DocumentCode :
2437017
Title :
Plasma density measurements within Tungsten wire-array z-pinches on the cobra accelerator
Author :
Douglass, J.D. ; Hammer, D.A. ; McBride, R.D. ; Bell, K.S. ; Knapp, F. ; Greenly, J.B. ; Pikuz, S.A. ; Shelkovenko, T.A.
Author_Institution :
Lab. for Plasma Studies, Cornell Univ. Ithaca, Ithaca, NY
fYear :
2008
fDate :
15-19 June 2008
Firstpage :
1
Lastpage :
1
Abstract :
The COBRA pulsed-power generator, with a nominal peak current of 1.1 MA and a minimum zero-to-peak rise-time of 95 ns, is being used to study the early phases of wire-array Z-pinch development with a variety of diagnostics. Here we present the results of applying point-projection X-ray radiography using up to five X pinches in the return current circuit to make accurate, high-resolution measurements of the plasma density distributions in tungsten (W) wire-array Z-pinch implosions. Plasma density measurements are calibrated by comparing X-ray transmission recorded on photographic films to transmission through W steps with known thicknesses. Plasma density distributions as a function of time with sub-ns time resolution and few-mum spatial resolution are presented for the coronal plasma close to each wire (1018-1020/cm3), ablation streams moving towards the axis (<1020/cm2 areal density) and on-axis (<1019/cm3) plasmas. X-ray images ranging from 70 to 170 ns after the start of the current pulse have been analyzed. Dense cores appear to expand to a radius, rf, that is linearly proportional to initial wire radius. The final radius is reached before 70 ns for 7.4-12.7 mum wires, with rf = 7.0 r0 - 9.6, where r0 is the initial radius and all units are in mum, within ~10%. Larger wires appear to continue to expand during the entire 70-170 ns observation window. The final radius, rf, is found from the Abel inversions of coronal plasmas, taking the radius at which the plasma density drops to 3times1020/cm3. This trend was not affected by the number of wires in the array or the array radius, implying that the initial wire diameter is more significant than the inter-wire gap for a fixed array mass. The coronal plasma areal density outside the dense core radius, rf, scales as 1/(r-rf/2)2- - starting from the value at rf. The areal density of the plasma in the ablation streams moving toward the axis falls off as 1/r, where r is the distance from the center of the dense wire core. Detailed results will be presented.
Keywords :
Z pinch; corona; exploding wires; explosions; particle accelerators; plasma density; plasma devices; plasma diagnostics; plasma production; radiography; tungsten; Abel inversion; COBRA accelerator; COBRA pulsed power generator; W; ablation stream; coronal plasma; current 1.1 MA; plasma density measurement; plasma diagnostics; point projection X-ray radiography; radius 7.4 mum to 12.7 mum; return current circuit X pinch; time 95 ns; tungsten wire array Z-pinch implosion; wire array Z-pinch development; wire radius; Acceleration; Density measurement; Plasma accelerators; Plasma density; Plasma measurements; Plasma x-ray sources; Pulse generation; Spatial resolution; Tungsten; Wire;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Plasma Science, 2008. ICOPS 2008. IEEE 35th International Conference on
Conference_Location :
Karlsruhe
ISSN :
0730-9244
Print_ISBN :
978-1-4244-1929-6
Electronic_ISBN :
0730-9244
Type :
conf
DOI :
10.1109/PLASMA.2008.4590762
Filename :
4590762
Link To Document :
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