Effects of limiter biasing on the ATF torsatron

• Published in: Journal of nuclear materials 1992-12, Vol.196, p.308-311
• Main Authors: Uckan, T., Aceto, S.C., Baylor, L.R., Bell, J.D., Bigelow, T.S., England, A.C., Harris, J.H., Isler, R.C., Jernigan, T.C., Lyon, J.F., Ma, C.H., Mioduszewski, P.K., Murakami, M., Rasmussen, D.A., Wilgen, J.B., Zielinski, J.J.
• Format: Article
• Language: English
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/S0022-3115(06)80051-6

Positive limiter biasing on the currentless ATF torsatron produces a significant increase in the particle confinement with no improvement in the energy confinement. Experiments have been carried out in 1-T plasmas with ∼400 kW of ECH. Two rail limiters located at the last closed flux surface (LCFS), one at the top and one at the bottom of the device, are biased at positive and negative potentials with respect to the vessel. When the limiters are positively biased at up to 300 V, the density increases sharply to the ECH cutoff value. At the same time, the H α radiation drops, indicating that the particle confinement improves. When the density is kept constant, the H α radiation is further reduced and there is almost no change of plasma stored energy. Under these conditions, the density profiles become peaked and the electric field becomes outward-pointing outside the LCFS and more negative inside the LCFS. In contrast, negative biasing yields some reduction of the density and stored energy at constant gas feed, and the plasma potential profile remains the same. Biasing has almost no effect on the intrinsic impurity levels in the plasma.