Experimental proof of mirror instabilities in the Isar I theta pinch

In the Isar I linear theta pinchm=0 instabilities were observed and experimentally investigated. The variation of the plasma parameters over a wide range (τ _ii =10^?2... 10²μsec) showed that them=0 instabilities only occurred in sufficiently hot and thin plasmas, and so they are most probably due to the anisotropic pressure of the ions and should be mirror instabilities. Perturbations of the plasma limited in space and time were observed by measuring the continuum radiation, by 90 ° laser scattering measurements and by measuring the magnetic field and the local neutron rate. All measurements showed distinct, correlated, local perturbations of the plasma cylinder. These perturbations were accompanied by bulging of the plasma cylinder and increasing density. The extent in the axial direction was of the order of the plasma diameter. It may be assumed that the observed instabilities contribute appreciably to relaxation of the anisotropic ion pressure and increase the end losses.