High-density plasma production with potential confinement in the GAMMA 10 tandem mirror

Abstract

539͔ by axisymmetrization of heating systems for the plasma production, heating, and potential formation. A significant increase of the density and diamagnetism by the potential confinement was observed. In the previous experiment, it was difficult to increase the central cell density higher than 2.7ϫ10 18 m Ϫ3. One of the possible mechanisms is the density clamping due to the eigenmode formation of the ion-cyclotron-range of frequency ͑ICRF͒ waves in the axial direction. With high harmonic ICRF waves ͑RF3͒, the experiments to overcome this problem have been performed. In preliminary experiments with RF3 and NBI the maximum density of 4ϫ10 18 m Ϫ3 was attained.

Improvement of ICRF Antenna Loading in the Minimum-B Configuration on GAMMA 10

“…On the GAMMA10 tandem mirror, high performance plasmas are achieved with magneto-hydrodynamic (MHD) stability attained by the high-B plasmas in the minimum-B anchor cells [1,2]. On GAMMA10, waves in the IonCyclotron Range of Frequency (ICRF) are used for ion heating in the minimum-B field.…”

Eigenmode formations ofm= 1 fast Alfvén waves in the ion-cyclotron frequency range in the GAMMA 10 central cell

“…In the present tandem mirror experiments, production of high density plasmas of more than 10 19 m −3 is required. In GAMMA 10, although the high ion temperature above 10 keV has been realized, the density is relatively low on such a high performance discharge [3,4]. In the GAMMA 10 central cell, the fast Alfvén waves with the m = 1 azimuthal mode number (co-rotation with electrons) are mainly used for the plasma production.…”

“…In the GAMMA 10 central cell, the fast Alfvén waves with the m = 1 azimuthal mode number (co-rotation with electrons) are mainly used for the plasma production. While the RF sources whose frequency is near the fundamental ion-cyclotron frequency have been used for the plasma production, saturation in the plasma density has been observed [4].…”

“…The waves with higher frequency are thought to be more effective in forming the eigenmodes multiply and continuously in the plasma. High-harmonic fast waves (HHFWs) have been employed for high density plasma production, and a significant increase in density has been observed [4]. HHFW is used in the spherical tokamaks with the aim of providing electron heating and current drive [5].…”

“…In order to investigate the eigenmode formations of the waves excited in the axisymmetric central cell, a two-dimensional full wave code has been adopted [6,7]. In the previous study in the central cell, the formation of a radial eigenmode was calculated using a simple model, where the plasma was assumed to be cylindrically uniform [4]. Since the wavelength is comparable to the dimensions of the plasma, uniform plasma approximation is not appropriate and the boundary conditions as well as the inhomogeneity of the plasma parameters become important.…”