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1

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

2

Investigation of asymmetric dielectric barrier discharge plasma actuator, driven by repetitive nanosecond pulses.  

NASA Astrophysics Data System (ADS)

DBD plasma actuators are known to be effective for low speed flow control. A comprehensive physically-based numerical model has been developed for explanation of DBD operation. The modeling showed the advantages of using repetitive nanosecond pulses with bias over the sine voltage. If the sine voltage is applied, it carries two functions -- plasma generation and producing the body force on the gas. In the pulse case these processes are separated. The plasma is generated using repetitive nanosecond pulses, and the driving of charge particles, which produces the force on the gas, is between the pulses. In pulse configuration the variation of pulse amplitude, sign and the voltage between pulses can produce different force and heating effects on the flow. The verification of the modeling has been done in the experimental investigation of DBD. A new experimental approach for non-intrusive diagnostic of DBD induced flows in quiescent gas was proposed. The schlieren technique, burst mode of plasma actuator operation, and 2D Navier-Stokes numerical model coupled together allowed restoring the entire 2D induced flow and characteristics of the plasma induced force.

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

2007-10-01

3

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

NASA Astrophysics Data System (ADS)

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.; Macheret, Sergey O.

2008-08-01

4

Light-Driven Polymeric Bimorph Actuators  

NASA Technical Reports Server (NTRS)

Light-driven polymeric bimorph actuators are being developed as alternatives to prior electrically and optically driven actuators in advanced, highly miniaturized devices and systems exemplified by microelectromechanical systems (MEMS), micro-electro-optical-mechanical systems (MEOMS), and sensor and actuator arrays in smart structures. These light-driven polymeric bimorph actuators are intended to satisfy a need for actuators that (1) in comparison with the prior actuators, are simpler and less power-hungry; (2) can be driven by low-power visible or mid-infrared light delivered through conventional optic fibers; and (3) are suitable for integration with optical sensors and multiple actuators of the same or different type. The immediate predecessors of the present light-driven polymeric bimorph actuators are bimorph actuators that exploit a photorestrictive effect in lead lanthanum zirconate titanate (PLZT) ceramics. The disadvantages of the PLZT-based actuators are that (1) it is difficult to shape the PLZT ceramics, which are hard and brittle; (2) for actuation, it is necessary to use ultraviolet light (wavelengths < 380 nm), which must be generated by use of high-power, high-pressure arc lamps or lasers; (3) it is difficult to deliver sufficient ultraviolet light through conventional optical fibers because of significant losses in the fibers; (4) the response times of the PLZT actuators are of the order of several seconds unacceptably long for typical applications; and (5) the maximum mechanical displacements of the PLZT-based actuators are limited to those characterized by low strains beyond which PLZT ceramics disintegrate because of their brittleness. The basic element of a light-driven bimorph actuator of the present developmental type is a cantilever beam comprising two layers, at least one of which is a polymer that exhibits a photomechanical effect (see figure). The dominant mechanism of the photomechanical effect is a photothermal one: absorption of light energy causes heating, which, in turn, causes thermal expansion.

Adamovsky, Gregory; Sarkisov, Sergey S.; Curley, Michael J.

2009-01-01

5

Artificial annelid robot driven by soft actuators.  

PubMed

The annelid provides a biological solution of effective locomotion adaptable to a large variety of unstructured environmental conditions. The undulated locomotion of the segmented body in the annelid is characterized by the combination of individual motion of the muscles distributed along the body, which has been of keen interest in biomimetic investigation. In this paper, we present an annelid-like robot driven by soft actuators based on dielectric elastomer. To mimic the unique motion of the annelid, a novel actuation method employing dielectric elastomer is developed. By using the actuator, a three-degree-of-freedom actuator module is presented, which can provide up-down translational motion, and two rotational degree-of-freedom motion. The proposed actuation method provides advantageous features of reduction in size, fast response and ruggedness in operation. By serially connecting the actuator modules, a micro-robot mimicking the motion of the annelid is developed and its effectiveness is experimentally demonstrated. PMID:17671328

Jung, Kwangmok; Koo, Ja Choon; Nam, Jae-do; Lee, Young Kwan; Choi, Hyouk Ryeol

2007-06-01

6

Surface chemistry driven actuation in nanoporous gold  

SciTech Connect

Although actuation in biological systems is exclusively powered by chemical energy, this concept has not been realized in man-made actuator technologies, as these rely on generating heat or electricity first. Here, we demonstrate that surface-chemistry driven actuation can be realized in high surface area materials such as nanoporous gold. For example, we achieve reversible strain amplitudes in the order of a few tenths of a percent by alternating exposure of nanoporous Au to ozone and carbon monoxide. The effect can be explained by adsorbate-induced changes of the surface stress, and can be used to convert chemical energy directly into a mechanical response thus opening the door to surface-chemistry driven actuator and sensor technologies.

Biener, J; Wittstock, A; Zepeda-Ruiz, L; Biener, M M; Zielasek, V; Kramer, D; Viswanath, R N; Weissmuller, J; Baumer, M; Hamza, A V

2008-04-14

7

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

PubMed

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. PMID:24089880

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

2013-09-01

8

A vacuum-driven peristaltic micropump with valved actuation chambers  

NASA Astrophysics Data System (ADS)

This paper presents a simple peristaltic micropump design incorporated with valved actuation chambers and propelled by a pulsed vacuum source. The vacuum-driven peristaltic micropump offers high pumping rates, low backflow, appreciable tolerance to air bubbles, and minimal destruction to fluid contents. The pumping device, fabricated by laser micromachining and plasma bonding of three polydimethylsiloxane (PDMS) layers, includes a pneumatic network, actuation membranes, and microfluidic channels. As the key to peristaltic motion, the sequential deflection of the elastic membranes is achieved by periodic pressure waveforms (negative) traveling through the pneumatic network, provided by a vacuum source regulated by an electromagnetic valve. This configuration eliminates the complicated control logic typically required in peristaltic motion. Importantly, the valved actuation chambers substantially reduce backflow and improve the pumping rates. In addition, the pneumatic network with negative pressure provides a means to effectively remove air bubbles present in the microflow through the gas-permeable PDMS membrane, which can be highly desired in handling complex fluidic samples. Experimental characterization of the micropump performance has been conducted by controlling the resistance of the pneumatic network, the number of normally closed valves, the vacuum pressure, and the frequency of pressure pulses. A maximal flow rate of 600 µL min-1 has been optimized at the pulsed vacuum frequency of 30 Hz with a vacuum pressure of 50 kPa, which is comparable to that of compressed air-actuated peristaltic micropumps.

Cui, Jianguo; Pan, Tingrui

2011-06-01

9

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

10

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.

11

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

12

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

13

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

14

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

15

An arm wrestling robot driven by dielectric elastomer actuators  

Microsoft Academic Search

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

Gabor Kovacs; Patrick Lochmatter; Michael Wissler

2007-01-01

16

Circular cylinder drag reduction by three-electrode plasma actuators  

Microsoft Academic Search

The drag reduction in a circular cylinder was explored by means of a novel three electrode plasma actuator (DBDE). The DBDE actuator can reduce the drag coefficient up to a ~25% respect to the base flow drag coefficient. It has been demonstrated that, within the present experimental conditions, the DBDE actuator, for a fixed value of the power coefficient, adds

R. Sosa; J. D'Adamo; G. Artana

2009-01-01

17

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

18

Electro-actuation characteristics of Cl2 and SF6 plasma-treated IPMC actuators  

NASA Astrophysics Data System (ADS)

This paper describes plasma treatments that improve the actuation properties by modifying the surface morphology of ionic polymer metal composites (IPMC). The proposed Cl2 and SF6 plasmas change the surface appearance of the electroactive polymer, and scanning electron microscopy (SEM) of the plasma-treated surfaces reveals the development of round and cone-shaped microstructures. After electroless chemical metal plating, these microstructures significantly alter the characteristics of the IPMC electrode. In plasma-treated IPMCs, the densely packed platinum nanoparticles have produced a relatively thick electrode layer. This configuration has led to the improvement in the electrical properties of the IPMC: surface resistance is noticeably decreased, whereas electrical capacitance is increased. These changes in the electrical properties have considerably enhanced the actuation parameters: displacement, force and operational life are increased by more than three times relative to the conventional IPMC. Our experimental data suggest a relationship between the IPMC actuator's electrical properties and actuation parameters: actuators with lower surface resistance generate large deflection and actuators with higher capacitance generate large actuation force. The actuation tests including coin lifting suggests the potential of the modified IPMC for artificial muscle applications.

Saher, Saim; Kim, Woojin; Moon, Sungwon; Kim, H. Jin; Hyup Kim, Yong

2010-10-01

19

Fast, strong and compliant pneumatic actuation for dexterous tendon-driven hands  

E-print Network

Fast, strong and compliant pneumatic actuation for dexterous tendon-driven hands Vikash Kumar, Zhe Xu and Emanuel Todorov Abstract--We describe a pneumatic actuation system for dexterous robotic hands dexterity naturally leads to the choice of pneumatic actuation. Indeed this may be the only available

Todorov, Emanuel

20

Variable Structure Model for Flow-Induced Tonal Noise Control with Plasma Actuators  

E-print Network

to the plasma actuator [3]. More recently, plasma actuator technology has been applied to aeroacousticVariable Structure Model for Flow-Induced Tonal Noise Control with Plasma Actuators Xun Huang of plasma actuators in attenuating low-speed flow-induced cavity tones from a control point of view

Huang, Xun

21

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

22

Separation control over low pressure turbine blades using plasma actuators  

NASA Astrophysics Data System (ADS)

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 "PakB" shaped blades. Flow visualization, pressure measurements, LDV measurements; and hot-wire measurements were conducted to examine the flow fields with and without separation control. Experimental conditions were chosen to give a range of chord Reynolds numbers from 10,000 to 100,000, and a range of freestream turbulence intensities from u'/ Uinfinity = 0.08% to 2.85%. The blade pressure distributions were measured and used to define a region of separation that depends on the freestream conditions. The location of separation was found to be relatively insensitive to the experimental conditions. However, the reattachment location was very sensitive to the Reynolds number and the turbulence intensity. Separation control was performed using plasma actuators. Both steady and unsteady actuation were implemented and found to work well. For the steady actuators, it was found that the separation control is the most effective when applied slightly upstream the separation location. There exists a threshold plasma amplitude for the actuator to take effect for separation control. However, the effectiveness of the actuator is saturated when the plasma amplitude is greater than certain value. The effectiveness of the steady actuator is not sensitive to the orientation of the plasma electrodes. For the unsteady actuators, there exists an optimum excitation frequency at which the unsteady actuator was the most effective. The optimum excitation frequency was corresponded to the unity Strouhal number, which is defined as St = fLsep/Umid-channel. It was also found that lowest plasma duty cycle (10% in this work) was as effective as the highest plasma duty cycle (50% in this work). This has an advantage for reducing the power to the actuators. The comparison between the steady and unsteady actuators showed that the unsteady actuators worked better than the steady ones. 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.

Huang, Junhui

23

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

24

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

25

Model-based condition monitoring of an actuator system driven by a brushless DC motor  

Microsoft Academic Search

Air pressure in passenger aircrafts is controlled by opening and closing an outflow valve, which serves to release air from the cabin. Early identification of potential malfunctions in the underlying actuator-driven system is important both from the point of view of cost-efficient maintenance as well as overall safety. This paper presents a system for diagnosing faults in a valve actuator

?ani Juri?i?; Olaf Moseler; Andrej Rakar

2001-01-01

26

Rehabilitative Knee Orthosis Driven by Electro-Rheological Fluid Based Actuators  

E-print Network

Rehabilitative Knee Orthosis Driven by Electro-Rheological Fluid Based Actuators Jason Nikitczuk1, fabrication and testing of an ERF based knee orthotic device and the innova- tive ERF actuators it uses. The knee orthotic is achieved through a standard brace design with a polycentric hinge and gear system

Mavroidis, Constantinos

27

Design of a high-speed, meso-scale nanopositioners driven by electromagnetic actuators  

E-print Network

The purpose of this thesis is to generate the design and fabrication knowledge that is required to engineer high-speed, six-axis, meso-scale nanopositioners that are driven by electromagnetic actuators. When compared to ...

Golda, Dariusz, 1979-

2008-01-01

28

Controlling shedding from circular cylinders using plasma actuators  

NASA Astrophysics Data System (ADS)

Plasma actuators were used to control the phase relationship between vortex shedding from two side-by-side circular cylinders from Red = 16,700 to 76,500 in a low-speed flow. The motivation was to create, in a compressible cascade, a 'clean' and predictable upstream-propagating potential disturbance using synchronized shedding from a row of multiple cylinders so that the interaction of the disturbance with the trailing edge of a cascade vane could be investigated. In the low-speed flow, two cylinders of L/d = 8 were installed perpendicular to the flow, with the pitch-to-diameter ratio of 4. The 'natural' vortex shedding for this spacing is, predominantly, 180° out-of-phase. The performance of the plasma actuators was best, when they were installed on the sides (approximately +/-90° from the forward stagnation point) of each cylinder, along the full span. These actuators, by the formation of plasma, produce an air jet in downstream direction. The phase relationship of vortex shedding was determined using cross correlation of streamwise velocities, measured by hot-wire probes located downstream of each cylinder at symmetric positions with respect to the cylinder axes. The cross correlation of the unsteady velocities showed the effectiveness of the plasma actuators in phase synchronizing the vortex shedding. The coefficients of +0.4 to +0.6 (or -0.6 to -0.4) were obtained when the plasma actuators were activated, showing the in-phase (or out-of-phase) synchronization of the vortex shedding. The effectiveness of the plasma actuators was further demonstrated by the arbitrary-phase synchronization of vortex shedding. The phase synchronization up to the Reynolds number of 76,500 was obtained. No other method has been able to achieve the vortex-shedding control up to this high a Reynolds number. The power input to the actuators, before reaching a certain asymptotic value, increased with the increase in Reynolds number. The phase synchronization was sensitive to the excitation frequency, input power, and Reynolds number. Flow visualization was used to obtain a global view of the phase-synchronized shedding. The spanwise coherence of vortex shedding increased when the flow was excited. The upstream effect of the phase-synchronized shedding of cylinders in the low-speed flow (Re = 16,700) was investigated using PIV. The controlled in-phase shedding also produced a synchronized unsteady velocity field upstream of the cylinders. Through the scaling of the body force produced by the plasma actuator, it is demonstrated that it is possible to phase synchronize vortex shedding in a higher-speed, weakly-compressible, geometrically-similar flow.

Asghar, Asad

29

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

30

Impedance matching for an asymmetric dielectric barrier discharge plasma actuator  

E-print Network

. © 2007 American Institute of Physics. DOI: 10.1063/1.2773932 Active control of air flow using surface plasma actuators has emerged in recent years. Such control involves modify- ing air flow pattern- strated for flow modification along flat plates4 and for stall control over airfoils.5 The weakly ionized

Roy, Subrata

31

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

32

Indirect Adaptive Robust Control of Electro-Hydraulic Systems Driven by Single-Rod Hydraulic Actuator  

E-print Network

Indirect Adaptive Robust Control of Electro-Hydraulic Systems Driven by Single-Rod Hydraulic) of electro-hydraulic systems driven by single- rod hydraulic actuators. Unlike the tracking that the proposed IARC achieves good tracking performance and accurate parameter estimation. INTRODUCTION Electro-hydraulic

Yao, Bin

33

Finite element modeling analysis of photostrictively driven optical actuators for excitation of microdevices  

NASA Astrophysics Data System (ADS)

Photostriction is a phenomenon in which strain is induced in the sample by incident light. In principle, this effect arises from a superposition of the photovoltaic effect, i.e. the generation of large voltage from the irradiation of light, and the converse piezoelectric effect, i.e. expansion or contraction under the voltage applied. Photostrictive materials are ferrodielectric ceramics that have a photostrictive effect. Some photostrictive materials are (Pb, La)(Zr, Ti) O3 ceramics doped with WO3, called PLZT, which exhibit large photostriction under uniform illumination with high-energy light. They have potential use in numerous micro-electro-mechanical system (MEMS) devices where actuation of microbeams is a common phenomenon. The objective of this research is to develop and analyze a finite element model to study the feasibility of photostrictively driven actuators for excitation of microdevices. Much work has been carried out toward developing microdevices which are capacitively driven or piezoelectrically driven. The effect of different parameters such as actuator thickness, incident light intensity and convective heat transfer coefficient on the actuation of a beam using thin film photostrictive actuators has been investigated. Also the derived finite element for static analysis of photostrictive thin films has been used to investigate the application of photostrictive actuators for different structures and various boundary conditions of microbeams with various actuator locations and lengths. A successful conclusion of these tasks will affirm the potential of the technology for use in actual microdevices.

Rahman, Mosfequr; Nawaz, Masud

2011-11-01

34

Plasma actuated heat transfer Subrata Roya  

E-print Network

crossflow creating a three-dimensional flow field entraining some hot gas to bend toward the blade the domain of influence as shown in Fig. 2 schematic below. The momentum transfer between the plasma and gas introduce plasmas for film cooling enhancement in gas turbines and other engineering applications. We

Roy, Subrata

35

Experimental Investigation of Lift Enhancement and Roll Control Using Plasma Actuators  

E-print Network

Experimental Investigation of Lift Enhancement and Roll Control Using Plasma Actuators Alexander N.2514/1.34659 An experimental investigation into the use of trailing-edge-mounted plasma actuators for lift enhancement and roll control is described. Data are presented showing the effect that the actuators have on lift, pitch

Jumper, Eric

36

Thermally driven multi-layer actuator for 2D cantilever arrays  

Microsoft Academic Search

The present work reports on novel four-layer thermally driven piezoresistive cantilevers implemented in one- and two-dimensional\\u000a arrays for parallel proximity scanning. There, the heater (metallic meander), the piezoresistive deflection sensor, and the\\u000a metal actuation film with significantly higher thermal expansion coefficient make up separate layers. Actuation efficiency\\u000a and cross-talk of the novel cantilever design are studied and compared with two

Y. Sarov; T. Ivanov; A. Frank; I. W. Rangelow

2011-01-01

37

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

38

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

39

Separation Control in a 3D Diffuser using Plasma Actuators  

NASA Astrophysics Data System (ADS)

Control experiments were conducted for the fully-turbulent flow in a 3D diffuser with an expansion ratio of 4.8. The uncontrolled flow for the same diffuser has a stable, three-dimensional separation zone which begins as a slender bubble in one corner before spreading across the entire width of the diffuser, giving the opportunity to develop and test active separation control devices. Dielectric-barrier discharge actuators were used to actively control the flow separation with the goal of improving the pressure recovery. The most effective control was achieved using spanwise acting plasma actuators in the inlet section of the diffuser which create streamwise vortices. The pressure recovery can be clearly improved or degraded depending on whether the actuators are operated pulsed or continuously. Parameter studies showed the dependence of the pressure recovery along the diffuser wall on the actuator operating parameters, including the modulation frequency and duty cycle. Velocity profile measurements in the inlet and outlet planes of the diffuser show the creation of the streamwise vortices and their influence on the uniformity of the velocity in the end of the diffuser. Frequency spectra taken in the exit plane using a hotwire probe show the influence of the operating parameters on the diffuser flow. A closed-loop control circuit for the automated adaption of the operating parameters is being tested.

Grundmann, Sven; Eaton, John K.

2009-11-01

40

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

41

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

42

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

43

Research on the Peristaltic Flow Acceleration Performance of Asynchronous and Duty Cycle Pulsed DBD Plasma Actuation  

NASA Astrophysics Data System (ADS)

Using a plexiglas plate model, the performance of peristaltic flow acceleration induced by multiple DBD (dielectric barrier discharge) plasma actuators was studied based on PIV (particle image velocimetry). The asynchronous and the duty cycle pulsed actuation modes were proposed and tested. The velocity fields induced by multiple DBD plasma actuators with different phase angles and duty cycle ratios were acquired and the momentum transfer characteristics of the flow field were discussed. Consequently, the mechanism of the peristalsis-acceleration multiple DBD plasma actuation was analyzed. The results show that the peristaltic flow acceleration effect of multiple plasma actuators occurs mainly in paraelectric direction, and the mechanism of peristaltic flow acceleration is ejection pushing effect rather than injection pumping effect. The asynchronous and the duty cycle pulsed actuation modes can, with energy consumption increase of merely 10%, achieve 65% and 42% increase of downstream velocity, and thus are promising in velocity improvement and energy saving.

Li, Feng; Gao, Chao; Zheng, Borui; Wang, Yushuai

2014-09-01

44

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

45

Analysis, Design and Control of a Planar Micro-robot Driven by Two Centripetal-Force Actuators*  

E-print Network

/s, and is presented in [4]. A different motion mechanism based on piezo-tubes is utilized by the Nano Walker micro-robotAnalysis, Design and Control of a Planar Micro-robot Driven by Two Centripetal-Force Actuators of a novel, low cost, sliding micro-robot, which is actuated by centripetal forces generated by robot mounted

Papadopoulos, Evangelos

46

Integrated prognosis of AC servo motor driven linear actuator using Hidden Semi-Markov models  

Microsoft Academic Search

Motor prognosis has great benefit for motion control systems. It is desirable to develop the so-called integrated prognosis capability for motion control products, i.e. with only the existing sensors of a motor drive. This paper presents a scheme of integrated wear prognosis for linear actuators driven by AC servo motor with only current measurement. The hidden semi-Markov model (HSMM) was

Xin Wu; Yaoyu Li; Thomas D. Lundell; Arun K. Guru

2009-01-01

47

Current in wave driven plasmas  

SciTech Connect

A theory for the generation of current in a toroidal plasma by radio-frequency waves is presented. The effect of an opposing electric field is included, allowing the case of time varying currents to be studied. The key quantities that characterize this regime are identified and numerically calculated. Circuit equations suitable for use in ray-tracing and transport codes are given.

Karney, C.F.F.; Fisch, N.J.

1985-06-01

48

PIV measurements of flow characteristics induced by mini plate-wing plasma actuators  

NASA Astrophysics Data System (ADS)

The surface DBD plasma actuator is known to be effective for flow control process. Plasma is produced on actuator and gives a body force to the ambient air which is the mechanism for active flow control. Until now, the actuators have been mounted on the wall surface. The plasma actuator is thin and controllable electrically. If we combine the plasma actuator and the passive devices like a vortex generator and Large Eddy Break Up device, those passive devices would be activated. As the basis of the combination use, this paper investigated the wing-like plasma actuators, the width and chord length of which were 96mm and 19.6mm respectively. The electric wind was generated in the absence of external flow by the plasma actuator. Two electrodes were separated by a Kapton thin wing plate and were located at 5.75mm or 14mm from the leading edge. The induced flow was compared as a function of the distance from the leading edge to the actuator position. It was found that the increase in the distance shifted the point of maximum velocity downstream but the induce wake flow indicated the same momentum integral.

Mominul Islam Mukut, A. N. M.; Mizunuma, Hiroshi; Segawa, Takehiko; Hiromichi, Obara

2010-11-01

49

Control of supersonic axisymmetric base flows using passive splitter plates and pulsed plasma actuators  

NASA Astrophysics Data System (ADS)

An experimental investigation evaluating the effects of flow control on the near-wake downstream of a blunt-based axisymmetric body in supersonic flow has been conducted. To better understand and control the physical phenomena that govern these massively separated high-speed flows, this research examined both passive and active flow-control methodologies designed to alter the stability characteristics and structure of the near-wake. The passive control investigation consisted of inserting splitter plates into the recirculation region. The active control technique utilized energy deposition from multiple electric-arc plasma discharges placed around the base. The flow-control authority of both methodologies was evaluated with experimental diagnostics including particle image velocimetry, schlieren photography, surface flow visualization, pressure-sensitive paint, and discrete surface pressure measurements. Using a blowdown-type wind tunnel reconstructed specifically for these studies, baseline axisymmetric experiments without control were conducted for a nominal approach Mach number of 2.5. In addition to traditional base pressure measurements, mean velocity and turbulence quantities were acquired using two-component, planar particle image velocimetry. As a result, substantial insight was gained regarding the time-averaged and instantaneous near-wake flow fields. This dataset will supplement the previous benchmark point-wise laser Doppler velocimetry data of Herrin and Dutton (1994) for comparison with new computational predictive techniques. Next, experiments were conducted to study the effects of passive triangular splitter plates placed in the recirculation region behind a blunt-based axisymmetric body. By dividing the near-wake into 1/2, 1/3, and 1/4 cylindrical regions, the time-averaged base pressure distribution, time-series pressure fluctuations, and presumably the stability characteristics were altered. While the spatial base pressure distribution was influenced considerably, the area-integrated pressure was only slightly affected. Normalized RMS levels indicate that base pressure fluctuations were significantly reduced with the addition of the splitter plates. Power-spectral-density estimates revealed a spectral broadening of fluctuating energy for the 1/2 cylinder configuration and a bimodal distribution for the 1/3 and 1/4 cylinder configurations. It was concluded that the recirculation region is not the most sensitive location to apply flow control; rather, the shear layer may be a more influential site for implementing flow control methodologies. For active flow control, pulsed plasma-driven fluidic actuators were investigated. Initially, the performance of two plasma actuator designs was characterized to determine their potential as supersonic flow control devices. For the first actuator considered, the pulsed plasma jet, electro-thermal heating from an electric discharge heats and pressurizes gas in a small cavity which is exhausted through a circular orifice forming a synthetic jet. Depending on the electrical energy addition, peak jet velocities ranged between 130 to nearly 500 m/s when exhausted to quiescent, ambient conditions. The second plasma actuator investigated is the localized arc filament plasma actuator (LAFPA), which created fluidic perturbations through the rapid, local thermal heating, generated from an electric arc discharge between two electrodes within a shallow open cavity. Electrical and emission properties of the LAFPA were first documented as a function of pressure in a quiescent, no-flow environment. Rotational and vibrational temperatures from N2 spectra were obtained for select plasma conditions and ambient pressures. Results further validate that the assumption of optically thin conditions for these electric arc plasmas is not necessary valid, even at low ambient pressure. Breakdown voltage, sustained plasma voltage, power, and energy per pulse were demonstrated to decrease with decreasing pressure. Implementing an array of eight electric arcs circumferentially around the base nea

Reedy, Todd Mitchell

50

Microphysics of Cosmic Ray Driven Plasma Instabilities  

NASA Astrophysics Data System (ADS)

Energetic nonthermal particles (cosmic rays, CRs) are accelerated in supernova remnants, relativistic jets and other astrophysical objects. The CR energy density is typically comparable with that of the thermal components and magnetic fields. In this review we discuss mechanisms of magnetic field amplification due to instabilities induced by CRs. We derive CR kinetic and magnetohydrodynamic equations that govern cosmic plasma systems comprising the thermal background plasma, comic rays and fluctuating magnetic fields to study CR-driven instabilities. Both resonant and non-resonant instabilities are reviewed, including the Bell short-wavelength instability, and the firehose instability. Special attention is paid to the longwavelength instabilities driven by the CR current and pressure gradient. The helicity production by the CR current-driven instabilities is discussed in connection with the dynamo mechanisms of cosmic magnetic field amplification.

Bykov, A. M.; Brandenburg, A.; Malkov, M. A.; Osipov, S. M.

51

Microphysics of Cosmic Ray Driven Plasma Instabilities  

NASA Astrophysics Data System (ADS)

Energetic nonthermal particles (cosmic rays, CRs) are accelerated in supernova remnants, relativistic jets and other astrophysical objects. The CR energy density is typically comparable with that of the thermal components and magnetic fields. In this review we discuss mechanisms of magnetic field amplification due to instabilities induced by CRs. We derive CR kinetic and magnetohydrodynamic equations that govern cosmic plasma systems comprising the thermal background plasma, comic rays and fluctuating magnetic fields to study CR-driven instabilities. Both resonant and non-resonant instabilities are reviewed, including the Bell short-wavelength instability, and the firehose instability. Special attention is paid to the longwavelength instabilities driven by the CR current and pressure gradient. The helicity production by the CR current-driven instabilities is discussed in connection with the dynamo mechanisms of cosmic magnetic field amplification.

Bykov, A. M.; Brandenburg, A.; Malkov, M. A.; Osipov, S. M.

2013-10-01

52

Microphysics of cosmic ray driven plasma instabilities  

E-print Network

Energetic nonthermal particles (cosmic rays, CRs) are accelerated in supernova remnants, relativistic jets and other astrophysical objects. The CR energy density is typically comparable with that of the thermal components and magnetic fields. In this review we discuss mechanisms of magnetic field amplification due to instabilities induced by CRs. We derive CR kinetic and magnetohydrodynamic equations that govern cosmic plasma systems comprising the thermal background plasma, comic rays and fluctuating magnetic fields to study CR-driven instabilities. Both resonant and non-resonant instabilities are reviewed, including the Bell short-wavelength instability, and the firehose instability. Special attention is paid to the longwavelength instabilities driven by the CR current and pressure gradient. The helicity production by the CR current-driven instabilities is discussed in connection with the dynamo mechanisms of cosmic magnetic field amplification.

Bykov, A M; Malkov, M A; Osipov, S M

2013-01-01

53

Airfoil Roll Control by Bang-Bang Optimal Control Method with Plasma Actuators  

E-print Network

The bang-bang optimal control method was proposed for glow discharge plasma actuators, taking account of practical issues, such as limited actuation states with instantaneously varied aerodynamic control performance. Hence, the main contribution of this Note is to integrate flight control with active flow control in particular for plasma actuators. Flow control effects were examined in wind tunnel experiments, which show that the plasma authority for flow control is limited. Flow control effects are only obvious at pitch angles near stall. However, flight control simulations suggest that even those small plasma-induced roll moments can satisfactorily fulfill the maneuver tasks and meet flight quality specifications. In addition, the disturbance from volatile plasma-induced roll moments can be rejected. Hence, the proposed bang-bang control method is a promising candidate of control design methodology for plasma actuators.

Wei, Qingkai; Chen, Bao; Huang, Xun

2012-01-01

54

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

55

Closed loop control of a rotational joint driven by two antagonistic dielectric elastomer actuators  

NASA Astrophysics Data System (ADS)

Dielectric elastomers are a subclass of electronic EAPs able to produce large deformations (and thus mechanical work) when an external electric field is applied. While the intrinsic compliance of this kind of polymeric actuators have been always addressed as major benefit with respect to traditional electromagnetic motors, unable to fully capture the capabilities and mechanical properties of biological muscles, their polymeric nature poses peculiar challenges in controlling a system which is subject to nonlinearities, hysteresis and viscous creep behavior. In this paper we explore the controllability properties of a simple rotational joint driven by two dielectric elastomer actuators arranged in an antagonistic configuration. A number of sensors are used to obtain information about the state of controlled system: the angular position of the joint is measured by an angular encoder, custom-designed tension sensors are used to monitor the tension of the two driving tendons and linear encoders provide accurate measurements of the displacements generated by the two actuators. Using this feedback information, a control algorithm has been implemented on a microcontroller unit in order to independently activate the two actuators, allowing a closed loop control of both the angular position of the joint (position control) and the tensions of its tendons (force control). A description of the developed control strategy and its performances under different load conditions are discussed in this paper.

Randazzo, Marco; Fumagalli, Matteo; Metta, Giorgio; Sandini, Giulio

2010-04-01

56

Experimental Results in DBD Plasma Actuators for Air Flow Control  

Microsoft Academic Search

In this paper, several planar dielectric barrier discharge fluid-dynamics actuators have been experimentally investigated. The actuator is made by an electrode pair separated by a dielectric. It is characterized by a planar geometry, and it induces a volume force on the gas above it which modifies the fluid dynamics within the aerodynamic boundary layer. Several actuator geometries, dielectric materials, ac

Gabriele Neretti; Andrea Cristofolini; Carlo A. Borghi; Alessandro Gurioli; Roberto Pertile

2012-01-01

57

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

58

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

59

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. PMID:24385868

Inou, Norio

2013-01-01

60

Numerical analysis of plasma evolution on dielectric barrier discharge plasma actuator  

SciTech Connect

Time evolution of the discharge plasma in the dielectric barrier discharge (DBD) plasma actuator was simulated by the simple fluid model in which the electron and single positive ion species were considered. The characteristics of the discharge plasma evolution were investigated in detail, and the following results were obtained. When the positive-going voltage is applied, the streamer discharge is formed periodically. The periodically formed streamer expands from the exposed electrode, and its length becomes longer than the previous one. Periodic breakdown of the gas and step-by-step plasma expansion are also observed during the negative-going voltage; however, the streamer is not formed and the breakdown frequency is much higher. The simulation results with a triangular applied voltage waveform show the same characteristics as observed in the experiment; large discharge current spikes are observed during both the positive- and negative-going voltage phase, and the plasma in the negative-going voltage phase expands more smoothly than that in the positive phase because of its higher breakdown frequency. It was shown that even the simple numerical model could provide valuable insights into the physics of DBD plasma actuator; this indicates that the positive ions and electrons play a prominent role in determining the general characteristics of the plasma evolution.

Nishida, Hiroyuki [Mechanical Systems Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan); Abe, Takashi [Institute of Space and Astronautical Science, JAXA, Sagamihara, Kanagawa 229-8510 (Japan)

2011-07-01

61

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

62

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

E-print Network

in the atmosphere pressure air helps to yield an increase in flow control performance. Al- though the precise flowStreamwise and spanwise plasma actuators for flow-induced cavity noise control Xun Huang and Xin streamwise and spanwise actuators to control flow-induced noise from a cavity. It was found

Huang, Xun

63

Bio-Inspired Polymer Composite Actuator and Generator Driven by Water Gradients  

NASA Astrophysics Data System (ADS)

Here we describe the development of a water-responsive polymer film. Combining both a rigid matrix (polypyrrole) and a dynamic network (polyol-borate), strong and flexible polymer films were developed that can exchange water with the environment to induce film expansion and contraction, resulting in rapid and continuous locomotion. The film actuator can generate contractile stress up to 27 megapascals, lift objects 380 times heavier than itself, and transport cargo 10 times heavier than itself. We have assembled a generator by associating this actuator with a piezoelectric element. Driven by water gradients, this generator outputs alternating electricity at ~0.3 hertz, with a peak voltage of ~1.0 volt. The electrical energy is stored in capacitors that could power micro- and nanoelectronic devices.

Ma, Mingming; Guo, Liang; Anderson, Daniel G.; Langer, Robert

2013-01-01

64

Bio-inspired polymer composite actuator and generator driven by water gradients.  

PubMed

Here we describe the development of a water-responsive polymer film. Combining both a rigid matrix (polypyrrole) and a dynamic network (polyol-borate), strong and flexible polymer films were developed that can exchange water with the environment to induce film expansion and contraction, resulting in rapid and continuous locomotion. The film actuator can generate contractile stress up to 27 megapascals, lift objects 380 times heavier than itself, and transport cargo 10 times heavier than itself. We have assembled a generator by associating this actuator with a piezoelectric element. Driven by water gradients, this generator outputs alternating electricity at ~0.3 hertz, with a peak voltage of ~1.0 volt. The electrical energy is stored in capacitors that could power micro- and nanoelectronic devices. PMID:23307738

Ma, Mingming; Guo, Liang; Anderson, Daniel G; Langer, Robert

2013-01-11

65

Inductive currents in an rf driven plasma  

SciTech Connect

Inductive effects are included in a self-consistent current drive model for axisymmetric tokamak plasmas used in the two-dimensional current drive/MHD equilibrium code, RIP. Previous simulations of current driven equilibria allowed for the steady-state calculation of bootstrap and RF currents. The addition of an inductive current is applied to enhance accurate design and interpretation of tokamak experiments. A convenient expression for the ohmic resistance in a tokamak plasma is derived to aid in the design of reactor grade MHD equilibria. 7 refs., 3 figs., 1 tab.

Kinsey, J.; Ehst, D.A.

1991-08-01

66

Wave-driven Countercurrent Plasma Centrifuge  

SciTech Connect

A method for driving rotation and a countercurrent flow in a fully ionized plasma centrifuge is described. The rotation is produced by radiofrequency waves near the cyclotron resonance. The wave energy is transferred into potential energy in a manner similar to the ? channeling effect. The countercurrent flow may also be driven by radiofrequency waves. By driving both the rotation and the flow pattern using waves instead of electrodes, physical and engineering issues may be avoided.

A.J. Fetterman and N.J. Fisch

2009-03-20

67

An innovative ultra-capacitor driven shape memory alloy actuator with an embedded control system  

NASA Astrophysics Data System (ADS)

In this paper, an innovative ultra-capacitor driven shape memory alloy (SMA) actuator with an embedded control system is proposed targeting high power high-duty cycle SMA applications. The ultra-capacitor, which is capable of delivering massive amounts of instantaneous current in a compact dimension for high power applications, is chosen as the main component of the power supply. A specialized embedded system is designed from the ground up to control the ultra-capacitor driven SMA system. The control of the ultra-capacitor driven SMA is different from that of a regular constant voltage powered SMA system in that the energy and the voltage of the ultra-capacitor decrease as the system load increases. The embedded control system is also different from a computer-based control system in that it has limited computational power, and the control algorithm has to be designed to be simple while effective so that it can fit into the embedded system environment. The problem of a variable voltage power source induced by the use of the ultra-capacitor is solved by using a fuzzy PID (proportional integral and derivative) control. The method of using an ultra-capacitor to drive SMA actuators enabled SMA as a good candidate for high power high-duty cycle applications. The proposed embedded control system provides a good and ready-to-use solution for SMA high power applications.

Li, Peng; Song, Gangbing

2014-08-01

68

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

69

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

70

Effect of dielectric barrier discharge plasma actuators on non-equilibrium hypersonic flows  

NASA Astrophysics Data System (ADS)

A numerical study employing discontinuous Galerkin method demonstrating net surface heat reduction for a cylindrical body in Mach 17 hypersonic flow is presented. This application focuses on using sinusoidal dielectric barrier discharge plasma actuators to inject momentum near the stagnation point. A 5 species finite rate air chemistry model completes the picture by analyzing the effect of the actuator on the flow chemistry. With low velocity near the stagnation point, the plasma actuator sufficiently modifies the fluid momentum. This results in redistribution of the integrated surface heating load on the body. Specifically, a particular configuration of normally pinching plasma actuation is predicted to reduce the surface heat flux at the stagnation point. An average reduction of 0.246% for the integrated and a maximum reduction of 7.68% are reported for the surface heat flux. The temperature contours in the fluid flow (with maximum temperature over 12 000 K) are pinched away from the stagnation point, thus resulting in reduced thermal load. Plasma actuation in this configuration also affects the species concentration distribution near the wall, in addition to the temperature gradient. The combined effect of both, thus results in an average reduction of 0.0986% and a maximum reduction of 4.04% for non-equilibrium calculations. Thus, this study successfully demonstrates the impact of sinusoidal dielectric barrier discharge plasma actuation on the reduction of thermal load on a hypersonic body.

Bhatia, Ankush; Roy, Subrata; Gosse, Ryan

2014-10-01

71

Comparison of plasma treatment and sandblast preprocessing for IPMC actuator  

NASA Astrophysics Data System (ADS)

As a new kind of ionic-driven smart materials, ionic polymer metal composite (IPMC ) is normally fabricated by depositing noble metal (gold, platinum, palladium etc.) on both sides of base membrane (Nafion, Flemion etc.) and shows large bending deflection under low voltage. In the process of fabricating IPMC, surface roughening of base membrane has a significant effect on the performance of IPMC. At present, there are many ways to roughen the base membrane, including physical and chemical ways. In this paper, we analyze the effects of different surface treatment time by plasma etching on surface resistance and mechanical properties of IPMCs fabricated by the treated base membranes. Experimental results show that the base membrane treated by plasma etching displays uniform surface roughness, consequently reducing IPMC's surface resistance effectively and forming more uniform and homogeneous external and penetrative electrodes. However, due to the use of reactive gas, the plasma treatment leads to complex chemical reaction on Nafion surface, changing element composition and material properties and resulting in the performance degradation of IPMC. And sandblast way should be adopted and improved without any changes on element and material structure.

Zhang, Chi; Chen, Hualing; Wang, Yanjie; Wang, Yongquan; Jia, Shuhai

2014-03-01

72

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

NASA Astrophysics Data System (ADS)

This paper reports experimental results on using steady and unsteady plasma aerodynamic actuation to control the corner separation, which forms over the suction surface and end wall corner of a compressor cascade blade passage. Total pressure recovery coefficient distribution was adopted to evaluate the corner separation. Corner separation causes significant total pressure loss even when the angle of attack is 0°. Both steady and unsteady plasma aerodynamic actuations suppress the corner separation effectively. The control effect obtained by the electrode pair at 25% chord length is as effective as that obtained by all four electrode pairs. Increasing the applied voltage improves the control effect while it augments the power requirement. Increasing the Reynolds number or the angle of attack makes the corner separation more difficult to control. The unsteady actuation is much more effective and requires less power due to the coupling between the unsteady actuation and the separated flow. Duty cycle and excitation frequency are key parameters in unsteady plasma flow control. There are thresholds in both the duty cycle and the excitation frequency, above which the control effect saturates. The maximum relative reduction in total pressure loss coefficient achieved is up to 28% at 70% blade span. The obvious difference between steady and unsteady actuation may be that wall jet governs the flow control effect of steady actuation, while much more vortex induced by unsteady actuation is the reason for better control effect.

Li, Ying-Hong; Wu, Yun; Zhou, Min; Su, Chang-Bing; Zhang, Xiong-Wei; Zhu, Jun-Qiang

2010-06-01

73

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

74

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

75

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

76

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

E-print Network

densities (1 A=m2 ) [9­11]. DBD discharges generate low (room) temperature plasmas and rely on the EHD on the generation of a Lorentz force on the bulk flow owing to the interaction of electrical currentsCharacterization of a Direct-Current Glow Discharge Plasma Actuator in Low-Pressure Supersonic Flow

Raja, Laxminarayan L.

77

Power consumption, discharge capacitance and light emission as measures for thrust production of dielectric barrier discharge plasma actuators  

SciTech Connect

A new procedure of determining the time resolved capacitance of a plasma actuator during operation is introduced, representing a simple diagnostic tool that provides insight into the phenomenological behavior of plasma actuators. The procedure is demonstrated by presenting example correlations between consumed electrical energy, size of the plasma region, and the operating voltage. It is shown that the capacitance of a plasma actuator is considerably increased by the presence of the plasma; hence a system that has previously been impedance matched can be considerably de-tuned when varying the operating voltage of the actuator. Such information is fundamental for any attempts to increase the energy efficiency of plasma-actuator systems. A combined analysis of the capacitance, light emission, size of the plasma region, force production, and power consumption is presented.

Kriegseis, J. [Institute of Fluid Mechanics and Aerodynamics, Technische Universitaet Darmstadt, Flughafenstr. 19, D-64347 Greisheim (Germany); Grundmann, S. [Center of Smart Interfaces, Technische Universitaet Darmstadt, Flughafenstr. 19, D-64347 Greisheim (Germany); Tropea, C. [Institute of Fluid Mechanics and Aerodynamics, Technische Universitaet Darmstadt, Flughafenstr. 19, D-64347 Greisheim (Germany); Center of Smart Interfaces, Technische Universitaet Darmstadt, Flughafenstr. 19, D-64347 Greisheim (Germany)

2011-07-01

78

A tunable millimeter-wave phase shifter driven by dielectric elastomer actuators  

NASA Astrophysics Data System (ADS)

We present the successful operation of the first dielectric elastomer actuator (DEA) driven tunable millimeter-wave phase shifter. The development of dynamically reconfigurable microwave/millimeter-wave (MW/MMW) antenna devices is becoming a prime need in the field of telecommunications and sensing. The real time updating of antenna characteristics such as coverage or operation frequency is particularly desired. However, in many circumstances currently available technologies suffer from high EM losses, increased complexity and cost. Conversely, reconfigurable devices based on DEAs offer low complexity, low electromagnetic (EM) losses and analogue operation. Our tunable phase shifter consists of metallic strips suspended a fixed distance above a coplanar waveguide (CPW) by planar DEAs. The planar actuators displace the metallic strips (10 mm in length) in-plane by 500 ?m, modifying the EM field distribution, resulting in the desired phase shift. The demanding spacing (50 +/-5 ?m between CPW and metallic strips) and parallel alignment criteria required for optimal device operation are successfully met in our device design and validated using bespoke methods. Our current device, approximately 60 mm x 60 mm in planar dimensions, meets the displacement requirements and we observe a considerable phase shift (~95° at 25 GHz) closely matching numerical simulations. Moreover, our device achieves state of the art performance in terms of phase shift per EM loss ~235°/dB (35 GHz), significantly out performing other phase shifter technologies, such as MMIC phase shifters.

Araromi, O. A.; Romano, P.; Rosset, S.; Perruisseau-Carrier, J.; Shea, H. R.

2014-03-01

79

TEST RESULTS FOR A STIRLING-ENGINE-DRIVEN HEAT-ACTUATED HEAT PUMP BREADBOARD SYSTEM T.M. Moynihan  

E-print Network

849044 TEST RESULTS FOR A STIRLING-ENGINE-DRIVEN HEAT-ACTUATED HEAT PUMP BREADBOARD SYSTEM T and hydraulic transmission (Figure 2). Engine power is transferred to the i A Free-Piston Stirling Engine prime's performance/ Stirling Engine - Spring operation over the specified operating range, Driver -'i. i, C

Oak Ridge National Laboratory

80

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

81

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

82

Online-characterization of dielectric barrier discharge plasma actuators for optimized efficiency of aerodynamical flow control applications  

NASA Astrophysics Data System (ADS)

The impact of fluctuating and transient kinematic and thermodynamic airflow conditions on the performance of dielectric barrier discharge (DBD) plasma actuators is demonstrated. A novel online-characterization and control approach is introduced, revealing the possibility of compensating for impaired discharge performance due to changing airflow scenarios during actuator operation. The goal of controlling the plasma actuator performance online and in situ is achieved and successfully demonstrated.

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

2011-06-01

83

Study of a pseudo-empirical model approach to characterize plasma actuators  

NASA Astrophysics Data System (ADS)

The use of plasma actuators is a recent technology that imposes a localized electric force that is used to control air flows. A suitable representation of actuation enables to undertake plasma actuators optimization, to design flow-control strategies, or to analyse the flow stabilization that can be attained by plasma forcing. The problem description may be clearly separated in two regions. An outer region, where the fluid is electrically neutral, in which the flow is described by the Navier-Stokes equation without any forcing term. An inner region, that forms a thin boundary layer, where the fluid is ionized and electric forces are predominant. The outer limit of the inner solution becomes the boundary condition for the outer problem. The outer problem can then be solved with a slip velocity that is issued from the inner solution. Although the solution for the inner problem is quite complex it can be contoured proposing pseudo-empirical models where the slip velocity of the outer problem is determined indirectly from experiments. This pseudo-empirical model approach has been recently tested in different cylinder flows and revealed quite adapted to describe actuated flow behaviour. In this work we determine experimentally the influence of the duty cycle on the slip velocity distribution. The velocity was measured by means of a pitot tube and flow visualizations of the starting vortex (i.e. the induced flow when actuation is activated in a quiescent air) have been done by means of the Schlieren technique. We also performed numerical experiments to simulate the outer region problem when actuation is activated in a quiescent air using a slip velocity distribution as a boundary condition. The experimental and numerical results are in good agreement showing the potential of this pseudo-empirical model approach to characterize the plasma actuation.

Marziali Bermudez, M.; Sosa, R.; Grondona, D.; Márquez, A.; Kelly, H.; Artana, G.

2011-05-01

84

Physics of Laser-driven plasma-based acceleration  

SciTech Connect

The physics of plasma-based accelerators driven by short-pulse lasers is reviewed. This includes the laser wake-field accelerator, the plasma beat wave accelerator, the self-modulated laser wake-field accelerator, and plasma waves driven by multiple laser pulses. 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 direction, electron dephasing, laser pulse energy depletion, as well as 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 plasmas with preformed density channels. Instabilities relevant to intense short-pulse laser-plasma interactions, such as Raman, self-modulation, and hose instabilities, are discussed. Recent experimental results are summarized.

Esarey, Eric; Schroeder, Carl B.

2003-06-30

85

Simulations of Serpentine Plasma Actuators in a Laminar Boundary Layer  

E-print Network

as components of active and passive flow control systems. One concern with in applying these actuators of 11 American Institute of Aeronautics and Astronautics #12; Velocity ratio I Integrated value. Introduction Boundary layer control is one aspect of fluid dynamics that is becoming increasingly more

Roy, Subrata

86

Pulse-driven magnetostatic micro-actuator array based on ultrasoft elastomeric membranes for active surface applications  

NASA Astrophysics Data System (ADS)

An array of pulse-driven magnetostatic micro-actuators with 2 mm pitch is proposed for highly deformable active surfaces. A wide range of applications can benefit from such devices, from droplet manipulation and active flow control to tactile display, for which this device was initially designed. This design ensures robustness, ease of fabrication and mass production compatibility. The device is composed of an array of 4 × 4 highly resistant elastomeric membranes achieved using microfabrication techniques. The magnetostatic actuation system is based on the interaction between a miniature coil and a SmCo micro-magnet. This mechanism was optimized by the finite-element method, leading to the introduction of different ferromagnetic circuits. Mechanical characterizations were achieved by laser interferometry. The micro-actuators can be used either in continuous mode or in pulse mode, allowing wide bandwidth, from dc to 1.5 kHz, and vibration amplitudes up to 150 ?m for instantaneous forces of 30 mN. The device has good actuation homogeneity with ±20% amplitude variations between its actuators; low crosstalk (<5%) was also demonstrated. Finally, an improved actuation design benefiting from electroplated NiFe thin films is proposed and characterized, increasing performances (forces and displacements) by 50%.

Streque, J.; Talbi, A.; Pernod, P.; Preobrazhensky, V.

2012-09-01

87

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

88

High-lift airfoil trailing edge separation control using a single dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

Control of flow separation from the deflected flap of a high-lift airfoil up to Reynolds numbers of 240,000 (15 m/s) is explored using a single dielectric barrier discharge (DBD) plasma actuator near the flap shoulder. Results show that the plasma discharge can increase or reduce the size of the time-averaged separated region over the flap depending on the frequency of actuation. High-frequency actuation, referred to here as quasi-steady forcing, slightly delays separation while lengthening and flattening the separated region without drastically increasing the measured lift. The actuator is found to be most effective for increasing lift when operated in an unsteady fashion at the natural oscillation frequency of the trailing edge flow field. Results indicate that the primary control mechanism in this configuration is an enhancement of the natural vortex shedding that promotes further momentum transfer between the freestream and separated region. Based on these results, different modulation waveforms for creating unsteady DBD plasma-induced flows are investigated in an effort to improve control authority. Subsequent measurements show that modulation using duty cycles of 50-70% generates stronger velocity perturbations than sinusoidal modulation in quiescent conditions at the expense of an increased power requirement. Investigation of these modulation waveforms for trailing edge separation control similarly shows that additional increases in lift can be obtained. The dependence of these results on the actuator carrier and modulation frequencies is discussed in detail.

Little, Jesse; Nishihara, Munetake; Adamovich, Igor; Samimy, Mo

2010-03-01

89

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

90

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

91

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

92

RESEARCH ARTICLE The use of plasma actuators for bluff body broadband  

E-print Network

the attention of communities that live near airports to the problem of noise pollution (Raman and Mc (Crighton 1991; Macaraeg 1998). Since airframe noise is normally caused by the interactions betweenRESEARCH ARTICLE The use of plasma actuators for bluff body broadband noise control Yong Li · Xin

Huang, Xun

93

Modeling plasma actuators with air chemistry for effective flow control Kunwar Pal Singh and Subrata Roya  

E-print Network

Modeling plasma actuators with air chemistry for effective flow control Kunwar Pal Singh modifications of air flowing around flat plates and air craft wings have been documented both experi- mentally several benefits in active flow control appli- cations, including absence of moving parts, rapid on-off de

Roy, Subrata

94

American Institute of Aeronautics and Astronautics Induced Flow from Serpentine Plasma Actuators Acting in  

E-print Network

American Institute of Aeronautics and Astronautics 1 Induced Flow from Serpentine Plasma Actuators-957 Copyright © 2011 by the Authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. #12;American Institute of Aeronautics and Astronautics 2 Figure 1. Generic (standard) linear

Roy, Subrata

95

American Institute of Aeronautics and Astronautics On Multi-Barrier Plasma Actuators  

E-print Network

American Institute of Aeronautics and Astronautics 1 On Multi-Barrier Plasma Actuators Ryan January 2011, Orlando, Florida AIAA 2011-958 Copyright © 2011 by the Authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. #12;American Institute of Aeronautics

Roy, Subrata

96

American Institute of Aeronautics and Astronautics Novel Multi-Barrier Plasma Actuators for Increased Thrust  

E-print Network

American Institute of Aeronautics and Astronautics 1 Novel Multi-Barrier Plasma Actuators by the American Institute of Aeronautics and Astronautics, Inc., with permission. #12;American Institute of Aeronautics and Astronautics 2 and 1-20 kHz, respectively. Such a high potential difference weakly ionizes

Roy, Subrata

97

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

NASA Astrophysics Data System (ADS)

Experiments were conducted for the flow in a straight-walled 3D diffuser fed by a fully developed turbulent duct flow. Previous work found that this diffuser has a stable 3D separation bubble whose configuration is affected by the secondary flows in the upstream duct. Dielectric barrier discharge plasma actuators were used to produce low-momentum wall jets to determine if the separation behavior could be modified by weak forcing. Actuators producing a streamwise force along the wall where separation occurred in the baseline flow had a relatively small effect. However, spanwise acting plasma actuators that produced a pair of streamwise vortices in the inlet section of the diffuser had a strong effect on the diffuser pressure recovery. The diffuser performance could be either improved or degraded depending on the actuation parameters, including the actuator modulation frequency, duty cycle, and drive voltage. Velocity profile measurements in the diffuser inlet showed that the streamwise vortices affect the uniformity of the streamwise mean velocity accounting for some of the performance changes. However, phase-locked hotwire measurements at the diffuser exit indicate that the periodic nature of the forcing also plays an important role for cases with enhanced pressure recovery.

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

2011-01-01

98

Effect of external flow velocity on momentum transfer of dielectric barrier discharge plasma actuators  

NASA Astrophysics Data System (ADS)

An experimental study is performed towards identifying cross-talk effects between DBD plasma actuators and external flow. An actuator is positioned in a boundary layer operated in a range of free stream velocities from 0 to 60 m/s, and tested both in counter-flow and co-flow forcing configurations. Electrical measurements are used for estimating the power consumption and the discharge formation is visualized using a CCD camera. The actuator's force is measured using a sensitive load cell. Results show the power consumption is constant for different flow velocities and actuator configurations. The plasma light emission is constant for co-flow forcing but shows a trend of increasing intensity with counter-flow forcing for increasing free stream velocities. The measured force is constant for free stream velocities larger than 20 m/s, with same magnitude and opposite direction for the counter-flow and co-flow configurations. In quiescent conditions, the measured force is smaller due to the change in wall shear force by the induced wall-jet. An analytical model is presented to estimate the influence of external flow on the actuator force. It is based on conservation of momentum through the ion-neutral collisional process while including the contribution of the wall shear force. Satisfactory agreement is found between the prediction of the model and experimental data at different external flow velocities.

Pereira, Ricardo; Ragni, Daniele; Kotsonis, Marios

2014-09-01

99

One-equation modeling and validation of dielectric barrier discharge plasma actuator thrust  

NASA Astrophysics Data System (ADS)

Dielectric barrier discharge (DBD) plasma actuators with an asymmetric electrode configuration can generate a wall-bounded jet without mechanical moving parts, which require considerable modifications of existing aeronautical objects and which incur high maintenance costs. Despite this potential, one factor preventing the wider application of such actuators is the lack of a reliable actuator model. It is difficult to develop such a model because calculating the ion-electric field and fluid interaction consume a high amount calculation effort during the numerical analysis. Thus, the authors proposed a semi-empirical model which predicted the thrust of plasma actuators with a simple equation. It gave a numeric thrust value, and we implemented the value on a computational fluid dynamics (CFD) solver to describe the two-dimensional flow field induced by the actuator. However, the model had a narrow validation range, depending on the empirical formula, and it did not fully consider environment variables. This study presents an improved model by replacing the empirical formulae in the previous model with physical equations that take into account physical phenomena and environmental variables. During this process, additional operation parameters, such as pressure, temperature and ac waveforms, are newly taken to predict the thrust performance of the actuators with a wider range of existing parameters, the thickness of the dielectric barrier, the exposed electrode, the dielectric constant, the ac frequency and the voltage amplitude. Thrust prediction curves from the model are compared to those of earlier experimental results, showing that the average error is less than 5% for more than one hundred instances of data. As in the earlier work, the predicted thrust value is implemented on a CFD solver, and two-dimensional wall-jet velocity profiles induced by the actuator are compared to the previous experimental results.

Yoon, Jae-San; Han, Jae-Hung

2014-10-01

100

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

101

Generation of prescribed strain waves in an elastic bar by use of piezoelectric actuators driven by a linear power amplifier  

Microsoft Academic Search

The problem of generating prescribed strain waves in an elastic bar by means of a pair of piezoelectric actuators driven in phase by a linear power amplifier was considered theoretically and experimentally. The power amplifier was characterized by its DC voltage gain and 3dB cut-off frequency unloaded, and by its output resistance and inductance. With the assumption of one-dimensional (1D)

A. Jansson; U. Valdek; B. Lundberg

2007-01-01

102

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

Microsoft Academic Search

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

Sangki Lee; Kwang J. Kim

2006-01-01

103

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

104

Landau damping of a driven plasma wave from laser pulses  

SciTech Connect

The interaction between a laser pulse and a driven plasma wave with a phase velocity approaching the speed of light is studied, and our investigation is focused on the Gaussian laser pulse. It is demonstrated that when the resonance condition between the plasma wave and the laser pulse is satisfied, the Landau damping phenomenon of the plasma wave originated from the laser pulse will emerge. The dispersion relations for the plasma waves in resonance and non-resonance regions are obtained. It is proved that the Landau damping rate for a driven plasma wave is {gamma}>0 in the resonance region, so the laser pulse can produce an inverse damping effect, namely Landau growth effect, which leads an instability for the plasma wave. The Landau growth means that the energy is transmitted from the laser pulse to the plasma wave, which could be an effective process for enhancing the plasma wave.

Bu Zhigang [Department of Physics, Shanghai University, Shanghai 200444 (China); Ji Peiyong [Department of Physics, Shanghai University, Shanghai 200444 (China); The Shanghai Key Lab of Astrophysics, Shanghai 200234 (China)

2012-01-15

105

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

106

Performance enhancement of IPMC actuator by plasma surface treatment  

Microsoft Academic Search

IPMC (ionic polymer metal composite) is composed of ionic polymer and metal electrodes on both surfaces of the polymer. In this study, we changed the surface morphology of the ionic polymer by using plasma treatment. Plasma treatment made needle-shaped microstructures on the surface of the polymer and the microstructures helped to form a thicker uniform metal electrode which is deposited

Seong Jun Kim; In Taek Lee; Yong Hyup Kim

2007-01-01

107

1316 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 36, NO. 4, AUGUST 2008 Schlieren Imaging of Flow Actuation Produced  

E-print Network

comprises the supersonic free stream flowing parallel to a flat plate and abruptly turned by a 30 wedge Actuation Produced by Direct-Current Surface Glow Discharge in Supersonic Flows Jichul Shin, Noel T. Clemens. Index Terms--DC sheath, dc surface discharge, electrostatic force, plasma actuation, supersonic flow

Raja, Laxminarayan L.

108

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

109

Nanosecond-pulsed plasma actuation in quiescent air and laminar boundary layer  

NASA Astrophysics Data System (ADS)

An experimental investigation of the working principles of a nanosecond-pulsed dielectric barrier discharge (ns-DBD) plasma actuator has been conducted. Special emphasis is given on the thermal effects accompanying the rapid deposition of energy associated with this kind of actuation. A ns-DBD plasma actuator has been operated in quiescent air conditions as well as in a flat plate laminar boundary layer, with external flow velocity of 5 and 10 m s-1. Schlieren imaging and particle image velocimetry have been used to characterize the actuation. Additionally, the back-current shunt technique has been used for current measurements, from which energy input (per pulse) is calculated. Cases of 10-, 20- and 50-pulse bursts are tested. Schlieren imaging in still air conditions shows the formation of a high-temperature region in the vicinity of the discharge volume. The spatial extent of the visible ‘hot spot’ depends upon the number of pulses within the burst, following a power law. Schlieren imaging of the span-wise effect of the plasma actuator reveals weak compression waves originating from the loci of discharge filaments. The thermal ‘hot spots’ exhibit significant three-dimensionality. Particle image velocimetry is used to measure the velocity field resulting from the ns-DBDs acting on a laminar boundary layer. The disturbance leads to formation of a Tollmien-Schlichting wave train, with spectral content in good agreement with linear stability theory. It is observed that the group length of the wave train is proportional to the number of pulses within the burst.

Correale, G.; Michelis, T.; Ragni, D.; Kotsonis, M.; Scarano, F.

2014-03-01

110

High Mach Number Leading-edge Flow Separation Control using AC DBD Plasma Actuators  

NASA Astrophysics Data System (ADS)

Wind tunnel experiments were conducted to quantify the effectiveness of alternating current dielectric barrier discharge flow control actuators to suppress leading-edge stall on a NASA energy efficient transport airfoil at compressible freestream speeds. The objective of this research was to increase lift, reduce drag, and improve the stall characteristics of the supercritical airfoil near stall by flow reattachment at relatively high Mach and Reynolds numbers. In addition, the effect of unsteady (or duty cycle) operation on these aerodynamic quantities was also investigated. The experiments were conducted for a range of Mach numbers between 0.1 and 0.4. corresponding to a Reynolds number range of 560,000 through 2,260,000. Lift, drag, quarter chord moment, and suction side pressures were measured near stall for baseline, steady actuation, and a scan of nondimensional duty cycle frequencies. The results show that the plasma actuators were effective at reattaching the leading-edge separated flow as evidenced by the increase in maximum lift coefficient and stall angle (as much as 2.5 degrees). The experiment also showed that lift was increased the most when the plasma actuator was operated unsteady with a nondimensional frequency of unity.

Kelley, Christopher; Bowles, Patrick; Cooney, John; He, Chuan; Corke, Thomas; Osborne, Bradley; Silkey, Joseph; Zehnle, Joseph

2011-11-01

111

Plasma Jet Driven Magneto-Inertial Fusion (PJMIF)  

E-print Network

for collisionless shock experiments, funded by LANL-LDRD: Higher jet/liner energies can also potentially have fusionPlasma Jet Driven Magneto-Inertial Fusion (PJMIF) Scott Hsu Physics Division, LANL Fusion Power National Security, LLC for NNSA LA-UR-11-07030 #12;Plasma jet experiments can provide cm

112

Micro Actuators Electrostatic actuator  

E-print Network

·Piezoelectric actuator ·Shape memory alloy actuator ·Pneumatic actuator #12;Pneumatic Actuators Applications. #12;Pneumatic Microvalve ·External pneumatic power is required to actuate a actuator. ·Sustain high

Leu, Tzong-Shyng "Jeremy"

113

Energy characteristics of an explosively driven plasma compressor  

Microsoft Academic Search

Conclusions  Two basic parameters affect the energy characteristics of an explosively driven plasma compressor: the fill density and the\\u000a ratio of the mass of explosive to the plate mass. Despite the increase in plasma energy, as the filling density in the compression\\u000a chamber is increased, the specific energy of the plasma decreases due to the arrival of impurities from the chamber

V. I. Kirko

1979-01-01

114

Stall control at high angle of attack with plasma sheet actuators  

Microsoft Academic Search

We analyzed the modifications of the airflow around an NACA 0015 airfoil when the flow was perturbed with electrohydrodynamic\\u000a forces. The actuation was produced with a plasma sheet device (PSD) consisting in two bare electrodes flush mounted on the\\u000a surface of the wing profile operated to obtain a discharge contouring the body in the inter-electrode space. We analyze the\\u000a influence

Roberto Sosa; Guillermo Artana; Eric Moreau; Gérard Touchard

2007-01-01

115

One-dimensional analytical model development of a plasma-based actuator  

NASA Astrophysics Data System (ADS)

This dissertation provides a method for modeling the complex, multi-physics, multi-dimensional processes associated with a plasma-based flow control actuator, also known as the SparkJet, by using a one-dimensional analytical model derived from the Euler and thermodynamic equations, under varying assumptions. This model is compared to CFD simulations and experimental data to verify and/or modify the model where simplifying assumptions poorly represent the real actuator. The model was exercised to explore high-frequency actuation and methods of improving actuator performance. Using peak jet momentum as a performance metric, the model shows that a typical SparkJet design (1 mm orifice diameter, 84.8 mm3 cavity volume, and 0.5 J energy input) operated over a range of frequencies from 1 Hz to 10 kHz shows a decrease in peak momentum corresponding to an actuation cutoff frequency of 800 Hz. The model results show that the cutoff frequency is primarily a function of orifice diameter and cavity volume. To further verify model accuracy, experimental testing was performed involving time-dependent, cavity pressure and arc power measurements as a function of orifice diameter, cavity volume, input energy, and electrode gap. The cavity pressure measurements showed that pressure-based efficiency ranges from 20% to 40%. The arc power measurements exposed the deficiency in assuming instantaneous energy deposition and a calorically perfect gas and also showed that arc efficiency was approximately 80%. Additional comparisons between the pressure-based modeling and experimental results show that the model captures the actuator dependence on orifice diameter, cavity volume, and input energy but over-estimates the duration of the jet flow during Stage 2. The likely cause of the disagreement is an inaccurate representation of thermal heat transfer related to convective heat transfer or heat loss to the electrodes.

Popkin, Sarah Haack

116

Active control of massively separated high-speed/base flows with electric arc plasma actuators  

NASA Astrophysics Data System (ADS)

The current project was undertaken to evaluate the effects of electric arc plasma actuators on high-speed separated flows. Two underlying goals motivated these experiments. The first goal was to provide a flow control technique that will result in enhanced flight performance for supersonic vehicles by altering the near-wake characteristics. The second goal was to gain a broader and more sophisticated understanding of these complex, supersonic, massively-separated, compressible, and turbulent flow fields. The attainment of the proposed objectives was facilitated through energy deposition from multiple electric-arc plasma discharges near the base corner separation point. The control authority of electric arc plasma actuators on a supersonic axisymmetric base flow was evaluated for several actuator geometries, frequencies, forcing modes, duty cycles/on-times, and currents. Initially, an electric arc plasma actuator power supply and control system were constructed to generate the arcs. Experiments were performed to evaluate the operational characteristics, electromagnetic emission, and fluidic effect of the actuators in quiescent ambient air. The maximum velocity induced by the arc when formed in a 5 mm x 1.6 mm x 2 mm deep cavity was about 40 m/s. During breakdown, the electromagnetic emission exhibited a rise and fall in intensity over a period of about 340 ns. After breakdown, the emission stabilized to a near-constant distribution. It was also observed that the plasma formed into two different modes: "high-voltage" and "low-voltage". It is believed that the plasma may be switching between an arc discharge and a glow discharge for these different modes. The two types of plasma do not appear to cause substantial differences on the induced fluidic effects of the actuator. In general, the characterization study provided a greater fundamental understanding of the operation of the actuators, as well as data for computational model comparison. Preliminary investigations of actuator geometry in the supersonic base flow determined that inclined cavity and normal cavity actuators positioned on the base near the base edge could produce significant disturbances in the shear layer. The disturbances were able to be tracked in time with phase-locked schlieren imaging and particle image velocimetry (PIV). The final set of flow control experiments were therefore performed with an eight-actuator base using the inclined cavity actuator geometry. The actuators were able to cause moderate influences on the axisymmetric shear layer velocity profile and base pressure. The most substantial changes to the shear layer and base pressure were noted for the highest current and duty cycle tests. At 1 A and 20% duty cycle, the base pressure was reduced by 3.5%. Similar changes were noted for all modes and a range of frequencies from about 10-30 kHz. Increases in duty cycle between 4% and 20% caused a nearly linear decrease in base pressure. Analysis of the shear layer velocity profiles acquired through PIV show a local thickening of the shear layer in the region of the disturbances caused by the actuator. A slight increase in thickness was also observed away from the disturbance. Disturbances were able to be tracked at all frequencies and translated along the shear layer at a convective velocity of 430 +/- 20 m/s. A fairly clear trend of increasing velocity disturbance amplitude correlating to increasing base pressure changes was noted. Moreover, the ability of the disturbances to stay well organized further down the shear layer also appears to be a significant factor in the actuators' effect on base pressure. Consistent with these observations, it appears that increased duty cycle causes increased shear layer disturbance amplitudes. The use of PIV has enabled substantial insight to be gained into the effects of the actuators on the ensemble-averaged flow field and on the variability of the instantaneous flow field with and without control. A sensitive bimodal recirculation region behavior was found in the no-control flow field tha

DeBlauw, Bradley G.

117

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

118

Shockwave—boundary layer interaction control by plasma aerodynamic actuation: An experimental investigation  

NASA Astrophysics Data System (ADS)

The potential of controlling shockwave—boundary layer interactions (SWBLIs) in air by plasma aerodynamic actuation is demonstrated. Experiments are conducted in a Mach 3 in-draft air tunnel. The separation-inducing shock is generated with a diamond-shaped shockwave generator located on the wall opposite to the surface electrodes, and the flow properties are studied with schlieren imaging and static wall pressure probes. The measurements show that the separation phenomenon is weakened with the plasma aerodynamic actuation, which is observed to have significant control authority over the interaction. The main effect is the displacement of the reflected shock. Perturbations of incident and reflected oblique shocks interacting with the separation bubble in a rectangular cross section supersonic test section are produced by the plasma actuation. This interaction results in a reduction of the separation bubble size, as detected by phase-lock schlieren images. The measured static wall pressure also shows that the separation-inducing shock is restrained. Our results suggest that the boundary layer separation control through heating is the primary control mechanism.

Sun, Quan; Cui, Wei; Li, Ying-Hong; Cheng, Bang-Qin; Jin, Di; Li, Jun

2014-07-01

119

Simulation of an asymmetric single dielectric barrier plasma actuator  

SciTech Connect

Continuity equations governing electron and ion density are solved with Poisson's equation to obtain spatial and temporal profiles of electron density, ion density, and voltage. The motion of electrons and ions results in charge separation and generation of an electrostatic electric field. Electron deposition downstream of the overlap region of the electrode results in formation of a virtual negative electrode that always attracts the charge separation. The value of charge separation e(n{sub i}-n{sub e}) and the force per volume F=e(n{sub i}-n{sub e})E have been obtained near the dielectric surface for the 50th cycle. Domain integration of the force F=e(n{sub i}-n{sub e})E has been obtained for different plasma densities, frequencies, and rf voltage wave forms. The time average of the x force is positive and the y force is negative over the domain; therefore there is an average net force on the plasma in the positive x and negative y directions. This will result in a moving wave of plasma over the dielectric surface in the positive x direction, which can find application in flow control.

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

2005-10-15

120

Design and analysis of hydraulically driven actuation system For a parabolic solar trough  

E-print Network

This thesis documents Katarina Popovic's contribution to the design of hydraulic cylinder actuation system for day to day solar trough sun tracking, a semester long project within 2.752 Development of Mechanical Products ...

Popovi?, Katarina, S.B. Massachusetts Institute of Technology

2013-01-01

121

Analytical Model for the Microwave Driven Double ICP Plasma Jet  

NASA Astrophysics Data System (ADS)

For many technical applications, microwave driven plasma jets are possible alternatives to conventional RF plasma sources. Their construction is uncomplicated and they have the advantages of small size and large electrical efficiency. The microwave driven double ICP plasma jet is a recently developed variant. The core of the device is a cavity resonator with a resonance frequency close to 2 GHz. In good approximation, the resonator can be described as a circuit of two cylindrical one-turn coils parallel to a planar capacitor. Inside the coils are ceramic tubes which contain the plasma. Electromagnetic fields in the bulk and sheath reagion can be computed based on Maxwell's equations and the cold plasma model considering boundary conditions and the electric field due to the source on metalic cavity. A comparison of the simulation results with experimental data is performed.

Arshadi, Ali; Eremin, Denis; Mussenbrock, Thomas; Brinkmann, Ralf Peter; Awakowicz, Peter; Porteanu, Horia-Eugen; Gesche, Roland; Wandel, Klaus

2012-10-01

122

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

123

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

124

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

125

Feedback control of slowly-varying transient growth by an array of plasma actuators  

NASA Astrophysics Data System (ADS)

Closed-loop feedback control of boundary layer streaks embedded in a laminar boundary layer and experiencing transient growth, which is inherent to bypass boundary layer transition, is experimentally investigated. Streaky disturbances are introduced by a spanwise array of cylindrical roughness elements, and a counter disturbance is provided by a spanwise array of plasma actuators, which are capable of generating spanwise-periodic counter rotating vortices in the boundary layer. Feedback is provided by a spanwise array of shear stress sensors. An input/output model of the system is obtained from measurements of the boundary layer response to steady forcing, and used to design and analyze a proportional-integral controller, which targets a specific spanwise wavenumber of the disturbance. Attention is directed towards a quasi-steady case in which the controller update is slower than the convective time scale. This choice enables addressing issues pertinent to sensing, actuation, and control strategy that are also relevant to the control of unsteady disturbances but without the full complexity of transient effects. The feedback controller and plasma actuators perform well, attenuating the streamwise streaks both in the vicinity of the sensors and farther downstream. The controller remains effective for a range of off-design flow conditions, such as when the free-stream velocity is varied.

Hanson, Ronald E.; Bade, Kyle M.; Belson, Brandt A.; Lavoie, Philippe; Naguib, Ahmed M.; Rowley, Clarence W.

2014-02-01

126

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

127

Attosecond Plasma Wave Dynamics in Laser-Driven Cluster Nanoplasmas  

NASA Astrophysics Data System (ADS)

We introduce a microscopic particle-in-cell approach that allows bridging the microscopic and macroscopic realms of laser-driven plasma physics. As a first application, resonantly driven cluster nanoplasmas are investigated. Our analysis reveals an attosecond plasma-wave dynamics in clusters with radii R?30nm. The plasma waves are excited by electrons recolliding with the cluster surface and travel toward the center, where they collide and break. In this process, energetic electron hot spots are generated along with highly localized attosecond electric field fluctuations, whose intensity exceeds the driving laser by more than 2 orders of magnitude. The ionization enhancement resulting from both effects generates a strongly nonuniform ion charge distribution. The observed nonlinear plasma-wave phenomena have a profound effect on the ionization dynamics of nanoparticles and offer a route to extreme nanoplasmonic field enhancements.

Varin, Charles; Peltz, Christian; Brabec, Thomas; Fennel, Thomas

2012-04-01

128

PUBLISHED VERSION The beam driven plasma neutralizer  

E-print Network

is the source of the plasma, is described. Its success depends on the confinement of the free electrons of a low technological risk, inherently reliable and will not require a significant R&D programme) on a fusion power plant is dependent upon the power efficiency that can be achieved for these systems

129

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

130

Model of a chopper-driven magnetic actuator in an electrohydraulic system  

Microsoft Academic Search

An electrohydraulic system is modeled using a version of the electric circuit analysis program SPICE. The input is a typical DC voltage source and the output is a hydraulic pressure and flow. Analogies between hydraulic circuits and electrical circuits are used, along with nonlinear tables obtained by electromagnetic finite element analysis of a magnetic actuator that operates a proportional hydraulic

John R. Brauer

2001-01-01

131

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

132

Influence of operating pressure on surface dielectric barrier discharge plasma aerodynamic actuation characteristics  

SciTech Connect

This letter reports an experimental study of surface dielectric barrier discharge plasma aerodynamic actuation characteristics' dependence on operating pressure. As the pressure decreases, the N{sub 2}(C {sup 3}{pi}{sub u}) rotational temperature decreases, while its vibrational temperature decreases initially and then increases. In addition, the discharge mode changes from a filamentary type to a glow type at 45 Torr. In the filamentary mode, the electron density decreases with pressure, while the electron temperature remains almost unchanged. In the glow mode, however, both the electron density and the electron temperature increase while the pressure decreases. The induced velocity shows a maximum value at 445 Torr.

Wu Yun; Li Yinghong; Jia Min; Song Huimin [Engineering College, Air Force Engineering University, Xi'an 710038 (China); Guo Zhigang; Zhu Ximing; Pu Yikang [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China)

2008-07-21

133

Proposed method for high-speed plasma density measurement in proton-driven plasma wakefield acceleration  

SciTech Connect

Recently a proton-bunch-driven plasma wakefield acceleration experiment using the CERN-SPS beam was proposed. Different types of plasma cells are under study, especially laser ionization, plasma discharge, and helicon sources. One of the key parameters is the spatial uniformity of the plasma density profile along the cell that has to be within < 1% of the nominal density (6 Multiplication-Sign 10{sup 14} cm{sup -3}). Here a setup based on a photomixing concept is proposed to measure the plasma cut-off frequency and determine the plasma density.

Tarkeshian, R.; Reimann, O.; Muggli, P. [Max-Planck-Institut fuer Physik, 80805 Munich (Germany)

2012-12-21

134

Large range dual-axis micro-stage driven by electrostatic comb-drive actuators This article has been downloaded from IOPscience. Please scroll down to see the full text article.  

E-print Network

Large range dual-axis micro-stage driven by electrostatic comb-drive actuators This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2013 J. Micromech-stage driven by electrostatic comb-drive actuators Mohammad Olfatnia, Leqing Cui, Pankaj Chopra and Shorya

Awtar, Shorya

135

Pre-distorted sinewave-driven parallel-plate electrostatic actuator for harmonic displacement  

Microsoft Academic Search

Harmonic displacement of a parallel-plate electrostatic actuator up to 50% of the static pull-in displacement has been achieved despite the non-linear voltage-to-displacement function using a driving voltage with a pre-distorted waveform. The microstructure is fabricated in an epi-poly process and the circuit is implemented in a CMOS process and designed for operation of the MEMS in a frequency range up

G. De Graaf; L. Mol; L. A. Rocha; E. Cretu; R. F. Wolffenbuttel

2005-01-01

136

Large range dual-axis micro-stage driven by electrostatic comb-drive actuators  

NASA Astrophysics Data System (ADS)

This paper presents a micro XY stage that employs electrostatic comb-drive actuators and achieves a bi-directional displacement range greater than 225 µm per motion axis. The proposed XY stage design comprises four rigid stages (ground, motion stage, and two intermediate stages) interconnected via flexure modules. The motion stage, which has two translational degrees of freedom, is connected to two independent single degree of freedom intermediate stages via respective parallelogram (P) transmission flexures. The intermediate stages are connected to the ground via respective clamped paired double parallelogram (C-DP-DP) guidance flexures. The C-DP-DP flexure, unlike conventional flexures such as the paired double parallelogram flexure (DP-DP), provides high bearing direction stiffness (Kb) while maintaining low motion direction stiffness (Km) over a large range of motion direction displacement. This helps delay the onset of sideways instability in the comb-drive actuators that are integrated with the intermediate stages, thereby offering a significantly greater actuation stroke compared to existing designs. The presented work includes closed-form stiffness analysis of the proposed micro-stage, finite elements simulation, and experimental measurements of its static and dynamic behavior.

Olfatnia, Mohammad; Cui, Leqing; Chopra, Pankaj; Awtar, Shorya

2013-10-01

137

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

138

Simple and inexpensive current-driven magnetic multipole plasma homogenizer  

SciTech Connect

Magnetic multipole plasma confinement geometries employing permanent magnets are commonly used to confine laboratory plasmas and improve uniformity. Here we describe the design and operation of a particularly simple and low-cost kind of current-driven multipole system that makes use of a similar magnetic field structure but does not require permanent magnets. The magnetic field is generated by current carrying wires attached to the inside wall of a cylindrical supporting structure to provide a magnetic field resembling that of permanent multipole magnetic homogenizers. We demonstrate the use of the current-driven homogenizer to improve the uniformity of the radial density profile of a vacuum arc generated metal plasma. Our configuration of metal plasma gun, macroparticle filter, and current-driven homogenizer was used for thin film deposition, and was able to produce a relatively homogeneous film thickness profile while maintaining a deposition rate comparable to that at the peak point of the freely expanded beam at the same location. (c) 2000 American Institute of Physics.

Machima, P. [Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)] [Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States); Bilek, M. M. M. [Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)] [Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States); Monteiro, O. R. [Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)] [Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States); Brown, I. G. [Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)] [Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)

2000-09-01

139

Rubber gas actuator driven by hydrogen storage alloy for in-pipe inspection mobile robot with flexible structure  

Microsoft Academic Search

The authors describe rubber actuators using a hydrogen storage alloy for an in-pipe inspection robot, which is capable of moving inside pipelines with inner diameter as small as 2 in. Rubber actuators with both stretching and shrinking capability are shown for realization of such a robot. The proposed robot uses twelve actuators, including six kinds of independently controlled actuators, so

Toshio FUKUDA; Hidemi HOSOKAI; Masahiro UEMURA

1989-01-01

140

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

141

Spin-gradient-driven light amplification in a quantum plasma.  

PubMed

It is shown that the gradient "free-energy" contained in equilibrium spin vorticity can cause electromagnetic modes, in particular the light wave, to go unstable in a spin quantum plasma of mobile electrons embedded in a neutralizing ion background. For densities characteristic of both the solid state and very high density astrophysical systems, the growth rates are sufficiently high to overcome the expected collisional damping. Preliminary results suggest a powerful spin-inhomogeneity driven mechanism for stimulating light amplification. PMID:23215196

Braun, Stefanie; Asenjo, Felipe A; Mahajan, Swadesh M

2012-10-26

142

Laser-driven plasma beat-wave propagation in a density-modulated plasma.  

PubMed

A laser-driven plasma beat wave, propagating through a plasma with a periodic density modulation, can generate two sideband plasma waves. One sideband moves with a smaller phase velocity than the pump plasma wave and the other propagates with a larger phase velocity. The plasma beat wave with a smaller phase velocity can accelerate modest-energy electrons to gain substantial energy and the electrons are further accelerated by the main plasma wave. The large phase velocity plasma wave can accelerate these electrons to higher energies. As a result, the electrons can attain high energies during the acceleration by the plasma waves in the presence of a periodic density modulation. The analytical results are compared with particle-in-cell simulations and are found to be in reasonable agreement. PMID:22181524

Gupta, Devki Nandan; Nam, In Hyuk; Suk, Hyyong

2011-11-01

143

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

NASA Astrophysics Data System (ADS)

Comprehensive understanding of energetic-ion-driven global instabilities such as Alfvén 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.; Ogawa, K.; Isobe, M.; Osakabe, M.; Spong, D. A.; Todo, Y.

2011-02-01

144

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

E-print Network

. Such force successfully controlled flow separation on airfoils at a high angle-of-attack, increased the lift-consistent multibody system of neutral oxygen species and its plasma. The equations governing the motion of charged,15 The actuator power can be reduced by 90% and its durability can be improved by operating it in an unsteady

Roy, Subrata

145

Forcing mechanisms of dielectric barrier discharge plasma actuators at carrier frequency of 625 Hz  

NASA Astrophysics Data System (ADS)

The forcing behavior of a dielectric barrier discharge (DBD) actuator is investigated experimentally using a time-resolved particle image velocimetry (PIV) system in conjunction with a phase shifting technique. The spatio-temporal evolution of the induced flowfield is accurately captured within one high voltage (HV) cycle allowing the calculation of the instantaneous velocity and acceleration. Additional voltage and current measurements provide the power consumption for each case. Four different applied voltage waveform shapes are independently tested, namely, sine, square, positive sawtooth, and negative sawtooth at fixed applied voltage (10 kVpp) and carrier frequency (625 Hz). The instantaneous flowfields reveal the effect of the plasma forcing during the HV cycle. Sine waveform provides large positive forcing during the forward stroke, with minimal but still positive forcing during the backward stroke. Square waveform provides strong and concentrated positive and negative forcing at the beginning of the forward and backward stroke, respectively. Positive sawtooth provides positive but weak forcing during both strokes while the negative sawtooth case produces observable forcing only during the forward stroke. Results indicate the inherent importance of negative ions on the force production mechanisms of DBD's. Furthermore, the revealed influence of the waveform shape on the force production can provide guidelines for the design of custom asymmetric waveforms for the improvement of the actuator's performance.

Kotsonis, M.; Ghaemi, S.

2011-12-01

146

Flow-control-induced vibrations for power generation using pulsed plasma actuators  

NASA Astrophysics Data System (ADS)

This paper describes flow-control-induced vibrations using pulsed dielectric barrier discharge plasma actuators, in which boundary layer separation on a structure is actively controlled to produce periodic loads that lead to its vibration. The concept is intended for energy generation and is demonstrated experimentally using a one-degree-of-freedom pivoted cylindrical body mounted vertically within a blow-down wind tunnel. Subcritical Reynolds numbers, less than 105, were considered where typical shedding frequencies were several times larger than the system natural frequency. Static deflection experiments were performed to determine the maximum imposed aerodynamic loads as a function of control parameters and these were complemented with flow-field measurements. Periodic loading of the cylinder was achieved by periodic modulation of the actuator. Large amplitude oscillations were observed when the modulation frequency was close to the system natural frequency. In contrast to natural vortex induced vibration, the large amplitude oscillations were achieved by alternating dynamic separation and attachment of the boundary layer. Estimation of the transient loads was performed using a system identification technique and the power generated by the system was estimated on the basis of a piecewise linear model. Peak estimated power coefficients were relatively small (0.042) but can be improved by increasing the lateral force coefficients and by proportionately increasing the system's physical size.

Greenblatt, David; Treizer, Alexander; Eidelman, Alexander; Mueller-Vahl, Hanns

2012-10-01

147

A New Type of Plasma Wakefield Accelerator Driven By Magnetowaves  

SciTech Connect

We present a new concept for a plasma wakefield accelerator driven by magnetowaves (MPWA). This concept was originally proposed as a viable mechanism for the 'cosmic accelerator' that would accelerate cosmic particles to ultra-high energies in the astrophysical setting. Unlike the more familiar plasma wakefield accelerator (PWFA) and the laser wakefield accelerator (LWFA) where the drivers, the charged-particle beam and the laser, are independently existing entities, MPWA invokes the high-frequency and high-speed whistler mode as the driver, which is a medium wave that cannot exist outside of the plasma. Aside from the difference in drivers, the underlying mechanism that excites the plasma wakefield via the ponderomotive potential is common. Our computer simulations show that under appropriate conditions, the plasma wakefield maintains very high coherence and can sustain high-gradient acceleration over many plasma wavelengths. We suggest that in addition to its celestial application, the MPWA concept can also be of terrestrial utility. A proof-of-principle experiment on MPWA would benefit both terrestrial and celestial accelerator concepts.

Chen, Pisin; /KIPAC, Menlo Park /Taiwan, Natl. Taiwan U.; Chang, Feng-Yin; Lin, Guey-Lin; /Taiwan, Natl. Chiao Tung U. /Taiwan, Natl. Taiwan U.; Noble, Robert J.; /SLAC; Sydora, Richard; /Alberta U.

2011-09-12

148

Design Considerations for Plasma Accelerators Driven by Lasers or Particle Beams  

SciTech Connect

Plasma accelerators may be driven by the ponderomotive force of an intense laser or the space-charge force of a charged particle beam. The implications for accelerator design and the different physical mechanisms of laser-driven and beam-driven plasma acceleration are discussed. Driver propagation is examined, as well as the effects of the excited plasma wave phase velocity. The driver coupling to subsequent plasma accelerator stages for high-energy physics applications is addressed.

Schroeder, C. B.; Esarey, E.; Benedetti, C.; Toth, Cs.; Geddes, C. G. R.; Leemans, W.P.

2010-06-01

149

Design Considerations for Plasma Accelerators Driven by Lasers or Particle Beams  

SciTech Connect

Plasma accelerators may be driven by the ponderomotive force of an intense laser or the space-charge force of a charged particle beam. The implications for accelerator design and the different physical mechanisms of laser-driven and beam-driven plasma acceleration are discussed. Driver propagation is examined, as well as the effects of the excited plasma wave phase velocity. The driver coupling to subsequent plasma accelerator stages for high-energy physics applications is addressed.

Schroeder, C. B.; Esarey, E.; Benedetti, C.; Toth, Cs.; Geddes, C. G. R.; Leemans, W. P. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2010-11-04

150

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

151

Modeling of an IPMC Actuator-driven Zero-Net-Mass-Flux Pump for Flow Control  

Microsoft Academic Search

In this article, a systematic design method on an ionic polymer-metal composite (IPMC)-driven zero-net-mass-flux (ZNMF) pump is introduced for the flow control on a micro air vehicle ’s (MAV) wing. Since IPMC can generate a large deformation under a low input voltage along with its ability to operate in air, and its easier manufacture in a small size, it is

Sangki Lee; Kwang J. Kim; Hoon Cheol Park

2006-01-01

152

A piezoelectric actuator-driven loading device for mechanical condition during bone tissue engineering  

NASA Astrophysics Data System (ADS)

Bone cells live in an environment heavily influenced by mechanical forces. The researches of bone cell responses in hard scaffolds under differently mechanical conditions will be greatly beneficial to elucidating the mechanisms of bone mechanotransduction as well as applications of mechanical condition in bone tissue engineering. However, the appropriate device for the experiments is prerequisite. A loading device suitable to hard scaffold for study on mechanical responses of bone cells was made by usage of a kind of long-travel, high-load piezoelectric actuator. The device, which is so small enough to work in a standard incubator, can cause hard scaffolds with directly uniaxial compressive strains with more magnitudes, frequency components, and waveforms, including bone physiologically mechanical state, precisely controlled by a computer. The device achieves precise mechanical conditions by testing verification. The device may produce a model that will be suitable for investigating the influences of mechanical responses on bone cells in 3D hard scaffolds in vitro matching that in cancellous bone in vivo and may be applied during bone tissue engineering culture.

Zhang, C. Q.; Wu, H.; Dong, X.

2008-10-01

153

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

154

The Nonlinear Landau Damping Rate of a Driven Plasma Wave  

SciTech Connect

In this Letter, we discuss the concept of the nonlinear Landau damping rate, {nu}, of a driven electron plasma wave, and provide a very simple, practical, analytic formula for {nu} which agrees very well with results inferred from Vlasov simulations of stimulated Raman scattering. {nu} actually is more complicated an operator than a plain damping rate, and it may only be seen as such because it assumes almost constant values before abruptly dropping to 0. The decrease of {nu} to 0 is moreover shown to occur later when the wave amplitude varies in the direction transverse to its propagation.

Benisti, D; Strozzi, D J; Gremillet, L; Morice, O

2009-08-04

155

Nonlinear Landau Damping Rate of a Driven Plasma Wave  

SciTech Connect

In this Letter, we discuss the concept of the nonlinear Landau damping rate, nu, of a driven electron plasma wave, and provide a very simple, practical formula for nu, which agrees very well with results inferred from Vlasov simulations of stimulated Raman scattering. nu actually is more complicated an operator than a plain damping rate, and it may only be seen as such because it assumes almost constant values before abruptly dropping to 0. The decrease of nu to 0 is moreover shown to occur later when the wave amplitude varies in the direction transverse to its propagation.

Benisti, Didier; Gremillet, Laurent; Morice, Olivier [CEA, DAM, DIF 91297 Arpajon Cedex (France); Strozzi, David J. [Lawrence Livermore National Laboratory, University of California, Livermore, California 94550 (United States)

2009-10-09

156

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

157

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

158

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 Multiplication-Sign 10{sup 10} electrons, 20 Multiplication-Sign 20{mu}m{sup 2} spot, 20 - 100{mu}m length, 20GeV energy) when sent into a plasma source with a nominal density of {approx} 1 Multiplication-Sign 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 Multiplication-Sign 35cm{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 National Accelerator Laboratory, Menlo Park, CA 94025 (United States)

2012-12-21

159

Betatron radiation from a beam driven plasma source  

NASA Astrophysics Data System (ADS)

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 × 1010 electrons, 20 × 20?m2 spot, 20 - 100?m length, 20GeV energy) when sent into a plasma source with a nominal density of ˜ 1 × 1017 cm-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 × 35cm2 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.

2012-12-01

160

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

161

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

162

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

163

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

164

Editorial: Focus on Laser- and Beam-Driven Plasma Accelerators  

NASA Astrophysics Data System (ADS)

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 plasma accelerators for research, medical and industrial uses, and also relatively small and inexpensive plasma accelerators for high-energy physics at the frontier of particle physics. In this focus issue on laser- and beam-driven plasma accelerators, the latest advances in this field are described. Focus on Laser- and Beam-Driven Plasma Accelerators Contents Slow wave plasma structures for direct electron acceleration B D Layer, J P Palastro, A G York, T M Antonsen and H M Milchberg Cold injection for electron wakefield acceleration X Davoine, A Beck, A Lifschitz, V Malka and E Lefebvre Enhanced proton flux in the MeV range by defocused laser irradiation J S Green, D C Carroll, C Brenner, B Dromey, P S Foster, S Kar, Y T Li, K Markey, P McKenna, D Neely, A P L Robinson, M J V Streeter, M Tolley, C-G Wahlström, M H Xu and M Zepf Dose-dependent biological damage of tumour cells by laser-accelerated proton beams S D Kraft, C Richter, K Zeil, M Baumann, E Beyreuther, S Bock, M Bussmann, T E Cowan, Y Dammene, W Enghardt, U Helbig, L Karsch, T Kluge, L Laschinsky, E Lessmann, J Metzkes, D Naumburger, R Sauerbrey, M. Sc?rer, M Sobiella, J Woithe, U Schramm and J Pawelke The optimum plasma density for plasma wakefield excitation in the blowout regime W Lu, W An, M Zhou, C Joshi, C Huang and W B Mori Plasma wakefield acceleration experiments at FACET M J Hogan, T O Raubenheimer, A Seryi, P Muggli, T Katsouleas, C Huang, W Lu, W An, K A Marsh, W B Mori, C E Clayton and C Joshi Electron trapping and acceleration on a downward density ramp: a two-stage approach R M G M Trines, R Bingham, Z Najmudin, S Mangles, L O Silva, R Fonseca and P A Norreys Electro-optic shocks from blowout laser wakefields D F Gordon, A Ting, M H Helle, D Kaganovich and B Hafizi Onset of self-steepening of intense laser pulses in plasmas J Vieira, F Fiúza, L O Silva, M Tzoufras and W B Mori Analysis of laser wakefield dynamics in capillary tubes N E Andreev, K Cassou, F Wojda, G Genoud, M Burza, O Lundh, A Persson, B Cros, V E Fortov and C-G Wahlstrom Characterization of the beam loading effects in a laser plasma accelerator C Rechatin, J Faure, X Davoine, O Lundh, J Lim, A Ben-Ismaïl, F Burgy, A Tafzi, A Lifschitz, E Lefebvre and V Malka Energy gain scaling with plasma length and density in the plasma wakefield accelerator P Muggli, I Blumenfeld, C E Clayton, F J Decker, M J Hogan, C Huang, R Ischebeck, R H Iverson, C Joshi, T Katsouleas, N Kirby, W Lu, K A Marsh, W B Mori, E Oz, R H Siemann, D R Walz and M Zhou Generation of tens of GeV quasi-monoenergetic proton beams from a moving double layer formed by ultraintense lasers at intensity 1021-1023Wcm-2 Lu-Le Yu, Han Xu, Wei-Min Wang, Zheng-Ming Sheng, Bai-Fei Shen, Wei Yu and Jie Zhang Carbon ion acceleration from thin foil targets irradiated by ultrahigh-contrast, ultraintense laser pulses D C Carroll, O Tresca, R Prasad, L Romagnani, P S Foster, P Gallegos, S Ter-Avetisyan, J S Green, M J V Streeter, N Dover, C A J Palmer, C M Brenner, F H Cameron, K E Quinn, J Schreiber, A P L Robinson, T Baeva, M N Quinn, X H Yuan, Z Najmudin, M Zepf, D Neely, M Borghesi and P McKenna Numerical modelling of a 10-cm-long multi-GeV laser wakefield accelerator driven by a self-guided petawatt pulse S Y Kalmykov, S A Yi, A Beck, A F Lifschitz, X Davoine, E Lefebvre, A Pukhov, V Khudik, G Shvets, S A Reed, P Dong, X Wang, D Du, S Bedacht, R Zgadzaj, W Henderson, A Bernstein, G Dyer, M Martinez, E Gaul, T Ditmire and M C Downer Effects of laser prepulses on laser-induced proton generation D Batani, R Jafer, M Veltcheva, R Dezulian, O Lundh, F Lindau, A Persson, K Osvay, C-G Wahlström, D C Carroll, P McKenna, A Flacco and V Malka Proton accelerati

Joshi, Chan; Malka, Victor

2010-04-01

165

Laser-driven plasma-based accelerators: Wakefield excitation, channel guiding, and laser triggered particle injection*  

E-print Network

of photocathode rf guns. Novel schemes that rely on laser triggered injection of plasma electrons into plasmaLaser-driven plasma-based accelerators: Wakefield excitation, channel guiding, and laser triggered; accepted 18 February 1998 Plasma-based accelerators are discussed in which high-power short pulse lasers

Wurtele, Jonathan

166

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

167

Electrical and mechanical characteristics of surface AC dielectric barrier discharge plasma actuators applied to airflow control  

NASA Astrophysics Data System (ADS)

The present paper is a wide review on AC surface dielectric barrier discharge (DBD) actuators applied to airflow control. Both electrical and mechanical characteristics of surface DBD are presented and discussed. The first half of the present paper gives the last results concerning typical single plate-to-plate surface DBDs supplied by a sine high voltage. The discharge current, the plasma extension and its morphology are firstly analyzed. Then, time-averaged and time-resolved measurements of the produced electrohydrodynamic force and of the resulting electric wind are commented. The second half of the paper concerns a partial list of approaches having demonstrated a significant modification in the discharge behavior and an increasing of its mechanical performances. Typically, single DBDs can produce mean force and electric wind velocity up to 1 mN/W and 7 m/s, respectively. With multi-DBD designs, velocity up to 11 m/s has been measured and force up to 350 mN/m.

Benard, Nicolas; Moreau, Eric

2014-11-01

168

Effect of plasma inhomogeneity on plasma wakefield acceleration driven by long bunches  

SciTech Connect

Effects of plasma inhomogeneity on self-modulating proton bunches and accelerated electrons were studied numerically. The main effect is the change of the wakefield wavelength which results in phase shifts and loss of accelerated particles. This effect imposes severe constraints on density uniformity in plasma wakefield accelerators driven by long particle bunches. The transverse two stream instability that transforms the long bunch into a train of micro-bunches is less sensitive to density inhomogeneity than are the accelerated particles. The bunch freely passes through increased density regions and interacts with reduced density regions.

Lotov, K. V. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk, Russia and Novosibirsk State University, 630090 Novosibirsk (Russian Federation); Pukhov, A. [Institut fuer Theoretische Physik I, Heinrich-Heine-Universitaet Duesseldorf, 40225 Duesseldorf (Germany); Caldwell, A. [Max-Planck-Institut fuer Physik, 80805 Muenchen (Germany)

2013-01-15

169

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

170

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

171

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

172

Helical dielectric elastomer actuators  

Microsoft Academic Search

This paper presents a new type of contractile polymer-based electromechanical linear actuator. The device belongs to the class of dielectric elastomer actuators, which are typically capable of undergoing large deformations induced by an applied electric field. It is based on a novel helical configuration, suitable for the generation of electrically driven axial contractions and radial expansions. The architecture, the principle

Federico Carpi; Antonio Migliore; Giorgio Serra; Danilo DeRossi

2005-01-01

173

Nonlinear saturation of laser driven plasma beat wave by oscillating two-stream instability  

E-print Network

Nonlinear saturation of laser driven plasma beat wave by oscillating two-stream instability D. N due to the laser beams. As time grows, the plasma beat wave acquires large amplitude and it becomes.1063/1.1798431] I. INTRODUCTION The coherent wave-wave interactions are an important aspect of nonlinear plasma

Singh, Kunwar Pal

174

Revisiting shock-driven exploding pushers: Insights into plasma flows and fields, stopping power, nucleosynthesis, and  

E-print Network

Revisiting shock-driven exploding pushers: Insights into plasma flows and fields, stopping power of Technology 77 Massachusetts, Ave., Cambridge, MA 02139 USA E-mail: petrasso@psfc.mit.edu Abstract. Shock variety of experiments for radiographs of plasma-flow dynamics and self-generated fields in plasma jet

175

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

176

Microrobot actuated by soft actuators based on dielectric elastomer  

Microsoft Academic Search

In this paper a microrobot, mimicking annelid animals like the earthworm, is presented. The robot is composed of several ring-like segments. Each segment is able to generate three degree-of-freedom motions such as pan\\/tilt\\/up-down respectively, and it is actuated by three soft actuators located equidistantly along the circumferential direction. The soft actuator, called antagonistically-driven linear actuator (ANTLA), is based on polymer

H. R. Choi; S. M. Ryew; K. M. Jung; H. M. Kim; J. W. Jeon; J. D. Nam; R. Maeda; K. Tanie

2002-01-01

177

Design and test of a novel cost-effective piezo driven actuator with a two-stage flexure amplifier for chopping mirrors  

NASA Astrophysics Data System (ADS)

A fast chopping secondary mirror is the critical functioning assembly in an astronomical telescope for infrared observation. Normally, a chopping mirror is driven by precision high-load and high-stiffness linear actuators which are expected to be lightweight, compact and further cost-effective. The stroke of the actuator is typically required to up to several hundred microns with typical load capacity up to several hundred Newtons. We developed a novel piezo-based prototype linear actuator with a two-stage rhombic flexure amplifier. In this paper, first we present the detail design scheme of the actuator by analytical calculations with comprehensive Finite Element Analysis (FEA) verification. Afterwards, we also present the procedures and results of tests of linearity, load capacity, eigenfrequency, stability and repeatability. The selected piezoelectric drive unit is a block of 35x10x10 mm3 with output force up to 4000 N. The two-stage displacement amplifier is simply integrated by two identical singular rhombic flexures orthogonally mounted together. Each stage, one rhombic flexure with a longer axis of 76 mm long, is designed with an ideal amplification ratio of 3, which leads to a final theoretical compound amplification ration of 9. In order to realize the basic triangular-amplification principle in a rhombic flexure, we introduced flexure joints at all the eight ends of its four edge bars. The singular rhombic flexures can be efficiently manufactured by electrical discharge wire-cutting process at a time in batch by being overlapped in layers. Afterwards we carried out related measurements to test its performance.

Wu, Qingguo; Yang, Dehua; Li, Aihua; Zhou, Guohua; Yang, Bintang

2012-09-01

178

Enhanced Design of Turbo-jet LPT by Separation Control Using Phased Plasma Actuators  

NASA Technical Reports Server (NTRS)

This work deals with the documentation and control of flow separation that occurs over turbine blades in the low-pressure turbine stage at low Reynolds numbers that exist at high altitude cruise. We utilize a specially constructed linear cascade that is designed to study the flow field over a generic LPT cascade consisting of Pratt & Whitney 'Pak B' shaped blades. This facility was constructed under a previous one-year NASA Glenn RC initiative. The center blade in the cascade is instrumented to measure the surface pressure coefficient distribution. Optical access allows two-component LDV measurement for boundary layer profiles. Experimental conditions have been chosen to give a range of chord Reynolds numbers from 10 to 100K, and a range of free-stream turbulence levels from u'/U(sub infinity)= 0.08 to 3 percent. The surface pressure measurements were used to define a region of separation and reattachment that depend on the free-stream conditions. The location of separation was found to be relatively insensitive to the experimental conditions. However, reattachment location was very sensitive to the turbulence level and Reynolds number. Excellent agreement was found between the measured pressure distributions and predictions from Euler and RANS simulations. Two-component LDV measurements are presently underway to document the mean and fluctuating velocity components in the boundary layer over the center blade for the range of experimental conditions. The fabrication of the plasma actuator is underway. These are designed to produce either streamwise vortices, or a downstream-directed wall jet. A precursor experiment for the former approach was performed with an array of vortex generators placed just upstream of the separation line. These led to reattachment except for the lowest Reynolds number. Progress has also been made on the proposed concept for a laterally moving wake. This involved constructing a smaller wind tunnel and molding an array of symmetric airfoils to form an array. Following its development, it will be scaled up and used to introduce lateral moving wakes upstream up the Pak-B cascade.

Ashpis, David (Technical Monitor); Corke, Thomas C.; Thomas, Flint O.

2003-01-01

179

Summary report : working group 5 on 'electron beam-driven plasma and structure based acceleration concepts'.  

SciTech Connect

The talks presented and the work performed on electron beam-driven accelerators in plasmas and structures are summarized. Highlights of the working group include new experimental results from the E-157 Plasma Wakefield Experiment, the E-150 Plasma Lens Experiment and the Argonne Dielectric Structure Wakefield experiments. The presentations inspired discussion and analysis of three working topics: electron hose instability, ion channel lasers and the plasma afterburner.

Conde, M. E.; Katsouleas, T.

2000-10-19

180

Nonlinear frequency coupling in dual radio-frequency driven atmospheric pressure plasmas  

SciTech Connect

Plasma ionization, and associated mode transitions, in dual radio-frequency driven atmospheric pressure plasmas are governed through nonlinear frequency coupling in the dynamics of the plasma boundary sheath. Ionization in low-power mode is determined by the nonlinear coupling of electron heating and the momentary local plasma density. Ionization in high-power mode is driven by electron avalanches during phases of transient high electric fields within the boundary sheath. The transition between these distinctly different modes is controlled by the total voltage of both frequency components.

Waskoenig, J.; Gans, T. [Centre for Plasma Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom)

2010-05-03

181

Gas flow driven by thermal creep in dusty plasma T. M. Flanagan and J. Goree  

E-print Network

2009 Thermal creep flow TCF is a flow of gas driven by a temperature gradient along a solid boundary temperature gradient along a solid boundary. Since gas flows along the boundary, TCF is very different fromGas flow driven by thermal creep in dusty plasma T. M. Flanagan and J. Goree Department of Physics

Goree, John

182

Local and Bi-Global Stability Analysis of a Plasma Actuated Boundary Layer  

E-print Network

of active and passive flow control systems. This type of actuator has a number of beneficial properties, Associate Fellow AIAA 1 of 14 American Institute of Aeronautics and Astronautics #12;I. Introduction, the TS wave is the instability that is most closely tied to the controlled transition of turbulence

Roy, Subrata

183

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

E-print Network

. For these types of applications, the flow often has some level of laminar behavior, which is important for control behavior of the flow control mechanism relative to the standard `linear' actuator due to the introduction to reattach them are two highly documented issues in flow control research1 . The separated flows that can

Roy, Subrata

184

Active flow separation control using synthetic jet actuators  

E-print Network

The use of synthetic jet actuators for controlling the boundary layer flow and flow separation over a wing is investigated. A theory for the optimum design of actuators using motors is developed. A motor driven synthetic jet actuator is built...

Rao, Preetham P

2012-06-07

185

Improving plasma actuator performance at low pressure, and an analysis of the pointing capabilities of cubeSats using Plasmonic Force Propulsion (PFP) thrusters  

NASA Astrophysics Data System (ADS)

This thesis details the work done on two unrelated projects, plasma actuators, an aerodynamic flow control device, and Plasmonic Force Propulsion (PFP) thrusters, a space propulsion system for small satellites. The first half of the thesis is a paper published in the International Journal of Flow Control on plasma actuators. In this paper the thrust and power consumption of plasma actuators with varying geometries was studied at varying pressure. It was found that actuators with longer buried electrodes produce the most thrust over all and that they substantially improved thrust at low pressure. In particular actuators with 75 mm buried electrodes produced 26% more thrust overall and 34% more thrust at low pressure than the standard 15 mm design. The second half details work done modeling small satellite attitude and reaction control systems in order to compare the use of Plasmonic Force Propulsion thrusters with other state of the art reaction control systems. The model uses bang bang control algorithms and assumes the worst case scenario solar radiation pressure is the only disturbing force. It was found that the estimated 50-500 nN of thrust produced by PFP thrusters would allow the spacecraft which use them extremely high pointing and positioning accuracies (<10-9 degrees and 3 pm). PFP thrusters still face many developmental challenges such as increasing specific impulse which require more research, however, they have great potential to be an enabling technology for future NASA missions such as the Laser Interferometer Space Antenna, and The Stellar Imager.

Friz, Paul Daniel

186

GeV ELECTRON BEAMS FROM A CENTIMETER-SCALE LASER-DRIVEN PLASMA ACCELERATOR  

E-print Network

GeV ELECTRON BEAMS FROM A CENTIMETER-SCALE LASER-DRIVEN PLASMA ACCELERATOR A. J. Gonsalves, K of laser and plasma parameters. INTRODUCTION The accelerating gradient achievable with conventional radio frequency (RF) accelerators is limited by electrical breakdown within the accelerating cavity to a few tens

Geddes, Cameron Guy Robinson

187

Anomalous resistivity and heating in current-driven plasma thrusters* E. Y. Choueiri  

E-print Network

Propulsion and Plasma Dynamics Laboratory, Princeton University, Princeton, New Jersey 08544 Received 20 in current-driven plasma accelerators such as the magnetoplasmadynamic thruster MPDT . An electromagnetic that an instability akin to the generalized lower hybrid drift instability GLHDI exists for electromagnetic modes i

Choueiri, Edgar

188

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

189

Generation of DC-Driven Non-Thermal Plasma in Atmospheric Pressure Air  

Microsoft Academic Search

The main advantage of atmospheric pressure plasma processing is that it requires much lower investment costs, because no vacuum devices are needed, in the case of ambient air, not even a housing. From these points of view, a dc-driven atmospheric pressure air plasma generator, which is pen-type, has been developed in this paper. The main experimental results are as follows.

J. Choi; T. Namihira; S. Katsuki; H. Akiyama

190

Nonlinear and collective phenomena observed in plasma wakefield acceleration driven by multiple bunches  

SciTech Connect

Electron acceleration by plasma wakefields driven by multiple bunches was experimentally studied. It is expected that a wakefield driven by each bunch builds up to result in a large acceleration gradient. However, the build-up of wakefields was not ideal, due to the peaked plasma-density distribution in a small plasma chamber. Two puzzles were encountered. First, the amplitude of the wakefield observed was larger than that calculated based on a linear model. The observed wake structure was not sinusoidal. These results suggest that the plasma wave was nonlinear in spite of the fact that the perturbation of a plasma by the wave should be far smaller than unity. Second, a quadratic deformation was found in the shape of test beams; when it was focused transversely, it was defocused longitudinally, and vice versa. This contradicts the theory that the plasma-lens effect is uniform. {copyright} {ital 1997 American Institute of Physics.}

Kozawa, T.; Ueda, T.; Kobayashi, T.; Uesaka, M.; Shibata, H. [NERL or RCNS, The University of Tokyo, Tokai-mura, Naka-gun, Ibaraki-ken (Japan); Arinaga, M.; Kawakubo, T.; Nakajima, K.; Nakanishi, H.; Ogata, A. [National Laboratory for High Energy Physics (KEK), Tsukuba (Japan); Yoshida, Y. [ISIR, Osaka University, Mihogaoka, Ibaragi (Japan); Yugami, N.; Nishida, Y. [EEE Department, Utsunomiya University, Ishii-machi, Utsunomiya (Japan)

1997-02-01

191

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

192

Current Filament Merging Driven by Cross-Field Plasma Flows  

Microsoft Academic Search

The study of the penetration and mixing of plasmas with differing density, temperature, and species composition has wide-ranging applicability to space plasma systems such as coronal mass ejections, magnetic clouds, galactic jets, and super novae. In these laboratory experiments, two high-beta plasmas are created using a pair of 1.5J, 8ns lasers which strike facing solid carbon targets at right angles

S. Vincena; W. Gekelman; A. Collette; C. Cooper

2007-01-01

193

Please cite this article in press as: M.E. Piyasena, et al., Electroosmotically driven microfluidic actuators, Sens. Actuators B: Chem. (2009), doi:10.1016/j.snb.2009.05.014  

E-print Network

polymer devices that respond directly to electric fields, such as dielectric elastomer actuators (DEAs) [4 Accepted 11 May 2009 Available online xxx Keywords: Actuator Elastomer Microfluidics Electroosmosis PDMS the prototype was made from PDMS, which is an elastomer, the device was entirely flexible. The actuator

Shapiro, Benjamin

194

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

195

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

196

Driven one-component plasmas Felipe B. Rizzato,* Renato Pakter,  

E-print Network

these states 11,12 . Beams of electrons driven by accelerating vacuum de- vices, such as the thermionic valves question concerns the kinetic temperature distribu- tion in thermionic devices in which the directed, as for adiabatic or isothermal processes 15 . Instead, given the properties of thermionic filaments--such as say

Levin, Yan

197

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

198

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

199

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.

Schroeder, C. B.; Benedetti, C.; Esarey, E.; Leemans, W. P. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Gruener, F. J. [Universitaet Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany)

2011-09-30

200

Absorption Spectroscopy of Pulsed Power Driven Metal Plasmas  

Microsoft Academic Search

We present here the use of the continuum radiation from X-pinch-produced point x-ray sources for absorption spectroscopy as a new diagnostic to investigate the properties of aluminum plasmas created by pulsed power machines at 500 kA and 1 MA. This technique is being developed to provide a path towards determining time and space resolved plasma parameters (charge state, temperature and

Patrick Knapp; Sergei Pikuz; Tania Shelkovenko; Adam Cahill; John Greenly; David Hammer

2010-01-01

201

Numerical simulation of plasma transport driven by the Io torus  

NASA Technical Reports Server (NTRS)

The Rice convection model (RCM) has been modified to a form suitable for Jupiter (RCM-J) to study plasma interchange motion in and near the Io plasma torus. The net result of the interchange is that flux tubes, heavily loaded with torus plasma, are transported outward, to be replaced by tubes containing little low-energy (less than 1 keV) plasma. The process is numerically simulated in terms of time evolution from an initial torus that is longitudinally asymmetric and with gradually decreasing density outward from Io's orbit. In the simulations, the nonlinear stage of the instability characteristically exhibits outreaching fingers of heavily-loaded flux tubes that lengthen at an accelerating rate. The principal finding is that the primary geometrical form of outward transport of torus plasma in Jupiter's magnetosphere is through long, outward-moving fingers of plasma. In the simulations, the fingers mainly form in the active sector of the Io torus (the heavier side of the asymmetric torus), and they are spaced longitudinally roughly 20 deg apart.

Yang, Y. S.; Wolf, R. A.; Spiro, R. W.; Dessler, A. J.

1992-01-01

202

Current-Driven Plasma Acceleration Versus Current-Driven Energy Dissipation  

E-print Network

- terizing the current-driven microinstabilities behind the turbulent dissipation degrading the efficiency the electrostatic assumption and none have been directly compared to wave experiments. Our approach to the problem. Second is an engineering pro- gram in which these transport models are coupled to the flow through self

Choueiri, Edgar

203

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

204

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

205

SHEAR-DRIVEN INSTABILITIES IN HALL-MAGNETOHYDRODYNAMIC PLASMAS  

SciTech Connect

The large-scale dynamics of plasmas is well described within the framework of magnetohydrodynamics (MHD). However, whenever the ion density of the plasma becomes sufficiently low, the Hall effect is likely to become important. The role of the Hall effect has been studied in several astrophysical plasma processes, such as magnetic reconnection, magnetic dynamo, MHD turbulence, or MHD instabilities. In particular, the development of small-scale instabilities is essential to understand the transport properties in a number of astrophysical plasmas. The magneto-rotational instability (MRI), which takes place in differentially rotating accretion disks embedded in relatively weak magnetic fields, is just one example. The influence of the large-scale velocity flows on small-scale instabilities is often approximated by a linear shear flow. In this paper, we quantitatively study the role of the Hall effect on plasmas embedded in large-scale shear flows. More precisely, we show that an instability develops when the Hall effect is present, which we therefore term as the Hall magneto-shear instability. As a particular case, we recover the so-called MRI and quantitatively assess the role of the Hall effect on its development and evolution.

Bejarano, Cecilia; Gomez, Daniel O. [Instituto de Astronomia y Fisica del Espacio (Consejo Nacional de Investigaciones Cientificas y Tecnicas, Universidad de Buenos Aires), Ciudad Universitaria, 1428 C.A.B.A., Buenos Aires (Argentina); Brandenburg, Axel, E-mail: cbejarano@iafe.uba.ar, E-mail: gomez@iafe.uba.ar, E-mail: brandenb@nordita.org [NORDITA, AlbaNova University Center, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)

2011-08-20

206

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

NASA Astrophysics Data System (ADS)

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 100MeV-1GeV range, whereas electron-beam driven plasma accelerators have demonstrated the ability to double the energy of 42GeV 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.

2007-05-01

207

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

208

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

209

Summary Report of Working Group 5: Electron Beam Driven Plasma Accelerators  

SciTech Connect

Electron beam driven plasma accelerators have seen rapid progress over the last decade. Recent efforts have built on this success by constructing a concept for a plasma wakefield accelerator based linear collider. The needs for any future collider to deliver both energy and luminosity have substantial implications for interpreting current experiments and setting priorities for the future. This working group reviewed current experiments and ideas in the context of the demands of a future collider. The many discussions and presentations are summarized here.

Hogan, Mark J. [SLAC National Accelerator Laboratory Advanced Accelerator Research Department 2575 SandHill Road, Menlo Park, CA 94025 (United States); Conde, Manoel E. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne IL 60439 (United States)

2009-01-22

210

Nonlinear Hybrid Simulations of Multiple Energetic Particle driven Alfven Modes in Toroidal Plasmas  

NASA Astrophysics Data System (ADS)

Understanding of nonlinear behavior of energetic particle-driven instabilities in tokamaks is of fundamental importance for burning plasmas. Here we report recent advances in self-consistent nonlinear simulations of fast beam ion-driven Alfven modes in NSTX and DIII-D using the extended MHD code M3D [1]. In the hybrid model, the thermal electrons and ions are treated as an ideal fluid while the energetic species is described by either drift-kinetic equation or gyrokinetic equation. The effects of energetic particles are coupled to the MHD equations via the stress tensor term in the momentum equation. The hybrid code has been recently applied to study nonlinear dynamics of fishbone instability [2]. The code was also used to simulate nonlinear evolution of a single beam-driven TAE mode in NSTX. The result showed a weak frequency chirping about 20% consistent with experimental measurement [3]. In this work, we use the M3D code to simulate beam ion driven Alfven modes in NSTX plasmas with multiple unstable Alfven modes. It is found that mode saturation level of each mode can be enhanced significantly by presence of other unstable modes indicating strong nonlinear interaction between different modes. It is also found that a linearly stable n=2 mode can be nonlinearly driven by an n=1 mode at significant mode amplitude. These results together with simulation results of beam ion-driven Alfven modes in DIII-D reversed shear plasmas [4] will be presented. [1] W. Park, E.V. Belova, G.Y. Fu et al., Phy. Plasmas 6, 1796 (1999) [2] Fu, GY, Park, W, Strauss HR et al. PHYSICS OF PLASMAS 13, 052517 (2006) [3] Fu GY, Breslau J, Fredrickson E et al. ,Proceedings of 2004 IAEA Fusion Energy Conference, Vilamoura, Portugal, Paper TH/P4-38. [4] M.A., Van Zeeland, G.J. Kramer, M.E. Austin et al., Phys. Rev. Lett. 97, 135001 (2006).

Fu, Guoyong

2007-11-01

211

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

212

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

213

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

214

Alfvénic instabilities driven by runaways in fusion plasmas  

NASA Astrophysics Data System (ADS)

Runaway particles can be produced in plasmas with large electric fields. Here, we address the possibility that such runaway ions and electrons excite Alfvénic instabilities. The magnetic perturbation induced by these modes can enhance the loss of runaways. This may have important implications for the runaway electron beam formation in tokamak disruptions.

Fülöp, T.; Newton, S.

2014-08-01

215

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

216

American Institute of Aeronautics and Astronautics Physics Based Analysis of Horseshoe Plasma Actuator for Improving  

E-print Network

1 American Institute of Aeronautics and Astronautics Physics Based Analysis of Horseshoe Plasma. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. #12;2 American

Roy, Subrata

217

A self-organized criticality model for ion temperature gradient mode driven turbulence in confined plasma  

Microsoft Academic Search

A new self-organized criticality (SOC) model is introduced in the form of a cellular automaton (CA) for ion temperature gradient (ITG) mode driven turbulence in fusion plasmas. Main characteristics of the model are that it is constructed in terms of the actual physical variable, the ion temperature, and that the temporal evolution of the CA, which necessarily is in the

Heinz Isliker; Theophilos Pisokas; Dafni Strintzi; Loukas Vlahos

2010-01-01

218

Simultaneous Observation of Multiple Nonlocal Eigenmodes of an Inhomogeneity-Driven Plasma Instability  

NASA Astrophysics Data System (ADS)

Multiple eigenmodes of the inhomegeneous energy-density-driven instability are observed simultaneously with large and comparable amplitude. This is in sharp contrast to the usual case in plasmas in which one eigenmode dominates or the laboratory device's geometry is responsible for multiple local eigenmodes. Each feature in the experimentally observed spectrum is unambiguously identified with a specific eigenstate of the theoretical model.

Koepke, M. E.; Carroll, J. J., III; Zintl, M. W.; Selcher, C. A.; Gavrishchaka, V.

1998-02-01

219

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

220

Plasma-driven tunable liquid adhesion of superoleophobic aluminum surfaces  

NASA Astrophysics Data System (ADS)

With the aim of tuning adhesion with various liquids, we develop a convenient route to achieve sliding superoleophobicity and sticky superoleophobicity on the aluminum surfaces by surface fluorination and masked plasma treatment. Droplets of various liquids, such as oils, organic liquids, and water, can be tuned between rolling state and pinned state on the superoleophobic surfaces. The tunable adhesion of the superoleophobic surface is demonstrated by visible experimental results and measurements. The key to this effect is the combination of the oleophobic domains produced by masked plasma treatment as well as a permanently superoleophobic substrate and the hierarchical texture. Our results gave a useful attempt in understanding the fabrication principle of preparing superoleophobic surfaces with tunable liquid adhesion.

Yang, Jin; Song, Haojie; Tang, Hua; Ji, Haiyan; Li, Changsheng

2013-09-01

221

Absorption Spectroscopy of Pulsed Power Driven Metal Plasmas  

NASA Astrophysics Data System (ADS)

We present here the use of the continuum radiation from X-pinch-produced point x-ray sources for absorption spectroscopy as a new diagnostic to investigate the properties of aluminum plasmas created by pulsed power machines at 500 kA and 1 MA. This technique is being developed to provide a path towards determining time and space resolved plasma parameters (charge state, temperature and density) under conditions that are inaccessible to traditional x-ray spectroscopic diagnostics. The diagnostic apparatus, setup and characterization will be described, including estimates of spatial and spectral resolution. Preliminary results from exploding wires and wire array z-pinches are shown and compared with synthetic spectra. The technique is also applied to the dense core of exploding wires, which is known to exist in a multiphase state and has previously eluded quantitative study. This research is supported by the NNSA SSAA program under DOE Cooperative Agreement DE-FC03-02NA00057.

Knapp, Patrick; Pikuz, Sergei; Shelkovenko, Tania; Cahill, Adam; Greenly, John; Hammer, David

2010-11-01

222

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

223

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.

224

Sensor Driven Intelligent Control System For Plasma Processing  

SciTech Connect

This Cooperative Research and Development Agreement (CRADA) between Innovative Computing Technologies, Inc. (IC Tech) and Martin Marietta Energy Systems (MMES) was undertaken to contribute to improved process control for microelectronic device fabrication. Process data from an amorphous silicon thin film deposition experiment was acquired to validate the performance of an intelligent, adaptive, neurally-inspired control software module designed to provide closed loop control of plasma processing machines used in the microelectronics industry. Data acquisition software was written using LabView The data was collected from an inductively coupled plasma (ICP) source, which was available for this project through LMES's RF/Microwave Technology Center. Experimental parameters measured were RF power, RF current and voltage on the antenna delivering power to the plasma, hydrogen and silane flow rate, chamber pressure, substrate temperature and H-alpha optical emission. Experimental results obtained were poly-crystallin silicon deposition rate, crystallinity, crystallographic orientation and electrical conductivity. Owing to experimental delays resulting from hardware failures, it was not possible to assemble a complete data for IC Tech use within the time and resource constraints of the CRADA. IC Tech was therefore not able to verify the performance of their existing models and control structures and validate model performance under this CRADA.

Bell, G.; Campbell, V.B.

1998-02-23

225

An electrochemically driven poly(dimethylsiloxane) microfluidic actuator: oxygen sensing and programmable flows and pH gradients.  

PubMed

We describe the fabrication and performance of an integrated microelectrochemical reactor-a design possessing utility for multiple applications that include electrochemical sensing, the generation and manipulation of in-channel microfluidic pH gradients, and fluid actuation and flow. The device architecture is based on a three-electrode electrochemical cell design that incorporates a Pt interdigitated array (IDA) working (WE), a Pt counter (CE), and Ag pseudo-reference (RE) electrodes within a microfluidic network in which the WE is fully immersed in a liquid electrolyte confined in the channels. The microchannels are made from a conventional poly(dimethylsiloxane)(PDMS) elastomer, which serves also as a thin gas-permeable membrane through which gaseous reactants in the external ambient environment are supplied to the working electrode by diffusion. Due to the high permeability of oxygen through PDMS, the microfluidic cell supports significantly (>order of magnitude) higher current densities in the oxygen reduction reaction (ORR) than those measured in conventional (quiescent) electrochemical cells for the same electrode areas. We demonstrate in this work that, when operated at constant potential under mass transport control, the device can be utilized as a membrane-covered oxygen sensor, the response of which can be tuned by varying the thickness of the PDMS membrane. Depending on the experimental conditions under which the electrochemical ORR is performed, the data establish that the device can be operated as both a programmable pH gradient generator and a microfluidic pump. PMID:15915256

Mitrovski, Svetlana M; Nuzzo, Ralph G

2005-06-01

226

Visualization of Shock Wave Driven by Millimeter Wave Plasma in a Parabolic Thruster  

SciTech Connect

By focusing a high-power millimeter wave beam generated by a 170 GHz gyrotron, a breakdown occurred and a shock wave was driven by plasma heated by following microwave energy. The shock wave and the plasma around a focal point of a parabolic thruster were visualized by a shadowgraph method, and a transition of structures between the shock wave and the plasma was observed. There was a threshold local power density to make the transition, and the propagation velocity at the transition was around 800 m/s.

Yamaguchi, Toshikazu; Shimada, Yutaka; Shiraishi, Yuya; Shibata, Teppei; Komurasaki, Kimiya [Department of Advanced Energy, The University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa, Chiba, 277-8561 (Japan); Oda, Yasuhisa; Kajiwara, Ken; Takahashi, Koji; Kasugai, Atsushi; Sakamoto, Keishi [Plasma Heating Technology Group, Japan Atomic Energy Agency, 801-1 Mukoyama, Naka, Ibaraki, 311-0193 (Japan); Arakawa, Yoshihiro [Department of Aeronautics and Astronautics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 (Japan)

2010-05-06

227

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

228

Performance of dielectric elastomer actuators and materials  

Microsoft Academic Search

Dielectric elastomer actuators performance depends on their construction and the way they are driven. We describe the governing equations for the dynamic performance of actuators and show examples of their use. Both the properties of the base elastomer material and the compliant electrodes influence the actuators performance. The mechanical and electrical properties of elastomers are discussed with a focus on

Peter Sommer-Larsen; Guggi Kofod; M. H. Shridhar; Mohammed Benslimane; Peter Gravesen

2002-01-01

229

Combustion stabilization using serpentine plasma actuators Chin-Cheng Wang and Subrata Roya)  

E-print Network

to pinching and spreading effects suitable for rapid flow mixing. Here, the influence of serpentine plasma three- dimensional flow instabilities that can influence beyond the flow boundary layer. It not only has an overall effect of slowing gas-flow speed in the flame replicating a virtual bluff body

Roy, Subrata

230

American Institute of Aeronautics and Astronautics Microscale Dielectric Barrier Discharge Plasma Actuators  

E-print Network

American Institute of Aeronautics and Astronautics 1 Microscale Dielectric Barrier Discharge Plasma by the Authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. DownloadedbySubrataRoyonDecember27,2012|http://arc.aiaa.org|DOI:10.2514/6.2012-3091 #12;American Institute

Roy, Subrata

231

Turbulence in toroidally confined plasma: ion temperature gradient driven turbulence: dynamics of magnetic relaxation in current carrying plasma  

Microsoft Academic Search

This thesis is devoted to two studies of low-frequency turbulence in toroidally confined plasma. Low-frequency turbulence is believed to play an important role in anomalous transport in toroidal confinement devices. The first study pertains the development of an analytic theory of ion-temperature-gradient-driven turbulence in tokamaks. Energy conserving, renormalized spectrum equations are derived and solved in order to obtain the spectra

1986-01-01

232

Laser-driven plasma CVD of thin films  

NASA Astrophysics Data System (ADS)

A novel technique for CVD synthesis of materials, that does not demand a vacuum chamber and provides high deposition rates, have been developed. It is based on CW CO2-laser maintenance of a stationary optical discharge in a gas stream, exhausting over a substrate into the air. Nano- and polycrystalline diamond films were deposited on tungsten substrates from atmospherics pressure Xe(Ar):H2:CH4 gas mixtures at flow rates 2 1/min. 2,5 kW CO2-laser focused beam produced plasma. Deposition area was about 1 cm2 and growth rates up to 30-50 micrometers /hour. Peculiarities and advantages of laser plasmatrons are discussed.

Konov, Vitali I.; Prokhorov, Alexander M.; Uglov, S. A.; Bolshakov, A. P.; Leontiev, I. A.; Dausinger, Friedrich; Huegel, Helmut; Angstenberger, Birgit; Sepold, Gerd; Metev, Simeon

1998-10-01

233

Influence of electromagnetic oscillating two-stream instability on the evolution of laser-driven plasma beat-wave  

SciTech Connect

The electrostatic oscillating two-stream instability of laser-driven plasma beat-wave was studied recently by Gupta et al. [Phys. Plasmas 11, 5250 (2004)], who applied their theory to limit the amplitude level of a plasma wave in the beat-wave accelerator. As a self-generated magnetic field is observed in laser-produced plasma, hence, the electromagnetic oscillating two-stream instability may be another possible mechanism for the saturation of laser-driven plasma beat-wave. The efficiency of this scheme is higher than the former.

Gupta, D. N.; Singh, K. P.; Suk, H. [Center for Advanced Accelerators, Korea Electrotechnology Research Institute, Changwon 641-120 (Korea, Republic of); Computational Plasma Dynamics Laboratory, Kettering University, Flint, Michigan 48504 (United States); Center for Advanced Accelerators, Korea Electrotechnology Research Institute, Changwon 641-120 (Korea, Republic of)

2007-01-15

234

Energetic electron avalanches and mode transitions in planar inductively coupled radio-frequency driven plasmas operated in oxygen  

SciTech Connect

Space and phase resolved optical emission spectroscopic measurements reveal that in certain parameter regimes, inductively coupled radio-frequency driven plasmas exhibit three distinct operation modes. At low powers, the plasma operates as an alpha-mode capacitively coupled plasma driven through the dynamics of the plasma boundary sheath potential in front of the antenna. At high powers, the plasma operates in inductive mode sustained through induced electric fields due to the time varying currents and associated magnetic fields from the antenna. At intermediate powers, close to the often observed capacitive to inductive (E-H) transition regime, energetic electron avalanches are identified to play a significant role in plasma sustainment, similar to gamma-mode capacitively coupled plasmas. These energetic electrons traverse the whole plasma gap, potentially influencing plasma surface interactions as exploited in technological applications.

Zaka-ul-Islam, M.; Niemi, K. [Centre for Plasma Physics, School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast BT7 1NN, Northern Ireland (United Kingdom); Gans, T.; O'Connell, D. [Centre for Plasma Physics, School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast BT7 1NN, Northern Ireland (United Kingdom); York Plasma Institute, Department of Physics, University of York, Innovation Way, Heslington York YO10 5DQ (United Kingdom)

2011-07-25

235

Experimental characterization of railgun-driven supersonic plasma jets motivated by high energy density physics applications  

NASA Astrophysics Data System (ADS)

We report experimental results on the parameters, structure, and evolution of high-Mach-number (M) argon plasma jets formed and launched by a pulsed-power-driven railgun. The nominal initial average jet parameters in the data set analyzed are density ?2×1016 cm-3, electron temperature ?1.4 eV, velocity ?30 km/s, M?14, ionization fraction ?0.96, diameter ?5 cm, and length ?20 cm. These values approach the range needed by the Plasma Liner Experiment, which is designed to use merging plasma jets to form imploding spherical plasma liners that can reach peak pressures of 0.1-1 Mbar at stagnation. As these jets propagate a distance of approximately 40 cm, the average density drops by one order of magnitude, which is at the very low end of the 8-160 times drop predicted by ideal hydrodynamic theory of a constant-M jet.

Hsu, S. C.; Merritt, E. C.; Moser, A. L.; Awe, T. J.; Brockington, S. J. E.; Davis, J. S.; Adams, C. S.; Case, A.; Cassibry, J. T.; Dunn, J. P.; Gilmore, M. A.; Lynn, A. G.; Messer, S. J.; Witherspoon, F. D.

2012-12-01

236

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

237

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

238

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

239

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

240

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

241

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

242

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

243

Thrust Measurement of Dielectric Barrier Discharge (DBD) Plasma Actuators: New Anti-Thrust Hypothesis, Frequency Sweeps Methodology, Humidity and Enclosure Effects  

NASA Technical Reports Server (NTRS)

We discuss thrust measurements of Dielectric Barrier Discharge (DBD) plasma actuators devices used for aerodynamic active flow control. After a review of our experience with conventional thrust measurement and significant non-repeatability of the results, we devised a suspended actuator test setup, and now present a methodology of thrust measurements with decreased uncertainty. The methodology consists of frequency scans at constant voltages. The procedure consists of increasing the frequency in a step-wise fashion from several Hz to the maximum frequency of several kHz, followed by frequency decrease back down to the start frequency of several Hz. This sequence is performed first at the highest voltage of interest, then repeated at lower voltages. The data in the descending frequency direction is more consistent and selected for reporting. Sample results show strong dependence of thrust on humidity which also affects the consistency and fluctuations of the measurements. We also observed negative values of thrust, or "anti-thrust", at low frequencies between 4 Hz and up to 64 Hz. The anti-thrust is proportional to the mean-squared voltage and is frequency independent. Departures from the parabolic anti-thrust curve are correlated with appearance of visible plasma discharges. We propose the anti-thrust hypothesis. It states that the measured thrust is a sum of plasma thrust and anti-thrust, and assumes that the anti-thrust exists at all frequencies and voltages. The anti-thrust depends on actuator geometry and materials and on the test installation. It enables the separation of the plasma thrust from the measured total thrust. This approach enables more meaningful comparisons between actuators at different installations and laboratories. The dependence on test installation was validated by surrounding the actuator with a grounded large-diameter metal sleeve. Strong dependence on humidity is also shown; the thrust significantly increased with decreasing humidity, e.g., 44 percent increase as relative humidity changed from 18 percent and dew point 33 degF to 50 percent and dew point of 57 degF.

Ashpis, David E.; Laun, Matthew C.

2014-01-01

244

Plasma channel flows: Electro-fluid dynamic jets  

NASA Astrophysics Data System (ADS)

The present work builds on the success of a dielectric barrier discharge driven plasma channel by exploring an electrode configuration that directly actuates the bulk fluid minimizing jet impingement and viscosity related losses. Influence of several electrical and physical parameters including electrode materials are experimentally investigated. Results indicate significant variation of performance with these parameters and suggest that in comparison to surface dielectric barrier plasma actuator driven flows, at least an order of magnitude improvement in efficiency is possible. The jet produced from this plasma channel configuration allows greater versatility for applications in boundary layer flow control and internal flows.

Campbell, Nicholas S.; Roy, Subrata

2014-09-01

245

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

246

Instability of magnetic fields in electroweak plasma driven by neutrino asymmetries  

E-print Network

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 $\

Maxim Dvornikov; Victor B. Semikoz

2013-11-20

247

Hydrodynamic Scaling Analysis of Nuclear Fusion driven by ultra-intense laser-plasma interactions  

E-print Network

We discuss scaling laws of fusion yields generated by laser-plasma interactions. The yields are found to scale as a function of the laser power. The origin of the scaling law in the laser driven fusion yield is derived in terms of hydrodynamic scaling. We point out that the scaling properties can be attributed to the laser power dependence of three terms: the reaction rate, the density of the plasma and the projected range of the plasma particle in the target medium. The resulting scaling relations have a predictive power that enables estimating the fusion yield for a nuclear reaction which has not been investigated by means of the laser accelerated ion beams.

Sachie Kimura; Aldo Bonasera

2011-09-23

248

Hydrodynamic Scaling Analysis of Nuclear Fusion Driven by Ultra-Intense Laser-Plasma Interactions  

NASA Astrophysics Data System (ADS)

We discuss scaling laws of fusion yields generated by laser-plasma interactions. The yields are found to scale as a function of the laser power. The origin of the scaling law in the laser driven fusion yield is derived in terms of hydrodynamic scaling. We point out that the scaling properties can be attributed to the laser power dependence of three terms: the reaction rate, the density of the plasma and the projected range of the plasma particle in the target medium. The resulting scaling relations have a predictive power that enables estimating the fusion yield for a nuclear reaction which has not been investigated by means of the laser accelerated ion beams.

Kimura, Sachie; Bonasera, Aldo

2012-12-01

249

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

250

Laser-driven electron beamlines generated by coupling laser-plasma sources with conventional transport systems  

NASA Astrophysics Data System (ADS)

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.; Bacci, A.; Benedetti, C.; Chiadroni, E.; Ferrario, M.; Rossi, A. R.; Lancia, L.; Migliorati, M.; Mostacci, A.; Palumbo, L.; Serafini, L.

2012-08-01

251

Electrolytic phase transformation actuators  

NASA Astrophysics Data System (ADS)

The emerging field of materials-based actuation continues to be the focus of considerable research due to its inherent scalability and its promise to drive devices in ways that cannot be realized with conventional mechanical actuator strategies. Current approaches include electrochemically responsive conducting polymers, capacitance-driven carbon nanotubes actuators, pH responsive hydrogels, ionic polymer metal composites, electric field responsive elastomers, and field-driven electrostrictive polymers. However, simple electrochemical processes that lead to phase transformations, particularly from liquid to gas, have been virtually ignored. Although a few specialized applications have been proposed, the nature of the reactions and their implication for design, performance, and widespread applicability have not been addressed. Herein we report an electrolytic phase transformation (EPT) actuator, a device capable of producing strains surpassing 136,000% and stresses beyond 200 MPa. These performance characteristics are several orders of magnitude greater than those reported for other materials and could potentially compete with existing commercial hydraulic systems. Furthermore, unlike other materials-based systems that rely on bimorph structures to translate infinitesimally small volume changes into observable deflections, this device can direct all of its output towards linear motion. We show here that an unoptimized actuator prototype can produce volume and pressure changes close to the theoretically predicted values, with maximum stress (70 kPa) limited only by the mechanical strength of the apparatus. Expansion is very rapid and scales with applied current density. Retraction depends on the catalytic nature of the electrode, and state-of-the-art commercial fuel cell electrodes should allow rates surpassing 0.9 mL's-1.cm-2 and 370 kPa's-1.cm-2. We anticipate that this approach will provide a new direction for producing scalable, low-weight, high performance actuators that will be useful in a broad range of applications.

Cameron, Colin G.; Freund, Michael S.

2003-07-01

252

Ion drag and thermophoretic forces acting on free falling charged particles in an rf-driven complex plasma  

Microsoft Academic Search

Monodisperse plastic microspheres have been dropped through a long radio-frequency discharge column. The trajectories of the falling particles have been measured. It was observed that the particles are driven out of the plasma. From the trajectory analysis and plasma measurements the forces on the particles have been derived. Special attention has been paid to the thermophoresis and ion drag forces

C. Zafiu; A. Melzer; A. Piel

2002-01-01

253

Spontaneous reduction of the heat conductivity by a temperature gradient-driven instability in electron-ion plasmas  

Microsoft Academic Search

We have shown that there exist low-frequency growing modes driven by a global temperature gradient in electron and ion plasmas, by linear perturbation analysis within the frame work of plasma kinetic theory. The driving force of the instability is the local deviation of the distribution function from the Maxwell-Boltzmann due to a global temperature gradient. Our results suggest that the

Makoto Hattori; Keiichi Umetsu

2001-01-01

254

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

255

Role of impurity dynamics in resistivity-gradient-driven turbulence and tokamak edge plasma phenomena  

NASA Astrophysics Data System (ADS)

The role of impurity dynamics in resistivity-gradient-driven turbulence is investigated in the context of modeling tokamak edge plasma phenomena. The effects of impurity concentration fluctuations and gradients on the linear behavior of rippling instabilities and on the nonlinear evolution and saturation of resistivity-gradient-driven turbulence are studied both analytically and computationally. At saturation, fluctuation levels and particle and thermal diffusivities are calculated. In particular, the mean-square turbulent radial velocity is given by =(E0Ls/Bz)2 (L-1?+L-1z)2. Thus edged peaked impurity concentrations tend to enhance the turbulence, while axially peaked concentrations tend to quench it. The theoretical predictions are in semiquantitative agreement with experimental results from the TEXT [Bull. Am. Phys. Soc. 30, 1443 (1985)], Caltech [Phys. Fluids 29, 309 (1986)], and Tosca [in the Proceedings of the 12th European Conference on Controlled Fusion and Plasma Physics (European Physical Society, Budapest, 1985), Vol. I, p. 311] tokamaks. Finally, a theory of the density clamp observed during CO-NBI on the ISX-B tokamak [in Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1981), Vol. I, p. 377] is proposed.

Hahm, T. S.; Diamond, P. H.; Terry, P. W.; Garcia, L.; Carreras, B. A.

1987-05-01

256

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

257

Proton-driven plasma wakefield acceleration: a path to the future of high-energy particle physics  

E-print Network

New acceleration technology is mandatory for the future elucidation of fundamental particles and their interactions. A promising approach is to exploit the properties of plasmas. Past research has focused on creating large-amplitude plasma waves by injecting an intense laser pulse or an electron bunch into the plasma. However, the maximum energy gain of electrons accelerated in a single plasma stage is limited by the energy of the driver. Proton bunches are the most promising drivers of wakefields to accelerate electrons to the TeV energy scale in a single stage. An experimental program at CERN -- the AWAKE experiment -- has been launched to study in detail the important physical processes and to demonstrate the power of proton-driven plasma wakefield acceleration. Here we review the physical principles and some experimental considerations for a future proton-driven plasma wakefield accelerator.

Assmann, R; Bohl, T; Bracco, C; Buttenschon, B; Butterworth, A; Caldwell, A; Chattopadhyay, S; Cipiccia, S; Feldbaumer, E; Fonseca, R A; Goddard, B; Gross, M; Grulke, O; Gschwendtner, E; Holloway, J; Huang, C; Jaroszynski, D; Jolly, S; Kempkes, P; Lopes, N; Lotov, K; Machacek, J; Mandry, S R; McKenzie, J W; Meddahi, M; Militsyn, B L; Moschuering, N; Muggli, P; Najmudin, Z; Noakes, T C Q; Norreys, P A; Oz, E; Pardons, A; Petrenko, A; Pukhov, A; Rieger, K; Reimann, O; Ruhl, H; Shaposhnikova, E; Silva, L O; Sosedkin, A; Tarkeshian, R; Trines, R M G N; Tuckmantel, T; Vieira, J; Vincke, H; Wing, M; Xia, G

2014-01-01

258

Proton-driven plasma wakefield acceleration: a path to the future of high-energy particle physics  

E-print Network

New acceleration technology is mandatory for the future elucidation of fundamental particles and their interactions. A promising approach is to exploit the properties of plasmas. Past research has focused on creating large-amplitude plasma waves by injecting an intense laser pulse or an electron bunch into the plasma. However, the maximum energy gain of electrons accelerated in a single plasma stage is limited by the energy of the driver. Proton bunches are the most promising drivers of wakefields to accelerate electrons to the TeV energy scale in a single stage. An experimental program at CERN { the AWAKE experiment { has been launched to study in detail the important physical processes and to demonstrate the power of proton-driven plasma wakefield acceleration. Here we review the physical principles and some experimental considerations for a future proton-driven plasma wakefield accelerator.

Assmann, R et al

2014-01-01

259

Proton-driven plasma wakefield acceleration: a path to the future of high-energy particle physics  

E-print Network

New acceleration technology is mandatory for the future elucidation of fundamental particles and their interactions. A promising approach is to exploit the properties of plasmas. Past research has focused on creating large-amplitude plasma waves by injecting an intense laser pulse or an electron bunch into the plasma. However, the maximum energy gain of electrons accelerated in a single plasma stage is limited by the energy of the driver. Proton bunches are the most promising drivers of wakefields to accelerate electrons to the TeV energy scale in a single stage. An experimental program at CERN -- the AWAKE experiment -- has been launched to study in detail the important physical processes and to demonstrate the power of proton-driven plasma wakefield acceleration. Here we review the physical principles and some experimental considerations for a future proton-driven plasma wakefield accelerator.

AWAKE Collaboration; R. Assmann; R. Bingham; T. Bohl; C. Bracco; B. Buttenschon; A. Butterworth; A. Caldwell; S. Chattopadhyay; S. Cipiccia; E. Feldbaumer; R. A. Fonseca; B. Goddard; M. Gross; O. Grulke; E. Gschwendtner; J. Holloway; C. Huang; D. Jaroszynski; S. Jolly; P. Kempkes; N. Lopes; K. Lotov; J. Machacek; S. R. Mandry; J. W. McKenzie; M. Meddahi; B. L. Militsyn; N. Moschuering; P. Muggli; Z. Najmudin; T. C. Q. Noakes; P. A. Norreys; E. Oz; A. Pardons; A. Petrenko; A. Pukhov; K. Rieger; O. Reimann; H. Ruhl; E. Shaposhnikova; L. O. Silva; A. Sosedkin; R. Tarkeshian; R. M. G. N. Trines; T. Tuckmantel; J. Vieira; H. Vincke; M. Wing; G. Xia

2014-01-20

260

Physics-Based Model Driven by Plasma Drifts Obtained From the C/NOFS Satellite  

NASA Astrophysics Data System (ADS)

An important parameter in determining low-latitude ionospheric plasma density is the plasma drift. Two instruments on-board the Communication/Navigation Outage System (C/NOFS) satellite were designed to directly or indirectly measure the plasma drifts: the Ion Velocity Drift Meter (IVM) and the Vector Electric Field Instrument (VEFI). By using the electric field measurements obtained from VEFI, the physics-based model (PBMOD) developed at the Air Force Research Laboratory has been shown to qualitatively reproduce post-midnight density trenches observed in June 2008. In this presentation, we will demonstrate simulation results obtained from PBMOD driven by averaged IVM [Stoneback and Heelis, 2010] and VEFI data [Pfaff et al., 2010]. A wave-4 structure has been identified in averaged IVM data. Based on our preliminary study, the ion density output from IVM-driven PBMOD also presents a similar wave-four structure in geographical longitudes (GLON). In addition, the lowest density region occurs near 300 degree GLON for all seasons, where the magnetic equator declination is largest. Model results will be compared with those driven by the Scherliess-Fejer drift model, as well as in-situ density measurements obtained from the Planar Langmuir Probe (PLP). Stoneback, R. and R. Heelis (2010), Equatorial ion densities and meridional ion drifts in 2009, C/NOFS Science Workshop at Breckenridge, Colorado. Pfaff, R. , H. Freudenreich, J. Klenzing, D. Rowland, and K. Bromund (2010), DC electric fields as observed on the C/NOFS satellite during solar minimum conditions, C/NOFS Science Workshop at Breckenridge, Colorado.

Su, Y.; Retterer, J. M.; Stoneback, R.; de La Beaujardiere, O.; Roddy, P. A.; Heelis, R. A.; Pfaff, R. F.

2010-12-01

261

Laser experiments to simulate coronal mass ejection driven magnetospheres and astrophysical plasma winds on compact magnetized stars  

NASA Astrophysics Data System (ADS)

Laboratory experiments using a plasma wind generated by laser-target interaction are proposed to investigate the creation of a shock in front of the magnetosphere and the dynamo mechanism for creating plasma currents and voltages. Preliminary experiments are shown where measurements of the electron density gradients surrounding the obstacles are recorded to infer the plasma winds. The proposed experiments are relevant to understanding the electron acceleration mechanisms taking place in shock-driven magnetic dipole confined plasmas surrounding compact magnetized stars and planets. Exploratory experiments have been published [P. Brady, T. Ditmire, W. Horton, et al., Phys. Plasmas 16, 043112 (2009)] with the one Joule Yoga laser and centimeter sized permanent magnets.

Horton, W.; Ditmire, T.; Zakharov, Yu. P.

2010-06-01

262

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

263

Self-organized T(sub)e Redistribution during Driven Reconnection Processes in High Temperature Plasmas  

SciTech Connect

Two-dimensional (2-D) images of electron temperature fluctuations with a high temporal and spatial resolution were employed to study the sawtooth oscillation in TEXTOR tokamak plasmas. The new findings are: 1) 2-D images revealed that the reconnection is localized and permitted the determination of the physical dimensions of the reconnection zone in the poloidal and toroidal planes. 2) The combination of a pressure driven mode and a kink instability leads to an "X-point" reconnection process. 3) Reconnection can take place anywhere along the q~1 rational magnetic surface (both high and low field sides). 4) Heat flow from the core to the outside of the inversion radius during the reconnection time is highly asymmetric and the behavior is collective. These new findings are compared with the characteristics of various theoretical models and experimental results for the study of the sawtooth oscillation in tokamak plasmas.

Park, H.K.; Mazzucato, E.; Luhmann, N.C., Jr.; Domier, C.W.; Xia, Z.; Munsat, T.; Donné, A.J.H.; Classen, I.G.J.; van de Pol, M.J.; TEXTOR team

2005-12-01

264

Design of a free-electron laser driven by the LBNLlaser-plasma-accelerator  

SciTech Connect

We discuss the design and current status of a compactfree-electron laser (FEL), generating ultra-fast, high-peak flux, VUVpulses driven by a high-current, GeV electron beam from the existingLawrence Berkeley National Laboratory (LBNL) laser-plasma accelerator,whose active acceleration length is only a few cm. The proposedultra-fast source would be intrinsically temporally synchronized to thedrive laser pulse, enabling pump-probe studies in ultra-fast science withpulse lengths of tens of fs. Owing to the high current (&10 kA) ofthe laser-plasma-accelerated electron beams, saturated output fluxes arepotentially greater than 1013 photons/pulse. Devices based both on SASEand high-harmonic generated input seeds, to reduce undulator length andfluctuations, are considered.

Schroeder, C.B.; Fawley, W.M.; Montgomery, A.L.; Robinson, K.E.; Gruner, F.; Bakeman, M.; Leemans, W.P.

2007-09-10

265

Kinetic simulation of capacitively coupled plasmas driven by trapezoidal asymmetric voltage pulses  

NASA Astrophysics Data System (ADS)

A kinetic Particle-In-Cell simulation with Monte Carlo Collisions was performed of a geometrically symmetric capacitively coupled, parallel-plate discharge in argon, driven by trapezoidal asymmetric voltage pulses with a period of 200 ns. The discharge was electrically asymmetric, making the ion energy distributions at the two electrodes different from one another. The fraction of the period (?), during which the voltage was kept at a constant (top-flat) positive value, was a critical control parameter. For the parameter range investigated, as ? increased, the mean ion energy on the grounded electrode increased and the ions became more directional, whereas the opposite was found for the ions striking the powered electrode. The absolute value of the DC self-bias voltage decreased as ? increased. Plasma instabilities, promoted by local double layers and electric field reversals during the time of the positive voltage excursion, were characterized by electron plasma waves launched from the sheath edge.

Diomede, Paola; Economou, Demetre J.

2014-06-01

266

Plasma turbulence driven by transversely large-scale standing shear Alfven waves  

SciTech Connect

Using two-dimensional particle-in-cell simulations, we study generation of turbulence consisting of transversely small-scale dispersive Alfven and electrostatic waves when plasma is driven by a large-scale standing shear Alfven wave (LS-SAW). The standing wave is set up by reflecting a propagating LS-SAW. The ponderomotive force of the standing wave generates transversely large-scale density modifications consisting of density cavities and enhancements. The drifts of the charged particles driven by the ponderomotive force and those directly caused by the fields of the standing LS-SAW generate non-thermal features in the plasma. Parametric instabilities driven by the inherent plasma nonlinearities associated with the LS-SAW in combination with the non-thermal features generate small-scale electromagnetic and electrostatic waves, yielding a broad frequency spectrum ranging from below the source frequency of the LS-SAW to ion cyclotron and lower hybrid frequencies and beyond. The power spectrum of the turbulence has peaks at distinct perpendicular wave numbers (k{sub Up-Tack }) lying in the range d{sub e}{sup -1}-6d{sub e}{sup -1}, d{sub e} being the electron inertial length, suggesting non-local parametric decay from small to large k{sub Up-Tack }. The turbulence spectrum encompassing both electromagnetic and electrostatic fluctuations is also broadband in parallel wave number (k{sub ||}). In a standing-wave supported density cavity, the ratio of the perpendicular electric to magnetic field amplitude is R(k{sub Up-Tack }) = |E{sub Up-Tack }(k{sub Up-Tack })/|B{sub Up-Tack }(k{sub Up-Tack })| Much-Less-Than V{sub A} for k{sub Up-Tack }d{sub e} < 0.5, where V{sub A} is the Alfven velocity. The characteristic features of the broadband plasma turbulence are compared with those available from satellite observations in space plasmas.

Singh, Nagendra; Rao, Sathyanarayan [Electrical and Computer Engineering, University of Alabama, Huntsville, Alabama 35899 (United States)

2012-12-15

267

Plasma physical parameters along Coronal Mass Ejection-driven shocks: I observations  

E-print Network

In this work UV and white light (WL) coronagraphic data are combined to derive the full set of plasma physical parameters along the front of a shock driven by a Coronal Mass Ejection. Pre-shock plasma density, shock compression ratio, speed and inclination angle are estimated from WL data, while pre-shock plasma temperature and outflow velocity are derived from UV data. The Rankine-Hugoniot (RH) equations for the general case of an oblique shock are then applied at three points along the front located between $2.2-2.6$ R$_\\odot$ at the shock nose and at the two flanks. Stronger field deflection (by $\\sim 46^\\circ$), plasma compression (factor $\\sim 2.7$) and heating (factor $\\sim 12$) occur at the nose, while heating at the flanks is more moderate (factor $1.5-3.0$). Starting from a pre-shock corona where protons and electrons have about the same temperature ($T_p \\sim T_e \\sim 1.5 \\cdot 10^6$ K), temperature increases derived with RH equations could better represent the protons heating (by dissipation across...

Bemporad, A; Lapenta, G

2014-01-01

268

Driven magnetic reconnection evolution in an X-point magnetospheric plasma  

NASA Astrophysics Data System (ADS)

The nonlinear evolution of a plasma typical of the earth magnetosphere is studied, in the configuration of a neutral X-point with a guide field, which would be relevant for the day-side magnetosphere. For magnetospheric parameters, the electron inertial skin depth is smaller than the ion-sound gyroradius (de< ?s) while ?< 1 and the resisitivity is negligible. The ensuing magnetic reconnection driven by a plasma flow due to the incoming interplanetary plasma is studied using a reduced model derived for the relevant collisionless regime (Kuvshinov et al., J. Plasma Phys. (1998) 59, 727). This model is first analyzed in an asymptotic regime for long times, following Ramos et al. (Phys. Rev. Lett. (2002) 89, 055002) who made a study based on a linear analysis, valid when the forcing is small. Then a numerical solution is performed in order to verify the validity of the linear results and analyze the spatial structure of the magnetic configuration as it evolves to long times. The numerical solution gives also results valid for strong forcing, as in class-X solar flares, which turn out not to be very different from the small forcing. In particular, the reconnected magnetic flux approaches a constant value as t ->?, and the spatial variation scale length is of the order of de.

Martinell, Julio J.; Hernandez-Garcia, Alberto

2006-10-01

269

Preparation of magnetized nanodusty plasmas in a radio frequency-driven parallel-plate reactor  

NASA Astrophysics Data System (ADS)

Nanodust is produced in an rf-driven push-pull parallel-plate reactor using argon with an acetylene admixture at 5-30 Pa. A scheme for the preparation of nanodust clouds with particle radii up to 400 nm for investigations in magnetized plasmas is proposed. The confinement that keeps the nanodust of different radii inside a moderately magnetized discharge (B ? 500 mT) is investigated by a comparison of 2d-Langmuir probe measurements in the dust-free plasma without and with a magnetic field and by the analysis of scattered light of nanodust clouds. It is shown that the dust cloud changes its shape when the dust density changes. This results in a reversed ?-?' transition from a dense dust cloud with a central disk-like void to a dilute dust cloud with a toroidal void. When the dust density is further reduced, filaments are observed in the central part of the cloud, which were absent in the high-density phase. It is concluded that the dense nanodust cloud is able to suppress plasma filamentation in magnetized plasmas.

Tadsen, Benjamin; Greiner, Franko; Piel, Alexander

2014-10-01

270

High and low frequency instabilities driven by counter-streaming electron beams in space plasmas  

NASA Astrophysics Data System (ADS)

A four-component plasma composed of a drifting (parallel to ambient magnetic field) population of warm electrons, drifting (anti-parallel to ambient magnetic field) cool electrons, stationary hot electrons, and thermal ions is studied in an attempt to further our understanding of the excitation mechanisms of broadband electrostatic noise (BEN) in the Earth's magnetospheric regions such as the magnetosheath, plasmasphere, and plasma sheet boundary layer (PSBL). Using kinetic theory, beam-driven electrostatic instabilities such as the ion-acoustic, electron-acoustic instabilities are found to be supported in our multi-component model. The dependence of the instability growth rates and real frequencies on various plasma parameters such as beam speed, number density, temperature, and temperature anisotropy of the counter-streaming (relative to ambient magnetic field) cool electron beam are investigated. It is found that the number density of the anti-field aligned cool electron beam and drift speed play a central role in determining which instability is excited. Using plasma parameters which are closely correlated with the measurements made by the Cluster satellites in the PSBL region, we find that the electron-acoustic and ion-acoustic instabilities could account for the generation of BEN in this region.

Mbuli, L. N.; Maharaj, S. K.; Bharuthram, R.

2014-05-01

271

Convection in galaxy-cluster plasmas driven by active galactic nuclei and cosmic-ray buoyancy  

E-print Network

Turbulent heating may play an important role in galaxy-cluster plasmas, but if turbulent heating is to balance radiative cooling in a quasi-steady state, some mechanism must set the turbulent velocity to the required value. This paper explores one possible regulating mechanism associated with an active galactic nucleus at cluster center. A steady-state model for the intracluster medium is presented in which radiative cooling is balanced by a combination of turbulent heating and thermal conduction. The turbulence is generated by convection driven by the buoyancy of cosmic rays produced by a central radio source. The cosmic-ray luminosity is powered by the accretion of intracluster plasma onto a central black hole. The model makes the rather extreme assumption that the cosmic rays and thermal plasma are completely mixed. Although the intracluster medium is convectively unstable near cluster center in the model solutions, the specific entropy of the thermal plasma still increases outwards because of the cosmic-ray modification to the stability criterion. The model provides a self-consistent calculation of the turbulent velocity as a function of position, but fails to reproduce the steep central density profiles observed in clusters. The principal difficulty is that in order for the fully mixed intracluster medium to become convectively unstable, the cosmic-ray pressure must become comparable to or greater than the thermal pressure within the convective region. The large cosmic-ray pressure gradient then provides much of the support against gravity, reducing the thermal pressure gradient near cluster center and decreasing the central plasma density gradient. A more realistic AGN-feedback model of intracluster turbulence in which relativistic and thermal plasmas are only partially mixed may have greater success.

Benjamin D. G. Chandran

2004-07-18

272

Numerical Simulation of Waves Driven by Plasma Currents Generated by Low-Frequency Alfven Waves in a Multi-Ion Plasma  

NASA Technical Reports Server (NTRS)

When multi-ion plasma consisting of heavy and light ions is permeated by a lowfrequency Alfien (LFA) wave, the EXB and the polarization drifts of the different ion species and the electrons could be quite different. The relative drifts between the charged-particle species drive waves, which energize the plasma. Using 2.5-D particle-in-cell simulations, we study this process of wave generation and its nonlinear consequences in terms of acceleration and heating plasma. Specifically we study the situation for LFA wave frequency being lower than the heavyion cyclotron frequency in a multi-ion plasma. We impose such a wave to the plasma assuming that its wavelength is much larger than that of the waves generated by the relative drifts. For better understanding, the LFA-wave driven simulations are augmented by those driven by initialized ion beams.

Singh, Nagendra; Khazanov, George

2003-01-01

273

Gas- and plasma-driven hydrogen permeation through a reduced activation ferritic steel alloy F82H  

NASA Astrophysics Data System (ADS)

The first wall of a magnetic fusion power reactor will be subjected to hydrogen isotope permeation by the two mechanisms: one is gas-driven and the other is plasma-driven. Hydrogen transport through a reduced activation ferritic steel alloy F82H has been investigated using a steady-state laboratory-scale plasma device. Permeation parameters including permeability, solubility and diffusivity have been measured in the temperature range from 150 to 520 °C. The surface recombination coefficient for hydrogen has also been estimated by a one-dimensional steady-state permeation model with the input data taken from experiments. Using these parameters, the hydrogen plasma-driven permeation flux and inventory for a 0.5 cm thick first wall around 500 °C are estimated to be ?1.0 × 1013 atom cm-2 s-1 and ?2 × 1016 atom cm-3, respectively. Also, the implications of all these data on reactor operation are discussed.

Zhou, Haishan; Hirooka, Yoshi; Ashikawa, Naoko; Muroga, Takeo; Sagara, Akio

2014-12-01

274

First Observation of the High Field Side Sawtooth Crash and Heat Transfer during Driven Reconnection Processes in Magnetically Confined Plasmas  

SciTech Connect

High resolution (temporal and spatial), two-dimensional images of electron temperature fluctuations during sawtooth oscillations were employed to study driven reconnection processes in magnetically confined toroidal plasmas. The combination of kink and local pressure driven instabilities leads to an "X-point" reconnection process that is localized in the toroidal and poloidal planes. The reconnection is not always confined to the magnetic surfaces with minimum energy. The heat transport process from the core is demonstrated to be highly collective rather than stochastic.

Park, HK; Luhmann, NC; Donne, AJH; Classen, IGJ; Domier, CW; Mazzucato, E; Munsat, T; van de Pol, MJ; Xia, Z

2005-12-01

275

Collisionless shocks and particle acceleration in laser-driven laboratory plasmas  

NASA Astrophysics Data System (ADS)

Collisionless shocks are pervasive in space and astrophysical plasmas, from the Earth's bow shock to Gamma Ray Bursters; however, the microphysics underlying shock formation and particle acceleration in these distant sites is not yet fully understood. Mimicking these extreme conditions in laboratory is a grand challenge that would allow for a better understanding of the physical processes involved. Using ab initio multi-dimensional particle-in-cell simulations, shock formation and particle acceleration are investigated for realistic laboratory conditions associated with the interaction of intense lasers with high-energy-density plasmas. Weibel-instability-mediated shocks are shown to be driven by the interaction of an ultraintense laser with overcritical plasmas. In this piston regime, the laser generates a relativistic flow that is Weibel unstable. The strong Weibel magnetic fields deflect the incoming flow, compressing it, and forming a shock. The resulting shock structure is consistent with previous simulations of relativistic astrophysical shocks, demonstrating for the first time the possibility of recreating these structures in laboratory. As the laser intensity is decreased and near-critical density plasmas are used, electron heating dominates over radiation pressure and electrostatic shocks can be formed. The electric field associated with the shock front can reflect ions from the background accelerating them to high energies. It is shown that high quality 200 MeV proton beams, required for tumor therapy, can be generated by using an exponentially decaying plasma profile to control competing accelerating fields. These results pave the way for the experimental exploration of space and astrophysical relevant shocks and particle acceleration with current laser systems.

Fiuza, Frederico

2012-10-01

276

Femtosecond-Laser-Driven Cluster-Based Plasma Source for High-Resolution Ionography  

SciTech Connect

The intense isotropic source of multicharged ions, with energy above 300 keV, was produced by femtosecond Ti:Sa laser pulses irradiation (intensity of approx4x10{sup 17} W/cm{sup 2}) of the He and CO{sub 2} gases mixture expanded in supersonic jet. High contrast ionography images have been obtained for 2000 dpi metal mesh, 1 mum polypropylene and 100 nm Zr foils, as well as for different biological objects. Images were recorded on 1 mm thick CR-39 ion detector placed in contact with back surface of the imaged samples, at the distances 140-160 mm from the plasma source. The obtained spatial resolution of the image was approx600 nm. A 100 nm object thickness difference was resolved very well for both Zr and polymer foils. The multicharged ion energy for Carbon and Oxygen ions passing through the 1 mum polypropylene foil is estimated to give the energy of more than 300 keV. An almost equal number of ions were measured with total number of about 10{sup 8} per shot at a different direction from plasma source. Easy production of different sub-MeV ions in wide space angle, recognizes femtosecond-laser-driven-cluster-based plasma as a well-suited bright source for novel type of submicron ionography to image different media, including nanofoils, membranes, and other low-contrast objects.

Faenov, A. Ya.; Pikuz, T. A. [Kansai Photon Science Institute (KPSI), Japan Atomic Energy Agency (JAEA), Kizugawa-shi, Kyoto, 619-0215 (Japan); Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 (Russian Federation); Fukuda, Y.; Kando, M.; Kotaki, H.; Homma, T.; Kawase, K.; Kameshima, T.; Mori, M.; Sakaki, H.; Hayashi, Y.; Nakamura, T. [Kansai Photon Science Institute (KPSI), Japan Atomic Energy Agency (JAEA), Kizugawa-shi, Kyoto, 619-0215 (Japan); Pirozhkov, A.; Yogo, A.; Tampo, M.; Bolton, P.; Daido, H.; Tajima, T. [Kansai Photon Science Institute (KPSI), Japan Atomic Energy Agency (JAEA), Kizugawa-shi, Kyoto, 619-0215 (Japan); Photo-Medical Research Center, JAEA, Kizugawa-city, Kyoto 619-0215 (Japan); Pikuz, S. A. Jr.; Kartashev, V. [Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 (Russian Federation)

2009-07-25

277

The AWAKE Proton-driven Plasma Wakefield Acceleration Experiment at CERN  

NASA Astrophysics Data System (ADS)

We are planning an experiment at CERN to accelerate externally injected electrons e^- on the wake driven by a long, self-modulated proton p^+ bunch. In the plan the 12cm-long bunch from the SPS with 10^11 p^+ experiences a two-stream transverse instability that modulates the bunch radius at the plasma wake period. The bunch is focused to 200?m into a plasma with density in the 10^14-10^15cm-3 range. The modulation instability is seeded by co-propagating with the p^+ bunch a short laser pulse that ionizes a gas or vapor. The modulation resonantly drives wakefields to large amplitude. The low energy e^- ( 5-20MeV) produced by a rf-photoinjector gun are injected after the instability has saturated, 3-5m into the plasma and is accelerated to the GeV energy range. The e^- energy spectrum is measured by a large energy acceptance magnetic spectrometer. Bunch modulation diagnostics such as time resolved OTR and electro-optic measurements are also included. The general plans for the experiment as well as the latest developments will be presented.

Muggli, Patric

2012-10-01

278

Electrostatic plasma instabilities driven by neutral gas flows in the solar chromosphere  

NASA Astrophysics Data System (ADS)

We investigate electrostatic plasma instabilities of Farley-Buneman (FB) type driven by quasi-stationary neutral gas flows in the solar chromosphere. The role of these instabilities in the chromosphere is clarified. We find that the destabilizing ion thermal effect is highly reduced by the Coulomb collisions and can be ignored for the chromospheric FB-type instabilities. In contrast, the destabilizing electron thermal effect is important and causes a significant reduction of the neutral drag velocity triggering the instability. The resulting threshold velocity is found as function of chromospheric height. Our results indicate that the FB-type instabilities are still less efficient in the global chromospheric heating than the Joule dissipation of the currents driving these instabilities. This conclusion does not exclude the possibility that the FB-type instabilities develop in the places where the cross-field currents overcome the threshold value and contribute to the heating locally. Typical length-scales of plasma density fluctuations produced by these instabilities are determined by the wavelengths of unstable modes, which are in the range 10-102 cm in the lower chromosphere and 102-103 cm in the upper chromosphere. These results suggest that the decimetric radio waves undergoing scattering (scintillations) by these plasma irregularities can serve as a tool for remote probing of the solar chromosphere at different heights.

Gogoberidze, G.; Voitenko, Y.; Poedts, S.; De Keyser, J.

2014-03-01

279

Nonlinear Evolution of Current-Driven Instabilities in Weakly Magnetized Magnetospheric Plasmas  

NASA Astrophysics Data System (ADS)

In many regions of Earth's magnetosphere, including magnetic reconnection sites, the electrons are weakly magnetized according to the criterion ?e< ?e. These regions often contain strong currents with gradients perpendicular to B (i.e., shear). Reduced Vlasov simulations (N. Sen et al., this meeting), which permit computationally fast evaluation of phase-space dynamics of magnetized plasma species, are employed to simulate the nonlinear evolution of sheared current-driven instabilities in magnetospheric plasmas with weakly magnetized electrons and (effectively) unmagnetized ions. For sufficiently large currents, the plasma will be Buneman unstable. For currents near the Buneman threshold, double layers can form and accelerate electron beams, resulting in secondary two-stream instabilities. Both cases can lead to the formation of electron phase-space holes with bipolar electric field signatures such as those recently observed by Cluster near a reconnection site in Earth's magnetotail.ootnotetextC. A. Cattell et al., JGR, 110, A01211 (2005). In certain regimes, electron holes appear to form in regions of maximum current but later localize near the edge of the current-carrying region. The generation of low- and high-frequency waves and the evolution of the currents will also be discussed.

Newman, David L.

2005-10-01

280

Design and evolution of a piezoelectrically actuated miniature swimming vehicle  

Microsoft Academic Search

This work details the design of a miniature swimming vehicle that propels itself through oscillations of a flexible fin mounted in the stern. The fin is driven through a mechanism that is actuated by two curved-beam bending piezoelectric actuators. An optimization routine is used to design the mechanism for rigid body guidance. The actuators are modeled statically using the Bernoulli-Euler

Michael G. Borgen; Gregory N. Washington; Gary L. Kinzel

2003-01-01

281

Electrostatic plasma instabilities driven by neutral gas flows in the solar chromosphere  

E-print Network

We investigate electrostatic plasma instabilities of Farley-Buneman (FB) type driven by quasi-stationary neutral gas flows in the solar chromosphere. The role of these instabilities in the chromosphere is clarified. We find that the destabilizing ion thermal effect is highly reduced by the Coulomb collisions and can be ignored for the chromospheric FB-type instabilities. On the contrary, the destabilizing electron thermal effect is important and causes a significant reduction of the neutral drag velocity triggering the instability. The resulting threshold velocity is found as function of chromospheric height. Our results indicate that the FB type instabilities are still less efficient in the global chromospheric heating than the Joule dissipation of the currents driving these instabilities. This conclusion does not exclude the possibility that the FB type instabilities develop in the places where the cross-field currents overcome the threshold value and contribute to the heating locally. Typical length-scales...

Gogoberidze, G; Poedts, S; De Keyser, J

2013-01-01

282

Proton temperature-anisotropy-driven instabilities in weakly collisional plasmas: Hybrid simulations  

E-print Network

Kinetic instabilities in weakly collisional, high beta plasmas are investigated using two-dimensional hybrid expanding box simulations with Coulomb collisions modeled through the Langevin equation (corresponding to the Fokker-Planck one). The expansion drives a parallel or perpendicular temperature anisotropy (depending on the orientation of the ambient magnetic field). For the chosen parameters the Coulomb collisions are important with respect to the driver but are not strong enough to keep the system stable with respect to instabilities driven by the proton temperature anisotropy. In the case of the parallel temperature anisotropy the dominant oblique fire hose instability efficiently reduces the anisotropy in a quasilinear manner. In the case of the perpendicular temperature anisotropy the dominant mirror instability generates coherent compressive structures which scatter protons and reduce the temperature anisotropy. For both the cases the instabilities generate temporarily enough wave energy so that the ...

Hellinger, Petr

2014-01-01

283

Bifurcation Theory of the Transition to Collisionless Ion-temperature-gradient-driven Plasma Turbulence  

SciTech Connect

The collisionless limit of the transition to ion-temperature-gradient-driven plasma turbulence is considered with a dynamical-systems approach. The importance of systematic analysis for understanding the differences in the bifurcations and dynamics of linearly damped and undamped systems is emphasized. A model with ten degrees of freedom is studied as a concrete example. A four-dimensional center manifold (CM) is analyzed, and fixed points of its dynamics are identified and used to predict a ''Dimits shift'' of the threshold for turbulence due to the excitation of zonal flows. The exact value of that shift in terms of physical parameters is established for the model; the effects of higher-order truncations on the dynamics are noted. Multiple-scale analysis of the CM equations is used to discuss possible effects of modulational instability on scenarios for the transition to turbulence in both collisional and collisionless cases.

Kolesnikov, R.A.; Krommes, J.A.

2005-09-22

284

Tearing instabilities driven by nonideal effects in the tail plasma sheet  

SciTech Connect

Using an extended magnetohydrodynamic description, the excitation of tearing modes is analytically investigated in the tail plasma sheet region that includes the magnetic field components B{sub 0x}(x,z) and B{sub 0z}(x,z). Taking electron inertia and the Hall effect into account, a generalized technique is displayed for obtaining the tearing solutions near the singular layer, where the B{sub 0x}(x,z) field reverses sign at z=0. In two-dimensional tail geometry for scale lengths of order c/{omega}{sub pe}, it is shown that a localized tearing mode as well as a mode with broad spatial extent ({delta}{sup '}-driven mode) is excited near the field reversal region and these modes are mainly driven by electron inertia. For appropriate current sheet parameters, it is found that the localized mode becomes unstable in a couple of minutes while the mode with broad spatial width grows faster in 10 s. For three-dimensional perturbations wherein k{sub x},k{sub y}{ne}0, the combined effects of the Hall term and the electron inertia are shown to excite new localized tearing modes with considerably enhanced growth rates ({gamma}>{omega}{sub ci})

Sundaram, A. K

2008-05-15

285

Temporal evolution of atmosphere pressure plasma jets driven by microsecond pulses with positive and negative polarities  

NASA Astrophysics Data System (ADS)

Current-voltage characteristics, discharge images, and optical spectra of atmospheric pressure plasma jets (APPJs) are studied using a microsecond pulse length generator producing repetitive output pulses with different polarities. The experimental results show that the APPJs excited by the pulses with positive polarity have longer plume, faster propagation speed, higher power, and more excited species, such as \\text{N}2 , O, He, \\text{N}2+ , than that with the negatively excited APPJs. The images taken using an intensified charge-coupled device show that the APPJs excited by pulses with positive polarity are characterized by a bullet-like structure, while the APPJs excited by pulses with negative polarity are continuous. The propagation speed of the APPJs driven by a microsecond pulse length generator is about tens of km/s, which is similar to the APPJs driven by a kHz frequency sinusoidal voltage source. The analysis shows that the space charge accumulation effect plays an important role during the discharge. The transient enhanced electric field induced by the accumulated ions between the needle-like electrode and the nozzle in the APPJs excited by pulses with negative polarity enhances electron field emission from the cathode, which is illustrated by the bright line on the time-integrated images. This makes the shape of the APPJ excited using pulses with negative polarity different from the bullet-like shape of the APPJs excited by pulses with positive polarity.

Shao, Tao; Yang, Wenjin; Zhang, Cheng; Fang, Zhi; Zhou, Yixiao; Schamiloglu, Edl

2014-09-01

286

Normalization schemes for ultrafast x-ray diffraction using a table-top laser-driven plasma source  

SciTech Connect

We present an experimental setup of a laser-driven x-ray plasma source for femtosecond x-ray diffraction. Different normalization schemes accounting for x-ray source intensity fluctuations are discussed in detail. We apply these schemes to measure the temporal evolution of Bragg peak intensities of perovskite superlattices after ultrafast laser excitation.

Schick, D.; Bojahr, A.; Herzog, M. [Institut fuer Physik and Astronomie, Universitaet Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam (Germany); Korff Schmising, C. von [Institut fuer Optik und Atomare Physik, Technische Universitaet Berlin, Strasse des 17. Juni 135, 10623 Berlin (Germany); Shayduk, R.; Leitenberger, W.; Gaal, P.; Bargheer, M. [Helmholtz Zentrum Berlin, Albert-Einstein-Strasse 15, 12489 Berlin (Germany)

2012-02-15

287

A water bag model of driven phase space holes in non-neutral plasmas L. Friedland,1,a  

E-print Network

A water bag model of driven phase space holes in non-neutral plasmas I. Barth,1 L. Friedland,1,a; accepted 23 July 2008; published online 15 August 2008 The formation and control of stable multiphase space of the trap, and n is the multiplicity of the resonance the number of the phase space holes . An adiabatic

Friedland, Lazar

288

Laser-driven, magnetized quasi-perpendicular collisionless shocks on the Large Plasma Devicea)  

NASA Astrophysics Data System (ADS)

The interaction of a laser-driven super-Alfvénic magnetic piston with a large, preformed magnetized ambient plasma has been studied by utilizing a unique experimental platform that couples the Raptor kJ-class laser system [Niemann et al., J. Instrum. 7, P03010 (2012)] to the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles. This platform provides experimental conditions of relevance to space and astrophysical magnetic collisionless shocks and, in particular, allows a detailed study of the microphysics of shock formation, including piston-ambient ion collisionless coupling. An overview of the platform and its capabilities is given, and recent experimental results on the coupling of energy between piston and ambient ions and the formation of collisionless shocks are presented and compared to theoretical and computational work. In particular, a magnetosonic pulse consistent with a low-Mach number collisionless shock is observed in a quasi-perpendicular geometry in both experiments and simulations.

Schaeffer, D. B.; Everson, E. T.; Bondarenko, A. S.; Clark, S. E.; Constantin, C. G.; Vincena, S.; Van Compernolle, B.; Tripathi, S. K. P.; Winske, D.; Gekelman, W.; Niemann, C.

2014-05-01

289

Development and characterization of plasma targets for controlled injection of electrons into laser-driven wakefields  

NASA Astrophysics Data System (ADS)

Laser-driven wakefield acceleration within capillary discharge waveguides has been used to generate high-quality electron bunches with GeV-scale energies. However, owing to fluctuations in laser and plasma conditions in combination with a difficult to control self-injection mechanism in the non-linear wakefield regime these bunches are often not reproducible and can feature large energy spreads. Specialized plasma targets with tailored density profiles offer the possibility to overcome these issues by controlling the injection and acceleration processes. This requires precise manipulation of the longitudinal density profile. Therefore our target concept is based on a capillary structure with multiple gas in- and outlets. Potential target designs are simulated using the fluid code OpenFOAM and those meeting the specified criteria are fabricated using femtosecond-laser machining of structures into sapphire plates. Density profiles are measured over a range of inlet pressures utilizing gas-density profilometry via Raman scattering and pressure calibration with longitudinal interferometry. In combination these allow absolute density mapping. Here we report the preliminary results.

Kleinwaechter, Tobias; Goldberg, Lars; Palmer, Charlotte; Schaper, Lucas; Schwinkendorf, Jan-Patrick; Osterhoff, Jens

2012-10-01

290

Trapped energetic electron driven modes with second stable regime in tokamak plasmas  

NASA Astrophysics Data System (ADS)

Features of fishbone-like trapped energetic electrons driven modes (TEEMs), which are a particular manifestation of the fishbone gap modes, are investigated taking into account model radial profile and the pitch angle distribution of the energetic electrons (EEs). The TEEMs are found unstable only when the beta values of EEs ?h (=pressure of the energetic electrons/pressure of magnetic field) are higher than certain critical values which are proportional to perturbed energy ?W ?c of background plasma and much lower than that for traditional fishbone modes. In addition, TEEMs become stable again and enter a second stable regime when ?h values are higher than second critical values. Furthermore, the modes can only be excited in plasmas which are stable for MHD instabilities. The real frequency and growth rate of the modes are approximately linear and parabolic functions of ?h, respectively. The real frequency is very low but not zero in the vicinity of lower beta region, whereas it is comparable to the toroidal precession frequency of the EEs in higher critical beta region. The numerical results show that the second stable regime is easy to form when q = 1 flux surface is close to the magnetic axis. Suitable density gradient of EEs and magnetic shear are other two necessary conditions for excitation of the TEEMs.

He, Hongda; Dong, J. Q.; Zhao, K.; He, Zhixiong; Zheng, G. Y.; Lu, Gaimin; Hao, G. Z.; Tao, Xie; Wang, L. F.

2014-06-01

291

Two-dimensional PIC simulations of ion-beam instabilities in Supernova-driven plasma flows  

E-print Network

Supernova remnant (SNR) blast shells can reach the flow speed $v_s = 0.1 c$ and shocks form at its front. Instabilities driven by shock-reflected ion beams heat the plasma in the foreshock, which may inject particles into diffusive acceleration. The ion beams can have the speed $v_b \\approx v_s$. For $v_b \\ll v_s$ the Buneman or upper-hybrid instabilities dominate, while for $v_b \\gg v_s$ the filamentation and mixed modes grow faster. Here the relevant waves for $v_b \\approx v_s$ are examined and how they interact nonlinearly with the particles. The collision of two plasma clouds at the speed $v_s$ is modelled with particle-in-cell (PIC) simulations, which convect with them magnetic fields oriented perpendicular to their flow velocity vector. One simulation models equally dense clouds and the other one uses a density ratio of 2. Both simulations show upper-hybrid waves that are planar over large spatial intervals and that accelerate electrons to $\\sim$ 10 keV. The symmetric collision yields only short oscillatory wave pulses, while the asymmetric collision also produces large-scale electric fields, probably through a magnetic pressure gradient. The large-scale fields destroy the electron phase space holes and they accelerate the ions, which facilitates the formation of a precursor shock.

M. E. Dieckmann; A. Meli; P. K. Shukla; L. O. C. Drury; A. Mastichiadis

2008-04-16

292

Turbulence driven by two-stream instability in a magnetized plasma  

NASA Astrophysics Data System (ADS)

Although the nonlinear evolution of the two-stream instability has been a subject of numerical and theoretical studies for many years, recent spacecraft measurements of nonlinear electrostatic bipolar wave structures in the auroral ionosphere have prompted new studies. Using parallel two-dimensional (2D) particle-in-cell electrostatic simulations with initially counterstreaming cold electrons in a magnetized plasma, the evolution of wave turbulence and particle distributions has been followed for over 10 000 inverse plasma frequencies. Ions are introduced in the frame of one of the electron beams (motivated by measurements). Wave turbulence evolves in at least five separate stages. After tens of ?e-1, trapping produces bipolar wave structures with long range order across B. After hundreds of ?e-1, the structures break up and whistlers appear. After thousands of ?e-1, ion cyclotron waves driven by a bump-on-tail in the evolved electron distribution become prominent. After 6000 ?e-1, the ion cyclotron waves appear to undergo parametric decay into oblique waves.

Goldman, Martin V.; Crary, Frank; Newman, David L.; Oppenheim, Meers

2000-05-01

293

Thermally Actuated Hydraulic Pumps  

NASA Technical Reports Server (NTRS)

Thermally actuated hydraulic pumps have been proposed for diverse applications in which direct electrical or mechanical actuation is undesirable and the relative slowness of thermal actuation can be tolerated. The proposed pumps would not contain any sliding (wearing) parts in their compressors and, hence, could have long operational lifetimes. The basic principle of a pump according to the proposal is to utilize the thermal expansion and contraction of a wax or other phase-change material in contact with a hydraulic fluid in a rigid chamber. Heating the chamber and its contents from below to above the melting temperature of the phase-change material would cause the material to expand significantly, thus causing a substantial increase in hydraulic pressure and/or a substantial displacement of hydraulic fluid out of the chamber. Similarly, cooling the chamber and its contents from above to below the melting temperature of the phase-change material would cause the material to contract significantly, thus causing a substantial decrease in hydraulic pressure and/or a substantial displacement of hydraulic fluid into the chamber. The displacement of the hydraulic fluid could be used to drive a piston. The figure illustrates a simple example of a hydraulic jack driven by a thermally actuated hydraulic pump. The pump chamber would be a cylinder containing encapsulated wax pellets and containing radial fins to facilitate transfer of heat to and from the wax. The plastic encapsulation would serve as an oil/wax barrier and the remaining interior space could be filled with hydraulic oil. A filter would retain the encapsulated wax particles in the pump chamber while allowing the hydraulic oil to flow into and out of the chamber. In one important class of potential applications, thermally actuated hydraulic pumps, exploiting vertical ocean temperature gradients for heating and cooling as needed, would be used to vary hydraulic pressures to control buoyancy in undersea research vessels. Heretofore, electrically actuated hydraulic pumps have been used for this purpose. By eliminating the demand for electrical energy for pumping, the use of the thermally actuated hydraulic pumps could prolong the intervals between battery charges, thus making it possible to greatly increase the durations of undersea exploratory missions.

Jones, Jack; Ross, Ronald; Chao, Yi

2008-01-01

294

INJECTION OF PLASMA INTO THE NASCENT SOLAR WIND VIA RECONNECTION DRIVEN BY SUPERGRANULAR ADVECTION  

SciTech Connect

To understand the origin of the solar wind is one of the key research topics in modern solar and heliospheric physics. Previous solar wind models assumed that plasma flows outward along a steady magnetic flux tube that reaches continuously from the photosphere through the chromosphere into the corona. Inspired by more recent comprehensive observations, Tu et al. suggested a new scenario for the origin of the solar wind, in which it flows out in a magnetically open coronal funnel and mass is provided to the funnel by small-scale side loops. Thus mass is supplied by means of magnetic reconnection that is driven by supergranular convection. To validate this scenario and simulate the processes involved, a 2.5 dimensional (2.5D) numerical MHD model is established in the present paper. In our simulation a closed loop moves toward an open funnel, which has opposite polarity and is located at the edge of a supergranulation cell, and magnetic reconnection is triggered and continues while gradually opening up one half of the closed loop. Its other half connects with the root of the open funnel and forms a new closed loop which is submerged by a reconnection plasma stream flowing downward. Thus we find that the outflowing plasma in the newly reconnected funnel originates not only from the upward reconnection flow but also from the high-pressure leg of the originally closed loop. This implies an efficient supply of mass from the dense loop to the dilute funnel. The mass flux of the outflow released from the funnel considered in our study is calculated to be appropriate for providing the mass flux at the coronal base of the solar wind, though additional heating and acceleration mechanisms are necessary to keep the velocity at the higher location. Our numerical model demonstrates that in the funnel the mass for the solar wind may be supplied from adjacent closed loops via magnetic reconnection as well as directly from the footpoints of open funnels.

Yang Liping; He Jiansen; Tu Chuanyi; Chen Wenlei; Zhang Lei; Wang Linghua; Yan Limei [School of Earth and Space Sciences, Peking University, 100871 Beijing (China); Peter, Hardi [Max-Planck-Institut fuer Sonnensystemforschung, Max-Planck-Strasse, D-37191 Katlenburg-Lindau (Germany); Marsch, Eckart [Institute for Experimental and Applied Physics, Christian Albrechts University at Kiel, D-24118 Kiel (Germany); Feng, Xueshang, E-mail: jshept@gmail.com [SIGMA Weather Group, State Key Laboratory for Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, 100871 Beijing (China)

2013-06-10

295

Microwave Power for Smart Membrane Actuators  

NASA Technical Reports Server (NTRS)

The concept of microwave-driven smart membrane actuators is envisioned as the best option to alleviate the complexity associated with hard-wired control circuitry. A large, ultra-light space structure, such as solar sails and Gossamer spacecrafts, requires a distribution of power into individual membrane actuators to control them in an effective way. A patch rectenna array with a high voltage output was developed to drive smart membrane actuators. Networked patch rectenna array receives and converts microwave power into a DC power for an array of smart actuators. To use microwave power effectively, the concept of a power allocation and distribution (PAD) circuit is developed and tested for networking a rectenna/actuator patch array. For the future development, the PAD circuit could be imbedded into a single embodiment of rectenna and actuator array with the thin-film microcircuit embodiment. Preliminary design and fabrication of PAD circuitry that consists of a sixteen nodal elements were made for laboratory testing.

Choi, Sang H.; Song, Kyo D.; Golembiewski, Walter T.; Chu, Sang-Hyon; King, Glen C.

2002-01-01

296

Soft Actuator for Robotic Applications Based on Dielectric Elastomer: Dynamic Analysis and Applications  

Microsoft Academic Search

In this paper a new soft actuator based on dielectric elastomer is proposed. The actuator, called an antagonistically-driven linear actuator (ANTLA), has the muscle-like characteristics capable of performing the motions such as forward\\/backward\\/controllable compliance. In this paper, its dynamic analysis is performed with experimental verifications, and applications for robotic actuating devices are introduced

Hyoukryeol Choi; Sungmoo Ryew; K. M. Jung; H. M. Kim; Jae Wook Jeon; Jea-do Nam; Ryutaro Maeda; Kazuo Tanie

2002-01-01

297

D. Moreau IEA W60 Burning Plasma Physics and Simulation, Tarragona, July 2005 INTEGRATED REAL-TIME CONTROL  

E-print Network

-dominated burning plasma, the bootstrap current driven by the fusion power acts as the primary circuit of the current profile Requires integrated burn (fueling) and profile control (H&CD) (magnetic/kinetic - multiple and Simulation, Tarragona, July 2005 OUTLINE Burning plasma issues, actuators, sensors, non-linear couplings

298

Actuated atomizer  

NASA Technical Reports Server (NTRS)

An actuated atomizer is adapted for spray cooling or other applications wherein a well-developed, homogeneous and generally conical spray mist is required. The actuated atomizer includes an outer shell formed by an inner ring; an outer ring; an actuator insert and a cap. A nozzle framework is positioned within the actuator insert. A base of the nozzle framework defines swirl inlets, a swirl chamber and a swirl chamber. A nozzle insert defines a center inlet and feed ports. A spool is positioned within the coil housing, and carries the coil windings having a number of turns calculated to result in a magnetic field of sufficient strength to overcome the bias of the spring. A plunger moves in response to the magnetic field of the windings. A stop prevents the pintle from being withdrawn excessively. A pintle, positioned by the plunger, moves between first and second positions. In the first position, the head of the pintle blocks the discharge passage of the nozzle framework, thereby preventing the atomizer from discharging fluid. In the second position, the pintle is withdrawn from the swirl chamber, allowing the atomizer to release atomized fluid. A spring biases the pintle to block the discharge passage. The strength of the spring is overcome, however, by the magnetic field created by the windings positioned on the spool, which withdraws the plunger into the spool and further compresses the spring.

Tilton, Charles (Inventor); Weiler, Jeff (Inventor); Palmer, Randall (Inventor); Appel, Philip (Inventor)

2008-01-01

299

Pneumatic Actuators  

NSDL National Science Digital Library

This learning object covers cylinders and motor pneumatic actuators. It is hosted by the University of Wisconsin-Madison and consists of cylinders operations such as: single, duel acting, factors for cylinder speed. The program require Macromedia Flash player, and presents a very nice overall presentation format.

2008-11-14

300

On the Transition from Thermally-driven to Ponderomotively-driven Stimulated Brillouin Scattering and Filamentation of Light in Plasma  

SciTech Connect

The dispersion properties of ion acoustic waves and their nonlinear coupling to light waves through ponderomotive and thermal forces are sensitive to the strength of electron-ion collisions. Here, we consider the growth rate of stimulated Brillouin scattering (SBS) when the driven acoustic wave frequency and wavelength span the range of small to large compared to electron-ion collision frequency and mean free path respectively. We find in all cases the thermal contributions to the SBS growth rate are insignificant if the ion acoustic wave frequency is greater than the electron-ion collision frequency and the wavelength is much shorter than the electron-ion mean free path. On the other hand, the purely growing filamentation instability remains thermally driven for shorter wavelengths than SBS even when the growth rate is larger than the acoustic frequency.

R.L. Berger; E.J. Valeo; S. Brunner

2005-04-04

301

Numerical Simulation of Waves Driven by Plasma Currents Generated by Low-Frequency Alfven Waves in a Multi-Ion Plasma  

NASA Technical Reports Server (NTRS)

When multi-ion plasma consisting of heavy and light ions is permeated by a low-frequency Alfven (LFA) wave, the crossed-electric-and-magnetic field (E x B), and the polarization drifts of the different ion species and the electrons could be quite different. The relative drifts between the charged-particle species drive waves, which energize the plasma. Using 2.5-dimensional (2.5-D) particle-in-cell simulations, we study this process of wave generation and its nonlinear consequences in terms of acceleration and heating plasma. Specifically, we study the situation for LFA wave frequency being lower than the heavy-ion cyclotron frequency in a multi-ion plasma. We impose such a wave to the plasma assuming that its wavelength is much larger than that of the waves generated by the relative drifts. For better understanding, the LFA-wave driven simulations are augmented by those driven by initialized ion beams. The driven high-frequency (HF) wave modes critically depend on the heavy ion density nh; for small values of nh, the lower hybrid (LH) waves dominate. On the other hand, for large nh a significantly enhanced level of waves occurs over a much broader frequency spectrum below the LH frequency and such waves are interpreted here as the ion Bernstein (IB) mode near the light ion cyclotron harmonics. Irrespective of the driven wave modes, both the light and heavy ions undergo significant transverse acceleration, but for the large heavy-ion densities, even the electrons are significantly accelerated in the parallel direction by the waves below the LH frequency. Even when the LFA wave drive is maintained, the ion heating leads to the cessation of HF wave excitation just after a few cycles of the former wave. On the basis of marginal stability seen in the simulations, an empirical relation for LFA wave amplitude, frequency and ion temperature is given.

Singh, Nagendra; Khazanov, George

2004-01-01

302

High torque miniature rotary actuator  

NASA Astrophysics Data System (ADS)

This paper summarizes the design and the development of a miniature rotary actuator (36 mm diameter by 100 mm length) used in spacecraft mechanisms requiring high torques and/or ultra-fine step resolution. This actuator lends itself to applications requiring high torque but with strict volume limitations which challenge the use of conventional rotary actuators. The design challenge was to develop a lightweight (less than 500 grams), very compact, high bandwidth, low power, thermally stable rotary actuator capable of producing torques in excess of 50 N.m and step resolutions as fine as 0.003 degrees. To achieve a relatively high torsional stiffness in excess of 1000 Nm/radian, the design utilizes a combination of harmonic drive and multistage planetary gearing. The unique design feature of this actuator that contributes to its light weight and extremely precise motion capability is a redundant stepper motor driving the output through a multistage reducing gearbox. The rotary actuator is powered by a high reliability space-rated stepper motor designed and constructed by Moog, Inc. The motor is a three-phase stepper motor of 15 degree step angle, producing twenty-four full steps per revolution. Since micro-stepping is not used in the design, and un-powered holding torque is exhibited at every commanded step, the rotary actuator is capable of reacting to torques as high as 35 Nm by holding position with the power off. The output is driven through a gear transmission having a total train ratio of 5120:1, resulting in a resolution of 0.003 degrees output rotation per motor step. The modular design of the multi-stage output transmission makes possible the addition of designs having different output parameters, such as lower torque and higher output speed capability. Some examples of an actuator family based on this growth capability will be presented in the paper.

Nalbandian, Ruben

2005-07-01

303

Electrorepulsive actuator  

NASA Technical Reports Server (NTRS)

The invention is a linear actuator that operates under the principle that like charges repel and opposite charges attract. The linear actuator consists of first and second pairs of spaced opposed conductors where one member of each pair of conductors is attached to a fixed member, and where the other member of each pair of conductors is attached to a movable member such as an elongated rod. The two pairs of spaced conductors may be provided in the form of two spacedly interwound helical vanes where the conductors are located on the opposite sides of the two helical vanes. One helical vane extends inwardly from a housing and the other helical vane extends outwardly from an elongated rod. The elongated rod may be caused to move linearly with respect to the housing by applying appropriate charges of like or opposite polarity to the electrical conductors on the helical vanes.

Collins, Earl R., Jr. (inventor); Curry, Kenneth C. (inventor)

1992-01-01

304

Electron and Ion Phase Space Holes From Buneman Instabilities in a Current-Driven Plasma  

NASA Astrophysics Data System (ADS)

Recent 1-D simulations of a current-driven plasma(D. L. Newman, Invited Paper, this meeting) show that a strong local double-layer electric field accelerates electrons into a beam. The resulting two-stream instability produces electron phase-space holes traveling in the direction of the electron beam. In a later stage, after ions have been accelerated in the opposite direction by the same double-layer field, the simulation reveals a train of spatially-alternating electron and ion phase-space holes moving slowly in the direction of the ion beam. We postulate that this alternation results from the trapping of ions and electrons in successive potential minima and maxima of a wave train. The origin of this wave train is likely to be a modified Buneman instability, which can occur only in the presence of cold accelerated ions. This instability is slow because of kinetic effects in the hot electron distribution. By contrast, the initial current is stable to Buneman growth because both the initial ion and electron distributions are hot. Other aspects of Buneman instabilities and effects of higher dimensions are also discussed.

Goldman, M. V.; Newman, D. L.; Mangeney, A.

2001-10-01

305

Impurity transport driven by ion temperature gradient turbulence in tokamak plasmas  

SciTech Connect

Impurity transport driven by electrostatic turbulence is analyzed in weakly collisional tokamak plasmas using a semianalytical model based on a boundary layer solution of the gyrokinetic equation. Analytical expressions for the perturbed density responses are derived and used to determine the stability boundaries and the quasilinear particle fluxes. For moderate impurity charge number Z, the stability boundaries are very weakly affected by the increasing impurity charge for constant effective charge, while for lower impurity charge the influence of impurities is larger, if the amount of impurities is not too small. Scalings of the mode frequencies and quasilinear fluxes with charge number, effective charge, impurity density scale length, and collisionality are determined and compared to quasilinear gyrokinetic simulations with GYRO[J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] resulting in very good agreement. Collisions do not affect the mode frequencies, growth rates, and impurity fluxes significantly. The eigenfrequencies and growth rates depend only weakly on Z and Z{sub eff} but they are sensitive to the impurity density gradient scale length. An analytical approximate expression of the zero-flux impurity density gradient is derived and used to discuss its parametric dependencies.

Fueloep, T.; Pusztai, I. [Department of Applied Physics, Nuclear Engineering, Chalmers University of Technology and Euratom-VR Association, Goeteborg SE-41296 (Sweden); Braun, S. [Max-Planck-Institut fuer Plasmaphysik, Greifswald 17491 (Germany)

2010-06-15

306

Impurity transport driven by ion temperature gradient turbulence in tokamak plasmas  

NASA Astrophysics Data System (ADS)

Impurity transport driven by electrostatic turbulence is analyzed in weakly collisional tokamak plasmas using a semianalytical model based on a boundary layer solution of the gyrokinetic equation. Analytical expressions for the perturbed density responses are derived and used to determine the stability boundaries and the quasilinear particle fluxes. For moderate impurity charge number Z, the stability boundaries are very weakly affected by the increasing impurity charge for constant effective charge, while for lower impurity charge the influence of impurities is larger, if the amount of impurities is not too small. Scalings of the mode frequencies and quasilinear fluxes with charge number, effective charge, impurity density scale length, and collisionality are determined and compared to quasilinear gyrokinetic simulations with GYRO [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] resulting in very good agreement. Collisions do not affect the mode frequencies, growth rates, and impurity fluxes significantly. The eigenfrequencies and growth rates depend only weakly on Z and Zeff but they are sensitive to the impurity density gradient scale length. An analytical approximate expression of the zero-flux impurity density gradient is derived and used to discuss its parametric dependencies.

Fülöp, T.; Braun, S.; Pusztai, I.

2010-06-01

307

Numerical Simulations of Plasma Based Flow Control Applications  

NASA Technical Reports Server (NTRS)

A mathematical model was developed to simulate flow control applications using plasma actuators. The effects of the plasma actuators on the external flow are incorporated into Navier Stokes computations as a body force vector. In order to compute this body force vector, the model solves two additional equations: one for the electric field due to the applied AC voltage at the electrodes and the other for the charge density representing the ionized air. The model is calibrated against an experiment having plasma-driven flow in a quiescent environment and is then applied to simulate a low pressure turbine flow with large flow separation. The effects of the plasma actuator on control of flow separation are demonstrated numerically.

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

2005-01-01

308

Shear flow-driven electrostatic instabilities in low density and low temperature pair-ion plasmas with and without electrons  

SciTech Connect

The shear flow-driven electrostatic instabilities are investigated in ideal low density, low temperature pair-ion-electron and pure pair-ion plasmas in several different cases, including homogeneous and inhomogeneous density effects. In uniform pair-ion-electron plasma, when the shear flow is of the order of the acoustic speed, the purely growing D'Angelo mode can give rise to electrostatic fields. In the case of an inhomogeneous plasma, the drift wave becomes unstable. The presence of negative ions, however, reduces the growth rate. If the positive and negative ions are not in thermal equilibrium with each other, then the shear flow also gives rise to an electrostatic instability in pure pair-ion plasma.

Saleem, H.; Batool, N. [National Centre for Physics (NCP), Quaid-i-Azam University Campus, Islamabad (Pakistan); Poedts, S. [Centre for Plasma Astrophysics, Katholieke Universiteit Leuven, 3001 Leuven (Belgium)

2011-05-15

309

First Complete Determination of Plasma Physical Parameters Across a Coronal Mass Ejection-driven Shock  

NASA Astrophysics Data System (ADS)

We report on the study of a fast coronal mass ejection (CME)-driven shock associated with the solar eruption of 2002 March 22. This event was observed in the intermediate corona both in white light and the extreme ultraviolet (EUV) by the LASCO and UVCS instruments on board the Solar and Heliospheric Observatory, as well as in metric and decametric wavelengths through space- and ground-based radio observatories. Clear signatures of shock transit are (1) strong type II emission lanes observed after the CME initiation, (2) strong O VI ??1032, 1037 line profile broadenings (up to ~2 × 107 K) associated with the shock transit across the UVCS slit field of view, and (3) a density enhancement located in LASCO images above the CME front. Since the UVCS slit was centered at 4.1 R sun, in correspondence with the flank of the expanding CME, this observation represents the highest UV detection of a shock obtained so far with the UVCS instrument. White-light and EUV data have been combined in order to estimate not only the shock compression ratio and the plasma temperature, but also the strength of the involved coronal magnetic fields, by applying the Rankine-Hugoniot equations for the general case of oblique shocks. Results show that, for a compression ratio X = 2.06 as derived from LASCO data, the coronal plasma is heated across the shock from an initial temperature of 2.3 × 105 K up to 1.9 × 106 K, while at the same time the magnetic field undergoes a compression from a pre-shock value of ~0.02 G up to a post-shock field of ~0.04 G. Magnetic and kinetic energy density increases at the shock are comparable (in agreement with the idea of equipartition of energy), and both are more than two times larger than the thermal energy density increase. This is the first time that a complete characterization of pre- and post-shock plasma physical parameters has been derived in the solar corona.

Bemporad, A.; Mancuso, S.

2010-09-01

310

Design of an energy efficient and economical actuator for automobile windows  

E-print Network

This thesis describes the design and analysis of an efficient, yet low cost, drum driven window actuation system for an automotive power window. The design uses a novel approach that involves using cables to both actuate ...

Durand, Keith (Keith V.)

2007-01-01

311

Dielectric Actuation of Polymers  

NASA Astrophysics Data System (ADS)

Dielectric polymers are widely used in a plurality of applications, such as electrical insulation, dielectric capacitors, and electromechanical actuators. Dielectric polymers with large strain deformations under an electric field are named dielectric elastomers (DE), because of their relative low modulus, high elongation at break, and outstanding resilience. Dielectric elastomer actuators (DEA) are superior to traditional transducers as a muscle-like technology: large strains, high energy densities, high coupling efficiency, quiet operation, and light weight. One focus of this dissertation is on the design of DE materials with high performance and easy processing. UV radiation curing of reactive species is studied as a generic synthesis methodology to provide a platform for material scientists to customize their own DE materials. Oligomers/monomers, crosslinkers, and other additives are mixed and cured at appropriate ratios to control the stress-strain response, suppress electromechanical instability of the resulting polymers, and provide stable actuation strains larger than 100% and energy densities higher than 1 J/g. The processing is largely simplified in the new material system by removal of the prestretching step. Multilayer stack actuators with 11% linear strain are demonstrated in a procedure fully compatible with industrial production. A multifunctional DE derivative material, bistable electroactive polymer (BSEP), is invented enabling repeatable rigid-to-rigid deformation without bulky external structures. Bistable actuation allows the polymer actuator to have two distinct states that can support external load without device failure. Plasticizers are used to lower the glass transition temperature to 45 °C. Interpenetrating polymer network structure is established inside the BSEP to suppress electromechanical instability, providing a breakdown field of 194 MV/m and a stable bistable strain as large as 228% with a 97% strain fixity. The application of BSEP in tactile display is investigated by the prototyping of a large scale refreshable Braille display device. Braille is a critical way for the vision impaired community to learn literacy and improve life quality. Current piezoelectrics-based refreshable Braille display technologies are limited to up to 1 line of Braille text, due to the bulky size of bimorph actuators. Based on the unique actuation feature of BSEP, refreshable Braille display devices up to smartphone-size have been demonstrated by polymer sheet laminates. Dots in the devices can be individually controlled via incorporated field-driven BSEP actuators and Joule heater units. A composite material consisting of silver nanowires (AgNW) embedded in a polymer substrate is brought up as a compliant electrode candidate for BSEP application. The AgNW composite is highly conductive (Rs: 10 ?/sq) and remains conductive at strains as high as 140% (Rs: <10 3 ?/sq). The baseline conductivity has only small changes up to 90% strain, which makes it low enough for both field driving and stretchable Joule heating. An out-of-plane bistable area strain up to 68% under Joule heating is achieved.

Niu, Xiaofan

312

Chaos and chaos control in a strongly driven thermionic plasma diode  

Microsoft Academic Search

In a periodically driven thermionic diode period doubling cascades, period adding and low-dimensional chaos are found. Some dynamical properties of the driven discharge are comparable to strongly driven diode resonant circuits. The chaotic oscillations of the discharge current are controlled using occasional proportional feedback and an improved difference feedback method. Feedback constants are predetermined by the local analysis of the

T. Mausbach; T. Klinger; A. Piel

1999-01-01

313

Improved Electrohydraulic Linear Actuators  

NASA Technical Reports Server (NTRS)

A product line of improved electrohydraulic linear actuators has been developed. These actuators are designed especially for use in actuating valves in rocket-engine test facilities. They are also adaptable to similar industrial uses. Advantageous features of the electrohydraulic linear actuators with respect to shortcomings of prior electrohydraulic linear actuators are described.

Hamtil, James

2002-01-01

314

Tailoring electron energy distribution functions through energy confinement in dual radio-frequency driven atmospheric pressure plasmas  

SciTech Connect

A multi-scale numerical model based on hydrodynamic equations with semi-kinetic treatment of electrons is used to investigate the influence of dual frequency excitation on the effective electron energy distribution function (EEDF) in a radio-frequency driven atmospheric pressure plasma. It is found that variations of power density, voltage ratio, and phase relationship provide separate control over the electron density and the mean electron energy. This is exploited to directly influence both the phase dependent and time averaged effective EEDF. This enables tailoring the EEDF for enhanced control of non-equilibrium plasma chemical kinetics at ambient pressure and temperature.

O'Neill, C.; Waskoenig, J. [Centre for Plasma Physics, School of Maths and Physics, Queen's University Belfast, Belfast BT7 1NN (United Kingdom); Gans, T. [Centre for Plasma Physics, School of Maths and Physics, Queen's University Belfast, Belfast BT7 1NN (United Kingdom); York Plasma Institute, Department of Physics, University of York, York YO10 5DD (United Kingdom)

2012-10-08

315

Plasma structuring by the gradient drift instability at high latitudes and comparison with velocity shear driven processes  

NASA Technical Reports Server (NTRS)

Using results of the in situ measurements made by the DE 2 satellite, the nature of plasma structuring at high latitudes, caused by the gradient drift instability process, is described. Using noon-midnight and dawn-dusk orbits of the DE 2 satellite, it was possible to examine the simultaneous density and electric field spectra of convecting large-scale plasma density enhancements in the polar cap known as 'patches', in directions parallel and perpendicular to their antisunward convection. The results provide evidence for the existence of at least two generic classes of instabilities operating in the high-latitude ionosphere: one driven by large-scale density gradients in a homogeneous convection field with respect to the neutrals, and the other driven by the structured convection field itself in an ambient ionosphere where density fluctuations are ubiquitous.

Basu, Sunanda; Mackenzie, E.; Basu, S.; Coley, W. R.; Sharber, J. R.; Hoegy, W. R.

1990-01-01

316

An Experimental Study of Continuous Plasma Flows Driven by a Confined Arc in a Transverse Magnetic Field  

NASA Technical Reports Server (NTRS)

A crossed-field, continuous-flow plasma accelerator has been built and operated. The highest measured velocity of the flow, which was driven by the interaction of the electric and magnetic fields, was about 500 meters per second. Some of the problems discussed are ion slip, stability and uniformity of the discharge, effect of the magnetic field on electron emission, use of preionization, and electrode contamination.

Barger, R. L.; Brooks, J. D.; Beasley, W. D.

1961-01-01

317

Ferroelectric actuators in the electromechanical interface  

NASA Astrophysics Data System (ADS)

The requirements of a control actuator are examined, and the unique capabilities of the type of an actuator driven by ferroelectric materials that exhibit piezoelectric characteristics when electrically poled to meet these requirements are demonstrated. It is shown that, when substantial energy is required from an actuator, actuators configured as stacks of ferroelectric disks are most suitable. They develop high force, respond extremely fast, can be proportionately charged, have almost infinite resolution, require no holding current to maintain displacement, and are neither influenced by nor produce magnetic fields. In addition, ferroelectric actuators are not prone to corrosion and have no mechanically wearing components. A very fast and precise steering mirror system is described that employs a split stack assembly.

O'Neill, C. G.; O'Neill, C. H.

1990-11-01

318

Memory metal actuator  

NASA Technical Reports Server (NTRS)

A mechanical actuator can be constructed by employing a plurality of memory metal actuator elements in parallel to control the amount of actuating force. In order to facilitate direct control by digital control signals provided by a computer or the like, the actuating elements may vary in stiffness according to a binary relationship. The cooling or reset time of the actuator elements can be reduced by employing Peltier junction cooling assemblies in the actuator.

Ruoff, C. F. (inventor)

1985-01-01

319

Temperature-gradient-driven flows of ions and neutrals in dusty plasmas  

Microsoft Academic Search

It is shown that in low-temperature plasma devices with pulsed external current circuits such as thermal emission converters and plasma diodes, the only forces inducing plasma flows are due to the temperature stresses on ions. These flows are similar to the plasma “residual” rotations in tokamaks. However, they are connected with the perpendicular viscosity dependence of the ion heat fluxes,

V. S. Tsypin; S. V. Vladimirov; M. Tendler; A. S. de Assis; C. A. de Azevedo

1998-01-01

320

Temperature-gradient-driven flows of ions and neutrals in dusty plasmas  

Microsoft Academic Search

It is shown that in low-temperature plasma devices with pulsed external current circuits such as thermal emission converters and plasma diodes, the only forces inducing plasma flows are due to the temperature stresses on ions. These flows are similar to the plasma ``residual'' rotations in tokamaks. However, they are connected with the perpendicular viscosity dependence of the ion heat fluxes,

V. S. Tsypin; S. V. Vladimirov; M. Tendler; A. S. de Assis; C. A. de Azevedo

1998-01-01

321

Temperature-gradient-driven flows of ions and neutrals in dusty plasmas  

Microsoft Academic Search

It is shown that in the low-temperature plasma devices with pulsed external current circuits such as thermal emission converters and plasma diodes, the only forces inducing plasma flows are due to the temperature stresses on ions. These flows are similar to the plasma ``residual'' rotations in tokamaks. However, they are connected with the perpendicular viscosity dependence of the ion heat

V. S. Tsypin; S. V. Vladimirov; M. Tendler; C. A. de Azevedo; A. S. de Assis

1998-01-01

322

Temperature-gradient-driven flows of ions and neutrals in dusty plasmas  

Microsoft Academic Search

It is shown that in the low-temperature plasma devices with pulsed external current circuits such as thermal emission converters and plasma diodes, the only forces inducing plasma flows are due to the temperature stresses on ions. These flows are similar to the plasma “residual” rotations in tokamaks. However, they are connected with the perpendicular viscosity dependence of the ion heat

V. S. Tsypin; S. V. Vladimirov; M. Tendler; C. A. de Azevedo; A. S. de Assis

1998-01-01

323

Pressure-driven, resistive magnetohydrodynamic interchange instabilities in laser-produced high-energy-density plasmas  

E-print Network

laser beam interacting with a solid foil, a plasma bubble 6­9 is similar to those plasmas confined using proton backlighting of laser-foil interactions provide unique opportunities for studying magnetized plasma instabilities in laser-produced high-energy-density plasmas. Time-gated proton radiograph

324

The MJS-77 magnetometer actuator  

NASA Technical Reports Server (NTRS)

A two-position (0 deg and 180 deg) actuating mechanism (flipper) driven by alternately-heated wax motors (pellets) used to rotate the low field triaxial fluxgate magnetometer experiment on the 1977 Mariner Jupiter-Saturn spacecraft to its 0 deg and 180 deg positions is described. The magnetic field, power requirements, weight and volume of this device are discussed. The problems encountered in design and development of this mechanism are presented.

Stange, W. C.

1977-01-01

325

The MJS-77 magnetometer actuator  

NASA Technical Reports Server (NTRS)

A two-position (0 deg and 180 deg) actuating mechanism (flipper) driven by alternately-heated wax motors (pellets) will be used to rotate the low field triaxial fluxgate magnetometer experiment on the 1977 Mariner Jupiter-Saturn spacecraft to its 0 deg and 180 deg positions. The magnetic field, power requirements, weight and volume of this device are very restrictive. The problems encountered in design and development of this mechanism are presented.

Stange, W. C.

1977-01-01

326

Impact absorption of a dual-crawler-driven robot  

Microsoft Academic Search

This paper introduces a tracked robot that consists of the proposed crawler module, in which a planetary gear reducer is adopted as the power transmission device to give two different outputs with just one actuator. Compared with each module driven by two actuators, the module driven by just one actuator could perform a good impact absorption when a collision occurs

Qiquan Quan; Shugen Ma; Rongqiang Liu; Bin Li

2009-01-01

327

Piezoelectric multilayer actuator life test.  

PubMed

Potential NASA optical missions such as the Space Interferometer Mission require actuators for precision positioning to accuracies of the order of nanometers. Commercially available multilayer piezoelectric stack actuators are being considered for driving these precision mirror positioning mechanisms. These mechanisms have potential mission operational requirements that exceed 5 years for one mission life. To test the feasibility of using these commercial actuators for these applications and to determine their reliability and the redundancy requirements, a life test study was undertaken. The nominal actuator requirements for the most critical actuators on the Space Interferometry Mission (SIM) in terms of number of cycles was estimated from the Modulation Optics Mechanism (MOM) and Pathlength control Optics Mechanism (POM) and these requirements were used to define the study. At a nominal drive frequency of 250 Hz, one mission life is calculated to be 40 billion cycles. In this study, a set of commercial PZT stacks configured in a potential flight actuator configuration (pre-stressed to 18 MPa and bonded in flexures) were tested for up to 100 billion cycles. Each test flexure allowed for two sets of primary and redundant stacks to be mechanically connected in series. The tests were controlled using an automated software control and data acquisition system that set up the test parameters and monitored the waveform of the stack electrical current and voltage. The samples were driven between 0 and 20 V at 2000 Hz to accelerate the life test and mimic the voltage amplitude that is expected to be applied to the stacks during operation. During the life test, 10 primary stacks were driven and 10 redundant stacks, mechanically in series with the driven stacks, were open-circuited. The stroke determined from a strain gauge, the temperature and humidity in the chamber, and the temperature of each individual stack were recorded. Other properties of the stacks, including the displacement from a capacitance gap sensor and impedance spectra were measured at specific intervals. The average degradation in the stroke over the life test was found to be small (<3%) for the primary stacks and <4% for the redundant stacks. It was noted that about half of the stroke reduction occurred within the first 10 billion cycles. At the end of the life test, it was found that the actuator could recover about half of the lost stroke by applying a dc voltage of 100 V at room temperature. The data up to 100 billion cycles for these tests and the analysis of the experimental results are presented in this paper. PMID:21507759

Sherrit, Stewart; Bao, Xiaoqi; Jones, Christopher M; Aldrich, Jack B; Blodget, Chad J; Moore, James D; Carson, John W; Goullioud, Renaud

2011-04-01

328

Strategies for mitigating the ionization-induced beam head erosion problem in an electron-beam-driven plasma wakefield accelerator  

NASA Astrophysics Data System (ADS)

Strategies for mitigating ionization-induced beam head erosion in an electron-beam-driven plasma wakefield accelerator (PWFA) are explored when the plasma and the wake are both formed by the transverse electric field of the beam itself. Beam head erosion can occur in a preformed plasma because of a lack of focusing force from the wake at the rising edge (head) of the beam due to the finite inertia of the electrons. When the plasma is produced by field ionization from the space charge field of the beam, the head erosion is significantly exacerbated due to the gradual recession (in the beam frame) of the 100% ionization contour. Beam particles in front of the ionization front cannot be focused (guided) causing them to expand as in vacuum. When they expand, the location of the ionization front recedes such that even more beam particles are completely unguided. Eventually this process terminates the wake formation prematurely, i.e., well before the beam is depleted of its energy. Ionization-induced head erosion can be mitigated by controlling the beam parameters (emittance, charge, and energy) and/or the plasma conditions. In this paper we explore how the latter can be optimized so as to extend the beam propagation distance and thereby increase the energy gain. In particular we show that, by using a combination of the alkali atoms of the lowest practical ionization potential (Cs) for plasma formation and a precursor laser pulse to generate a narrow plasma filament in front of the beam, the head erosion rate can be dramatically reduced. Simulation results show that in the upcoming “two-bunch PWFA experiments” on the FACET facility at SLAC national accelerator laboratory the energy gain of the trailing beam can be up to 10 times larger for the given parameters when employing these techniques. Comparison of the effect of beam head erosion in preformed and ionization produced plasmas is also presented.

An, W.; Zhou, M.; Vafaei-Najafabadi, N.; Marsh, K. A.; Clayton, C. E.; Joshi, C.; Mori, W. B.; Lu, W.; Adli, E.; Corde, S.; Litos, M.; Li, S.; Gessner, S.; Frederico, J.; Hogan, M. J.; Walz, D.; England, J.; Delahaye, J. P.; Muggli, P.

2013-10-01

329

A Possible Route to Spontaneous Reduction of the Heat Conductivity by a Temperature Gradient-driven Instability in Electron-Ion Plasmas  

Microsoft Academic Search

We have shown that there exist low-frequency growing modes driven by a global temperature gradient in electron and ion plasmas by linear perturbation analysis within the framework of plasma kinetic theory. The driving force of the instability is the local deviation of the distribution function from the Maxwell-Boltzmann distribution due to a global temperature gradient. Application of the results to

Makoto Hattori; Keiichi Umetsu

2000-01-01

330

Electron shear-flow-driven instability in magnetized plasmas with magnetic field gradient  

SciTech Connect

It is found that the zero-order current associated with electron shear flow produces a drift wave in magnetized plasmas, which can become unstable under certain conditions. This wave will be particularly important in low density and low temperature plasmas of heavy ions. As an example, numerical estimates are presented for a barium plasma with parameters compatible with experiments.

Saleem, Hamid [National Centre for Physics (NCP), Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan); Eliasson, Bengt [Faculty of Physics and Astronomy, Ruhr-University Bochum, Bochum 44780 (Germany)

2011-05-15

331

Thermo-magnetic materials for use in designing intelligent actuators  

SciTech Connect

The authors present the concept of an intelligent thermal actuator designed by using thermally sensitive magnetic materials. The use of the magnetic transition of FeRh alloy is very effective in increasing the actuator functions. These functions are freedom of direction, tuning temperature, and increasing both sensitivity and power. Two new types of actuator, a remote controlled optical driven thermo-magnetic motor and a temperature sensitive spring-less valve, are proposed and experimental results are shown.

Ohtani, Yoshimutsu; Yoshimura, Fumikatsu; Hatakeyama, Iwao [NTT Interdisciplinary Research Labs., Tokai, Ibaraki (Japan); Ishii, Yoshikazu [NTT Interdisciplinary Research Labs., Musashino, Tokyo (Japan)

1994-12-31

332

Alternating current-driven non-thermal arc plasma torch working with air medium at atmospheric pressure  

NASA Astrophysics Data System (ADS)

This work is devoted to the investigation of the discharge characteristics of high-frequency alternating current (ac) plasma torch working with air medium using electrical and spectroscopic techniques. A simple structure and compact ac plasma torch associated with a resonance power supply allows the generation of low power discharges (lower than 1 kW) with high voltage and low current. The discharge shows a negative resistance characteristic, and its curve shifts up with gas flow increased. The effects of power on the emission intensity of NO (A 2?+ ? X 2?), OH (A 2? ? X 2?, 0-0), N2(C 3?u ? B 3?g), H? and O (3p^{5}P \\to 3S^{5}S_{2}^{0}) and their spatial distributions in plasma jet axial direction were investigated. It has been found that the emission intensities of NO, OH, N2, H? and O rise with an increase in power dissipation. With increasing axial distances of plasma jet from nozzle exit, the emission intensity of OH increases and then decreases, while the emission intensities of other species decrease sharply. The vibrational temperature is much higher than the gas temperature, which demonstrates the ac-driven arc discharge deviation from thermal equilibrium plasma.

Ni, Guohua; Lin, Qifu; Li, Lei; Cheng, Cheng; Chen, Longwei; Shen, Jie; Lan, Yan; Meng, Yuedong

2013-11-01

333

Evaluation of piezoceramic actuators for control of aircraft interior noise  

NASA Technical Reports Server (NTRS)

Results of an experiment to evaluate piezoceramic actuators as the control actuator for active control of interior noise in a large-scale fuselage model are presented. Control was demonstrated for tonal excitation using a time domain least mean squares algorithm. A maximum of four actuator channels and six error signals were used. The actuators were employed for control of noise at frequencies where interior cavity modes were the dominant response and for driven acoustic responses where a structure resonance was dominant. Global reductions of 9 to 12 dB were obtained for the cases examined. The most effective configuration of skin-mounted actuators was found to be a pure in-plane forcing function as opposed to a bending excitation. The frame-mounted actuators were found to be equally effective as the skin-mounted actuators. However, both configurations resulted in local regions of unacceptably high vibration response in the structure.

Silcox, Richard J.; Lefebvre, Sylvie; Metcalf, Vern L.; Beyer, Todd B.; Fuller, Chris R.

1992-01-01

334

The influence of surface properties on the plasma dynamics in radio-frequency driven oxygen plasmas: Measurements and simulations  

SciTech Connect

Plasma parameters and dynamics in capacitively coupled oxygen plasmas are investigated for different surface conditions. Metastable species concentration, electronegativity, spatial distribution of particle densities as well as the ionization dynamics are significantly influenced by the surface loss probability of metastable singlet delta oxygen (SDO). Simulated surface conditions are compared to experiments in the plasma-surface interface region using phase resolved optical emission spectroscopy. It is demonstrated how in-situ measurements of excitation features can be used to determine SDO surface loss probabilities for different surface materials.

Greb, Arthur; Niemi, Kari; O'Connell, Deborah; Gans, Timo [York Plasma Institute, Department of Physics, University of York, York, YO10 5DD (United Kingdom)] [York Plasma Institute, Department of Physics, University of York, York, YO10 5DD (United Kingdom)

2013-12-09

335

The influence of surface properties on the plasma dynamics in radio-frequency driven oxygen plasmas: Measurements and simulations  

NASA Astrophysics Data System (ADS)

Plasma parameters and dynamics in capacitively coupled oxygen plasmas are investigated for different surface conditions. Metastable species concentration, electronegativity, spatial distribution of particle densities as well as the ionization dynamics are significantly influenced by the surface loss probability of metastable singlet delta oxygen (SDO). Simulated surface conditions are compared to experiments in the plasma-surface interface region using phase resolved optical emission spectroscopy. It is demonstrated how in-situ measurements of excitation features can be used to determine SDO surface loss probabilities for different surface materials.

Greb, Arthur; Niemi, Kari; O'Connell, Deborah; Gans, Timo

2013-12-01

336

Efficient active actuation to imitate locomotion of gecko's toes using an ionic polymer-metal composite actuator enhanced by carbon nanotubes  

NASA Astrophysics Data System (ADS)

Active actuation of the adhesive pads is important for a gecko-robot climbing on walls. We demonstrate the fabrication of an ionic polymer-metal composite (IPMC) actuator enhanced with carbon nanotubes (CNTs) and its use for actively actuating an adhesive array to imitate the locomotion of gecko's toes. The as-fabricated IPMC actuator doped with CNTs exhibits a maximum blocking force of 3.59 gf driven at a low voltage of 3 V. It can be easily controlled by voltage signals to actuate an artificial gecko's toe to attach and detach from a surface. This will allow active, distributed actuation in a gecko robot.

Yu, Min; He, Qingsong; Yu, Dingshan; Zhang, Xiaoqing; Ji, Aihong; Zhang, Hao; Guo, Ce; Dai, Zhendong

2012-10-01

337

Plasma-Density Determination from X-Ray Radiography of Laser-Driven Spherical Implosions  

E-print Network

The fuel layer density of an imploding laser-driven spherical shell is inferred from framed x-ray radiographs. The density distribution is determined by using Abel inversion to compute the radial distribution of the opacity ...

Frenje, Johan A.

338

Observations of electron phase-space holes driven during magnetic reconnection in a laboratory plasma  

E-print Network

This work presents detailed experimental observations of electron phase-space holes driven during magnetic reconnection events on the Versatile Toroidal Facility. The holes are observed to travel on the order of or faster ...

Katz, N.

339

Microprocessor controlled force actuator  

NASA Technical Reports Server (NTRS)

The mechanical and electrical design of a prototype force actuator for vibration control of large space structures (LSS) is described. The force actuator is an electromagnetic system that produces a force by reacting against a proof-mass. The actuator has two colocated sensors, a digital microcontroller, and a power amplifier. The total weight of actuator is .998 kg. The actuator has a steady state force output of approximately 2.75 N from approximately 2 Hz to well beyond 1000 Hz.

Zimmerman, D. C.; Inman, D. J.; Horner, G. C.

1986-01-01

340

Improved plasma confinement and evidence for a pressure-driven instability from reduced magnetic field errors in the CTX spheromak  

SciTech Connect

The 0.67 m radius mesh flux conserver (MFC) in CTX was replaced by a solid flux conserver (SFC), resulting in greatly reduced field errors. Decreased spheromak open flux led to vastly improved decaying discharges, including increased global energy confinement times /tau//sub E/ (from 20 to 180 ..mu..s) and corresponding magnetic energy decay times /tau//sub B/sup 2// (from 0.7 to 2 ms). Improved confinement allowed the observation of a pressure-driven instability which ejects plasma from the spheromak interior to the wall. 9 refs., 3 figs.

Fernandez, J.C.; Wysocki, F.J.; Jarboe, T.R.; Barnes, C.W.; Henins, I.; Knox, S.O.; Marklin, G.J.

1989-01-01

341

Argon mini-arc meets its match: use of a laser-driven plasma source in ultraviolet-detector calibrations.  

PubMed

The National Institute of Standards and Technology operates two spectral comparator facilities, both of which are used to provide detector calibrations from the ultraviolet to the near-infrared spectral range. One, the Ultraviolet Spectral Comparator Facility (UV SCF), has been in operation for more than two decades, providing one of the core calibration services. Recently, the illumination source used in the UV SCF has been changed from an argon mini-arc source to a laser-driven plasma light source. This new source has higher brightness, a smaller source size, better temporal stability, and much better conversion efficiency than the previous source. The improvements in the capabilities are summarized. PMID:24663306

Arp, Uwe; Vest, Robert; Houston, Jeanne; Lucatorto, Thomas

2014-02-20

342

Minimizing Air Consumption of Pneumatic Actuators in Mobile Robots  

E-print Network

Minimizing Air Consumption of Pneumatic Actuators in Mobile Robots Grzegorz GRANOSIK1,2 and Johann--This paper introduces a new control method for pneumatic actuators, called "Proportional Position driven by a pneumatic cylinder with four ON-OFF valves. In addition, the proposed control system consumes

Borenstein, Johann

343

Surface resistance experiments with IPMC sensors and actuators  

Microsoft Academic Search

This paper describes experiments with the surface resistance of IPMC actuators and sensors. We measure the surface resistance of samples working as sensors or as a voltage driven actuators, as well as when insulated. The results show that in all cases the surface resistance of a sample is highly correlated to material curvature. Based on these observations we present an

A. Punning; M. Kruusmaa; A. Aabloo

2007-01-01

344

Particle in cell simulations of Buneman instability of a current-driven plasma with q-nonextensive electron velocity distribution  

NASA Astrophysics Data System (ADS)

The nonlinear evolution of low frequency Buneman instability in an unmagnetized current-driven plasma with q-nonextensive electron velocity distribution is investigated using particle in cell simulation. Simulation results show that the generation of electron phase space holes and the counter-streaming current induced in the plasma strongly depend on the q-parameter. It is found that by increasing the nonextensive parameter, the distribution of electron density becomes highly peaked. This density steepening or grating-like pattern occurs at the saturation time. In addition, a generalized dispersion relation is obtained using the kinetic theory. Analysis of the dispersion relation and the temporal evolution of the electric field energy density reveal that the growth rate of instability increases by increasing the q-parameter. Finally, the results of Maxwellian and q-nonextensive velocity distributions have been compared and discussed.

Niknam, A. R.; Roozbahani, H.; Hashemzadeh, M.; Komaizi, D.

2014-09-01

345

Physics-Based Model Driven by Plasma Drifts Obtained From the C\\/NOFS Satellite  

Microsoft Academic Search

An important parameter in determining low-latitude ionospheric plasma density is the plasma drift. Two instruments on-board the Communication\\/Navigation Outage System (C\\/NOFS) satellite were designed to directly or indirectly measure the plasma drifts: the Ion Velocity Drift Meter (IVM) and the Vector Electric Field Instrument (VEFI). By using the electric field measurements obtained from VEFI, the physics-based model (PBMOD) developed at

Y. Su; J. M. Retterer; R. Stoneback; O. de La Beaujardiere; P. A. Roddy; R. A. Heelis; R. F. Pfaff

2010-01-01

346

Superfluid helium sloshing dynamics induced oscillations and fluctuations of angular momentum, force and moment actuated on spacecraft driven by gravity gradient or jitter acceleration associated with slew motion  

NASA Technical Reports Server (NTRS)

The generalized mathematical formulation of sloshing dynamics for partially filled liquid of cryogenic superfluid helium II in dewar containers driven by the gravity gradient and jitter accelerations associated with slew motion for the purpose to perform scientific observation during the normal spacecraft operation are investigated. An example is given with the Advanced X-Ray Astrophysics Facility-Spectroscopy (AXAF-S) for slew motion which is responsible for the sloshing dynamics. The jitter accelerations include slew motion, spinning motion, atmospheric drag on the spacecraft, spacecraft attitude motions arising from machinery vibrations, thruster firing, pointing control of spacecraft, crew motion, etc. Explicit mathematical expressions to cover these forces acting on the spacecraft fluid systems are derived. The numerical computation of sloshing dynamics is based on the non-inertia frame spacecraft bound coordinate, and solve time-dependent, three-dimensional formulations of partial differential equations subject to initial and boundary conditions. The explicit mathematical expressions of boundary conditions to cover capillary force effect on the liquid-vapor interface in microgravity environments are also derived. The formulations of fluid moment and angular moment fluctuations in fluid profiles induced by the sloshing dynamics, together with fluid stress and moment fluctuations exerted on the spacecraft dewar containers have also been derived. Examples are also given for cases applicable to the AXAF-S spacecraft sloshing dynamics associated with slew motion.

Hung, R. J.

1994-01-01

347

Velocity-ion temperature gradient driven modes and angular momentum transport in magnetically confined plasmas  

E-print Network

Plasma confinement experiments continue to uncover fascinating phenomena that motivate theoretical discussion and exploration. In this thesis, we consider the phenomenon of angular momentum transport in magnetically confined ...

Thomas, John Chandler

2007-01-01

348

Design Considerations for Plasma Accelerators Driven by Lasers or Particle Beams  

E-print Network

laser-plasma accelerators were proposed, the technology toplasma physics, and not addressed the driver technology. Itplasma accelerators have benefitted greatly by recent improvements in linac technology

Schroeder, C. B.

2011-01-01

349

Electron properties and air mixing in radio frequency driven argon plasma jets at atmospheric pressure  

SciTech Connect

A time modulated radio frequency (RF) plasma jet operated with an Ar mixture is investigated by measuring the electron density and electron temperature using Thomson scattering. The measurements have been performed spatially resolved for two different electrode configurations and as a function of the plasma dissipated power and air concentration admixed to the Ar. Time resolved measurements of electron densities and temperatures during the RF cycle and after plasma power switch-off are presented. Furthermore, the influence of the plasma on the air entrainment into the effluent is studied using Raman scattering.

Gessel, Bram van; Bruggeman, Peter [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands)] [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Brandenburg, Ronny [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands) [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Leibniz Institute for Plasma Science and Technology (INP Greifswald), Felix-Hausdorff-Str. 2, D-17489 Greifswald (Germany)

2013-08-05

350

Bubble regime for ion acceleration in a laser-driven plasma  

SciTech Connect

Proton trapping and acceleration by an electron bubble-channel structure in laser interaction with high-density plasma is investigated by using three-dimensional particle-in-cell simulations. It is shown that protons can be trapped, bunched, and efficiently accelerated for appropriate laser and plasma parameters, and the proton acceleration is enhanced if the plasma consists mainly of heavier ions such as tritium. The observed results are analyzed and discussed in terms of a one-dimensional analytical three-component-plasma wake model.

Shen Baifei [Shanghai Institute of Optics and Fine Mechanics, P.O. Box 800-211, Shanghai 201800 (China); Accelerator Systems Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Argonne Accelerator Institute, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Li Yuelin [Accelerator Systems Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Argonne Accelerator Institute, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Yu, M. Y. [Institut fuer Theoretische Physik I, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Cary, John [Tech-X Corporation, Boulder, Colorado 80303 (United States); Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States)

2007-11-15

351

Multilayer Piezoelectric Stack Actuator Characterization  

NASA Technical Reports Server (NTRS)

Future NASA missions are increasingly seeking to use actuators for precision positioning to accuracies of the order of fractions of a nanometer. For this purpose, multilayer piezoelectric stacks are being considered as actuators for driving these precision mechanisms. In this study, sets of commercial PZT stacks were tested in various AC and DC conditions at both nominal and extreme temperatures and voltages. AC signal testing included impedance, capacitance and dielectric loss factor of each actuator as a function of the small-signal driving sinusoidal frequency, and the ambient temperature. DC signal testing includes leakage current and displacement as a function of the applied DC voltage. The applied DC voltage was increased to over eight times the manufacturers' specifications to investigate the correlation between leakage current and breakdown voltage. Resonance characterization as a function of temperature was done over a temperature range of -180C to +200C which generally exceeded the manufacturers' specifications. In order to study the lifetime performance of these stacks, five actuators from one manufacturer were driven by a 60volt, 2 kHz sine-wave for ten billion cycles. The tests were performed using a Lab-View controlled automated data acquisition system that monitored the waveform of the stack electrical current and voltage. The measurements included the displacement, impedance, capacitance and leakage current and the analysis of the experimental results will be presented.

Sherrit, Stewart; Jones, Christopher M.; Aldrich, Jack B.; Blodget, Chad; Bao, Xioaqi; Badescu, Mircea; Bar-Cohen, Yoseph

2008-01-01

352

High-quality electron beams from beam-driven plasma accelerators by wakefield-induced ionization injection.  

PubMed

We propose a new and simple strategy for controlled ionization-induced trapping of electrons in a beam-driven plasma accelerator. The presented method directly exploits electric wakefields to ionize electrons from a dopant gas and capture them into a well-defined volume of the accelerating and focusing wake phase, leading to high-quality witness bunches. This injection principle is explained by example of three-dimensional particle-in-cell calculations using the code OSIRIS. In these simulations a high-current-density electron-beam driver excites plasma waves in the blowout regime inside a fully ionized hydrogen plasma of density 5×10(17)cm-3. Within an embedded 100???m long plasma column contaminated with neutral helium gas, the wakefields trigger ionization, trapping of a defined fraction of the released electrons, and subsequent acceleration. The hereby generated electron beam features a 1.5 kA peak current, 1.5???m transverse normalized emittance, an uncorrelated energy spread of 0.3% on a GeV-energy scale, and few femtosecond bunch length. PMID:24483670

Martinez de la Ossa, A; Grebenyuk, J; Mehrling, T; Schaper, L; Osterhoff, J

2013-12-13

353

Breakdown of Electrostatic Predictions for the Nonlinear Dispersion Relation of a Stimulated Raman Scattering-Driven Plasma Wave  

SciTech Connect

The kinetic nonlinear dispersion relation, and frequency shift {delta}{omega}{sub srs}, of a plasma wave driven by stimulated Raman scattering (SRS) are presented. Our theoretical calculations are fully electromagnetic, and use an adiabatic expression for the electron susceptibility which accounts for the change in phase velocity as the wave grows. When k{lambda}{sub D} {approx}> 0.35 (k being the plasma wave number and {lambda}{sub D} the Debye length), {delta}{omega}{sub srs} is significantly larger than could be inferred by assuming that the wave is freely propagating. Our theory is in excellent agreement with 1-D Eulerian Vlasov-Maxwell simulations when 0.3 {le} k{lambda}{sub D} {le} 0.58, and allows discussion of previously proposed mechanisms for Raman saturation. In particular, we find that no 'loss of resonance' of the plasma wave would limit the Raman growth rate, and that saturation through a phase detuning between the plasma wave and the laser drive is mitigated by wave number shifts.

Benisti, D; Strozzi, D J; Gremillet, L

2007-05-08

354

Heating mechanisms and particle flow balancing of capacitively coupled plasmas driven by combined dc/rf sources  

SciTech Connect

Heating mechanisms and particle flow balancing of capacitively coupled plasmas driven by combined dc/rf sources have been investigated by particle-in-cell/Monte Carlo simulations. At low pressure, Ohmic heating will be suppressed and stochastic heating will be enhanced while increasing dc voltage. But the overall heating power will decrease. No heating mode transitions are observed. At high pressure, bulk plasma density decreases at low dc and rf voltage, and the one-side {alpha}-{gamma} transition will occur while increasing dc voltage. After the transition, the plasma density abruptly increases and average electron energy drops. As the result of that, the plasma is sustained by secondary electrons instead of the Ohmic heating of the bulk electrons. The dc source will reduce, or even eliminate at high voltage, the electron charge flowing into the dc powered electrode. Therefore the ratio of electron-to-ion charge flowing into the rf powered electrode over one period increases from -1.0 to -2.0--2.3 for low pressure and -2.2--5.0 for high pressure.

Jiang Wei; Xu Xiang; Dai Zhongling; Wang Younian [State Key Laboratory of Materials Modification, School of Physics and Optoelectronic Technology, Dalian University of Technology, 116024, Dalian (China)

2008-03-15

355

All-Optical Control of Nonlinear Self-Focusing in Plasmas Using Non-Resonantly Driven Plasma Wave  

SciTech Connect

Excitation of plasma density perturbations by an initially bi-color laser pulse helps to control nonlinear refraction in the plasma and enables various types of laser self-guiding. In this report we consider a setup that not only makes possible the transport of laser energy over cm-long relatively dense plasmas (n{sub 0} = 10{sup 18} cm{sup -3}) but also transforms the pulse into the unique format inaccessible to the conventional amplification techniques (relativistically intense periodic trains of few-cycle spikes). This well focusable pulse train is a novel light source interesting for ultra-fast high-field science applications. The opposite case of suppression of nonlinear self-focusing and dynamical self-guiding of an over-critical multi-frequency pulse is proposed for the proof-of-principle experimental study.

Kalmykov, S. Y.; Shadwick, B. A. [Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, NE 68588-0299 (United States); Downer, M. C. [The Department of Physics, C1500, University of Texas at Austin, Austin, TX 78712 (United States)

2010-11-04

356

Magnetically Driven Flows in Arched Plasma Structures E. V. Stenson* and P. M. Bellan  

E-print Network

Institute of Technology, Pasadena, California 91125, USA (Received 12 August 2011; published 13 August 2012 limitations; coronal events are not reproducible and cannot be measured in situ. Although advancements have an initial low-density plasma. This quickly evolves into a current- carrying, plasma-filled flux tube

Bellan, Paul M.

357

Synchro-Compton radiation from charges driven by circularly polarized large-amplitude plasma waves  

SciTech Connect

The spectral and angular characteristics of the power radiated by a streaming electron-positron plasma which is permeated by a circularly polarized large-amplitude hydrodynamic wave are evaluated. The modifications of the synchro-Compton process induced under these conditions are examined. Similar modifications are to be expected for more realistic large-amplitude plasma waves propagating in pulsar winds. 27 references.

Hoerhager, M.; Leubner, C.

1985-09-01

358

Effect of pressure-driven MHD instabilities on confinement in reactor-relevant high-beta helical plasmas  

SciTech Connect

Through the experiment data analysis in the large helical device (LHD), the influence of the global MHD instability and the relatively short wave length MHD instabilities driven turbulence on the confinement performance in reactor-relevant high-beta helical plasmas is studied. The comparison of the energy confinement time between just before global MHD instability disappears and after that, and the estimation of the saturated mode structure by the multi-channel soft x-ray measurement enable us to quantitatively estimate the influence of the global interchange type MHD instability with different saturated mode structures on the confinement performance. According to the comparison between thermal conductivities in experiments and those predicted by theoretical transport models, the transport properties in the peripheral region of high beta LHD plasmas are quite similar with anomalous transport model based on an interchange type MHD instability driven turbulence, and that result is supported by the dependence of the density fluctuation with relatively short wave length on beta value.

Watanabe, K. Y.; Takemura, Y.; Funaba, H.; Sakakibara, S.; Tanaka, K.; Ohdachi, S.; Toi, K.; Narushima, Y. [National Institute for Fusion Science, Toki 509-5292 (Japan); Masamune, S. [Kyoto Institute of Technology, Sakyo-ku, Kyoto 606-8585 (Japan); Watanabe, F. [Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)

2011-05-15

359

Application of a pulsed, RF-driven, multicusp source for low energy plasma immersion ion implantation  

SciTech Connect

The multicusp ion source can produce large volumes of uniform, quiescent, high density plasmas. A plasma chamber suited for plasma immersion ion implantation (PIII) was readily made. Conventional PIII pulses the bias voltage applied to the substrate which is immersed in a CW mode plasma. Here, a method by which the plasma itself is pulsed was developed. Typically pulse lengths of 500 {mu}s are used and are much shorter than that of the substrate voltage pulse (5-15 ms). This approach, together with low gas pressures and low bias voltages, permits the constant energy implantation of an entire wafer simultaneously without glow discharge. Results show that this process can yield implant currents of up to 2.5 mA/cm{sup 2}; thus very short implant times can be achieved. Uniformity of the ion flux is also discussed. As this method can be scaled to any dimension, it can be made to handle any size wafer.

Wengrow, A.B.; Leung, K.N.; Perkins, L.T.; Pickard, D.S.; Rickard, M.; Williams, M.D. [Lawrence Berkeley Lab., CA (United States); Tucker, M. [Spectrum Sciences, Inc., Santa Clara, CA (United States)

1996-06-01

360

Smart Material-Actuated Rotor Technology – SMART  

Microsoft Academic Search

Vibration, noise, and aerodynamic design compromises are primary barriers to further improvements in effectiveness of the helicopter. The MD900 light utility helicopter main rotor system is modified to include in-blade smart material actuation for active control. A piezoelectric (PE)-driven trailing edge flap is used for vibration, noise, and aerodynamic performance improvements. A shape memory alloy (SMA)-driven trailing edge trim tab

Friedrich K. Straub; Dennis K. Kennedy; David B. Domzalski; Ahmed A. Hassan; Hieu Ngo; V. Anand; Terry Birchette

2004-01-01

361

Simulation of sloshing dynamics induced forces and torques actuated on dewar container driven by gravity gradient and jitter accelerations in microgravity  

NASA Technical Reports Server (NTRS)

Some experimental spacecraft use superconducting sensors for gyro read-out and so must be maintained at a very low temperature. The boil-off from the cryogenic liquid used to cool the sensors can also be used, as the Gravity Probe B (GP-B) spacecraft does, as propellant to maintain attitude control and drag-free operation of the spacecraft. The cryogenic liquid for such spacecraft is, however, susceptible to both slosh-like motion and non-axisymmetric configurations under the influence of various kinds of gravity jitter and gravity gradient accelerations. Hence, it is important to quantify the magnitude of the liquid-induced perturbations on the spacecraft. We use the example of the GP-B to investigate such perturbations by numerical simulations. For this spacecraft disturbances can be imposed on the liquid by atmospheric drag, spacecraft attitude control maneuvers, and the earth's gravity gradient. More generally, onboard machinery vibrations and crew motion can also create disturbances. Recent studies suggest that high frequency disturbances are relatively unimportant in causing liquid motions in comparison to low frequency ones. The results presented here confirm this conclusion. After an initial calibration period, the GP-B spacecraft rotates in orbit at 0.1 rpm about the tank symmetry axis. For this rotation rate, the equilibrium liquid free surface shape is a 'doughnut' configuration for all residual gravity levels of 10(exp -6) g(sub 0) or less, as shown by experiments and by numerical simulations; furthermore, the superfluid behavior of the 1.8 K liquid helium used in GP-B eliminates temperature gradients and therefore such effects as Marangoni convection do not have to be considered. Classical fluid dynamics theory is used as the basis of the numerical simulations here, since Mason's experiments show that the theory is applicable for cryogenic liquid helium in large containers. To study liquid responses to various disturbances, we investigate and simulate three levels of gravity jitter (10(exp -6), 10(exp -7), and 10(exp -8) g(sub 0)) each at three predominant frequencies (0.1, 1.0, and 10 Hz), combined with a gravity gradient appropriate for the GP-B orbit. Dynamical evolution of sloshing dynamics excited fluid forces and torque fluctuations exerted on the dewar container driven by the combined gravity gradient and jitter accelerations are also investigated and simulated.

Hung, R. J.; Pan, H. L.

1993-01-01

362

Nanoporous carbon actuator and methods of use thereof  

DOEpatents

An electrochemically driveable actuator according to one embodiment includes a nanoporous carbon aerogel composition capable of exhibiting charge-induced reversible strain when wetted by an electrolyte and a voltage is applied thereto. An electrochemically driven actuator according to another embodiment includes a nanoporous carbon aerogel composition wetted by an electrolyte; and a mechanism for causing charge-induced reversible strain of the composition. A method for electrochemically actuating an object according to one embodiment includes causing charge-induced reversible strain of a nanoporous carbon aerogel composition wetted with an electrolyte to actuate the object by the strain.

Biener, Juergen (San Leandro, CA); Baumann, Theodore F. (Discovery Bay, CA); Shao, Lihua (Karlsruhe, DE); Weissmueller, Joerg (Stutensee, DE)

2012-07-31

363

The study of mode instability in rotamak plasmas driven by rotating magnetic field  

NASA Astrophysics Data System (ADS)

The instability modes, which include the n = 1 tilt, radial shift and kink-like mode, have been observed in rotamak plasma through the measurements of Mirnov coil array and the images of a high speed CCD camera. The effect of three instability modes on plasma discharge is completely different: plasma current can be decreased, terminated and enhanced respectively by tilt, radial shift and kink-like mode. Experiments clearly demonstrate that the appearance and suppression of instability modes strongly depends on the configuration and the strength of magnetic field (X. Yang, et al, Phys. Rev. Lett. 102, 255004 (2009)). Mode switching also has been observed in disruptive discharges.

Yang, Xiaokang; Goss, Jermain; Kalaria, Dharah; Houshmandyar, Saeid; Huang, Tian-Sen

2011-11-01

364

Plasma heating by a relativistic electron beam. II - Two-stream and return current driven instabilities  

NASA Astrophysics Data System (ADS)

Anomalous heating is investigated in the system composed of a plasma and a relativistic electron beam (REB) along a uniform external magnetic field. A wave kinetic equation derived previously is applied to the REB-plasma system. As the mechanism of plasma heating, the wave of the two-stream instability and Buneman or ion-acoustic wave induced by the return current are coupled through the nonlinear wave-particle interaction. High heating rate is obtained from the estimation of the stopping power. The turbulent collision frequency and the perpendicular energy transfer agree with the experimental and numerical results.

Okazaki, T.

1980-10-01

365

A Simple Type of Magnetically Driven Jets: an Astrophysical Plasma Gun  

Microsoft Academic Search

We propose a simple theoretical formulation of the problem of magnetically driven outflows when poloidal magnetic flux surfaces are absent, and the magnetic field has only a toroidal component. The present formulation is the limiting case of the more general Grad-Shafranov one, when Bp\\/Bphi --> 0. We show that the toroidal magnetic field alone is very efficient in accelerating and

J. Contopoulos

1995-01-01

366

New insights on Titan's plasma-driven Schumann resonance inferred from Huygens and Cassini data  

Microsoft Academic Search

After a preliminary analysis of the low-frequency data collected with the electric antenna of the Permittivity, Wave and Altimetry (PWA) experiment onboard the Huygens Probe that landed on Titan on 14 January, 2005, it was anticipated in a previous article [Béghin et al., 2007. A Schumann-like resonance on Titan driven by Saturn's magnetosphere possibly revealed by the Huygens Probe. Icarus,

C. Béghin; P. Canu; E. Karkoschka; C. Sotin; C. Bertucci; W. S. Kurth; J. J. Berthelier; R. Grard; M. Hamelin; K. Schwingenschuh; F. Simões

2009-01-01

367

Self-consistent Langmuir waves in resonantly driven thermal plasmas R. R. Lindberg,a  

E-print Network

with driven, electrostatic particle simulations over a range of temperatures. This extends earlier work, USA and Center for Beam Physics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 these conditions, one can derive the normal modes of the distribution function the singular Case­Van Kampen modes1

Wurtele, Jonathan

368

Semiconductor bridge (SCB) igniter studies: 1, Comparison of SCB and hot-wire pyrotechnic actuators  

SciTech Connect

Sandia National Laboratories has developed a means for igniting pyrotechnics, propellants and primary or secondary explosives using a semiconductor bridge (SCB) instead of the small metal bridgewires, called hot wires, conventionally used for explosive components. The SCB is a heavily n-doped silicon film, typically 100 ..mu..m long by 380 ..mu..m wide by 2 ..mu..m thick, which when driven with a short (20 ..mu..s), low-energy current pulse (less than 3 mJ), generates a hot plasma that ignites the explosives. We report in this paper a study of pyrotechnic actuators built with SCB igniters in which we obtained the Langlie All-Fire, Langlie No-Fire and Electrostatic Discharge (ESD) characteristics. Two SCB designs were tested. The first (designated as a type 3-2) was the rectangularly shaped bridge described above. The second (designated as a type 15) included a modification of the rectangular bridge consisting of a narrow waist region. We compare our data for these prototype SCB components with the same actuators built with conventional hot-wire igniters. The results obtained demonstrated the main characteristics of SCB devices: (1) the SCB actuators functioned at one-tenth the input energy of the hot-wire actuators, (2) had higher no-fire currents than the hot-wire devices, (3) passed ESD tests, and (4) functioned in a few tens of microseconds versus the millisecond response of the hot-wire components. 8 refs., 5 figs., 3 tabs.

Bickes, R.W. Jr.; Schlobohm, S.L.; Ewick, D.W.

1988-01-01

369

Heliopause Instabilities Driven by Plasma-Neutral Interaction: Linear Analysis from Fluid Model  

SciTech Connect

The heliopause (HP) is the outer edge of the heliosphere that separates the tenuous and hot heliosheath plasma from the relatively dense and cool magnetized plasma of the local interstellar medium (LISM). As a surface of tangential discontinuity, the HP is subject to both Rayleigh-Taylor (RT) and Kelvin-Helmholtz (KH) instabilities. The coupling between plasma ions and neutral atoms through charge exchange provides an ''effective gravity'' for RT, while shear flows due to the velocity difference between the heliosheath and the interstellar flows can drive KH modes. We derive the linearized dispersion relations for waves propagating along the surface of this discontinuity using a fluid picture, to study the possibility for both RT and KH instabilities, including a second population of energetic neutrals produced by charge exchange interactions between the hot solar wind plasma in the heliosheath with interstellar hydrogen. We show that due to charge exchange interactions, the HP is unconditionally unstable to all perturbations.

Dasgupta, B.; Avinash, K. [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Florinski, V.; Zank, G. P.; Heerikhuisen, J. [Department of Physics, University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Bandyopadhyay, A. [Department of Computer Science, Alabama A and M University, Normal, AL 35762 (United States)

2011-09-21

370

Extreme ultraviolet diagnostics of preformed plasma in laser-driven proton acceleration experiments  

NASA Astrophysics Data System (ADS)

Proton acceleration experiments involving a 5?m thick Ti foil target irradiation are carried out with the femtosecond Ti:sapphire laser JLITE-X. The plasma emission at 13.5nm is recorded employing concave multilayer mirrors, which image the front- and rear-side plasmas onto the sensitive surfaces of a fast x-ray photodiode and a backside-illuminated charge coupled device. Online time-of-flight fast-particle measurements are performed simultaneously with the extreme ultraviolet (XUV) measurements. A strong correlation is observed between the energetic proton signal and the spatiotemporal behavior of the XUV plasma emission. In particular, the longer duration of the prepulse-produced XUV plasma emission indicates a lowering of the maximum proton energy. This allows using the XUV emission for the diagnostics of the high-intensity laser-solid-target interaction.

Ragozin, Eugene N.; Pirozhkov, Alexander S.; Yogo, Akifumi; Ma, Jinglong; Ogura, Koichi; Orimo, Satoshi; Sagisaka, Akito; Mori, Michiaki; Li, Zhong; Nishiuchi, Mamiko; Daido, Hiroyuki

2006-12-01

371

Plasma Physical Parameters along Coronal-mass-ejection-driven Shocks. I. Ultraviolet and White-light Observations  

NASA Astrophysics Data System (ADS)

In this work, UV and white-light (WL) coronagraphic data are combined to derive the full set of plasma physical parameters along the front of a shock driven by a coronal mass ejection. Pre-shock plasma density, shock compression ratio, speed, and inclination angle are estimated from WL data, while pre-shock plasma temperature and outflow velocity are derived from UV data. The Rankine-Hugoniot (RH) equations for the general case of an oblique shock are then applied at three points along the front located between 2.2 and 2.6 R ? at the shock nose and at the two flanks. Stronger field deflection (by ~46°), plasma compression (factor ~2.7), and heating (factor ~12) occur at the nose, while heating at the flanks is more moderate (factor 1.5-3.0). Starting from a pre-shock corona where protons and electrons have about the same temperature (Tp ~ Te ~ 1.5 × 106 K), temperature increases derived with RH equations could better represent the proton heating (by dissipation across the shock), while the temperature increase implied by adiabatic compression (factor ~2 at the nose, ~1.2-1.5 at the flanks) could be more representative of electron heating: the transit of the shock causes a decoupling between electron and proton temperatures. Derived magnetic field vector rotations imply a draping of field lines around the expanding flux rope. The shock turns out to be super-critical (sub-critical) at the nose (at the flanks), where derived post-shock plasma parameters can be very well approximated with those derived by assuming a parallel (perpendicular) shock.

Bemporad, A.; Susino, R.; Lapenta, G.

2014-04-01

372

Low-frequency Waves Driven by Kelvin-Helmholtz Instability in a Bounded Plasma Flow  

NASA Astrophysics Data System (ADS)

Kelvin-Helmholtz instability in a plane three-layered plasma is investigated. A general dispersion relation for the case of arbitrarily orientated magnetic fields and flow velocities is derived, and its solutions for a bounded plasma flow in a longitudinal magnetic field are studied numerically. On analyzing Kelvin-Helmholtz instability for different ion acoustic velocities, perturbations with wavelengths on the order of or longer than the flow thickness are shown to grow in an arbitrary direction even at a zero temperature. In a low-temperature plasma, solutions resulting in kink-like deformations of the plasma flow turns out to grow at a higher rate than ones resulting in sausage-like deformations. Oscillations excited at small angles with respect to the magnetic field exist in a limited range of the small wavenumbers even if the finite width of the transition region between the flow and the ambient plasma neglegted. The results obtained are applied to explain the excitation of the low-frequency long-wavelength oscillations propagating along the magnetic field in the plasma sheet boundary layer of the Earth's magnetotail.

Shevelev, M. M.; Burinskaya, T. M.

2011-10-01

373

Series Elastic Actuators  

E-print Network

This thesis presents the design, construction, control and evaluation of a novel force controlled actuator. Traditional force controlled actuators are designed from the premise that "Stiffer is better''. This approach ...

Williamson, Matthew M.

1995-09-07

374

Micromachined electrostatic vertical actuator  

SciTech Connect

A micromachined vertical actuator utilizing a levitational force, such as in electrostatic comb drives, provides vertical actuation that is relatively linear in actuation for control, and can be readily combined with parallel plate capacitive position sensing for position control. The micromachined electrostatic vertical actuator provides accurate movement in the sub-micron to micron ranges which is desirable in the phase modulation instrument, such as optical phase shifting. For example, compact, inexpensive, and position controllable micromirrors utilizing an electrostatic vertical actuator can replace the large, expensive, and difficult-to-maintain piezoelectric actuators. A thirty pound piezoelectric actuator with corner cube reflectors, as utilized in a phase shifting diffraction interferometer can be replaced with a micromirror and a lens. For any very precise and small amplitudes of motion, micromachined electrostatic actuation may be used because it is the most compact in size, with low power consumption and has more straightforward sensing and control options.

Lee, A.P.; Sommargren, G.E.; McConaghy, C.F.; Krulevitch, P.A.

1999-10-19

375

Micromachined electrostatic vertical actuator  

DOEpatents

A micromachined vertical actuator utilizing a levitational force, such as in electrostatic comb drives, provides vertical actuation that is relatively linear in actuation for control, and can be readily combined with parallel plate capacitive position sensing for position control. The micromachined electrostatic vertical actuator provides accurate movement in the sub-micron to micron ranges which is desirable in the phase modulation instrument, such as optical phase shifting. For example, compact, inexpensive, and position controllable micromirrors utilizing an electrostatic vertical actuator can replace the large, expensive, and difficult-to-maintain piezoelectric actuators. A thirty pound piezoelectric actuator with corner cube reflectors, as utilized in a phase shifting diffraction interferometer can be replaced with a micromirror and a lens. For any very precise and small amplitudes of motion` micromachined electrostatic actuation may be used because it is the most compact in size, with low power consumption and has more straightforward sensing and control options.

Lee, Abraham P. (Walnut Creek, CA); Sommargren, Gary E. (Santa Cruz, CA); McConaghy, Charles F. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA)

1999-10-19

376

Low backlash direct drive actuator  

DOEpatents

A low backlash direct drive actuator is described which comprises a motor such as a stepper motor having at least 200 steps per revolution; a two part hub assembly comprising a drive hub coaxially attached to the shaft of the motor and having a plurality of drive pins; a driven hub having a plurality of bores in one end thereof in alignment with the drive pins in the drive hub and a threaded shaft coaxially mounted in an opposite end of the driven hub; and a housing having a central bore therein into which are fitted the drive hub and driven hub, the housing having a motor mount on one end thereof to which is mounted the stepper motor, and a closed end portion with a threaded opening therein coaxial with the central bore in the housing and receiving therein the threaded shaft attached to the driven hub. Limit switches mounted to the housing cooperate with an enlarged lip on the driven hub to limit the lateral travel of the driven hub in the housing, which also acts to limit the lateral travel of the threaded shaft which functions as a lead screw. 10 figs.

Kuklo, T.C.

1994-10-25

377

Low backlash direct drive actuator  

DOEpatents

A low backlash direct drive actuator is described which comprises a motor such as a stepper motor having at least 200 steps per revolution; a two part hub assembly comprising a drive hub coaxially attached to the shaft of the motor and having a plurality of drive pins; a driven hub having a plurality of bores in one end thereof in alignment with the drive pins in the drive hub and a threaded shaft coaxially mounted in an opposite end of the driven hub; and a housing having a central bore therein into which are fitted the drive hub and driven hub, the housing having a motor mount on one end thereof to which is mounted the stepper motor, and a closed end portion with a threaded opening therein coaxial with the central bore in the housing and receiving therein the threaded shaft attached to the driven hub. Limit switches mounted to the housing cooperate with an enlarged lip on the driven hub to limit the lateral travel of the driven hub in the housing, which also acts to limit the lateral travel of the threaded shaft which functions as a lead screw.

Kuklo, Thomas C. (Oakland, CA)

1994-01-01

378

Design of an XUV FEL Driven by the Laser-Plasma Accelerator at theLBNL LOASIS Facility  

SciTech Connect

We present a design for a compact FEL source of ultrafast, high-peak flux, soft x-ray pulses employing a high-current, GeV-energy electron beam from the existing laser-plasma accelerator at the LBNL LOASIS laser facility. The proposed ultra-fast source would be intrinsically temporally synchronized to the drive laser pulse, enabling pump-probe studies in ultra-fast science with pulse lengths of tens of fs. Owing both to the high current ({approx} 10 kA) and reasonable charge/pulse ({approx} 0.1-0.5 nC) of the laser-plasma-accelerated electron beams, saturated output fluxes are potentially 10{sup 13}--10{sup 14} photons/pulse. We examine devices based both on SASE and high-harmonic generated input seeds to give improved coherence and reduced undulator length, presenting both analytic scalings and numerical simulation results for expected FEL performance. A successful source would result in a new class of compact laser-driven FELs in which a conventional RF accelerator is replaced by a GeV-class laser-plasma accelerator whose active acceleration region is only a few cm in length.

Schroeder, Carl B.; Fawley, W.M.; Esarey, Eric; Leemans, W.P.

2006-09-01

379

Transition from interpulse to afterglow plasmas driven by repetitive short-pulse microwaves in a multicusp magnetic field  

SciTech Connect

In the power-off phase, plasmas generated by repetitive short-pulse microwaves in a multicusp magnetic field show a transitive nature from interpulse to afterglow as a function of pulse duration t{sub w} = 20-200 {mu}s. The ionized medium can be driven from a highly non equilibrium to an equilibrium state inside the pulses, thereby dictating the behavior of the plasma in the power-off phase. Compared to afterglows, interpulse plasmas observed for t{sub w} < 50 {mu}s are characterized by a quasi-steady-state in electron density that persists for {approx} 20-40 {mu}s even after the end of the pulse and has a relatively slower decay rate ({approx} 4.3 Multiplication-Sign 10{sup 4} s{sup -1}) of the electron temperature, as corroborated by optical measurements. The associated electron energy probability function indicates depletion in low energy electrons which appear at higher energies just after the end of the pulse. The transition occurs at t{sub w} {approx} 50 {mu}s as confirmed by time evolution of integrated electron numbers densities obtained from the distribution function.

Pandey, Shail; Sahu, Debaprasad; Bhattacharjee, Sudeep [Department of Physics, Indian Institute of Technology, Kanpur 208016 (India)

2012-08-15

380

Electromagnetic rotational actuation.  

SciTech Connect

There are many applications that need a meso-scale rotational actuator. These applications have been left by the wayside because of the lack of actuation at this scale. Sandia National Laboratories has many unique fabrication technologies that could be used to create an electromagnetic actuator at this scale. There are also many designs to be explored. In this internship exploration of the designs and fabrications technologies to find an inexpensive design that can be used for prototyping the electromagnetic rotational actuator.

Hogan, Alexander Lee

2010-08-01

381

An optimal real-time controller for vertical plasma stabilization  

E-print Network

Modern Tokamaks have evolved from the initial axisymmetric circular plasma shape to an elongated axisymmetric plasma shape that improves the energy confinement time and the triple product, which is a generally used figure of merit for the conditions needed for fusion reactor performance. However, the elongated plasma cross section introduces a vertical instability that demands a real-time feedback control loop to stabilize the plasma vertical position and velocity. At the Tokamak \\`a Configuration Variable (TCV) in-vessel poloidal field coils driven by fast switching power supplies are used to stabilize highly elongated plasmas. TCV plasma experiments have used a PID algorithm based controller to correct the plasma vertical position. In late 2013 experiments a new optimal real-time controller was tested improving the stability of the plasma. This contribution describes the new optimal real-time controller developed. The choice of the model that describes the plasma response to the actuators is discussed. The ...

Cruz, N; Coda, S; Duval, B P; Le, H B; Rodrigues, A P; Varandas, C A F; Correia, C M B A; Goncalves, B S

2014-01-01

382

Explosive-driven hemispherical implosions for generating fusion plasmas. Interim report  

Microsoft Academic Search

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 resulting from the fusion of deuterium. Several approaches were used to initiate fusion in deuterium. The simpliest and most direct proved to be in predetonated stoichiometric mixture of deuterium-oxygen. The

D. Sagie; I. I. Glass

1982-01-01

383

Theory of trapped-ion-temperature-gradient-driven turbulence and transport in low-collisionality plasmas  

Microsoft Academic Search

A novel theory for the nonlinear evolution of the trapped-ion-temperature-gradient-driven mode, based on the turbulent trapping of resonant ions in the electrostatic potential of the waves, is proposed. A statistical description is adopted whereby the self-consistent evolution of the two-point correlation function of the trapped-particle distribution function is followed in phase space. Threshold-dependent, non-steady-state turbulence (nonlinear instability) is shown to

H. Biglari; P. H. Diamond; P. W. Terry

1988-01-01

384

Electrical Servo Actuator Bracket.  

National Technical Information Service (NTIS)

A bracket for an electrical servo actuator is disclosed which was developed particularly for jet engine fuel control values. Said servo actuator is mounted on a support arm which is allowed to pivot on a bolt through a fixed mounting bracket. The actuator...

R. V. Sawyer

1980-01-01

385

Folded dielectric elastomer actuators  

Microsoft Academic Search

Polymer-based linear actuators with contractile ability are currently demanded for several types of applications. Within the class of dielectric elastomer actuators, two basic configurations are available today for such a purpose: the multi-layer stack and the helical structure. The first consists of several layers of elementary planar actuators stacked in series mechanically and parallel electrically. The second configuration relies on

Federico Carpi; Claudio Salaris; Danilo DeRossi

2007-01-01

386

Dual drive actuators  

NASA Technical Reports Server (NTRS)

A new class of electromechanical actuators is described. These dual drive actuators were developed for the NASA-JPL Galileo Spacecraft. The dual drive actuators are fully redundant and therefore have high inherent reliability. They can be used for a variety of tasks, and they can be fabricated quickly and economically.

Packard, D. T.

1982-01-01

387

Probe characterization of high-current driven metal plasma in a vacuum-arc rail gun  

NASA Astrophysics Data System (ADS)

The characteristics of metal plasma launched by high-current electric arc in a vacuum-arc rail gun are determined by employing electrical and magnetic probes. These measurements are validated by results from theoretical simulations. The arc coupled nonlinear circuit equations are solved simultaneously with the Newtonian arc motion and revealed the undercritically damped behavior of the arc current identical to the arc-current signal recorded by the Rogowski magnetic probe. Similarly the arc velocity and displacement derived from the signatures of B-dot probes are shown to concur closely with the results of J ×B propulsion from simulation. The heating of plasma is formulated in a three-electron population regime with direct arc energy coupling through magnetohydrodynamic, ion-acoustic, Coulomb, and neutral interactions. This results in high temperature (Te) of hundreds of eV in the arc as revealed by the simulation. Hence Te of the rapidly cooling and equilibrating plasma that emerged from the muzzle is high around 80-90eV, which is confirmed by Langmuir electric probe measurements. Density ne of this metal plasma is shown to be in the range 4×1021-6×1021m-3 and includes multiple ion charge states. The exit velocity of the plasma measured by a pair of Langmuir probes is close to 2.2×106cm/s and matched well with the arc velocity determined by the B-dot probes and the results from simulation.

Vijayan, T.; Roychowdhury, P.; Venkatramani, N.

2004-10-01

388

A large-stroke electrostatic micro-actuator  

NASA Astrophysics Data System (ADS)

Voltage-driven parallel-plate electrostatic actuators suffer from an operation range limit of 30% of the electrostatic gap; this has restrained their application in microelectromechanical systems. In this paper, the travel range of an electrostatic actuator made of a micro-cantilever beam above a fixed electrode is extended quasi-statically to 90% of the capacitor gap by introducing a voltage regulator (controller) circuit designed for low-frequency actuation. The voltage regulator reduces the actuator input voltage, and therefore the electrostatic force, as the beam approaches the fixed electrode so that balance is maintained between the mechanical restoring force and the electrostatic force. The low-frequency actuator also shows evidence of high-order superharmonic resonances that are observed here for the first time in electrostatic actuators.

Towfighian, S.; Seleim, A.; Abdel-Rahman, E. M.; Heppler, G. R.

2011-07-01

389

Self - Organization of Zonal Flows Driven by Drift Mode Turulence in Space and Astrophysical Plasmas  

NASA Astrophysics Data System (ADS)

The interaction between broadband drill mode turbulence and zonal flows is an important topic associated with transport at plasma boundaries. The generation of zonal flows by the modulational instability of broad band drift waves has resulted in the observation of self organized solitary wave structures at the magnetopause. To understand these structures and their importance in space and astrophysical plasmas we have developed a unique numerical simulation code that describes drift wave - zonal flow turbulence. We show that observations by cluster space craft confirms the role of drift wave zonal Mow turbulence at the Earth's magnetopause and further demonstrates that the magnetopause boundary acts in a similar manner to transport barriers in tokamak fusion devices. Applications to other plasmas will also be presented.

Bingham, R.; Trines, R.; Mendonca, J. T.; Silva, L. O.; Shukla, P. K.; Dunlop, M. W.; Vaivads, A.; Davies, J. A.; Bamford, R. A.; Mori, W.; Tynan, G.

2008-12-01

390

Spatial distribution of the plasma parameters in a radio-frequency driven negative ion sourcea)  

NASA Astrophysics Data System (ADS)

Results from initial stage of modeling of the SPIDER source of negative hydrogen/deuterium ions currently under development in Consorzio RFX (Padova) regarding ITER are presented. A 2D model developed within the fluid plasma theory for low-pressure discharges (free-fall regime maintenance) is applied to the gas-discharge conditions planned and required for the SPIDER source: gas pressure of 0.3 Pa and radio-frequency (rf) power of 100 kW absorbed in a single driver. The results are for the spatial distribution of the plasma characteristics (charged particle densities, electron temperature and electron energy flux, plasma potential, and dc electric field) with conclusions for the role of the electron energy flux in the formation of the discharge structure.

Todorov, D.; Tarnev, Kh.; Paunska, Ts.; Lishev, St.; Shivarova, A.

2014-02-01

391

Spatial distribution of the plasma parameters in a radio-frequency driven negative ion source.  

PubMed

Results from initial stage of modeling of the SPIDER source of negative hydrogen/deuterium ions currently under development in Consorzio RFX (Padova) regarding ITER are presented. A 2D model developed within the fluid plasma theory for low-pressure discharges (free-fall regime maintenance) is applied to the gas-discharge conditions planned and required for the SPIDER source: gas pressure of 0.3 Pa and radio-frequency (rf) power of 100 kW absorbed in a single driver. The results are for the spatial distribution of the plasma characteristics (charged particle densities, electron temperature and electron energy flux, plasma potential, and dc electric field) with conclusions for the role of the electron energy flux in the formation of the discharge structure. PMID:24593544

Todorov, D; Tarnev, Kh; Paunska, Ts; Lishev, St; Shivarova, A

2014-02-01

392

Laser-driven hole boring and gamma-ray emission in high-density plasmas  

E-print Network

Ion acceleration in laser-produced dense plasmas is a key topic of many recent investigations thanks to its potential applications. Besides, at forthcoming laser intensities ($I \\gtrsim 10^{23} \\text{W}\\,\\text{cm}^{-2}$) interaction of laser pulses with plasmas can be accompanied by copious gamma-ray emission. Here we demonstrate the mutual influence of gamma-ray emission and ion acceleration during relativistic hole boring in high-density plasmas with ultra-intense laser pulses. If gamma-ray emission is abundant, laser pulse reflection and hole-boring velocity are lower and gamma-ray radiation pattern is narrower than in the case of low emission. Conservation of energy and momentum allows one to elucidate the effects of gamma-ray emission which are more pronounced at higher hole-boring velocities.

Nerush, Evgeny

2014-01-01

393

The effect of plasma heating on sublimation-driven flow in Io's atmosphere  

NASA Technical Reports Server (NTRS)

The atmospheric flow on Io is numerically computed in a flat 2-D axisymmetric geometry for a sublimation atmosphere on the trailing hemisphere subjected to plasma bombardment, UV heating, and IR cooling. Calculations are performed for subsolar vapor pressures of approximately 6.5 x 10(exp -3) Pa (approximately 3 x 10(exp 18) SO2/sq cm) and 6.8 x 10(exp -4) Pa (approximately 4 x 10(exp 17) SO2/sq cm); the latter approximates the vapor pressure of F. P. Fanale et al. (1982). The amount of plasma energy deposited in the atmosphere is 20% of the plasma flow energy due to corotation (J. A. Linker et al., 1988). It is found that plasma heating significantly inflates the upper atmosphere, increasing both the exobase altitude and the amount of surface covered by more than an exospheric column of gas. This in turn controls the supply of the Io plasma torus (M. A. McGrath and R. E. Johnson, 1987). The horizontal flow of mass and energy is also important in determining the exobase altitude; and it is shown that IR cooling can be important, although our use of the equilibrium, cool-to-space approximation for a pure SO2 gas (E. Lellouch et al., 1992) may overestimate this effect. The calculated exobase altitudes are somewhat lower than those suggested by McGrath and Johnson (1987) for supplying the torus, indicating the details of the plasma energy deposition and sputter ejection rate near the exobase, as well as the IR emission from this region need to be examined. In addition, the molecules sublimed (or sputtered) from the surface are transported to the exobase in times short compared to the molecular photodissociation time. Therefore, the exobase is dominated by molecular species and the exobase is supplied by a small region of the surface.

Wong, Mau C.; Johnson, Robert E.

1995-01-01

394

Influence of Ambient Plasmas to the Field Dynamics of Laser Driven Mass-Limited Targets  

SciTech Connect

Dilute plasmas surrounding mass-limited targets provide sufficient current for influencing strong fields, which are built up due to the interaction of an intense and ultrafast laser pulse. Such situation occurs, where evaporation of the target surface is present. The high-intensity laser pulse interacts with the quasi-isolated mass-limited target and the spatial wings of the intensity distribution account for ionization of the ambient plasma. A fast change of strong electrical fields following intense laser irradiation of water droplets (16 micron diameter) has been measured with proton imaging. An analytical model explains charge transport accounting for the observation.

Schnuerer, M.; Sokollik, T.; Steinke, S.; Nickles, P. V.; Sandner, W. [Max-Born Institut, Max-Born-Strasse 2a, D-12489 Berlin (Germany); Toncian, T.; Amin, M.; Willi, O. [Heinrich-Heine-Universtaet, D-40225Duessesldorf (Germany); Andreev, A. A. [Max-Born Institut, Max-Born-Strasse 2a, D-12489 Berlin (Germany); STC Vavilov State Optical Institut, 12 Birzhevaya line, 199034 St. Petersburg (Russian Federation)

2010-02-02

395

Possible energy gain for a plasma-liner-driven magneto-inertial fusion concept  

NASA Astrophysics Data System (ADS)

A one-dimensional parameter study of a Magneto-Inertial Fusion (MIF) concept indicates that significant gain may be achievable. This concept uses a dynamically formed plasma shell with inwardly directed momentum to drive a magnetized fuel to ignition, which in turn partially burns an intermediate layer of unmagnetized fuel. The concept is referred to as Plasma Jet MIF or PJMIF. The results of an adaptive mesh refinement Eulerian code (Crestone) are compared to those of a Lagrangian code (LASNEX). These are the first published results using the Crestone and LASNEX codes on the PJMIF concept.

Knapp, C. E.; Kirkpatrick, R. C.

2014-07-01

396

Effect of non-uniform electron energy distribution function on plasma production in large arc driven negative ion source  

SciTech Connect

Spatially non-uniform electron energy distribution function (EEDF) in an arc driven negative ion source (JAEA 10A negative ion source: 10 A NIS) is calculated numerically by a three-dimensional Monte Carlo kinetic model for electrons to understand spatial distribution of plasma production (such as atomic and ionic hydrogen (H{sup 0}/H{sup +}) production) in source chamber. The local EEDFs were directly calculated from electron orbits including electromagnetic effects and elastic/inelastic collision forces. From the EEDF, spatial distributions of H{sup 0}/H{sup +} production rate were obtained. The results suggest that spatial non-uniformity of H{sup 0}/H{sup +} productions is enhanced by high energy component of EEDF.

Shibata, T. [Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama 223-8522 (Japan); Fusion Research and Development Directorate, Japan Atomic Energy Agency, 801-1 Mukoyama, Naka 311-0193 (Japan); Koga, S.; Terasaki, R.; Hatayama, A. [Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama 223-8522 (Japan); Inoue, T.; Dairaku, M.; Kashiwagi, M.; Taniguchi, M.; Tobari, H.; Tsuchida, K.; Umeda, N.; Watanabe, K. [Fusion Research and Development Directorate, Japan Atomic Energy Agency, 801-1 Mukoyama, Naka 311-0193 (Japan)

2012-02-15

397

Considerations for Contractile Electroactive Materials and Actuators  

SciTech Connect

Ras Labs produces contractile electroactive polymer (EAP) based materials and actuators that bend, swell, ripple, and contract (new development) with low electric input. In addition, Ras Labs produces EAP materials that quickly contract and expand, repeatedly, by reversing the polarity of the electric input, which can be cycled. This phenomenon was explored using molecular modeling, followed by experimentation. Applied voltage step functions were also investigated. High voltage steps followed by low voltage steps produced a larger contraction followed by a smaller contraction. Actuator control by simply adjusting the electric input is extremely useful for biomimetic applications. Muscles are able to partially contract. If muscles could only completely contract, nobody could hold an egg, for example, without breaking it. A combination of high and low voltage step functions could produce gross motor function and fine manipulation within the same actuator unit. Plasma treated electrodes with various geometries were investigated as a means of providing for more durable actuation.

Lenore Rasmussen, David Schramm, Paul Rasmussen, Kevin Mullaly, Ras Labs, LLC, Intelligent Materials for Prosthetics & Automation, Lewis D. Meixler, Daniel Pearlman and Alice Kirk

2011-05-23

398

Bimorphic polymeric photomechanical actuator  

NASA Technical Reports Server (NTRS)

A bimorphic polymeric photomechanical actuator, in one embodiment using polyvinylidene fluoride (PVDF) as a photosensitive body, transmitting light over fiber optic cables, and controlling the shape and pulse duration of the light pulse to control movement of the actuator. Multiple light beams are utilized to generate different ranges of motion for the actuator from a single photomechanical body and alternative designs use multiple light beams and multiple photomechanical bodies to provide controlled movement. Actuator movement using one or more ranges of motion is utilized to control motion to position an actuating element in three dimensional space.

Sarkisov, Sergey S. (Inventor); Curley, Michael J. (Inventor); Adamovsky, Grigory (Inventor); Sarkisov, Jr., Sergey S. (Inventor); Fields, Aisha B. (Inventor)

2006-01-01

399

Omnidirectional Actuator Handle  

NASA Technical Reports Server (NTRS)

Proposed actuator handle comprises two normally concentric rings, cables, and pulleys arranged such that relative displacement of rings from concentricity results in pulling of cable and consequent actuation of associated mechanism. Unlike conventional actuator handles like levers on farm implements, actuated from one or two directions only, proposed handle reached from almost any direction and actuated by pulling or pushing inner ring in any direction with respect to outer ring. Flanges installed on inner ring to cover gap between inner ring and housing to prevent clothing from being caught.

Moetteli, John B.

1995-01-01

400

Formation of Optical Bullets in Laser-Driven Plasma Bubble Accelerators  

SciTech Connect

Electron density bubbles generated in plasma of density n{sub e{approx}10{sup 19}/cm{sup 3}} are shown to reshape copropagating probe pulses into optical 'bullets'. The bullets, reconstructed by frequency-domain interferometric techniques, are used to visualize bubble formation independently of relativistic electron generation.

Dong, P.; Reed, S. A.; Yi, S. A.; Shvets, G.; Downer, M. C. [Department of Physics, University of Texas at Austin, Austin, TX 78712 (United States); Kalmykov, S. [University of Nebraska, Lincoln, NE (United States); Matlis, N. H. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); McGuffey, C.; Bulanov, S. S.; Chvykov, V.; Kalintchenko, G.; Krushelnick, K.; Maksimchuk, A.; Matsuoka, T.; Thomas, A. G. R.; Yanovsky, V. [Center for Ultrafast Optical Science, University of Michigan, 2200 Bonisteel Blvd, Ann Arbor, MI 48109 (United States)

2010-11-04

401

Ion acoustic instability driven by a temperature gradient in laser-produced plasmas  

Microsoft Academic Search

The return current instability excited in laser-produced plasmas by a temperature gradient has been studied using a nonlocal theory of electron transport. The transport model is applicable for an arbitrary ratio of the temperature inhomogeneity scale length to the collisional mean free path. It is demonstrated that nonlocal thermal effects have a significant impact on the ion acoustic instability growth

A. V. Brantov; V. Yu. Bychenkov; W. Rozmus

2001-01-01

402

Linear Ion Temperature Gradient Driven Drift Modes in a Reversed Field Pinch Plasma  

Microsoft Academic Search

In Reversed Field Pinch (RFP) plasmas, tearing modes are usually considered responsible for global confinement losses. However, recently improved confinement has been observed when tearing modes are suppressed through current profile control. Although diffusivity has improved, it still exceeds classical and neoclassical estimates. The new mechanism is poorly understood but believed to be associated with smaller scale instabilities, and estimates

Varun Tangri; Paul Terry; R. E. Waltz

2008-01-01

403

The role of Nonlinear Ion Temperature Gradient Driven Drift Modes in a Reversed Field Pinch Plasma  

Microsoft Academic Search

The Ion Temperature gradient (ITG) mode has been rarely investigated in Reversed Field pinch (RFP) plasmas, although its role tokamak turbulence has been studied extensively. In this work, we investigate if it is plausible that ITG may play a role in particle and heat confinement in such devices. The linear stability and nonlinear saturation of ITG is investigated in the

Varun Tangri; Paul Terry; R. E. Waltz

2009-01-01

404

Large and powerful rf-driven hydrogen plasmas: negative ions for the heating systems of ITER  

NASA Astrophysics Data System (ADS)

Negative ion sources are an excellent example for the manifold of applications of low temperature plasmas which ranges from basic research to industrial applications. One of the outstanding application areas is in fusion, where a large and powerful negative hydrogen ion source is as a central component of the neutral beam injection systems for heating and current drive of the international fusion project ITER. The challenge to extract an ion current of 57 A (D) and 69 A (H) from a low temperature hydrogen plasma at low pressure (0.3 Pa) is accompanied by the challenge to accelerate the beam to 1 MeV. Large RF sources with the size of a door operating at a power of up to 800 kW must deliver a uniform and stable negative hydrogen ion current density higher than 200 A/m^2 over the total area for one hour. Simultaneously, the amount of co-extracted electrons should be kept below one in order to avoid severe damages of the extraction system. These requirements can be met only by combining the disciplines of low temperature plasma physics, plasma surface interaction, ion beam optics, beam physics, and mechanical and electrical engineering. The state of the art and prospects of the negative hydrogen ion source development will be discussed with emphasis on the physical aspects.

Fantz, Ursel

2012-10-01

405

Observation of Self-Generated Flows in Tokamak Plasmas with Lower-Hybrid-Driven Current  

E-print Network

In Alcator C-Mod discharges lower hybrid waves have been shown to induce a countercurrent change in toroidal rotation of up to 60??km/s in the central region of the plasma (r/a~<0.4). This modification of the toroidal ...

Rice, John E.

406

Magnetic fields in highly compressed plasma formed at the front of a laser-driven channel  

SciTech Connect

Dynamics of two-dimensional steady-state supersonic magnetized plasma flows around the head of the hole bored in short-pulse laser-target interactions has been studied. An ideal MHD simulation is used to examine the general structure of the flow and the dependence of the strong magnetic fields on its characteristics is considered.

Tatarinov, A. V.; Boyd, T. J. M. [Department of Physics, University of Essex, Colchester CO4 3SQ (United Kingdom)

1998-02-20

407

Strongly driven drift modes independent of resistivity in finite beta plasmas  

NASA Astrophysics Data System (ADS)

We study drift waves (DW) in collinear magnetic field, beta ˜ O(1) systems (e.g., FRCs), wherein the sonic and Alfven drift branches are strongly coupled. For isothermal perturbations, we find that finite beta is strongly stabilizing. With temperature perturbations, we find a rapidly growing instability, mediated by the Braginskii thermal force but not requiring resistivity. The growth rate peaks at the drift frequency. This mode has been described by Mikhailovskii but has not been well studied. The nonlocal and nonlinear theory of this mode is investigated. A finite beta 3D 2-fluid code with Hall terms and thermal force has been developed. The linear thermal force DW is confirmed. The code is also used to investigate dispersion characteristics and the ensuing turbulence. The code will also be used to study the interplay between DWs and the plasma thermoelectric effect. The latter effect generates a B x grad[T] current in magnetized plasmas and is of the same order as the plasma resistivity limited current in finite beta plasmas. It is of interest to study how drift wave turbulence would influence the thermoelectric effect and vice-versa.

Hung, Chingpui; Hassam, Adil

2010-11-01

408

Vlasov-Maxwell kinetic simulations of radio-frequency-driven ion flows in magnetized plasmas.  

PubMed

The generation of a coherent ion flow due to the injection in a plasma of a purely electrostatic wave of finite amplitude, propagating at right angle with the ambient uniform magnetic field, is investigated making use of a kinetic code which solves the fully nonlinear Vlasov equations for electrons and ions, coupled with the Maxwell equations, in one spatial and two velocity dimensions. A uniformly magnetized slab plasma is considered. The wave frequency is assumed in the range of the fourth harmonic of the ion cyclotron frequency, and the wave vector is chosen in order to model the propagation of an ion Bernstein wave. The computation of the first-order moment of the ion distribution function shows that indeed a quasistationary transverse average ion drift velocity is produced. The time evolution of the ion distribution function undergoes a "resonant" interaction of Cherenkov type, even if the plasma ions are magnetized (omega(ci)/omega(pi) approximately 0.5). During the wave-plasma interaction, the electron distribution function remains Gaussian-like, while increasing its energy content. PMID:12636820

Marchetto, Chiara; Califano, Francesco; Lontano, Maurizio

2003-02-01

409

Lower hybrid instability driven by mono-energy {alpha}-particles with finite pitch angle spread in a plasma  

SciTech Connect

A kinetic formalism of lower hybrid wave instability, driven by mono-energy {alpha}-particles with finite pitch angle spread, is developed. The instability arises through cyclotron resonance interaction with high cyclotron harmonics of {alpha}-particles. The {alpha}-particles produced in D-T fusion reactions have huge Larmor radii ({approx}10 cm) as compared to the wavelength of the lower hybrid wave, whereas their speed is an order of magnitude smaller than the speed of light in vacuum. As a result, large parallel phase velocity lower hybrid waves, suitable for current drive in tokamak, are driven unstable via coupling to high cyclotron harmonics. The growth rate decreases with increase in pitch angle spread of the beam. At typical electron density of {approx}10{sup 19} m{sup -3}, magnetic field {approx}4 Tesla and {alpha}-particle concentration {approx}0.1%, the large parallel phase velocity lower hybrid wave grows on the time scale of 20 ion cyclotron periods. The growth rate decreases with plasma density.

Kumar, Pawan; Singh, Vishwesh; Tripathi, V. K. [Department of Physics, IIT Delhi, New Delhi-110016 (India)

2013-02-15

410

The Next Generation of Space Plasma Analyzer - Deployable Radial Imaging for Velocity, Energy, and Density (DRIVEN)  

NASA Astrophysics Data System (ADS)

We present initial developments towards a space plasma analyzer capable of making simultaneous observations of cold (<1eV) and high-energy (5keV) space plasmas at revolutionary temporal and spatial resolution. "Top Hat" plasma analyzers [1] (the current "state of the art") typically have modest azimuthal resolution (c.f. 10 degrees, for reasons of electronic practicality), and can only read out a single energy at a time, thereby requiring a swept voltage to sample a range of energies. True energy imaging of particle populations was achieved with the Freja Cold Plasma Analyzer [2], and at higher time and energy resolution on subsequent sounding rocket flights using a CCD-based detection scheme, but only at energies below 200 eV [3]. We propose to overcome these shortcomings using novel particle optics and directly imaging space plasma distributions using a revolutionary 2D position-sensitive readout technique, thereby covering particle energies from cold to energetic while eliminating the need for an energy sweep. Measurements of <1eV electrons and ions are currently very challenging owing to effects of spacecraft charging. Existing s/c systems such as ASPOC on Cluster are complex, expensive and have a limited lifetime. Our boom-mounted sensor will automatically compensate for changes in spacecraft potential through the reverse biasing of its outer skin according to measurements from an integrated Langmuir probe. [1] Carlson et al., Adv. Space Res., 2(7), 67, (1982) [2] Whalen et al., Space Sci. Rev., (70), 541. (1994) [3] Knudsen et al., Rev. Sci. Instrum., (74), 202. (2003)

Collinson, G. A.; Moore, T. E.; Durachka, D.; Olson, D. K.; Knudsen, D. J.; Rozmarynowski, P.; Beamer, A. A.; Klenzing, J. H.

2010-12-01

411

Convection in Galaxy-Cluster Plasmas Driven by Active Galactic Nuclei and Cosmic-Ray This article has been downloaded from IOPscience. Please scroll down to see the full text article.  

E-print Network

Convection in Galaxy-Cluster Plasmas Driven by Active Galactic Nuclei and Cosmic-Ray Buoyancy This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2004 ApJ 616 IOPscience #12;CONVECTION IN GALAXY-CLUSTER PLASMAS DRIVEN BY ACTIVE GALACTIC NUCLEI AND COSMIC-RAY BUOYANCY

Chandran, Ben

412

Networked Rectenna Array for Smart Material Actuators  

NASA Technical Reports Server (NTRS)

The concept of microwave-driven smart material actuators is envisioned as the best option to alleviate the complexity associated with hard-wired control circuitry. Networked rectenna patch array receives and converts microwave power into a DC power for an array of smart actuators. To use microwave power effectively, the concept of a power allocation and distribution (PAD) circuit is adopted for networking a rectenna/actuator patch array. The PAD circuit is imbedded into a single embodiment of rectenna and actuator array. The thin-film microcircuit embodiment of PAD circuit adds insignificant amount of rigidity to membrane flexibility. Preliminary design and fabrication of PAD circuitry that consists of a few nodal elements were made for laboratory testing. The networked actuators were tested to correlate the network coupling effect, power allocation and distribution, and response time. The features of preliminary design are 16-channel computer control of actuators by a PCI board and the compensator for a power failure or leakage of one or more rectennas.

Choi, Sang H.; Golembiewski, Walter T.; Song, Kyo D.

2000-01-01

413

Improved Electrohydraulic Linear Actuators  

NASA Technical Reports Server (NTRS)

A product line of improved electrohydraulic linear actuators has been developed. These actuators are designed especially for use in actuating valves in rocket-engine test facilities. They are also adaptable to similar industrial uses. The advantageous features of the improved electrohydraulic linear actuators are best described with respect to shortcomings of prior electrohydraulic linear actuators that the improved ones are intended to supplant. The shortcomings are the following: They perform unreliably and inconsistently as positioning devices. Their capabilities for end-of-stroke buffering (that is, deceleration to gentle stops at designated stopping positions) range from unsatisfactory to nonexistent, with consequent potential for inducing catastrophic failures. It takes long times to modify standard actuators to meet specifications, and the costs of such modifications are high. In the cases of actuators equipped with fail-safe shutdown systems, the stroking times of these systems cannot be adjusted in the field.

Hamtil, James; Selinsky, T.

2002-01-01

414

Explosive-driven hemispherical implosions for generating fusion plasmas. Interim report  

SciTech Connect

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 resulting from the fusion of deuterium. Several approaches were used to initiate fusion in deuterium. The simpliest and most direct proved to be in predetonated stoichiometric mixture of deuterium-oxygen. The other successful method was 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. Nevertheless, this is the only known work where fusion neutrons were produced by chemical energy only in a direct and indirect manner.

Sagie, D.; Glass, I.I.

1982-03-01

415

Tuneable Auxiliary Control Mechanisms For RUM Actuators  

NASA Technical Reports Server (NTRS)

Tuneable auxiliary control mechanisms for rotating unbalanced-mass (RUM) actuators used to maximize scan amplitudes and/or minimize power consumption during changing conditions. This type of mechanism more sophisticated version of type of mechanism described in "Auxiliary Control Mechanisms for RUM Actuators" (MFS-28817). Torsional stiffness of torsionally flexible coupling made adjustable on command. Torsionally flexible coupling in tuneable version of auxiliary control mechanism adjustable by use of stepping-motor-driven worm-gear mechanism that varies bending length of flexible blade.

Polites, Michael E.; Alhorn, Dean C.

1995-01-01

416

Studies of {approx}ps laser driven plasmas in line focus geometry  

SciTech Connect

Measurements of X-ray emission along linear plasmas produced in short pulse (2-12 ps) experiments using the Rutherford Appleton Laboratory glass (1.06 {mu}m) and KrF (0.268 {mu}m) lasers are interpreted to provide information about the uniformity and lateral and axial energy transport of X-ray laser gain media. For fiber targets, the difficulties of achieving uniform irradiation and accurate plasma length measurements are illustrated and discussed. For slab targets, it is shown that the ratio of the distance between the critical density surface and the ablation surface to the laser focal width controls lateral transport in a similar manner as for spot focus experiments.

Tallents, G. J.; Al-Hadithi, Y.; Dwivedi, L.; Behjat, A.; Demir, A.; Holden, M.; Krishnan, J.; Zhang, J.; Key, M. H.; Neely, D.; Norreys, P. A.; Lewis, C. L. S.; MacPhee, A. G. [Department of Physics, University of Essex, Colchester CO4 3 SQ (United Kingdom); Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Central Laser Facility, Rutherford Appleton Laboratory, Chilton OX11 0QX (United Kingdom); Central Laser Facility, Rutherford Appleton Laboratory, Chilton OX11 0QX (United Kingdom); Department of Pure and Applied Physics, Queen's University Belfast, Belfast BT7 1NN (United Kingdom)

1995-05-01

417

Wakefield driven by Gaussian (1,0) mode laser pulse and laser-plasma electron acceleration  

NASA Astrophysics Data System (ADS)

An ultraintense Gaussian (1,0) mode pulsed laser applied to laser-plasma electron acceleration is investigated based on 2.5-dimensional particle-in-cell simulation (PIC). It has been found that Gaussian (1,0) mode laser pulse may blow out plasma electrons and form two symmetrical electron cavities with an electron wall between them. This electron wall separates two twisting bunches of transverse injected electrons and lets each of them be accelerated in one cavity, respectively. At the front of the wall, a bunch of reflux electrons with a magnetic field contributes to the electron self-bunching effect. This mechanism may generate two symmetrical, high-density, and monoenergetic electron beams with small transverse emittances.

Che, H. O.; Kong, Q.; Mao, Q. Q.; Wang, P. X.; Ho, Y. K.; Kawata, S.