Initial reversed-field pinch experiments on ZT-40 and recent advances in RFP theory Page: 4 of 13
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The ZT-40 experiment is one of the intermediate-sized, reversed-field pinch
experiments (RFP) that include ETA BETA II (Italy), IIBTX-lA (U.K.), and TPL-1R
(Japan). The goal is to extend the plasma temperatures and confinement times
an order of magnitude above previous small RFP experiments[1,2,3,4] and to
establish the physics base for the next generation of devices.
This paper summarizes the initial experimental results obtained on ZT-40
and new RFP theoretical results on start-up, ohmic heating, ignition and burn,
helical ohmic states, linear and nonlinear stability, and magnetoacoustlc
2. ZT-40 EXPERIMENT
ZT-40 is designed so that current rlsetlmcs can be varied by changing the
number of toroidal current feeds and the number of toroidal field windings.
Wirh four current feeds the toroidal current riAetime is 0.1 ms and is the
arrangement used for most of the results reported here. The toroidal field
risetime is 0.05 ms.
The experiment has a 99.5% alumina vacuum chamber (R/a - 114 cm/20 cm)
surrounded by an aluminum shell (R/a ■ 114 cm/22 cm) and magnetic cores couple
the toroidal current circuit to the plasma. Toroidal plasma currents up to
600 kA and toroidal fields up to 5 kG are passively clamped. An active clamp
circuit (power crowbar) has only recently been added.
3.1 Modes of Operation
ZT-40 has several modes of startup: (1) a non-reversed field pinch
(NRFP) (known historically as a stabilized pinch); (2) a self-reversed
toroidal field; and (3) a programmed reversal of the current in the
toroidal field windings (called aided reversal). Sample waveforms are
shown in Figs. 1, 2, and 3.
I»«l Itftl I ••••
Non-reversed field pinch. Toroidal
current (kA), average toroidal
field (0), and toroidal, field
at the wall (k<!) vs Lime (jis).
|U( 1211 lift IMM Itliff I'll
So l f-reversed pLnch. Same measure-
ments as In Fig,. 1.
3.2 Start-up Pin timnena
Mu! 11 -chord Interferometer measurements of an NRFP shows that
Initially the electron density peaks .smoothly near the walL persisting for
the first 30 }is. lie low 15 mtorr a striking transition occurs; the sheath
becomes unstable and fluctuations In density appear. AL the lower
pressures there Is a marked Increase In x-ray production and a shortening
of the current decay time. As discussed In the next section, the marked
deterioration of decay time at Low pressures is overcome when the
discharge Is operated as an RFP.
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Baker, D.A.; Buchenauer, C.J. & Burkhardt, L.C. Initial reversed-field pinch experiments on ZT-40 and recent advances in RFP theory, article, January 1, 1980; New Mexico. (digital.library.unt.edu/ark:/67531/metadc1065796/m1/4/: accessed November 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.