Diagnostic characterization of a prepulsed carbon fiber Z pinch using spectral line intensity analyses

Plasma formation and x-ray generation efficiency of a carbon fiber Z pinch are dramatically improved by means of an optimized current prepulse. In thi s article results are presented of time-integrated and also time-resolved e lectron temperature measurements using the optical line emission of the cor onal plasma surrounding a still, cold fiber. Two phases of discharges with current prepulse are studied: the preionization phase only in which time-in tegrated spectra of C II-C IV emission are recorded and time resolution of the heating phase after onset of the main current pulse using C III and C I V line emission. Experimentally obtained, n=3-4, 3-3, line ratios are fitte d with collisional radiative, ADAS computations of line intensity ratios as a function of electron temperature, density, n(e) and variable confinement , tau. All levels up to n=5 are included with the influence of higher level s also accounted for. Deviations from coronal balance give an effective val ue for the product [n(e)tau]. As a result, the electron temperature of the preionized coronal plasma is estimated at T-e =5 eV at a density of n(e) ap proximate to 10(17) cm(-3). The temperature rises to about 12 eV at the sam e density after the start of the main current with prepulse. Similar analyt ic techniques are applied to time-integrated C V and C VI XUV resonance lin es from the main pinch and give plasma parameters in accord with the x-ray continuum diagnostics. (C) 1999 American Institute of Physics. [S0034-6748( 99)68501-X].