Study of the confinement properties in a reversed-field pinch with mode rotation and gas fuelling

• Published in: Plasma physics and controlled fusion 2002-08, Vol.44 (8), p.1625-1638, Article 314
• Main Authors: Cecconello, M, Malmberg, J-A, Nielsen, P, Pasqualotto, R, Drake, J R
• Format: Article
• Language: English
• Subjects: Atom- och molekylfysik; Atomic and molecular physics; ENERGY CONFINEMENT; FLUCTUATIONS; Fysik; NATURAL SCIENCES; NATURVETENSKAP; Physics; POLOIDAL CURRENT DRIVE; RFX; VUV
• ISSN: 0741-3335; 1361-6587; 1361-6587
• DOI: 10.1088/0741-3335/44/8/314

An extensive investigation of the global confinement properties in different operating scenarios in the rebuilt EXTRAP T2R reversed-field pinch (RFP) experiment is reported here. In particular, the role of a fast gas puff valve system, used to control plasma density, on confinement is studied. Without gas puffing, the electron density decays below 0.5 x 10(19) M-3. The poloidal beta varies between 5% and 15%, decreasing at large I/N. The energy confinement time ranges from 70 to 225 mus. With gas puffing, the density is sustained at n(e) approximate to 1.5 x 10(19) m(-3). However, a general slight deterioration of the plasma performances is observed for the same values of I/N: the plasma becomes cooler and more radiative. The poloidal beta is comparable to that in the scenarios without puff but the energy confinement time drops ranging from 60 to 130 mus. The fluctuation level and the energy confinement time have been found to scale with the Lundquist number as S-0.05+/-0.07 and S0.5+/-0.1, respectively. Mode rotation is typical for all the discharges and rotation velocity is observed to increase with increasing electron diamagnetic velocity.