Heating and confinement of a deuterium plasma by a rising axial magnetic field in cylindrical geometry is investigated as a function of applied voltage, mirror ratio (Rm), discharge tube material and tube shape for several scaling geometries at a given aspect ratio D/L = 0.44. Diagnostic methods include internal and external magnetic probes, fast streak photography and magnetic flux and neutron measurements. Magnetic probes show the existence of trapped reverse fields and the subsequent intermixing of plasma and field during the second half and later compression cycles. Plasma confinement from the walls during the second and third half discharge cycle is inferred from strealc photographs and the duration of neutron production. As the mirror ratio is reduced to ∼ 1 , the yield and duration of neutron production increases while plasma end streaming is enhanced. Azimuthal asymmetries in the axial field in the mirror are associated with neutron production. Reducing the θ-asymmetry to ∼ 1% reduces neutron production by a factor of ∼ 3. The main effects of the small field perturbations may be explained in terms of the nonuniform formation and detachment of the current sheath from the discharge tube walls. This can lead to the influx of wall impurities which may account for the lower nuclear yields.
Recent progress in plasma confinement and heating in open-ended magnetic traps