Theoretical comparison of coupling of a recessed cavity antenna and a conventional loop antenna for fast waves and ion Bernstein waves

Abstract

A numerical code has been developed to calculate the loading of a cavity loop antenna in threedimensional geometry. The loading of the cavity is calculated for fast wave and ion Bernstein wave coupling and compared with the loading of a conventional loop antenna. For fast waves, the cavity loading increases with increasing edge density, while the conventional loop loading is less sensitive to the edge density but shows a slight decrease of loading because of a steeper density gradient. For ion Bernstein waves, the two types of antenna behave similarly; however, in contrast to the loading for fast waves, the loading for ion Bernstein waves increases with decreased edge density and a steeper density gradient.

Coupling of fast waves in the ion cyclotron range of frequencies to H-mode plasmas in DIII-D

“…It is important to note here that the inclusion of the antenna side-walls in the modelling is essential for reproducing the measured dependence of L-mode and Ohmic coupling on density. When a conventional antenna model is used in which the sidewalls are neglected, the coupling code actually predicts a slight decrease in loading with n, rather than the observed increase in loading with n [34]. A conventional model also fails to reproduce the strong depen-dence of loading on n ^ shown in Fig.…”

“…The only change made to the code was in the solution of the vacuum fields, where the boundary condition associated with a recessed conducting wall was included. The details of these modifications will be presented in a separate publication [34]. In the present modelling, we invoke a radiation condition in COUPLING FAST WAVES TO H-MODE PLASMAS IN DIII-D the plasma interior, i.e.…”

Efficient 3D/1D self-consistent integral-equation analysis of ICRH antennae

“…The pioneering works in this field [1][2][3][4][5] (to cite only a few) were forced to limit both the plasma description and the current on the antenna conductors to simplified forms, yet attempting to maintain self-consistency in determining the antenna currents. Further works [6][7][8][9][10] consistently improved the plasma description, up to the inclusion of finite Larmor radius (FLR) effects and varying plasma parameters down to the scrape-off layer (SOL) region. Following another thread, other research groups improved likewise the plasma description, yet employing out-of-code modelling of antenna currents, based on transmission line (TL) equivalence and computation of TL equivalent parameters via two-dimensional (2D) plasma simulations [11]; the emphasis here was on plasma loading.…”

“…A full plasma validation would call for a check against measured values in actual experiment of input impedance or reflection coefficients; unfortunately, no such data are available in the literature (to the best of the authors' knowledge). It has to be noted that all the antenna parameters are extremely sensitive to the plasma parameters, especially the edge density and the SOL density profile and extension [5,10] and therefore a very accurate measurement of densities is of paramount importance in reliably predicting the antenna response in front of the plasma. A remarkable work in this sense is reported in [24] for the D-IIID machine, although only for the so-called 'loading resistance' (called 'radiation' resistance elsewhere), defined (for the concerned single-terminal-pair antenna) as [10] R load = P rad I 2 max;rms…”

Interaction of fast waves with ions

“…Typically, about 28 to 42 rays are calculated in the main spectra which are determined &om a coupling code VlDARY (coupled to FELICE) [2]. The wave information from CURRAY are input into the bounce averaged Fokker-Planck code CQL3D [3] which calculates the ion distribution in the presence of the rf quasilinear diffusion and neutral beam sources on specified flux surfaces.…”