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Title: Runaway electron production during intense electron beam penetration in dense plasma

Abstract

Relativistic electrons are efficiently generated when multiterawatt lasers focused to ultrahigh intensities > or approx. 10{sup 19} W/cm{sup 2} illuminate the surface of dense plasma targets. A theoretical study finds that during typical picosecond pulse widths, significant amounts of Dreicer produced runaway electrons can build up due to the high axial electric field driving the neutralizing return current. An important consequence is that there will be a conversion of plasma current to runaway electron current, which is maximized at some optimum value of the beam-to-plasma density ratio N{sub b}=n{sub b}/n{sub e}, depending on the plasma collisionality. At collisionalities representative of solid target experiments, complete conversion to runaway electrons can only take place over a certain range of N{sub b} values. At higher collisionalities and pulse widths, applicable to the fast ignition concept for inertial confinement fusion, it was found that conversion to runaways has a peak at {approx}90% around N{sub b}{approx}0.06. Significant lessening of target material heating by Joule current dissipation is also possible, since part of the beam energy loss is transferred through the electric field directly to the formation of energetic runaways. Implications for beam transport inhibition by the electric field are also discussed.

Authors:
;  [1];  [2]
  1. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20960117
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 1; Other Information: DOI: 10.1063/1.2424430; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BEAM TRANSPORT; BEAM-PLASMA SYSTEMS; ELECTRIC CURRENTS; ELECTRIC FIELDS; ELECTRON BEAMS; ENERGY LOSSES; HEATING; INERTIAL CONFINEMENT; PLASMA DENSITY; PULSES; RELATIVISTIC PLASMA; RELATIVISTIC RANGE; RUNAWAY ELECTRONS; THERMONUCLEAR IGNITION

Citation Formats

Parks, P. B., Cowan, T. E., and University of Nevada-Nevada Terawatt Facility, Reno, Nevada 89557-0042. Runaway electron production during intense electron beam penetration in dense plasma. United States: N. p., 2007. Web. doi:10.1063/1.2424430.
Parks, P. B., Cowan, T. E., & University of Nevada-Nevada Terawatt Facility, Reno, Nevada 89557-0042. Runaway electron production during intense electron beam penetration in dense plasma. United States. doi:10.1063/1.2424430.
Parks, P. B., Cowan, T. E., and University of Nevada-Nevada Terawatt Facility, Reno, Nevada 89557-0042. Mon . "Runaway electron production during intense electron beam penetration in dense plasma". United States. doi:10.1063/1.2424430.
@article{osti_20960117,
title = {Runaway electron production during intense electron beam penetration in dense plasma},
author = {Parks, P. B. and Cowan, T. E. and University of Nevada-Nevada Terawatt Facility, Reno, Nevada 89557-0042},
abstractNote = {Relativistic electrons are efficiently generated when multiterawatt lasers focused to ultrahigh intensities > or approx. 10{sup 19} W/cm{sup 2} illuminate the surface of dense plasma targets. A theoretical study finds that during typical picosecond pulse widths, significant amounts of Dreicer produced runaway electrons can build up due to the high axial electric field driving the neutralizing return current. An important consequence is that there will be a conversion of plasma current to runaway electron current, which is maximized at some optimum value of the beam-to-plasma density ratio N{sub b}=n{sub b}/n{sub e}, depending on the plasma collisionality. At collisionalities representative of solid target experiments, complete conversion to runaway electrons can only take place over a certain range of N{sub b} values. At higher collisionalities and pulse widths, applicable to the fast ignition concept for inertial confinement fusion, it was found that conversion to runaways has a peak at {approx}90% around N{sub b}{approx}0.06. Significant lessening of target material heating by Joule current dissipation is also possible, since part of the beam energy loss is transferred through the electric field directly to the formation of energetic runaways. Implications for beam transport inhibition by the electric field are also discussed.},
doi = {10.1063/1.2424430},
journal = {Physics of Plasmas},
number = 1,
volume = 14,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • In the present paper, it is reported that a large production of runaway electrons has been observed during the flattop phase of electron cyclotron resonance heating (ECRH) discharges and in the presence of supersonic molecular beam injection (SMBI) in the HuanLiuqi-2A (commonly referred to as HL-2A) [Q. W. Yang, Nucl. Fusion 47, S635 (2007)] tokamak. For the set of discharges carried out in the present experiment, the ranges of ECRH power and plasma electron density are 0.8-1.0 MW and (3.0-4.0)x10{sup 19} m{sup -3}, respectively. A large number of superthermal electrons are produced through the avalanche effect [A. Lazaros, Phys. Plasmasmore » 8, 1263 (2001)] during ECRH. The loop voltage increase due to SMBI gives rise to a decline in the critical runaway energy, which leads to that many superthermal electrons could be converted into runaway region. Therefore, this phenomenon may come from the synergetic effects of ECRH and SMBI. That is, the superthermal electrons created by ECRH are accelerated into runaway regime via the Dreicer process which is triggered by SMBI. The experimental results are in well agreement with the calculational ones based on the superthermal electron avalanche effect and the Dreicer runaway theory.« less
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