[1] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA
[2] Univ Wisconsin, Ctr Magnet Selforg Astrophys, Madison, WI 53706 USA
[3] Univ Wisconsin, Lab Plasmas, Madison, WI 53706 USA
[4] Wheaton Coll, Dept Phys, Wheaton, IL 60187 USA
[5] Univ Wisconsin, Dept Phys, Madison, WI 53706 USA