[1] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA
[2] Univ Wisconsin, Dept Phys, Madison, WI 53706 USA
[3] Univ Wisconsin, Ctr Magnet Self Org Astrophys, Madison, WI 53706 USA
[4] Univ Wisconsin, Lab Plasmas, Madison, WI 53706 USA