Long-duration quiescent high-β hydrogen plasmas.

Radiofrequency-heated, high-β, magnetized hydrogen plasmas in the Princeton field-reversed-configuration-2 device, with its magnetic-field-parallel radial boundary formed by eight discrete room-temperature coaxial copper rings, display constant density for times exceeding 150 ms. When the copper rings are cooled to LN2 temperature, the line-average plasma density decreases, in a few ms, from its initial peak value by a factor exceeding 5. Providing a single ms-duration hydrogen gas puff at the discharge's boundary, 3 to 70 ms after the density decay, returns the plasma density to its original high value at which it remains for 10s to 100s of ms. Commencing at the brief gas puff, the amplitudes of rotational modes and low-frequency turbulence in the plasma decrease by more than a factor of 10 and remain low throughout the constant plasma-density phase.