L. C. Burkhardt

Characteristics of a Magnetic Energy Storage System Using Exploding Foils

A capacitor bank operating at 15 kV and 34 kJ is used to energize an inductive system of 40 nH. Interrupting the current of ∼800 kA, by means of an exploding copper foil fuse, produces voltages across the fuse of the order of 80 kV. The opening time of the fuse, as well as the characteristics of the voltage developed across the fuse are examined as a function of the fuse dimensions. If transfer of the current into a matching inductive load is to take place at the time of peak voltage, energy transfer efficiency is of the order of 8% with Is of the order of 2×1012 A/sec.

Polarized radial magnetic fields and outward plasma fluxes during shallow‐reversal discharges in the ZT‐40M reversed‐field pinch

The characteristics of edge‐region electromagnetic disturbances and of pulsed radial fluxes of plasma to the liner as well as the detailed interrelationship among these processes have been studied on the ZT‐40M reversed‐field pinch in its normal, shallow‐reversal operating regime. The dominant magnetic disturbances are spiky (pulsewidth ∼5–10 μs) low‐amplitude (‖Br/Bθ‖≲10−2) poloidally symmetric radial‐field structures intersecting the vacuum wall and precessing toroidally in the anti‐Iφ sense. The effect of even slight toroidal‐field reversal (‖Bφ(a)‖≊Bθ(a)/10) is to polarize these radial‐field spikes preferentially positive (i.e., Br>0) and to increase the speed of the minority (Br 0) spikes. Synchronous with the polarized Br spikes are intense radially outward fluxes of plasma (instantaneously ≳1022 m−2 s−1) leading to recurrent, large amplitude (‖Δn/n≳25%) depletion of the density in the outer quarter of minor radius. The resulting time‐averaged global...

Plasma Injection and Trapping in a Caulked Stuffed Cusp Magnetic Field

A minimum‐average‐B‐stable toroidal magnetic well with high shear is obtained from the combined fields of a solenoid, axial conductors, and an internal ring conductor. Results of measurements of the injection and trapping of high‐energy plasma from a coaxial gun are described. The confinement times are dependent on both particle energy and magnetic field. The density e‐folding time is independent of the ion velocity under conditions of low shear and well depth. As they are increased the e‐folding time varies roughly as 1/vi2. Trapped 0.9‐keV plasma decays with an e‐folding time that increases by a factor of 6 to 110 μsec as shear and magnetic well depth increase. The initial density of the plasma (0.5 to 3 keV) is ∼ 5 × 1011 cm−3 for field magnitudes resulting in a 40‐μsec lifetime of 0.9‐keV deuterons. This lifetime is independent of density over the range from ∼ 5 × 1011 cm−3 to 109 cm−3. The range of magnetic field magnitude is limited by the decreasing amount of plasma injected from the gun with incre...

Magnetic Shielding of Current Feeds in Plasma Containment Systems

Experimental tests of the effectiveness of the magnetic shielding of current leads or supports in the form of linear dipoles are described. Results show that this technique may be useful in experimental plasma confinement devices.

Design of the ZT-1 toroidal pinch experiment

Electrical design details are given for a toroidal Z-pinch device named ZT-1 that uses field programming to achieve a stable, reversed field pinch. The plasma is formed in a 4-mm-thick, 10.3-cm-i.d., high alumina, segmented ceramic vacuum chamber. Voltages as high as 70 kV are routinely attained by interrupting with a fuse 800 kA in an inductive store. The current is diverted from the fuse to the primary of a single-turn transformer divided into quadrants. A total of 280 kV at 200 kA can then be applied to the plasma, which forms the secondary circuit of the transformer. This system produces dB/sub theta//dts of up to 8 T/

Current Sheet in a Coaxial Plasma Gun

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Preliminary equilibrium and field-error studies on ZT-40M

s; with modifications to the electrical system, dB/sub theta//dts as low as 0.1 T/

Stability and temperature measurements on ZT-1

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Current, temperature, and confinement time scaling in toroidal reversed-field pinch experiments ZT-I and ZT-S

s are obtained. The B/sub z/ bias field of up to 0.25 T can be reversed at a rate of up to 0.2 T/

High voltage, high current, pulsed energy source having dI/dt's of 2 times 10 to the 12th power A/s

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