics solver. One possible model, based on pressure waves created by the rapid localized heating that occurs at the actuator, is investigated using simplified axisymmetric simulations. The results of these simulations will be used to determine the validity of the model before more realistic and time consuming three-dimensional simulations are conducted to ultimately determine the scalability of the LAFPA system.

Brown, Clifford A.

2008-01-01

37

Mechanisms of plasma actuators for hypersonic flow control  

Microsoft Academic Search

A summary of recent research progress in hypersonic plasma actuators for flow control is attempted. It is found that the most effective plasma actuator is derived from an electromagnetic perturbation and amplifies by a subsequent viscous–inviscid interaction. Computational efforts using drift-diffusion theory and a simple phenomenological plasma model, as well as experiments in a hypersonic plasma channel, have shown the

J. S. Shang; S. T. Surzhikov; R. Kimmel; D. Gaitonde; J. Menart; J. Hayes

2005-01-01

38

Scratch Drive Actuator Driven Self-assembled Variable Optical Attenuator  

Microsoft Academic Search

This paper describes the new concept and design for a self-assembled variable optical attenuator (VOA) derived by using surface micromachining technology. A residual stress-induced flexure curved beam with corrugated trench anchors can lift up the reflective mirror shutter. This self-assembled reflective shutter can be driven by a set of scratch drive actuator (SDA), then slides into the spacing between input

Chengkuo Lee; Yen-Jyh Lai; Chia-Yu Wu; Yu-Shen Lin; Ming Hung Tasi; Ruey-Shing Huang; Min-Shyong Lin

2004-01-01

39

Variable area nozzle for gas turbine engines driven by shape memory alloy actuators  

NASA Technical Reports Server (NTRS)

A gas turbine engine includes a variable area nozzle having a plurality of flaps. The flaps are actuated by a plurality of actuating mechanisms driven by shape memory alloy (SMA) actuators to vary fan exist nozzle area. The SMA actuator has a deformed shape in its martensitic state and a parent shape in its austenitic state. The SMA actuator is heated to transform from martensitic state to austenitic state generating a force output to actuate the flaps. The variable area nozzle also includes a plurality of return mechanisms deforming the SMA actuator when the SMA actuator is in its martensitic state.

Rey, Nancy M. (Inventor); Miller, Robin M. (Inventor); Tillman, Thomas G. (Inventor); Rukus, Robert M. (Inventor); Kettle, John L. (Inventor); Dunphy, James R. (Inventor); Chaudhry, Zaffir A. (Inventor); Pearson, David D. (Inventor); Dreitlein, Kenneth C. (Inventor); Loffredo, Constantino V. (Inventor)

2001-01-01

40

Active Flow Control by Surface Smooth Plasma Actuators  

Microsoft Academic Search

\\u000a Surface smooth plasma actuators were used to control leading-edge flow separation on the flying wing airfoil Eppler E338 for\\u000a angles of attack of up to 12° past stall at low Reynolds numbers. The plasma actuators were operated over a range of free-stream\\u000a speeds from 2.2 to 6.6 m\\/s giving chord Reynolds numbers from 26K to 79K. The plasma actuators produced

B. Göksel; I. Rechenberg

41

CONTROL OF LAMINAR AND TURBULENT SHEAR FLOWS USING PLASMA ACTUATORS  

Microsoft Academic Search

The use of AC discharge plasma actuators in flow control applications is experimentally investigated using PIV. Exper- imental observations include actuators in quiescent flow, a flat plate boundary layer, and a low pressure turbine blade cascade. The actuators are shown to generate a high ve- locity region near the wall downstream of the interface with large fluctuating components. Even in

Jamey D. Jacob; Karthik Ramakumar; Rich Anthony; Richard B. Rivir

42

Scratch Drive Actuator Driven Self-assembled Variable Optical Attenuator  

NASA Astrophysics Data System (ADS)

This paper describes the new concept and design for a self-assembled variable optical attenuator (VOA) derived by using surface micromachining technology. A residual stress-induced flexure curved beam with corrugated trench anchors can lift up the reflective mirror shutter. This self-assembled reflective shutter can be driven by a set of scratch drive actuator (SDA), then slides into the spacing between input and output fiber ends. The attenuation range of proposed microelectromechanical systems (MEMS) VOA is determined by the vertical position of self-assembled pop-up polysilicon reflective shutter in which it is controlled by the value of applied dc voltage. This new VOA demonstrates continuous attenuation capability and wide attenuation range based on using an electrostatic actuator that is a new residual stress-induced flexure curved beam with corrugated-trench anchors. This device exhibits attenuation range of 70 dB and insertion loss less than 1 dB.

Lee, Chengkuo; Lai, Yen-Jyh; Wu, Chia-Yu; Lin, Yu-Shen; Tasi, Ming Hung; Huang, Ruey-Shing; Lin, Min-Shyong

2004-06-01

43

Experimental Investigation on Airfoil Shock Control by Plasma Aerodynamic Actuation  

NASA Astrophysics Data System (ADS)

An experimental investigation on airfoil (NACA64—215) shock control is performed by plasma aerodynamic actuation in a supersonic tunnel (Ma = 2). The results of schlieren and pressure measurement show that when plasma aerodynamic actuation is applied, the position moves forward and the intensity of shock at the head of the airfoil weakens. With the increase in actuating voltage, the total pressure measured at the head of the airfoil increases, which means that the shock intensity decreases and the control effect increases. The best actuation effect is caused by upwind-direction actuation with a magnetic field, and then downwind-direction actuation with a magnetic field, while the control effect of aerodynamic actuation without a magnetic field is the most inconspicuous. The mean intensity of the normal shock at the head of the airfoil is relatively decreased by 16.33%, and the normal shock intensity is relatively reduced by 27.5% when 1000 V actuating voltage and upwind-direction actuation are applied with a magnetic field. This paper theoretically analyzes the Joule heating effect generated by DC discharge and the Lorentz force effect caused by the magnetic field. The discharge characteristics are compared for all kinds of actuation conditions to reveal the mechanism of shock control by plasma aerodynamic actuation.

Sun, Quan; Cheng, Bangqin; Li, Yinghong; Cui, Wei; Jin, Di; Li, Jun

2013-11-01

44

Experimental Demonstration of Multi Barrier Plasma Actuators (MBPA).  

National Technical Information Service (NTIS)

This report is a summary of a one-year effort on demonstration experiments of a novel set of multi-barrier plasma actuators (MBPA) by the PI s research team. The typical dielectric barrier discharge (DBD) plasma actuator consists of two electrodes separat...

R. Durscher S. Roy

2011-01-01

45

Experimental damping of boundary-layer oscillations using DBD plasma actuators  

Microsoft Academic Search

In the present work artificially excited Tollmien–Schlichting waves were cancelled using plasma actuators operated both in continuous and pulsed modes. To achieve this a vibrating surface, driven by an electromagnetic turbulator, was flush-mounted in a flat plate to excite the TS waves. These were amplified by an adverse pressure gradient induced by an insert on the upper wall of the

Sven Grundmann; Cameron Tropea

2009-01-01

46

Modeling plasma actuators with air chemistry for effective flow control  

SciTech Connect

An asymmetric dielectric barrier discharge model is presented for real gas air chemistry using a self-consistent multibody system of plasma, dielectric, and neutral gas modeled together to predict the electrodynamic force imparted to the working gas. The equations governing the motion of charged and neutral species are solved with Poisson equation using finite element method using a Galerkin weak formulation. Electric field profile changes with the increase in grounded electrode and the density increases downstream. The electrodynamic force development mechanism is studied over a flat plate due to charge and neutral species production from adjacent air in a radio frequency driven barrier discharge. The time average of the force shows mostly acceleration above the actuator. Numerical simulation confirms that the magnitude of force increases very slightly with the increase in the length of grounded electrode.

Singh, Kunwar Pal; Roy, Subrata [Computational Plasma Dynamics Laboratory and Test Facility, Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611-6300 (United States)

2007-06-15

47

Experimental transition delay using glow-discharge plasma actuators  

Microsoft Academic Search

In the present work plasma actuators were applied in a flat-plate boundary layer with an adverse pressure gradient to influence\\u000a the transition of the boundary layer. The first actuator downstream of the leading edge is operated in pulsed mode to introduce\\u000a perturbations into the boundary layer to promote transition. Two steady operating actuators further downstream damp the perturbations\\u000a significantly, which

Sven Grundmann; Cameron Tropea

2007-01-01

48

Parametric Optimization of Single Dielectric Barrier Discharge (SDBD) Plasma Actuators.  

NASA Astrophysics Data System (ADS)

There has been growing interest in flow control using dielectric barrier discharge plasma actuators in recent years. However, studies regarding optimization of plasma actuators are relatively scarce. Current study is intended to optimize the body force produced by plasma discharge (steady and unsteady) which is a function of various parameters such as dielectric material, size of electrodes, their overlap, frequency, voltage, etc. Detailed experiments are performed in a controlled environment with no-external-flow condition with several different dielectric materials of various thicknesses. Plasma induced velocity (using glass pitot probe), body force (using high precision weighing scale), and power dissipation are measured at various voltages and frequencies. Optimal voltage waveform and frequency has been found which resulted in time averaged maximum induced velocity and body force. This has resulted in an order of magnitude improvement of the actuator effect. The results obtained follow a relatively simple mathematical model that allows one to derive analytical expressions for electrical characteristics of plasma actuators.

Iqbal, Muhammad O.; Kozlov, Alexey; Schatzman, David; Othman, Hesham; Thomas, Flint; Corke, Thomas

2006-11-01

49

Surface plasma actuators modeling for flow control  

NASA Astrophysics Data System (ADS)

The surface plasma actuators over the entire speed region have been intensely investigated for flow control. Most of the fundamental phenomena have been firmly identified by experimental observations but ambiguities still remained. The direct computational simulation for multiple microdischarges is presently beyond our reach, thus the essential physics may be better understood on the framework of physics-based modeling. To achieve this objective, the drift-diffusion approximation is adopted as a transport property approximation to the nonequilibrium air plasma. The most challenging issue of electron impact ionization process at the low-temperature environment is addressed by the Townsend mechanism together with electron attachment, detachment, bulk, and ion-ion recombination. The effects and quantifications of Joule heating, periodic electrostatic force, as well as, the Lorentz acceleration for flow control are examined. The clarification to the hot spot of heat transfer in direct current discharge and the orientations of the periodic force associated with AC cycle of dielectric barrier discharge are also included.

Shang, J. S.; Huang, P. G.

2014-05-01

50

Characterization of linear plasma synthetic jet actuators in an initially quiescent medium  

SciTech Connect

The plasma synthetic jet actuator (PSJA) is a geometrical variant of the aerodynamic plasma actuator that can be used to produce zero-mass flux jets similar to those created by mechanical devices. This jet can be either three-dimensional using annular electrode arrays (annular PSJA) or nearly two dimensional using two rectangular-strip exposed electrodes and one embedded electrode (linear PSJA). Unsteady pulsing of the PSJA at time scales decoupled to the ac input frequency results in a flow field dominated by counter-rotating vortical structures similar to conventional synthetic jets, and the peak velocity and momentum of the jet is found to be affected by a combination of the pulsing frequency and input power. This paper investigates the fluid dynamic characteristics of linear plasma synthetic jet actuators in an initially quiescent medium. Two-dimensional particle image velocimetry measurements on the actuator are used to validate a previously developed numerical model wherein the plasma behavior is introduced into the Navier-Stokes equations as an electrohydrodynamic force term calculated from Maxwell's equations and solved for the fluid momentum. The numerical model was implemented in an incompressible, unstructured grid code. The results of the simulations are observed to reproduce some aspects of the qualitative and quantitative experimental behavior of the jet for steady and pulsed modes of actuator operation. The self-similarity behavior of plasma synthetic jets are examined and compared to mechanically driven continuous and synthetic jets.

Santhanakrishnan, Arvind [Department of Mathematics, Phillips Hall, CB 3250, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3250 (United States); Reasor, Daniel A. Jr. [School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); LeBeau, Raymond P. Jr. [Department of Mechanical Engineering, University of Kentucky, Lexington, Kentucky 40506 (United States)

2009-04-15

51

Plasma Actuators for Separation Control on Stationary and Oscillating Airfoils.  

National Technical Information Service (NTIS)

Given the importance of separation control associated with retreating blade stall on helicopters, the primary objective of this work was to develop a plasma actuator flow control device for its use in controlling leading-edge separation on stationary and ...

M. L. Post T. Corke

2004-01-01

52

Determination of the phase-resolved body force produced by a dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

Dielectric barrier discharge (DBD) plasma actuators are a promissing tool for active flow control applications. In order to determine the time-resolved body force induced by a DBD plasma actuator, which was driven by a 9.5 kHz sinusoidal signal, the flow has to be captured with a high spatial and temporal resolution. For this purpose we applied a laser Doppler velocity profile sensor for the measurements of the two-component velocity field and Lagrangian acceleration. A temporal and spatial resolution of 7.3 µs and 40 µm was achieved. We present the time-resolved local flow behaviours induced by the DBD actuator. Based on these measurement data the time-resolved body force generated by the plasma actuator was derived. Experiments revealed a defined dependence of the force direction on the phase angle of the ac operating voltage. This result is a contribution to the controversy on the temporal behaviour of the body force of plasma actuators.

Neumann, Mathias; Friedrich, Christian; Czarske, Jürgen; Kriegseis, Jochen; Grundmann, Sven

2013-01-01

53

Jet noise control using the dielectric barrier discharge plasma actuators  

NASA Astrophysics Data System (ADS)

We study experimentally how plasma actuators operating on the basis of surface barrier high-frequency discharge affect jet noise characteristics. The results of investigations of air jets (100-200 m/s) have demonstrated that the studied plasma actuators have control authority over the noise characteristics of these jets. An actuator's effect on the jet in the applied configuration is related to acoustic discharge excitation and to a large extent is similar to the well-known Vlasov-Ginevsky effect. It has been shown that jet excitation in the case of St ˜ 0.5 using the barrier-discharge plasma actuator leads to broadband amplification of jet sound radiation. The jet excitation in the case of St > 2 leads to broadband noise reduction if the action is sufficiently intensive.

Kopiev, V. F.; Bityurin, V. A.; Belyaev, I. V.; Godin, S. M.; Zaitsev, M. Yu.; Klimov, A. I.; Kopiev, V. A.; Moralev, I. A.; Ostrikov, N. N.

2012-07-01

54

Separation Control on Generic ROBIN Rotorcraft Fuselage Using Plasma Actuators  

NASA Astrophysics Data System (ADS)

Active flow control, in the form of dielectric barrier discharge (DBD) plasma actuators, is applied to a NASA ROBIN mod7 generic rotorcraft fuselage model. The control objective is reduce the massive 3-D flow separation occurring over the aft ramp section of the fuselage, thereby improving the vehicle flight characteristics. The plasma actuation methods investigated include: plasma streamwise vortex generators (PSVGs), as well as steady and unsteady spanwise actuation, combined with passive geometric modifications to the ramp section. Experiments were conducted at freestream Mach and Reynolds numbers of M?= 0.12 and ReL= 2.65 x10^6, respectively. Aerodynamic loads from each technique were quantified by means of 3-component force balance measurements (drag, lift, and pitching moment), a 128 count static pressure array, and time-resolved PIV wake surveys. Results are compared with previous studies that utilized active flow control in the form of pulsed jets and combustion actuators.

Coleman, Dustin

2011-11-01

55

Thermomechanically Driven Polymer Actuator for High-Precision Optical Alignment  

Microsoft Academic Search

Precise thermomechanical positioning has been demonstrated in an actuator device based on a silicone elastomer with a high thermal expansion coefficient. The actuator performance has been characterized using optical microscopy, and the actuator has been deployed in an optical coupling experiment to demonstrate the precise positioning of a ball lens between two single-mode fibers. Tuning of the coupling efficiency has

G. Jordan; A. M. Lyons

2007-01-01

56

A small biomimetic quadruped robot driven by multistacked dielectric elastomer actuators  

NASA Astrophysics Data System (ADS)

A kind of dielectric elastomer (DE) material, called ‘synthetic elastomer’, has been developed based on acrylonitrile butadiene rubber (NBR) to be used as a dielectric elastomer actuator (DEA). By stacking single layers of synthetic elastomer, a linear actuator, called a multistacked actuator, is produced, and used by mechatronic and robotic systems to generate linear motion. In this paper, we demonstrate the application of the multistacked dielectric elastomer actuator in a biomimetic legged robot. A miniature robot driven by a biomimetic actuation system with four 2-DOF (two-degree-of-freedom) legged mechanisms is realized. Based on the experimental results, we evaluate the performance of the proposed robot and validate the feasibility of the multistacked actuator in a locomotion system as a replacement for conventional actuators.

Nguyen, Canh Toan; Phung, Hoa; Dat Nguyen, Tien; Lee, Choonghan; Kim, Uikyum; Lee, Donghyouk; Moon, Hyungpil; Koo, Jachoon; Nam, Jae-do; Ryeol Choi, Hyouk

2014-06-01

57

Surface charge in dielectric barrier discharge plasma actuators  

SciTech Connect

Direct measurements of the dielectric surface potential and its dynamics in asymmetric dielectric barrier discharge (DBD) plasma actuators show that the charge builds up at the dielectric surface and extends far downstream of the plasma. The surface charge persists for a long time (tens of minutes) after the driving voltage has been turned off. For a sinusoidal voltage waveform, the dielectric surface charges positively. With the voltage waveform consisting of nanosecond pulses superimposed on a dc bias, the sign of the dielectric surface charge is the same as the sign (polarity) of the bias voltage. The surface charging significantly affects DBD plasma actuator performance.

Opaits, D. F.; Shneider, M. N.; Miles, Richard B. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Likhanskii, A. V. [Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Macheret, S. O. [Lockheed Martin Aeronautics Company, Palmdale, California 93599 (United States)

2008-07-15

58

Boundary Layer Control by Means of Plasma Actuators  

SciTech Connect

The development of controlled transition in a flat-plate boundary layer is investigated using Large Eddy Simulations (LES) with the dynamic Smagorinsky model. The analysis of flow control with the objective to optimize the effects of Tollmien-Schlichting waves on a flat plate by means of plasma actuators was studied. The plasma effect is modeled as a body force in the momentum equations. These equations are solved in a uniform grid using a 2nd-order finite difference scheme in time and space. The response of plasma actuators operating in different time-dependent conditions, produced by transient or periodic inputs at different frequencies, is also analyzed.

Quadros, R. [UFRGS/PPGMAp-TUD-Stroemungslehre und Aerodynamik, Technische Universitaet Darmstadt, Petersenstr. 30, 64287 Darmstadt (Germany); Bortoli, A. L. de [UFRGS/DMPA-Departamento de Matematica Pura e Aplicada, Bento Goncalves 9500, Agronomia-P.O. Box 15080, Porto Alegre-RS (Brazil); Tropea, C. [TUD/SLA-Stroemungslehre und Aerodynamik, Technische Universitaet Darmstadt, Petersenstr. 30, 64287 Darmstadt (Germany)

2007-09-06

59

Active cancellation of artificially introduced Tollmien–Schlichting waves using plasma actuators  

Microsoft Academic Search

In the present work artificially excited Tollmien–Schlichting (TS) waves were cancelled using plasma actuators operated in\\u000a pulsed mode. In order to achieve this a vibrating surface driven by an electromagnetic turbulator was flush mounted in a flat\\u000a plate to excite the TS waves. These were amplified by an adverse pressure gradient induced by an insert on the upper wall\\u000a of

Sven Grundmann; Cameron Tropea

2008-01-01

60

Control of an axisymmetric subsonic air jet by plasma actuator  

Microsoft Academic Search

It is known that surface non-thermal plasma actuators have proved their efficiency for aerodynamics flow control. In this\\u000a study, a dielectric barrier discharge (DBD) is mounted on the diffuser of an axisymmetric turbulent air jet in order to control\\u000a the flow separation along a 12-degree diffuser bevel. The momentum created by the actuator is applied to separate an air flow

N. Benard; J. Jolibois; M. Forte; G. Touchard; E. Moreau

2007-01-01

61

Effects of Boundary Layer Flow Control Using Plasma Actuator Discharges.  

National Technical Information Service (NTIS)

This study addresses the usage and effects of atmospheric plasma discharges on the near wall flow conditions for a Pak-B low-pressure turbine blade. A plasma actuator was built normal to the freestream flow in a low-speed wind tunnel. The test section of ...

J. M. Newcamp

2005-01-01

62

Experimental Investigation of Hypersonic Flow and Plasma Aerodynamic Actuation Interaction  

NASA Astrophysics Data System (ADS)

For hypersonic flow, it was found that the most effective plasma actuator is derived from an electromagnetic perturbation. An experimental study was performed between hypersonic flow and plasma aerodynamic actuation interaction in a hypersonic shock tunnel, in which a Mach number of 7 was reached. The plasma discharging characteristic was acquired in static flows. In a hypersonic flow, the flow field can affect the plasma discharging characteristics. DC discharging without magnetic force is unstable, and the discharge channel cannot be maintained. When there is a magnetic field, the energy consumption of the plasma source is approximately three to four times larger than that without a magnetic field, and at the same time plasma discharge can also affect the hypersonic flow field. Through schlieren pictures and pressure measurement, it was found that plasma discharging could induce shockwaves and change the total pressure and wall pressure of the flow field.

Sun, Quan; Cheng, Bangqin; Li, Yinghong; Cui, Wei; Yu, Yonggui; Jie, Junhun

2013-09-01

63

Suppression of Trailing-Edge Noise Using a Plasma Actuator  

NASA Astrophysics Data System (ADS)

Suppression control of noise generation from an airfoil trailing edge is examined experimentally by using a plasma actuator for a NACA0012 airfoil at an angle of attack of -2°, at a chord Reynolds number Re = 1.54 × 105. The boundary layer on the suction surface undergoes transition to turbulence at a location upstream of the trailing edge at the present flow condition and the generation of tonal trailing-edge noise is governed by vortex roll-up of boundary layer on the pressure surface in the vicinity of the trailing-edge which produces a strong acoustic (dipole) source by diffraction of vortex-induced fluctuations at the trailing-edge. When the plasma actuator is operated at an appropriate location on the pressure-side boundary layer, the trailing-edge noise is completely suppressed through delaying the development of the boundary-layer instability wave by the blowing effect of plasma actuator.

Inasawa, A.; Asai, M.; Itoh, K.; Kamijo, T.

2011-09-01

64

Driven one-component plasmas  

SciTech Connect

A statistical theory is presented that allows the calculation of the stationary state achieved by a driven one-component plasma after a process of collisionless relaxation. The stationary Vlasov equation with appropriate boundary conditions is reduced to an ordinary differential equation, which is then solved numerically. The solution is then compared with the molecular-dynamics simulation. A perfect agreement is found between the theory and the simulations. The full current-voltage phase diagram is constructed.

Rizzato, Felipe B.; Pakter, Renato; Levin, Yan [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, Porto Alegre 91501-970, RS (Brazil)

2009-08-15

65

Fabrication of corrugated curved beam type electrostatic actuator and SDA driven self-assembling mechanism for VOA applications  

Microsoft Academic Search

In this paper, we present an innovative design of corrugated curved beam type electrostatic actuator with continuous motion capability, and SDA (scratch drive actuator) driven self-assembling mechanism for axial type MEMS VOA application.

Yen-Jyh Lai; Chengkuo Lee; Chia-Yu Wu; Yu-Shen Lin; Ming Hung Tasi; Ruey-Shing Huang; Min-Shyong Lin

2003-01-01

66

Numerical simulation of the effect of plasma aerodynamic actuation on improving film hole cooling performance  

NASA Astrophysics Data System (ADS)

The primary goal of this paper is to study film cooling performance for a cylindrical hole with plasma aerodynamic actuation. The simulation model of plasma aerodynamic actuation on improving film hole cooling effectiveness was established. The heat effect of plasma aerodynamic actuation model was taken into consideration. It was firstly found that the velocity and blowing ratio greatly affect the film cooling effectiveness. Then, position, power input, and the number of plasma actuators were particularly investigated.

Yu, Jin-Lu; He, Li-ming; Zhu, Yi-fei; Ding, Wei; Wang, Yu-qian

2013-06-01

67

Design and demonstration of a fish robot actuated by a SMA-driven actuation system  

NASA Astrophysics Data System (ADS)

This paper presents a concept of a fish robot actuated by an SMA-based actuator. The bending-type actuator system is composed of a 0.1mm diameter SMA wire and a 0.5mm thick glass/epoxy strip. The SMA wire is installed to the bent composite strip. The actuator can produce about 200gf of blocking force and 3.5mm displacement at the center of the glass/epoxy strip. The bending motion of the actuator is converted into the tail-beat motion of a fish robot through a linkage system. The fish robot is evaluated by measuring the tail-beat angle, swimming speed and thrust produced by the fish robot. The tail-beat angle is about 20° and the maximum swimming speed is about 1.6cm/s. The measured thrust is about 0.4gf when the fish robot is operated at 0.9Hz.

Le, Chan H.; Nguyen, Quang S.; Park, Hoon C.

2010-03-01

68

Streamwise and spanwise plasma actuators for flow-induced cavity noise control  

Microsoft Academic Search

Plasma actuators operating in atmospheric air can induce a body force through collisions between electrically charged particles and neutral air molecules by an externally applied electric field. The fast response and the simple structure make the plasma actuator a promising option in aerospace applications. In this work, experiments were performed with several alternative current excited plasma (streamwise and spanwise) actuators

Xun Huang; Xin Zhang

2008-01-01

69

Sensing and control of flow separation using plasma actuators.  

PubMed

Single dielectric barrier discharge plasma actuators have been used to control flow separation in a large number of applications. An often used configuration involves spanwise-oriented asymmetric electrodes that are arranged to induce a tangential wall jet in the mean flow direction. For the best effect, the plasma actuator is placed just upstream of where the flow separation will occur. This approach is generally more effective when the plasma actuator is periodically pulsed at a frequency that scales with the streamwise length of the separation zone and the free-stream velocity. The optimum frequency produces two coherent spanwise vortices within the separation zone. It has been recently shown that this periodic pulsing of the plasma actuator could be sensed by a surface pressure sensor only when the boundary layer was about to separate, and therefore could provide a flow separation indicator that could be used for feedback control. The paper demonstrates this approach on an aerofoil that is slowly increasing its angle of attack, and on a sinusoidally pitching aerofoil undergoing dynamic stall. Short-time spectral analysis of time series from a static pressure sensor on the aerofoil is used to determine the separation state that ranges from attached, to imminent separation, to fully separated. A feedback control approach is then proposed, and demonstrated on the aerofoil with the slow angle of attack motion. PMID:21382825

Corke, Thomas C; Bowles, Patrick O; He, Chuan; Matlis, Eric H

2011-04-13

70

Use of Plasma Actuators as a Moving-Wake Generator.  

National Technical Information Service (NTIS)

The work documented in this report tests the concept of using plasma actuators as a simple and easy way to generate a simulated moving-wake and the disturbances associated with it in turbines. This wake is caused by the blades of the upstream stages of th...

F. O. Thomas T. C. Corke

2007-01-01

71

Use of Plasma Actuators as a Moving-Wake Generator  

NASA Technical Reports Server (NTRS)

The work documented in this report tests the concept of using plasma actuators as a simple and easy way to generate a simulated moving-wake and the disturbances associated with it in turbines. This wake is caused by the blades of the upstream stages of the turbine. Two types of devices, one constructed of arrays of NACA 0018 airfoils, and the one constructed of flat plates were studied. The airfoils or plates were equipped with surface mounted dielectric barrier discharge (DBD) plasma actuators, which were used to generate flow disturbances resembling moving-wakes. CTA hot-wire anemometry and flow visualization using a smoke-wire were used to investigate the wake independence at various spacings and downstream locations. The flat plates were found to produce better results than the airfoils in creating large velocity fluctuations in the free-stream flow. Different dielectric materials, plasma actuator locations, leading edge contours, angles of attack and plate spacings were investigated, some with positive results. The magnitudes of the velocity fluctuations were found to be comparable to existing mechanical moving-wake generators, thus proving the feasibility of using plasma actuators as a moving-wake generator.

Corke, Thomas C.; Thomas, Flint O.; Klapetzky Michael J.

2007-01-01

72

Measurement of the body force field of plasma actuators  

Microsoft Academic Search

A novel technique is proposed and investigated for the estimation of the body force field resulting from the operation of a dielectric barrier discharge plasma actuator. The technique relies on the measurement of the spatio-temporal evolution of the induced velocity field using high-speed particle image velocimetry (PIV). The technique has the advantage of providing spatial distribution of the body force

M. Kotsonis; S. Ghaemi; L. Veldhuis; F. Scarano

2011-01-01

73

SDBD plasma actuator with nanosecond pulse-periodic discharge  

Microsoft Academic Search

This paper presents a detailed explanation of the physical mechanism of the nanosecond pulsed surface dielectric barrier discharge (SDBD) effect on the flow. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed show overheating in the discharge region on fast (tau sime 1 µs) thermalization of the plasma input energy. The mean values of such heating of

A. Yu Starikovskii; A. A. Nikipelov; M. M. Nudnova; D. V. Roupassov

2009-01-01

74

Electrohydrodynamic force in dielectric barrier discharge plasma actuators  

Microsoft Academic Search

Surface dielectric barrier discharges (DBDs) have been proposed as actuators for flow control. In this paper we discuss the basic mechanisms responsible for the electrohydrodynamic (EHD) force exerted by the discharge on the gas molecules. A two-dimensional fluid model of the DBD is used to describe the plasma dynamics, to understand the basic physics associated with the EHD force and

J. P. Boeuf; Y. Lagmich; Th Unfer; Th Callegari; L. C. Pitchford

2007-01-01

75

Mechanisms of plasma actuators for hypersonic flow control  

NASA Astrophysics Data System (ADS)

A summary of recent research progress in hypersonic plasma actuators for flow control is attempted. It is found that the most effective plasma actuator is derived from an electromagnetic perturbation and amplifies by a subsequent viscous-inviscid interaction. Computational efforts using drift-diffusion theory and a simple phenomenological plasma model, as well as experiments in a hypersonic plasma channel, have shown the effectiveness of using electro-aerodynamic interaction as a hypersonic flow control mechanism. In principle, the plasma actuator based on magneto-aerodynamic interaction should have an added mechanism in the Lorentz force, making it even more effective as a flow control mechanism. However, this approach also incurs additional challenges and complications due to the Hall effect. Magneto-aerodynamic interactions have also been demonstrated for separated flow control, albeit in a very limited scope. Numerical simulations based on a simple phenomenological plasma model have shown the feasibility of separated flow suppression in shock-boundary-layer interaction over a compression ramp at a hypersonic flow of Mach 14.1. The control mechanism relies on the Lorentz force to energize the retarded shear layer in the viscous interacting region, but the effectiveness of momentum transfer via inelastic collision requires further validation.

Shang, J. S.; Surzhikov, S. T.; Kimmel, R.; Gaitonde, D.; Menart, J.; Hayes, J.

2005-11-01

76

Micro-Ball-Lens Optical Switch Driven by SMA Actuator  

NASA Technical Reports Server (NTRS)

The figure is a simplified cross section of a microscopic optical switch that was partially developed at the time of reporting the information for this article. In a fully developed version, light would be coupled from an input optical fiber to one of two side-by-side output optical fibers. The optical connection between the input and the selected output fiber would be made via a microscopic ball lens. Switching of the optical connection from one output fiber to another would be effected by using a pair of thin-film shape-memory-alloy (SMA) actuators to toggle the lens between two resting switch positions. There are many optical switches some made of macroscopic parts by conventional fabrication techniques and some that are microfabricated and, hence, belong to the class of microelectromechanical systems (MEMS). Conventionally fabricated optical switches tend to be expensive. MEMS switches can be mass-produced at relatively low cost, but their attractiveness has been diminished by the fact that, heretofore, MEMS switches have usually been found to exhibit high insertion losses. The present switch is intended to serve as a prototype of low-loss MEMS switches. In addition, this is the first reported SMA-based optical switch. The optical fibers would be held in V grooves in a silicon frame. The lens would have a diameter of 1 m; it would be held by, and positioned between, the SMA actuators, which would be made of thin films of TiNi alloy. Although the SMA actuators are depicted here as having simple shapes for the sake of clarity of illustration, the real actuators would have complex, partly net-like shapes. With the exception of the lens and the optical fibers, the SMA actuators and other components of the switch would be made by microfabrication techniques. The components would be assembled into a sandwich structure to complete the fabrication of the switch. To effect switching, an electric current would be passed through one of the SMA actuators to heat it above its transition temperature, thereby causing it to deform to a different "remembered" shape. The two SMA actuators would be stiff enough that once switching had taken place and the electrical current was turned off, the lens would remain latched in the most recently selected position. In a test, the partially developed switch exhibited an insertion loss of only -1.9 dB and a switching contrast of 70 dB. One the basis of prior research on SMA actuators and assuming a lens displacement of 125 m between extreme positions, it has been estimated that the fully developed switch would be capable of operating at a frequency as high as 10 Hz.

Yang, Eui-Hyeok

2003-01-01

77

The manipulation of an unstarting supersonic flow by plasma actuator  

NASA Astrophysics Data System (ADS)

The manipulation of an unstarting supersonic flow is demonstrated using a dielectric barrier discharge (DBD). Experiments are carried out in a Mach 4.7 model inlet flow. Flow features, such as boundary layers and shockwaves at low freestream static pressure (1 kPa) and temperature (60 K) are visualized with Rayleigh scattering from condensed CO2 particles. Flow unstart, initiated by mass injection, is studied for three model inlet flow configurations, distinguished by the initial conditions (untripped or tripped, plasma actuated or not) of the boundary layers. Unstart in the presence of thick, tripped boundary layers is characterized by the formation of an oblique unstart shock just upstream of a separating and propagating boundary layer. The presence of plasma actuation of this tripped boundary layer seems to arrest the boundary layer separation and leads to the formation of a quasi-stationary pseudo-shock, delaying unstart. The flow generated with DBD actuation is more characteristic of what is seen when unstart is generated in a model flow in which thin boundary layers grow naturally. Planar laser Rayleigh scattering visualizations suggest that the DBD actuation thins the tripped boundary layer over the exposed electrode region.

Im, S.; Do, H.; Cappelli, M. A.

2012-12-01

78

Air Plasma Actuators for Effective Flow Control.  

National Technical Information Service (NTIS)

An asymmetric dielectric barrier discharge model is presented for real gas eight species air chemistry using a self-consistent multi-body system of plasma, dielectric and neutral gas modeled together to predict the electrodynamic momentum imparted to the ...

D. V. Gaitonde K. P. Singh S. Roy

2007-01-01

79

Experimental Characterization of the Plasma Synthetic Jet Actuator  

NASA Astrophysics Data System (ADS)

The plasma synthetic jet is a novel active flow control method because of advantages such as fast response, high frequency and non-moving parts, and it has received more attention recently, especially regarding its application to high-speed flow control. In this paper, the experimental characterization of the plasma synthetic jet actuator is investigated. The actuator consists of a copper anode, a tungsten cathode and a ceramic shell, and with these three parts a cavity can be formed inside the actuator. A pulsed-DC power supply was adopted to generate the arc plasma between the electrodes, through which the gas inside was heated and expanded from the orifice. Discharge parameters such as voltage and current were recorded, respectively, by voltage and current probes. The schlieren system was used for flow visualization, and jet velocities with different discharge parameters were measured. The schlieren images showed that the strength of plasma jets in a series of pulses varies from each other. Through velocity measurement, it is found that at a fixed frequency, the jet velocity hardly increases when the discharge voltage ranges from 16 kV to 20 kV. However, with the discharge voltage fixed, the jet velocity suddenly decreases when the pulse frequency rises above 500 Hz, whereas at other testing frequencies no such decrease was observed. The maximum jet velocity measured in the experiment was up to 110 m/s, which is believed to be effective for high-speed flow control.

Jin, Di; Li, Yinghong; Jia, Min; Song, Huimin; Cui, Wei; Sun, Quan; Li, Fanyu

2013-10-01

80

Numerical Investigation of Serpentine Plasma Actuators for Separation Control at Low Reynolds Number.  

National Technical Information Service (NTIS)

Dielectric Barrier Discharge (DBD) plasma actuators with serpentine shaped electrodes cause a change in the operational behavior of the flow control mechanism relative to the standard linear actuator due to the introduction of fully three dimensional vort...

M. Riherd M. Visbal S. Roy

2011-01-01

81

Centrifugally driven diffusion of Iogenic plasma  

Microsoft Academic Search

The plasma distribution around Io as measured by Voyager 1 displays an asymmetric discontinuity at Io's orbit that has been suggested to be the signature of centrifugally driven interchange diffusion fed by plasma derived from Io. This hypothesis is explored further and found to be valid. The particular form for the diffusion coefficient appropriate to centrifugally driven turbulence is derived.

G. L. Siscoe; Danny Summers

1981-01-01

82

Molecular actuators driven by cooperative spin-state switching.  

PubMed

Molecular switches have great potential to convert different forms of energy into mechanical motion; however, their use is often limited by the narrow range of operating conditions. Here we report on the development of bilayer actuator devices using molecular spin crossover materials. Motion of the bilayer cantilever architecture results from the huge spontaneous strain accompanying the spin-state switching. The advantages of using spin crossover complexes here are substantial. The operating conditions used to switch the device can be manipulated through chemical modification, and there are many existing compounds to choose from. Spin crossover materials may be switched by diverse stimuli including light, temperature, pressure, guest molecules and magnetic field, allowing complex input combinations or highly specific operation. We demonstrate the versatility of this approach by fabricating actuators from four different spin crossover materials and by using both thermal variation and light to induce motion in a controlled direction. PMID:24153221

Shepherd, Helena J; Gural'skiy, Il'ya A; Quintero, Carlos M; Tricard, Simon; Salmon, Lionel; Molnár, Gábor; Bousseksou, Azzedine

2013-01-01

83

Molecular actuators driven by cooperative spin-state switching  

NASA Astrophysics Data System (ADS)

Molecular switches have great potential to convert different forms of energy into mechanical motion; however, their use is often limited by the narrow range of operating conditions. Here we report on the development of bilayer actuator devices using molecular spin crossover materials. Motion of the bilayer cantilever architecture results from the huge spontaneous strain accompanying the spin-state switching. The advantages of using spin crossover complexes here are substantial. The operating conditions used to switch the device can be manipulated through chemical modification, and there are many existing compounds to choose from. Spin crossover materials may be switched by diverse stimuli including light, temperature, pressure, guest molecules and magnetic field, allowing complex input combinations or highly specific operation. We demonstrate the versatility of this approach by fabricating actuators from four different spin crossover materials and by using both thermal variation and light to induce motion in a controlled direction.

Shepherd, Helena J.; Gural'Skiy, Il'Ya A.; Quintero, Carlos M.; Tricard, Simon; Salmon, Lionel; Molnár, Gábor; Bousseksou, Azzedine

2013-10-01

84

Turbine Tip Clearance Flow Control using Plasma Actuators  

Microsoft Academic Search

The tip clearance gap leakage ?ow is of continuing concern in reducing e-ciency losses that occur within turbines. Active ?ow control using a blade-tip-mounted unsteady plasma actuator was implemented in a low pressure linear turbine cascade. Downstream ?ow velocity and pressure were acquired using a flve-hole probe to document changes in leakage vortex size and strength. Reynolds numbers of 5£104

Daniel K. Van Ness II; Thomas C. Corke; Scott C. Morris; Axial Blade Chord; Fifl Pitch; Yaw Angles; Debye Length; Plasma Net Charge Density

85

Discharge characteristics of plasma sheet actuators  

Microsoft Academic Search

The electrical characteristics of a plasma sheet device used for subsonic airflow control are studied in this paper. Experiments are undertaken with a two-wire asymmetrical (different diameters, opposite polarity) electrode configuration connected to dc high voltage sources in the presence of a dielectric plate and under different gases (dry air, nitrogen and oxygen). For large distances electrode-plates it has been

R. Sosa; G. Artana; D. Grondona; H. Kelly; A. Márquez; F. Minotti

2007-01-01

86

Development and use of localized arc filament plasma actuators for high-speed flow control  

Microsoft Academic Search

The paper discusses recent results on the development of localized arc filament plasma actuators and their use in controlling high-speed and high Reynolds number jet flows. Multiple plasma actuators (up to 8) are controlled using a custom-built 8-channel high-voltage pulsed plasma generator. The plasma generator independently controls pulse repetition rate (0-200 kHz), duty cycle and phase for each individual actuator.

Yurii G. Utkin; Saurabh Keshav; Jin-Hwa Kim; Jeff Kastner; Igor V. Adamovich; Mo Samimy

2007-01-01

87

Shock Generation and Control Using DBD Plasma Actuators  

NASA Technical Reports Server (NTRS)

This report is the final report of a NASA Phase I SBIR contract, with some revisions to remove company proprietary data. The Shock Boundary Layer Interaction (SBLI) phenomena in a supersonic inlet involve mutual interaction of oblique shocks with boundary layers, forcing the boundary layer to separate from the inlet wall. To improve the inlet efficiency, it is desired to prevent or delay shock-induced boundary layer separation. In this effort, Innovative Technology Applications Company (ITAC), LLC and the University of Notre Dame (UND) jointly investigated the use of dielectric-barrier-discharge (DBD) plasma actuators for control of SBLI in a supersonic inlet. The research investigated the potential for DBD plasma actuators to suppress flow separation caused by a shock in a turbulent boundary layer. The research involved both numerical and experimental investigations of plasma flow control for a few different SBLI configurations: (a) a 12 wedge flow test case at Mach 1.5 (numerical and experimental), (b) an impinging shock test case at Mach 1.5 using an airfoil as a shock generator (numerical and experimental), and (c) a Mach 2.0 nozzle flow case in a simulated 15 X 15 cm wind tunnel with a shock generator (numerical). Numerical studies were performed for all three test cases to examine the feasibility of plasma flow control concepts. These results were used to guide the wind tunnel experiments conducted on the Mach 1.5 12 degree wedge flow (case a) and the Mach 1.5 impinging shock test case (case b) which were at similar flow conditions as the corresponding numerical studies to obtain experimental evidence of plasma control effects for SBLI control. The experiments also generated data that were used in validating the numerical studies for the baseline cases (without plasma actuators). The experiments were conducted in a Mach 1.5 test section in the University of Notre Dame Hessert Laboratory. The simulation results from cases a and b indicated that multiple spanwise actuators in series and at a voltage of 75 kVp-p could fully suppress the flow separation downstream of the shock. The simulation results from case c showed that the streamwise plasma actuators are highly effective in creating pairs of counter-rotating vortices, much like the mechanical vortex generators, and could also potentially have beneficial effects for SBLI control. However, to achieve these effects, the positioning and the quantity of the DBD actuators used must be optimized. The wind tunnel experiments mapped the baseline flow with good agreement to the numerical simulations. The experimental results were conducted with spanwise actuators for cases a and b, but were limited by the inability to generate a sufficiently high voltage due to arcing in the wind-tunnel test-section. The static pressure in the tunnel was lower than the static pressure in an inlet at flight conditions, promoting arching and degrading the actuator performance.

Patel, Mehul P.; Cain, Alan B.; Nelson, Christopher C.; Corke, Thomas C.; Matlis, Eric H.

2012-01-01

88

Demonstration of Separation Control Using Glow-Discharge Plasma Actuators  

NASA Technical Reports Server (NTRS)

Active flow control of boundary-layer separation using glow-discharge plasma actuators is studied experimentally. Separation is induced on a flat plate installed in a closed-circuit wind tunnel by a shaped insert on the opposite wall. The flow conditions represent flow over the suction surface of a modem low-pressure-turbine airfoil. The Reynolds number, based on wetted plate length and nominal exit velocity, is varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low (0.2%) and high (2.5%) free-stream turbulence intensities are set using passive grids. A spanwise-oriented phased-plasma-array actuator, fabricated on a printed circuit board, is surface-flush-mounted upstream of the separation point and can provide forcing in a wide frequency range. Static surface pressure measurements and hot-wire anemometry of the base and controlled flows are performed and indicate that the glow-discharge plasma actuator is an effective device for separation control.

Hultgren, Lennart S.; Ashpis, David E.

2003-01-01

89

Demonstration of Separation Delay With Glow-Discharge Plasma Actuators  

NASA Technical Reports Server (NTRS)

Active flow control of boundary-layer separation using glow-discharge plasma actuators is studied experimentally. Separation is induced on a flat plate installed in a closed-circuit wind tunnel by a shaped insert on the opposite wall. The flow conditions represent flow over the suction surface of a modern low-pressure-turbine airfoil. The Reynolds number, based on wetted plate length and nominal exit velocity, is varied from 50; 000 to 300,000, covering cruise to takeoff conditions. Low (0.2%) and high (2.5%) free-stream turbulence intensities are set using passive grids. A spanwise-oriented phased-plasma-array actuator, fabricated on a printed circuit board, is surface-flush-mounted upstream of the separation point and can provide forcing in a wide frequency range. Static surface pressure measurements and hot-wire anemometry of the base and controlled flows are performed and indicate that the glow-discharge plasma actuator is an effective device for separation control.

Hultgren, Lennart S.; Ashpis, David E.

2003-01-01

90

Demonstration of Separation Delay with Glow-Discharge Plasma Actuators  

NASA Technical Reports Server (NTRS)

Active flow control of boundary-layer separation using glow-discharge plasma actuators is studied experimentally. Separation is induced on a flat plate installed in a closed-circuit wind tunnel by a shaped insert on the opposite wall. The flow conditions represent flow over the suction surface of a modern low-pressure-turbine airfoil. The Reynolds number, based on wetted plate length and nominal exit velocity, is varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low (0.2 percent) and high (2.5 percent) free-stream turbulence intensities are set using passive grids. A spanwise-oriented phased-plasma-array actuator, fabricated on a printed circuit board, is surface-flush-mounted upstream of the separation point and can provide forcing in a wide frequency range. Static surface pressure measurements and hot-wire anemometry of the base and controlled flows are performed and indicate that the glow-discharge plasma actuator is an effective device for separation control.

Hultgren, Lennart S.; Ashpis, David E.

2004-01-01

91

Fiber-optical switch using cam-micromotor driven by scratch drive actuators  

Microsoft Academic Search

We fabricated a 1 × 1 fiber-optic switch using a cam-micromotor driven by scratch drive actuators (SDAs). Using the cam-micromotor, mechanical translation and precise positioning of an optical fiber were performed. An optical fiber of diameter 50 µm was bent and pushed out with a cam-mechanism driven by the SDAs fabricated by surface micromachining. The maximum rotation speed of the

Y. Kanamori; Y. Aoki; M. Sasaki; H. Hosoya; A. Wada; K. Hane

2005-01-01

92

Performance improvement of plasma actuators using asymmetric high voltage waveforms  

NASA Astrophysics Data System (ADS)

An experimental study is conducted on high voltage waveforms used to power plasma actuators. Shapes that present an asymmetry between the two half cycles are investigated by means of induced thrust and velocity measurements. A parametric study is performed based on thrust measurements in order to find the optimum shape within the tested range. An asymmetric waveform which is made as a combination of sinusoidal and square shapes is found to increase produced thrust by almost 30% compared with the conventional sinusoidal waveform. The asymmetric waveform is further analysed using time-resolved particle image velocimetry in order to reveal the forcing mechanism governed by the shape differences. It is shown that the shape of the waveform has a significant effect on the performance of the actuator. Push and pull events occur within the actuation period and their respective strength and duration closely correlates with the shape of the waveform. It is found that the pull event is significantly weakened for the case of the optimized asymmetric waveform in comparison with the sinusoidal shape. This effectively increases the net momentum transfer and an improvement of approximately 40% in maximum induced velocity is achieved compared with sine waveform. Power consumption due to the asymmetric waveform is marginally increased which provides a significant increase in the actuator's relative efficiency.

Kotsonis, M.; Ghaemi, S.

2012-02-01

93

Competition between pressure effects and airflow influence for the performance of plasma actuators  

NASA Astrophysics Data System (ADS)

The present work addresses the combined influence of pressure variations and different airflow velocities on the discharge intensity of plasma actuators. Power consumption, plasma length, and discharge capacitance were investigated systematically for varying pressure levels (p = 0.1-1 bar) and airflow velocities (U?=0-100 m/s) to characterize and quantify the favorable and adverse effects on the discharge intensity. In accordance with previous reports, an increasing plasma actuator discharge intensity is observed for decreasing pressure levels. At constant pressure levels, an adverse airflow influence on the electric actuator performance is demonstrated. Despite the improved discharge intensity at lower pressure levels, the seemingly improved performance of the plasma actuators is accompanied with a more pronounced drop of the relative performance. These findings demonstrate the dependency of the (kinematic and thermodynamic) environmental conditions on the electric performance of plasma actuators, which in turn affects the control authority of plasma actuators for flow control applications.

Kriegseis, J.; Barckmann, K.; Frey, J.; Tropea, C.; Grundmann, S.

2014-05-01

94

Plasma Actuators for Turbomachinery Flow Control  

NASA Technical Reports Server (NTRS)

This report is Part I of the final report of NASA Cooperative Agreement contract no. NNX07AC02A. The period of performance was January 1, 2007 to December 31, 2010. This report includes the project summary, a list of publications and reprints of the publications that appeared in archival journals. Part II of the final report includes a Ph.D. dissertation and is published separately as NASA/CR-2012-2172655. The research performed under this project was focused on the operation of surface dielectric barrier discharge (DBD) devices driven by high voltage, nanosecond scale pulses plus constant or time varying bias voltages. The main interest was in momentum production and the range of voltages applied eliminated significant heating effects. The approach was experimental supplemented by computational modeling. All the experiments were conducted at Princeton University. The project provided comprehensive understanding of the associated physical phenomena. Limitations on the performance of the devices for the generation of high velocity surface jets were established and various means for overcoming those limitations were proposed and tested. The major limitations included the maximum velocity limit of the jet due to electrical breakdown in air and across the dielectric, the occurrence of backward breakdown during the short pulse causing reverse thrust, the buildup of surface charge in the dielectric offsetting the forward driving potential of the bias voltage, and the interaction of the surface jet with the surface through viscous losses. It was also noted that the best performance occurred when the nanosecond pulse and the bias voltage were of opposite sign. Solutions include the development of partially conducting surface coatings, the development of a semiconductor diode inlaid surface material to suppress the backward breakdown. Extension to long discharge channels was studied and a new ozone imaging method developed for more quantitative determination of surface jet properties.

Miles, Richard, B; Shneider, Mikhail, N.

2012-01-01

95

Measurements and simulations of a channel flow powered by plasma actuators  

NASA Astrophysics Data System (ADS)

Experimental measurements and numerical simulations of a dielectric barrier discharge driven flow inside a finite length channel have been performed. Plasma actuators have been used to impart momentum to the flow in the near wall region, which diffuses throughout the height of the channel as it convects downstream. This momentum addition is found to be of sufficient magnitude to create an unsteady channel flow with exit velocities on the order of 1-3 m/s. Pressure and velocity measurements have been taken in order to quantify the effects of varying the number of symmetrically placed pairs of plasma actuators in the channel and the operating voltage applied to the actuators, showing a monotonic increase with respect to both parameters. Power law relationships have been determined for these measurements with respect to the operating voltage, with exponents of 2.0 for the exit velocity and of 5.6 for the maximum pressure differential. The pressure measurements also suggest that the pressure increase due to each actuator is independent of the bulk flow inside the channel. Numerical predictions also agree with the measured pressure and velocity distributions across the channel. The bulk velocity and pressure measurements allow for efficiency calculations of the plasma channel, which are shown to also fit into a power law relationship with respect to the operating voltage. The data collected show that the efficiency of these devices is low, less than 0.1%, but that it increases with a power law exponent of 4.09 to 4.35 indicating the possibility of using such channel for pumping small flows.

Riherd, Mark; Roy, Subrata

2012-09-01

96

Control of endwall secondary flow in a compressor cascade with dielectric barrier discharge plasma actuation  

Microsoft Academic Search

Three dielectric barrier discharge plasma actuators were mounted at the positions of 20%, 40% and 60% of chord length on the\\u000a endwall in a compressor cascade. The downstream flow field of the cascade has been measured with a mini five-hole pressure\\u000a probe with and without the plasma actuation. The measured results show that the plasma actuation most effectively reduces\\u000a total

Gang Li; YanJi Xu; Bin Lin; JunQiang Zhu; ChaoQun Nie; HongWei Ma; ZhaoFeng Wang

2009-01-01

97

Streamwise and spanwise plasma actuators for flow-induced cavity noise control  

SciTech Connect

Plasma actuators operating in atmospheric air can induce a body force through collisions between electrically charged particles and neutral air molecules by an externally applied electric field. The fast response and the simple structure make the plasma actuator a promising option in aerospace applications. In this work, experiments were performed with several alternative current excited plasma (streamwise and spanwise) actuators to control flow-induced noise from a cavity. It was found that the streamwise actuator induced three-dimensional variations in the shear layer. The spanwise actuator, however, has little influence on the global flow field. As a result, the streamwise actuator is more effective than the spanwise actuator in cavity noise attenuation.

Huang Xun; Zhang Xin [Aeronautics and Astronautics, School of Engineering Sciences, University of Southampton, Southampton SO17 1BJ (United Kingdom)

2008-03-15

98

Flow separation control by plasma actuator with nanosecond pulse discharge  

NASA Astrophysics Data System (ADS)

Boundary layer separation control by plasma actuator with high-voltage pulsed periodic nanosecond excitation is presented. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed have shown overheating of discharge region at fast (? 1 ?s) thermalization of the plasma imputed energy. The mean values of such heating for the plasma layer can reach 70, 200 and even 400 K for 7, 12 and 50 ns pulse duration, respectively. The emerging shock wave together with the secondary vortex flows disturbs the main flow. The resulting pulsed-periodic disturbance causes an efficient transversal momentum transfer into the boundary layer and further flow attachment to the airfoil surface. Thus for pulsed nanosecond periodic DBD the main mechanism of impact is the energy transfer and heating the near-surface gas layer. The following pulse-periodic vortex movement stimulates redistribution of the main flow momentum. The experiments have shown high efficiency of the given mechanism to control boundary layer separation, lift and drag force coefficients, and acoustic noise reduction in the Mach number range of 0.05 to 0.85.

Starikovskii, Andrei; Roupassov, Dmirty; Nikipelov, Andrei; Nudnova, Maryia

2008-10-01

99

Turbulent boundary-layer control with plasma actuators.  

PubMed

This paper reviews turbulent boundary-layer control strategies for skin-friction reduction of aerodynamic bodies. The focus is placed on the drag-reduction mechanisms by two flow control techniques-spanwise oscillation and spanwise travelling wave, which were demonstrated to give up to 45 per cent skin-friction reductions. We show that these techniques can be implemented by dielectric-barrier discharge plasma actuators, which are electric devices that do not require any moving parts or complicated ducting. The experimental results show different modifications to the near-wall structures depending on the control technique. PMID:21382824

Choi, Kwing-So; Jukes, Timothy; Whalley, Richard

2011-04-13

100

Three-dimensional effects of curved plasma actuators in quiescent air  

NASA Astrophysics Data System (ADS)

This paper presents results on a new class of curved plasma actuators for the inducement of three-dimensional vortical structures. The nature of the fluid flow inducement on a flat plate, in quiescent conditions, due to four different shapes of dielectric barrier discharge (DBD) plasma actuators is numerically investigated. The three-dimensional plasma kinetic equations are solved using our in-house, finite element based, multiscale ionized gas (MIG) flow code. Numerical results show electron temperature and three dimensional plasma force vectors for four shapes, which include linear, triangular, serpentine, and square actuators. Three-dimensional effects such as pinching and spreading the neighboring fluid are observed for serpentine and square actuators. The mechanisms of vorticity generation for DBD actuators are discussed. Also the influence of geometric wavelength (?) and amplitude (?) of the serpentine and square actuators on vectored thrust inducement is predicted. This results in these actuators producing significantly better flow mixing downstream as compared to the standard linear actuator. Increasing the wavelengths of serpentine and square actuators in the spanwise direction is shown to enhance the pinching effect giving a much higher vertical velocity. On the contrary, changing the amplitude of the curved actuator varies the streamwise velocity significantly influencing the near wall jet. Experimental data for a serpentine actuator are also reported for validation purpose.

Wang, Chin-Cheng; Durscher, Ryan; Roy, Subrata

2011-04-01

101

Three-dimensional effects of curved plasma actuators in quiescent air  

SciTech Connect

This paper presents results on a new class of curved plasma actuators for the inducement of three-dimensional vortical structures. The nature of the fluid flow inducement on a flat plate, in quiescent conditions, due to four different shapes of dielectric barrier discharge (DBD) plasma actuators is numerically investigated. The three-dimensional plasma kinetic equations are solved using our in-house, finite element based, multiscale ionized gas (MIG) flow code. Numerical results show electron temperature and three dimensional plasma force vectors for four shapes, which include linear, triangular, serpentine, and square actuators. Three-dimensional effects such as pinching and spreading the neighboring fluid are observed for serpentine and square actuators. The mechanisms of vorticity generation for DBD actuators are discussed. Also the influence of geometric wavelength ({lambda}) and amplitude ({Lambda}) of the serpentine and square actuators on vectored thrust inducement is predicted. This results in these actuators producing significantly better flow mixing downstream as compared to the standard linear actuator. Increasing the wavelengths of serpentine and square actuators in the spanwise direction is shown to enhance the pinching effect giving a much higher vertical velocity. On the contrary, changing the amplitude of the curved actuator varies the streamwise velocity significantly influencing the near wall jet. Experimental data for a serpentine actuator are also reported for validation purpose.

Wang Chincheng; Durscher, Ryan; Roy, Subrata

2011-04-15

102

Toward hybrid simulation of flow generation in DBD plasma actuator  

NASA Astrophysics Data System (ADS)

We developed a particle code based on the PIC-MCC method and a plasma fluid code solving drift-diffusion equations. Fluid simulation produces a streamer-type discharge for a positively biased input applied to the exposed electrode against to the buried electrode as obtained in particle simulation. However, we found differences in micro-discharge formation around the exposed electrode between the results of the two codes, suggesting that a hybrid approach based on particle and fluid models may be needed for a long-term precise simulation. Our hybrid code and perspective models are presented for reliably predicting the entire dynamics from micro-discharge to flow generation in a DBD plasma actuator.

Sugimoto, Kazuya; Ohnishi, Naofumi

2012-11-01

103

Solder self-assembled micro axial flow fan driven by a scratch drive actuator rotary motor  

Microsoft Academic Search

This work presents the first micro-sized axial flow fan driven by a scratch drive actuator rotary motor. The eight fan blades are mass assembled using the surface tension of molten 4 mil diameter 63 Sn\\/37 Pb manufactured solder spheres. A sample size of 27 blade angles was measured with a mean assembly angle of 107.24°. The actual mean of the

Paul E. Kladitis; Ryan J. Linderman; Victor M. Bright

2001-01-01

104

Indirect adaptive robust control of electro-hydraulic systems driven by single-rod hydraulic actuator  

Microsoft Academic Search

This paper presents an indirect adaptive robust control (IARC) of electro-hydraulic systems driven by single-rod hydraulic actuators. Unlike the tracking-performance-oriented direct adaptive robust control (DARC) algorithm, in addition to good output tracking performance, the IARC also focuses on accurate parameter estimates for secondary purposes such as machine health monitoring and prognostics. Accurate parameter estimates are obtained through parameter estimation algorithms

Song Liu; Bin Yao

2003-01-01

105

Force measurements of single and double barrier DBD plasma actuators in quiescent air  

Microsoft Academic Search

We present the results of our experimental measurements of how variations in the discharge geometry of surface-mounted dielectric barrier discharges (DBDs) affect the force transferred to atmospheric pressure air. Our studies include both single barrier plasma actuators (one electrode insulated) and double barrier plasma actuators (both electrodes insulated) operated in quiescent air. Stagnation probe measurements of the induced air flow

A R Hoskinson; N Hershkowitz; D E Ashpis

2008-01-01

106

Effects of plasma aerodynamic actuation on oblique shock wave in a cold supersonic flow  

Microsoft Academic Search

Wedge oblique shock wave control using an arc discharge plasma aerodynamic actuator was investigated both experimentally and theoretically. Schlieren photography measurements in a small-scale short-duration supersonic wind tunnel indicated that the shock wave angle decreased and its start point shifted upstream with the plasma aerodynamic actuation. Also the shock wave intensity weakened, as shown by the decrease in the gas

Jian Wang; Yinghong Li; Bangqin Cheng; Changbing Su; Huimin Song; Yun Wu

2009-01-01

107

Preliminary Experiments of Barrier Discharge Plasma Actuators using Dry and Humid Air  

Microsoft Academic Search

Experiments are performed using dry and humid air to ascertain the effect of humidity on the performance of a plasma actuator in flight conditions. These actuators are becoming popular in controlling flow about low to moderate speed aerospace vehicles. These experiments are performed at a new Test Facility of the Computational Plasma Dynamics Laboratory (CPDL) in Kettering University. A blow-down

Richard Anderson; Subrata Roy

2006-01-01

108

Plasma actuators for airflow control: measurement of the non-stationary induced flow velocity  

Microsoft Academic Search

This paper deals with the measurement of the instantaneous flow velocity induced by surface plasma actuators in air at atmospheric pressure. More accurately, experiments with Laser Doppler Velocimetry (LDV) are conducted with two different types of plasma actuators in order to determine the establishment time of the induced airflow. DC corona discharges and AC dielectric barrier discharges are investigated in

Maxime Forte; Luc Leger; Jérôme Pons; Eric Moreau; Gérard Touchard

2005-01-01

109

Fiber-optical switch using cam-micromotor driven by scratch drive actuators  

NASA Astrophysics Data System (ADS)

We fabricated a 1 × 1 fiber-optic switch using a cam-micromotor driven by scratch drive actuators (SDAs). Using the cam-micromotor, mechanical translation and precise positioning of an optical fiber were performed. An optical fiber of diameter 50 µm was bent and pushed out with a cam-mechanism driven by the SDAs fabricated by surface micromachining. The maximum rotation speed of the cam-micromotor was 7.5 rpm at a driving frequency of 1.5 kHz. The transient time of the switch to attenuate coupling efficiency less than -40 dB was around 10 ms.

Kanamori, Y.; Aoki, Y.; Sasaki, M.; Hosoya, H.; Wada, A.; Hane, K.

2005-01-01

110

Receptivity of Laminar Boundary Layers to Spanwise-Periodic Forcing by an Array of Plasma Actuators  

NASA Astrophysics Data System (ADS)

This work is concerned with the response of a Blasius boundary layer to dielectric-barrier- discharge (DBD) plasma actuators for the purpose of using these devices in bypass transition control. The plasma actuators consist of a spanwise-periodic array of high voltage electrodes, which are oriented to produce streamwise vortex pairs. The structure of actuator-induced streaks is measured using hot-wire anemometry over a streamwise distance of approximately 100 boundary layer thicknesses, and is decomposed into 4 span-wise Fourier modes. The modal content and corresponding streamwise growth characteristics are discussed for ten plasma actuator geometries over multiple excitation voltages and freestream velocities. Actuator power consumption was found to control the streak amplitude, whereas freestream velocity affected both amplitude and streamwise extent of the streaks. A common relationship between disturbance energy and power consumption was found among actuators of different dielectric thickness and similar electrode geometry.

Osmokrovic, Luke

111

Study of flow induced by sine wave and saw tooth plasma actuators  

NASA Astrophysics Data System (ADS)

The effect of plasma actuator that uses saw-tooth or sine-wave shape electrodes on boundary layer flows is experimentally investigated. The measurement results are compared with a corresponding standard configuration (conventional design using two rectangular strip electrodes)—the actuator that produces a nearly two-dimensional horizontal wall jet upon actuation. PIV measurements are used to characterize the actuators in a quiescent chamber. Operating in a steady manner, the new actuators result in the formation of streamwise and spanwise vortices. That is to say, the new actuators render the plasma actuators inducing three-dimensional variations in the shear layer, offering significant flexibility in flow control. The affected flowfield with the new actuators is significantly larger than that with the conventional linear actuators. While the conventional linear actuators affect primarily the boundary layer flow on a scale of about 1 cm above the wall, the new actuators affect the near wall region at a significantly larger scale. This new design broadens the applicability and enhances the flow control effects and it is potentially a more efficient flow control device.

Liu, Zhifeng; Wang, Lianze; Fu, Song

2011-11-01

112

Strongly driven laser-plasma coupling  

Microsoft Academic Search

An improved understanding of strongly driven laser-plasma coupling is important for optimal use of the National Ignition Facility (NIF) for both inertial fusion and for a variety of advanced applications. Such applications range from high-energy x-ray sources and high-temperature hohlraums to fast ignition and laser radiography. We discuss a novel model for the scaling of strongly driven stimulated Brillouin and

W. L. Kruer; E. M. Campbell; C. D. Decker; S. C. Wilks; J. Moody; T. Orzechowski; L. Powers; L. J. Suter; B. B. Afeyan; N. Dague

1999-01-01

113

Active Joint Mechanism Driven by Multiple Actuators Made of Flexible Bags: A Proposal of Dual Structural Actuator  

PubMed Central

An actuator is required to change its speed and force depending on the situation. Using multiple actuators for one driving axis is one of the possible solutions; however, there is an associated problem of output power matching. This study proposes a new active joint mechanism using multiple actuators. Because the actuator is made of a flexible bag, it does not interfere with other actuators when it is depressurized. The proposed joint achieved coordinated motion of multiple actuators. This report also discusses a new actuator which has dual cylindrical structure. The cylinders are composed of flexible bags with different diameters. The joint torque is estimated based on the following factors: empirical formula for the flexible actuator torque, geometric relationship between the joint and the actuator, and the principle of virtual work. The prototype joint mechanism achieves coordinated motion of multiple actuators for one axis. With this motion, small inner actuator contributes high speed motion, whereas large outer actuator generates high torque. The performance of the prototype joint is examined by speed and torque measurements. The joint showed about 30% efficiency at 2.0?Nm load torque under 0.15?MPa air input.

Inou, Norio

2013-01-01

114

Active joint mechanism driven by multiple actuators made of flexible bags: a proposal of dual structural actuator.  

PubMed

An actuator is required to change its speed and force depending on the situation. Using multiple actuators for one driving axis is one of the possible solutions; however, there is an associated problem of output power matching. This study proposes a new active joint mechanism using multiple actuators. Because the actuator is made of a flexible bag, it does not interfere with other actuators when it is depressurized. The proposed joint achieved coordinated motion of multiple actuators. This report also discusses a new actuator which has dual cylindrical structure. The cylinders are composed of flexible bags with different diameters. The joint torque is estimated based on the following factors: empirical formula for the flexible actuator torque, geometric relationship between the joint and the actuator, and the principle of virtual work. The prototype joint mechanism achieves coordinated motion of multiple actuators for one axis. With this motion, small inner actuator contributes high speed motion, whereas large outer actuator generates high torque. The performance of the prototype joint is examined by speed and torque measurements. The joint showed about 30% efficiency at 2.0 Nm load torque under 0.15 MPa air input. PMID:24385868

Kimura, Hitoshi; Matsuzaki, Takuya; Kataoka, Mokutaro; Inou, Norio

2013-01-01

115

Driven Resonance in Partially Relaxed Plasmas  

NASA Astrophysics Data System (ADS)

A Taylor-relaxed plasma (j=kB with k a constant) under external magnetic helicity injection encounters resonances in spatial frequencies of its force-free eigenmodes. Such driven resonance underlies the physics of magnetic self-organization and determines the flux amplification in laboratory helicity injection applications. Here we show that for partially relaxed plasmas where the deviation from the fully relaxed Taylor state, for example, a flux-dependent k, is a function of the normalized flux ?/?a with ?a the poloidal flux at the magnetic axis, a modified driven resonance persists even if k(?) has an order-unity variation across the flux surfaces.

Tang, X. Z.

2007-04-01

116

Optimization of Airfoil Design for Flow Control with Plasma Actuators  

NASA Astrophysics Data System (ADS)

Using computer simulations and design optimization methods, this research examines the implementation of active flow control devices on wind turbine blades. Through modifications to blade geometry in order to maximize the effectiveness of flow control devices, increases in aerodynamic performance and control of aerodynamic performance are expected. Due to this compliant flow, an increase in the power output of wind turbines is able to be realized with minimal modification and investment to existing turbine blades. This is achieved through dynamic lift control via virtual camber control. Methods using strategic flow separation near the trailing edge are analyzed to obtain desired aerodynamic performance. FLUENT is used to determine the aerodynamic performance of potential turbine blade design, and the post-processing uses optimization techniques to determine an optimal blade geometry and plasma actuator operating parameters. This work motivates the research and development of novel blade designs with flow control devices that will be tested at Notre Dame's Laboratory for Enhanced Wind Energy Design.

Williams, Theodore; Corke, Thomas; Cooney, John

2011-11-01

117

Physics of plasma actuator operating in atmospheric air  

SciTech Connect

The physics of plasma actuator operating in the atmospheric air has been numerically investigated. The O{sup -}, O{sub 2}{sup -}, O{sub 2}{sup +}, and N{sub 2}{sup +} ions have been included in the air chemistry to identify their role. For the specific case study, we find the density of positive ions is an order of magnitude higher at the positive peak of the cycle than that at the negative peak of the cycle. This difference in density levels of the species causes the development of the directional bias of the electrodynamic force. Numerical simulations indicate that positive ions play major role in the development of the positive force.

Singh, Kunwar Pal; Roy, Subrata [Computational Plasma Dynamics Laboratory and Test Facility, Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611-6300 (United States)

2008-03-17

118

Mechanism of flow separation control using plasma actuation  

NASA Astrophysics Data System (ADS)

The mechanism of flow separation control was investigated experimentally and computationally using pulse-modulated dielectric barrier discharge (DBD) plasma actuation on a stalled flat plate airfoil at a Reynolds number of 3000. Load measurements were complimented with two-dimensional phase-averaged particle image velocimetry performed in the flowfield above the airfoil. A parametric study was carried out where the pulse-modulation frequency, duty cycle, and peak plasma body-force were varied. The two-dimensional Navier-Stokes equations, with no turbulence modeling, were solved directly using a commercial flow solver and a simple but satisfactory heuristic DBD plasma body-force model was incorporated. The overall experimental trends were well predicted by the computations, where the frequencies that produced the largest increases in lift coefficient excited bluff-body shedding at a frequency corresponding approximately to its unforced sub-harmonic. At non-dimensional frequencies most effective for increasing lift (~0.2 to 0.5), the leading-edge shear layer was severed by the perturbations and then merged with a downstream vortex. In a time-mean sense this mechanism forced relatively high momentum fluid towards the surface with typically two re-circulating structures present on the airfoil. Although the essential flow control mechanism was captured by the computation, the idealized 2D approach was identified as a weakness due to the shedding instability not being present in the baseline experiments and the inability to account for three-dimensional structures in the shear layer.

Greenblatt, David; Schneider, Torsten; Schüle, Chan Yong

2012-07-01

119

Study of radiative plasma structures in laser driven ablating plasmas  

SciTech Connect

The mechanism is analyzed that generates radiative plasma structures (RPS) [J. P. Dahlburg {ital et al.}, J. Quant Spectros. Radiat. Transfer {bold 54}, 113 (1995)] in driven, ablating plasmas of subcritical density. A reduced set of radiation-hydrodynamics equations is derived which model the onset of RPS phenomenon. {copyright} {ital 1999 American Institute of Physics. }

Hazak, G.; Velikovich, A.L. [Berkeley Research Associates Inc., Springfield, Virginia 22150 (United States)] [Berkeley Research Associates Inc., Springfield, Virginia 22150 (United States); Klapisch, M. [ARTEP Inc, Columbia, Maryland 20145 (United States)] [ARTEP Inc, Columbia, Maryland 20145 (United States); Schmitt, A.J.; Dahlburg, J.P.; Colombant, D. [Plasma Physics Division, Naval Research Laboratory, Washington, D.C. (United States)] [Plasma Physics Division, Naval Research Laboratory, Washington, D.C. (United States); Gardner, J.H.; Phillips, L. [LCPFD Naval Research Laboratory, Washington, D.C. (United States)] [LCPFD Naval Research Laboratory, Washington, D.C. (United States)

1999-10-01

120

Study of radiative plasma structures in laser driven ablating plasmas  

NASA Astrophysics Data System (ADS)

The mechanism is analyzed that generates radiative plasma structures (RPS) [J. P. Dahlburg et al., J. Quant Spectros. Radiat. Transfer 54, 113 (1995)] in driven, ablating plasmas of subcritical density. A reduced set of radiation-hydrodynamics equations is derived which model the onset of RPS phenomenon.

Hazak, G.; Velikovich, A. L.; Klapisch, M.; Schmitt, A. J.; Dahlburg, J. P.; Colombant, D.; Gardner, J. H.; Phillips, L.

1999-10-01

121

Strongly-driven laser plasma coupling  

Microsoft Academic Search

An improved understanding of strongly-driven laser plasma coupling is important for optimal use of the National Ignition Facility (NIF) for ;\\u000aboth inertial fusion and for a variety of advanced applications. Such applications range from high energy x- ray sources and high ;\\u000atemperature hohlraums to fast ignition and laser radiography. We discuss a novel model for the scaling of

L Suter; B Afeyan; E M Campbell; C D Decker; W L Kruer; J Moody; T Orzechowski; L Powers; S C Wilks

1998-01-01

122

Current Driven Modes in the LHD Plasmas  

Microsoft Academic Search

The internal and the external current-driven instabilities in the LHD plasmas carrying net toroidal current are discussed. If the current density profile is peaked at the magnetic axis, as is in the case of the beam current, equilibria with two resonant surfaces with the same rotational transform can be obtained. In this case, the internal kink mode becomes unstable at

Katsuji Ichiguchi; Noriyoshi Nakajima; Masao Okamoto; John L. Johnson; Yuji Nakamura; Masahiro Wakatani

1999-01-01

123

Centrifugally driven diffusion of Iogenic plasma  

NASA Technical Reports Server (NTRS)

The plasma distribution around Io as measured by Voyager 1 displays an asymmetric discontinuity at Io's orbit that has been suggested to be the signature of centrifugally driven interchange diffusion fed by plasma derived from Io. This hypothesis is explored further and found to be valid. The particular form for the diffusion coefficient appropriate to centrifugally driven turbulence is derived. The nonlinear character of this kind of diffusion is thereby made explicit. Solutions to the nonlinear, time-independent and linearized, time-dependent diffusion equations are given. These display a markedly conservative behavior. The nonlinear, steady state solutions are identical in form to the solutions of the previously studied equation of linear, atmospherically driven diffusion. The linearized, time-dependent solutions exhibit a negative feed-back quality that buffers the response of the density to changes in the source strength. Estimates of the source strength, the diffusion coefficient, and the signal propagation speed are also given.

Siscoe, G. L.; Summers, D.

1981-01-01

124

A new type of a direct-drive valve system driven by a piezostack actuator and sliding spool  

NASA Astrophysics Data System (ADS)

A direct-drive valve (DDV) system is a kind of electrohydraulic servo valve system, in which the actuator directly drives the spool of the valve. In conventional DDV systems, the spool is generally driven by an electromagnetic actuator. Performance characteristics such as frequency bandwidth of DDV systems driven by the electromagnetic actuator are limited due to the actuator response property. In order to improve the performance characteristics of conventional DDV systems, in this work a new configuration for a direct-drive valve system actuated by a piezostack actuator with a flexible beam mechanism is proposed (in short, a piezo-driven DDV system). Its benefits are demonstrated through both simulation and experiment. After describing the geometric configuration and operational principle of the proposed valve system, a governing equation of the whole system is obtained by combining the dynamic equations of the fluid part and the structural parts: the piezostack, the flexible beam, and the spool. In the structural parts of the piezostack and flexible beam, a lumped parameter modeling method is used, while the conventional rule of the fluid momentum is used for the fluid part. In order to evaluate valve performances of the proposed system, an experimental apparatus consisting of a hydraulic circuit and the piezo-driven DDV system is established. The performance characteristics are evaluated in terms of maximum spool displacement, flow rate, frequency characteristics, and step response. In addition, in order to advocate the feasibility of the proposed dynamic model, a comparison between simulation and experiment is undertaken.

Jeon, Juncheol; Han, Chulhee; Han, Young-Min; Choi, Seung-Bok

2014-07-01

125

Active Control of Flow around NACA 0015 Airfoil by Using DBD Plasma Actuator  

NASA Astrophysics Data System (ADS)

In this study, effect of plasma actuator on a flat plate and manipulation of flow separation on NACA0015 airfoil with plasma actuator at low Reynolds numbers were experimentally investigated. In the first section of the study, plasma actuator which consists of positive and grounded electrode couple and dielectric layer, located on a flat plate was actuated at different frequencies and peak to peak voltages in range of 3-5 kHz and 6-12 kV respectively. Theinduced air flow velocity on the surface of flat plate was measured by pitot tube at different locations behind the actuator. The influence of dielectricthickness and unsteady actuation with duty cycle was also examined. In the second section, the effect of plasma actuator on NACA0015 airfoil was studied atReynolds number 15000 and 30000. Four plasma actuators were placed at x/C = 0.1, 0.3, 0.5 and 0.9, and different electrode combinations were activated by sinusoidal signal. Flow visualizations were done when the attack angles were 0°, 5°, 10°, 15° and 20°. The results indicate that up to the 15° attack angle, the separated flow was reattached by plasma actuator at 12kV peak to peak voltage and 4 kHz frequency. However, 12 kVpp voltage was insufficient to reattach the flow at 20° angle of attack. The separated flow could be reattached by increasing the voltage up to 13 kV. Lift coefficient was also increased by the manipulated flow over the airfoil. Results showed that even high attack angles, the actuators can control the flow separation and prevent the airfoil from stall at low Reynolds numbers.

Akansu, Y. E.; Karakaya, F.; ?anl?soy, A.

2013-04-01

126

Control of a high Reynolds number Mach 0.9 heated jet using plasma actuators  

Microsoft Academic Search

The results of particle image velocimetry (PIV) measurements in a high subsonic, heated, jet forced using localized arc filament plasma actuators (LAFPAs) show that LAFPAs can consistently produce significant mixing enhancement over a wide range of temperatures. These actuators have been used successfully in high Reynolds number, high-speed unheated jets. The facility consists of an axisymmetric jet with different nozzle

M. Kearney-Fischer; J.-H. Kim; M. Samimy

2009-01-01

127

Separation control using plasma actuators: application to a free turbulent jet  

Microsoft Academic Search

This experimental work deals with active airflow control using non-thermal surface plasma actuators in the case of a rectangular cross section turbulent jet. A wide-angle diffuser composed of two adjustable hinged baseplates is linked at the jet exit. Two types of actuators are considered: the DC corona discharge and the dielectric barrier discharge (DBD). In both cases, an ionic wind

A. Labergue; E. Moreau; N. Zouzou; G. Touchard

2007-01-01

128

SDBD plasma actuator with nanosecond pulse-periodic discharge  

NASA Astrophysics Data System (ADS)

This paper presents a detailed explanation of the physical mechanism of the nanosecond pulsed surface dielectric barrier discharge (SDBD) effect on the flow. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed show overheating in the discharge region on fast (? sime 1 µs) thermalization of the plasma input energy. The mean values of such heating of the plasma layer can reach 70 K, 200 K and even 400 K for 7 ns, 12 ns and 50 ns pulse durations, respectively. The emerging shock wave together with the secondary vortex flows disturbs the main flow. The resulting pulsed-periodic disturbance causes an efficient transversal momentum transfer into the boundary layer and further flow attachment to the airfoil surface. Thus, for periodic pulsed nanosecond dielectric barrier discharge, the main mechanism of impact is the energy transfer and heating of the near-surface gas layer. The following pulse-periodic vortex movement stimulates redistribution of the main flow momentum.

Starikovskii, A. Yu; Nikipelov, A. A.; Nudnova, M. M.; Roupassov, D. V.

2009-08-01

129

Progress of Laser-Driven Plasma Accelerators  

SciTech Connect

There is a great interest worldwide in plasma accelerators driven by ultra-intense lasers which make it possible to generate ultra-high gradient acceleration and high quality particle beams in a much more compact size compared with conventional accelerators. A frontier research on laser and plasma accelerators is focused on high energy electron acceleration and ultra-short X-ray and Tera Hertz radiations as their applications. These achievements will provide not only a wide range of sciences with benefits of a table-top accelerator but also a basic science with a tool of ultrahigh energy accelerators probing an unknown extremely microscopic world.Harnessing the recent advance of ultra-intense ultra-short pulse lasers, the worldwide research has made a tremendous breakthrough in demonstrating high-energy high-quality particle beams in a compact scale, so called ''dream beams on a table top'', which represents monoenergetic electron beams from laser wakefield accelerators and GeV acceleration by capillary plasma-channel laser wakefield accelerators. This lecture reviews recent progress of results on laser-driven plasma based accelerator experiments to quest for particle acceleration physics in intense laser-plasma interactions and to present new outlook for the GeV-range high-energy laser plasma accelerators.

Nakajima, Kazuhisa [High Energy Accelerator Research Organization 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)

2007-07-11

130

Development of Localized Arc Filament RF Plasma Actuators for High- Speed and High Reynolds Number Flow Control.  

National Technical Information Service (NTIS)

Recently developed Localized Arc Filament Plasma Actuators (LAFPAs) have shown tremendous control authority in high-speed and high Reynolds number flow for mixing enhancement and noise mitigation. Previously, these actuators were powered by a high voltage...

I. V. Adamovich J. H. Kim M. Nishihara M. Samimy S. V. Gorbatov

2010-01-01

131

On the classification of dielectric barrier discharge plasma actuators: A comprehensive performance evaluation study  

NASA Astrophysics Data System (ADS)

The increasing popularity and maturity of plasma actuators for many flow control applications requires a common standard for plasma actuator performance evaluation. In the present work, a comprehensive comparative study of existing and new evaluation measures is presented, based on results from identical plasma-actuator configurations. A power-flow diagram is introduced that covers the entire range of power stages from the energy source to the flow-control success. All individual power stages are explained, existing controversial definitions are clarified, and an evaluation guideline is applied to previously obtained data. Finally, the defined systematic analysis is applied to the results of a recently conducted plasma-actuator in-flight experiment.

Kriegseis, J.; Duchmann, A.; Tropea, C.; Grundmann, S.

2013-08-01

132

Pulsed Plasma Actuators for Active Flow Control at MAV Reynolds Numbers  

Microsoft Academic Search

An experimental investigation of separation control using steady and pulsed plasma actuators was carried out on an Eppler\\u000a E338 airfoil at typical micro air vehicle Reynolds numbers (20,000?Re?140,000). Pulsing was achieved by modulating the high frequency plasma excitation voltage. The actuators were calibrated\\u000a directly using a laser doppler anemometer, with and without free-stream velocity, and this allowed the quantification of

B. Göksel; D. Greenblatt; I. Rechenberg; Y. Kastantin; C. N. NAYERI; C. O. PASCHEREIT

133

Flow separation control by plasma actuator with nanosecond pulse periodic discharge  

Microsoft Academic Search

Currently, the problem of flow active control by low-temperature plasma is considered to be one of the most booming realms of aerodynamics . The paper presents a results on controlling boundary layer attachment by plasma actuator withhighvoltage pulsed periodic nanosecond excitation. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed show overheating in the discharge region at

D. V. Roupassov; A. A. Nikipelov; M. M. Nudnova; A. Yu. Starikovskii

2008-01-01

134

Experimental and Numerical Investigations of Boundary-Layer Influence Using Plasma-Actuators  

Microsoft Academic Search

This is a fundamental study about the influence of plasma-actuators on boundary-layer flows, including both experimental and\\u000a numerical investigations. The first set of experiments is conducted in quiescent air and these results are used to calibrate\\u000a a numerical model which simulates the plasma-actuator in an existing RANS (Reynolds Averaged Navier-Stokes) code. The second\\u000a set of experiments involves a flat-plate boundary

S. Grundmann; S. Klumpp; C. Tropea

135

Design and characterization of a 3D MEMS VOA driven by hybrid electromagnetic and electrothermal actuation mechanisms  

NASA Astrophysics Data System (ADS)

By using a CMOS compatible process technology, a MEMS variable optical attenuator (VOA) is characterized in terms of actuation mechanisms. A dual-fiber collimator is aligned perpendicularly to the micromirror in a three-dimensional (3D) free space configuration, where the micromirror is mechanically connected with an electromagnetic actuator and two sets of electrothermal actuators. Three types of attenuation schemes based on electromagnetic, electrothermal and hybrid, i.e. combination of electrothermal and electromagnetic, actuations have been explored and studied. Dynamic attenuation ranges of 40 dB have been achieved at 4 Vdc, 26 mW and 3 Vdc, 20 mW by electromagnetic and electrothermal attenuation schemes respectively. Wavelength-dependent loss has been demonstrated to be less than 0.6 dB at all attenuation states for both attenuation schemes. In the hybrid attenuation scheme, various voltage combinations are made to the electromagnetic and electrothermal actuators. An optical attenuation of approximately 40 dB can be obtained when two volts are applied to both the electromagnetic and electrothermal actuators simultaneously, while the electrical power consumption of the actuators is 17 mW in total. Our unique design of using both electrothermal and electromagnetic actuators simultaneously to achieve attenuation is the first demonstration of such a hybrid-driven CMOS compatible MEMS VOA device.

How Koh, Kah; Qian, You; Lee, Chengkuo

2012-10-01

136

Experimental Investigation on the Characteristics of Sliding Discharge Plasma Aerodynamic Actuation  

NASA Astrophysics Data System (ADS)

A new electrical discharge called sliding discharge was developed to generate plasma aerodynamic actuation for flow control. A microsecond-pulse high voltage with a DC component was used to energize a three-electrode actuator to generate sliding discharge. The characteristics of plasma aerodynamic actuation by sliding discharge were experimentally investigated. Discharge morphology shows that sliding discharge is formed when energized by properly adjusting microsecond-pulse and DC voltage. Compared to dielectric barrier discharge (DBD), the plasma extension of sliding discharge is quasi-diffusive and stable but longer and more intensive. Results from particle image velocimetry (PIV) test indicate that plasma aerodynamic actuation by sliding discharge can induce a ‘starting vortex’ and a quasi-steady ‘near-wall jet’. Body force induced by plasma aerodynamic actuation is about the order of mN, which is stronger than that induced by single DBD. It is inferred that microsecond-pulse sliding discharge may be more effective to generate large-scale plasma aerodynamic actuation, which is very promising for improving aircraft aerodynamic characteristics and propulsion efficiency.

Song, Huimin; Li, Yinghong; Zhang, Qiaogen; Jia, Min; Wu, Yun

2011-10-01

137

Numerical simulation of a plasma actuator based on ion transport  

NASA Astrophysics Data System (ADS)

Two-dimensional numerical simulation of ion transport and flow around a single dielectric barrier discharge plasma actuator (PA) is performed. Spatial distributions of ions and electrons as well as their time evolution are obtained by solving the transport equations of monovalent positive ions, monovalent negative ions, and electrons. Voltage and frequency of the driving alternating-current signal are assumed to be 8 kV and 5 kHz, respectively. Special focus is laid upon the effect of voltage gradient dV/dt on the magnitude of the body force. The validity of steady force models often used in flow simulation is also examined. The simulation results show that the magnitude of the body force induced by the PA increases as the voltage gradient dV/dt increases and its increase rate becomes milder at higher voltage. The mechanism of body force generation is explained from the time evolution of number density fields of ions and electrons. A comparison between flow simulations using a time-resolved body force and its time-averaged counterpart demonstrates that the time-averaged model gives sufficiently accurate results when the time scale of the flow is more than 30 times greater than that of the PA.

Yamamoto, Seiya; Fukagata, Koji

2013-06-01

138

Numerical simulation of a plasma actuator based on ion transport  

SciTech Connect

Two-dimensional numerical simulation of ion transport and flow around a single dielectric barrier discharge plasma actuator (PA) is performed. Spatial distributions of ions and electrons as well as their time evolution are obtained by solving the transport equations of monovalent positive ions, monovalent negative ions, and electrons. Voltage and frequency of the driving alternating-current signal are assumed to be 8 kV and 5 kHz, respectively. Special focus is laid upon the effect of voltage gradient dV/dt on the magnitude of the body force. The validity of steady force models often used in flow simulation is also examined. The simulation results show that the magnitude of the body force induced by the PA increases as the voltage gradient dV/dt increases and its increase rate becomes milder at higher voltage. The mechanism of body force generation is explained from the time evolution of number density fields of ions and electrons. A comparison between flow simulations using a time-resolved body force and its time-averaged counterpart demonstrates that the time-averaged model gives sufficiently accurate results when the time scale of the flow is more than 30 times greater than that of the PA.

Yamamoto, Seiya; Fukagata, Koji [Department of Mechanical Engineering, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522 (Japan)] [Department of Mechanical Engineering, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522 (Japan)

2013-06-28

139

Current-driven plasma instabilities in superconductors  

SciTech Connect

We examine here the possibility of current-driven plasma instabilities in superconductors in two temperature regimes. At low temperatures (Tapprox. =0) an instability can be generated in a layered system. Near the critical temperature (Tapprox. =T/sub c/) an instability can occur in a single superconductor for sufficiently large drifts which might be achievable in the new high-T/sub c/ materials. These instabilities offer possibilities for new radiation-source device applications.

Kempa, K.; Cen, J.; Bakshi, P.

1989-02-01

140

Influence of shock wave propagation on dielectric barrier discharge plasma actuator performance  

NASA Astrophysics Data System (ADS)

Interest in plasma actuators as active flow control devices is growing rapidly due to their lack of mechanical parts, light weight and high response frequency. Although the flow induced by these actuators has received much attention, the effect that the external flow has on the performance of the actuator itself must also be considered, especially the influence of unsteady high-speed flows which are fast becoming a norm in the operating flight envelopes. The primary objective of this study is to examine the characteristics of a dielectric barrier discharge (DBD) plasma actuator when exposed to an unsteady flow generated by a shock tube. This type of flow, which is often used in different studies, contains a range of flow regimes from sudden pressure and density changes to relatively uniform high-speed flow regions. A small circular shock tube is employed along with the schlieren photography technique to visualize the flow. The voltage and current traces of the plasma actuator are monitored throughout, and using the well-established shock tube theory the change in the actuator characteristics are related to the physical processes which occur inside the shock tube. The results show that not only is the shear layer outside of the shock tube affected by the plasma but the passage of the shock front and high-speed flow behind it also greatly influences the properties of the plasma.

Erfani, Rasool; Zare-Behtash, Hossein; Kontis, Konstantinos

2012-06-01

141

Three-dimensional simulations of discharge plasma evolution on a dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

To develop simulation techniques for reconstructing microdischarges in a dielectric barrier discharge (DBD) plasma actuator and analyze spanwise non-uniformity in a body force field, three-dimensional discharge plasma simulations of a DBD plasma actuator were conducted assuming step-like positive and negative applied voltages. Our study showed that to break the spanwise uniformity, some disturbances were required in the computational conditions to reconstruct the three-dimensional microdischarges, and the attachment of some minute bumps (several tens of micrometers in size) on the electrode edge allowed for the successful reconstruction of glow-type microdischarges and streamer-type filamentary discharges in the negative and positive applied voltage cases, respectively. The tentative body force field has strong spanwise non-uniformity corresponding to the plasma structure, and in addition, a spanwise directional body force also exists, especially in the streamer discharge. However, the spanwise averaged body force has the same spatial-distribution and time-evolution characteristics obtained with the two-dimensional simulation.

Nishida, Hiroyuki; Nonomura, Taku; Abe, Takashi

2014-04-01

142

Performance evaluation of a valveless micropump driven by a ring-type piezoelectric actuator.  

PubMed

Presented in this paper is the study of the performance evaluation of a valveless micropump driven by a ring-type piezoelectric actuator. The application of this micropump is to circulate fuel inside a miniaturized direct methanol fuel cell (DMFC) power system. A theoretical model based on the theory of plates and shells is established to estimate the deflection and the volume change of this micropump without liquid loading. Both finite-element method (FEM) and experimental method are applied to verify this model. Using this model, the optimal design parameters such as the dimensions and the mechanical properties of the micropump can be obtained. Furthermore, various system parameters that will affect the performance of the micropump system with liquid loading are identified and analyzed experimentally. It is expected that this study will provide some vital information for many micropump applications such as fuel delivery in fuel cells, ink jet printers, and biofluidics. PMID:16529122

Zhang, Tao; Wang, Qing-Ming

2006-02-01

143

Measurements and Simulations of Surface Dielectric Barrier Discharges Used as Plasma Actuators  

NASA Technical Reports Server (NTRS)

This report is a Ph.D. dissertation performed under NRA cooperative agreement and submitted as part of the final report. Asymmetric surface dielectric barrier discharges (DBDs) have shown promise for use as aerodynamic actuators for active flow control. In this project we studied DBD actuators experimentally and numerically. Our DBDs used a symmetric triangular high voltage waveform to generate plasma in atmospheric pressure air. Time-averaged measurements indicated that the induced force of a single barrier actuator design (one electrode insulated from the plasma) can be increased exponentially above the results of previous studies by decreasing both the length and thickness of the electrode exposed to the plasma. This increased force may allow these devices to control flow separation in a wider range of flow environments. Experiments using an intensified digital camera to examine the plasma on time scales of a few nanoseconds showed that, in addition to the previously-observed filamentary and jet-like plasma structures, discharges with very thin exposed electrodes exhibited a weak but constant plasma immediately adjacent to those electrodes. In double-barrier actuators (both electrodes insulated), decreasing the diameter of the narrower electrode lead to increasing forces, and recorded images showed the simultaneous existence of both filamentary and jet-like plasma structures. The development and application of a time-dependent, two-dimensional computational fluid plasma model has aided in understanding the detailed physics of surface DBDs at all-time scales. For simulated single-barrier discharges, the model qualitatively reproduced the filamentary and jet-like micro-discharge structures. The model was somewhat successful in reproducing the observed characteristics of double-barrier actuators. For both actuator geometries, the model indicated that the majority of the forces induced on the neutral gas occur in between micro-discharges as the plasmas decay.

Hoskinson, Alan R.

2012-01-01

144

Achievement of precise force control for a tendon-driven rotary actuator with thrust wires and a PE line  

Microsoft Academic Search

Robots are taken attention as one of key solutions for nursing care field along with aging of population. In the nursing care field, the robots have to work in the limited space and contact with humans directly. Therefore miniaturization and precise force control are two important issues for nursing care robots. Then a tendon-driven rotary actuator with thrust wires and

Yusuke Suzuki; Keisuke Sugawara; Kouhei Ohnishi

2010-01-01

145

Transpiration actuation: the design, fabrication and characterization of biomimetic microactuators driven by the surface tension of water  

Microsoft Academic Search

We have designed, fabricated and characterized large displacement distributed-force polymer actuators driven only by the surface tension of water. The devices were inspired by the hygroscopic spore dispersal mechanism in fern sporangia. Microdevices were fabricated through a single mask process using a commercial photo-patternable silicone polymer to mimic the mechanical characteristics of plant cellulose. An analytical model for predicting the

Ruba T Borno; Joseph D Steinmeyer; Michel M Maharbiz

2006-01-01

146

Flow Control over a Conical Forebody by Periodic Pulsed Plasma Actuation  

NASA Astrophysics Data System (ADS)

The flow control mechanism of plasma actuators with periodic pulsed discharge to control the bi-stable vortices over a cone-cylinder is investigated. The actuators are installed on the leeward surface near the apex of a cone which has a semi-apex angle of 10°. The effectiveness of the plasma actuation under different free-stream velocities and angles of attack is analyzed. The pressure distributions over the conical forebody are measured by both steady and dynamic pressure transducers. The transient dynamic pressure distribution tends to gradually become steady as the free-stream velocity increases, that is, the pulsed actuation approximates a continuous one. Furthermore, the flow control effectiveness becomes less noticeable as the free-stream velocity or the angle of attack increases under certain controlling electrical parameters.

Zheng, Borui; Gao, Chao; Li, Yibin; Liu, Feng; Luo, Shijun

2013-04-01

147

Optical and electrical characterization of a surface dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

An experimental characterization of the properties of asymmetric surface dielectric barrier discharges used as plasma actuators was performed. Optical emission spectroscopy was used to measure the radiated power and some plasma parameters such as the electron and vibrational temperature. Electrical characterization of the discharge was executed by recording individual current pulses with high temporal resolution, and collecting a large dataset of these events. Statistical analysis performed on them allowed one to correlate microdischarge (MD) properties with the voltage phase and to spot differences arising from the actual breakdown mechanism in such asymmetric configurations. In particular, the asymmetry between the two different half-cycles of the discharges was characterized, and it was found that it directly influences plasma actuator efficiency. Differences arising in the multiplicity, amplitude and temporal duration of the MDs were investigated. Some effects connected with the dielectric material and high voltage supply properties were evaluated and correlated with the induced velocity provided by the plasma actuators.

Biganzoli, I.; Barni, R.; Riccardi, C.; Gurioli, A.; Pertile, R.

2013-04-01

148

Separation Control from the Flap of a High-Lift Airfoil using DBD Plasma Actuators  

Microsoft Academic Search

Control of separation from the deflected flap of a high-lift airfoil is explored using two asymmetric dielectric barrier discharge (DBD) plasma actuators straddling the flap shoulder for Reynolds numbers of 240,000 and 410,000. Actuators are found to be most effective when operated in an unsteady fashion at the natural oscillation frequency of the trailing edge flow field. The use of

Jesse Little; Munetake Nishihara; Igor Adamovich; Mo Samimy

2009-01-01

149

Control of Transitional and Turbulent Flows Using Plasma-Based Actuators  

Microsoft Academic Search

An exploratory numerical study of the control of transitional and turbulent separated flows by means of asymmetric dielectric-barrier-discharge (DBD) actuators is presented. The flow fields are simulated employ- ing an extensively validated high-fidelity Navier-Stokes s olver which is augmented with both phenomenological and first-principles models representing the plasma-induc ed body forces imparted by the actuator on the fluid. Several applications

Miguel R. Visbal; Datta V. Gaitonde; Subrata Roy

150

Spatiotemporal structure of a millimetric annular dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

The spatiotemporal structure of a millimetric annular dielectric barrier discharge plasma actuator is investigated using a photomultiplier tube, a high-sensitivity camera, particle image velocimetry, and electrohydrodynamics simulations. Plasma actuators have typically demonstrated their utility in flow separation control, but on a millimetric scale they have also shown to be promising in the control of crossflow instabilities in crossflow-dominated laminar-turbulent boundary-layer transition. In view of the subtleties associated with creating an initial disturbance to excite subcritical wavelengths, it is desirable to characterize the local plasma discharge structure, body force organization, and induced velocity field in detail. The results show that, similar to their linear centimetric counterpart, the plasma discharge has a highly dynamic and somewhat organized spatiotemporal structure. Under quiescent flow conditions, the actuator induces a velocity field that consists of two counter-rotating vortices, accompanied by a wall-normal synthetic jet region, which in three-dimensions describes a toroidal vortex around the aperture's periphery. The surprising result, however, is that these vortices rotate in the opposite direction to vortices generated by similar centimetric annular designs. Three-dimensional electrohydrodynamics simulations correctly reproduce this behavior. Because the body force organization may be qualitatively perceived as being the axisymmetric counterpart of the more classical linear actuator, this flow reversal is thought to be due to the actuator scale. When an array of millimetric actuators is considered in close proximity, an interaction takes place between the vortices created from each actuator and those of neighboring actuators, resulting in a significant reduction in vortex size compared with the single aperture case, accompanied by an increase in the maximum induced flow velocity magnitude.

Humble, R. A.; Craig, S. A.; Vadyak, J.; McClure, P. D.; Hofferth, J. W.; Saric, W. S.

2013-01-01

151

Modeling and Experiment of Leading Edge Separation Control Using SDBD Plasma Actuators  

Microsoft Academic Search

This work presents the study of the single-dielectric barrier discharge aerodynamic plasma actuator. To model the physics of the plasma discharge, a space-time lumped- element circuit model was developed. The model solution compared well to some of the characteristic features of the discharge such as the dependence of the sweep velocity and maximum extent of the ionized air as functions

Dmitriy M. Orlov; Thomas Apker; Chuan He; Hesham Othman; Thomas C. Corke

2007-01-01

152

Aerogel and ferroelectric dielectric materials for plasma actuators  

NASA Astrophysics Data System (ADS)

This paper presents performance evaluation of two thick materials with extreme permittivity as dielectric barrier discharge actuators. Specifically, the use of silica aerogels and ferroelectrics is investigated. Due to high polarizability of the ferroelectric material the supplied power manifests itself primarily as heat generation with no measurable thrust. The silica aerogel, however, has a significant impact on thrust saturation as compared with other dielectrics reported to date. Specifically, the silica aerogel is found to have an order of magnitude better thrust to actuator weight ratio than acrylic and twice than that of Kapton with no power penalty, making it potentially useful for small vehicle applications.

Durscher, Ryan; Roy, Subrata

2012-01-01

153

Phase effect on flow control for dielectric barrier plasma actuators  

SciTech Connect

Active control of flow has a wide range of applications. Specifically, mitigation of detachment due to the weakly ionized gas flow past a flat plate at an angle of attack is studied using two asymmetric sets of electrode pairs kept at a phase lag. The equations governing the dynamics of electrons, helium ions, and neutrals are solved self-consistently with charge-Poisson equation. The electrodynamic forces produced by two actuators largely depend on the relative phase between the potentials applied to rf electrodes and distance between them. A suitable phase and an optimum distance exist between two actuators for effective separation control.

Singh, K. P.; Roy, Subrata [Computational Plasma Dynamics Laboratory, Mechanical Engineering, Kettering University, Flint, Michigan 48504 (United States)

2006-07-03

154

Low voltage driven piggy-back actuator of hard disk drives  

Microsoft Academic Search

Fine positioning by a piggy-back actuator is essential in order to increase the recording density of hard disk drives (HDDs). We therefore developed a piggy-back actuator that generates a 1.4-?m displacement at 5 V. This displacement is twice as large as that of the usual piggy-back actuators. This actuator satisfies all requirements for HDDs including track density of 30 kilotracks

I. Naniwa; S. Nakamura; S. Saegusa; K. Sato

1999-01-01

155

Current Driven Plasma Instabilities in Lower Dimensional Systems.  

National Technical Information Service (NTIS)

Our earlier work on the possibility of spontaneous generation of plasma waves in current driven lower dimensional solid state systems is reviewed and extended, and new directions are suggested. Feasibility of plasma wave generation has been shown for unif...

P. Bakshi K. Kempa

1995-01-01

156

Comparisons of Force Measurement Methods for DBD Plasma Actuators in Quiescent Air  

NASA Technical Reports Server (NTRS)

We have performed measurements of the force induced by both single (one electrode insulated) and double (both electrodes insulated) dielectric barrier discharge plasma actuators in quiescent air. We have shown that, for single barrier actuators with cylindrical exposed electrodes, as the electrode diameter decrease the force efficiencies increase much faster than a previously reported linear trend. This behavior has been experimentally verified using two different measurement techniques: stagnation probe measurements of the induced flow velocity and direct measurement of the force using an electronic balance. Actuators with rectangular cross-section exposed electrodes do not show the same rapid increase at small thicknesses. We have also shown that the induced force is independent of the material used for the exposed electrode. The same techniques have shown that the induced force of a double barrier actuator increases with decreasing narrow electrode diameter.

Hoskinson, Alan R.; Hershkowitz, Noah; Ashpis, David E.

2009-01-01

157

Surface dielectric barrier discharge: Effect of encapsulation of the grounded electrode on the electromechanical characteristics of the plasma actuator  

Microsoft Academic Search

Active flow control is a rapidly developing topic because the associated industrial applications are of immense importance, particularly for aeronautics. Among all the flow control actuators, plasma-based devices are very promising. In most cases, the plasma actuator is based on a surface dielectric barrier discharge (DBD) established between two electrodes flush mounted on both sides of a dielectric layer. In

Jean-Charles Laurentie; Jérôme Jolibois; Eric Moreau

2009-01-01

158

Design and characterization of a plasma actuator for controlling dynamic stall  

NASA Astrophysics Data System (ADS)

A repetitive pulsed spark discharge inside of a ˜1 mm cavity generates a high velocity (100-600 m/s) gas jets potentially capable of controlling dynamic stall on an airfoil at Re ˜1e6. High temperature compressible 2D CFD was used to determine the design and geometry of the actuator slot and plasma cavity. Experimental results measuring the time dependent plasma discharge emission and density variations (using gated ICCD and Schlieren) indicate that the plasma can be modeled as constant volume heating over 100 ns. The energy input to the actuator is controlled by the high voltage and capacitance initiating the discharge. During the discharge air in the cavity is rapidly heated. Temperature and pressure increase 5-10x, causing strong gradients and shocks. The flow is directed using an angled slot. In CFD designed geometries shock fronts and high temperature gas velocities are experimentally determined. The force generated by the actuator is also experimentally determined. Experimental results from the actuator show that velocities of 500 m/s can be achieved through 1mm2 orifices with energy inputs of 50 mJ. The CFD model predicts time scales and velocities similar to those observed, and it also indicates cavity cooling as important in optimizing the actuator pulse repetition rate.

Pollard, William; Staack, David

2012-10-01

159

Damping Tollmien-Schlichting waves in a boundary layer using plasma actuators  

NASA Astrophysics Data System (ADS)

The response of a zero pressure gradient boundary layer modified by flow-wise oriented momentum injection similar to that of a plasma actuator is calculated using a two-dimensional (bi-global) stability analysis. It is found that the addition of momentum into the boundary layer has a significant impact on Tollmien-Schlichting waves, which may be damped by up to two orders of magnitude. Changes to the exponential growth rate of the perturbations are also measured. These stabilizing effects are largely due to the momentum addition modifying the downstream boundary layer profiles, but localized stabilization effects are also noted. The relative stabilization of the TS wave appears to be a linear function with respect to the ratio of the plasma-induced wall jet velocity under quiescent conditions and the free-stream velocity for lower levels of plasma actuation (i.e. velocity ratios less than 0.1). For higher levels of plasma actuation, the relative stabilization of the TS wave appears to be exponential with respect to the total momentum addition to the boundary layer by the plasma actuator.

Riherd, Mark; Roy, Subrata

2013-12-01

160

On factors influencing arc filament plasma actuator performance in control of high speed jets  

NASA Astrophysics Data System (ADS)

Localized arc filament plasma actuators (LAFPAs) have been developed and used at The Gas Dynamics and Turbulence Laboratory for the purpose of controlling high-speed and high Reynolds number jets. The ability of LAFPAs for use in both subsonic and supersonic jets has been explored, and experiments to date have shown that these actuators have significant potential for mixing enhancement and noise control applications. While it has been established that the actuators manipulate instabilities of the jet, the exact nature of how the actuation couples to the flow is still unclear. All of the results previously reported have been based on a nozzle extension that has an azimuthal groove of 1 mm width and 0.5 mm depth along the inner surface approximately 1 mm upstream of nozzle extension exit. The ring groove was initially added to shield the plasma arcs from the high-momentum flow. However, the effect of the ring groove on the actuation mechanism is not known. To explore this effect, a new nozzle extension is designed, which relocates the actuators to the nozzle extension face and eliminates the ring groove. Schlieren images, particle image velocimetry and acoustic results of a Mach 0.9 jet of Reynolds number ~6.1 × 105 show similar trends and magnitudes with and without a ring groove. Thus, it is concluded that the ring groove does not play a primary role in the LAFPAs' control mechanism. Furthermore, the effect of the duty cycle of the actuator input pulse on the LAFPAs' control authority is investigated. The results show that the minimum duty cycle that provides complete plasma formation has the largest control over the jet.

Hahn, Casey; Kearney-Fischer, Martin; Samimy, Mo

2011-12-01

161

Fabrication and characterization of laterally-driven piezoelectric bimorph MEMS actuator with sol-gel-based high-aspect-ratio PZT structure  

NASA Astrophysics Data System (ADS)

This paper reports on the fabrication and characterization of a novel laterally-driven piezoelectric bimorph micro electro mechanical systems actuator with high aspect-ratio (AR) lead-zirconate-titanate (PZT) structures. The PZT structures (AR=8) sandwiched with Pt sidewall electrodes were fabricated by a nanocomposite sol-gel process with micromachined silicon templates. A single-cantilever-type lateral bimorph actuator was successfully fabricated, and no initial vertical bending was observed, even on a 500 µm long actuator. A lateral displacement of 10 µm was obtained in bimorph actuation at driving voltages of +25 V/-5 V. Then the piezoelectric property of the PZT structure was characterized from the actuator's performance. The lateral piezoelectric actuator has a variety of potential applications as a replacement for electrostatic comb drive actuators occupying a large area.

Yoshida, Shinya; Wang, Nan; Kumano, Masafumi; Kawai, Yusuke; Tanaka, Shuji; Esashi, Masayoshi

2013-06-01

162

Flow and Noise Control in High Speed and High Reynolds Number Jets Using Plasma Actuators  

NASA Technical Reports Server (NTRS)

The idea of manipulating flow to change its characteristics is over a century old. Manipulating instabilities of a jet to increase its mixing and to reduce its radiated noise started in the 1970s. While the effort has been successful in low-speed and low Reynolds number jets, available actuators capabilities in terms of their amplitude, bandwidth, and phasing have fallen short in control of high-speed and high Reynolds number jets of practical interest. Localized arc filament plasma actuators have recently been developed and extensively used at Gas Dynamics and Turbulence Laboratory (GDTL) for control of highspeed and high Reynolds number jets. While the technique has been quite successful and is very promising, all the work up to this point had been carried out using small high subsonic and low supersonic jets from a 2.54 cm diameter nozzle exit with a Reynolds number of about a million. The preliminary work reported in this paper is a first attempt to evaluate the scalability of the technique. The power supply/plasma generator was designed and built in-house at GDTL to operate 8 actuators simultaneously over a large frequency range (0 to 200 kHz) with independent control over phase and duty cycle of each actuator. This allowed forcing the small jet at GDTL with azimuthal modes m = 0, 1, 2, 3, plus or minus 1, plus or minus 2, and plus or minus 4 over a large range of frequencies. This power supply was taken to and used, with minor modifications, at the NASA Nozzle Acoustic Test Rig (NATR). At NATR, 32 actuators were distributed around the 7.5 in. nozzle (a linear increase with nozzle exit diameter would require 60 actuators). With this arrangement only 8 actuators could operate simultaneously, thus limiting the forcing of the jet at NATR to only three azimuthal modes m = plus or minus 1, 4, and 8. Very preliminary results at NATR indicate that the trends observed in the larger NASA facility in terms of the effects of actuation frequency and azimuthal modes are similar in both small GDTL and larger NASA jets. However, the actuation authority seems to fall short in the larger jet at higher Mach numbers, resulting in decreased amplitude response compared to the small jet, which is attributed at this point to the lack of sufficient number of actuators. The preliminary results seem also to suggest that amplitude of actuation tones is similar in both the small and larger jets.

Samimy, M.; Kastner, J.; Kim, J.-H.; Utkin, Y.; Adamovich, I.; Brown, C. A.

2006-01-01

163

Current-Driven Filament Instabilities in Relativistic Plasmas. Final report  

SciTech Connect

This grant has supported a study of some fundamental problems in current- and flow-driven instabilities in plasmas and their applications in inertial confinement fusion (ICF) and astrophysics. It addressed current-driven instabilities and their roles in fast ignition, and flow-driven instabilities and their applications in astrophysics.

Chuang Ren

2013-02-13

164

Aerodynamic plasma actuators: A directional micro-jet device  

Microsoft Academic Search

In recent years electroaerodynamic actuators have been rather intensively studied in order to control airflow [H. Velkoff, R. Godfrey, J. of Heat Transfer 101 (1979) 157; S. El-Khabiry, G.M. Colver, Phys. Fluids 9 3 (1997) 587; A. Soldati, S. Banerjee, Phys. Fluids 10 (1998) 1742; R. Vilela Mendes, J.A. Dente, J. Fluids Eng. 120 (1998) 626; A. Schütze, et al.,

Nicolas Bénard; Jérôme Jolibois; Eric Moreau; Roberto Sosa; Guillermo Artana; Gérard Touchard

2008-01-01

165

Velocity-information-based force-term estimation of dielectric-barrier discharge plasma actuators  

NASA Astrophysics Data System (ADS)

Particle image velocimetry measurements in close proximity to dielectric-barrier discharge plasma actuators are conducted to quantify the momentum transfer of the plasma to the surrounding air flow. Based on these data a comparative analysis of six existing approaches to estimate the induced body force is presented. Integral methods calculate an integral value for the actuator force based on the momentum-balance equation. Insight into the spatial distribution of the body force is provided by differential methods, which are based either on the Navier-Stokes equations or on the vorticity equation. It is demonstrated that the intensity as well as the domain of the force increase with increasing operating power levels. Emphasis is also placed on the issue of self-induced drag. It is shown that 30% of the induced momentum is consumed by wall friction. All results are validated with previously obtained balance force data and luminosity analysis of identical actuators.

Kriegseis, J.; Schwarz, C.; Tropea, C.; Grundmann, S.

2013-02-01

166

Propagating-arc magnetohydrodynamic plasma actuator for directional high-authority flow control in atmospheric air  

NASA Astrophysics Data System (ADS)

A propagating-arc magnetohydrodynamic plasma actuator for aerodynamic flow control is reported. The actuator comprises two rail electrodes flush mounted on an aerodynamic surface. A pulsed arc is propelled down the length of the rails by Lorentz forces supported by a self-induced magnetic field. The arc induces a high velocity pulsed air wall jet due to the pushing and entrainment actions. Experiments in quiescent air demonstrate that the plasma arc achieves a peak velocity of around 100 m s-1 and requires a discharge energy on the order of 300 J per pulse. Wind tunnel tests on a 14.5 inch chord airfoil section, at a Reynolds number of 0.45 million show induced flow velocities on the order of 10's m s-1 with significant penetration of the flow actuation effect perpendicular to the wall surface.

Pafford, Brent; Sirohi, Jayant; Raja, Laxminarayan L.

2013-12-01

167

Combining Model-Based and Feature-Driven Diagnosis Approaches - A Case Study on Electromechanical Actuators  

NASA Technical Reports Server (NTRS)

Model-based diagnosis typically uses analytical redundancy to compare predictions from a model against observations from the system being diagnosed. However this approach does not work very well when it is not feasible to create analytic relations describing all the observed data, e.g., for vibration data which is usually sampled at very high rates and requires very detailed finite element models to describe its behavior. In such cases, features (in time and frequency domains) that contain diagnostic information are extracted from the data. Since this is a computationally intensive process, it is not efficient to extract all the features all the time. In this paper we present an approach that combines the analytic model-based and feature-driven diagnosis approaches. The analytic approach is used to reduce the set of possible faults and then features are chosen to best distinguish among the remaining faults. We describe an implementation of this approach on the Flyable Electro-mechanical Actuator (FLEA) test bed.

Narasimhan, Sriram; Roychoudhury, Indranil; Balaban, Edward; Saxena, Abhinav

2010-01-01

168

LES of a Jet Excited by the Localized Arc Filament Plasma Actuators  

NASA Technical Reports Server (NTRS)

The fluid dynamics of a high-speed jet are governed by the instability waves that form in the free-shear boundary layer of the jet. Jet excitation manipulates the growth and saturation of particular instability waves to control the unsteady flow structures that characterize the energy cascade in the jet.The results may include jet noise mitigation or a reduction in the infrared signature of the jet. The Localized Arc Filament Plasma Actuators (LAFPA) have demonstrated the ability to excite a high-speed jets in laboratory experiments. Extending and optimizing this excitation technology, however, is a complex process that will require many tests and trials. Computational simulations can play an important role in understanding and optimizing this actuator technology for real-world applications. Previous research has focused on developing a suitable actuator model and coupling it with the appropriate computational fluid dynamics (CFD) methods using two-dimensional spatial flow approximations. This work is now extended to three-dimensions (3-D) in space. The actuator model is adapted to a series of discrete actuators and a 3-D LES simulation of an excited jet is run. The results are used to study the fluid dynamics near the actuator and in the jet plume.

Brown, Clifford A.

2011-01-01

169

Capacitances and energy deposition curve of nanosecond pulse surface dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

Nanosecond pulse surface dielectric barrier discharge (NPSDBD) plasma actuator is preferred to generate aerodynamic actuation which relies on the deposited energy during nanosecond time scale, named as the mechanism of fast thermalization. It is very important to understand the energy deposition process of NPSDBD plasma actuator. In this paper, an equivalent circuit model is presented to describe a typical asymmetric NPSDBD plasma actuator first. Of the three key capacitances in the equivalent circuit, the values of Capacitance Cm and Cg can be gotten by the calculation of the electric field, with the method of undetermined coefficients, while the value of Capacitance Cd is determined from the charge-voltage (Q-V) plot, also called Lissajous figure. It is found that the value of Capacitance Cd varies with the amplitude of applied pulse voltage, due to the change of the dimension of plasma sheet. Based on the circuit parameters and the measured waveforms of discharge voltage and current, the time varying characteristics of deposited energy can be obtained finally. It is indicated that the calculated results of deposited energy show a good agreement with conventional method.

Pang, Lei; He, Kun; Di, Dongxu; Zhang, Qiaogen; Liu, Chunliang

2014-05-01

170

Study of Control Parameters for Separation Mitigation Using an Asymmetric Single Dielectric Barrier Plasma Actuator.  

National Technical Information Service (NTIS)

Separation mitigation using asymmetric dielectric barrier discharges is studied by considering the neutral gas flow past a flat plate at an angle of attack. A self-consistent plasma actuator model is employed to couple the electric force field to the mome...

D. V. Gaitonde K. P. Singh S. Roy

2006-01-01

171

Capacitances and energy deposition curve of nanosecond pulse surface dielectric barrier discharge plasma actuator.  

PubMed

Nanosecond pulse surface dielectric barrier discharge (NPSDBD) plasma actuator is preferred to generate aerodynamic actuation which relies on the deposited energy during nanosecond time scale, named as the mechanism of fast thermalization. It is very important to understand the energy deposition process of NPSDBD plasma actuator. In this paper, an equivalent circuit model is presented to describe a typical asymmetric NPSDBD plasma actuator first. Of the three key capacitances in the equivalent circuit, the values of Capacitance Cm and Cg can be gotten by the calculation of the electric field, with the method of undetermined coefficients, while the value of Capacitance Cd is determined from the charge-voltage (Q-V) plot, also called Lissajous figure. It is found that the value of Capacitance Cd varies with the amplitude of applied pulse voltage, due to the change of the dimension of plasma sheet. Based on the circuit parameters and the measured waveforms of discharge voltage and current, the time varying characteristics of deposited energy can be obtained finally. It is indicated that the calculated results of deposited energy show a good agreement with conventional method. PMID:24880363

Pang, Lei; He, Kun; Di, Dongxu; Zhang, Qiaogen; Liu, Chunliang

2014-05-01

172

Separation control in low pressure turbines using plasma actuators with passing wakes  

NASA Astrophysics Data System (ADS)

A Dielectric Barrier Discharge (DBD) plasma actuator is operated in flow over the suction surface of a Pack-B Low Pressure Turbine (LPT) airfoil at a Reynolds number of 50,000 (based on exit velocity and suction surface length) and inlet free-stream turbulence intensity of 2.5%. Preliminary characterization studies were made of the effect of varying actuator pulsing frequency and duty cycle, actuator edge effects, and orientation of the actuator with the flow. Flow control was demonstrated with the actuator imparting momentum opposite to the stream-wise flow direction, showing that it is possible to use disturbances alone to destabilize the flow and effect transition. No frequencies of strong influence were found over the range tested, indicating that a broad band of effective frequencies exists. Edge effects were found to considerably enhance separation control. Total pressure measurements of the flow without passing wakes were taken using a glass total-pressure tube. Corrections for streamline displacement due to shear and wall effects were made, and comparisons with previous hot-wire measurements were used to validate data. Performance features of conventional two-electrode and a novel three-electrode actuator configuration were compared. Hot-wire anemometry was used to take time-varying ensemble-averaged near-wall velocity measurements of the flow with periodic passing wakes. Corrections were made for near-wall effects, temperature effects, and interference of the electric field. The wakes were generated by a wake generator mechanism located upstream of the airfoil passage. The near-suction-surface total pressure field (flow without wakes) and velocity field (flow with wakes) in the trailing part of the airfoil passage, and the wall-normal gradient of these quantities, were used to demonstrate effective prevention of flow separation using the plasma actuator. Both flows (with and without passing wakes) showed fully attached flow (or very thin separation zones) when the actuator was activated. The flow with passing wakes and the actuator on showed relatively little time variation in the boundary layer, and qualitative similarities to the corresponding flow without passing wakes and with the actuator on were noted.

Burman, Debashish

173

Printed artificial cilia from liquid-crystal network actuators modularly driven by light  

Microsoft Academic Search

Polymeric microactuators are potentially useful in micromechanical systems and lab-on-a-chip systems. However, manufacturing of miniature polymeric actuators has been complicated owing to the necessity of including electrodes for actuation or using lithographic techniques for patterning. Here, we demonstrate that all-polymer microdevices can be fabricated using inkjet printing technology in combination with self-organizing liquid-crystal network actuators. We exploit the self-assembling properties

Cees W. M. Bastiaansen; Dirk J. Broer; Casper L. van Oosten

2009-01-01

174

Research on Properties of Water Hydraulic Servo Valve Driven by Diphase Oppositing Giant Magnetostrictive Actuator  

Microsoft Academic Search

A new type of diphase oppositing giant magetostrictive self-sensing actuator force-feedback water hydraulic servo valve is introduced, including its structure and working principle. The electro-mechanical convert model of the diphase oppositing magetostrictive self-sensing actuator is established, based on this, the mathematical model of the servo valve is constructed. The static output characteristics of the actuator is simulated in MATLAB and

Wang Xinhua; Li Wei; Ruan Zhongyan; Zheng Jian; Sun Shuwen

2010-01-01

175

Plasma bolometry using a multislit shutter with piezoelectric actuator  

SciTech Connect

We offer to apply a shutter with a piezoelectric bimorph actuator as a modulator of radiation and particle fluxes. Such shutters may be useful to provide measurements in steady state regimes of tokamaks and stellarators because they allow one to avoid amplifier drifts and to simplify diagnostics calibration. Signal modulation makes it possible to apply the lock-in amplification technique, increasing the sensitivity and reducing the neutron doze collected by sensors. Experiments with pyroelectric sensors (LiTaO{sub 3}) at 350 Hz modulation frequency have demonstrated the detection limit at 30 Hz equal to 15 {mu}W/cm{sup 2}, which is comparable to metallic bolometers.

Kuteev, Boris V.; Outkine, Andrew A.; Gabdullin, Pavel G.; Kostrioukov, Artem Yu.; Kapralov, Vladimir G. [Nuclear Fusion Institute, RRC Kurchatov Institute, Moscow 123182 (Russian Federation); Technical University Applied Physics Ltd., St. Petersburg 195251 (Russian Federation)

2004-10-01

176

Parametric study of vortex train generated by plasma actuator in dependency on input voltage waveform  

NASA Astrophysics Data System (ADS)

This article is based on previous work of authors. The vortex train is created by a plasma DBD actuator after application of low-frequency amplitude modulation on high-frequency high-voltage carrier waveform. Data acquisition of flow field around actuators will be performed using time-resolved PIV measurement technique in plane parallel to flow and in cross-section. Phase-averaging will be used due to pseudo-periodical character of this process. The vortex behaviour dependency on modulation frequency, duty cycle, voltage value, electrode gap and other parameters will be shown. The generated flow patterns are to be applied for control of a boundary layer.

Procházka, P.; Uruba, V.

2013-04-01

177

[Experimental investigation on plasma assistant combustion actuator in argon/air].  

PubMed

In order to obtain the characteristics of argon/air plasma assistant combustion actuators, experiments of three different actuators with normal, paratactic and meshy electrode configurations were respectively performed in argon/air mixture firstly, the results showed that the shape of electrode has little influence on the discharge characteristics. Then normal electrode was applied to study spectrum and discharge characteristics under the condition of 100% air and 10% argon/90% air. The comparison showed that, though in mixture the law of discharge characteristic was the same as that of pure air, discharge current and emission spectrum were strengthened, and initial discharge voltage reduced from 27 to 24 kV. PMID:22512154

Du, Hong-liang; He, Li-ming; Ding, Wei; Zhao, Bing-bing; Wang, Feng

2012-02-01

178

Development of localized arc filament RF plasma actuators for high-speed and high Reynolds number flow control  

Microsoft Academic Search

Recently developed localized arc filament plasma actuators (LAFPAs) have shown tremendous control authority in high-speed\\u000a and high Reynolds number flow for mixing enhancement and noise mitigation. Previously, these actuators were powered by a high-voltage\\u000a pulsed DC plasma generator with low energy coupling efficiency of 5–10%. In the present work, a new custom-designed 8-channel\\u000a pulsed radio frequency (RF) plasma generator has

J.-H. Kim; M. Nishihara; I. V. Adamovich; M. Samimy; S. V. Gorbatov; F. V. Pliavaka

2010-01-01

179

Expanding Plasma Region of an Inductively Driven Hydrogen Discharge  

Microsoft Academic Search

The spatial distribution of the plasma parameters - electron density and temperature as well as plasma and floating potentials - in the region of plasma expansion of an inductively driven low-pressure discharge in hydrogen is studied by probe diagnostics. Electron cooling and a decrease of the electron density with formation of regions with different axial gradients are outlined as basic

Zhivko Kiss'ovski; Stanimir Kolev; Antonia Shivarova; Tsanko Tsankov

2007-01-01

180

CNT/conductive polymer composites for low-voltage driven EAP actuators  

NASA Astrophysics Data System (ADS)

We investigated the effects of additives incorporated into the electrode layer in order to improve the actuation performance of dry-type carbon nanotube (CNT) actuators. Especially, the addition of conductive nano-particles such as polyaniline (PANI) and polypyrrole (PPy) improves actuation performance very much rather than the addition of nonconductive nano-particles such as mesoprous silica (MCM-41 type). In this paper, we studied on the influences of applied voltage, species of ionic liquid (IL), amounts of IL, thickness of actuator to optimize actuation performance. Imidazolium type ionic liquids with three different anions, that is, 1-ethyl-3-methylimidazolium (EMI) as a cation and tetrafluoroborate (BF4), trifluoromethanesulfonate (OTf), and bis(trifluoromethanesulfonyl)imide (TFSI) as anions were chosen in this study. EMIBF4 is the most suitable IL for our CNT actuator including PANI in the electrode layer. We tuned the amount of IL and the thickness of actuator. As a result, the strain was improved to be 2.2% at 0.1 Hz by applying the voltage of 2.5 V. This improved value is almost 2 times larger than our previous results. We also show the potential of improved CNT actuators for a thin and light Braille display.

Sugino, Takushi; Shibata, Yoshiyuki; Kiyohara, Kenji; Asaka, Kinji

2012-03-01

181

An instant multi-responsive porous polymer actuator driven by solvent molecule sorption.  

PubMed

Fast actuation speed, large-shape deformation and robust responsiveness are critical to synthetic soft actuators. A simultaneous optimization of all these aspects without trade-offs remains unresolved. Here we describe porous polymer actuators that bend in response to acetone vapour (24?kPa, 20?°C) at a speed of an order of magnitude faster than the state-of-the-art, coupled with a large-scale locomotion. They are meanwhile multi-responsive towards a variety of organic vapours in both the dry and wet states, thus distinctive from the traditional gel actuation systems that become inactive when dried. The actuator is easy-to-make and survives even after hydrothermal processing (200?°C, 24?h) and pressing-pressure (100?MPa) treatments. In addition, the beneficial responsiveness is transferable, being able to turn 'inert' objects into actuators through surface coating. This advanced actuator arises from the unique combination of porous morphology, gradient structure and the interaction between solvent molecules and actuator materials. PMID:24980606

Zhao, Qiang; Dunlop, John W C; Qiu, Xunlin; Huang, Feihe; Zhang, Zibin; Heyda, Jan; Dzubiella, Joachim; Antonietti, Markus; Yuan, Jiayin

2014-01-01

182

Force Measurements of Single and Double Barrier DBD Plasma Actuators in Quiescent Air  

NASA Technical Reports Server (NTRS)

We have performed measurements of the force induced by both single (one electrode insulated) and double (both electrodes insulated) dielectric barrier discharge plasma actuators in quiescent air. We have shown that, for single barrier actuators, as the electrode diameter decreased below those values previously studied the induced Force increases exponentially rather than linearly. This behavior has been experimentally verified using two different measurement techniques: stagnation probe measurements of the induced flow velocity and direct measurement of the force using an electronic balance. In addition, we have shown the the induced force is independent of the material used for the exposed electrode. The same techniques have shown that the induced force of a double barrier actuator increases with decreasing narrow electrode diameter.

Hoskinson, Alan R.; Hershkowitz, Noah; Ashpis, David E.

2008-01-01

183

Control of oblique shock wave/boundary layer interactions using plasma actuators  

NASA Astrophysics Data System (ADS)

Localized arc filament plasma actuators (LAFPAs) are used for shock wave/boundary layer interaction induced separation control in a Mach 2.3 flow. The boundary layer is fully turbulent with a Reynolds number based on the incompressible momentum thickness of 22,000 and shape factor of 1.37, and the impinging shock wave is generated by a 10° compression ramp. The LAFPAs are observed to have significant control authority over the interaction. The main effect is the displacement of the reflected shock and most of the interaction region upstream by approximately one boundary layer thickness (~5 mm). The initial goal of the control was to manipulate the low-frequency ( St~0.03) unsteadiness associated with the interaction region. A detailed investigation of the effect of actuator placement, frequency, and duty cycle on the control authority indicates the actuators' primary control mechanism is not the manipulation of low-frequency unsteadiness. Detailed measurements and analysis indicate that a modification to the boundary layer through heat addition by the actuators is the control mechanism, despite the extremely small power input of the actuators.

Webb, N.; Clifford, C.; Samimy, M.

2013-06-01

184

Role of the electric waveform supplying a dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

The paper compares the influence of different waveforms as input for a dielectric barrier discharge plasma actuator investigated in context of plasma-assisted flow control. The electrical aspects, the plasma morphology, the body force production, and the two-component time-resolved electric wind produced over a single ac period of signal are investigated. Results shown that square waveform is optimal in terms of body force and mean electric wind production, but the velocity fluctuations are enhanced by using a sinusoidal waveform. The time-resolved measurements of the produced velocity demonstrate that the electromechanical conversion mechanism is quasi-linear in the vicinity of the discharge.

Benard, N.; Moreau, E.

2012-05-01

185

Two-dimensional scanning probe driven by a solenoid-based single actuator for optical coherence tomography.  

PubMed

We propose the two-dimensional scanning probe operating with a single actuator, which is thought useful as a sample probe for optical coherence tomography (OCT). The probe was designed to use a single-body lensed fiber cantilever loaded with an iron-bead and driven by a single-solenoid actuator. Elliptic spiral trace patterns were achieved using off-axis magnetic fields of the solenoid. A three-dimensional OCT image was obtained for a scanning area of 3.8 mm × 3.4 mm at an acquisition speed of 16.7 s/V. Up to 27 Hz B-scan rate, the proposed probe worked well, and 1000 A-scans were made per each B-scan. PMID:21633416

Min, Eun Jung; Shin, Jun Geun; Kim, Yuri; Lee, Byeong Ha

2011-06-01

186

Short wavelength temperature gradient driven modes in tokamak plasmas.  

PubMed

New unstable temperature gradient driven modes in an inhomogeneous tokamak plasma are identified. These modes represent temperature gradient (ion and electron) driven modes destabilized in the short wavelength regions with k( perpendicular )rho(i,e)>1, respectively. The instability occurs due to a specific plasma response that significantly deviates from Boltzmann distribution in the regions k( perpendicular )rho(i,e)>1. PMID:12225092

Smolyakov, A I; Yagi, M; Kishimoto, Y

2002-09-16

187

Reattachment of a Separated Boundary Layer on a Flat Plate in a Highly Adverse Pressure Gradient Using a Plasma Actuator(POSTPRINT).  

National Technical Information Service (NTIS)

An experimental study was performed to examine the phase-dependent response characteristics of a dielectric barrier discharge plasma flow control actuator. The actuator was investigated on a fully separated flat plate boundary layer with an adverse freest...

I. G. Boxx R. B. Rivir J. M. Newcamp N. M. Woods

2006-01-01

188

Reattachment of a Separated Boundary Layer on a Flat Plate in a Highly Adverse Pressure Gradient Using a Plasma Actuator (Postprint).  

National Technical Information Service (NTIS)

An experimental study was performed to examine the phase-dependent response characteristics of a dielectric barrier discharge plasma flow control actuator. The actuator was investigated on a fully separated flat plate boundary layer with an adverse freest...

I. G. Boxx J. M. Newcamp N. M. Woods R. B. Rivir

2006-01-01

189

Simulations of the linear plasma synthetic jet actuator utilizing a modified Suzen-Huang model  

NASA Astrophysics Data System (ADS)

The linear plasma synthetic jet actuator (L-PSJA) is a unique form of flow control device which harnesses the interaction of induced flows from two linear plasma actuators to form an upward jet. Since each injection can be manipulated in intensity, the synthetic jet has thrust vectoring properties. Our study simulates the L-PSJA by utilizing a modified Suzen-Huang (S-H) model that accounts for drift and diffusive properties in the surface charge. The results of the present model show that the centreline velocity is closer to the experimental values found in literature as compared to the default form of S-H modelling. Thrust vectoring simulations were also performed to demonstrate the feasibility of flow directional variation in the L-PSJA.

Ibrahim, I. H.; Skote, M.

2012-11-01

190

Numerical study of boundary layer separation control using magnetogasdynamic plasma actuators  

SciTech Connect

In this study, an efficient, time dependent, two-dimensional Navier-Stokes numerical code for shockwave boundary layer interaction in air is developed. Nonthermal surface plasma actuation is evaluated for effective shockwave induced boundary layer separation control within supersonic inlets. Specifically, high speed magnetogasdynamic plasma actuators are of interest. In these, localized ionization is produced close to the wall surface and then the flow is accelerated using strong magnetic fields. To replicate the experiments done at large boundary layer thickness, the code is divided into time independent and time dependent regimes to significantly reduce computation time. Computational results are in good agreement with experiments in terms of the flow structure as shown by Schlieren imaging, acetone planar laser scattering, and the static pressure profile on the test section wall.

Kalra, Chiranjeev S.; Shneider, Mikhail N.; Miles, Richard B. [Department of Mechanical and Aerospace Engineering, Applied Physics Group, Princeton University, Princeton, New Jersey 08544 (United States)

2009-10-15

191

Fabrication of a bubble-driven arrayed actuator for a tactile display  

NASA Astrophysics Data System (ADS)

A chip-sized arrayed actuator device has been developed for application to a tactile display. Each actuator uses a liquid-vapour phase change to drive a microneedle that stimulates receptors in a finger in contact with the array. The actuators have a flexible diaphragm structure and a bottom plate bonded together to create a cavity between them. A microneedle and a microheater are formed on the diaphragm and plate of each actuator, respectively. The sealed cavity is filled with an operating liquid. Activating the heater and generating bubbles, which is similar to the process of a thermal ink jet, increase the pressure in the cavity. As a result, the flexible membrane deforms and it drives the needle upwards to stimulate receptors. Microelectromechanical systems technologies are used to fabricate the three components of the actuators, which are manually assembled to form a 3 × 3 arrayed actuator device. The total size of the device is 15 × 15 × 1 mm. The device performance is experimentally evaluated and a large needle displacement (61 µm) is obtained with an input energy of 457 mJ.

Shikida, Mitsuhiro; Imamura, Tsubasa; Ukai, Shinji; Miyaji, Takaaki; Sato, Kazuo

2008-06-01

192

Sensitivity of an asymmetric 3D diffuser to plasma-actuator induced inlet condition perturbations  

Microsoft Academic Search

Experiments were conducted for the flow in a straight-walled 3D diffuser fed by a fully developed turbulent duct flow. Previous\\u000a work found that this diffuser has a stable 3D separation bubble whose configuration is affected by the secondary flows in\\u000a the upstream duct. Dielectric barrier discharge plasma actuators were used to produce low-momentum wall jets to determine\\u000a if the separation

S. Grundmann; E. L. Sayles; J. K. Eaton

2011-01-01

193

Active Noise Control in a Mach 1.3 Ideally-Expanded Jet with Plasma Actuators  

Microsoft Academic Search

Our earlier work in noise mitigation using localized arc filament plasma actuators in a Mach 0.9 axisymmetric jet was extended in this paper to an ideally expanded Mach 1.3 axisymmetric jet. Far-field noise was measured at 30? and 90? locations relative to the jet axis to investigate the effects of azimuthal mode and forcing Strouhal number on the far-field noise.

J. H. Kim; I. Adamovich; M. Samimy

2008-01-01

194

Spatio-temporal filament behaviour in a dielectric barrier discharge plasma actuator  

Microsoft Academic Search

The behaviour of filaments in a dielectric barrier discharge plasma actuator in atmospheric air has been visualized through high-speed framing photography. A filament is recognized by its radiation emission in the positive, ascending phase of an applied ac voltage (1-5 kV, 1-5 kHz). A current pulse appears with a random time-interval typically of the order of 10 µs. A filament

A. Sasoh; K. Kikuchi; T. Sakai

2007-01-01

195

Control of the corner separation in a compressor cascade by steady and unsteady plasma aerodynamic actuation  

Microsoft Academic Search

This paper reports experimental results on using steady and unsteady plasma aerodynamic actuation to control the corner separation,\\u000a which forms over the suction surface and end wall corner of a compressor cascade blade passage. Total pressure recovery coefficient\\u000a distribution was adopted to evaluate the corner separation. Corner separation causes significant total pressure loss even\\u000a when the angle of attack is

Ying-hong LiYun; Yun Wu; Min Zhou; Chang-Bing Su; Xiong-Wei Zhang; Jun-Qiang Zhu

2010-01-01

196

Airflow control by non-thermal plasma actuators  

Microsoft Academic Search

Active flow control is a topic in full expansion due to associated industrial applications of huge importance, particularly for aeronautics. Among all flow control methods, such as the use of mechanical flaps, wall synthetic jets or MEMS, plasma-based devices are very promising. The main advantages of such systems are their robustness, simplicity, low power consumption and ability for real-time control

Eric Moreau

2007-01-01

197

Numerical Simulations of Flow Separation Control in Low-Pressure Turbines using Plasma Actuators  

NASA Technical Reports Server (NTRS)

A recently introduced phenomenological model to simulate flow control applications using plasma actuators has been further developed and improved in order to expand its use to complicated actuator geometries. The new modeling approach eliminates the requirement of an empirical charge density distribution shape by using the embedded electrode as a source for the charge density. The resulting model is validated against a flat plate experiment with quiescent environment. The modeling approach incorporates the effect of the plasma actuators on the external flow into Navier Stokes computations as a body force vector which is obtained as a product of the net charge density and the electric field. The model solves the Maxwell equation to obtain the electric field due to the applied AC voltage at the electrodes and an additional equation for the charge density distribution representing the plasma density. The new modeling approach solves the charge density equation in the computational domain assuming the embedded electrode as a source therefore automatically generating a charge density distribution on the surface exposed to the flow similar to that observed in the experiments without explicitly specifying an empirical distribution. The model is validated against a flat plate experiment with quiescent environment.

Suzen, Y. B.; Huang, P. G.; Ashpis, D. E.

2007-01-01

198

An experimental study of a plasma actuator in absence of free airflow: Ionic wind velocity profile  

SciTech Connect

In this study, we are interested in the direct current electrical corona discharge created between two wire electrodes. The experimental results are related to some electroaerodynamic actuators based on the direct current corona discharge at the surface of a dielectric material. Several geometrical forms are selected for the dielectric surface, such as a plate, a cylinder, and a NACA 0015 aircraft wing. The current density-electric field characteristics are presented for different cases in order to determine the discharge regimes. The corona discharge produces nonthermal plasma, so it is called plasma discharge. Plasma discharge creates a tangential ionic wind above the surface at the vicinity of the wall. The ionic wind induced by the corona discharge is measured in absence of free external airflow. The ionic wind velocity profiles and the maximum induced tangential force are given for different surface forms, so it is possible to compare the actuators effect based on the span of the ionic wind velocity and thrust values. The higher ionic wind velocity is obtained with the NACA profile, which shows the effectiveness of this actuator for the airflow control.

Mestiri, R.; Hadaji, R.; Ben Nasrallah, S. [Ecole Nationale d'Ingenieurs de Monastir, Monastir 5019 (Tunisia)

2010-08-15

199

Enthalpy Measurement of Laser Driven Inductively Coupled Plasma Generator Flows  

Microsoft Academic Search

A laser driven inductively coupled plasma generator was developed. Firstly, the radio frequency (RF) of 13.56 MHz was applied to atmospheric argon laser sustained plasma (LSP) in a quartz tube. As a result, inductive coupling was successful and expansion of emission region was observed. Next, the LSP was produced ahead of a ceramic convergent-divergent nozzle throat and the RF was

Makoto MATSUI; Suisei YAMAGISHI; Kimiya KOMURASAKI; Yoshiki YAMAGIWA; Yoshihiro ARAKAWA

200

Plasma Rotation Effects on the Externally Driven Magnetic Island Formation  

Microsoft Academic Search

We investigate the effects of the current sheet caused by the Alfven resonance on the magnetic island formation by the externally applied perturbation in rotating plasmas. One of the important problems of the driven magnetic island formation is the onset of the rapid island growth after the flow-suppressed growth phase. This onset is triggered by the plasma rotation reduction around

Yasutomo Ishii; Andrei Smolyakov

2007-01-01

201

Behavior of Excited Argon Atoms in Inductively Driven Plasmas  

Microsoft Academic Search

Laser induced fluorescence has been used to measure the spatial distribution of the two lowest energy argon excited states, 1sâ and 1sâ, in inductively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the 1sâ level is metastable and the 1sâ level is radiatively coupled to

GREGORY A. HEBNER; PAUL A. MILLER

1999-01-01

202

Tethered cube stabilization by means of leading-edge DBD plasma actuation  

NASA Astrophysics Data System (ADS)

An experimental investigation was carried out to assess the effectiveness of active flow control as a means for suppressing oscillations of a tethered cube. Two experimental configurations were considered: a static configuration involving surface pressure and particle image velocimetry (PIV) flow field measurements and a dynamic, tethered, configuration. Corner-mounted, dielectric barrier discharge plasma actuators were employed at the leading-edges and were pulsed at reduced frequencies of order one and at varying duty cycles. On the static configuration, actuation changed the direction of the side-forces and virtually eliminated yawing-moment excursions. Surface pressure and flow field measurements showed that control of separation bubbles on the surfaces, as well as control of the separated shear layer, were responsible for these effects. Phase-averaged PIV measurements elucidated the mechanism whereby actuation severs the leading-edge vortex that subsequently sheds downstream. For the tethered cube, actuation dramatically reduced the yawing motions, particularly when the momentum coefficient exceeded 0.3 %. Drag reduction, based on the deflection of the cube, was estimated to be approximately 12 %, consistent with the static data. Reduced frequency and duty cycle had a marked effect on control effectiveness.

Goyta, Snir; Mueller-Vahl, Hanns; Greenblatt, David

2013-01-01

203

Progress Toward Accurate Measurements of Power Consumptions of DBD Plasma Actuators  

NASA Technical Reports Server (NTRS)

The accurate measurement of power consumption by Dielectric Barrier Discharge (DBD) plasma actuators is a challenge due to the characteristics of the actuator current signal. Micro-discharges generate high-amplitude, high-frequency current spike transients superimposed on a low-amplitude, low-frequency current. We have used a high-speed digital oscilloscope to measure the actuator power consumption using the Shunt Resistor method and the Monitor Capacitor method. The measurements were performed simultaneously and compared to each other in a time-accurate manner. It was found that low signal-to-noise ratios of the oscilloscopes used, in combination with the high dynamic range of the current spikes, make the Shunt Resistor method inaccurate. An innovative, nonlinear signal compression circuit was applied to the actuator current signal and yielded excellent agreement between the two methods. The paper describes the issues and challenges associated with performing accurate power measurements. It provides insights into the two methods including new insight into the Lissajous curve of the Monitor Capacitor method. Extension to a broad range of parameters and further development of the compression hardware will be performed in future work.

Ashpis, David E.; Laun, Matthew C.; Griebeler, Elmer L.

2012-01-01

204

Curvature Driven Instabilities in Toroidal Plasmas.  

National Technical Information Service (NTIS)

The electromagnetic ballooning mode, the curvature driven trapped electron mode and the toroidally induced ion temperature gradient mode have been studied. Eigenvalue equations have been derived and solved both numerically and analytically. For electromag...

P. Andersson

1986-01-01

205

Dust-driven and plasma-driven currents in the inner magnetosphere of Saturn  

NASA Astrophysics Data System (ADS)

General equations for dust-driven currents and current systems JD in magnetized plasmas are derived and, as a concrete example, applied to the E ring of Saturn at radial distances 3RSdriven current systems down to the ionosphere of Saturn, both rotating with the magnetospheric plasma. One of these closes across the polar cap, and the other over a limited range in latitude. These dust-driven current systems are embedded in three systems of plasma-driven currents Jp: a ring current, a cross-polar-cap current system, and an ion pickup current system. Both the JD and the Jp current systems have been quantitatively assessed from a data set for the E ring of Saturn in which the unknown distribution of small dust is treated by a power law extrapolation from the known distribution of larger dust. From data on the magnetic perturbations during a crossing of the equatorial plane, an approximate constraint on the fraction of the electrons that can be trapped on the dust is derived. For this amount of electron capture, it is demonstrated that all three types of dust-driven currents are, within somewhat more than an order of magnitude, of the same strength as the corresponding types of plasma-driven currents. Considering also that both plasma and dust densities vary with the geyser activity at the south pole of Enceladus, it is concluded that both the dust-driven and the plasma-driven contributions to the current system associated with the E ring need to be retained for a complete description.

Olson, J.; Brenning, N.

2012-04-01

206

Multiple vs. single harmonics AC-driven atmospheric plasma jet  

NASA Astrophysics Data System (ADS)

In this paper, we report a comparison between the most commonly used single harmonics (sine voltage waveform) and the original multiple harmonics AC-driven atmospheric-pressure plasma jet. The designed multiple harmonics source was applied to a single-electrode plasma jet. In this research, we characterized and studied the advantages of a single-electrode jet which was powered with multiple harmonics voltage waves, fundamental frequency was varied between 5 and 60 kHz. Optical emission spectroscopy, electric probes and plasma jet visible length measurements lead to the conclusion that the optical emission intensity of emitting plasma species correlates with the discharge current RMS (Root Mean Square), whereas the jet visible length correlates with the electrode discharge voltage amplitude. These properties of the plasma jet cannot be obtained with single harmonics AC-driven plasma jets.

Zaplotnik, R.; Kregar, Z.; Biš?an, M.; Vesel, A.; Cvelbar, U.; Mozeti?, M.; Miloševi?, S.

2014-04-01

207

Aerospace induction motor actuators driven from a 20-kHz power link  

NASA Technical Reports Server (NTRS)

Aerospace electromechanical actuators utilizing induction motors are under development in sizes up to 40 kW. While these actuators have immediate application to the Advanced Launch System (ALS) program, several potential applications are currently under study including the Advanced Aircraft Program. Several recent advances developed for the Space Station Freedom have allowed induction motors to be selected as a first choice for such applications. Among these technologies are bi-directional electronics and high frequency power distribution techniques. Each of these technologies are discussed with emphasis on their impact upon induction motor operation.

Hansen, Irving G.

1990-01-01

208

Direct in situ observation of structural transition driven actuation in VO2 utilizing electron transparent cantilevers  

NASA Astrophysics Data System (ADS)

Direct imaging and quantification of actuation in nanostructures that undergo structural phase transitions could advance our understanding of collective phenomena in the solid state. Here, we demonstrate visualization of structural phase transition induced actuation in a model correlated insulator vanadium dioxide by in situ Fresnel contrast imaging of electron transparent cantilevers. We quantify abrupt, reversible cantilever motion occurring due to the stress relaxation across the structural transition from a monoclinic to tetragonal phase with increasing temperature. Deflections measured in such nanoscale cantilevers can be directly correlated with macroscopic stress measurements by wafer curvature studies as well as temperature dependent electrical conduction allowing one to interrogate lattice dynamics across length scales.

Viswanath, B.; Ramanathan, Shriram

2013-07-01

209

Transpiration actuation: the design, fabrication and characterization of biomimetic microactuators driven by the surface tension of water  

NASA Astrophysics Data System (ADS)

We have designed, fabricated and characterized large displacement distributed-force polymer actuators driven only by the surface tension of water. The devices were inspired by the hygroscopic spore dispersal mechanism in fern sporangia. Microdevices were fabricated through a single mask process using a commercial photo-patternable silicone polymer to mimic the mechanical characteristics of plant cellulose. An analytical model for predicting the microactuator behavior was developed using the principle of virtual work, and a variety of designs were simulated and compared to the empirical data. Fabricated devices experienced tip deflections of more than 3.5 mm and angular rotations of more than 330° due to the surface tension of water. The devices generated forces per unit length of 5.75 mN m-1 to 67.75 mN m-1. We show initial results indicating that the transient water-driven deflections can be manipulated to generate devices that self-assemble into stable configurations. Our model shows that devices should scale well into the submicron regime. Lastly, the actuation mechanism presented may provide a robust method for embedding geometry-programmable and environment-scavenged force generation into common materials.

Borno, Ruba T.; Steinmeyer, Joseph D.; Maharbiz, Michel M.

2006-11-01

210

Magnetized Target Fusion Driven by Plasma Liners  

NASA Technical Reports Server (NTRS)

Magnetized target fusion (MTF) attempts to combine the favorable attributes of magnetic confinement fusion (MCF) for energy confinement with the attributes of inertial confinement fusion (ICF) for efficient compression heating and wall-free containment of the fusing plasma. It uses a material liner to compress and contain a magnetized plasma. For practical applications, standoff drivers to deliver the imploding momentum flux to the target plasma remotely are required. Spherically converging plasma jets have been proposed as standoff drivers for this purpose. The concept involves the dynamic formation of a spherical plasma liner by the merging of plasma jets, and the use of the liner so formed to compress a spheromak or a field reversed configuration (FRC). For the successful implementation of the scheme, plasma jets of the requisite momentum flux density need to be produced. Their transport over sufficiently large distances (a few meters) needs to be assured. When they collide and merge into a liner, relative differences in velocity, density and temperature of the jets could give rise to instabilities in the development of the liner. Variation in the jet properties must be controlled to ensure that the growth rate of the instabilities are not significant over the time scale of the liner formation before engaging with the target plasma. On impact with the target plasma, some plasma interpenetration might occur between the liner and the target. The operating parameter space needs to be identified to ensure that a reasonably robust and conducting contact surface is formed between the liner and the target. A mismatch in the "impedance" between the liner and the target plasma could give rise to undesirable shock heating of the liner leading to increased entropy (thermal losses) in the liner. Any irregularities in the liner will accentuate the Rayleigh-Taylor instabilities during the compression of the target plasma by the liner.

Thio, Y. C. Francis; Eskridge, Richard; Smith, James; Lee, Michael; Richeson, Jeff; Schmidt, George; Knapp, Charles E.; Kirkpatrick, Ronald C.; Turchi, Peter J.; Rodgers, Stephen L. (Technical Monitor)

2001-01-01

211

Experimental investigation on a vectorized aerodynamic dielectric barrier discharge plasma actuator array  

NASA Astrophysics Data System (ADS)

The Electro-Hydro-Dynamics (EHD) interaction, induced in atmospheric pressure still air by a surface dielectric barrier discharge (DBD) actuator, had been experimentally studied. A plasma aerodynamic actuator array, able to produce a vectorized jet, with the induced airflow oriented toward the desired direction, had been developed. The array was constituted by a sequence of single surface DBD actuators with kapton as dielectric material. An ac voltage in the range of 0-6 kV peak at 15 kHz had been used. The vectorization had been obtained by feeding the upper electrodes with different voltages and by varying the electrical connections. The lower electrodes had been connected either to ground or to the high voltage source, to produce the desired jet orientation and to avoid plasma formation acting in an undesired direction. Voltage and current measurements had been carried out to evaluate waveforms and to estimate the active power delivered to the discharge. Schlieren imaging allowed to visualize the induced jet and to estimate its orientation. Pitot measurements had been performed to obtain velocity profiles for all jet configurations. A proportional relation between the jet deflection angle and the applied voltage had been found. Moreover, a linear relation had been obtained between the maximum speed in the jet direction and the applied voltage. The active power of the discharge is approximated by both a power law function and an exponential function of the applied voltage.

Neretti, Gabriele; Cristofolini, Andrea; Borghi, Carlo A.

2014-04-01

212

Airflow influence on the discharge performance of dielectric barrier discharge plasma actuators  

NASA Astrophysics Data System (ADS)

In the present work, the effect of the airflow on the performance of dielectric barrier discharge plasma-actuators is investigated experimentally. In order to analyze the actuator's performance, luminosity measurements have been carried out simultaneously with the recording of the relevant electrical parameters. A performance drop of about 10% is observed for the entire measured parameter range at a flow speed of M = 0.145 (U?=50 m/s). This insight is of particular importance, since the plasma-actuator control authority is already significantly reduced at this modest speed level. The results at higher Mach numbers (0.4

Kriegseis, J.; Grundmann, S.; Tropea, C.

2012-07-01

213

Laser-driven Acceleration in Clustered Plasmas  

SciTech Connect

We propose a new approach to avoid dephasing limitation of laser wakefield acceleration by manipulating the group velocity of the driving pulse using clustered plasmas. We demonstrated the control of phase velocity in clustered plasmas by third harmonic generation and frequency domain interferometry experiments. The results agree with a numerical model. Based on this model, the group velocity of the driving pulse in clustered plasmas was calculated and the result shows the group velocity can approach the speed of light c in clustered plasmas.

Gao, X.; Wang, X.; Shim, B.; Downer, M. C. [Department of Physics, University of Texas at Austin, Austin, TX 78712 (United States)

2009-01-22

214

The analysis of pulse driven multilayer piezoelectric actuators for diesel fuel injection  

Microsoft Academic Search

Continuously tightening emission standards for heavy-duty diesel engines worldwide have led to a tremendous increase in the required capabilities of the diesel fuel injection systems in the last ten-twenty years, and this trend is expected to continue. ^ One of the significant enabling technologies available to the fuel injection system developer is the application of a piezoelectric actuation, in lieu

Yury Kalish

2006-01-01

215

Magnetized Target Fusion Driven by Plasma Liners  

NASA Technical Reports Server (NTRS)

For practical applications of magnetized target fusion, standoff drivers to deliver the imploding momentum flux to the target plasma remotely are required. Quasi-spherically converging plasma jets have been proposed as standoff drivers for this purpose. The concept involves the dynamic formation of a quasi-spherical plasma liner by the merging of plasma jets, and the use of the liner so formed to compress a spheromak or a field reversed configuration (FRC). Theoretical analysis and computer modeling of the concept are presented. It is shown that, with the appropriate choice of the flow parameters in the liner and the target, the impact between the liner and the target plasma can be made to be shockless in the liner or to generate at most a very weak shock in the liner. Additional information is contained in the original extended abstract.

Thio, Y. C. Francis; Cassibry, Jason; Eskridge, Richard; Kirkpatrick, Ronald C.; Knapp, Charles E.; Lee, Michael; Martin, Adam; Smith, James; Wu, S. T.; Rodgers, Stephen L. (Technical Monitor)

2001-01-01

216

Physics of laser-driven plasma-based electron accelerators  

SciTech Connect

Laser-driven plasma-based accelerators, which are capable of supporting fields in excess of 100 GV/m, are reviewed. This includes the laser wakefield accelerator, the plasma beat wave accelerator, the self-modulated laser wakefield accelerator, plasma waves driven by multiple laser pulses, and highly nonlinear regimes. The properties of linear and nonlinear plasma waves are discussed, as well as electron acceleration in plasma waves. Methods for injecting and trapping plasma electrons in plasma waves are also discussed. Limits to the electron energy gain are summarized, including laser pulse diffraction, electron dephasing, laser pulse energy depletion, and beam loading limitations. The basic physics of laser pulse evolution in underdense plasmas is also reviewed. This includes the propagation, self-focusing, and guiding of laser pulses in uniform plasmas and with preformed density channels. Instabilities relevant to intense short-pulse laser-plasma interactions, such as Raman, self-modulation, and hose instabilities, are discussed. Experiments demonstrating key physics, such as the production of high-quality electron bunches at energies of 0.1-1 GeV, are summarized.

Esarey, E.; Schroeder, C. B.; Leemans, W. P. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2009-07-15

217

Detachment and attachment of an axisymmetric non-reactive jet with turbulent shear layer: Control by plasma actuator  

Microsoft Academic Search

The control of an axisymmetric air jet equipped with a small-angle diffuser exhaust using a single non-thermal plasma actuator is studied with a stereoscopic PIV system. A single Dielectric Barrier Discharge (DBD) actuator is used to separate a naturally attached flow (12° angle diffuser) or to reattach a naturally separated one (22° angle diffuser). The experimental set-up allows us to

N. Benard; P. Braud; G. Touchard; E. Moreau

2008-01-01

218

Magnetized Target Fusion Driven by Plasma Liners  

NASA Technical Reports Server (NTRS)

Magnetized target fusion is an emerging, relatively unexplored approach to fusion for electrical power and propulsion application. The physical principles of the concept are founded upon both inertial confinement fusion (ICF) and magnetic confinement fusion (MCF). It attempts to combine the favorable attributes of both these orthogonal approaches to fusion, but at the same time, avoiding the extreme technical challenges of both by exploiting a fusion regime intermediate between them. It uses a material liner to compress, heat and contain the fusion reacting plasma (the target plasma) mentally. By doing so, the fusion burn could be made to occur at plasma densities as high as six orders of magnitude higher than conventional MCF such as tokamak, thus leading to an approximately three orders of magnitude reduction in the plasma energy required for ignition. It also uses a transient magnetic field, compressed to extremely high intensity (100's T to 1000T) in the target plasma, to slow down the heat transport to the liner and to increase the energy deposition of charged-particle fusion products. This has several compounding beneficial effects. It leads to longer energy confinement time compared with conventional ICF without magnetized target, and thus permits the use of much lower plasma density to produce reasonable burn-up fraction. The compounding effects of lower plasma density and the magneto-insulation of the target lead to greatly reduced compressional heating power on the target. The increased energy deposition rate of charged-particle fusion products also helps to lower the energy threshold required for ignition and increasing the burn-up fraction. The reduction in ignition energy and the compressional power compound to lead to reduced system size, mass and R&D cost. It is a fusion approach that has an affordable R&D pathway, and appears attractive for propulsion application in the nearer term.

Thio, Y. C. Francis; Kirkpatrick, Ronald C.; Knapp, Charles E.; Rodgers, Stephen L. (Technical Monitor)

2002-01-01

219

A micromachined silicon valve driven by a miniature bi-stable electro-magnetic actuator  

Microsoft Academic Search

In this paper a novel combination of a micromachined silicon valve with low dead volume and a bi-stable electromagnetic actuator produced by conventional machining is presented. The silicon valve part, 7×7×1 mm3 in dimensions, is a sandwich construction of two KOH etched silicon wafers with a layer of chemical resistant silicone rubber bonded in between. This middle layer provides the

S. Bohm; G. J. Burger; M. T. Korthorst; F. Roseboom

2000-01-01

220

Real-time thickness measurement of biological tissues using a microfabricated magnetically-driven lens actuator.  

PubMed

A fiber optic confocal catheter with a micro scanning lens was developed for real-time and non-contact thickness measurement of biological tissue. The catheter has an outer diameter and rigid length of 4.75 mm and 30 mm respectively and is suitable for endoscopic applications. The catheter incorporates a lens actuator that is fabricated using microelectromechanical systems (MEMS) technology. The lens is mounted on a folded flexure made of nickel and is actuated by magnetic field. Thickness measurements are performed by positioning the catheter in front of the tissue and actuating the lens scanner in the out-of-plane direction. A single-mode optical fiber (SMF) is used to deliver a 785 nm laser beam to the tissue and relay back the reflected light from the tissue to a photomultiplier tube (PMT). When the focal point of the scanning lens passes tissue boundaries, intensity peaks are detected in the reflecting signal. Tissue thickness is calculated using its index of refraction and the lens displacement between intensity peaks. The utility of the confocal catheter was demonstrated by measuring the cornea and skin thicknesses of a mouse. Measurement uncertainty of 8.86 µm within 95% confidence interval has been achieved. PMID:21468630

Mansoor, Hadi; Zeng, Haishan; Chiao, Mu

2011-08-01

221

Protein binding reaction enhanced by bi-directional flow driven by on-chip thermopneumatic actuator.  

PubMed

A microfluidic immunoassay system was developed for the study of the enhancement of protein binding reaction. The system mainly consisted of a thermopneumatic actuator and a reaction chamber. Reagent was pre-installed in the on-chip reservoir and manipulated by the actuator. Such design could eliminate the external tubing connections in order to reduce the waste of reagent and improve the portability. The on-chip actuator could manipulate the reagent bi-directionally to induce vortexes in the chamber. Enhancement of protein binding reaction was demonstrated by the protein model pair, i.e., mouse IgG and anti-mouse IgG. By such bi-directional fluid motion, more binding opportunities between suspended protein and its surface-immobilized counterpart were generated to improve the performance of immunoassay. It showed that an 83.74 % enhancement of the binding reaction was achieved, compared with the static situation. As a whole, the proposed microfluidic system is highly integrated and can enhance the protein binding efficiency using such novel design. The developed system can be easily extended to multi-reagents immunoassay protocols and provides a useful platform for point-of-care applications. PMID:24474184

Lei, Kin Fong; Chen, Kuan-Hao; Chang, Yu-Chen

2014-04-01

222

On the benefits of hysteresis effects for closed-loop separation control using plasma actuation  

NASA Astrophysics Data System (ADS)

Flow separation control by a non-thermal plasma actuator is considered for a NACA 0015 airfoil at a chord Reynolds number of 1.9 × 105. Static hysteresis in the lift coefficient is demonstrated for increasing and then decreasing sinusoidal voltage amplitude supplying a typical single dielectric barrier discharge actuator at the leading edge of the model. In addition to these open-loop experiments, unsteady surface pressure signals are examined for transient processes involving forced reattachment and natural separation. The results show that strong pressure oscillations in the relatively slow separation process, compared to reattachment, precede the ultimate massive flow separation. To enhance the contrast between the parts of the signal related to the attached flow and those related to the incipient separation, RMS estimate of filtered values of Cp is used to define a flow separation predictor that is implemented in feedback control. Two simple controllers are proposed, one based on a predefined threshold of the unsteady Cp and another that utilizes the flow separation predictor to identify incipient separation. The latter effectively leverages the hysteresis in the post-stall regime to reduce the electrical power consumed by the actuator while maintaining continuously attached flow.

Benard, N.; Cattafesta, L. N.; Moreau, E.; Griffin, J.; Bonnet, J. P.

2011-08-01

223

Plasma morphology and induced airflow characterization of a DBD actuator with serrated electrode  

NASA Astrophysics Data System (ADS)

Plasma morphology and airflow induced by a dielectric barrier discharge (DBD) actuator, whose exposed electrode geometry is designed with a serrated configuration, are investigated in quiescent air and compared with a DBD actuator consisting of electrodes designed with a standard linear strip configuration. ICCD imaging, electrical measurements and three-component laser Doppler velocimetry were carried out to compare various features of these two actuators. With the serrated configuration, ICCD images of the discharge show that streamers are bent, whereas with the linear configuration they are straight. These curved streamers induce a three-dimensional flow topology, which is confirmed by friction line visualization and velocity measurements. Whereas a two-dimensional wall-jet is induced with the linear configuration, a transverse velocity component is measured with the serrated configuration, implying the creation of spanwise-periodic vorticity. Phase-averaged velocity measurements allow the temporal variation of this transverse velocity to be highlighted. On both sides of a tooth, it has qualitatively the same variation as the longitudinal velocity with respect to the negative or positive half-cycles of the high voltage signal. Moreover, with the same electrical operating parameters, the measured longitudinal velocity was higher, particularly at the tips.

Joussot, R.; Leroy, A.; Weber, R.; Rabat, H.; Loyer, S.; Hong, D.

2013-03-01

224

A New Inductively Driven Plasma Generator (IPG) Source  

NASA Astrophysics Data System (ADS)

As part of the partnership between the Center for Astrophysics, Space Physics and Engineering Research (CASPER) at Baylor University and the Institut fur Raumfahrtsysteme (IRS) at the University of Stuttgart, a new design for a modular, inductively driven plasma generator (IPG) source is being developed and tested within CASPER and the IRS. The current IPG design is built on a well-established heritage of modular inductively driven plasma generators designed and operated at IRS. This latest IPG source enables the electrodeless generation of high-enthalpy plasmas and will provide CASPER researchers the ability to operate with various gases at plasma powers of approximately 20 KW. It will also provide minimized field losses and operation over a wide scope of parameters not possible using existing designs requiring flow-controlled stabilization. Both research and technical applications will be discussed.

Hyde, Truell; Laufer, Rene; Herdrich, Georg; Dropmann, Michael; Peters, Susanne; Matthews, Lorin; Cook, Michael; Schmoke, Jimmy

2011-11-01

225

Current Transport in Tokamak Plasmas with Neutral Beam Driven Currents  

NASA Astrophysics Data System (ADS)

Recent neutral beam current drive (NBCD) experiments on DIII--D have focused on independently measuring the conductivity and neutral beam driven currents to investigate the physical processes limiting noninductive ramp-up via NBCD. Detailed comparisons with theory indicate that frequently the current transport models are inadequate to describe the experimental results. As with studies of particle and heat transport, there is an ambiguity which arises when attempting to separately determine the sources and transport coefficients; in this problem, the source is the noninductively driven current and the transport coefficient is the plasma resistivity. These quantities can only be independently resolved through transient techniques. Using determination of the local current density and parallel electric field from internal measurements of the time evolving poloidal magnetic field,(C.B. Forest, et.al.), Phys. Rev. Lett. (1995). a measurement of the electrical skin depth (and thus the conductivity) has been made by modulating the plasma current and measuring the amplitude and phase of the perturbed electric field. Comparisons of the measured conductivity with neoclassical theory offer a new technique for characterizing the MHD activity. Under the assumption of neoclassical resistivity, measurements of the neutral beam driven current profile have been made for a large range of plasma parameters and compared with theory. Under conditions in which tearing modes are present, the neutral beam driven current is anomalously low (by up to 80%) when compared to TRANSP and ONETWO calculations of neutral beam driven currents.(C.B. Forest, et.al.), to be published in Phys. Rev. Lett. July 7, 1997. This reduction in neutral beam driven currents due to the soft ? limit imposed by neoclassical MHD illustrates the need for including islands in the modeling, and it places a strong constraint on plasma current ramp-up by neutral beam injection. Low density (2×10^13 cm-3) high-?p H--mode plasmas have been obtained using the newly installed cryopump, for the purpose of optimizing the fraction of beam driven current. Plasma currents have been sustained for up to 3 s with no applied flux from the external coils, yet local analysis shows that the 30% of the current is being inductively driven by the back EMF produced by the slowly decaying plasma current.

Forest, C. B.

1997-11-01

226

Behavior of excited argon atoms in inductively driven plasmas  

Microsoft Academic Search

Laser induced fluorescence has been used to measure the spatial distribution of the two lowest energy argon excited states, 1s5 and 1s4, in inductively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the 1s5 level is metastable and the 1s4 level is radiatively coupled to

G. A. Hebner; P. A. Miller

2000-01-01

227

Theoretical performance of plasma driven railguns  

Microsoft Academic Search

The overall efficiency of a railgun launch system is the product of efficiencies of its subsystems: prime mover, energy storage, pulse forming network, and accelerator. In this paper, the efficiency of the accelerator is examined in terms of the processes occurring in the accelerator. The principal loss mechanisms include Joule heating in the plasma, in the rails, kinetic energy of

Y. C. Thio; I. R. McNab; W. C. Condit

1983-01-01

228

GeV plasma accelerators driven in waveguides  

NASA Astrophysics Data System (ADS)

During the last few years laser-driven plasma accelerators have been shown to generate quasi-monoenergetic electron beams with energies up to several hundred MeV. Extending the output energy of laser-driven plasma accelerators to the GeV range requires operation at plasma densities an order of magnitude lower, i.e. 1018 cm-3, and increasing the distance over which acceleration is maintained from a few millimetres to a few tens of millimetres. One approach for achieving this is to guide the driving laser pulse in the plasma channel formed in a gas-filled capillary discharge waveguide. We present transverse interferometric measurements of the evolution of the plasma channel formed and compare these measurements with models of the capillary discharge. We describe in detail experiments performed at Lawrence Berkeley National Laboratory and at Rutherford Appleton Laboratory in which plasma accelerators were driven within this type of waveguide to generate quasi-monoenergetic electron beams with energies up to 1 GeV.

Hooker, S. M.; Brunetti, E.; Esarey, E.; Gallacher, J. G.; Geddes, C. G. R.; Gonsalves, A. J.; Jaroszynski, D. A.; Kamperidis, C.; Kneip, S.; Krushelnick, K.; Leemans, W. P.; Mangles, S. P. D.; Murphy, C. D.; Nagler, B.; Najmudin, Z.; Nakamura, K.; Norreys, P. A.; Panasenko, D.; Rowlands-Rees, T. P.; Schroeder, C. B.; Tóth, C. s.; Trines, R.

2007-12-01

229

Design of IPMC actuator-driven valve-less micropump and its flow rate estimation at low Reynolds numbers  

NASA Astrophysics Data System (ADS)

This paper presents the design and flow rate predictions of an IPMC (ionic polymer-metal composite) actuator-driven valve-less micropump. It should be noted that IPMC is a promising material candidate for micropump applications since it can be operated with low input voltages and can produce large stroke volumes, while having controllable flow rates. The micropump manufacturing process with IPMC is also convenient; it is anticipated that the manufacturing cost of the IPMC micropump is competitive with other technologies. In order to design an effective IPMC diaphragm that functions as an actuating motor for a micropump, a finite element analysis (FEA) was utilized to optimize the electrode shape of the IPMC diaphragm and estimate its stroke volumes. In addition, the effect of the pump chamber pressure on the stroke volume was numerically investigated. Appropriate inlet and outlet nozzle/diffuser elements were also studied for the valve-less micropump. Based on the selected geometry of nozzle/diffuser elements and the estimated stroke volume of the IPMC diaphragm, the flow rate of the micropump was estimated at a low Reynolds number of about 50.

Lee, Sangki; Kim, Kwang J.

2006-08-01

230

Current driven instability in collisional dusty plasmas  

SciTech Connect

The current driven electromagnetic instability in a collisional, magnetized, dusty medium is considered in the present work. It is shown that in the presence of the magnetic field aligned current, the low-frequency waves in the medium can become unstable if the ratio of the current to the ambient field is larger than the light speed times the wave number. The growth rate of the instability depends upon the ratio of the Alfven to the dust cyclotron frequency as well as on the ratio of the current density J to the dust charge density Zen{sub d}, where Z is the number of electronic charge on the grain, e is the electron charge, and n{sub d} is the dust number density. The typical growth rate of this instability is on the order of Alfven frequency which compares favorably with the electrostatic, cross-field current driven, Farley-Buneman instability and thus could play an important role in the Earth's ionosphere.

Pandey, B. P. [Department of Physics, Macquarie University, Sydney, New South Wales 2109 (Australia); Vladimirov, S. V.; Samarian, A. [Complex Systems, School of Physics, University of Sydney, New South Wales 2006 (Australia)

2009-11-15

231

Ion-acoustic filamentation of a current-driven plasma  

NASA Astrophysics Data System (ADS)

The effect of thermal motion of charged particles in the filamentation of a nonrelativistic current-driven plasma in the ion-acoustic frequency region is investigated. The period and the establishment time of the filamentation structure and the threshold for instability development are obtained.

Shokri, B.; Khorashadi, S. M.; Dastmalchi, M.

2002-08-01

232

Plasma decontamination and energy transport by impurity driven modes  

Microsoft Academic Search

An investigation is conducted of the impurity driven plasma modes in a number of different collision and wavelength regimes, taking into account the quasi-linear effects that the modes can have on the transport of impurity ion across the magnetic field and on the related ion thermal energy transport. The characteristics of the regimes of interest are examined and dissipative fluid

Bruno Coppi; Gregory Rewoldt; Theo Schep

1976-01-01

233

Force generation due to three-dimensional plasma discharge on a conical forebody using pulsed direct current actuators  

SciTech Connect

Understanding the behavior of three-dimensional plasmas around a pulsed dc actuator can be useful for its efficient operation in many applications. The effect of such actuators is studied using a self-consistent multibody system of neutral oxygen species and its plasma. The equations governing the motion of charged species are solved with the drift diffusion approximation. The electrostatic potential is computed from Poisson's equation. The electric field and ionization level are the highest close to the junction of electrodes and dielectric. The plasma body force thus generated also follows a similar characteristic. Results also show some dc corona instabilities. The temporal average of such force shows mostly acceleration from anode to cathode above the actuator.

Singh, Kunwar Pal; Roy, Subrata [Computational Plasma Dynamics Laboratory and Test Facility, Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611 (United States)

2008-05-15

234

Parametric considerations for inductively driven plasma implosions  

Microsoft Academic Search

This report explores the system aspects of driving implosion loads with inductive sources. High-speed plasma implosions represent an attractive approach to the production of an intense radiation source for use in an X-ray Effects Simulator. The nature of the implosion and the energy levels required for an X-ray Simulator make the use of inductive energy sources for driving the implosion

R. E. Reinovsky; D. L. Smith

1981-01-01

235

A voice coil actuator driven active vibration isolation system with the consideration of flexible modes.  

PubMed

We develop a four-mount active vibration isolation system (AVIS) using voice coil actuators. The flexible body modes in the upper plate of the AVIS can cause an instability problem due to control signal whose frequency is close to the resonant frequency of the flexible modes. The loop shaping technique is applied to reduce the amplitude of the control signal. We investigate the performances of the active vibration isolation system proposed in the word in the time domain and frequency domain by comparing to the passive isolation system. PMID:18601436

Park, Kyihwan; Choi, Dongyoub; Ozer, Abdullah; Kim, Sangyoo; Lee, Yongkwan; Joo, Dongik

2008-06-01

236

Response of a circular cylinder wake to a symmetric actuation by non-thermal plasma discharges  

NASA Astrophysics Data System (ADS)

In this study, the flow past a circular cylinder is manipulated by two plasma discharges placed on both sides of the model (at ±50°). A parametric investigation by force balance is conducted to define the sensitivity of the flow field to unsteady perturbations imparted by plasma actuators (dielectric barrier discharge) at 15.6 m/s ( Re D = 40,000). Effects of simple sinusoidal waveform, burst modulation and amplitude modulation are compared for low-frequency excitations. Regardless of the excitation mode, the cylinder experiences a large increase in the drag coefficient. The larger drag increase is observed for excitation related to the lock-on regime. Fast PIV measurements and triple decomposition by proper orthogonal decomposition are performed to extract the dynamical changes in the cylinder wake and to discriminate the control effects on the coherent and fluctuating turbulence. As expected, the control principally acts on the coherent flow structures. When forced, the vortices form closer to the base of the cylinder regardless of the actuation mode. This results in the drag increase observed by force measurements. The effectiveness of burst modulation is also due to the suppression of irregular shedding that is observed in the natural flow sequence and to a high level of correlation between the upper and lower vortex shedding. Finally, flow visualizations indicate that similar results can be obtained at higher Reynolds number ( Re D = 128,000, 50 m/s).

Benard, N.; Moreau, E.

2013-02-01

237

Reduced-order modeling of high-speed jets controlled by arc filament plasma actuators  

NASA Astrophysics Data System (ADS)

Arc filament plasma actuators applied to high-speed and high Reynolds number jets have demonstrated significant mixing enhancement when operated near the jet column mode (JCM) frequency. A feedback-oriented reduced-order model is developed for this flow from experimental data. The existent toolkit of stochastic estimation, proper orthogonal decomposition, and Galerkin projection is adapted to yield a 35-dimensional model for the unforced jet. Explicit inclusion of a "shift mode" stabilizes the model. The short-term predictive capability of instantaneous flow fields is found to degrade beyond a single flow time step, but this horizon may be adequate for feedback control. Statistical results from long-term simulations agree well with experimental observations. The model of the unforced jet is augmented to incorporate the effects of plasma actuation. Periodic forcing is modeled as a deterministic pressure wave specified on the inflow boundary of the modeling domain. Simulations of the forced model capture the nonlinear response that leads to optimal mixing enhancement in a small range of frequencies near the JCM.

Sinha, Aniruddha; Serrani, Andrea; Samimy, Mo

2013-02-01

238

Numerical simulation of plasma processes driven by transverse ion heating  

NASA Technical Reports Server (NTRS)

The plasma processes driven by transverse ion heating in a diverging flux tube are investigated with numerical simulation. The heating is found to drive a host of plasma processes, in addition to the well-known phenomenon of ion conics. The downward electric field near the reverse shock generates a doublestreaming situation consisting of two upflowing ion populations with different average flow velocities. The electric field in the reverse shock region is modulated by the ion-ion instability driven by the multistreaming ions. The oscillating fields in this region have the possibility of heating electrons. These results from the simulations are compared with results from a previous study based on a hydrodynamical model. Effects of spatial resolutions provided by simulations on the evolution of the plasma are discussed.

Singh, Nagendra; Chan, C. B.

1993-01-01

239

Current-driven plasma acceleration versus current-driven energy dissipation. I - Wave stability theory  

NASA Technical Reports Server (NTRS)

The dominant unstable electrostatic wave modes of an electromagnetically accelerated plasma are investigated. The study is the first part of a three-phase program aimed at characterizing the current-driven turbulent dissipation degrading the efficiency of Lorentz force plasma accelerators such as the MPD thruster. The analysis uses a kinetic theory that includes magnetic and thermal effects as well as those of an electron current transverse to the magnetic field and collisions, thus combining all the features of previous models. Analytical and numerical solutions allow a detailed description of threshold criteria, finite growth behavior, destabilization mechanisms and maximized-growth characteristics of the dominant unstable modes. The lower hybrid current-driven instability is implicated as dominant and was found to preserve its character in the collisional plasma regime.

Kelly, A. J.; Jahn, R. G.; Choueiri, E. Y.

1990-01-01

240

Plasma Radiation and Acceleration Effectiveness of CME-driven Shocks  

NASA Astrophysics Data System (ADS)

CME-driven shocks are effective radio radiation generators and accelerators for Solar Energetic Particles (SEPs). We present simulated 3 D time-dependent radio maps of second order plasma radiation generated by CME- driven shocks. The CME with its shock is simulated with the 3 D BATS-R-US CME model developed at the University of Michigan. The radiation is simulated using a kinetic plasma model that includes shock drift acceleration of electrons and stochastic growth theory of Langmuir waves. We find that in a realistic 3 D environment of magnetic field and solar wind outflow of the Sun the CME-driven shock shows a detailed spatial structure of the density, which is responsible for the fine structure of type II radio bursts. We also show realistic 3 D reconstructions of the magnetic cloud field of the CME, which is accelerated outward by magnetic buoyancy forces in the diverging magnetic field of the Sun. The CME-driven shock is reconstructed by tomography using the maximum jump in the gradient of the entropy. In the vicinity of the shock we determine the Alfven speed of the plasma. This speed profile controls how steep the shock can grow and how stable the shock remains while propagating away from the Sun. Only a steep shock can provide for an effective particle acceleration.

Gopalswamy, N.; Schmidt, J. M.

2008-05-01

241

Plasma radiation and acceleration effectiveness of CME-driven shocks  

NASA Astrophysics Data System (ADS)

CME-driven shocks are effective radio radiation generators and accelerators for Solar Energetic Particles (SEPs). We present simulated 3 D time-dependent radio maps of second order plasma radiation generated by CME-driven shocks. The CME with its shock is simulated with the 3 D BATS-R-US CME model developed at the University of Michigan. The radiation is simulated using a kinetic plasma model that includes shock drift acceleration of electrons and stochastic growth theory of Langmuir waves. We find that in a realistic 3 D environment of magnetic field and solar wind outflow of the Sun the CME-driven shock shows a detailed spatial structure of the density, which is responsible for the fine structure of type II radio bursts. We also show realistic 3 D reconstructions of the magnetic cloud field of the CME, which is accelerated outward by magnetic buoyancy forces in the diverging magnetic field of the Sun. The CME-driven shock is reconstructed by tomography using the maximum jump in the gradient of the entropy. In the vicinity of the shock we determine the Alfven speed of the plasma. This speed profile controls how steep the shock can grow and how stable the shock remains while propagating away from the Sun. Only a steep shock can provide for an effective particle acceleration.

Schmidt, Joachim

242

Spectroscopic investigation of wave driven microwave plasmas  

NASA Astrophysics Data System (ADS)

Large H atom line broadening was found throughout the volume of surface wave generated He-H2 and H2 microwave plasmas at low pressures. The measured Doppler temperatures corresponding to the H?, H?, H?, H?, and H? line profiles were found to be higher than the rotational temperature of the hydrogen molecular Fulcher-? band and the Doppler temperature of the 667.1 nm singlet He line. No excessive broadening has been found. The Lorentzian and Gaussian widths as determined by fitting the spectral lines with a Voigt profile increase with the principal quantum number of the upper level. In contrast, no such dependence for the Gaussian width has been observed in an Ar-H2 discharge. No population inversion has been observed from measurements of the relative intensities of transitions within the Balmer series.

Wijtvliet, R.; Felizardo, E.; Tatarova, E.; Dias, F. M.; Ferreira, C. M.; Nijdam, S.; Veldhuizen, E. V.; Kroesen, G.

2009-11-01

243

Filamentation instability of counterstreaming laser-driven plasmas.  

PubMed

Filamentation due to the growth of a Weibel-type instability was observed in the interaction of a pair of counterstreaming, ablatively driven plasma flows, in a supersonic, collisionless regime relevant to astrophysical collisionless shocks. The flows were created by irradiating a pair of opposing plastic (CH) foils with 1.8 kJ, 2-ns laser pulses on the OMEGA EP Laser System. Ultrafast laser-driven proton radiography was used to image the Weibel-generated electromagnetic fields. The experimental observations are in good agreement with the analytical theory of the Weibel instability and with particle-in-cell simulations. PMID:24329452

Fox, W; Fiksel, G; Bhattacharjee, A; Chang, P-Y; Germaschewski, K; Hu, S X; Nilson, P M

2013-11-27

244

Coherent structures in plasma-actuator controlled supersonic jets: Axisymmetric and mixed azimuthal modes  

NASA Astrophysics Data System (ADS)

High-fidelity simulations are employed to study the effect of eight localized arc filament plasma actuators placed around the periphery of a Mach 1.3 converging-diverging nozzle exit. Emphasis is placed on understanding the coherent structures generated by axisymmetric (m = 0), flapping or first mixed (m = +/-1) and second mixed (m = +/-2) modes, which are excited at the jet column-mode frequency corresponding to a Strouhal number based on jet diameter of 0.3. Baseline (no control) and constant excitation (actuators on continuously) cases are also simulated. Comparisons with experimental results indicate that the computational model reproduces the main features induced by the actuators. Furthermore, the mean flow exhibits many similarities with the theoretical predictions of Cohen and Wygnanski [J. Fluid Mech. 176, 221 (1987)]. Overall, the results indicate a complex coherent structure generation, evolution, and disintegration process. For m = +/-1, the phase-averaged flow reveals successive distorted elliptic vortex rings with axes in the flapping plane but alternating on either side of the jet axis. This generates a chain of structures each of which interacts with its predecessor on one side of the major plane and its successor on the other. Through self and mutual induction, the leading segment of each loop is pinched and passes through the previous ring before rapidly breaking up. The m = +/-2 mode yields elliptic structures with major axes of successive rings being aligned with the two symmetry planes, which are orthogonal to each other. The minor axis side is pulled downstream faster than the rest of the structure because of the higher velocity near the jet centerline and self-induced effects, yielding a horse-shoe shape when viewed in profile. The m = 0 mode exhibits axisymmetric roll-up events, with vortex ribs in the braid regions connecting successive large coherent structures. The constant excitation (with largest energy input) and baseline cases are similar to each other, indicating that the direct effect of heating is negligible.

Gaitonde, D. V.; Samimy, M.

2011-09-01

245

Force-free magnetic relaxation in driven plasmas  

NASA Astrophysics Data System (ADS)

J. B. Taylor (1974) postulated that the helicity-conserving minimum magnetic energy state is the consequence of plasma self-organization via turbulent relaxation bounded by a magnetic surface. The Taylor state j=? B is a force-free plasma with ? a global constant. For a driven plasma with open flux intercepting the boundary B\\cdothat nneq 0, Taylor relaxation is constrained by the Jensen-Chu theory (1984), which predicted rigorous barriers in ? for the accessible relaxed state. Both the magnetic helicity and energy formally diverge at the eigenvalues (?_i) of linear equation nabla×B=?i B with homogeneous boundary condition B\\cdothat n=0. The Jensen-Chu-Taylor paradigm suggests that force-free magnetic relaxation in a driven plasma results in a constant ? state with ? bounded by the smallest eigenvalue ?_1. More complicated force-free solutions such as toroidal field reversal (e.g. flipped spheromak) and multiple internal magnetic islands, are not energetically accessible. In an actual driven plasma, the plasma can be force-free but only partially relaxed, i.e. ?(?)=?0 + ? sumi c_i?^i weakly depends on the magnetic flux (? ? 1). We find that the Jensen-Chu singularities are regularized and a broad range of force-free solutions become accessible, sometimes suggesting a tortured path toward relaxation. This new result contradicts an earlier work by Kitson and Browning (1990). Its implications on laboratory helicity injection experiments and the structure of astrophysical magnetic field will be explained. Work supported by DOE OFES.

Tang, Xianzhu; Boozer, Allen H.

2004-11-01

246

A laser driven fusion plasma for space propulsion  

NASA Astrophysics Data System (ADS)

The present inertial-confinement fusion concept employs a magnetized target pellet that is driven by a laser beam in conjunction with a tungsten shell whose inner surface is coated with a deuterium-tritium fusion fuel mixture. A laser beam that enters the pellet through a hole simultaneously creates a fusion-grade plasma and gives rise to a powerful, instantaneous magnetic field which thermally insulates the plasma from the material wall. The plasma lifetime of this self-generated magnetic field scheme is dictated by the shock speed in the tungsten shell rather than by the speed of sound in the plasma: it consequently burns much longer and efficiently than plausible alternatives. A manned mission could by these means be completed in a few months rather than a few years, in virtue of the great specific impulse achieved.

Kammash, T.; Galbraith, D. L.

1992-07-01

247

The impulse response of a high-speed jet forced with localized arc filament plasma actuators  

NASA Astrophysics Data System (ADS)

We present experimental and theoretical analyses of the response of high-speed, high-Reynolds-number, round jets to impulsive forcing with arc-filament-plasma actuators. The impulse response is obtained with forcing Strouhal numbers, based on the nozzle exit diameter and exit center line velocity, less than 0.1. The resulting phase-averaged near-field pressure signature displays a compact wave with a positive peak preceding a negative one, indicative of a large scale structure in the shear layer of the jet. Scaling laws derived by operating the jet at four subsonic Mach numbers are used to distinguish this hydrodynamic component of the phase-averaged jet response from the direct actuator noise. As the forcing frequency increases, the compact waves in the near-field pressure signal overlap each other, indicating interaction of the growing seeded structures. For this regime, the phase-averaged response is approximately replicated by linear superposition of the impulse response, thereby demonstrating the quasi-linearity of structure interaction. A novel application of linear parabolized stability theory yields a successful model of the impulse response.

Sinha, Aniruddha; Alkandry, Hind; Kearney-Fischer, Martin; Samimy, Mo; Colonius, Tim

2012-12-01

248

Control of a high Reynolds number Mach 0.9 heated jet using plasma actuators  

SciTech Connect

The results of particle image velocimetry (PIV) measurements in a high subsonic, heated, jet forced using localized arc filament plasma actuators (LAFPAs) show that LAFPAs can consistently produce significant mixing enhancement over a wide range of temperatures. These actuators have been used successfully in high Reynolds number, high-speed unheated jets. The facility consists of an axisymmetric jet with different nozzle blocks of exit diameter of 2.54 cm and variable jet temperature in an anechoic chamber. The focus of this paper is on a high subsonic (M{sub j}=0.9) jet. Twelve experiments with various forcing azimuthal modes (m=0, 1, and {+-}1) and temperatures (T{sub o}/T{sub a}=1.0, 1.4, and 2.0) at a fixed forcing Strouhal number (St{sub DF}=0.3) have been conducted and PIV results compared with the baseline results to characterize the effectiveness of LAFPAs for mixing enhancement. Centerline velocity and turbulent kinetic energy as well as jet width are used for determining the LAFPAs' effectiveness. The characteristics of large-scale structures are analyzed through the use of Galilean streamlines and swirling strength. Across the range of temperatures collected, the effectiveness of LAFPAs improves as temperature increases. Possible reasons for the increase in effectiveness are discussed.

Kearney-Fischer, M.; Kim, J.-H.; Samimy, M. [Department of Mechanical Engineering, Gas Dynamics and Turbulence Laboratory, Ohio State University (GDTL/OSU), 2300 West Case Road, Columbus, Ohio 43235-7531 (United States)

2009-09-15

249

Helicity-flux-driven ? effect in laboratory and astrophysical plasmas.  

PubMed

The constraint imposed by magnetic helicity conservation on the ? effect is considered for both magnetically and flow dominated self-organizing plasmas. Direct numerical simulations are presented for a dominant contribution to the ? effect, which can be cast in the functional form of a total divergence of an averaged helicity flux, called the helicity-flux-driven ? (H?) effect. Direct numerical simulations of the H? effect are presented for two examples-the magnetically dominated toroidal plasma unstable to tearing modes, and the flow-dominated accretion disk. PMID:24724656

Ebrahimi, F; Bhattacharjee, A

2014-03-28

250

Thermal Efficiency of Laser Driven Inductively Coupled Plasma Generator Flows  

NASA Astrophysics Data System (ADS)

A laser driven inductively coupled plasma generator was developed. Firstly, the radio frequency (RF) of 13.56 MHz was applied to the atmospheric argon laser sustained plasma (LSP) in a quartz tube. As a result, the RF was successfully coupled to the LSP and following expansion of an emission region was observed. Next, the LSP was produced ahead of a ceramic convergent-divergent nozzle throat and the RF was applied from outside of the nozzle. The thermal efficiency estimated by a sonic flow method was ranged from 26 % to 13 %.

Matsui, Makoto; Yamagishi, Suisei; Komurasaki, Kimiya; Yamagiwa, Yoshiki; Arakawa, Yoshihiro

251

Helicity-Flux-Driven ? Effect in Laboratory and Astrophysical Plasmas  

NASA Astrophysics Data System (ADS)

The constraint imposed by magnetic helicity conservation on the ? effect is considered for both magnetically and flow dominated self-organizing plasmas. Direct numerical simulations are presented for a dominant contribution to the ? effect, which can be cast in the functional form of a total divergence of an averaged helicity flux, called the helicity-flux-driven ? (H?) effect. Direct numerical simulations of the H? effect are presented for two examples—the magnetically dominated toroidal plasma unstable to tearing modes, and the flow-dominated accretion disk.

Ebrahimi, F.; Bhattacharjee, A.

2014-03-01

252

Current driven instabilities of an electromagnetically accelerated plasma  

NASA Technical Reports Server (NTRS)

A plasma instability that strongly influences the efficiency and lifetime of electromagnetic plasma accelerators was quantitatively measured. Experimental measurements of dispersion relations (wave phase velocities), spatial growth rates, and stability boundaries are reported. The measured critical wave parameters are in excellent agreement with theoretical instability boundary predictions. The instability is current driven and affects a wide spectrum of longitudinal (electrostatic) oscillations. Current driven instabilities, which are intrinsic to the high-current-carrying magnetized plasma of the magnetoplasmadynmic (MPD) accelerator, were investigated with a kinetic theoretical model based on first principles. Analytical limits of the appropriate dispersion relation yield unstable ion acoustic waves for T(i)/T(e) much less than 1 and electron acoustic waves for T(i)/T(e) much greater than 1. The resulting set of nonlinear equations for the case of T(i)/T(e) = 1, of most interest to the MPD thruster Plasma Wave Experiment, was numerically solved to yield a multiparameter set of stability boundaries. Under certain conditions, marginally stable waves traveling almost perpendicular to the magnetic field would travel at a velocity equal to that of the electron current. Such waves were termed current waves. Unstable current waves near the upper stability boundary were observed experimentally and are in accordance with theoretical predictions. This provides unambiguous proof of the existence of such instabilites in electromagnetic plasma accelerators.

Chouetri, E. Y.; Kelly, A. J.; Jahn, R. G.

1988-01-01

253

Magnetic and Velocity Shear Driven Instabilities in the Heliospheric Plasma  

NASA Astrophysics Data System (ADS)

We have addressed the problem of combined magnetic and velocity shear driven instabilities in the context of the heliospheric plasma. New high-order numerical methods have been used to analyze the instability dynamics of the heliospheric current-sheet interacting with the structure determined by the slow component of the solar wind on the solar equatorial plane above the helmet streamers. Preliminary results are presented.

Bettarini, L.; Landi, S.; Velli, M.; Londrillo, P.

2009-04-01

254

A laser driven fusion plasma for space propulsion  

Microsoft Academic Search

The present inertial-confinement fusion concept employs a magnetized target pellet that is driven by a laser beam in conjunction with a tungsten shell whose inner surface is coated with a deuterium-tritium fusion fuel mixture. A laser beam that enters the pellet through a hole simultaneously creates a fusion-grade plasma and gives rise to a powerful, instantaneous magnetic field which thermally

T. Kammash; D. L. Galbraith

1992-01-01

255

Plasma-driven catalyst process for the decomposition of VOCs  

Microsoft Academic Search

This paper describes the decomposition of volatile organic compounds (VOCs), such as benzene, formic acid, oxylene, m-xylene, p-xylene, and toluene, using plasma-driven catalyst (PDC) reactor. The behaviors of different VOCs were compared in terms of decomposition efficiency, carbon balance, reaction kinetics, and CO2 selectivity. In contrast to the conventional reactors, the decomposition of VOCs using the PDC reactor showed no

Hyun-Ha Kirn; Seung-Min Oh; Atsushi Ogata; Shigeru Futamura

2004-01-01

256

Transient chaos and crisis phenomena in butterfly valves driven by solenoid actuators  

NASA Astrophysics Data System (ADS)

Chilled water systems used in the industry and on board ships are critical for safe and reliable operation. It is hence important to understand the fundamental physics of these systems. This paper focuses in particular on a critical part of the automation system, namely, actuators and valves that are used in so-called "smart valve" systems. The system is strongly nonlinear, and necessitates a nonlinear dynamic analysis to be able to predict all critical phenomena that affect effective operation and efficient design. The derived mathematical model includes electromagnetics, fluid mechanics, and mechanical dynamics. Nondimensionalization has been carried out in order to reduce the large number of parameters to a few critical independent sets to help carry out a broad parametric analysis. The system stability analysis is then carried out with the aid of the tools from nonlinear dynamic analysis. This reveals that the system is unstable in a certain region of the parameter space. The system is also shown to exhibit crisis and transient chaotic responses; this is characterized using Lyapunov exponents and power spectra. Knowledge and avoidance of these dangerous regimes is necessary for successful and safe operation.

Naseradinmousavi, Peiman; Nataraj, C.

2012-11-01

257

Local stability effects of plasma actuation on a zero pressure gradient boundary layer  

NASA Astrophysics Data System (ADS)

The effects of plasma actuation in a flat plate boundary layer with zero pressure gradient have been simulated. Based on these simulations, non-dimensional parameters and a combined wall jet/boundary layer model of the velocity profile have been developed. A parametric study using local linear stability analysis has been performed to examine the hydrodynamic stability of the velocity profiles created through this model. Convective and absolute instability mechanisms are found to be important, some of which have not been previously documented. Neutral stability curves have been computed for the different instabilities, and when put in terms of the shape factor, they still compare favorably with reported canonical results, indicating that the critical Reynolds number is primarily a function of the shape factor. These results are also discussed in relation to existing experimental results as well as with respect to their implementation.

Riherd, Mark; Roy, Subrata; Balachandar, S.

2013-04-01

258

Local stability effects of plasma actuation on a zero pressure gradient boundary layer  

NASA Astrophysics Data System (ADS)

The effects of plasma actuation in a flat plate boundary layer with zero pressure gradient have been simulated. Based on these simulations, non-dimensional parameters and a combined wall jet/boundary layer model of the velocity profile have been developed. A parametric study using local linear stability analysis has been performed to examine the hydrodynamic stability of the velocity profiles created through this model. Convective and absolute instability mechanisms are found to be important, some of which have not been previously documented. Neutral stability curves have been computed for the different instabilities, and when put in terms of the shape factor, they still compare favorably with reported canonical results, indicating that the critical Reynolds number is primarily a function of the shape factor. These results are also discussed in relation to existing experimental results as well as with respect to their implementation.

Riherd, Mark; Roy, Subrata; Balachandar, S.

2014-02-01

259

Transport scaling in interchange-driven toroidal plasmas  

SciTech Connect

Two-dimensional fluid simulations of a simple magnetized torus are presented, in which the vertical and toroidal components of the magnetic field create helicoidal field lines that terminate on the upper and lower walls of the plasma chamber. The simulations self-consistently evolve the full radial profiles of the electric potential, density, and electron temperature in the presence of three competing effects: the cross-field turbulent transport driven by the interchange instability, parallel losses to the upper and lower walls, and the input of particles and heat by external plasma sources. Considering parameter regimes in which equilibrium ExB shear flow effects are weak, we study the dependence of the plasma profiles--in particular the pressure profile scale length--on the parameters of the system. Analytical scalings are obtained that show remarkable agreement with the simulations.

Ricci, Paolo [Association EURATOM-Confederation Suisse, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne (Switzerland); Rogers, B. N. [Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755 (United States)

2009-06-15

260

Energetic-ion-driven global instabilities in stellarator/helical plasmas and comparison with tokamak plasmas  

SciTech Connect

Comprehensive understanding of energetic-ion-driven global instabilities such as Alfven eigenmodes (AEs) and their impact on energetic ions and bulk plasma is crucially important for tokamak and stellarator/helical plasmas and in the future for deuterium-tritium (DT) burning plasma experiments. Various types of global modes and their associated enhanced energetic ion transport are commonly observed in toroidal plasmas. Toroidicity-induced AEs and ellipticity-induced AEs, whose gaps are generated through poloidal mode coupling, are observed in both tokamak and stellarator/helical plasmas. Global AEs and reversed shear AEs, where toroidal couplings are not as dominant were also observed in those plasmas. Helicity induced AEs that exist only in 3D plasmas are observed in the large helical device (LHD) and Wendelstein 7 Advanced Stellarator plasmas. In addition, the geodesic acoustic mode that comes from plasma compressibility is destabilized by energetic ions in both tokamak and LHD plasmas. Nonlinear interaction of these modes and their influence on the confinement of the bulk plasma as well as energetic ions are observed in both plasmas. In this paper, the similarities and differences in these instabilities and their consequences for tokamak and stellarator/helical plasmas are summarized through comparison with the data sets obtained in LHD. In particular, this paper focuses on the differences caused by the rotational transform profile and the 2D or 3D geometrical structure of the plasma equilibrium. Important issues left for future study are listed.

Toi, K. [National Institute for Fusion Science, Toki, Japan; Ogawa, K. [Nagoya University, Japan; Isobe, M. [National Institute for Fusion Science, Toki, Japan; Osakabe, M. [National Institute for Fusion Science, Toki, Japan; Spong, Donald A [ORNL; Todo, Yasushi [National Institute for Fusion Science, Toki, Japan

2011-01-01

261

Deep Drilling and Sampling via the Wireline Auto-Gopher Driven by Piezoelectric Percussive Actuator and EM Rotary Motor  

NASA Technical Reports Server (NTRS)

The ability to penetrate subsurfaces and perform sample acquisition at depths of meters is critical for future NASA in-situ exploration missions to bodies in the solar system, including Mars and Europa. A corer/sampler was developed with the goal of acquiring pristine samples by reaching depths on Mars beyond the oxidized and sterilized zone. To developed rotary-hammering coring drill, called Auto-Gopher, employs a piezoelectric actuated percussive mechanism for breaking formations and an electric motor rotates the bit to remove the powdered cuttings. This sampler is a wireline mechanism that is incorporated with an inchworm mechanism allowing thru cyclic coring and core removal to reach great depths. The penetration rate is being optimized by simultaneously activating the percussive and rotary motions of the Auto-Gopher. The percussive mechanism is based on the Ultrasonic/Sonic Drill/Corer (USDC) mechanism that is driven by piezoelectric stack and that was demonstrated to require low axial preload. The Auto-Gopher has been produced taking into account the a lessons learned from the development of the Ultrasonic/Sonic Gopher that was designed as a percussive ice drill and was demonstrated in Antarctica in 2005 to reach about 2 meters deep. A field demonstration of the Auto-Gopher is currently being planned with objective of reaching as deep as 3 to 5 meters in tufa subsurface.

Bar-Cohen, Yoseph; Badescu, Mircea; Sherrit, Stewart; Zacny, Kris; Paulsen, Gale L; Beegle, Luther; Bao, Xiaoqi

2012-01-01

262

Deep drilling and sampling via the wireline auto-gopher driven by piezoelectric percussive actuator and EM rotary motor  

NASA Astrophysics Data System (ADS)

The ability to penetrate subsurfaces and perform sample acquisition at depths of meters is critical for future NASA in-situ exploration missions to bodies in the solar system, including Mars, Europa, and Enceladus. A corer/sampler was developed with the goal of acquiring pristine samples by reaching depths on Mars beyond the oxidized and sterilized zone. The developed rotary-hammering coring drill, called Auto-Gopher, employs a piezoelectric actuated percussive mechanism for breaking formations and an electric motor rotates the bit to remove the powdered cuttings. This sampler is a wireline drill that is incorporated with an inchworm mechanism allowing thru cyclic coring and core removal to reach great depths. The penetration rate is optimized by simultaneously activating the percussive and rotary motions of the Auto-Gopher. The percussive mechanism is based on the Ultrasonic/Sonic Drill/Corer (USDC) mechanism, which is driven by a piezoelectric stack, demonstrated to require low axial preload. The Auto-Gopher has been produced taking into account the lessons learned from the development of the Ultrasonic/Sonic Gopher that was designed as a percussive ice drill and was demonstrated in Antarctica in 2005 to reach about 2 meters deep. A field demonstration of the Auto-Gopher is currently being planned with the objective of reaching as deep as 3 to 5 meters in tufa formation.

Bar-Cohen, Yoseph; Badescu, Mircea; Sherrit, Stewart; Zacny, Kris; Paulsen, Gale L.; Beegle, Luther; Bao, Xiaoqi

2012-03-01

263

Double-Layer Driven Plasma Filaments in the Upward Current Region of the Auroral Plasma  

NASA Astrophysics Data System (ADS)

Simulations of double layers (DL) were performed using a 2.5-dimensional particle-in-cell code. The simulations included hot and cold plasmas on the low- and high-potential sides of the DL, respectively. This configuration of plasma and polarity of the potential corresponds to the DL, which accelerate electrons downward and ions upward in the auroral plasma. Both electrons and ions in the simulations are strongly magnetized. A persistent feature of the simulations performed for a variety of combinations of the densities and temperatures of the cold and hot plasmas is that the formation of a planar DL is immediately followed by the formation of thin and magnetic-field aligned plasma filaments. The process of filament formation begins just above the DL in the hot plasma permeated by an ion beam accelerated by the DL itself. A preliminary analysis shows that the beam-driven electrostatic ion-cyclotron (EIC) modes filament the DL and the hot plasma as the driven waves propagate upward with the beam velocity. The filamented structures appear in the plasma density, electron and ion energies as well as in parallel and perpendicular electric fields. When the filamented DL rises sufficiently above the ionospheric cold-plasma boundary, the plasma heating below the DL depletes the plasma creating a density cavity. In response to the cavity formation, the filamented DL moves downward filling the cavity with the hot plasma from the top. During the period of this downward motion, the DL tends to regain its initial laminar (planar) feature. As soon as the laminar DL reforms, the EIC waves are triggered again and the above process involving the filament formation reoccurs. The relevance of the recurring process of filament formation driven by a DL to satellite observations will be discussed.

Singh, N.

2004-12-01

264

Flow control over a NACA 0012 airfoil using dielectric-barrier-discharge plasma actuator with a Gurney flap  

NASA Astrophysics Data System (ADS)

Flow control study of a NACA 0012 airfoil with a Gurney flap was carried out in a wind tunnel, where it was demonstrated that a dielectric-barrier-discharge (DBD) plasma actuator attached to the flap could increase the lift further, but with a small drag penalty. Time-resolved PIV measurements of the near-wake region indicated that the plasma forcing shifted the wake downwards, reducing its recirculation length. Analysis of wake vortex dynamics suggested that the plasma actuator initially amplified the lower wake shear layer by adding momentum along the downstream surface of the Gurney flap. This enhanced mutual entrainment between the upper and lower wake vortices, leading to an increase in lift on the airfoil.

Feng, Li-Hao; Jukes, Timothy N.; Choi, Kwing-So; Wang, Jin-Jun

2012-06-01

265

Effects of Plasma Aerodynamic Actuation on Corner Separation in a Highly Loaded Compressor Cascade  

NASA Astrophysics Data System (ADS)

This paper reports experimental results on the effects of plasma aerodynamic actuation (PAA) on corner separation control in a highly loaded, low speed, linear compressor cascade. Total pressure loss coefficient distribution was adopted to evaluate the corner separation control effect in wind tunnel experiments. Results of pressure measurements and particle image velocimetry (PIV) show that the control effect of pitch-wise PAA on the endwall is much better than that of stream-wise PAA on the suction surface. When both the pitch-wise PAA on the endwall and stream-wise PAA on the suction surface are turned on simultaneously, the control effect is the best among all three PAA types. The mechanisms of nanosecond discharge and microsecond discharge PAA are different in corner separation control. The control effect of microsecond discharge PAA turns out better with the increase of discharge voltage and duty cycle. Compared with microsecond discharge PAA, nanosecond discharge PAA is more effective in preventing corner separation when the freestream velocity increases. Frequency is one of the most important parameters in plasma flow control. The optimum excitation frequency of microsecond discharge PAA is 500 Hz, which is different from the frequency corresponding to the case with a Strouhal number of unity.

Wang, Xuede; Zhao, Xiaohu; Li, Yinghong; Wu, Yun; Zhao, Qin

2014-03-01

266

Solar Wind Driven Plasma Fluxes from the Venus Ionosphere  

NASA Astrophysics Data System (ADS)

SOLAR WIND DRIVEN PLASMA FLUXES FROM THE VENUS IONOSPHERE H. Pérez-de-Tejada (1), R. Lundin (2), H. Durand-Manterola (1), S. Barabash (2), T. L. Zhang (3), J. A., Sauvaud (4), and M. Reyes-Ruiz (5) 1 - Institute of Geophysics, UNAM, México, D. F. 2 - Swedish Institute of Space Physics, Kiruna, Sweden 3 - Space Research Institute, Graz, Austria 4 - CESR, Toulouse, France 5 - Institute of Astronomy, UNAM, Ensenada, México Measurements conducted with the ASPERA-4 instrument and the magnetometer of the Venus Express spacecraft show that the kinetic pressure of planetary O+ ion fluxes measured in the Venus wake can be significantly larger than the local magnetic pressure and, as a result, those ions are not being driven by magnetic forces but by the kinetic energy of the solar wind. Beams of planetary O+ ions with those properties have been detected in several orbits of the Venus Express through the wake as the spacecraft traverses by the noon-midnight plane along its near polar trajectory. The momentum flux of the O+ ions leads to superalfvenic flow conditions. It is suggested that such O+ ion beams are produced in the vicinity of the magnetic polar regions of the Venus ionosphere where the solar wind erodes the local plasma leading to plasma channels that extend downstream from those regions.

Perez De Tejada, H. A.; Lundin, R. N.; Zhang, T.; Sauvaud, J. A.; Reyes-Ruiz, M.

2012-12-01

267

Magnetic Fluctuation-Driven Intrinsic Flow in a Toroidal Plasma  

NASA Astrophysics Data System (ADS)

Magnetic fluctuations have been long observed in various magnetic confinement configurations. These perturbations may arise naturally from plasma instabilities such as tearing modes and energetic particle driven modes, but they can also be externally imposed by error fields or external magnetic coils. It is commonly observed that large MHD modes lead to plasma locking (no rotation) due to torque produced by eddy currents on the wall, and it is predicted that stochastic field induces flow damping where the radial electric field is reduced. Flow generation is of great importance to fusion plasma research, especially low-torque devices like ITER, as it can act to improve performance. Here we describe new measurements in the MST reversed field pinch (RFP) showing that the coherent interaction of magnetic and particle density fluctuations can produce a turbulent fluctuation-induced kinetic force, which acts to drive intrinsic plasma rotation. Key observations include; (1) the average kinetic force resulting from density fluctuations, ˜ 0.5 N/m^3, is comparable to the intrinsic flow acceleration, and (2) between sawtooth crashes, the spatial distribution of the kinetic force is directed to create a sheared parallel flow profile that is consistent with the measured flow profile in direction and amplitude, suggesting the kinetic force is responsible for intrinsic plasma rotation.

Brower, D. L.; Ding, W. X.; Lin, L.; Almagri, A. F.; den Hartog, D. J.; Sarff, J. S.

2012-10-01

268

Simulation Tool for Dielectric Barrier Discharge Plasma Actuators at Atmospheric and Sub-Atmospheric Pressures: SBIR Phase I Final Report  

NASA Technical Reports Server (NTRS)

This report is the final report of a SBIR Phase I project. It is identical to the final report submitted, after some proprietary information of administrative nature has been removed. The development of a numerical simulation tool for dielectric barrier discharge (DBD) plasma actuator is reported. The objectives of the project were to analyze and predict DBD operation at wide range of ambient gas pressures. It overcomes the limitations of traditional DBD codes which are limited to low-speed applications and have weak prediction capabilities. The software tool allows DBD actuator analysis and prediction for subsonic to hypersonic flow regime. The simulation tool is based on the VORPAL code developed by Tech-X Corporation. VORPAL's capability of modeling DBD plasma actuator at low pressures (0.1 to 10 torr) using kinetic plasma modeling approach, and at moderate to atmospheric pressures (1 to 10 atm) using hydrodynamic plasma modeling approach, were demonstrated. In addition, results of experiments with pulsed+bias DBD configuration that were performed for validation purposes are reported.

Likhanskii, Alexandre

2012-01-01

269

Sheared Poloidal Flow Driven by Mode Conversion in Tokamak Plasmas  

NASA Astrophysics Data System (ADS)

A two-dimensional integral full-wave model is used to calculate poloidal forces driven by mode conversion in tokamak plasmas. In the presence of a poloidal magnetic field, mode conversion near the ion-ion hybrid resonance is dominated by a transition from the fast magnetosonic wave to the slow ion cyclotron wave. The poloidal field generates strong variations in the parallel wave spectrum that cause wave damping in a narrow layer near the mode conversion surface. The resulting poloidal forces in this layer drive sheared poloidal flows comparable to those in direct launch ion Bernstein wave experiments.

Jaeger, E. F.; Berry, L. A.; Myra, J. R.; Batchelor, D. B.; D'Azevedo, E.; Bonoli, P. T.; Phillips, C. K.; Smithe, D. N.; D'Ippolito, D. A.; Carter, M. D.; Dumont, R. J.; Wright, J. C.; Harvey, R. W.

2003-05-01

270

Sheared poloidal flow driven by mode conversion in tokamak plasmas.  

PubMed

A two-dimensional integral full-wave model is used to calculate poloidal forces driven by mode conversion in tokamak plasmas. In the presence of a poloidal magnetic field, mode conversion near the ion-ion hybrid resonance is dominated by a transition from the fast magnetosonic wave to the slow ion cyclotron wave. The poloidal field generates strong variations in the parallel wave spectrum that cause wave damping in a narrow layer near the mode conversion surface. The resulting poloidal forces in this layer drive sheared poloidal flows comparable to those in direct launch ion Bernstein wave experiments. PMID:12785951

Jaeger, E F; Berry, L A; Myra, J R; Batchelor, D B; D'Azevedo, E; Bonoli, P T; Phillips, C K; Smithe, D N; D'Ippolito, D A; Carter, M D; Dumont, R J; Wright, J C; Harvey, R W

2003-05-16

271

Asymmetry-driven structure formation in pair plasmas  

SciTech Connect

The nonlinear propagation of electromagnetic waves in pair plasmas, in which the electrostatic potential plays a very important but subdominant role of a 'binding glue' is investigated. Several mechanisms for structure formation are investigated, in particular, the 'asymmetry' in the initial temperatures of the constituent species. It is shown that the temperature asymmetry leads to a (localizing) nonlinearity that is qualitatively different from the ones originating in ambient mass or density difference. The temperature-asymmetry-driven focusing-defocusing nonlinearity supports stable localized wave structures in 1-3 dimensions, which, for certain parameters, may have flat-top shapes.

Mahajan, S. M.; Shatashvili, N. L.; Berezhiani, V. I. [Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States); Andronikashvili Institute of Physics, Tbilisi 0177 (Georgia) and Faculty of Exact and Natural Sciences, Department of Physics, Javakhishvili Tbilisi State University, Tbilisi 0128 (Georgia)

2009-12-15

272

Instability-driven electromagnetic fields in coronal plasmas  

SciTech Connect

Filamentary electromagnetic fields previously observed in the coronae of laser-driven spherical targets [F. H. Séguin et al., Phys. Plasma. 19, 012701 (2012)] have been further investigated in laser-irradiated plastic foils. Face-on proton-radiography provides an axial view of these filaments and shows coherent cellular structure regardless of initial foil-surface conditions. The observed cellular fields are shown to have an approximately constant scale size of ?210 ?m throughout the plasma evolution. A discussion of possible field-generation mechanisms is provided and it is demonstrated that the likely source of the cellular field structure is the magnetothermal instability. Using predicted temperature and density profiles, the fastest growing modes of this instability were found to be slowly varying in time and consistent with the observed cellular size.

Manuel, M. J.-E.; Li, C. K.; Séguin, F. H.; Sinenian, N.; Frenje, J. A.; Casey, D. T.; Petrasso, R. D. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)] [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Hager, J. D.; Betti, R.; Hu, S. X.; Delettrez, J.; Meyerhofer, D. D. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York, 14623 (United States)] [Laboratory for Laser Energetics, University of Rochester, Rochester, New York, 14623 (United States)

2013-05-15

273

Electron-temperature-gradient-driven instability in tokamak boundary plasma  

SciTech Connect

A general method is developed for calculating boundary plasma fluctuations across a magnetic separatrix in a tokamak with a divertor or a limiter. The slab model, which assumes a periodic plasma in the edge reaching the divertor or limiter plate in the scrape-off layer (SOL), should provide a good estimate, if the radial extent of the fluctuation quantities across the separatrix to the edge is small compared to that given by finite particle banana orbit. The Laplace transform is used for solving the initial value problem. The electron-temperature-gradient (ETG)-driven instability is found to grow like [ital t][sup [minus]1/2][ital e][sup [gamma][sub [ital m]t

Xu, X.Q. (Electronics Research Laboratory, University of California, Berkeley, California 94720 (United States)); Rosenbluth, M.N.; Diamond, P.H. (Department of Physics, University of California, San Diego, California 92093 (United States))

1993-07-01

274

Electron temperature gradient driven instability in the tokamak boundary plasma  

SciTech Connect

A general method is developed for calculating boundary plasma fluctuations across a magnetic separatrix in a tokamak with a divertor or a limiter. The slab model, which assumes a periodic plasma in the edge reaching the divertor or limiter plate in the scrape-off layer(SOL), should provide a good estimate, if the radial extent of the fluctuation quantities across the separatrix to the edge is small compared to that given by finite particle banana orbit. The Laplace transform is used for solving the initial value problem. The electron temperature gradient(ETG) driven instability is found to grow like t{sup {minus}1/2}e{sup {gamma}mt}.

Xu, X.Q.; Rosenbluth, M.N.; Diamond, P.H.

1992-12-15

275

A compact and continuously driven supersonic plasma and neutral source  

SciTech Connect

A compact and repetitively driven plasma source has been developed by utilizing a magnetized coaxial plasma gun (MCPG) for diagnostics requiring deep penetration of a large amount of neutral flux. The system consists of a MCPG 95mm in length with a DN16 ConFlat connection port and an insulated gate bipolar transistor (IGBT) inverter power unit. The power supply consists of an array of eight IGBT units and is able to switch the discharge on and off at up to 10 kV and 600 A with a maximum repetitive frequency of 10 kHz. Multiple short duration discharge pulses maximize acceleration efficiency of the plasmoid. In the case of a 10 kHz operating frequency, helium-plasmoids in the velocity range of 20 km/s can be achieved.

Asai, T.; Itagaki, H.; Numasawa, H.; Terashima, Y.; Hirano, Y. [Department of Physics, College of Science and Technology, Nihon University, Tokyo 101-8308 (Japan); Hirose, A. [Plasma Physics Laboratory, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2 (Canada)

2010-10-15

276

A compact and continuously driven supersonic plasma and neutral source  

NASA Astrophysics Data System (ADS)

A compact and repetitively driven plasma source has been developed by utilizing a magnetized coaxial plasma gun (MCPG) for diagnostics requiring deep penetration of a large amount of neutral flux. The system consists of a MCPG 95mm in length with a DN16 ConFlat connection port and an insulated gate bipolar transistor (IGBT) inverter power unit. The power supply consists of an array of eight IGBT units and is able to switch the discharge on and off at up to 10 kV and 600 A with a maximum repetitive frequency of 10 kHz. Multiple short duration discharge pulses maximize acceleration efficiency of the plasmoid. In the case of a 10 kHz operating frequency, helium-plasmoids in the velocity range of 20 km/s can be achieved.

Asai, T.; Itagaki, H.; Numasawa, H.; Terashima, Y.; Hirano, Y.; Hirose, A.

2010-10-01

277

Dielectric Barrier Discharge Plasma Actuators with Novel Geometries for Flow Modification: Experimental Measurements and Validation with a 2-D Fluid Model.  

National Technical Information Service (NTIS)

Optical characteristics of surface dielectric barrier discharge (DBD) plasma actuators with wire/planar electrodes were studied using an intensified charge-coupled device camera and a monochromator in atmospheric pressure air. Spatial and temporal images ...

N. Hershkowitz R. Bonazza

2013-01-01

278

Laser-and Beam-Driven Plasma Accelerators  

NASA Astrophysics Data System (ADS)

Scientists have been trying to use the tremendous electric fields in relativistic plasma waves to accelerate charged particles, and are now making substantial progress. If they succeed, future high energy accelerators will use plasma waves rather than microwave cavities as accelerating structures.Some accelerators, such as those used for radiation therapy will fit on a tabletop. Research on using plasma waves to accelerate particles began in earnest following the suggestion by John Dawson and his colleagues [1-3] that a relativistically propagating plasma wave or a wake field could be excited by using a powerful but short laser -or electron -beam as a driver pulse.Since their original suggestion the research on plasma --based accelerators has spread worldwide A series of experiments by the UCLA/USC/SLAC collaboration ,using the 30 GeV beam of the Stanford Linear Accelerator Center (SLAC), has demonstrated high-gradient acceleration of electrons and positrons using the the wake left by the SLAC beam as it passes through a lithium plasma. Electrons have been accelerated by more than 30 GeV in less than one meter. This acceleration gradient is about a thousand times larger than in conventional microwave-driven accelerators. It is a first step toward a ``plasma afterburner,'' which would be placed at the end of a kilometers-long conventional accelerator and double its beam energy in a few tens of meters. In addition to the acceleration of particle beams, these experiments have demonstrated the rich physics bounty to be reaped from relativistic beam-plasma interactions. This includes the generation of intense and narrowly collimated x-ray beams, refraction of particles at a plasma interface, and the creation of intense beams of positrons. These results are leading the way to similar tabletop accelerators based on plasma wakes excited by lasers rather than electron beams. Applications for tabletop accelerators include gamma radiography, radiation therapy, and ultra-fast materials science. [1] T.Tajima and J.M.Dawson Phys.Rev.Lett. 43,267.(1979) [2] P.Chen et.al. Phys.Rev.Lett.54,693,(1985) [3]C.Joshi et.al. Nature 311,525,(1984) In collaboration with all my past and present students and co-workers and in particular collaborators on E157,162,164 and 167 experiments at SLAC.

Joshi, Chandrashekhar

2006-10-01

279

Solar wind-driven plasma fluxes from the Venus ionosphere  

NASA Astrophysics Data System (ADS)

conducted with the ASPERA-4 instrument and the magnetometer of the Venus Express spacecraft show that the kinetic pressure of planetary O+ ion fluxes measured in the Venus wake can be significantly larger than the local magnetic pressure, and as a result, those ions are not solely being driven by magnetic forces but also by the kinetic energy of the solar wind. Beams of planetary O+ ions with those properties have been detected in several orbits of the Venus Express through the Venus wake as the spacecraft traverses by the noon-midnight plane along its near-polar trajectory. The momentum flux of the O+ ions leads to superalfvenic flow conditions. It is suggested that such O+ ion beams are produced in the vicinity of the magnetic polar regions of the Venus ionosphere where the solar wind erodes the local plasma leading to plasma channels that extend downstream from those regions. The distribution of the number of cases where superalfvenic and subalfvenic conditions are measured along the Venus Express trajectory leads to dominant values when the total kinetic plasma pressure (including that of the solar wind protons) and the magnetic pressure are comparable, thus suggesting a possible equipartition of energy between the plasma and the magnetic field.

Pérez-de-Tejada, H.; Lundin, R.; Durand-Manterola, H.; Barabash, S.; Zhang, T. L.; Sauvaud, J. A.; Reyes-Ruiz, M.

2013-12-01

280

Modelling of microwave-driven micro-plasmas in HCPCF  

NASA Astrophysics Data System (ADS)

New UV sources based on microwave-driven micro-plasmas filling a Hollow-Core Photonic Crystal Fibre (HCPCF) [1], exhibit an unprecedented compactness, flexibility, low-cost and high conversion efficiency. The micro-plasma (>10^14 cm-3 electron density, estimated by electromagnetic calculations) is produced by a surface-wave discharge (2.45 GHz frequency) in argon, at 1000-1400 K gas temperatures (measured by OES diagnostics). Our first approach to simulate this system replaces the cladding structure of the fibre (air-holes region) by a capillary cylindrical quartz tube. Simulations use a one-dimensional (radial) stationary model that solves the fluid transport equations for electrons and positive ions, the electron mean energy transport equations, Poisson's and Maxwell's equations for the fields and the gas energy balance equation, coupled to the electron Boltzmann equation for the calculation of the relevant electron parameters [2,3]. We analyze the modification of the plasma with changes in the work conditions, presenting simulations for various HCPCF core radii (50--500 ?m) and electron densities (1--5x10^14 cm-3), at 1mbar pressure. [1] B. Debord et al, ECOC conference Mo.2.LeCervin.5. (2011) [2] L.L. Alves et al, Phys. Rev. E 79, 016403 (2009) [3] J. Greg'orio et al, Plasma Sources Sci. Technol. 21, 015013 (2012)

Alves, L. L.; Leroy, O.; Boisse-Laporte, C.; Leprince, P.; Debord, B.; Gerome, F.; Jamier, R.; Benabid, F.

2012-10-01

281

Spherically symmetric simulation of plasma liner driven magnetoinertial fusion  

NASA Astrophysics Data System (ADS)

Spherically symmetric simulations of the implosion of plasma liners and compression of plasma targets in the concept of the plasma jet driven magnetoinertial fusion have been performed using the method of front tracking. The cases of single deuterium and xenon liners and double layer deuterium-xenon liners compressing various deuterium-tritium targets have been investigated, optimized for maximum fusion energy gains, and compared with theoretical predictions and scaling laws of [P. Parks, Phys. Plasmas 15, 062506 (2008)]. In agreement with the theory, the fusion gain was significantly below unity for deuterium-tritium targets compressed by Mach 60 deuterium liners. The most optimal setup for a given chamber size contained a target with the initial radius of 20 cm compressed by a 10 cm thick, Mach 60 xenon liner, achieving a fusion energy gain of 10 with 10 GJ fusion yield. Simulations also showed that composite deuterium-xenon liners reduce the energy gain due to lower target compression rates. The effect of heating of targets by alpha particles on the fusion energy gain has also been investigated.

Samulyak, Roman; Parks, Paul; Wu, Lingling

2010-09-01

282

Spherically symmetric simulation of plasma liner driven magnetoinertial fusion  

SciTech Connect

Spherically symmetric simulations of the implosion of plasma liners and compression of plasma targets in the concept of the plasma jet driven magnetoinertial fusion have been performed using the method of front tracking. The cases of single deuterium and xenon liners and double layer deuterium-xenon liners compressing various deuterium-tritium targets have been investigated, optimized for maximum fusion energy gains, and compared with theoretical predictions and scaling laws of [P. Parks, Phys. Plasmas 15, 062506 (2008)]. In agreement with the theory, the fusion gain was significantly below unity for deuterium-tritium targets compressed by Mach 60 deuterium liners. The most optimal setup for a given chamber size contained a target with the initial radius of 20 cm compressed by a 10 cm thick, Mach 60 xenon liner, achieving a fusion energy gain of 10 with 10 GJ fusion yield. Simulations also showed that composite deuterium-xenon liners reduce the energy gain due to lower target compression rates. The effect of heating of targets by alpha particles on the fusion energy gain has also been investigated.

Samulyak, Roman [Department of Applied Mathematics and Statistics, Stony Brook University, Stony Brook, New York 11794 (United States); Computational Science Center, Brookhaven National Laboratory, Upton, New York 11973 (United States); Parks, Paul [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Wu Lingling [Department of Applied Mathematics and Statistics, Stony Brook University, Stony Brook, New York 11794 (United States)

2010-09-15

283

Betatron Radiation from a Beam Driven Plasma Source  

SciTech Connect

Photons produced by the betatron oscillation of electrons in a beam-driven plasma wake provide a uniquely intense and high-energy source of hard X-rays and gamma rays. This betatron radiation is interesting not only for its high intensity and spectral characteristics, but also because it can be used as a diagnostic for beam matching into the plasma, which is critical for maximizing the energy extraction efficiency of a plasma accelerator stage. At SLAC, gamma ray detection devices have been installed at the dump area of the FACET beamline where the betatron radiation from the plasma source used in the E200 plasma wakefield acceleration experiment may be observed. The ultra-dense, high-energy beam at FACET (2 x 10{sup 10} electrons, 20 x 20 {micro}m{sup 2} spot, 20-100 {micro}m length, 20 GeV energy) when sent into a plasma source with a nominal density of {approx} 1 x 10{sup 17} cm{sup -3} will generate synchrotron-like spectra with critical energies well into the tens of MeV. The intensity of the radiation can be increased by introducing a radial offset to the centroid of the witness bunch, which may be achieved at FACET through the use of a transverse deflecting RF cavity. The E200 gamma ray detector has two main components: a 30 x 35 cm{sup 2} phosphorescent screen for observing the transverse extent of the radiation, and a sampling electromagnetic calorimeter outfitted with photodiodes for measuring the on-axis spectrum. To estimate the spectrum, the observed intensity patterns across the calorimeter are fit with a Gaussian-integrated synchrotron spectrum and compared to simulations. Results and observations from the first FACET user run (April-June 2012) are presented.

Litos, M.; Corde, S.; /SLAC

2012-08-13

284

Integrated magnetic and kinetic control of advanced tokamak plasmas on DIII-D based on data-driven models  

NASA Astrophysics Data System (ADS)

The first real-time profile control experiments integrating magnetic and kinetic variables were performed on DIII-D in view of regulating and extrapolating advanced tokamak scenarios to steady-state devices and burning plasma experiments. Device-specific, control-oriented models were obtained from experimental data using a generic two-time-scale method that was validated on JET, JT-60U and DIII-D under the framework of the International Tokamak Physics Activity for Integrated Operation Scenarios (Moreau et al 2011 Nucl. Fusion 51 063009). On DIII-D, these data-driven models were used to synthesize integrated magnetic and kinetic profile controllers. The neutral beam injection (NBI), electron cyclotron current drive (ECCD) systems and ohmic coil provided the heating and current drive (H&CD) sources. The first control actuator was the plasma surface loop voltage (i.e. the ohmic coil), and the available beamlines and gyrotrons were grouped to form five additional H&CD actuators: co-current on-axis NBI, co-current off-axis NBI, counter-current NBI, balanced NBI and total ECCD power from all gyrotrons (with off-axis current deposition). Successful closed-loop experiments showing the control of (a) the poloidal flux profile, ?(x), (b) the poloidal flux profile together with the normalized pressure parameter, ?N, and (c) the inverse of the safety factor profile, \\bar{\\iota}(x)=1/q(x) , are described.

Moreau, D.; Walker, M. L.; Ferron, J. R.; Liu, F.; Schuster, E.; Barton, J. E.; Boyer, M. D.; Burrell, K. H.; Flanagan, S. M.; Gohil, P.; Groebner, R. J.; Holcomb, C. T.; Humphreys, D. A.; Hyatt, A. W.; Johnson, R. D.; La Haye, R. J.; Lohr, J.; Luce, T. C.; Park, J. M.; Penaflor, B. G.; Shi, W.; Turco, F.; Wehner, W.; the ITPA-IOS Group members; experts

2013-06-01

285

Integrated Plasma Simulation of Ion Cyclotron and Lower Hybrid Range of Frequencies Actuators in Tokamaks  

NASA Astrophysics Data System (ADS)

Recent upgrades to the ion cyclotron RF (ICRF) and lower hybrid RF (LHRF) components of the Integrated Plasma Simulator [1] have made it possible to simulate LH current drive in the presence of ICRF minority heating and mode conversion electron heating. The background plasma is evolved in these simulations using the TSC transport code [2]. The driven LH current density profiles are computed using advanced ray tracing (GENRAY) and Fokker Planck (CQL3D) [3] components and predictions from GENRAY/CQL3D are compared with a ``reduced'' model for LHCD (the LSC [4] code). The ICRF TORIC solver is used for minority heating with a simplified (bi-Maxwellian) model for the non-thermal ion tail. Simulation results will be presented for LHCD in the presence of ICRF heating in Alcator C-Mod. [4pt] [1] D. Batchelor et al, Journal of Physics: Conf. Series 125, 012039 (2008).[0pt] [2] S. C. Jardin et al, J. Comp. Phys. 66, 481 (1986).[0pt] [3] R. W. Harvey and M. G. McCoy, Proc. of the IAEA Tech. Comm. Meeting on Simulation and Modeling of Therm. Plasmas, Montreal, Canada (1992).[0pt] [4] D. Ignat et al, Nucl. Fus. 34, 837 (1994).[0pt] [5] M. Brambilla, Plasma Phys. and Cont. Fusion 41,1 (1999).

Bonoli, P. T.; Shiraiwa, S.; Wright, J. C.; Harvey, R. W.; Batchelor, D. B.; Berry, L. A.; Chen, Jin; Poli, F.; Kessel, C. E.; Jardin, S. C.

2012-10-01

286

Active Separation Control over a NACA0024 by DBD Plasma Actuator and FBG Sensor  

NASA Astrophysics Data System (ADS)

Dielectric barrier discharge plasma actuators (DBD-PA) and fiber Bragg grating (FBG) sensors have been investigated for active control of flow separation around a NACA0024 airfoil. Tangential jets were produced in the vicinity of the DBD-PA slightly aft of the leading edge of the airfoil. The flow separation control ability was evaluated at low Reynolds number in an open-circuit wind tunnel. Phase- and time-averaged velocity distributions around the airfoil were measured using Particle Image Velocimetry, and the flow separation control ability of the DBD-PA was assessed at 8°, 12° and 16° angle of attack. An FBG sensor was attached to a chord-wise cantilever near the trailing edge of the airfoil on the pressure surface. This was used to measure strain fluctuations in the cantilever root due to flow-induced oscillations. The feasibility of this system to detect flow separation was studied, where the standard deviations of strain fluctuations significantly increased when the flow was separated. This was utilized in an open-loop control system to detect flow separation by FBG then apply active control with the DBD-PA to reattach the flow.

Jukes, Timothy; Segawa, Takehiko; Walker, Seth; Furutani, Hirohide; Iki, Norihiko; Takekawa, Shinya

287

Inter- and intracellular signaling induced by magnetomechanical actuation of plasma membrane channels  

NASA Astrophysics Data System (ADS)

Magnetic particles allow for non-invasive control over their spatial orientation and motion which makes them ideally suitable for studying real-time processes in living cells. Lithographically defined ferromagnetic disks with spin-vortex ground state have the advantage of zero net magnetization in remanence. This eliminates long-range magnetic forces which otherwise lead to the interaction between particles and their agglomeration. Moreover, magnetically soft permalloy particles have high magnetization of saturation thus requiring very low external field for inducing high magnetomotive force, compared to superparamagnetic particles. Our group has previously demonstrated that micron-sized permalloy disks can be used for destruction of cancer cells (D.-H. Kim, E. A. Rozhkova, I. V. Ulasov, S. D. Bader, T. Rajh, M. S. Lesniak, V. Novosad, Nat. Mater. 9, 165-171 (2010). In this work, we investigate the effects of magnetomechanical stimulation of human brain cancer cells with these particles. It will be shown that the actuation of ion channels in cell plasma membrane induces, on the one hand side, intracellular signaling triggering cell apoptosis and, on the other hand, it stimulates the energy transfer between the cells which carries the information about apoptotic signal.

Vitol, Elina A.; Rozhkova, Elena A.; Novosad, Valentyn; Bader, Samuel D.

2012-02-01

288

Laboratory Studies of Magnetically Driven, Radiatively Cooled Supersonic Plasma Jets  

NASA Astrophysics Data System (ADS)

Results of the recent experiments with radiatively cooled jets performed on the pulsed power MAGPIE facility (1.5MA, 250ns) at Imperial College will be presented. The experiments are scalable to astrophysical flows in that critical dimensionless numbers such as the plasma collisionality, the plasma beta, Reynolds number and the magnetic Reynolds number are all in the astrophysically appropriate ranges. The experimental results will be compared with computer simulations performed with laboratory plasma codes and with astrophysical codes. The main part of the presentation will concentrate on the dynamics of magnetically driven jets, in particular on formation of episodic outflows [1]. The experimental results show the periodic ejections of magnetic bubbles naturally evolving into a heterogeneous jet propagating inside a channel made of self-collimated magnetic cavities. Experimental data on the energy balance in the magnetically driven jets, the conversion of the Poynting flux energy into kinetic energy of the outflow, will be also presented. *) In collaboration with A. CIARDI, F.A. SUZUKI-VIDAL, S.N. BLAND, M. BOCCHI, G. BURDIAK, J.P. CHITTENDEN, P. de GROUCHY, G. HALL, A. HARVEY-THOMSON, A. MAROCCHINO, G. SWADLING, A. FRANK, E. G. BLACKMAN, C. STEHLE, M. CAMENZIND. This research was sponsored by EPSRC, by the OFES DOE, by the NNSA under DOE Cooperative Agreement No. DE-FC03-02NA00057 and by the European Community's Marie Curie Actions within the JETSET network under Contract No. MRTNCT- 2004 005592. References [1] A. Ciardi, S.V. Lebedev, A. Frank et al., The Astrophysical Journal, 691: L147-L150 (2009).

Lebedev, Sergey V.

2010-05-01

289

Steady control of laminar separation over airfoils with plasma sheet actuators  

Microsoft Academic Search

This work analyzes the effects produced by an EHD actuator on the flow around an airfoil at low Re numbers (Re?104). The analysis is undertaken from flow visualizations and measurements of the surface pressure distributions. The experiments indicate that, for low Re number, the effects of the actuation depend on the power added to the flow and on the relative

Roberto Sosa; Guillermo Artana

2006-01-01

290

Development and characterization of plasma actuators for high-speed jet control  

Microsoft Academic Search

Active control of high Reynolds number and high-speed jets has been hampered due to the lack of suitable actuators. Some of the attributes that would make an actuator suitable for such flows are: high amplitude and bandwidth; small size for distribution around the jet; phase-locking ability for jet azimuthal mode forcing; and sufficient ruggedness for hot jets. We have been

M. Samimy; I. Adamovich; B. Webb; J. Kastner; J. Hileman; S. Keshav; P. Palm

2004-01-01

291

Transport and drift-driven plasma flow components in the Alcator C-Mod boundary plasma  

NASA Astrophysics Data System (ADS)

Boundary layer flows in the Alcator C-Mod tokamak are systematically examined as magnetic topology (upper versus lower-null) and plasma density are changed. Utilizing a unique set of scanning Langmuir-Mach probes, including one on the high-field side (HFS) midplane, the poloidal variation of plasma flow components in the parallel, diamagnetic and radial directions are resolved in detail. It is found that the plasma flow pattern can be decomposed into two principal parts: (1) a drift-driven component, which lies within a magnetic flux surface and is divergence-free and (2) a transport-driven component, which gives rise to near-sonic parallel flows on the HFS scrape-off layer (SOL). Toroidal rotation, Pfirsch-Schlüter and transport-driven contributions are unambiguously identified. Transport-driven parallel flows are found to dominate the HFS particle fluxes; the total poloidal-directed flow accounts for ˜1/3 to all of the ion flux arriving on the inner divertor. As a result, heat convection is found to be an important player in this region, consistent with the observation of divertor asymmetries that depend on the direction of B × ?B relative to the active x-point. In contrast, the poloidal projection of parallel flow in the low-field SOL largely cancels with Er × B flow; toroidal rotation is the dominant plasma motion there. The magnitude of the transport-driven poloidal flow is found to be quantitatively consistent with fluctuation-induced radial particle fluxes on the low-field side (LFS), identifying this as the primary drive mechanism. Fluctuation-induced fluxes on the HFS are found to be essentially zero, excluding turbulent inward transport as the mechanism that closes the circulation loop in this region.

Smick, N.; LaBombard, B.; Hutchinson, I. H.

2013-02-01

292

The Plasma Jet/Laser Driven Compression of Compact Plasmoids to Fusion Conditions  

NASA Astrophysics Data System (ADS)

Magneto-inertial fusion (MIF) is based on both magnetic and inertial confinement. An embedded magnetic field is compressed along with the target plasma to achieve magnetic insulation and fusion condition. Several magnetic systems for plasma confinement may be used for laser-driven (LD) and plasma jet driven (PJ) magnetic flux compression. Estimations show the possibility in principle to realize regimes of PJMIF system with a plasma gain factor Q > 10.

Chirkov, Alexei Yu.; Ryzhkov, Sergei V.

2012-02-01

293

Documentation and Control of Flow Separation on a Low Pressure Turbine Linear Cascade of Pak-B Blades Using Plasma Actuators  

NASA Technical Reports Server (NTRS)

This work involved the documentation and control of flow separation that occurs over low pressure turbine (LPT) blades at low Reynolds numbers. A specially constructed linear cascade was utilized to study the flow field over a generic LPT cascade consisting of Pratt & Whitney "Pak-B" shaped blades. Flow visualization, surface pressure measurements, LDV measurements, and hot-wire anemometry were conducted to examine the flow fields with and without separation control. Experimental conditions were chosen to give a range of chord Reynolds numbers (based on axial chord and inlet velocity) from 10,000 to 100,000, and a range of freestream turbulence intensities from u'/U(infinity) = 0.08 to 2.85 percent. The blade pressure distributions were measured and used to identify the region of separation that depends on Reynolds number and the turbulence intensity. Separation control was performed using dielectric barrier discharge (DBD) plasma actuators. Both steady and unsteady actuation were implemented and found to work well. The comparison between the steady and unsteady actuators showed that the unsteady actuators worked better than the steady ones. For the steady actuators, it was found that the separated region is significantly reduced. For the unsteady actuators, where the signal was pulsed, the separation was eliminated. The total pressure losses (a low Reynolds number) was reduced by approximately a factor of two. It was also found that lowest plasma duty cycle (10 percent in this work) was as effective as the highest plasma duty cycle (50 percent in this work). The mechanisms of the steady and unsteady plasma actuators were studied. It was suggested by the experimental results that the mechanism for the steady actuators is turbulence tripping, while the mechanism for the unsteady actuators is to generate a train of spanwise structures that promote mixing.

Corke, Thomas c.; Thomas, FLint, O.; Huang, Junhui

2007-01-01

294

Stochastic electron motion driven by space plasma waves  

NASA Astrophysics Data System (ADS)

Stochastic motion of relativistic electrons under conditions of the nonlinear resonance interaction of particles with space plasma waves is studied. Particular attention is given to the problem of the stability and variability of the Earth's radiation belts. It is found that the interaction between whistler-mode waves and radiation-belt electrons is likely to involve the same mechanism that is responsible for the dynamical balance between the accelerating process and relativistic electron precipitation events. We have also considered the efficiency of the mechanism of stochastic surfing acceleration of cosmic electrons at the supernova remnant shock front, and the accelerating process driven by a Langmuir wave packet in producing cosmic ray electrons. The dynamics of cosmic electrons is formulated in terms of a dissipative map involving the effect of synchrotron emission. We present analytical and numerical methods for studying Hamiltonian chaos and dissipative strange attractors, and for determining the heating extent and energy spectra.

Khazanov, G. V.; Tel'nikhin, A. A.; Kronberg, T. K.

2014-01-01

295

Gas flow driven by thermal creep in dusty plasma  

NASA Astrophysics Data System (ADS)

Thermal creep flow (TCF) is a flow of gas driven by a temperature gradient along a solid boundary. Here, TCF is demonstrated experimentally in a dusty plasma. Stripes on a glass box are heated by laser beam absorption, leading to both TCF and a thermophoretic force. The design of the experiment allows isolating the effect of TCF. A stirring motion of the dust particle suspension is observed. By eliminating all other explanations for this motion, we conclude that TCF at the boundary couples by drag to the bulk gas, causing the bulk gas to flow, thereby stirring the suspension of dust particles. This result provides an experimental verification, for the field of fluid mechanics, that TCF in the slip-flow regime causes steady-state gas flow in a confined volume.

Flanagan, T. M.; Goree, J.

2009-10-01

296

CENTER FOR PULSED POWER DRIVEN HIGH ENERGY DENSITY PLASMA STUDIES  

SciTech Connect

This annual report summarizes the activities of the Cornell Center for Pulsed-Power-Driven High-Energy-Density Plasma Studies, for the 12-month period October 1, 2005-September 30, 2006. This period corresponds to the first year of the two-year extension (awarded in October, 2005) to the original 3-year NNSA/DOE Cooperative Agreement with Cornell, DE-FC03-02NA00057. As such, the period covered in this report also corresponds to the fourth year of the (now) 5-year term of the Cooperative Agreement. The participants, in addition to Cornell University, include Imperial College, London (IC), the University of Nevada, Reno (UNR), the University of Rochester (UR), the Weizmann Institute of Science (WSI), and the P.N. Lebedev Physical Institute (LPI), Moscow. A listing of all faculty, technical staff and students, both graduate and undergraduate, who participated in Center research activities during the year in question is given in Appendix A.

Professor Bruce R. Kusse; Professor David A. Hammer

2007-04-18

297

Pulsed radiobiology with laser-driven plasma accelerators  

NASA Astrophysics Data System (ADS)

Recently, a high efficiency regime of acceleration in laser plasmas has been discovered, allowing table top equipment to deliver doses of interest for radiotherapy with electron bunches of suitable kinetic energy. In view of an R&D program aimed to the realization of an innovative class of accelerators for medical uses, a radiobiological validation is needed. At the present time, the biological effects of electron bunches from the laser-driven electron accelerator are largely unknown. In radiobiology and radiotherapy, it is known that the early spatial distribution of energy deposition following ionizing radiation interactions with DNA molecule is crucial for the prediction of damages at cellular or tissue levels and during the clinical responses to this irradiation. The purpose of the present study is to evaluate the radio-biological effects obtained with electron bunches from a laser-driven electron accelerator compared with bunches coming from a IORT-dedicated medical Radio-frequency based linac's on human cells by the cytokinesis block micronucleus assay (CBMN). To this purpose a multidisciplinary team including radiotherapists, biologists, medical physicists, laser and plasma physicists is working at CNR Campus and University of Pisa. Dose on samples is delivered alternatively by the "laser-linac" operating at ILIL lab of Istituto Nazionale di Ottica and an RF-linac operating for IORT at Pisa S. Chiara Hospital. Experimental data are analyzed on the basis of suitable radiobiological models as well as with numerical simulation based on Monte Carlo codes. Possible collective effects are also considered in the case of ultrashort, ultradense bunches of ionizing radiation.

Giulietti, Antonio; Grazia Andreassi, Maria; Greco, Carlo

2011-05-01

298

DBD Plasma Actuators for Flow Control in Air Vehicles and Jet Engines - Simulation of Flight Conditions in Test Chambers by Density Matching  

NASA Technical Reports Server (NTRS)

Dielectric Barrier Discharge (DBD) Plasma actuators for active flow control in aircraft and jet engines need to be tested in the laboratory to characterize their performance at flight operating conditions. DBD plasma actuators generate a wall-jet electronically by creating weakly ionized plasma, therefore their performance is affected by gas discharge properties, which, in turn, depend on the pressure and temperature at the actuator placement location. Characterization of actuators is initially performed in a laboratory chamber without external flow. The pressure and temperature at the actuator flight operation conditions need to be simultaneously set in the chamber. A simplified approach is desired. It is assumed that the plasma discharge depends only on the gas density, while other temperature effects are assumed to be negligible. Therefore, tests can be performed at room temperature with chamber pressure set to yield the same density as in operating flight conditions. The needed chamber pressures are shown for altitude flight of an air vehicle and for jet engines at sea-level takeoff and altitude cruise conditions. Atmospheric flight conditions are calculated from standard atmosphere with and without shock waves. The engine data was obtained from four generic engine models; 300-, 150-, and 50-passenger (PAX) aircraft engines, and a military jet-fighter engine. The static and total pressure, temperature, and density distributions along the engine were calculated for sea-level takeoff and for altitude cruise conditions. The corresponding chamber pressures needed to test the actuators were calculated. The results show that, to simulate engine component flows at in-flight conditions, plasma actuator should be tested over a wide range of pressures. For the four model engines the range is from 12.4 to 0.03 atm, depending on the placement of the actuator in the engine. For example, if a DBD plasma actuator is to be placed at the compressor exit of a 300 PAX engine, it has to be tested at 12.4 atm for takeoff, and 6 atm for cruise conditions. If it is to be placed at the low-pressure turbine, it has to be tested at 0.5 and 0.2 atm, respectively. These results have implications for the feasibility and design of DBD plasma actuators for jet engine flow control applications. In addition, the distributions of unit Reynolds number, Mach number, and velocity along the engine are provided. The engine models are non-proprietary and this information can be used for evaluation of other types of actuators and for other purposes.

Ashpis, David E.; Thurman, Douglas R.

2011-01-01

299

Complete Oxidation of Volatile Organic Compounds (VOCs) Using Plasma-Driven Catalysis and Oxygen Plasma  

Microsoft Academic Search

The decomposition of volatile organic compounds (VOCs) was investigated using a flow-type plasma-driven catalysis (PDC) system and a cycled system. In the flow-type PDC reactor a trade-off relation was observed between the formation of nitrogen oxides and the decomposition of VOCs. Complete decomposition of VOC to CO2 was achieved with the cycled system without forming CO, aerosol, and any nitrogen

H. H. Kim; A. Ogata; S. Futamura

300

Positive and negative sawtooth signals applied to a DBD plasma actuator – influence on the electric wind  

Microsoft Academic Search

The influence of the electric signal shape applied to a surface dielectric barrier discharge (DBD) actuator is investigated in order to optimise the produced electric wind. This report also gives insights on the mechanisms involved in the electro-fluido-dynamic (EFD) operated by actuators based on atmospheric non-thermal discharges in air. The parameters of the electric signal that maximises the produced electric

N. Balcon; N. Benard; Y. Lagmich; J.-P. Boeuf; G. Touchard; E. Moreau

2009-01-01

301

Alpha-driven mironoinstability in tandem mirror plasma  

SciTech Connect

Alpha particles born at deuterium-tritium (D-T) fusion are mirror confined in the tandem mirror with a loss-cone-type distribution in the velocity space. The anisotropy created is susceptible to microinstabilities and the objective of this work is to study possible instabilities that can be driven by the alpha loss-cone. The low-frequency (at the order of the ion cyclotron frequency) wave spectrum is examined to seek the waves that can be destabilized by the alphas. A marginal stability boundary in ion density-temperature space is found. The central cell of the tandem mirror is modeled by an infinite, long plasm cylinder with azimuthal symmetry. The plasma consists of both deuteron and triton as fuel ions and is assumed to be cold since the ion velocity is much smaller than that of the alpha. This model also considers a sharp boundary plasma, with a vacuum region separating it from the conducting wall. To examine reactor implication, the authors have calculated the stability boundary for the cases of the MARS and MINIMARS parameters. The operating regime for both cases is found to be unstable. this could be a key problem for reactor operation and deserves more study. 4 refs., 2 figs.

Ho, S.K.; Miley, G.H.; Smith, G.R.; Nevins, W.M.

1986-01-01

302

Membrane Nano-Actuation by Light-Driven Manipulation of van der Waals Forces: A Progress Report  

NASA Astrophysics Data System (ADS)

An ongoing proof-of-concept demonstration of the resonant actuation of a thin membrane by periodic van der Waals forces between an illuminated semiconducting layer and a vibrating sensing element is reported. In the first phase of our effort, we have studied the mechanical response of a microphone membrane modified by a central rigid silica disk under the action of an electrostatic actuator inside a vacuum chamber. Unlike previous, and quite approximate, efforts by others, we obtained the first successful verification of the frequency response of a modified vibrating membrane to the excitation by an especially designed electrostatic actuator for the first three cylindrically symmetrical resonant modes of the system. In order to properly calibrate the capacitive device for the detection of membrane actuation by the van der Waals force, we proceeded by obtaining accurate calculations of the electrostatic force between the actuator and the modified microphone membrane. This demanding numerical effort, conducted in cylindrical coordinates by means of a simultaneous overrelaxation (SOR) algorithm coded in Compaq Fortran 90, has already exposed some undetected errors in the existing literature. We have also quantitatively proven that capacitance estimates from standard analytical equations appreciably depart from those obtained by accurate finite-difference models. This finding is extremely important since a detailed understanding of electrostatic calibration is at the basis of most contemporary experiments on van der Waals forces. We conclude by illustrating the next steps of our proof-of-concept activities and we comment on the overall technological relevance of our demonstration.

Pinto, Fabrizio

2008-01-01

303

Experimental investigations of driven Alfven wave resonances in a Tokamak plasma using carbon dioxide laser interferometry  

NASA Astrophysics Data System (ADS)

The first direct observation of the internal structure of driven globed Alfven eigenmodes in a Tokamak plasma is presented. A carbon dioxide laser scattering/interferometer has been designed, built, and installed on the PRETEXT Tokamak. The resonance conditions required for, and the spatial wave field structure of, driven plasma eigenmodes at frequencies below the ion cyclotron frequency in a confined, high temperature, Tokamak plasma are investigated.

Evans, T. E.

1984-09-01

304

MTF Driven by Plasma Liner Dynamically Formed by the Merging of Plasma Jets: An Overview  

NASA Technical Reports Server (NTRS)

One approach for standoff delivery of the momentum flux for compressing the target in MTF consists of using a spherical array of plasma jets to form a spherical plasma shell imploding towards the center of a magnetized plasma, a compact toroid (Figure 1). A 3-year experiment (PLX-1) to explore the physics of forming a 2-D plasma liner (shell) by merging plasma jets is described. An overview showing how this 3-year project (PLX-1) fits into the program plan at the national and international level for realizing MTF for energy and propulsion is discussed. Assuming that there will be a parallel program in demonstrating and establishing the underlying physics principles of MTF using whatever liner is appropriate (e.g. a solid liner) with a goal of demonstrating breakeven by 2010, the current research effort at NASA MSFC attempts to complement such a program by addressing the issues of practical embodiment of MTF for propulsion. Successful conclusion of PLX-1 will be followed by a Physics Feasibility Experiment (PLX-2) for the Plasma Liner Driven MTF.

Thio, Y. C. Francis; Eskridge, Richard; Martin, Adam; Smith, James; Lee, Michael; Rodgers, Stephen L. (Technical Monitor)

2001-01-01

305

A neuromusculoskeletal model of the human lower limb: Towards EMG-driven actuation of multiple joints in powered orthoses  

Microsoft Academic Search

This paper presents a novel neuromusculoskeletal (NMS) model of the human lower limb that uses the electromyo- graphic (EMG) signals from 16 muscles to estimate forces generated by 34 musculotendon actuators and the resulting joint moments at the hip, knee and ankle joints during varied contractile conditions. Our proposed methodology allows over- coming limitations on force computation shown by currently

Massimo Sartori; Monica Reggiani; David G. Lloyd; Enrico Pagello

2011-01-01

306

Sheared Buneman Instabilities in Current-Driven Plasmas  

NASA Astrophysics Data System (ADS)

Simulation studies of magnetic reconnection in strongly magnetized plasmas1 have indicated that electron phase-space holes evolve out of current-driven Buneman instabilities and that these holes play an important role in supplying the needed dissipation in the reconnection process by acting as electron scattering centers. Drake and collaborators have shown in simulations that the evolution of electron holes is mediated by lower hybrid waves. We have shown independently, via 2-D simulations of the evolution of Buneman instabilities, that electron phase space holes evolve and interact with lower hybrid waves in a manner similar to that seen in the reconnection simulations2 Perpendicular shear in the parallel velocity and the current will be present near the edges and elsewhere in realistic current sheets associated with magnetic reconnection. We have studied the effects of such shear on the nature and evolution of Buneman instabilities and the resulting electron phase space holes. Both linear theory and 2-D Vlasov simulations are employed. It is shown that even a small amount of velocity shear can have a large effect on the nonlinear evolution of holes and lower hybrid waves. 1Drake, J. F., M. Swisdak, C. Cattell, M. A. Shay, B. N. Rogers, and A.~Zeiler, Formation of Electron Holes and Particle Energization During Magnetic Reconnection, Science, 299, (2003). 2Martin V. Goldman, D. L. Newman, A. Mangeney, F. Califano, Theory and Simulation of Sheared Electron Beam Instabilities in Strongly Magnetized Plasmas, COSPAR04-A-02395; D3.5-0015-04, 35th COSPAR Scientific Assembly Paris, France, 18 - 25 July 2004. This research was supported by DOE, NSF and NASA.

Goldman, M. V.; Newman, D. L.; Sen, N.

2005-05-01

307

Resistive pressure gradient-driven turbulence at stellarator plasma edge  

SciTech Connect

High resolution calculations of resistive pressure gradient-driven turbulence for the plasma edge parameters of the Advanced Toroidal Facility (ATF) [J. F. Lyon {ital et al.}, Fusion Technol. {bold 10}, 179 (1986)] electron cyclotron heated discharges give fluctuation levels, consistent with the experimental measurements. This turbulence model is also used to simulate the transition from the low confinement to the high confinement mode. The transition is triggered through the poloidal flow amplification induced by the Reynolds stress. After the transition, the confinement improvement is relatively low (30{percent}{endash}40{percent}), even for unrealistically low poloidal viscosity. In the high confinement mode, the characteristic radial scale length of the poloidal flow in the three-dimensional calculations (separation between the lowest-n resonant surfaces) is different from the single helicity results (radial correlation length of the fluctuations). The simple criterion based on the ratio of shearing rate to the linear growth rate does not quantitatively account for the fluctuation reduction. {copyright} {ital 1997 American Institute of Physics.}

Garcia, L. [Universidad Carlos III, Madrid (Spain)] [Universidad Carlos III, Madrid (Spain); Carreras, B.A.; Lynch, V.E.; Leboeuf, J.N.; Newman, D.E. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (United States)] [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (United States)

1997-09-01

308

Laboratory Astrophysics Experiments with Magnetically Driven Plasma Jets  

NASA Astrophysics Data System (ADS)

We present experimental results on the formation of supersonic, radiatively cooled jets driven by the toroidal magnetic field generated by the 1.5 MA, 250 ns current from the MAGPIE generator. The morphology of the jet produced in the experiments is relevant to astrophysical jet scenarios in which the jet on the axis of a magnetic cavity expanding into an ambient medium is collimated by a toroidal magnetic field. The jets in our experiments have similar Mach number, plasma beta and cooling parameter to those in protostellar jets and additionally the Reynolds, magnetic Reynolds and Peclet numbers are much larger than unity, allowing the experiments to be scaled to astrophysical flows. The experimental configuration generates episodic magnetic cavities, suggesting that periodic formation of jets in astrophysical situations could be responsible for some of the variability observed in astrophysical jets. The dynamics of the formation of laboratory jets are presented, together with new results including preliminary measurements of magnetic, kinetic and Poynting energy of the outflows. In addition first estimates of jet temperature and trapped toroidal magnetic field are presented and discussed.

Suzuki-Vidal, F.; Lebedev, S. V.; Ciardi, A.; Bland, S. N.; Hall, G. N.; Swadling, G.; Harvey-Thompson, A. J.; Burdiak, G.; de Grouchy, P.; Chittenden, J. P.; Bocchi, M.; Bott, S. C.; Frank, A.

2014-05-01

309

Lift and drag performances of an axisymmetric airfoil controlled by plasma actuator  

Microsoft Academic Search

A Dielectric Barrier Discharge (DBD) is mounted at the leading edge of a NACA 0015 airfoil model. The effects of steady and unsteady actuations on the lift and drag coefficients are investigated by time-averaged force measurements. Results demonstrate that the stall regime can be delayed of one or two degrees while the drag coefficient is reduced. The aerodynamic performances are

N. Benard; J. Jolibois; E. Moreau

2009-01-01

310

A micro transportation system (MTS) with large movement of containers driven by electrostatic comb-drive actuators  

NASA Astrophysics Data System (ADS)

This paper describes a Si micro transportation system (MTS) to drive micro containers in straight movement based on a ratchet mechanism and electrostatic comb-drive actuators. This MTS consists of linear comb actuators, micro containers and ratchet racks. The lateral movements of ratchet racks push the micro containers which move straight in a perpendicular direction with different velocities. The MTS was fabricated from a SOI wafer by using only one mask. In our experiments, the movement of the micro container has been tested with driving frequency ranges from 1 Hz to 20 Hz. The velocity of the micro container was proportional to the driving frequency, and it matched well with the theoretical calculation.

Pham, Phuc Hong; Viet Dao, Dzung; Sugiyama, Susumu

2007-10-01

311

Observation of a current-driven plasma instability at the outer zone-plasma sheet boundary.  

NASA Technical Reports Server (NTRS)

Several spacecraft experimenters have reported on the detection of large temporal variations in trapped electron fluxes near L = 5 to 6 at midlatitudes in the night hemisphere. In this report we describe in detail the particle, wave, and field changes measured when Ogo 5 traversed an outer-zone trapping boundary of this type on September 7, 1968. It is shown that thermal proton concentrations and E greater than 50-keV electron fluxes abruptly decreased when electrons with (1-4) keV mean energy were detected. It is also shown that currents flowed along the average geomagnetic field direction near the plasma boundaries and that these were accompanied by intense VLF electrostatic waves. It is proposed that turbulent resistivity produced by current-driven plasma instabilities allows parallel dc electric fields to develop along this boundary.

Scarf, F. L.; Fredricks, R. W.; Russell, C. T.; Kivelson, M.; Neugebauer, M.; Chappell, C. R.

1973-01-01

312

Towards Experimental Verification and Device Applications of Current Driven Plasma Instabilities in Solid State Systems.  

National Technical Information Service (NTIS)

In this program, we have identified theoretically the most promising candidate for current driven plasma instabilities (CDPI) in semiconductor based systems: the modulated lower dimensional systems. We also investigated the effects of a grating coupler an...

P. Bakshi K. Kempa

1993-01-01

313

Toward Noise Mitigation in High Speed and High Reynolds Number Jets Using Plasma Actuators  

Microsoft Academic Search

5 . Eight actuators, distributed azimuthally inside the nozzle, near the nozzle exit, were used to excite various azimuthal modes of the jet over a large frequency range (StDF of 0.1 to 5.0). Dynamic pressure measurements were used to investigate the growth and decay of perturbations and instability waves in the flow, PIV measurements were used to evaluate the effects

M. Samimy; I. Adamovich; Y. Utkin; J. Kastner

2006-01-01

314

Three-dimensional flow measurements induced from serpentine plasma actuators in quiescent air  

NASA Astrophysics Data System (ADS)

This paper presents three-dimensional flow measurements performed on a dielectric barrier discharge (DBD) actuator with the electrodes in a serpentine design. Such a configuration induces a local pinching and a local spreading of the fluid as one follows along the span of the actuator. In this work two different variations on the serpentine configuration are evaluated: one constructed from patterned circular arcs and one from patterned rectangles. The influence of applied voltage is studied for the former case. To quantify these effects stereo particle image velocimetry (PIV) is used to generate time averaged, spatially resolved measurements of the detailed flow structure. The three components of the velocity vector are measured along spanwise and streamwise cuts. These slices are then reconstructed to provide a three-dimensional view of the induced flow field. The results for the induced flow fields are also compared with stereo-PIV measurements made on a standard linear DBD actuator. A truly three-dimensional induced flow field was observed as a result of the serpentine configuration. These designs could be beneficial for rapid mixing of the local fluid.

Durscher, R. J.; Roy, S.

2012-01-01

315

Two-dimensional scanning realized by an asymmetry fiber cantilever driven by single piezo bender actuator for optical coherence tomography.  

PubMed

We develop a fiber based probe that is capable of two-dimensional scanning applicable in optical coherence tomography (OCT). Based on the resonance of the fiber cantilever with asymmetry structure which has two distinguished resonant frequencies in orthogonal directions, Lissajous pattern is produced suitable for two-dimensional scanning upon a sample. Orthogonal resonances of the fiber cantilever are simultaneously excited by single piezo bender actuator with one driving signal consisting of two components corresponding to above-mentioned two resonant frequencies. By integrating a backward-placed two-dimensional position sensitive detector (PSD) into the probe, real-time lateral position of the scanning pattern is registered simultaneously for image reconstruction. Dynamical characteristics of the fiber cantilever are experimentally studied with special consideration on factors determining the resolution of the scanning pattern, including frequency and amplitude ratios between two components of the driving signal and fetching duration used for an en face image. With the developed probe implemented in our established OCT system, en face OCT images of typical samples are obtained with satisfying resolution and contrast, demonstrating the feasibility of such fiber cantilever with asymmetry structure for realizing two dimensional scanning by single actuator, potentially applicable to endoscopic OCT imaging. PMID:19654788

Wu, Tong; Ding, Zhihua; Wang, Kai; Chen, Minghui; Wang, Chuan

2009-08-01

316

Plasma evolution from laser-driven gold disks. II. Computational design and analysis  

Microsoft Academic Search

The LASNEX computer code (Comments Plasma Phys. Controlled Fusion {bold 2}, 51 (1975)) was used in the design and analysis of an experimental study of laser-driven plasma blowoff from gold disks. In the study, several temporal profiles of 0.53 mm laser illumination were used, including square pulses, picket pulse trains, and pulses with graduated leading edges. Preliminary modeling suggested diagnostic

D. Ress; L. J. Suter; E. F. Gabl; B. H. Failor

1990-01-01

317

Plasma evolution from laser-driven gold disks. II. Computational design and analysis  

Microsoft Academic Search

The lasnex computer code [Comments Plasma Phys. Controlled Fusion 2, 51 (1975)] was used in the design and analysis of an experimental study of laser-driven plasma blowoff from gold disks. In the study, several temporal profiles of 0.53 mm laser illumination were used, including square pulses, picket pulse trains, and pulses with graduated leading edges. Preliminary modeling suggested diagnostic techniques

D. Ress; L. J. Suter; E. F. Gabl; B. H. Failor

1990-01-01

318

Numerical study of plasma formation from aluminum rods driven by megaampere currents  

Microsoft Academic Search

Summary form only given. Recent aluminum rod experiments driven by 1-MA Zebra generator at University of Nevada, Reno (UNR) have provided a benchmark for magnetohydrodynamic (MHD) modeling. The innovative 'hourglass' and 'barbell' load geometries used in the experiments made it possible to distinguish between plasma formation due to Ohmic heating, which can be studied numerically utilizing MHD codes, and plasma

M. A. Angelova; V. Makhin; B. S. Bauer; I. R. Lindemuth; R. E. Siemon

2009-01-01

319

Explosive-Driven Hemispherical Implosions for Generating Fusion Plasmas.  

National Technical Information Service (NTIS)

The UTIAS explosive-driven-implosion facility was used to produce stable, centered and focussed hemispherical implosions to generate neutrons from D-D reactions. A high-resolution scintillator-detection system measured the neutrons and gamma rays resultin...

D. Sagie I. I. Glass

1982-01-01

320

Explosive-Driven Hemispherical Implosions for Generating Fusion Plasmas.  

National Technical Information Service (NTIS)

The UTIAS explosive-driven-implosion facility was used to produce stable, centered and focussed hemispherical implosions to generate neutrons from D-D reactions. A high resolution scintillator-detection system measured the neutrons and gamma-rays resultin...

D. Sagie I. I. Glass

1982-01-01

321

Explosive-Driven Hemispherical Implosions for Generating Fusion Plasmas.  

National Technical Information Service (NTIS)

An explosive-driven-implosion facility was used to produce stable, centered and focussed hemispherical implosions to generate neutrons from D-D reactions. A high resolution scintillator-detection system measured the neutrons and gamma rays resulting from ...

D. Sagie I. I. Glass

1982-01-01

322

Contribution of positive and negative ions to the electrohydrodynamic force in a dielectric barrier discharge plasma actuator operating in air  

SciTech Connect

We present a parametric study of the electrohydrodynamic force generated by surface dielectric barrier discharge plasma actuators in air for sinusoidal voltage waveforms. The simulation results confirm that momentum is transferred from the charged particles to the neutral species in the same direction during both positive and negative parts of the cycle. The momentum transfer is due to positive ions during the positive part of the cycle (electrode above the dielectric layer is the anode), and to negative ions during the negative part of the cycle. The relative contribution of the positive and negative parts of the cycle depends on the voltage amplitude and frequency. The model predicts that the contribution of negative ions tends to be dominant at low voltage frequencies and high voltage amplitudes.

Boeuf, J. P.; Lagmich, Y.; Pitchford, L. C. [UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d'Energie), Universite de Toulouse, 118 route de Narbonne, F-31062 Toulouse Cedex 9 (France); LAPLACE, CNRS, F-31062 Toulouse (France)

2009-07-15

323

Progress In Magnetized Target Fusion Driven by Plasma Liners  

NASA Technical Reports Server (NTRS)

Magnetized target fusion (MTF) attempts to combine the favorable attributes of magnetic confinement fusion (MCF) for energy confinement with the attributes of inertial confinement fusion (ICF) for efficient compression heating and wall-free containment of the fusing plasma. It uses a material liner to compress and contain a magnetized plasma. For practical applications, standoff drivers to deliver the imploding momentum flux to the target plasma remotely are required. Spherically converging plasma jets have been proposed as standoff drivers for this purpose. The concept involves the dynamic formation of a spherical plasma liner by the merging of plasma jets, and the use of the liner so formed to compress a spheromak or a field reversed configuration (FRC).

Thio, Francis Y. C.; Kirkpatrick, Ronald C.; Knapp, Charles E.; Cassibry, Jason; Eskridge, Richard; Lee, Michael; Smith, James; Martin, Adam; Wu, S. T.; Schmidt, George; Rodgers, Stephen L. (Technical Monitor)

2001-01-01

324

Linear Proof-Mass Actuator  

NASA Technical Reports Server (NTRS)

Linear proof-mass actuator (LPMA) is friction-driven linear mass actuator capable of applying controlled force to structure in outer space to damp out oscillations. Capable of high accelerations and provides smooth, bidirectional travel of mass. Design eliminates gears and belts. LPMA strong enough to be used terrestrially where linear actuators needed to excite or damp out oscillations. High flexibility designed into LPMA by varying size of motors, mass, and length of stroke, and by modifying control software.

Holloway, Sidney E., III; Crossley, Edward A.; Miller, James B.; Jones, Irby W.; Davis, C. Calvin; Behun, Vaughn D.; Goodrich, Lewis R., Sr.

1995-01-01

325

Para: a computer simulation code for plasma driven electromagnetic launchers  

SciTech Connect

A computer code for simulation of rail-type accelerators utilizing a plasma armature has been developed and is described in detail. Some time varying properties of the plasma are taken into account in this code thus allowing the development of a dynamical model of the behavior of a plasma in a rail-type electromagnetic launcher. The code is being successfully used to predict and analyse experiments on small calibre rail-gun launchers.

Thio, Y.-C.

1983-03-01

326

Rayleigh-Taylor instability driven nonlinear vortices in dusty plasmas  

Microsoft Academic Search

The low frequency stability of a dusty plasma with a nonuniform mass and charge distribution of the dust component is studied. It is shown that the inverse stratification of the dust mass density in a gravitational field may lead to a Rayleigh-Taylor-like instability. In the nonlinear regime this instability can produce an incompressible flow pattern of spontaneously rotating dust plasma

B. M. Veeresha; Amita Das; Abhijit Sen

2005-01-01

327

Modeling of High-Explosive Driven Plasma Compression Opening Switches.  

National Technical Information Service (NTIS)

The initial path of the current through a plasma compression switch is through a thin (500-nm thick) metal foil. The current explodes the foil to form the seed for the conducting plasma. The behavior of the foil at this point is the same as an exploding m...

A. E. Greene I. R. Lindemuth J. H. Goforth

1986-01-01

328

Modeling of high-explosive driven plasma compression opening switches  

Microsoft Academic Search

The initial path of the current through a plasma compression switch is through a thin (500-nm thick) metal foil. The current explodes the foil to form the seed for the conducting plasma. The behavior of the foil at this point is the same as an exploding metal fuse for which we have a simple model. We have, therefore, chosen this

A. E. Greene; I. R. Lindemuth; J. H. Goforth

1986-01-01

329

A 30 mm Wide DC-Driven Brush-Shaped Cold Air Plasma Without Airflow Supplement  

NASA Astrophysics Data System (ADS)

This paper reports a cold atmospheric pressure DC-driven air plasma brush. Three stainless steel needles are symmetrically mounted on a slot shaped PVC slab to act as the electrodes. The brush driven by a direct current (DC) power supply can generate an air plasma glow up to 30 mm wide with no inert gas addition and no air flow supplement. The plasma glow appears uniform no matter what kinds of material are processed. The measured current and the simulated current all show that each pulsed discharge including two peaks always occurs for different gaps between electrodes. Emission spectra measurement result shows that the obtained rotational temperatures are 300 K and the vibrational temperatures are 2250 K. Some reactive species are presented in the plasma glow, which suggest that the proposed plasma brush is beneficial to practical applications.

Chen, Zhaoquan; Zheng, Xiaoliang; Xia, Guangqing; Li, Ping; Hu, Yelin; Du, Zhiwen; Zhu, Longji; Liu, Minghai; Chen, Minggong; Hu, Xiwei

2014-04-01

330

Effect of negative ions on oscillating two stream instability of a laser driven plasma beat wave in a homogeneous plasma  

Microsoft Academic Search

A long wavelength plasma wave is driven by two copropagating lasers with frequencies omegaL1 and omegaL2 such that omegaL1 - omegaL2 ap omegap. The plasma beat wave (omega0, k0) grows in amplitude and becomes susceptible to oscillating two stream instability, producing a low frequency electrostatic mode (omega,k) and two shorter wavelength Langmuir wave sidebands (omegas,f, ks,f ) with omegas,f =

Sandeep Kumar; Hitendra K. Malik

2006-01-01

331

Comparison of the characteristics of potential drop and current-driven double layers. [of auroral plasma  

NASA Technical Reports Server (NTRS)

The characteristics of double layers driven by an applied potential drop and by an injected current into a plasma are compared. In the latter case the potential drop across the double layer appears because of the formation of a virtual cathode. The double layers formed by the two mechanisms show striking similarities with regard to their structure, temporal evolution, and dynamics. However, in the case of current-driven double layers a large energization of ions trapped in the virtual cathode region is observed. Such a large energization of trapped ions is not seen in the case of the potential-drop driven double layers. The interrelation between the field-aligned currents and potential drops for the auroral plasma is discussed. For current-driven double layers, it is found that the current density is proportional to the 1/2 power of the potential drop.

Singh, N.; Schunk, R. W.

1983-01-01

332

Visualization by discharge illumination technique and modification by plasma actuator of rarefied Mach 2 airflow around a cylinder  

NASA Astrophysics Data System (ADS)

The use of plasma actuators for flow control has received considerable attention in recent years. This kind of device seems to be an appropriate means of raising abilities in flow control thanks to total electric control, no moving parts and a fast response time. The experimental work presented here shows, firstly, the non-intrusive character of the visualization of the density field of an airflow around a cylinder obtained using a plasma luminescence technique. Experiments are made in a continuous supersonic wind tunnel. The static pressure in the flow is 8 Pa, the mean free path is about 0.3 mm and the airflow velocity is 510 m s-1. Pressure measurements obtained by means of glass Pitot tube without the visualization discharge are proposed. Measured and simulated pressure profiles are in good agreement in the region near the cylinder. There is good correlation between numerical simulations of the supersonic flow field, analytical model predictions and experimental flow visualizations obtained by a plasma luminescence technique. Consequently, we show that the plasma luminescence technique is non-intrusive. Secondly, the effect of a dc discharge on a supersonic rarefied air flow around a cylinder is studied. An electrode is flush mounted on the cylinder. Stagnation pressure profiles are examined for different electrode positions on the cylinder. A shock wave modification depending on the electrode location is observed. The discharge placed at the upstream stagnation point induces an upstream shift of the bow shock, whereas a modification of the shock wave shape is observed when it is placed at 45° or 90°.

Leger, L.; Sellam, M.; Barbosa, E.; Depussay, E.

2013-06-01

333

Filamentation instability of current-driven dust ion-acoustic waves in a collisional dusty plasma  

NASA Astrophysics Data System (ADS)

A theoretical investigation has been made of the dust ion-acoustic filamentation instability in an unmagnetized current-driven dusty plasma by using the Lorentz transformation formulas. The effect of collision between the charged particles with neutrals and their thermal motion on this instability is considered. Developing the filamentation instability of the current-driven dust ion-acoustic wave allows us to determine the period and the establishment time of the filamentation structure and threshold for instability development.

Niknam, A. R.; Haghtalab, T.; Khorashadizadeh, S. M.

2011-11-01

334

Filamentation instability of current-driven dust ion-acoustic waves in a collisional dusty plasma  

SciTech Connect

A theoretical investigation has been made of the dust ion-acoustic filamentation instability in an unmagnetized current-driven dusty plasma by using the Lorentz transformation formulas. The effect of collision between the charged particles with neutrals and their thermal motion on this instability is considered. Developing the filamentation instability of the current-driven dust ion-acoustic wave allows us to determine the period and the establishment time of the filamentation structure and threshold for instability development.

Niknam, A. R. [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran 19839-63113 (Iran, Islamic Republic of); Haghtalab, T.; Khorashadizadeh, S. M. [Physics Department, Birjand University, Birjand 97179-63384 (Iran, Islamic Republic of)

2011-11-15

335

Scaling of maximum velocity, body force, and power consumption of dielectric barrier discharge plasma actuators via particle image velocimetry  

NASA Astrophysics Data System (ADS)

This study presents Particle Image Velocimetry (PIV) measurements of the induced flow characteristics generated by single dielectric barrier discharge (DBD) actuators in quiescent conditions. The primary aim is to establish accurate empirical trends for model development on both the maximum induced velocity and body force with voltage and consumed power. The results reveal a power law variation for the maximum velocity at low voltages which is followed by an asymptotic behavior. In contrast, the body force is characterized by two power law regions. The power law exponent is shown to be a function of the dielectric thickness, frequency and dielectric constant. Reducing the former or increasing the latter two result in a higher coefficient and lower voltage at which the trend changes. The onset of the second region occurs at a Re ~ 100 (based on the maximum velocity, um, and corresponding half height, y1/2) and is characterized by a velocity profile which no longer agrees with the laminar profile of Glauert whilst moving increasingly towards the turbulent case. Phase locked PIV measurements show that as the voltage increases the peak momentum transfer shifts from the middle of the AC cycle to the latter end of the forward stroke. Lissajous plots of um? against the corresponding x location and plasma length ?x demonstrate that the peak momentum transfer remains relatively fixed in space as the voltage and plasma length increase.

Murphy, J. P.; Kriegseis, J.; Lavoie, P.

2013-06-01

336

Prospects for studying temperature-anisotropy-driven instabilities in a high-beta laboratory plasma  

NASA Astrophysics Data System (ADS)

The mirror and firehose instabilities are driven unstable in magnetized, high-beta plasmas with anisotropic ion distribution functions. Evidence for the action of these instabilities has been found in space plasmas, in particular solar wind observations [1], and they are thought to be important in a number of astrophysical plasmas (e.g. accretion disks). Studying these important instabilities in the lab requires a high-beta, magnetized plasma and the creation of sufficient temperature anisotropy. We will discuss prospects for laboratory experiments making use of the Enormous Toroidal Plasma Device (ETPD) at UCLA. Firehose-unstable (T? > T?) ion distributions might be driven in plasmas flowing into an expanding magnetic field (similar to the solar wind). Enhanced anisotropy could be provided by the formation of a double layer in the expanding plasma, which leads to the production of ion beams in expanding laboratory plasmas [2]. We will report on: initial experiments in LAPD studying expanding plasmas, measurements of plasma parameters in ETPD and on theoretical projections for acheivable anisotropy and instability thresholds in ETPD. [1] S.D. Bale, et al., PRL 103, 211101 (2009). [2] C. Charles, et al., PoP 11, 1706 (2004).

Carter, T. A.; Dorfman, S. E.; Bardoczi, L.; Geraldini, A.; Robertson, J.; Tang, S.; Tripathi, S.; Vincena, S. T.; Gekelman, W. N.

2013-12-01

337

Development of Underwater Microrobot using ICPF Actuator  

Microsoft Academic Search

It is our purpose to develop an underwater microrobot that has the characteristics of flexibility, driven by a low voltage, good response and safety in body. In this paper, we propose a new prototype model of an underwater microrobot utilizing ionic conducting polymer film (ICPF) actuator as the servo actuator. The fish-like propulsion using ICPF actuator as a propulsion tail

Shuxiang Guo; Toshio Fukuda; Norihiko Kato; Keisuke Oguro

1998-01-01

338

Characteristics of a Direct Current-driven plasma jet operated in open air  

SciTech Connect

A DC-driven plasma jet has been developed to generate a diffuse plasma plume by blowing argon into the ambient air. The plasma plume, showing a cup shape with a diameter of several centimeters at a higher voltage, is a pulsed discharge despite a DC voltage is applied. The pulse frequency is investigated as a function of the voltage under different gap widths and gas flow rates. Results show that plasma bullets propagate from the hollow needle to the plate electrode by spatially resolved measurement. A supposition about non-electroneutral trail of the streamer is proposed to interpret these experimental phenomena.

Li, Xuechen; Bao, Wenting [College of Physics Science and Technology, Hebei University, Baoding 071002 (China) [College of Physics Science and Technology, Hebei University, Baoding 071002 (China); Key Laboratory of Photo-Electronics Information Materials of Hebei Province, Baoding 071002 (China); Di, Cong; Jia, Pengying [College of Physics Science and Technology, Hebei University, Baoding 071002 (China)] [College of Physics Science and Technology, Hebei University, Baoding 071002 (China)

2013-09-30

339

Growth and phase velocity of self-modulated beam-driven plasma waves  

SciTech Connect

A long, relativistic particle beam propagating in an overdense plasma is subject to the self-modulation instability. This instability is analyzed and the growth rate is calculated, including the phase relation. The phase velocity of the wake is shown to be significantly less than the beam velocity. These results indicate that the energy gain of a plasma accelerator driven by a self-modulated beam will be severely limited by dephasing. In the long-beam, strongly-coupled regime, dephasing is reached in a homogeneous plasma in less than four e-foldings, independent of beam-plasma parameters.

Benedetti, Carlo; Esarey, Eric; Gruener, Florian; Leemans, Wim

2011-09-20

340

Reactive hydroxyl radical-driven oral bacterial inactivation by radio frequency atmospheric plasma  

NASA Astrophysics Data System (ADS)

We demonstrated bacterial (Streptococcus mutans) inactivation by a radio frequency power driven atmospheric pressure plasma torch with H2O2 entrained in the feedstock gas. Optical emission spectroscopy identified substantial excited state •OH generation inside the plasma and relative •OH formation was verified by optical absorption. The bacterial inactivation rate increased with increasing •OH generation and reached a maximum 5-log10 reduction with 0.6% H2O2 vapor. Generation of large amounts of toxic ozone is drawback of plasma bacterial inactivation, thus it is significant that the ozone concentration falls within recommended safe allowable levels with addition of H2O2 vapor to the plasma.

Kang, Sung Kil; Choi, Myeong Yeol; Koo, Il Gyo; Kim, Paul Y.; Kim, Yoonsun; Kim, Gon Jun; Mohamed, Abdel-Aleam H.; Collins, George J.; Lee, Jae Koo

2011-04-01

341

On the velocity variation in atmospheric pressure plasma plumes driven by positive and negative pulses  

SciTech Connect

To better understand the variation in the ''plasma bullet'' velocity, the dynamics of an atmospheric pressure plasma plume driven by positive and negative pulses are investigated in detail. It is found that, before the plasma exits the nozzle, the plasma propagates at a speed of about 30 km/s for both positive and negative pulses. As soon as the plasma exits the nozzle, the plasma propagation speed increases dramatically for both cases. The peak velocity for the case of the positive pulse is much higher than that of the negative pulse, it is approximately 150 km/s and 70 km/s, respectively. According to the optical emission spectra, the acceleration behavior of the plasma bullet when it exits the nozzle is due to the increase in the N{sub 2}{sup +} concentration.

Xiong, Z.; Lu, X.; Xian, Y.; Jiang, Z.; Pan, Y [College of Electrical and Electronic Engineering, HuaZhong University of Science and Technology, WuHan, Hubei 430074 (China)

2010-11-15

342

Explosive-driven hemispherical implosions for generating fusion plasmas  

NASA Astrophysics Data System (ADS)

An explosive-driven-implosion facility was used to produce stable, centered and focussed hemispherical implosions to generate neutrons from D-D reactions. A high resolution scintillator-detection system measured the neutrons and gamma rays resulting from the fusion of deuterium. Several approaches were used to initiate fusion in deuterium. The simplest and most direct proved to be in a predetonated stoichiometric mixture of deuterium-oxygen. The other successful method was a miniature Voitenko-type compressor where a plane diaphragm was driven by the implosion wave into a secondary small spherical cavity that contained pure deuterium gas at one atmosphere. A great deal of work still remains in order to measure accurately the neutron flux and its velocity distribution as well as the precise interactions of the neutrons with the steel chamber which produced the gamma rays.

Sagie, D.; Glass, I. I.

1982-03-01

343

Explosive-driven hemispherical implosions for generating fusion plasmas  

Microsoft Academic Search

An explosive-driven-implosion facility was used to produce stable, centered and focussed hemispherical implosions to generate neutrons from D-D reactions. A high resolution scintillator-detection system measured the neutrons and gamma rays resulting from the fusion of deuterium. Several approaches were used to initiate fusion in deuterium. The simplest and most direct proved to be in a predetonated stoichiometric mixture of deuterium-oxygen.

D. Sagie; I. I. Glass

1982-01-01

344

Editorial: Focus on Laser and Beam-Driven Plasma Accelerators  

Microsoft Academic Search

The ability of short but intense laser pulses to generate high-energy electrons and ions from gaseous and solid targets has been well known since the early days of the laser fusion program. However, during the past decade there has been an explosion of experimental and theoretical activity in this area of laser-matter interaction, driven by the prospect of realizing table-top

Chan Joshi; Victor Malka

2010-01-01

345

The development of laser- and beam-driven plasma accelerators as an experimental field  

SciTech Connect

Since its inception in the early 1980s, the field of plasma-based particle accelerators has made remarkable advances. Robust plasma accelerating structures can now be excited over centimeter scales using short laser pulses and over meter scales using ultrarelativistic particle beams. Accelerating fields in excess of tens of GV/m can be sustained over these lengths. Laser-driven plasma accelerators now routinely produce monoenergetic, low divergence electron beams in the 100 MeV-1 GeV range, whereas electron-beam driven plasma accelerators have demonstrated the ability to double the energy of 42 GeV electrons using a high-energy collider beam in less than one meter. The development of this field is traced through a series of path breaking experiments.

Joshi, C. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States)

2007-05-15

346

Laser-driven plasma waves in capillary tubes  

SciTech Connect

The excitation of plasma waves over a length of up to 8 cm is demonstrated using laser guiding of intense laser pulses through hydrogen-filled glass capillary tubes. The plasma waves are diagnosed by spectral analysis of the transmitted laser radiation. The dependence of the spectral redshift--measured as a function of filling pressure, capillary tube length, and incident laser energy - is in excellent agreement with simulation results. The longitudinal accelerating field inferred from the simulations is in the range of 1-10 GV/m.

Wojda, F.; Cassou, K.; Cros, B. [Laboratoire Physique Gaz et Plasmas, CNRS-Universite Paris-Sud 11, F-91405 Orsay Cedex (France); Genoud, G.; Burza, M.; Glinec, Y.; Lundh, O.; Persson, A.; Wahlstroem, C.-G. [Department of Physics, Lund University, P.O. Box 118, S-22100 Lund (Sweden); Vieux, G.; Brunetti, E.; Shanks, R. P.; Jaroszynski, D. [Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Andreev, N. E. [Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow 125412 (Russian Federation)

2009-12-15

347

Beam plasma neutron sources based on beam-driven mirror  

Microsoft Academic Search

The design and performance of a relatively low-cost, plasma-based, 14-MeV D-T neutron source for accelerated end-of-life testing of fusion reactor materials are described in this article. An intense flux (up to 5×1018 n\\/m2·s) of 14-MeV neutrons is produced in a fully-ionized high-density tritium target (ne ˜ 3×1021 m-3) by injecting a current of 150-keV deuterium atoms. The tritium plasma target

F. H. Coensgen; T. A. Casper; D. L. Correll; C. C. Datum; A. H. Futch; B. G. Logan; A. W. Molvik; C. E. Walter

1989-01-01

348

Rayleigh-Taylor instability driven nonlinear vortices in dusty plasmas  

SciTech Connect

The low frequency stability of a dusty plasma with a nonuniform mass and charge distribution of the dust component is studied. It is shown that the inverse stratification of the dust mass density in a gravitational field may lead to a Rayleigh-Taylor-like instability. In the nonlinear regime this instability can produce an incompressible flow pattern of spontaneously rotating dust plasma fluid. This result can have potential applications in the interpretation of vortical patterns observed in laboratory experiments as well as in a variety of astrophysical situations where the generation and sustenance of angular momentum are important issues.

Veeresha, B.M.; Das, Amita; Sen, Abhijit [Institute for Plasma Research, Bhat, Gandhinagar 382428 (India)

2005-04-15

349

Current delivery and radiation yield in plasma flow switch-driven implosions  

Microsoft Academic Search

Vacuum inductive-store, plasma flow switch-driven implosion experiments have been performed using the Shiva Star capacitor bank (1300 μf, 3 nH, 120 kV, 9.4 MJ). A coaxial plasma gun arrangement is employed to store magnetic energy in the vacuum volume upstream of a dynamic discharge during the 3- to 4-μs rise of current from the capacitor bank. Motion of the discharge

W. L. Baker; J. H. Degnan; J. D. Beason

1995-01-01

350

Parametric dispersion and amplification characteristics of hot electron driven diffusive semiconductor plasmas*  

NASA Astrophysics Data System (ADS)

In this paper, an analytical expression for hot electron driven diffusion induced second-order susceptibility is obtained under non-resonant laser irradiation in magnetised semiconductor plasma. The hot electron effect due to intense pump modifies the momentum transfer collision frequency and diffusion coefficient which in turns enhances the dispersion as well as gain of the medium. The analysis deals with the qualitative behaviour of the anomalous parametric dispersion and the gain profile of the n-InSb semiconductor plasma.

Nimje, Nilesh; Ghosh, S.

2013-06-01

351

Study of driven magnetic reconnection in a laboratory plasma  

Microsoft Academic Search

MRX (Magnetic Reconnection Experiment) was constructed in the fall of 1995 to investigate the fundamental physics of magnetic reconnection(M. Yamada et al. Bull. APS, vol.40 1877 (1995)), and has yielded many exciting and original results. The MRX experiment satisfies the criteria for MHD plasmas ( S >> 1, rhoi << L), and the boundary condition can be controlled externally. In

Masaaki Yamada; Hantao Ji; Scott Hsu; Troy Carter; Russell Kulsrud; Norton Bretz; Forrest Jobes; Yasushi Ono; Francis Perkins

1997-01-01

352

Current gradient driven flute vortices in magnetized plasmas  

Microsoft Academic Search

It is shown that an external electron current gradient in a nonuniform magnetized plasma can drive a purely growing instability involving coupled convective cells and magnetostatic modes. Accounting for the mode coupling, it is demonstrated that the quasi-stationary state of the unstable flute modes can lead to a spatially ordered dipolar vortex structure. The latter could alter the transport properties

P. K. Shukla

1987-01-01

353

Ion temperature gradient-driven dipolar vortices in dusty plasmas  

Microsoft Academic Search

The nonlinear dynamics of the ion temperature gradient (ITG) mode is investigated in a dusty plasma assuming the dust grains to be tiny and highly charged. The electrostatic drift waves cannot be ignored in the linear dispersion relation if polarization drifts of ions and dust are taken into account. The dipolar vortices are predicted to be formed in the nonlinear

Q. Haque; H. Saleem

2006-01-01

354

Numerical Simulation of Plasma Behavior in a Magnetic Nozzle of a Laser-plasma Driven Nuclear Electric Propulsion System  

SciTech Connect

Numerical simulations of plasma behavior in a magnetic nozzle of a Laser-Plasma Driven Nuclear Electric Propulsion System are conducted. The propellant is heated and accelerated by the laser and expanded isotropically. The magnetic nozzle is a combination of solenoidal coils and used to collimate and guide the plasma to produce thrust. Simulation calculations by a three-dimensional hybrid code are conducted to examine the plasma behaviors in the nozzle and to estimate the thrust efficiency. We also estimate a fraction ({alpha}) of plasma particles leaking in the forward (spacecraft) direction. By a combination of a few coils, we could decrease {alpha} value without degrading the thrust efficiency. Finally, the shaped propellant is proposed to increase the thrust efficiency.

Kajimura, Y. [Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan); Japan Science and Technology Agency (JST), CREST 4-1-8 Hon-chou, Kawaguchi, Saitama 332-0012 (Japan); Matsuda, N.; Hayashida, K.; Maeno, A.; Nakashima, H. [Department of Advanced Energy Engineering Science, Interdisciplinary Graduate school of Engineering Sciences, Kyushu University, Kasugakouen 6-1, Kasuga, Fukuoka 816-580 (Japan)

2008-12-31

355

Electron self-injection in the proton-driven-plasma-wakefield acceleration  

SciTech Connect

The self-injection process of plasma electrons in the proton-driven-plasma-wakefield acceleration scheme is investigated using a two-dimensional, electromagnetic particle-in-cell method. Plasma electrons are self-injected into the back of the first acceleration bucket during the initial bubble formation period, where the wake phase velocity is low enough to trap sufficient electrons. Most of the self-injected electrons are initially located within a distance of the skin depth c/?{sub pe} to the beam axis. A decrease (or increase) in the beam radius (or length) leads to a significant reduction in the total charges of self-injected electron bunch. Compared to the uniform plasma, the energy spread, emittance and total charges of the self-injected bunch are reduced in the plasma channel case, due to a reduced injection of plasma electrons that initially located further away from the beam axis.

Hu, Zhang-Hu; Wang, You-Nian [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)] [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)

2013-12-15

356

Characterization of Inductively Coupled Plasma Driven with Ferrite Cores at 400 kHz  

Microsoft Academic Search

Summary form only given. A very effective inductively coupled plasma (ICP) source free of capacitive coupling and transmission line effect is developed according to Godyak's concept. The discharge is driven via six toroidal ferromagnetic cores whose primary windings are connected to an RF power source operated at 400 kHz. The source operates in a wide range of the input RF

WonKi Lee; Chin-Wook Chung; V. A. Godyak

2005-01-01

357

Spectroscopic temperature measurements in hydrogen inductively-driven plasmas at low pressures  

Microsoft Academic Search

Optical emission spectroscopy is applied to obtain the rotational and gas temperatures of an inductively-driven tandem plasma source of negative hydrogen ions. Discharges are maintained in hydrogen at fixed frequency f = 27 MHz, applied power P = 500 W, and low gas pressure in the range p = (26 - 60) mTorr. The rotational and gas temperatures are determined

S. Iordanova

2008-01-01

358

Nozzle Driven Shocks in Post-CME Plasma  

NASA Astrophysics Data System (ADS)

Models of patchy reconnection allow for heating and acceleration of plasma along reconnected field lines but do not offer a mechanism for transport of energy and momentum across field lines. Here we present a simple 2D model in which a localized region of reconnected flux creates an apparent constriction in the surrounding layer of unreconnected field. The moving constriction acts as a de Laval nozzle and ultimately leads to shocks which can extend out to several times the diameter of the flux tube, altering the density and temperature of the plasma in that region. These findings have direct implications for observations in the solar corona, particularly in regard to such phenomena as wakes seen behind supra-arcade downflows and high temperatures in post-CME current sheets. This work was supported by a joint grant from the NSF and DOE.

Scott, Roger B.; Longcope, D. W.; McKenzie, D. E.

2012-05-01

359

Transient strain driven by a dense electron-hole plasma.  

PubMed

We measure transient strain in ultrafast laser-excited Ge by time-resolved x-ray anomalous transmission. The development of the coherent strain pulse is dominated by rapid ambipolar diffusion. This pulse extends considerably longer than the laser penetration depth because the plasma initially propagates faster than the acoustic modes. X-ray diffraction simulations are in agreement with the observed dynamics. PMID:14611411

DeCamp, M F; Reis, D A; Cavalieri, A; Bucksbaum, P H; Clarke, R; Merlin, R; Dufresne, E M; Arms, D A; Lindenberg, A M; MacPhee, A G; Chang, Z; Lings, B; Wark, J S; Fahy, S

2003-10-17

360

Plasma Driven Implosions of a Bubble-Liner  

Microsoft Academic Search

Thin bubbles (? < 1 ?m) are imploded by a coaxial snowplough. The current sheet remains separated from the dense part of the bubble-liner, the latter compressing a deuterium plasma to ion densities > 1020 ions\\/cm3. Cylindrical and quasi-spherical implosions are obtained. Results of Schlieren and soft X-ray photography are reported. The application of the spherical implosions to the generation

A. Bortolotti; J. G. Linhart; J. Krava´rik

1994-01-01

361

Modeling of high-explosive driven plasma compression opening switches  

SciTech Connect

The initial path of the current through a plasma compression switch is through a thin (500-nm thick) metal foil. The current explodes the foil to form the seed for the conducting plasma. The behavior of the foil at this point is the same as an exploding metal fuse for which we have a simple model. We have, therefore, chosen this model as our starting point. The fuse model assumes that the foil material is homogeneous and is characterized by a single temperature and density. The thickness of the foil is assumed to be much less than the magnetic diffusion skin depth so that the magnetic field varies linearly across the foil. For the present application we assume that the side of the foil away from the channel is fixed in space while the side by the channel is untamped. The foil/plasma will, therefore, cross the channel at the expansion velocity as the foil explodes. Equations for the electrical resistance of the foil, the magnetic fields, the motion of the foil, and the kinetic and internal energies are all solved selfconsistantly. The electrical resistivity, the pressure, and the specific energy of aluminium are taken from the Los Alamos SESAME EOS library. In the case of aluminum we have created a SESAME-style table based on the theory of More and Lee which we have modified to agree with experiment where possible.

Greene, A.E.; Lindemuth, I.R.; Goforth, J.H.

1986-01-01

362

Modeling of high-explosive driven plasma compression opening switches  

NASA Astrophysics Data System (ADS)

The initial path of the current through a plasma compression switch is through a thin (500-nm thick) metal foil. The current explodes the foil to form the seed for the conducting plasma. The behavior of the foil at this point is the same as an exploding metal fuse for which we have a simple model. We have, therefore, chosen this model as our starting point. The fuse model assumes that the foil material is homogeneous and is characterized by a single temperature and density. The thickness of the foil is assumed to be much less than the magnetic diffusion skin depth so that the magnetic field varies linearly across the foil. For the present application we assume that the side of the foil away from the channel is fixed in space while the side by the channel is untamped. The foil/plasma will, therefore, cross the channel at the expansion velocity as the foil explodes. Equations for the electrical resistance of the foil, the magnetic fields, the motion of the foil, and the kinetic and internal energies are all solved selfconsistantly. The electrical resistivity, the pressure, and the specific energy of aluminum are taken from the Los Alamos SESAME EOS library. In the case of aluminum we have created a SESAME-style table based on the theory of More and Lee which we have modified to agree with experiment where possible.

Greene, A. E.; Lindemuth, I. R.; Goforth, J. H.

363

Current-driven Alfvén waves in dusty magnetospheric plasmas  

NASA Astrophysics Data System (ADS)

It is shown that the sheared flow of electrons and ions in the presence of heavy stationary dust gives rise to unstable Alfvén waves. The coupling of newly studied low frequency electrostatic current-driven mode with the electromagnetic Alfvén and drift waves is investigated. The instability conditions and the growth rates of both inertial and kinetic Alfvén waves are estimated. The theoretical model is applied to the night side boundary regions of Jupiter's magnetosphere which contain positive dust. The growth rates increase with increase in sheared flow speed. In the nonlinear regime, both inertial and kinetic Alfvén waves form dipolar vortices whose speed and amplitude depend upon the magnitude of the zero-order current.

Ali Shan, S.; Haque, Q.; Saleem, H.

2014-01-01

364

Localized arc filament plasma actuators for noise mitigation and mixing enhancement  

NASA Technical Reports Server (NTRS)

A device for controlling fluid flow. The device includes an arc generator coupled to electrodes. The electrodes are placed adjacent a fluid flowpath such that upon being energized by the arc generator, an arc filament plasma adjacent the electrodes is formed. In turn, this plasma forms a localized high temperature, high pressure perturbation in the adjacent fluid flowpath. The perturbations can be arranged to produce vortices, such as streamwise vortices, in the flowing fluid to control mixing and noise in such flows. The electrodes can further be arranged within a conduit configured to contain the flowing fluid such that when energized in a particular frequency and sequence, can excite flow instabilities in the flowing fluid. The placement of the electrodes is such that they are unobtrusive relative to the fluid flowpath being controlled.

Samimy, Mohammad (Inventor); Adamovich, Igor (Inventor)

2008-01-01

365

Mirror, firehose and cosmic-ray-driven instabilities in a high-? plasma  

NASA Astrophysics Data System (ADS)

I consider low-frequency instabilities in a plasma with high-? plasma, with ? the ratio of thermal and magnetic pressures. I derive the mirror and firehose instabilities, due to pressure anisotropy, for such a plasma. This derivation uncovers clear modifications with the more familiar, low-? case. I also consider the interplay between these instabilities and the current-driven instability (the Bell-Lucek instability) that occurs near a shock that accelerates cosmic rays. It is shown that the two instability mechanisms in combination can lead to a stronger instability over a wider range of wavelengths.

Achterberg, A.

2013-11-01

366

Dust-acoustic filamentation of a current-driven dusty plasma  

NASA Astrophysics Data System (ADS)

The thermal motion effect of charged particles in the filamentation of a current-driven dusty plasma in the dust-acoustic frequency region is investigated by using the Lorentz transformed conductivity of the dusty plasma components and the total dielectric permittivity tensor of the dusty plasma in the laboratory frame. Obtaining the dispersion relation for dust-acoustic waves and considering the filamentation instability, the establishment time of the filamentation structure and the instability development threshold are derived. Moreover, it is shown that the current layer divides into separate current filaments.

Khorashadizadeh, S. M.; Niknam, A. R.; Haghtalab, T.

2011-06-01

367

Dust-acoustic filamentation of a current-driven dusty plasma  

SciTech Connect

The thermal motion effect of charged particles in the filamentation of a current-driven dusty plasma in the dust-acoustic frequency region is investigated by using the Lorentz transformed conductivity of the dusty plasma components and the total dielectric permittivity tensor of the dusty plasma in the laboratory frame. Obtaining the dispersion relation for dust-acoustic waves and considering the filamentation instability, the establishment time of the filamentation structure and the instability development threshold are derived. Moreover, it is shown that the current layer divides into separate current filaments.

Khorashadizadeh, S. M.; Haghtalab, T. [Physics Department, Birjand University, Birjand, 97179-63384 (Iran, Islamic Republic of); Niknam, A. R. [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran, 19839-63113 (Iran, Islamic Republic of)

2011-06-15

368

Characterization of a Direct-Current Glow Discharge Plasma Actuator in Low-Pressure Supersonic Flow  

Microsoft Academic Search

DOI: 10.2514\\/1.27197 An experimental study of a direct-current, nonequilibrium glow plasma discharge in the presence of a Mach 2.85 supersonic flow is presented. The discharge is generated with pinlike electrodes flush-mounted on a plane surface with sustaining currents between 25 to 300 mA. In the presence of a supersonic flow, two distinct discharge modes (diffuse and constricted) are observed depending

Jichul Shin; V. Narayanaswamy; Laxminarayan L. Raja; Noel T. Clemens

2007-01-01

369

Spring-based actuators  

NASA Astrophysics Data System (ADS)

A new concept of a spring actuator based on the ferromagnetic shape memory alloy (FSMA) is presented. The coil spring made by a FSMA is activated by the attractive magnetic force produced by electromagnets, which is usually not uniform. When the magnetic field is applied, each turn of the spring comes into contact with the neighboring turns one by one, stacking from the turn closer to the yoke of the electromagnet. As a result, entire shrinkage of the spring accompanied by large liner stroke is achieved. This actuator is energy-efficient, since almost all magnet flux originated from electromagnet discharges into the ferromagnetic spring. The performance of the spring actuator, i.e. the output force and stroke, depends on many factors, such as the diameter and the pitch of the spring or the dimension of the cross section of the spring wire, and so on. We processed successfully a spring actuator driven by a hybrid magnet based on the above principle by using polycrystalline FePd alloy. Since the stiffness of the FePd coil spring become softer due to the martensite phase transformation, the movement of the actuator is accelerated during actuation.

Wada, Taishi; Taya, Minoru

2002-07-01

370

Laser Plasma Jet Driven Microparticles for DNA/Drug Delivery  

PubMed Central

This paper describes a microparticle delivery device that generates a plasma jet through laser ablation of a thin metal foil and uses the jet to accomplish particle delivery into soft living targets for transferring biological agents. Pure gold microparticles of 1 µm size were coated with a plasmid DNA, pIG121Hm, and were deposited as a thin layer on one surface of an aluminum foil. The laser (Nd:YAG, 1064 nm wavelength) ablation of the foil generated a plasma jet that carried the DNA coated particles into the living onion cells. The particles could effectively penetrate the target cells and disseminate the DNA, effecting the transfection of the cells. Generation of the plasma jet on laser ablation of the foil and its role as a carrier of microparticles was visualized using a high-speed video camera, Shimadzu HPV-1, at a frame rate of 500 kfps (2 µs interframe interval) in a shadowgraph optical set-up. The particle speed could be measured from the visualized images, which was about 770 m/s initially, increased to a magnitude of 1320 m/s, and after a quasi-steady state over a distance of 10 mm with an average magnitude of 1100 m/s, started declining, which typically is the trend of a high-speed, pulsed, compressible jet. Aluminum launch pad (for the particles) was used in the present study to make the procedure cost-effective, whereas the guided, biocompatible launch pads made of gold, silver or titanium can be used in the device during the actual clinical operations. The particle delivery device has a potential to have a miniature form and can be an effective, hand-held drug/DNA delivery device for biological applications.

Menezes, Viren; Mathew, Yohan; Takayama, Kazuyoshi; Kanno, Akira; Hosseini, Hamid

2012-01-01

371

Experimental results from SHIVA Star vacuum inductive store/plasma flow switch driven implosions  

NASA Astrophysics Data System (ADS)

A 1313-microF, 3-nH, 120-kV, 9.4-MJ SHIVA Star capacitor bank, has been used to perform vacuum inductive store/plasma flow switch (PFS) driven implosions of low mass (200-400 microgram/sq m) cylindrical foil liners of 2-cm height and 5-cm radius. This technique employs a coaxial discharge through a plasma armature, which stores magnetic energy over 3-4 microsec and rapidly switches it to an imploding load as the plasma armature exits the coaxial gun muzzle. The current transferred to the load by the PFS has a rise time of less than 200 nsec. With 5-MJ stored energy, fast liner implosions have been driven with a current of over 9 MA, obtaining an isotropic equivalent 2.7-TW 500-kJ X-ray yield.

Degnan, J. H.; Baker, W. L.; Hackett, K. E.; Hall, D. J.; Holmes, J. L.

1987-12-01

372

Electron beam driven lower hybrid waves in a dusty plasma  

SciTech Connect

An electron beam propagating through a magnetized dusty plasma drives electrostatic lower hybrid waves to instability via Cerenkov interaction. A dispersion relation and the growth rate of the instability for this process have been derived taking into account the dust charge fluctuations. The frequency and the growth rate of the unstable wave increase with the relative density of negatively charged dust grains. Moreover, the growth rate of the instability increases with beam density and scales as the one-third power of the beam density. In addition, the dependence of the growth rate on the beam velocity is also discussed.

Prakash, Ved; Vijayshri [School of Sciences, Indira Gandhi National Open University, Maidan Garhi, New Delhi-110 068 (India)] [School of Sciences, Indira Gandhi National Open University, Maidan Garhi, New Delhi-110 068 (India); Sharma, Suresh C. [Department of Applied Physics, Delhi Technological University, Shahbad Daulatpur, Bawana Road, Delhi-110 042 (India)] [Department of Applied Physics, Delhi Technological University, Shahbad Daulatpur, Bawana Road, Delhi-110 042 (India); Gupta, Ruby [Department of Physics, Swami Shraddhanand College, University of Delhi, Alipur, Delhi-110 036 (India)] [Department of Physics, Swami Shraddhanand College, University of Delhi, Alipur, Delhi-110 036 (India)

2013-05-15

373

Pressure-driven reconnection and quasi periodical oscillations in plasmas  

NASA Astrophysics Data System (ADS)

This paper presents a model for an ohmically heated plasma in which a feedback exists between thermal conduction and transport, on one side, and the magneto-hydro-dynamical stability of the system, on the other side. In presence of a reconnection threshold for the magnetic field, a variety of periodical or quasi periodical oscillations for the physical quantities describing the system are evidenced. The model is employed to interpret the observed quasi periodical oscillations of electron temperature and perturbed magnetic field around the so called "Single Helical" state in the reversed field pinch, but its relevance for other periodical phenomena observed in magnetic confinement systems, especially in tokamaks, is suggested.

Paccagnella, R.

2014-03-01

374

The 'Finger'-instability in radiatively driven dusty plasmas  

NASA Astrophysics Data System (ADS)

We investigate the dynamics of a three-fluid plasma consisting of electrons, ions and charged dust particles. In our work the plasma is illuminated by a radiation field which, through absorption, accelerates these dust particles. By direct and Coulomb collisions the gained momentum is partially transmitted to electrons and ions. A steady state can be achieved by an external gravitational field acting against the radiation. After presenting the steady state flow, linear perturbations of dynamical variables with the wave vector perpendicular to the radiation flux are considered. It is demonstrated that when the drag force between ions and dust particles is a decreasing function of their relative velocity, the steady state is unstable against the formation of neighbouring regions with high and low relative flow velocities, ie. multiple current sheets or flux tubes. The results of multifluid simulations of the interstellar medium are shown to elucidate the relevance of this instability for the formation of the observed dust filaments in edge-on galaxies.

Schröer, A.; Shchekinov, Yu.

2000-12-01

375

Beam-Driven Turbulence in Laboratory and Space Plasmas.  

NASA Astrophysics Data System (ADS)

New kinetic simulations are carried out in which low density electron beams are injected at a boundary, as in UCLA laboratory experiments(A. Y. Wong and P. Y. Cheung, PRL, 52), 1222--1225 (1984). on strong Langmuir turbulence, and in beam-generated Langmuir turbulence in Earth's electron foreshock. Vlasov simulations in 1-D and highly-parallel PIC simulations in 2-D (with over 20 million particles) have revealed the conditions for strong Langmuir turbulence in both venues. New evidence is supplied for the role of stimulated backscatter of beam-modes off ion density fluctuations as well as ``break-up'' (possibly modulational) instabilities as routes to strong Langmuir turbulence. Collapsing Langmuir wavepackets renucleate in density cavities, as shown by DuBois et al. Evolution of the beam in real space and velocity space is studied and compared with experiment, with attention to processes such as the Bers ``meniscus'' effect and velocity-space diffusion. Further simulations suggest that strong Langmuir turbulence may be driven by high-velocity beams near Earth's foreshock boundary.

Goldman, M. V.; Newman, D. L.; Oppenheim, M.

1997-11-01

376

Substorm current wedge driven by plasma flow vortices: THEMIS observations  

NASA Astrophysics Data System (ADS)

A multipoint analysis of magnetospheric plasma flow vortices and conjugate ionospheric flow vortices during the formation of the substorm current wedge (SCW) is presented. During the substorm, the THEMIS spacecraft were engulfed by a clockwise flow vortex and a counterclockwise flow vortex, corresponding to a downward and an upward field-aligned current (FAC), respectively. Using the THEMIS ground network of magnetometers, a pair of flow vortices with opposite rotational sense simultaneously appeared in the ionosphere as inferred from equivalent ionospheric currents (EICs). We demonstrate that the space vortices generated the field-aligned current of the SCW at the beginning of the substorm expansion phase and coupled to the ionosphere causing the ionospheric flow vortices. In addition to physical properties such as radius, velocity and current density of the forming flow vortices, we show model calculations of the FACs associated with the SCW based on midlatitude ground magnetometer data.

Keiling, A.

2009-04-01

377

Substorm current wedge driven by plasma flow vortices: THEMIS observations  

NASA Astrophysics Data System (ADS)

A multipoint analysis of conjugate magnetospheric and ionospheric flow vortices during the formation of the substorm current wedge (SCW) on 19 February 2008 is presented. During the substorm, four Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft were located close to the neutral sheet in the premidnight region between 9 and 12 R E geocentric distance, of which three closely (˜1-2 R E ) clustered at ˜23 MLT and one was farther west at ˜21 MLT. The closely clustered spacecraft were engulfed by a counterclockwise plasma flow vortex, while the single spacecraft recorded a clockwise plasma flow vortex. Simultaneously, a pair of conjugate flow vortices with clockwise and counterclockwise rotation appeared in the ionosphere, as inferred from equivalent ionospheric currents. The counterclockwise space vortex, which corresponded to a downward field-aligned current, was at least 1-2 R E in diameter and had rotational flow speeds of up to 900 km/s. Current density estimates associated with the formation of the space vortex in the first 30 s yielded 2.8 nA/m2 (14 ?A/m2 mapped to the ionosphere), or a total current of 1.1 × 105 A. Model calculations based on midlatitude ground magnetometer data show a gradual increase of the field-aligned current, with 1-2 × 105 A within the first minute and a peak value of 7 × 105 A after 10 min, associated with the SCW, and a matching meridian of the downward current of the SCW and the downward current (counterclockwise) space vortex. The combined ground and space observations, together with the model results, present a scenario in which the space vortices generated the field-aligned current of the SCW at the beginning of the substorm expansion phase and coupled to the ionosphere, causing the ionospheric vortices.

Keiling, A.; Angelopoulos, V.; Runov, A.; Weygand, J.; Apatenkov, S. V.; Mende, S.; McFadden, J.; Larson, D.; Amm, O.; Glassmeier, K.-H.; Auster, H. U.

2009-05-01

378

Parametrization of nonlinear and chaotic oscillations in driven beam-plasma diodes  

NASA Astrophysics Data System (ADS)

Nonlinear phenomena in a driven plasma diode are studied using a fluid code and the particle-in-cell simulation code xpdp1. When a uniform electron beam is injected to a bounded diode filled with uniform ion background, the beam is destabilized by the Pierce instability and a perturbation grows to exhibit nonlinear oscillations including chaos. Two standard routes to chaos, period doubling and quasiperiodicity, are observed. Mode lockings of various winding numbers are observed in an ac driven system. A new diagnostic quantity is used to parametrize various nonlinear oscillations.

Hur, Min Sup; Lee, Hae June; Lee, Jae Koo

1998-07-01

379

Plasma And Beam Homogeneity Of The RF-Driven Negative Hydrogen Ion Source For ITER NBI  

SciTech Connect

The neutral beam injection (NBI) system of ITER is based on a large RF driven negative hydrogen ion source. For good beam transmission ITER requires a beam homogeneity of better than 10%. The plasma uniformity and the correlation with the beam homogeneity are being investigated at the prototype ion sources at IPP. Detailed studies are carried out at the long pulse test facility MANITU with a source of roughly 1/8 of the ITER source size. The plasma homogeneity close to plasma grid is measured by optical emission spectroscopy and by fixed Langmuir probes working in the ion saturation region. The beam homogeneity is measured with a spatially resolved H{sub {alpha}} Doppler-shifted beam spectroscopy system. The plasma top-to-bottom symmetry improves with increasing RF power and increasing bias voltage which is applied to suppress the co-extracted electron current. The symmetry is better in deuterium than in hydrogen. The boundary layer near the plasma grid determines the plasma symmetry. At high ion currents with a low amount of co-extracted electrons the plasma is symmetrical and the beam homogeneity is typically 5-10%(RMS). The size scaling and the influence of the magnetic field strength of the filter field created by a plasma grid current is studied at the test facility RADI (roughly a 1/2 size ITER source) at ITER relevant RF power levels. In volume operation in deuterium (non-cesiated source), the plasma illumination of the grid is satisfying.

Fantz, U.; Franzen, P.; Kraus, W.; Wuenderlich, D.; Gutser, R.; Berger, M. [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, D-85748 Garching (Germany)

2009-03-12

380

Charge-Driven Plasma Instabilities on Auroral Field Lines  

NASA Astrophysics Data System (ADS)

The Polar satellite in its initial orbit regularly observed time-dispersed earthward bursts of hot protons (tens of keV and less) along high-latitude magnetic field lines, together with hot electrons and outflowing accelerated ions from the ionosphere. Beside their dispersion signatures, these bursts, when observed at several Earth radii altitude, have a filamentary structure with transverse scale sizes comparable to the local hot proton gyroradii, often less than 100 km. This fine a structure implies that the protons and accompanying electrons must undergo differential mirroring and electric charge separation, with the strongest electric fields generated transverse to the magnetic field. It can be reasonably assumed that these fields grow sufficiently strong and non-uniform to locally disrupt the first invariant of ions, especially of any ambient O+ ions, and generate strong plasma waves. Indeed, it is easy to find burst events that have very large amplitude electric fields (~ 0.1 Vm-1) fluctuating at roughly the O+ gyration frequency. The observed scale sizes, when projected to Earth, are those of auroral arcs.

Lennartsson, O. W.

2005-12-01

381

Multilayer ceramic actuator commercialization  

NASA Astrophysics Data System (ADS)

AVX is the largest US manufacturer of multilayer ceramic capacitors, producing 10's of millions per day. Multilayer ceramic actuators are manufactured using virtually identical fabrication methods. Fabrication from this ceramic tape allows tremendous latitude in device shape, size and material choice. This paper will discuss several different actuator configurations-including stacks, plates and chips- with respect to performance and cost tradeoffs. Virtually all developing smart material applications are 'technology driven,' however the widespread availability of devices at commercial scale relies on 'market pull' to achieve a balance of high annualized volumes and low cost. Given sufficient demand, devices can be produced such that the raw materials themselves dominate the unit cost. Generalized price-volume-performance relationships for the different actuator configurations can both guide system designers and focus long-term component development efforts.

Ritter, Andrew P.

1995-05-01

382

Current-Driven Plasma Instabilities in Solid-State Layered Systems with a Grating. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

We have investigated the effects of a grating on current-driven plasma instabilities in layered solid-state systems. By quenching the excess momentum of the plasma mode the grating makes it possible to convert the plasma wave energy into the electromagnet...

K. Kempa P. Bakshi H. Xie

1993-01-01

383

Effect of the voltage waveform on induced flow of a dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

Flow control technique using surface plasma is attracting a lot of attention because of its ability to be the innovative technology for the wide range application. In this paper, we have conducted experiments to inspect relationship of velocity of the induced flow, frequency and voltage of power source. First, when sinusoidal voltage was applied between the electrodes, the result showed the induced flow was the faster, the greater the power was, regardless of the frequency and voltage. Then, the waveform was changed to bipolar pulse with shorter ON period than that of sine wave with a frequency of 3 kHz, almost the same induced velocity was observed at the same power, regardless of the voltage waveform. By the same experiment with a frequency of 10 kHz, the relationship of induced velocity and the power was affected by the waveform unlike the case of frequency at 3 kHz. The highest induced velocity was observed in case of sine wave. Induced velocity was able to be expressed as a function of the full width half maximum of voltage waveform, under constant power. From these facts, it is believed that it is required for external electric field to be applied for more than certain period of time in order for ions to be accelerated by electric field even in a case that almost same amount of ions were generated under an almost same condition of discharge power.

Shimura, Naohiko; Tanaka, Motofumi; Yasui, Hiroyuki

2012-10-01

384

Kinetic Alfvén wave instability driven by a field-aligned current in high-? plasmas.  

PubMed

Including the ion-gyroradius effect, a general low-frequency kinetic dispersion equation is presented, which simultaneously takes account of a field-aligned current and temperature anisotropy in plasmas. Based on this dispersion equation, kinetic Alfvén wave (KAW) instability driven by the field-aligned current, which is carried by the field-aligned drift of electrons relative to ions at a drift velocity V(D), is investigated in a high-? plasma, where ? is the kinetic-to-magnetic pressure ratio in the plasma. The numerical results show that the KAW instability driven by the field-aligned current has a nonzero growth rate in the parallel wave-number range 0plasma particles, the result shows that the instability conditions for these two driven mechanisms are both modified considerably, in which the growing parametric ranges of KAWs widen. The results have potential importance in understanding the physics of space and astrophysical plasma active phenomena since the field-aligned current, also called the Birkeland current, is one of the most active factors in plasma phenomena. PMID:22181282

Chen, L; Wu, D J; Hua, Y P

2011-10-01

385

Subcutoff microwave driven plasma ion sources for multielemental focused ion beam systems  

SciTech Connect

A compact microwave driven plasma ion source for focused ion beam applications has been developed. Several gas species have been experimented including argon, krypton, and hydrogen. The plasma, confined by a minimum B multicusp magnetic field, has good radial and axial uniformity. The octupole multicusp configuration shows a superior performance in terms of plasma density ({approx}1.3x10{sup 11} cm{sup -3}) and electron temperature (7-15 eV) at a power density of 5-10 W/cm{sup 2}. Ion current densities ranging from a few hundreds to over 1000 mA/cm{sup 2} have been obtained with different plasma electrode apertures. The ion source will be combined with electrostatic Einzel lenses and should be capable of producing multielemental focused ion beams for nanostructuring and implantations. The initial simulation results for the focused beams have been presented.

Mathew, Jose V.; Chowdhury, Abhishek; Bhattacharjee, Sudeep [Department of Physics, Indian Institute of Technology, Kanpur 208016 (India)

2008-06-15

386

High-Harmonic Fast Wave Driven H-mode Plasmas on NSTX  

SciTech Connect

The launch of High-Harmonic Fast Waves (HHFW) routinely provides auxiliary power to NSTX plasmas, where it is used to heat electrons and pursue drive current. H-mode transitions have been observed in deuterium discharges, where only HHFW and ohmic heating, and no neutral beam injection (NBI), were applied to the plasma. The usual H-mode signatures are observed. A drop of the Da light marks the start of a stored energy increase, which can double the energy content. These H-mode plasmas also have the expected kinetic profile signatures with steep edge density and electron temperature pedestal. Similar to its NBI driven counterpart--also observed on NSTX-- the HHFW H mode have density profiles that features ''ears'' in the peripheral region. These plasmas are likely candidates for long pulse operation because of the combination of bootstrap current, associated with H-mode kinetic profiles, and active current drive, which can be generated with HHFW power.

B.P. LeBlanc; R.E. Bell; S.I. Bernabei; K. Indireshkumar; S.M. Kaye; R. Maingi; T.K. Mau; D.W. Swain; G. Taylor; P.M. Ryan; J.B Wilgen; J.R. Wilson

2003-05-01

387

Shock creation and particle acceleration driven by plasma expansion into a rarefied medium  

SciTech Connect

The expansion of a dense plasma through a more rarefied ionized medium is a phenomenon of interest in various physics environments ranging from astrophysics to high energy density laser-matter laboratory experiments. Here this situation is modeled via a one-dimensional particle-in-cell simulation; a jump in the plasma density of a factor of 100 is introduced in the middle of an otherwise equally dense electron-proton plasma with an uniform proton and electron temperature of 10 eV and 1 keV, respectively. The diffusion of the dense plasma, through the rarefied one, triggers the onset of different nonlinear phenomena such as a strong ion-acoustic shock wave and a rarefaction wave. Secondary structures are detected, some of which are driven by a drift instability of the rarefaction wave. Efficient proton acceleration occurs ahead of the shock, bringing the maximum proton velocity up to 60 times the initial ion thermal speed.

Sarri, G.; Kourakis, I.; Borghesi, M. [Centre for Plasma Physics, The Queen's University of Belfast, Belfast BT7 1NN (United Kingdom); Dieckmann, M. E. [VITA ITN, Linkoping University, 60174 Norrkoping (Sweden)

2010-08-15

388

Convection-driven delivery of plasma sheet material to the inner magnetosphere.  

NASA Astrophysics Data System (ADS)

We present data from the MENA instrument onboard the IMAGE satellite taken during a period of enhanced convection on 26 June 2001. During the interval, MENA observes energetic neutral atoms (ENAs) in the magnetotail and an Earthwards-propagating enhancement in their flux, at the same time as the convection strength increases (as measured by the Kp and MBI indices). Data from the magnetospheric plasma analyser (MPA) instrument onboard satellites in geosynchronous orbit indicate that enhanced ion and electron fluxes at plasma sheet energies (~1-45 keV) are detected at the same time as enhanced ENA flux are observed at the satellite location. We interpret the results as a convection-driven delivery of plasma sheet material, the ENA signature of which we observe with IMAGE/MENA. We use the rate of the propagation of the ENA enhancement to infer the speed of the plasma sheet delivery to the inner magnetosphere.

Denton, M. H.; Thomsen, M. F.; Lavraud, B.; Skoug, R. M.; Henderson, M. G.; Funsten, H. O.; Jahn, J.; Pollock, C. J.; Weygand, J.

2005-12-01

389

Fusion for Space Propulsion and Plasma Liner Driven MTF  

NASA Technical Reports Server (NTRS)

The need for fusion propulsion for interplanetary flights is discussed. For a propulsion system, there are three important system attributes: (1) The absolute amount of energy available, (2) the propellant exhaust velocity, and (3) the jet power per unit mass of the propulsion system (specific power). For human exploration and development of the solar system, propellant exhaust velocity in excess of 100 km/s and specific power in excess of 10 kW/kg are required. Chemical combustion cannot meet the requirement in propellant exhaust velocity. Nuclear fission processes typically result in producing energy in the form of heat that needs to be manipulated at temperatures limited by materials to about 2,800 K. Using the energy to heat a low atomic weight propellant cannot overcome the problem. Alternatively the energy can be converted into electricity which is then used to accelerate particles to high exhaust velocity. The necessary power conversion and conditioning equipment, however, increases the mass of the propulsion system for the same jet power by more than two orders of magnitude over chemical system, thus greatly limits the thrust-to-weight ratio attainable. If fusion can be developed, fusion appears to have the best of all worlds in terms of propulsion - it can provide the absolute amount, the propellant exhaust velocity, and the high specific jet power. An intermediate step towards pure fusion propulsion is a bimodal system in which a fission reactor is used to provide some of the energy to drive a fusion propulsion unit. The technical issues related to fusion for space propulsion are discussed. There are similarities as well as differences at the system level between applying fusion to propulsion and to terrestrial electrical power generation. The differences potentially provide a wider window of opportunities for applying fusion to propulsion. For example, pulsed approaches to fusion may be attractive for the propulsion application. This is particularly so in the light of significant development of the enabling pulsed power component technologies that have occurred in the last two decades because of defense and other energy requirements. The extreme states of matter required to produce fusion reactions may be more readily realizable in the pulsed states with less system mass than in steady states. Significant saving in system mass may result in pulsed fusion systems using plasmas in the appropriate density regimes. Magnetized target fusion, which attempts to combine the favorable attributes of magnetic confinement and inertial compression-containment into one single integrated fusion scheme, appears to have benefits that are worth exploring for propulsion application.

Thio, Y.C. Francis; Rodgers, Stephen L. (Technical Monitor)

2001-01-01

390

Shear-flow-driven ion cyclotron and ion sound-drift instabilities of cylindrical inhomogeneous plasma  

SciTech Connect

The effects of the shear flow along the magnetic field on the development of the ion cyclotron, ion sound, and drift instabilities in the radially inhomogeneous cylindrical plasma are studied on the ground of a kinetic approach. It is shown that flow shear not only modifies the frequencies and growth rates of known current driven electrostatic ion cyclotron, ion sound, and drift instabilities, but is the source of the development of specific shear-flow-driven ion cyclotron, ion sound, and drift instabilities. These instabilities are excited at the levels of current along the ambient magnetic field which is below the critical value for the development of the modified by flow shear current driven ion cyclotron, ion sound, and drift instabilities.

Mikhailenko, V. S.; Chibisov, D. V. [Kharkov National University, 61108, Kharkov (Ukraine)

2007-08-15

391

Structure of parallel-velocity-shear driven mode in toroidal plasmas  

SciTech Connect

It is shown that the Fourier-ballooning representation is appropriate for the study of short wavelength drift-like perturbation in toroidal plasmas with a parallel velocity shear (PVS). The radial structure of the mode driven by a PVS is investigated in a torus. The Reynolds stress created by PVS turbulence and proposed as one of the sources for a sheared poloidal plasma rotation is analyzed. It is demonstrated that a finite ion temperature may strongly enhance the Reynolds stress creation ability from PVS driven turbulence. The correlation of this observation with the requirement that ion heating power be higher than a threshold value for the formation of an internal transport barrier is discussed.

Dong, J.Q.; Xu, W.B.; Zhang, Y.Z. [Southwestern Inst. of Physics, Chengdu (China); Horton, W. [Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies

1998-09-15

392

Intense Geodesic Acousticlike Modes Driven by Suprathermal Ions in a Tokamak Plasma  

SciTech Connect

Intense axisymmetric oscillations driven by suprathermal ions injected in the direction counter to the toroidal plasma current are observed in the DIII-D tokamak. The modes appear at nearly half the ideal geodesic acoustic mode frequency, in plasmas with comparable electron and ion temperatures and elevated magnetic safety factor (q{sub min}{>=}2). Strong bursting and frequency chirping are observed, concomitant with large (10%-15%) drops in the neutron emission. Large electron density fluctuations (n-tilde{sub e}/n{sub e}{approx_equal}1.5%) are observed with no detectable electron temperature fluctuations, confirming a dominant compressional contribution to the pressure perturbation as predicted by kinetic theory. The observed mode frequency is consistent with a recent theoretical prediction for the energetic-particle-driven geodesic acoustic mode.

Nazikian, R.; Fu, G. Y.; Budny, R. V.; Gorelenkov, N. N.; Kramer, G. J.; Solomon, W. M. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Austin, M. E.; Berk, H. L. [University of Texas at Austin, Austin, Texas 78712 (United States); Heidbrink, W. W. [University of California Irvine, Irvine, California 92697 (United States); Holcomb, C. T.; Makowski, M. A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); McKee, G. R.; Shafer, M. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Strait, E. J.; Van Zeeland, M. A. [General Atomics, San Diego, California 92186-5608 (United States)

2008-10-31

393

Intense geodesic acousticlike modes driven by suprathermal ions in a tokamak plasma.  

PubMed

Intense axisymmetric oscillations driven by suprathermal ions injected in the direction counter to the toroidal plasma current are observed in the DIII-D tokamak. The modes appear at nearly half the ideal geodesic acoustic mode frequency, in plasmas with comparable electron and ion temperatures and elevated magnetic safety factor (q_{min}>or=2). Strong bursting and frequency chirping are observed, concomitant with large (10%-15%) drops in the neutron emission. Large electron density fluctuations (n[over ]_{e}/n_{e} approximately 1.5%) are observed with no detectable electron temperature fluctuations, confirming a dominant compressional contribution to the pressure perturbation as predicted by kinetic theory. The observed mode frequency is consistent with a recent theoretical prediction for the energetic-particle-driven geodesic acoustic mode. PMID:18999835

Nazikian, R; Fu, G Y; Austin, M E; Berk, H L; Budny, R V; Gorelenkov, N N; Heidbrink, W W; Holcomb, C T; Kramer, G J; McKee, G R; Makowski, M A; Solomon, W M; Shafer, M; Strait, E J; Zeeland, M A Van

2008-10-31

394

Experimental investigation of explosive-driven plasma-compression opening switches  

SciTech Connect

Plasma-compression opening-switch techniques are being developed for use in explosive-driven magnetic-flux-compresssion-generator applications. A new test bed for performing low-cost experimentation is described. Experiments with approx.0.15 MA/cm linear current density in the switch have achieved resistance increases of a factor of 10 in a few hundred nanoseconds. Peak field strengths of 30 kV/cm are generated in these tests. Data are presented from preliminary tests that indicate reduced pressure in the plasma cavity enhanced switch performance.

Goforth, J.H.; Caird, R.S.

1983-01-01

395

Observation of plasma rotation driven by static nonaxisymmetric magnetic fields in a tokamak.  

PubMed

We present the first evidence for the existence of a neoclassical toroidal rotation driven in a direction counter to the plasma current by nonaxisymmetric, nonresonant magnetic fields. At high beta and with large injected neutral beam momentum, the nonresonant field torque slows down the plasma toward the neoclassical "offset" rotation rate. With small injected neutral beam momentum, the toroidal rotation is accelerated toward the offset rotation, with resulting improvement in the global energy confinement time. The observed magnitude, direction, and radial profile of the offset rotation are consistent with neoclassical theory predictions. PMID:19113280

Garofalo, A M; Burrell, K H; DeBoo, J C; deGrassie, J S; Jackson, G L; Lanctot, M; Reimerdes, H; Schaffer, M J; Solomon, W M; Strait, E J

2008-11-01

396

Observation of Plasma Rotation Driven by Static Nonaxisymmetric Magnetic Fields in a Tokamak  

SciTech Connect

We present the first evidence for the existence of a neoclassical toroidal rotation driven in a direction counter to the plasma current by nonaxisymmetric, nonresonant magnetic fields. At high beta and with large injected neutral beam momentum, the nonresonant field torque slows down the plasma toward the neoclassical 'offset' rotation rate. With small injected neutral beam momentum, the toroidal rotation is accelerated toward the offset rotation, with resulting improvement in the global energy confinement time. The observed magnitude, direction, and radial profile of the offset rotation are consistent with neoclassical theory predictions [A. J. Cole et al., Phys. Rev. Lett. 99, 065001 (2007)].

Garofalo, A. M.; Burrell, K. H.; DeBoo, J. C.; DeGrassie, J. S.; Jackson, G. L.; Schaffer, M. J.; Strait, E. J. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Lanctot, M.; Reimerdes, H. [Columbia University, 2960 Broadway, New York, New York 10027-1754 (United States); Solomon, W. M. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States)

2008-11-07

397

Dynamics of fast electrons driven by the lower hybrid wave in giant sawtoothing plasmas  

PubMed

By hard x-ray tomography of the nonthermal bremsstrahlung emission, a detailed investigation of the dynamics of the fast electrons driven by the lower hybrid wave in the presence of giant sawteeth is carried out. While sawtooth activity is clearly observed on the bulk contribution, no modulation is detected on radiations emitted by the suprathermal population. This original effect is interpreted as the consequence of a poor penetration of the wave in the core of the plasma due to reduced accessibility conditions. Implications for current drive in sawtoothing plasmas are discussed. PMID:11018964

Imbeaux; Peysson

2000-03-27

398

Radiochemistry and secondary reactions for the diagnostics of laser-driven fusion plasmas  

SciTech Connect

Radiochemical measurements have been developed for the diagnostics of laser-driven implosion plasmas. The excellent calibration for neutron-yield measurement has been done using ..beta..-..gamma.. coincidence technique. The multiactivable tracer method has been examined for measuring the pusher areal density by means of a high-purity germanium detector. The first experimental success of the secondary nuclear fusion reaction method is also demonstrated for the direct measurement of the fuel rhoR-italic.

Miyanaga, N.; Azechi, H.; Stapf, R.O.; Itoga, K.; Nakaishi, H.; Shiraga, H.; Yamanaka, M.; Yamanaka, T.; Tsuji, R.; Ido, S.; Sakurai, K.; Nishihara, K.; Yabe, T.; Takagi, M.; Nakatsuka, M.; Izawa, Y.; Nakai, S.; Yamanaka, C.; Kobayashi, K.; Kimura, I.; Morinobu, S.

1986-08-01

399

The Transition to Collisionless Ion-temperature-gradient-driven Plasma Turbulence: A Dynamical Systems Approach  

SciTech Connect

The transition to collisionless ion-temperature-gradient-driven plasma turbulence is considered by applying dynamical systems theory to a model with ten degrees of freedom. Study of a four-dimensional center manifold predicts a ''Dimits shift'' of the threshold for turbulence due to the excitation of zonal flows and establishes the exact value of that shift in terms of physical parameters. For insight into fundamental physical mechanisms, the method provides a viable alternative to large simulations.

R.A. Kolesnikov; J.A. Krommes

2004-10-21

400

Spectroscopic temperature measurements in hydrogen inductively-driven plasmas at low pressures  

NASA Astrophysics Data System (ADS)

Optical emission spectroscopy is applied to obtain the rotational and gas temperatures of an inductively-driven tandem plasma source of negative hydrogen ions. Discharges are maintained in hydrogen at fixed frequency f = 27 MHz, applied power P = 500 W, and low gas pressure in the range p = (26 - 60) mTorr. The rotational and gas temperatures are determined by analyzing the intensity distribution of the H2 Fulcher-? band (d 3?u ? a3?g+) line emission.

Iordanova, S.

2008-05-01

401

Atmospheric plasma-driven catalysis for the low temperature decomposition of dilute aromatic compounds  

Microsoft Academic Search

The decomposition of volatile organic compounds (VOCs)---six aromatic compounds of benzene derivatives and formic acid---was investigated using a plasma-driven catalysis (PDC) system at atmospheric pressure. In the PDC reactor, the decomposition efficiency of VOCs was mostly determined by the specific input energy (SIE) and insensitivity to the gas hourly space velocity from 11 000 to 55 000 h-1. Formic acid

Hyun-Ha Kim; Atsushi Ogata; Shigeru Futamura

2005-01-01

402

Rotary Actuator.  

National Technical Information Service (NTIS)

A rotary actuator suited for use in environments where rolling and sliding friction is to be avoided, such as in a high vacuum celestial space environment, is described. The actuator is characterized by the utilization of a plurality of spaced tri-flex pi...

C. Kallins J. Ostroff

1970-01-01

403

Generation of episodic magnetically driven plasma jets in a radial foil Z-pinch  

NASA Astrophysics Data System (ADS)

We present experimental results of the formation of magnetically driven plasma jets, showing for the first time a way of producing episodic jet/ouflows in the laboratory. The jets are produced using a 6.5 ?m thick aluminum disk (a radial foil), which is subjected to the 1 MA, 250 ns current pulse from the MAGPIE generator [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)]. The early time motion of the foil is characterized by the bulk motion of the mass due to the magnetic pressure, together with the formation of a surface plasma following the direction of the J×B force. A low density plasma fills the region above the foil preceding the formation of subsequent magnetically driven jets on the axis of expanding magnetic bubbles. The outflows emerge in timescales of ~30-40 ns and their episodic nature is the result of current reconnection in the foil, aided by the formation of current-driven instabilities in the jet and the distribution of mass available from the foil. The additional inductance due to the new current path inside the cavities was measured using an inductive probe, allowing to estimate the energy balance associated with the episodes. The measured temperature of the compressed jet resulted in Te~300 eV and a magnetic Reynolds number of ReM~200-1000, allowing the experiments to be in the regime relevant for scaled representations of astrophysical outflows.

Suzuki-Vidal, Francisco; Lebedev, Sergey V.; Bland, Simon N.; Hall, Gareth N.; Swadling, George; Harvey-Thompson, Adam J.; Chittenden, Jeremy P.; Marocchino, Alberto; Ciardi, Andrea; Frank, Adam; Blackman, Eric G.; Bott, Simon C.

2010-11-01

404

Statistics of beam-driven waves in plasmas with ambient fluctuations: Reduced-parameter approach  

SciTech Connect

A reduced-parameter (RP) model of quasilinear wave-plasma interactions is used to analyze statistical properties of beam-driven waves in plasmas with ambient density fluctuations. The probability distribution of wave energies in such a system is shown to have a relatively narrow peak just above the thermal wave level, and a power-law tail at high energies, the latter becoming progressively more evident for increasing characteristic amplitude of the ambient fluctuations. To better understand the physics behind these statistical features of the waves, a simplified model of stochastically driven thermal waves is developed on the basis of the RP model. An approximate analytic solution for stationary statistical distribution of wave energies W is constructed, showing a good agreement with that of the original RP model. The 'peak' and 'tail' features of the wave energy distribution are shown to be a result of contributions of two groups of wave clumps: those subject to either very slow or very fast random variations of total wave growth rate (due to fluctuations of ambient plasma density), respectively. In the case of significant ambient plasma fluctuations, the overall wave energy distribution is shown to have a clear power-law tail at high energies, P(W){proportional_to}W{sup -{alpha}}, with nontrivial exponent 1<{alpha}<2, while for weak fluctuations it is close to the lognormal distribution predicted by pure stochastic growth theory. The model's wave statistics resemble the statistics of plasma waves observed by the Ulysses spacecraft in some interplanetary type III burst sources. This resemblance is discussed qualitatively, and it is suggested that the stochastically driven thermal waves might be a candidate for explaining the power-law tails in the observed wave statistics without invoking mechanisms such as self-organized criticality or nonlinear wave collapse.

Tyshetskiy, Yu.; Cairns, I. H.; Robinson, P. A. [School of Physics, University of Sydney, Sydney, 2006 New South Wales (Australia)

2008-09-15

405

New Radiation Sources Through Generation and Resonant Enhancement of Current Driven Plasma Instabilities in Lower Dimensional Solid State Systems.  

National Technical Information Service (NTIS)

In this program, we have identified theoretically the most promising candidates for current driven plasma instabilities (CDPI) in semiconductor based systems: the modulated quantum wires and lateral surface superlattices (LSSL). Feasibility of CDPI at muc...

P. Bakshi K. Kempa

1994-01-01

406

Computational model of collisional-radiative nonequilibrium plasma in an air-driven type laser propulsion  

SciTech Connect

A thrust power of a gas-driven laser-propulsion system is obtained through interaction with a propellant gas heated by a laser energy. Therefore, understanding the nonequilibrium nature of laser-produced plasma is essential for increasing available thrust force and for improving energy conversion efficiency from a laser to a propellant gas. In this work, a time-dependent collisional-radiative model for air plasma has been developed to study the effects of nonequilibrium atomic and molecular processes on population densities for an air-driven type laser propulsion. Many elementary processes are considered in the number density range of 10{sup 12}/cm{sup 3}<=N<=10{sup 19}/cm{sup 3} and the temperature range of 300 K<=T<=40,000 K. We then compute the unsteady nature of pulsively heated air plasma. When the ionization relaxation time is the same order as the time scale of a heating pulse, the effects of unsteady ionization are important for estimating air plasma states. From parametric computations, we determine the appropriate conditions for the collisional-radiative steady state, local thermodynamic equilibrium, and corona equilibrium models in that density and temperature range.

Ogino, Yousuke; Ohnishi, Naofumi [Department of Aerospace Engineering, Tohoku University, Sendai 980-8579 (Japan)

2010-05-06

407

Instability of magnetic fields in electroweak plasma driven by neutrino asymmetries  

NASA Astrophysics Data System (ADS)

The magnetohydrodynamics (MHD) is modified to incorporate the parity violation in the Standard Model leading to a new instability of magnetic fields in the electroweak plasma in the presence of nonzero neutrino asymmetries. The main ingredient for such a modified MHD is the antisymmetric part of the photon polarization tensor in plasma, where the parity violating neutrino interaction with charged leptons is present. We calculate this contribution to the polarization tensor connected with the Chern-Simons term in effective Lagrangian of the electromagnetic field. The general expression for such a contribution which depends on the temperature and the chemical potential of plasma as well as on the photon's momentum is derived. The instability of a magnetic field driven by the electron neutrino asymmetry for the ?-burst during the first second of a supernova explosion can amplify a seed magnetic field of a protostar, and, perhaps, can explain the generation of strongest magnetic fields in magnetars. The growth of a cosmological magnetic field driven by the neutrino asymmetry density ?n? = n?-nbar nu?0 is provided by a lower bound on |??e| = |??e|/T which is consistent with the well-known Big Bang nucleosynthesis (upper) bound on neutrino asymmetries in a hot universe plasma.

Dvornikov, Maxim; Semikoz, Victor B.

2014-05-01

408

Laser-driven electron beamlines generated by coupling laser-plasma sources with conventional transport systems  

SciTech Connect

Laser-driven electron beamlines are receiving increasing interest from the particle accelerator community. In particular, the high initial energy, low emittance, and high beam current of the plasma based electron source potentially allow generating much more compact and bright particle accelerators than what conventional accelerator technology can achieve. Using laser-generated particles as injectors for generating beamlines could significantly reduce the size and cost of accelerator facilities. Unfortunately, several features of laser-based particle beams need still to be improved before considering them for particle beamlines and thus enable the use of plasma-driven accelerators for the multiple applications of traditional accelerators. Besides working on the plasma source itself, a promising approach to shape the laser-generated beams is coupling them with conventional accelerator elements in order to benefit from both a versatile electron source and a controllable beam. In this paper, we perform start-to-end simulations to generate laser-driven beamlines using conventional accelerator codes and methodologies. Starting with laser-generated electrons that can be obtained with established multi-hundred TW laser systems, we compare different options to capture and transport the beams. This is performed with the aim of providing beamlines suitable for potential applications, such as free electron lasers. In our approach, we have analyzed which parameters are critical at the source and from there evaluated different ways to overcome these issues using conventional accelerator elements and methods. We show that electron driven beamlines are potentially feasible, but exploiting their full potential requires extensive improvement of the source parameters or innovative technological devices for their transport and capture.

Antici, P. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Frascati, Via E. Fermi, 40, 00044 Frascati (Italy); SAPIENZA, University of Rome, Dip. SBAI, Via A. Scarpa 14, 00161 Rome (Italy); INFN - Sezione di Roma, c/o Dipartimento di Fisica - SAPIENZA, University of Rome, P.le Aldo Moro, 2 - 00185 Rome (Italy); Bacci, A.; Chiadroni, E.; Ferrario, M.; Rossi, A. R. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Frascati, Via E. Fermi, 40, 00044 Frascati (Italy); Benedetti, C. [University of Bologna and INFN - Bologna (Italy); Lancia, L.; Migliorati, M.; Mostacci, A.; Palumbo, L. [SAPIENZA, University of Rome, Dip. SBAI, Via A. Scarpa 14, 00161 Rome (Italy); INFN - Sezione di Roma, c/o Dipartimento di Fisica - SAPIENZA, University of Rome, P.le Aldo Moro, 2 - 00185 Rome (Italy); Serafini, L. [INFN-Milan and Department of Physics, University of Milan, Via Celoria 16, 20133 Milan (Italy)

2012-08-15

409

Miniature hybrid plasma focus extreme ultraviolet source driven by 10 kA fast current pulse  

SciTech Connect

A miniature hybrid plasma focus device, operated in xenon gas medium and driven by a 10 kA fast current pulse, has been used to generate extreme ultraviolet radiation in the range of 6-15 nm. At present the radiation characteristics from xenon plasma were mainly assessed qualitatively using standard tools such as visible light framing camera, extreme ultraviolet (EUV) pinhole camera, and EUV photodiode. Strong pinching of xenon plasma is indicative from both visible and EUV imagings. The maximum size of the EUV emitting zone is estimated to be of the order of 0.21x1.55 mm and the estimated value is within the accepted value as benchmarked by industries. The EUV intensity measurement by photodiode showed fairly isotropic radiation at least in a half solid angle. This device can be developed further as a competent source for EUV metrology or lithography applications.

Mohanty, S.R.; Sakamoto, T.; Kobayashi, Y.; Song, I.; Watanabe, M.; Kawamura, T.; Okino, A.; Horioka, K.; Hotta, E. [Department of Energy Sciences, Tokyo Institute of Technology, Nagatsuta, Yokohama 226-8502 (Japan)

2006-04-15

410

Observations of an Ion-Driven Instability in Non-Neutral Plasmas Confined on Magnetic Surfaces  

SciTech Connect

The first detailed experimental study of an instability driven by the presence of a finite ion fraction in an electron-rich non-neutral plasma confined on magnetic surfaces is presented. The instability has a poloidal mode number m=1, implying that the parallel force balance of the electron fluid is broken and that the instability involves rotation of the entire plasma, equivalent to ion-resonant instabilities in Penning traps and toroidal field traps. The mode appears when the ion density exceeds approximately 10% of the electron density. The measured frequency decreases with increasing magnetic field strength, and increases with increasing radial electric field, showing that the instability is linked to the ExB flow of the electron plasma. The frequency does not, however, scale exactly with E/B, and it depends on the ion species that is introduced, implying that the instability consists of interacting perturbations of ions and electrons.

Marksteiner, Q. R.; Pedersen, T. Sunn; Berkery, J. W.; Hahn, M. S.; Mendez, J. M.; Durand de Gevigney, B. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States); Himura, H. [Kyoto Institute of Technology, Department of Electronics, Matsugasaki, Kyoto 606-8585 (Japan)

2008-02-15

411

Observations of an ion-driven instability in non-neutral plasmas confined on magnetic surfaces.  

PubMed

The first detailed experimental study of an instability driven by the presence of a finite ion fraction in an electron-rich non-neutral plasma confined on magnetic surfaces is presented. The instability has a poloidal mode number m=1, implying that the parallel force balance of the electron fluid is broken and that the instability involves rotation of the entire plasma, equivalent to ion-resonant instabilities in Penning traps and toroidal field traps. The mode appears when the ion density exceeds approximately 10% of the electron density. The measured frequency decreases with increasing magnetic field strength, and increases with increasing radial electric field, showing that the instability is linked to the E x B flow of the electron plasma. The frequency does not, however, scale exactly with E/B, and it depends on the ion species that is introduced, implying that the instability consists of interacting perturbations of ions and electrons. PMID:18352482

Marksteiner, Q R; Pedersen, T Sunn; Berkery, J W; Hahn, M S; Mendez, J M; Durand de Gevigney, B; Himura, H

2008-02-15

412

A new on-chip whole blood/plasma separator driven by asymmetric capillary forces.  

PubMed

A new on-chip whole blood/plasma separator driven by asymmetric capillary forces, which are produced through a microchannel with sprayed nanobead multilayers, has been designed, fabricated and fully characterized. The silica nanobead multilayers revealing as superhydrophilic surfaces have been fabricated using a spray layer-by-layer (LbL) nano-assembly method. This new on-chip blood plasma separator has been targeted for a sample-to-answer (S-to-A) microfluidic lab-on-a-chip (LOC) toward point-of-care clinical testing (POCT). Effective plasma separation from undiluted whole blood was achieved through the microchannel which was composed of asymmetric superhydrophilic surfaces with a 10 mm hydrophobic patch. Blood cells were continuously accumulated over the hydrophobic patch while the blood plasma was able to flow over the patch. Therefore, the blood plasma was successfully separated from the whole blood throughout the accumulated blood cells which worked as a so-called 'self-built-in blood cell microfilter'. The separated plasma was approximately 102 nL from a single drop of 3 ?L whole blood within 10 min, which is very suitable for single-use disposable POCT devices. PMID:23793507

Lee, Kang Kug; Ahn, Chong H

2013-08-21

413

MHD Evolution in Point-Source Helicity Injection Driven Plasmas on Pegasus  

NASA Astrophysics Data System (ADS)

Point-source helicity injection for non-solenoidal startup on Pegasus produces plasmas with Ip<=0.17 MA consistent with Taylor relaxation. The helicity injection supplies an effective loop voltage Veff inversely proportional to the plasma toroidal flux ?T. Accurate measurement of the Veff evolution requires equilibrium reconstructions. Helicity injection-driven plasmas originate on the outboard, low-field side and expand inward to fill the vessel. This evolution increases ?T, reducing Veff from >= 10 V to <= 2 V. Supplemental loop voltage from poloidal field induction is used to obtain higher plasma current. Ip growth is accompanied by bursts of n=1 magnetic activity with frequencies between 10--150 kHz, abrupt inward motion of the plasma, and a drop in internal inductance. This magnetic activity persists during helicity injection. Afterward, MHD quiescence is obtained and persists in discharges subsequently sustained by ohmic induction. The spectral content of these magnetic fluctuations measured with a scanning Mirnov probe does not differ significantly with distance from the plasma edge.

Barr, J. L.; Bongard, M. W.; Burke, M. G.; Fonck, R. J.; Hinson, E. T.; Redd, A. J.

2011-11-01

414

Current-driven plasma instability in lower dimensional solid state systems  

NASA Astrophysics Data System (ADS)

The object of this study was to investigate the feasibility of generating Current Driven Plasma Instabilities (CDPI) in lower dimensional solid state systems. This thesis presents a complete formalism and results of numerical calculations of CDPI in lower dimensional uniform and modulated solid state systems. Random phase approximation has been used to study the response of a plasma system. The presence of a driving field, collisional heating and damping effects, as well as the inter-particle and wave-particle effects have been taken into account in the analysis of the mode structure and growth rate of unstable plasma modes. We have compared plasma waves amplification performance of different uniform two dimensional layered systems, studying in detail the effects of various material parameters on the growth rates of the unstable plasma modes. We have studied the efficiency of a grating coupler which can he used to convert the plasma wave energy into electromagnetic radiation. We have also investigated CDPI in lower dimensional solid state systems with a periodic modulation of density. CDPI can be generated at much lower applied electric fields for the modulated than for the corresponding uniform systems. The fastest and the strongest growing waves which can be generated in the systems we analyzed are relevant for device applications for radiation sources in the millimeter and sub-millimeter wave ranges.

Xie, Hanzhen

415

Beam-Driven Plasma Wakefield Acceleration of Electrons in Lithium and Rubidium Plasmas  

NASA Astrophysics Data System (ADS)

We report on the plasma wakefield experiments performed at the newly commissioned FACET facility at the SLAC National Laboratory. A beam of 2x10^10 20.5 GeV electrons was focused through a 20-40 cm long vapor column of lithium or rubidium produced in a heat-pipe oven. The electron beam tunnel-ionized the metal vapor and then drove a large amplitude plasma wake. The resulting interaction was investigated for different plasma densities and beam parameters. The primary diagnostic was the energy gain and loss features observed using an imaging magnetic spectrometer. Preliminary data and a comparison between acceleration in rubidium and lithium plasmas will be presented.

Vafaei-Najafabadi, Navid; Marsh, Kenneth; Clayton, Christopher; Joshi, Chandrasekhar; Adli, Erik; Corde, Sebastien; Litos, Michael; Li, Selina; Gessner, Spencer; Frederico, Joel; Hogan, Mark; Walz, Dieter; England, Joel; An, Weiming; Lu, Wei; Mori, Warren; Muggli, Patric; Delahaye, Jean-Pierre

2012-10-01

416

Rotary Actuator.  

National Technical Information Service (NTIS)

Rotary actuators and other mechanical devices incorporating shape memory alloys are provided herein. Shape memory alloys are a group of metals which when deformed at temperatures below their martensite temperatures, resume the shapes which they had prior ...

M. Brudnicki

1993-01-01

417

Kinetic Alfvén wave instability driven by field-aligned currents in a low-? plasma  

NASA Astrophysics Data System (ADS)

Kinetic Alfvén waves (KAWs) can play an important role in the energization of plasma particles and the formation of filamentous structures, which commonly are encountered and frequently accompanied by field-aligned currents in various magneto-plasmas, such as laboratory, auroral, and coronal plasmas. Based on a low-frequency kinetic dispersion equation in frequency ?driven by a field-aligned current, which is carried by the field-aligned drift of electrons at velocity VD, is investigated in a low-? plasma of ?plasma ? parameter as well as the drift velocity VD. The results show that the KAW instability occurs in the perpendicular wave number range of k? -plasma ?parameter decreases, the growing wave number range also widens, and the maximal-growing wave number and growth rate both increase. These results have potential importance in understanding the physics of the electric current dissipation and plasma active phenomena since the field-aligned current is one of the most active factors in space and astrophysical plasmas.

Chen, L.; Wu, D. J.; Huang, J.

2013-06-01

418

Plasma driven permeation of hydrogen through Nb: influence of the surface and bulk defects  

SciTech Connect

Plasma driven permeation of hydrogen through 25 {mu}m Nb foils was investigated under low-energy hydrogen ion irradiation in the range of membrane temperature 450-800 K and at different surface conditions. The interaction of hydrogen at molecular, atomic and ionizated states with niobium was under experimental research. The maximum value of low-temperature steady state permeation efficiency (SPE) was observed at Ar plasma cleaned inlet surface and with insignificant influence of outlet surface conditions. Such result is unusual and contradicts the developed classical representations and other published data for high-temperature range plasma-driven permeation. We explain this phenomenon by influence of defect structure of the polycrystalline membrane. The defects lead to the enhanced diffusion of hydrogen atoms along the crystallite sides. Such diffusion can essentially increase SPE of hydrogen through metal at low temperatures. The validity of this explanation was proved by the comparison of molecular hydrogen sorption and desorption measurements in poly- and mono-crystal Nb samples. The weighing method was used in that case. The phase transition {beta}'{yields}{alpha} in the Nb-H system is important for an explanation of SPE temperature dependencies in low-temperature range. The defects initiate phase transitions. The short-time enhanced hydrogen permeation was observed after irradiation of a membrane surface by Ar ions. The surface dissociation of the molecular ions, excited molecules and partially ordinary unexcited molecules of hydrogen can explain these observations.

Spitsyn, A.; Skovoroda, A.; Stolyarov, V.; Pustovoit, Yu [Nuclear Fusion Institute of RRC 'Kurchatov Institute', Moscow, 123182 (Russian Federation); Petrov, V.; Bykov, D.; Voronkin, E. [Moscow State Institute of Electronics and Mathematics, Moscow, 109028 (Russian Federation)

2006-05-24

419

Prolonged plasma production at current-driven implosion of wire arrays on Angara5-1 facility  

Microsoft Academic Search

Results of experimental investigation and modeling of prolonged plasma production during implosion of cylindrical wire arrays are presented. Results of the radiography of dense cores of imploding wire array and the measurements of internal azimuthal magnetic field in wire array give new experimental evidences of prolonged plasma production phenomenon. This phenomenon is an important property of current-driven implosion of the

V. V. Alexandrov; I. N. Frolov; M. V. Fedulov; E. V. Grabovsky; K. N. Mitrofanov; S. L. Nedoseev; G. M. Oleinik; I. Yu. Porofeev; A. A. Samokhin; P. V. Sasorov; V. P. Smirnov; G. S. Volkov; M. M. Zurin; G. G. Zukakischvili

2002-01-01

420

Numerical Modeling and Testing of an Inductively-Driven and High-Energy Pulsed Plasma Thrusters  

NASA Technical Reports Server (NTRS)

Pulsed Plasma Thrusters (PPTs) are advanced electric space propulsion devices that are characterized by simplicity and robustness. They suffer, however, from low thrust efficiencies. This summer, two approaches to improve the thrust efficiency of PPTs will be investigated through both numerical modeling and experimental testing. The first approach, an inductively-driven PPT, uses a double-ignition circuit to fire two PPTs in succession. This effectively changes the PPTs configuration from an LRC circuit to an LR circuit. The LR circuit is expected to provide better impedance matching and improving the efficiency of the energy transfer to the plasma. An added benefit of the LR circuit is an exponential decay of the current, whereas a traditional PPT s under damped LRC circuit experiences the characteristic "ringing" of its current. The exponential decay may provide improved lifetime and sustained electromagnetic acceleration. The second approach, a high-energy PPT, is a traditional PPT with a variable size capacitor bank. This PPT will be simulated and tested at energy levels between 100 and 450 joules in order to investigate the relationship between efficiency and energy level. Arbitrary Coordinate Hydromagnetic (MACH2) code is used. The MACH2 code, designed by the Center for Plasma Theory and Computation at the Air Force Research Laboratory, has been used to gain insight into a variety of plasma problems, including electric plasma thrusters. The goals for this summer include numerical predictions of performance for both the inductively-driven PPT and high-energy PFT, experimental validation of the numerical models, and numerical optimization of the designs. These goals will be met through numerical and experimental investigation of the PPTs current waveforms, mass loss (or ablation), and impulse bit characteristics.

Parma, Brian

2004-01-01

421

Fabrication of thin vertical mirrors through plasma etch and KOH:IPA polishing for integration into MEMS electrostatic actuators  

NASA Astrophysics Data System (ADS)

We developed a process for the fabrication of thin vertical mirrors as integrated structures of MEMS electrostatic actuators. The mirrors can be implemented as a vertical extension of the actuator sidewall, or can be positioned at any movable part of the actuator. The process involves the fabrication of a mesa structure on the handle layer of a silicon-oninsulator (SOI) wafer through deep reactive ion etching (DRIE). The etch/passivation cycles of the DRIE process were optimized to achieve vertical etch profiles with a depth of up to 200 ?m with an aspect ratio of 10:1. The DRIE process introduced typical etch scallops with peak-to-valley and rms roughnesses on the order of 100 nm and 30 nm, respectively. A mask layer was used to pattern a 2.1 ?m sacrificial oxide layer for the mesa structure. A second mask layer allowed us to define a large etch cavity for handle layer back-etch. The DRIE etched mesa structure was then etched with diluted potassium hydroxide (KOH) in isopropyl alcohol (IPA). Temperature and etch concentration were optimized for the removal of etch scallops without the formation of <111> etch facets. The etch scallops were almost completely removed and mirror quality surfaces were achieved. The developed mesa structures are suitable for integration into actuators that are patterned in the device layer. A third masking layer, aligned through infrared camera, was used to position the thin vertical mirror at the actuator sidewall. The process provides design flexibility in integrating vertical mirrors of adjustable dimensions to movable elements of MEMS structures.

Huda, M. Q.; Amin, T. M. F.; Ning, Y.; McKinnon, G.; Tulip, J.; Jäger, W.

2013-03-01

422

Improvements In Ball-Screw Linear Actuators  

NASA Technical Reports Server (NTRS)

Report describes modifications of design of type of ball-screw linear actuator driven by dc motor, with linear-displacement feedback via linear variable-differential transformer (LVDT). Actuators used to position spacecraft engines to direct thrust. Modifications directed toward ensuring reliable and predictable operation during planned 12-year cruise and interval of hard use at end of cruise.

Iskenderian, Theodore; Joffe, Benjamin; Summers, Robert

1996-01-01

423

Kinetic simulation of an extreme ultraviolet radiation driven plasma near a multilayer mirror  

NASA Astrophysics Data System (ADS)

Future generation lithography tools will use extreme ultraviolet radiation to enable the printing of sub-50 nanometer features on silicon wafers. The extreme ultraviolet radiation, coming from a pulsed discharge, photoionizes the low pressure background gas in the tool. A weakly ionized plasma is formed, which will be in contact with the optical components of the lithography device. In the plasma sheath region ions will be accelerated towards the surfaces of multilayer mirrors. A self-consistent kinetic particle-in-cell model has been applied to describe a radiation driven plasma. The simulations predict the plasma parameters and notably the energy at which ions impact on the plasma boundaries. We have studied the influence of photoelectron emission from the mirror on the sheath dynamics and on the ion impact energy. Furthermore, the ion impact energy distribution has been convoluted with the formula of Yamamura and Tawara [At. Data Nucl. Data Tables 62, 149 (1996)] for the sputter yield to obtain the rate of physical sputtering. The model predicts that the sputter rate is dominated by the presence of doubly ionized argon ions.

van der Velden, M. H. L.; Brok, W. J. M.; van der Mullen, J. J. A. M.; Banine, V.

2006-10-01

424

Current-driven plasma instabilities and auroral-type particle acceleration at Venus  

NASA Technical Reports Server (NTRS)

Above the ionosphere of Venus, several instruments on the Pioneer Orbiter detect correlated wave, field and particle phenomena suggestive of current-driven anomalous resistivity and auroral-type particle acceleration. In localized regions the plasma wave instrument measures intense mid-frequency turbulence levels together with strong field-aligned currents. Here the local parameters indicate that there is marginal stability for ion acoustic waves, and the electron temperature probe finds evidence that energetic primaries are present. This suggests an auroral-type energy deposition into the upper atmosphere of Venus. These results appear to be consistent with the direct measurements of auroral emissions from the Pioneer-Venus ultraviolet imaging spectrometer.

Scarf, F. L.; Brace, L. H.; Russell, C. T.; Luhmann, J. G.; Stewart, A. I. F.

1985-01-01

425

Parallel viscosity-driven neoclassical fluxes in the banana regime in nonsymmetric toroidal plasmas  

SciTech Connect

Analytic expressions for the parallel viscosity-driven neoclassical fluxes in the banana regime in arbitrary nonsymmetric toroidal plasmas are derived without considering boundary layer effects. They can be evaluated numerically if the Fourier decomposition of the strength of the magnetic field Vertical BarBVertical Bar is known. Since no averaging over the high-frequency component of the Fourier decomposition of Vertical BarBVertical Bar has been employed, these expressions can reproduce all the known results in symmetric systems and predict the possibility of reversing the direction of the bootstrap current and Ware pinch flux in a stellarator.

Shaing, K.C.; Hirshman, S.P.; Tolliver, J.S.

1986-08-01

426

FIRST MEASUREMENT OF PRESSURE GRADIENT-DRIVEN CURRENTS IN TOKAMAK EDGE PLASMAS  

SciTech Connect

Localized currents driven by pressure gradients play a pivotal role in the magnetohydrodynamic stability of toroidal plasma confinement devices. We have measured the currents generated in the edge of L- (low) and H- (high confinement) mode discharges on the DIII-D tokamak, utilizing the Zeeman effect in an injected lithium beam to obtain high resolution profiles of the poloidal magnetic field. We find current densities in excess of 1 MA/m{sup 2} in a 1 to 2 cm region near the peak of the edge pressure gradient. These values are sufficient to challenge edge stability theories based on specific current formation models.

THOMAS DM; LEONARD AW; LAO LL; OSBORNE TH; MUELLER HW; FINKENTHAL DK

2003-11-01

427

Characterization of Heat-Wave Propagation through Laser-Driven Ti-Doped Underdense Plasma  

SciTech Connect

The propagation of a laser-driven heat-wave into a Ti-doped aerogel target was investigated. The temporal evolution of the electron temperature was derived by means of Ti K-shell x-ray spectroscopy, and compared with two-dimensional radiation hydrodynamic simulations. Reasonable agreement was obtained in the early stage of the heat-wave propagation. In the later phase, laser absorption, the propagation of the heat wave, and hydrodynamic motion interact in a complex manner, and the plasma is mostly re-heated by collision and stagnation at the target central axis.

Tanabe, M; Nishimura, H; Ohnishi, N; Fournier, K B; Fujioka, S; Iwamae, A; Hansen, S B; Nagai, K; Girard, F; Primout, M; Villette, B; Brebion, D; Mima, K

2009-02-23

428

Global Hybrid Simulations of Energetic Particle-driven Modes in Toroidal Plasmas  

SciTech Connect

Global hybrid simulations of energetic particle-driven MHD modes have been carried out for tokamaks and spherical tokamaks using the hybrid code M3D. The numerical results for the National Spherical Tokamak Experiments (NSTX) show that Toroidal Alfven Eigenmodes are excited by beam ions with their frequencies consistent