Spheromak Buildup in SSPX using a Modular Capacitor Bank Page: 4 of 6
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provide slow and fast-rise time current pulses. Two independently controlled high voltage
charging supplies can be used to charge individual modules or groups of modules to different
voltages. Each module is fired independently using a solid-state optically triggered thyristor.
The modular bank was designed to provide a variety of injector current waveforms. The
SSPX pulsed power circuit was modeled using a SPICE program and some of the predicted
current waveforms are shown in Figure 1; the standard formation followed by sustainmentwaveform is also plotted for comparison
high current pulse, which is obtained by
firing all 30 modules simultaneously.
The output from the 30 modules is
estimated to be near a mega-ampere.
The second objective is an extended
formation pulse. This is achieved by
firing a portion of the modules. The
third objective is a low current
sustained pulse much like the output of
the present sustainment bank. This is
achieved by firing modules at equal
intervals. The peak output current
decreases as the time between firing
intervals increases. Another waveform
objective (not shown) includes a train
of fast rise time pulses on top of a low
current sustainment pulse. This is
achieved by firing groups of modules at(Fig. Id). The first waveform objective is a single
1000
800
600
400
200II
0 2 4 6 8 10
Time (ms)
Figure 1. Predicted current waveforms from
the new modular bank; a) ~1 mega-ampere
current pulse, b) extended formation current
pulse, c) long current pulse and d) standard
formation with sustainment pulse for
comparison. Multiple current pulse not shown.
equally spaced time intervals. The modular bankprovides a high degree of flexibility in injected current pulse shape that can be used with or
without the initial formation and, or, sustainment banks.
Experimental Results
Shown in Figure 2 is a time history of a discharge with a single high current formation
pulse (solid lines); a standard formation followed by sustaiment discharge is plotted (dashed
lines) for comparison. For this discharge, the formation bank and modular bank (15 modules)
are configured to provide a 500s, 540kA current pulse (Fig 2a.). As seen in Figure 2c, the
edge poloidal field builds to 0.45T, the highest value ever measured on SSPX. For the
spheromak to be a viable fusion concept using helicity injection as a means to generate the
magnetic fields, a high current amplification (ratio of toroidal plasma current to gun current)
is needed [9]. Because the toroidal current is not measured directly, but computed from MHD
equilibrium reconstruction, we use the ratio of the measured edge poloidal field to the- -- - - - -- (KAmps)
b)
c)
d)
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Wood, R. D.; McLean, H. S.; Hill, D. N.; Hooper, E. B. & Romero-Talamas, C. A. Spheromak Buildup in SSPX using a Modular Capacitor Bank, article, June 13, 2006; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc880893/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.