High-density compression experiments at ILE, Osaka

Abstract

Direct-drive implosion experiments on the GEKKO XII laser (9 kJ, 0.5 /xm, 2 ns) with deuterium and tritium (DT) exchanged plastic hollow shell targets demonstrated fuel areal densities (pR) of -0.1 g/cm 2 and fuel densities of -600 times liquid density at fuel temperatures of -0.3 keV. (The density and pR values refer only to DT and do not include carbons in the plastic targets.) These values are to be compared with thermonuclear ignition conditions, i.e., fuel densities of 500-1000 times liquid density, fuel areal densities greater than 0.3 g/cm 2 , and fuel temperatures greater than 5 keV. The irradiation nonuniformity in these experiments was significantly reduced to a level of <5°/o in root mean square by introducing random-phase plates. The target irregularity was controlled to a 1% level. The fuel pR was directly measured with the neutron activation of Si, which was originally compounded in the plastic targets. The fuel densities were estimated from the pR values using the mass conservation relation, where the ablated mass was separately measured using the time-dependent X-ray emission from multilayer targets. Although the observed densities were in agreement with one-dimensional calculation results with convergence ratios of 25-30, the observed neutron yields were significantly lower than those of the calculations. This suggests the implosion uniformity is not sufficient to create a hot spark in which most neutrons should be generated.

Measurements of High Density Plasmas after Pulsed Discharges in Liquid Helium

“…The rate of formation of He; from He; was found to be faster than the formation of He; through reaction (2) and (3) at 76 K. Further studies made by other researchers indicated that ~e ; ion was, in fact, the dominant ion in 76 K He afterglow and the neutralization of these ion species produced ~e ; and He (211.…”

“…6~1 0 '~ cm" and 1 . 3~1 0 '~ cm-3 at the earliest stage of td = 0.2 ps in the cases (I), (2) and (3), respectively. They are 8x10'~ ~m -~, 6 x 1 0 '~ cm-3 and 6 x 1 0 '~ ~m '~, respectively, at t d = 3.8 ps.…”

“…For many years, a variety of high-density plasnlas that were beyond the scope of conventional laboratory experiments have been generated by novel methods such as laser implosion of a small target [I, 21. Azechi et al [2] generated a strongly coupled (non-ideal) and partly degenerated plasma with density on the order of ~m -~ and electron temperature of 0.5 keV attained by the laser implosion. Here, the strongly coupled plasma means that the Coulomb coupling coefficient r defined by the ratio of the average Coulomb energy to the average kinetic energy is not much less than unity.…”

Negative energy waves and quantum relativistic Buneman instabilities

“…used in laser-compressed plasma interaction experiments [28,29]. To safely satisfy the cold beam assumption, one may chose v = 0.9c, so that v F /v = 0.06.…”

Optimal laser intensity profiles for a uniform target illumination in direct-drive inertial confinement fusion

“…These analyses always provide axially symmetric laser intensity profiles where all the N B laser intensities are equal. These solutions can be applied to laser configurations such as Gekko XII [8] (N B = 12) or Omega [9] (60 beams) but are not suitable for laser configurations like the National Ignition Facility (NIF) [10] , the Laser…”