Formation of a Spheromak Plasma Configuration

Abstract

As seen in Fig. 1(a), the diabatic signal does indeed increase as the value of n increases. In addition, both ionization features are evident at slew rates differing by a factor of 2 from that used to obtain the data in Fig. 1.When both lasers are polarized parallel to the direction of the electric field, then theoretically no | m x | = 2 can be produced and, in this case, we observe a dramatic decrease in the signal obtained at the diabatic threshold. In view of this test, and since the probability for diabatic passage in a given field slew rate is larger for \m l \ = 2 states than for | raj = lor |raj = 0 states, we conclude that the diabatic high-field peak is due primarily, if not wholly, to |raj = 2.The signal at electric fields between the adiabatic threshold and the diabatic threshold is attributed to a combination of adiabatic and diabatic passage through level crossings. As n increases, the ratio of this intermediate signal to the diabatic signal drops rapidly.These measurements demonstrate, for the first time, the passage of highly excited atoms from low electric fields to ionizing electric fields along predominantly diabatic paths. Clearly, it is important to account for the possibility of diabatic thresholds whenever one observes atomic states of high n using field ionization.A compact, toroidal configuration of magnetized plasma is produced by a combination of Z-and 0~pinch discharges. A paramagnetic toroidal field is produced by currents circulating in the plasma on closed flux surfaces.We report here our initial results on the formation of a plasma confinement configuration with the generic name of spheromak. 1 ' 2 This compact toroidal configuration has both toroidal (B^) and poloidal (B r ,B 2 ) magnetic field components with the toroidal field maintained by circulating plasma currents rather than by an external coil through the toroidal hole, as in a tokamak. Configurations of this type were first studied theoretically in an astrophysical context. 3 * 4 Related laboratory experiments involving plasma guns, 5 * 6 electron beams, 7 and pinches 8 have been performed. Our experiment, called paramagnetic spheromak (PS-1), makes use of Z-and 6 -pinch techniques to produce a prolate spheroid configuration. The results show, for the first time, that it is possible to establish the desired closed poloidal flux surfaces with a stabilizing paramagnetic toroidal field (i.e., with the peak magnitude of B(p near the magnetic axis). Figure 1 illustrates the formation phase. We start with a cylindrical deuterium gas column of radius 11.4 cm and a pressure of 15 mTorr. The column contains an axial bias magnetic field {-B z ) produced by I 9 currents 9 in an external, single-turn mirror coil with a mirror ratio of 1.1. The bias field is produced by a 20-kV, 18-\xY capacitor bank capable of producing fields with magnitude up to 8 kG. Typically fields of 4 kG are used. The field rises in 3 to 5 jusee (depending on the external inductance) and is clamped. Following this a Z-directed current shell is produced by disc...

Special topics in plasma confinement

“…FIGURE 31. Methods to create a spheromak discharge: (a) by plasma gun (reproduced with permission from Turner et al 1983Turner et al , copyright 1983, AIP Publishing LLC), (b) by combined θ -z discharge (reprinted with permission from Goldenbaum et al 1980Goldenbaum et al , copyright 1980 by the American Physical Society) and (c) by inductive flux core in S-1 (reprinted with permission from Yamada et al 1981Yamada et al , copyright 1981 by the American Physical Society).…”

Magnetic flux conversion and relaxation toward a minimum-energy state in S-1 spheromak plasmas

“…The toroidal magnetic field in the plasma is sustained entirely by poloidal plasma currents, thereby eliminating the need to link the plasma topologically. It has been possible to create [2][3][4][5] these configurations with poloidal-and toroidal-field profiles which satisfy the equations for force-free fields: 7 x j3_ » A_B. Agreement between experiment and theory was confirmed predominantly by identification of the experimental equilibria's profiles with the lowest-energy, force-free eigenmodes predicted by theory.…”

“…Agreement between experiment and theory was confirmed predominantly by identification of the experimental equilibria's profiles with the lowest-energy, force-free eigenmodes predicted by theory. [2][3][4][5][6][7] Experimental profiles were obtained from magnetic probes inserted into and around the plasmas.…”

Pulse Discharge Network Development for a Heavy Gas Field Reversed Configuration Plasma Device

“…Thrust is generated through pulsed expulsion of plasma in the form of FRCs. The following description of conventional FRC formation follows the sequence given by Goldenbaum 10 and Bellan 9 and has four main steps: 1) preionization; 2) implosion; 3) reconnection; and 4) equilibrium.…”

“…Plasma is then created and this effectively pre-ionizes the gas as shown in Figure 2. 9,10 Next, a fast capacitor bank discharges through the theta coil and creates a reversed magnetic field. The field is reversed on a timescale that is less than the magnetic diffusion time ("Implosion" in Figure 2).…”