Numerical and experimental results on the production of weakly compressed thermonuclear plasmas in the Garching high-voltage theta and belt pinch

The production of high-temperature weakly compressed plasmas by high-β shocks is investigated in a high-voltage theta and belt pinch. Density, electron and ion temperatures and magnetic field profiles are measured by laser-light scattering, neutron yield and probes. Shock dynamics is simulated with a 1-d hybrid fluid-particle code; turbulent transport coefficients used in this code are derived from investigations of the ion-acoustic instability in a separate 2-d particle code. Magnetic field profiles and electron temperature in the shock (Tsub(e)=2 keV) are consistent with transport coefficients for ion-acoustic turbulence. Enhanced resistivity and reduced axial heat conduction can be explained by the same turbulent ''collision frequency'' νsub(eff) approximately 5x10-3 ωsub(pe). Experiment and simulation show that the neutron yield is due to counterstreaming beams of ions reflected at the potential jump in the piston. After shock compression a dense (4x1014 cm-3) β=1 plasma core consisting of hot ions (Esub(i)=1.5 keV) and cold electrons is observed. A compression ratio Rsub(c)/rsub(pl) approximately 1.8 is reached. The observed plasma halo surrounding the main plasma column is due to MHD-instabilities with high m-number. The wavelength of these modes is found experimentally to be lambda proportional to n0sup(-1/2). First results in the belt-pinch geometry show that weakly compressed high-temperature plasmas can also be produced in toroidal systems. (author)