Compressing magnetic fields with high-energy lasers

Abstract

Laser-driven magnetic-field compression producing a magnetic field of tens of megaGauss is reported for the first time. A shock wave formed during the implosion of a cylindrical target traps an initial (seed) magnetic field that is amplified via conservation of magnetic flux. Such large fields are expected to magnetize the electrons in the hot, central plasma, leading to a cyclotron frequency exceeding the collision frequency. The Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] was used to implode cylindrical CH targets filled with deuterium gas and seeded with an external field (>50 kG) from a magnetic pulse generator. This seed field is trapped and rapidly compressed by the imploding shell, minimizing the effect of resistive flux diffusion. The compressed field was probed via proton deflectrometry using 14.7 MeV protons from the D+H3e fusion reaction emitted by an imploding glass microballoon. Line-averaged magnetic fields of the imploded core were measured to between 30 and 40 MG. Experimental data were analyzed with both a magnetohydrodynamic version of the one-dimensional hydrocode LILAC [J. Delettrez et al., Phys. Rev. A 36, 3926 (1987); N. W. Jang et al., Bull. Am. Phys. Soc. 51, 144 (2006)] and the particle propagation code GEANT4 [S. Agostinelli et al., Nucl. Instrum. Methods Phys. Res. A 506, 250 (2003)].

Magnetothermal instability in laser plasmas including hydrodynamic effects

“…The remainder of this section, therefore, is devoted to more speculative estimates of the magnetothermal instability's possible impact under conditions in which magnetic fields are self-generated: first, to experiments by Li et al designed to study magnetic field structures on the surface of plasma bubbles; [11][12][13] and second, to both inertial confinement [3][4][5] and magneto-inertial fusion. [6][7][8] However, these preliminary estimates based on Eq. (31), and which assume l T $ Àl B , should be treated with some caution.…”

“…[3][4][5][6][7][8][9][10][11][12][13] The magnetothermal instability is driven by collisional transport phenomena alone and therefore of particular interest because it acts to destabilise plasmas in the absence of more usual mechanisms. In particular, unstable growth results from coupling between (i) the Nernst effect, that is, advection of B with the diffusive heat-flow q ?…”

“…studies, in which magnetic-fields are directly imposed on the imploding target, there exist more detailed simulation data concerning field gradients. [6][7][8] Following a 4ns implosion of the target-to compress both the seed field and Deuterium fuel (D 2 ; Z ¼ 1)-electron temperature and field gradients are parallel, with l T $ 5 lm and l B $ 10 lm. 7,8 Since this makes l T =l B $ 0:5, M.I.F.…”

“…[3][4][5] and magneto-inertial fusion (M.I.F.) [6][7][8] schemes but also for more general experimental topics, such as the suppression of heat transport, 9 the control of density channels, 10 and the evolution of plasma bubbles.…”

Magneto-Inertial Fusion

“…The University of Rochester has introduced seed magnetic fields into the center of targets at the OMEGA laser facility, and compressed those fields by imploding a liner with the OMEGA laser. They have obtained record values of magnetic field and demonstrated increases in neutron yields [8][9][10]. Sandia is developing magnetized liner inertial fusion (MagLIF), in which a magnetically driven beryllium liner, imploded by the Z-machine, adiabatically compresses a laser-preheated magnetized DT target plasma [11][12][13][14].…”