First experiments on ICRF discharge generation by a W7-X-like antenna in the Uragan-2M stellarator

Abstract

In support of the ICRF experiments planned on the Wendelstein 7-X (W7-X) stellarator, i.e. fast ion generation, wall conditioning, target plasma production and heating, a first experimental study on plasma production has been made in the Uragan-2M (U-2M) stellarator using W7-X-like two-strap antenna. In all the experiments, antenna monopole phasing was used. The W7-X-like antenna operation with launched radiofrequency power of ~100 kW have been performed in helium (p = (4–14) × 10−2 Pa) with the vacuum vessel walls pre-loaded with hydrogen. Production of plasma with a density higher than 1012 cm−3 was observed near the first harmonic of the hydrogen cyclotron frequency. Operation at first hydrogen harmonic is feasible in W7-X future ICRF experiments.

Two-Strap Rf Antenna in Uragan-2m Stellarator

“…The two-strap antenna in fact plays the role of three-half-turn antenna used earlier. the further experiments show [12] that the two-strap antenna can create plasma n e ≈1•10 12 cm -3 in a weak magnetic field (0.01...0.07 T) without initial plasma created with the frame antenna. So the two-strap antenna can be used together with the frame antenna and independently.…”

“…U-2M device is a mid-size stellarator (torsatron) with twin helical coils l=2 having a small pitch angle, m=4 helical field periods and the additional toroidal field coils ( Fig. 1) [5][6][7][8][12][13][14]. The major torus radius is R 0 =1.7 m, the average last closed flux surface minor radius is ā ≈ 0.2 m. The maximum toroidal magnetic field strength with respect to mechanical stresses is 2.4 T. The vacuum chamber is toroidal with inner radius of r c = 0.34 m and volume V с = 3.879 m 3 (without volumes of the vacuum ports); torus surface area is S = 22.819 m 2 .…”

“…The paper presents a multifunctional unshielded twostrap antenna description and its first usage in wall conditioning regime in U-2M. The two-strap antenna was used to create target plasma later experiments [12].…”

Status and Prospects in Stellarator Research at Ipp Kipt

“…In support of the ICRF experiments planned on the W7-X stellarator, that is, fast ion generation, wall conditioning, target plasma production and heating, a new two-strap antenna is recently installed at U-2M (Fig. 1) [1,2]. Its shape is similar to W-7X ICRH antenna and the main distinction is that it is just smaller.…”

“…A first experimental study on plasma production has been made in the U-2M stellarator using this antenna [1,2].…”