Determination of the imploded mass in laser-imploded shell targets

Abstract

A new method of experimental measurement of the imploded mass of laser-imploded shell targets is proposed. This method is based on simultaneous measurements of the velocity spectrum of the neutral atom flux emitted from the imploded part of the target, and the total energy carried by them. A semiconductor diode with a shallowly located p -n junction was used as the low energy neutral particle detector. By means of the time of flight method neutral atom fluxes with velocities v ~( 0 -6 -1-8) x 10 7 cm/s were registered in experiments carried out on the 6-beam laser system "Delfin". DiscussionIn investigating the efficiency of targets imploded by means of a laser radiation pulse (Basov et al. 1982) one measures the absorbed energy of laser radiation -E a and the kinetic energy of the target:Diagnostic methods of the velocity measurement of the imploded part of the target are based on the measurement of the compression time t*, when the change in the direction of the movement of the observed surface of plasma is registered by both X-ray diagnostics (Attwood 1978;Kilkenny et al. 1981) and by optical ones (Basov et al. 1978;1983).In fact, in the expression for the kinetic energy of the microsphere, the value u mnx(' m ) is replaced by the average velocity of implosion v(t*). The measuring accuracy of the fast streak cameras used is very high and equal to At* It* ~ 10%. The measuring accuracy for the absorbed laser radiation energy E a is also very high and equal to AE a /E a ~ 10%.The error connected with the measurement of the microsphere mass at the moment of its maximum compression m(t*) = m impi and has a fundamental influence on. the accuracy of determining the efficiency of the hydrodynamic compression y\ = E k l E a -figure 1. This mass is calculated as the difference between the initial mass of the microsphere m 0 and the mass of the ablating part of the microsphere m aM = rht*, (w im pi = m 0 -m a b l ). Measurement of the mass ablation rate -m can be performed by means of X-ray-spectral methods (Goldsack et al. 1982) and by the methods of the mass spectrometry (Wotowski et al. 1985). Both methods give comparable results. It

<title>Ion measurements of laser-produced Al plasma on PERUN laser system</title>

“…The factor 0.5 takes into account secondary ion-electron emission U U(t) "" The mean ion energy was defined as = (EN)/(N) (5) The relation between the mean ion energy E and the electron temperature T has the following general form E= C( + a)T (6) where C is a constant (3.33 5) depending on the model of laserplasma interaction9"1, is the averaged ionization state of ions in the hot region of plasma pith the electron temperature T , a = T1/T T. is the ion temperature of plasma. 3), in is the ion mass, R is the loading resistance, e is the electron charg, S is the area of collector (S iD4 fora planar ion collector and S = t!,l for cylindrical Langmuir probe), z is the averaged ionization state of ions at the collector posit.on.…”