Formation and sustainment of a low-aspect ratio tokamak by coaxial helicity injection
- University of Washington, Seattle, Washington 98195 (United States)
Low-aspect-ratio tokamaks with toroidal currents, {ital I}{sub {ital p}}, up to 250 kA are formed and sustained in the Helicity Injected Tokamak experiment [Nelson {ital et} {ital al}., Phys. Rev. Lett. {bold 72}, 3666 (1994)] using coaxial helicity injection. These plasmas are produced without use of a current drive transformer. Average toroidal currents are sustained at high values, {l_angle}{ital I}{sub {ital p}}{r_angle}=225 kA for 2 ms, where electron thermal energies are measured up to 80 eV with spectroscopy data suggesting burnthrough to the higher ionization states of oxygen. Currents can also be sustained for longer periods at lower values, {l_angle}{ital I}{sub {ital p}}{r_angle}=138 kA for 7 ms. These tokamaks are characterized by a rotating, {ital n}=1 distortion, with poloidal distortions approximately following the field line pitch, which only occur on the outer bad-curvature region. Equilibrium reconstructions show these plasmas have a tokamak {ital q} profile ({ital q}{sub 0}=5 -- 8, {ital q}{sub 95}=10 -- 12, {ital q}{sub cyl}{congruent}3.6), with a hollow toroidal current profile and up to 170 kA of closed field toroidal current in a low-aspect-ratio, {ital A}=1.68 configuration.
- OSTI ID:
- 55899
- Journal Information:
- Physics of Plasmas, Vol. 2, Issue 6; Other Information: PBD: Jun 1995
- Country of Publication:
- United States
- Language:
- English
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