Stable High Beta Plasmas Confined by a Dipole Magnetic Field

Stable high-beta plasma is created and confined by the magnetic field of a superconducting coil that is suspended within a large vacuum chamber by thin supports. Discharges containing trapped electrons form when microwaves cause strong perpendicular heating at cyclotron resonance. At low gas fueling rates, an instability appears that resonates with the magnetic drifts of fast electrons and causes rapid radial transport. Higher gas fueling stabilizes the instability and allows the fast electron pressure to rise until the ratio of plasma to magnetic pressure, β ≡ 2μ0 p/B2, attains 20%. PACS numbers: 52.55.-s, 52.50.SW, 52.35.-g