Research of asymmetry of radiation drive implosion on ShenGuang II laser facility

Abstract

Institute of applied physics and computational mathematics P.0.Boz 8009, Beijing 10088, P.R.China Good radiation drive symmetry is crucial for forming "hot core" in inertid confioement fusion. In practice in hohlraum x-ray flux is asymmetrical. So it is necessary to optimize the parameters of hohlraum for forming better x-ray drive symmetry. Using 2 0 numerical code LARED-I, a series of results of asymmetrical compression are obtained with variation of length of hohlraum.In experiments on ShenGuang I1 laser facility, by x-ray imaging of the sell-emission from the compressed dense core, asymmetrical implosion is diagnosed. X-ray imaging of the distorted core of capsule provides a picture that can be compared with theoretical modeling. On the other hand, asymmetry of implosion decreases DD neutron yield. ~~2 7Temperature and Density Measurement b y using a Double P r o b e of Pseudospark Discharge Plasma JetWe have been doing research on the new type of plasma jet. Plasma jet is device that makes high temperature and hgh-density plasma flow at high speed In this research, we investigate the a p plication of pseudospark discharge (PSD) to high power plasma jet in particular. PSD is low-pressure gas discharge. Electrodes have a hole on the center axis of parallel plane electrode and cathode has cylindrical hollow cavity behind the circular hole. Characteristics of PSD are as follows. When discharge is formed by using this hollow cathode and on the condition in the lowpressure region on the left hand side of the lowest point of a Paschen's curve, discharge current becomes large because breakdown voltage is high. Moreover in this low-pressure region, since discharge dose not formed along the short discharge path but the long one, discharge path passes through the center hole from reverse side of electrodes. As a result, the points of the discharge to the cathode spread to the back surface in the hollow cathode. Due to the hollow cathode effect, discharge is kept on the glow mode at the high current discharge, resulting that damage on electrode will be small. To spout the high temperature and high-density plasma in PSD, geometric structure of electrode of PSD is modified. Due to the modification of the PSD electrodes, plasma is spouted from anode hole by the power of the Lorentz power. Characteristics of this plasma jet are as follows.Since discharge current is large, high temperature plasma is casily generable., During the discharge, strong self-magnetic field occurs at the electrode holes.Power of plasma jet is as large as that of the magnet&" dynamic (MPD) arc jet.Due to the pinch effect, density of plasma jet will be high. Device can use for long time because PSD discharge is like glow mode.In this research, electronic temperature and density of a plasma jet were measured using the double probe, which has floated in potential. The experiment used hydrogen and discharge current is about 10[kAl. On the downstream of 22(mml from the anode hole, it turns out that electronic temperature is about 20 [eV] and electron dens...