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Results for “BEAM-PLASMA SYSTEMS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Detection of electromagnetic pulses produced by hypervelocity micro particle impact plasmas

Hypervelocity micro particles (mass < 1 ng), including meteoroids and space debris, routinely impact spacecraft and produce plasmas that are initially dense (∼10{sup 28} m{sup −3}), but rapidly expand into the surrounding vacuum. We report the detection of radio frequency (RF) emission associated with electromagnetic pulses (EMPs) from hypervelocity impacts of micro particles in ground-based experiments using micro particles that are 15 orders of magnitude less massive than previously observed. The EMP production is a stochastic process that is influenced by plasma turbulence such that the EMP detection rate that is strongly dependent on impact speed and on the electrical charge conditions at the impact surface. In particular, impacts of the fastest micro particles occurring under spacecraft charging conditions representative of high geomagnetic activity are the most likely to produce RF emission. This new phenomenon may provide a source for unexplained RF measurements on spacecraft charged to high potentials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Ultra-bright, ultra-broadband hard x-ray driven by laser-produced energetic electron beams

We propose a new method of obtaining a compact ultra-bright, ultra-broadband hard X-ray source. This X-ray source has a high peak brightness in the order of 10{sup 22} photons/(s mm{sup 2} mrad{sup 2} 0.1\%BW), an ultrashort duration (10 fs), and a broadband spectrum (flat distribution from 0.1 MeV to 4 MeV), and thus has wide-ranging potential applications, such as in ultrafast Laue diffraction experiments. In our scheme, laser-plasma accelerators (LPAs) provide driven electron beams. A foil target is placed oblique to the beam direction so that the target normal sheath field (TNSF) is used to provide a bending force. Using this TNSF-kick scheme, we can fully utilize the advantages of current LPAs, including their high charge, high energy, and low emittance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Optical emission spectroscopy at the large RF driven negative ion test facility ELISE: Instrumental setup and first results

One of the main topics to be investigated at the recently launched large (A{sub source}= 1.0 × 0.9 m{sup 2}) ITER relevant RF driven negative ion test facility ELISE (Extraction from a Large Ion Source Experiment) is the connection between the homogeneity of the plasma parameters close to the extraction system and the homogeneity of the extracted negative hydrogen ion beam. While several diagnostics techniques are available for measuring the beam homogeneity, the plasma parameters are determined by optical emission spectroscopy (OES) solely. First OES measurements close to the extraction system show that without magnetic filter field the vertical profile of the plasma emission is more or less symmetric, with maxima of the emission representing the projection of the plasma generation volumes, and a distinct minimum in between. The profile changes with the strength of the magnetic filter field but under all circumstances the plasma emission in ELISE is much more homogeneous compared to the smaller IPP prototype sources. Planned after this successful demonstration of the ELISE OES system is to combine OES with tomography in order to determine locally resolved values for the plasma parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Acceleration of positrons by a relativistic electron beam in the presence of quantum effects

Using the quantum magnetohydrodynamic model and obtaining the dispersion relation of the Cherenkov and cyclotron waves, the acceleration of positrons by a relativistic electron beam is investigated. The Cherenkov and cyclotron acceleration mechanisms of positrons are compared together. It is shown that growth rate and, therefore, the acceleration of positrons can be increased in the presence of quantum effects.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Self-pinched transport of a high ν/γ electron beam

The self-pinched transport of a 0.5 MeV, 18 kA cylindrical electron beam has been studied experimentally and computationally. The relatively low voltage and high current required for materials surface modification applications leads to complicated beam dynamics as the Alfven limit is approached. Transport and focusing of the high ν/γ beam was done in a sub-Torr, neutral gas-filled, conducting tube in the ion-focused regime. In this regime, beam space charge forces are progressively neutralized to allow focusing of the beam by its self-magnetic field. The beam exhibits stable envelope oscillations as it is efficiently and reproducibly propagated for distances greater than a betatron wavelength. Experimental results follow the trends seen in 2-D particle-in-cell simulations. Results show that the input electron beam can be periodically focused to a peaked profile with the beam half-current radius decreased by a factor of 2.84. This results in an increase of a factor of 8 in beam current density. This focusing is sufficient to produce desired effects in the surface layers of metallic materials.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

The beat in laser-accelerated ion beams

Regular modulation in the ion velocity distribution becomes detectable if intense femtosecond laser pulses with very high temporal contrast are used for target normal sheath acceleration of ions. Analytical and numerical analysis of the experimental observation associates the modulation with the half-cycle of the driving laser field period. In processes like ion acceleration, the collective and laser-frequency determined electron dynamics creates strong fields in plasma to accelerate the ions. Even the oscillatory motion of electrons and its influence on the acceleration field can dominate over smoothing effects in plasma if a high temporal contrast of the driving laser pulse is given. Acceleration parameters can be directly concluded out of the experimentally observed modulation period in ion velocity spectra. The appearance of the phenomenon at a temporal contrast of ten orders between the intensity of the pulse peak and the spontaneous amplified emission background as well as remaining intensity wings at picosecond time-scale might trigger further parameter studies with even higher contrast.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Turning point temperature and competition between relativistic and ponderomotive effects in self-focusing of laser beam in plasma

The propagation characters of Gaussian laser beam in collisionless plasma are investigated by considering the ponderomotive and relativistic nonlinearities. The second-order differential equation of dimensionless beam width parameter is solved numerically, taking into account the effect of electron temperature. The results show that the ponderomotive force does not facilitate the relativistic self-focusing in all intensity ranges. In fact, there exists a certain intensity value that, if below this value, the ponderomotive nonlinearity can contribute to the relativistic self-focusing, or obstruct it, if above. It is also indicated that there is a temperature interval in which self-focusing can occur, while the beam diverges outside of this region. In addition, the results represent the existence of a “turning point temperature” in the mentioned interval that the self-focusing has the strongest power. The value of the turning point is dependent on laser intensity in which higher intensities result in higher turning point.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Effect of laser beam filamentation on coexisting stimulated Raman and Brillouin scattering

This paper presents the study of stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) when both of these processes are coexisting and pump laser beam initial power is more than filamentation threshold. On account of the ponderomotive nonlinearity, the pump laser beam gets filamented, and both the scattering processes (SRS and SBS) get affected. Simultaneous presence of SRS and SBS (five wave interaction case) also affect the pump filamentation process due to pump depletion. Both the scattering processes (SRS and SBS) are enhanced due to filamentation of laser beam. Results are also compared with the three wave interaction case (either SRS or SBS) with and without filamentation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Linear stability and nonlinear dynamics of the fishbone mode in spherical tokamaks

Extensive linear and nonlinear simulations have been carried out to investigate the energetic particle-driven fishbone instability in spherical tokamak plasmas with weakly reversed q profile and the q{sub min} slightly above unity. The global kinetic-MHD hybrid code M3D-K is used. Numerical results show that a fishbone instability is excited by energetic beam ions preferentially at higher q{sub min} values, consistent with the observed appearance of the fishbone before the “long-lived mode” in MAST and NSTX experiments. In contrast, at lower q{sub min} values, the fishbone tends to be stable. In this case, the beam ion effects are strongly stabilizing for the non-resonant kink mode. Nonlinear simulations show that the fishbone saturates with strong downward frequency chirping as well as radial flattening of the beam ion distribution. An (m, n) = (2, 1) magnetic island is found to be driven nonlinearly by the fishbone instability, which could provide a trigger for the (2, 1) neoclassical tearing mode sometimes observed after the fishbone instability in NSTX.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Numerical investigation of electron self-injection in the nonlinear bubble regime

The process of electron self-injection in the nonlinear bubble wake generated by a short and intense laser pulse propagating in a uniform underdense plasma is studied by means of fully self-consistent particle-in-cell simulations and test-particle simulations. We consider a wake generated by a non-evolving laser driver traveling with a prescribed velocity, which then sets the structure and the velocity of the wake, so the injection dynamics is decoupled from driver evolution, but a realistic structure for the wakefield is retained. We show that a threshold for self-injection into a non-evolving bubble wake exists, and we characterize the dependence of the self-injection threshold on laser intensity, wake velocity, and plasma temperature for a range of parameters of interest for current and future laser-plasma accelerators.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Effect of collisions on amplification of laser beams by Brillouin scattering in plasmas

We report on particle in cell simulations of energy transfer between a laser pump beam and a counter-propagating seed beam using the Brillouin scattering process in uniform plasma including collisions. The results presented show that the ion acoustic waves excited through naturally occurring Brillouin scattering of the pump field are preferentially damped without affecting the driven Brillouin scattering process resulting from the beating of the pump and seed fields together. We find that collisions, including the effects of Landau damping, allow for a more efficient transfer of energy between the laser beams, and a significant reduction in the amount of seed pre-pulse produced.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Intense terahertz emission from relativistic circularly polarized laser pulses interaction with overdense plasmas

During the interaction of a relativistic circularly polarized laser pulse with an overdense plasma target, the longitudinal motion of bunches of electrons under the action of light pressure and electrostatic restore force can emit intense terahertz (THz) pulses. This mechanism allows high pump laser intensity and large electron number participating in the emission. Two-dimensional particle-in-cell simulations are carried out to investigate the THz emission. The results suggest that such a source can produce remarkably intense THz pulses with energy of several mJ/sr and power of tens of gigawatts, which could find applications in nonlinear studies and relativistic laser-plasma interaction diagnostics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Interaction of nonthermal muon beam with electron-positron-photon plasma: A thermal field theory approach

Interaction of a muon beam with hot dense QED plasma is investigated. Plasma system contains electrons and positrons with Fermi-Dirac distribution and Bose-Einstein distributed photons while the beam particles have nonthermal distribution. The energy loss of the beam particles during the interaction with plasma is calculated to complete leading order of interaction in terms of the QED coupling constant using thermal field theory approach. The screening effects of the plasma are computed consistently using resummation of perturbation theory with hard thermal loop approximation according to the Braaten-Pisarski method. Time evolution of the plasma characteristics and also plasma identifications during the interaction are investigated. Effects of the nonthermal parameter of the beam distribution on the energy exchange and the evolution of plasma-beam system are also explained.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Charge steering of laser plasma accelerated fast ions in a liquid spray — creation of MeV negative ion and neutral atom beams

The scenario of “electron capture and loss” has been recently proposed for the formation of negative ion and neutral atom beams with up to MeV kinetic energy [S. Ter-Avetisyan, et al., Appl. Phys. Lett. 99, 051501 (2011)]. Validation of these processes and of their generic nature is here provided in experiments where the ion source and the interaction medium have been spatially separated. Fast positive ions accelerated from a laser plasma source are sent through a cold spray where their charge is changed. Such formed neutral atom or negative ion has nearly the same momentum as the original positive ion. Experiments are released for protons, carbon, and oxygen ions and corresponding beams of negative ions and neutral atoms have been obtained. The electron capture and loss phenomenon is confirmed to be the origin of the negative ion and neutral atom beams. The equilibrium ratios of different charge components and cross sections have been measured. Our method is general and allows the creation of beams of neutral atoms and negative ions for different species which inherit the characteristics of the positive ion source.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Observation of laser multiple filamentation process and multiple electron beams acceleration in a laser wakefield accelerator

The multiple filaments formation process in the laser wakefield accelerator (LWFA) was observed by imaging the transmitted laser beam after propagating in the plasma of different density. During propagation, the laser first self-focused into a single filament. After that, it began to defocus with energy spreading in the transverse direction. Two filaments then formed from it and began to propagate independently, moving away from each other. We have also demonstrated that the laser multiple filamentation would lead to the multiple electron beams acceleration in the LWFA via ionization-induced injection scheme. Besides, its influences on the accelerated electron beams were also analyzed both in the single-stage LWFA and cascaded LWFA.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Detection of significant differences between absorption spectra of neutral helium and low temperature photoionized helium plasmas

In this work, spectral investigations of photoionized He plasmas were performed. The photoionized plasmas were created by irradiation of helium stream, with intense pulses from laser-plasma extreme ultraviolet (EUV) source. The EUV source was based on a double-stream Xe/Ne gas-puff target irradiated with 10 ns/10 J Nd:YAG laser pulses. The most intense emission from the source spanned a relatively narrow spectral region below 20 nm, however, spectrally integrated intensity at longer wavelengths was also significant. The EUV radiation was focused onto a gas stream, injected into a vacuum chamber synchronously with the EUV pulse. The long-wavelength part of the EUV radiation was used for backlighting of the photoionized plasmas to obtain absorption spectra. Both emission and absorption spectra in the EUV range were investigated. Significant differences between absorption spectra acquired for neutral helium and low temperature photoionized plasmas were demonstrated for the first time. Strong increase of intensities and spectral widths of absorption lines, together with a red shift of the K-edge, was shown.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

High pressure generation by hot electrons driven ablation

A previous model [Piriz et al. Phys. Plasmas 19, 122705 (2012)] for the ablation driven by the hot electrons generated in collisionless laser-plasma interactions in the framework of shock ignition is revisited. The impact of recent results indicating that for a laser wavelength λ = 0.35 μm the hot electron temperature θ{sub H} would be independent of the laser intensity I, on the resulting ablation pressure is considered. In comparison with the case when the scaling law θ{sub H}∼(Iλ{sup 2}){sup 1/3} is assumed, the generation of the high pressures needed for driving the ignitor shock may be more demanding. Intensities above 10{sup 17} W/cm{sup 2} would be required for θ{sub H}=25−30 keV.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2013

Role of positive ions on the surface production of negative ions in a fusion plasma reactor type negative ion source—Insights from a three dimensional particle-in-cell Monte Carlo collisions model

Results from a 3D self-consistent Particle-In-Cell Monte Carlo Collisions (PIC MCC) model of a high power fusion-type negative ion source are presented for the first time. The model is used to calculate the plasma characteristics of the ITER prototype BATMAN ion source developed in Garching. Special emphasis is put on the production of negative ions on the plasma grid surface. The question of the relative roles of the impact of neutral hydrogen atoms and positive ions on the cesiated grid surface has attracted much attention recently and the 3D PIC MCC model is used to address this question. The results show that the production of negative ions by positive ion impact on the plasma grid is small with respect to the production by atomic hydrogen or deuterium bombardment (less than 10%)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗