[en] This paper presents an analysis of a large aspect ratio (R/a about 9) tokamak reactor, with a circular plasma cross-section, operating in the high-beta second stability regime. Engineering advantages of such a system include good access, simple poloidal coil design with no coils inside the toroidal magnet set, low toroidal plasma current, and higher toroidal magnetic field on axis. MHD equilibria which are stable at high beta exist for this configuration. The gap between the first and second stable regimes of operation is narrowed considerably at high aspect ratio. Reactor designs based on present confinement scaling data are presented together with a description of a medium sized experiment which can explore the important physics questions associated with this attractive class of fusion reactor

[en] In an effort to determine the mechanisms responsible for plasma transport, the scaling of the cross-field diffusion coefficient in the Wisconsin Leviated Octupole with density, temperature, and magnetic field strength was measured over a wide range of plasma parameters. This study included a density range of 6 x 10⁶ cm^-3 to 2 x 10¹² cm^-3, a temperature range of approximately 0.1 eV to 20 eV for the ions and approximately 0.1 to approximately 10 eV for the electrons, and a magnetic field range of approximately 40 G to approximately 2 kG. The scaling and magnitude of the diffusion was measured by three independent methods. The first method used the actual measured flux of plasma to the surface of an internal ring and the observed density gradient near the ring to infer a diffusion coefficient. The second method used the temporal part of the separable diffusion equation which was solved in the octupole geometry to match the observed density decay in time. The third used the spatial part of the diffusion equation to compare the shape of the observed density profile to the shape calculated assuming a particular scaling of the diffusion coefficient. By varying the plasma parameters and observing the change in the diffusion coefficient with these parameters, the scaling of D could be demonstrated

[en] The main research objectives during the past year fell into four areas: (1) detailed observations over a range of high-beta tokamak equilibria; (2) fabrication of an improved and more flexible high-beta tokamak based on our understanding of the present Torus II; (3) extension of the pulse length to 100 usec with power crowbar operation of the equilibrium field coil sets; and (4) comparison of our equilibrium and stability observations with computational models of MHD equilibrium and stability

[en] Our main research objectives during the past year fell into four areas: (1) construction and initial operation of the new tokamak, HBT; (2) further numerical modeling of the Torus II experimental equilibria using the PPPL equilibrium and stability codes; (3) diagnostic development; and (4) ICRF antenna coupling calculation in 2D and rf current drive

[en] A plasma focus electrode is described which utilizes a cylindrical hollow conductive anode having a concentric cylindrical insulator. This anode is used in conjunction with a lithium vortex cathode in the formation of a plasma focus for the liberation of neutrons from a plasma at the focus

[en] A diagnostic has been developed for measurements of the evolution of plasma density distributions in 2D using the principles of computed emission tomography. The system measures the near infrared emission along several chords through the plasma cross-section and the emission profile is then reconstructed using a maximum entropy based algorithm. This paper will present details of the reconstruction algorithm; the data collection system; the verification of the diagnostic using both physical and numerical phantom sources; evidence for the correlation between n² and the infrared emission intensity; initial measurements on a tokamak plasma

[en] A new detector system for single shot measurement of electron temperature and density profiles in a magnetically confined plasma has been developed. Preliminary results have been obtained with this multi-point Thomson scattering diagnostic on Torus II, a high beta tokamak. It has a density range of 2 x 10¹³cm^-3 less than or equal to n_e less than or equal to 5 x 10¹⁴cm^-3 in the preionization phase and density of 5 x 10¹⁴cm^-3 less than or equal to n_e less than or equal to 2 x 10¹⁵cm^-3 in the tokamak phase. Electron temperatures range from T_e > 6 eV in the preionization phase to T_e approx. 100 eV in the tokamak phase. The detector used is a multi-anode microchannel plate (MCP) with a 25 mm diameter multi-alkali photocathode. A 10 x 10 array of anodes collect the current, which has been amplified by as much as 10⁶. Each anode is independent so the MCP can be viewed as a parallel array of 100 independent photomultiplier tubes

[en] A review is given of the Torus II operating parameters and the CO₂ scattering apparatus. Subsequent sections address the questions of beam deflection, phase shift of the transmitted beam, and scattering measurements made on the time scale of the Torus II plasma lifetime

[en] The Columbia Linear Machine has been redesigned to enter the parameter regime of the collisionless, curvature-driven, trapped-particle instability. With the new machine configuration, a strong (n/N > 60%), coherent mode is observed which bears all the characteristics of this instability. These include strong localization to the mirror cell, broad radial-mode structure, and MHD-like body motion of the plasma column. Furthermore, the mode exhibits all the correct parametric dependences of increasing mode amplitude with increasing mirror ratio and rf power, and decreasing mirror-cell length

[en] Density fluctuations delta n/n < approximately 20%, were observed to have no effect on the classical diffusion of a collisional helium plasma across a poloidal octupole field with an additional weak toroidal field. The implication of these results on tokamak scattering experiments is discussed. (Auth.)