Plasma Experiments with a Three-Meter θ Pinch

Abstract

Measurements are reported on the plasma produced in an 830-kJ theta pinch (scylla IV) with a 3-m compression coil in which the compression field is extended to 120 μsec by means of “crowbar” switches. Double-exposure holographic interferometry, side-on streak photographs, and neutron-emission measurements establish the following comparison with the previous version of the experiment: (1) The plasma confinement time and neutron emission have been extended from 3 to 10 μsec. (2) The scaling of confinement time and plasma temperature from the 1-m device is accounted for by simple end-loss and shock-compression considerations. (3) An m = 1 “wobble”of the plasma column is observed in the present experiment and is interpreted in terms of plasma rotation propagating from the ends at approximately the Alfvén speed.

Vacuum ultraviolet emission from a neon-seeded theta pinch

“…The energy source for this drive field was obtained from a lowinductance high-energy (~180kJ) capacitor bank consisting of 54 capacitors (60 kV, 1.8 /iF), each switched with a low-inductance 4-eIectrode spark gap. 5 The coil dimensions and drive current risetime are similar to Scylla 111 values. 6 A 7.5-jiF capacitor (charged to 15 kV), with ignitron switch and crowbar, was cabled to hollow electrodes at the discharge tube ends to supply a linear discharge for preionization.…”

Studies of end loss from a theta pinch using a Twyman--Green interferometer. Scientific report 77-4

“…Holographic interferometry (3,7,(15)(16)(17)(18)(19)(20) consists of making two holograms of the region which contains the plasma on the same photographic plate. One hologram is made when there is no plasma in the region in question and the second hologram is made when the plasma is present.…”

“…Since the number density profiles for t = 0 ysec and t = 2 ysec after implosion could not be determined experimentally, a functional profile which fits available data was used. It was assumed that the number density profile was Gaussian in shape, so that -Cr/r / (t)) 2 n r (t) = n a Ct)e 1/e , (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) where n ft) is the number density on-axis (i.e., r = 0 mm) at a time t, and r 1 , (t) is the value of the radius, at a time t, where the number density has decreased by a factor of 1/e from the on-axis value. This assumption of a Gaussian distribution was based on the results of other experiments CIS, 19).…”

“…Work has been done with the Mach-Zehnder interferometer using a pulsed C0 2 laser (13) for dense plasma (n g -10 16 -10 17 cm -3 ) and a HCN laser (12) for low density plasma (n % 10 -10 cm" ).…”

“…Using the values of n (2) and r. , (2) calculated from the first method, the final number density profiles at t = 2 ysec after implosion were determined to be; 2 n r (2) = 2.02xl0 16 an exaggerated scatter in the data. It was found that a 50 millitorr case was the minimum fill pressure for which the interferometer could be used on this particular theta pinch device.…”