Beta-dependent upper bound on ion temperature anisotropy in a laboratory plasma

Laser induced fluorescence measurements of ion temperatures, parallel and p erpendicular to the local magnetic field, in the Large Experiment on Instab ilities and Anisotropies space simulation chamber (a steady-state, high bet a, argon plasma) display an inverse correlation between the upper bound on the ion temperature anisotropy and the parallel ion beta (beta = 8 pi nkT/B -2). These observations are consistent with in situ spacecraft measurements in the Earth's magnetosheath and with a theoretical/computational model th at predicts that such an upper bound is imposed by scattering from enhanced fluctuations due to growth of the ion cyclotron anisotropy instability (th e Alfven ion cyclotron instability). (C) 2000 American Institute of Physics . [S1070-664X(00)05102-8].