Systematic trends in x-ray emission characteristics of variable-wire-number, fixed-mass, aluminum-array, Z-pinch implosions

Abstract

Increasing the number of wires an order of magnitude from 10 to almost 200 while simultaneously fixing the total wire mass in annular aluminum-wire-array Z-pinch implosions on the 20 TW Saturn generator [Proceedings of the 6th International IEEE Pulsed Power Conference (Institute of Electrical and Electronics Engineers, Piscataway, NJ, 1987), p. 310] demonstrates two separate power-law trends in the measured x-ray characteristics as a function of the initial interwire gap (g). These trends are approximately independent of the array radius. When g decreases from ∼6 to 0.4 mm, the peak total radiated power increases by a factor of 20 and the total energy by a factor of 2. There is a more rapid increase in peak power and energy radiated as g decreases for gaps greater than ∼2 mm. This increase is related to a measured decrease in precursor plasma and to a calculated decreased sensitivity of the implosion to azimuthal asymmetries that occurs when individual wire plasmas begin to merge following their vaporization. The substantial increase in power arises from an inferred increase in plasma compression and can be correlated with an almost linear reduction in the calculated effective thickness of the plasma annulus near stagnation as g decreases.

Optimal Wire-Number Range for High X-Ray Power in Long-Implosion-Time AluminumZPinches

“…The load currents were similar for the shots, but the total power waveforms show distinct differences with increasing wire number. As observed in experiments with short implosion times [6,14], the K shell and total powers increased with increased wire number (decreased IWG). Variations of greater than a factor of 2 were observed in the K-shell power (and total power) over the range of interwire gaps studied (see Table I).…”

“…The powers and yields are similar to those observed in the short pulse mode. Note that a decrease in the K-shell and total powers is observed at the smallest IWG with both the 40 and 32 mm diam wire arrays, an effect not previously seen in short or long pulse experiments [6][7][8]14,16].…”

“…This produces compressed plasmas with high temperatures and densities that radiate multiterawatts of x-ray power. For example, Saturn (8 MA) produces up to 75 TW from tungsten and 30 TW from aluminum with a 60 ns implosion time [13,14]. Note that the K-shell power from the short pulse aluminum wire arrays on Saturn is approximately 4 TW [14].…”

“…To study this effect, a systematic scan of wire number using 40 mm diameter aluminum wire arrays was performed. Aluminum was chosen for several reasons, including the need for information relevant to K-shell scaling laws, the ability to diagnose plasma conditions, and the availability of short pulse data [14] for comparison. In the experimental series discussed in this paper, the wire number was varied from 32 to 282 wires, corresponding to interwire gaps (IWG) of 3.9 to 0.45 mm.…”

Increased x-ray power generated from low-mass large-number aluminum-wire-array Z-pinch implosions

“…For interwire spacings greater than 2Ϯ0.6 mm, the power increases, with decreasing spacing as the spacing raised to the Ϫ1.8Ϯ0.3 power; for spacings less than 2 mm, the power increases as the spacing raised to the Ϫ0.84Ϯ0.1 power. 3 The transition at ϳ2 mm may be associated with the change in pinch topology seen in x-y ͑''endon''͒ radiation-magnetohydrodynamic-code ͑RMHC͒ calculations. 1,3,4 In these calculations, a transition from the implosion of separate wire plasmas to that of a more uniform plasma shell ͑formed by the merger of the individual wire plasmas prior to implosion͒ occurs with increased wire number at a spacing of about 2 mm.…”