Results of localized Alfvén wave heating in TCABR

Abstract

Using two dimensional numerical codes, we show that the direct electron heating found with electron cyclotron emission (ECE) radiometry is related to local Alfvén wave resonances in Tokamak Chauffage Alfvén Brésilean (TCABR) plasmas. The m/N =1/2, 0/2 and 0/3 modes are dominant in the observed wave heating, due to Alfvén wave continuum absorption. In particular, the resonant absorption of the m = 0 sideband harmonic plays an important role in the central core and peripheral heating. The increase of the electron temperature during the radio frequency pulse was accompanied by a local density rise that produced a cut-off of the ECE emission. The observed heating profile is also consistent with the reflectometer measurements of the density fluctuations induced by radio frequency fields in the local Alfvén wave resonance of the m/N =-1/-2, 1/-3 modes in TCABR.

Comparative electron temperature measurements of Thomson scattering and electron cyclotron emission diagnostics in TCABR plasmas

“…24508 the rf power delivered by the antenna was less than 40 kW and the frequency was fixed at 5.0 MHz. Different theoretical models 5,14 agree in that the radial distribution of the power absorbed by the plasma is strongly localized around r = 2, 10, and 16 cm, with a spatial resolution around 4 cm. Currently, these resonances cannot be detected by the TSD diagnostic, since there is a single observation volume.…”

“…A 7 ms pulse of radio-frequency ͑rf͒ power has been applied to the plasma starting at t = 70 ms, during the quasistationary phase of the plasma current. 5 Although the antenna straps are protected by boron nitride ͑BN͒ lateral plates, the rf power still causes desorption at their metal surface, which leads to an increase of the plasma density. Consequently, as the average electron density-depicted in the first graph of instabilities that are clearly visible in the Mirnov coil-third graph in Fig.…”

“…Alfvén waves ͑AWs͒ are regularly lunched into the TCABR tokamak for local and global plasma heating 5,10 and for plasma diagnostic. 11 AW heating is based on mode conversion of an externally driven rf field into kinetic or electrostatic Alfvén waves at the localized Alfvén resonance layer.…”

Identification of local Alfvén wave resonances with reflectometry as a diagnostic tool in tokamaks

“…To obtain good accuracy, 473x99 mesh points are used in the code calculations. Here, we analyze the AW absorption in TCABR shot N o 10668 [7,9] (minor radius a=0.18m, major radius For 0.2kW/m 3 of power density at the resonance surface r A =0.65(R-R 0 ) (or about of 1kW of absorbed power), we obtain δn/n e ≈1.10 -4 , which is of the level that can be detected by a modern reflectometer. The sensitivity of the system may be improved with locked frequency detection at the AW frequency.…”

Desenvolvimento e utilização de um injetor de pastilhas de impurezas no estudo da mitigação de disrupções e atenuação de raios-X de altas energias

“…No tokamak TCABR, tem sido pesquisado ao longo dos últimos anos o aquecimento do plasma utilizando ondas de Alfvén [5,6] e, logo no início destes estudos, uma nova forma de descargas runaway foi descoberta [5].…”