Rotation and Structure of Low-Frequency Oscillations inside the ST-Tokamak Plasma

Abstract

the linear heating times estimated for the present experiment give AT e <l eV/^sec near the upper hybrid frequency. The enhancement at the second harmonic is many orders of magnitude smaller. Since our measurements show (see Fig. 3) that under these conditions AT e -20-30 eV/Vsec, and that very energetic particles are also produced within a microsecond (L7<500 eV), it is clear that linear theories do not explain our results. We believe that similar processes may occur in a number of experiments where heating near the upper hybrid or the cyclotron harmonics have been observed. 5 * 10 In contrast to recent heating experiments with frequencies below the electron cyclotron frequency where mainly heating of the tail of the distribution function was observed, 11 in the present case considerable heating of the main body of electrons was also observed. This is believed to be due to the strong interaction of the excited Bernstein waves with thermal electrons. Thus, heating at frequencies above the electron-cyclotron frequency may be more favorable for possible applications whereThe two phases of magnetohydrodynamic (MHD) instability observed in tokamaks 1 ' 2 appear conjointly; low-frequency, low-amplitude oscillatory modes with helical magnetic field perturba-are observed to grow leading into the more deleterious "disruptive" instability characterized by a negative spike on the plasma loop voltage (v^) and a partial depletion of the energy stored in the plasma {9 and <p are the minor and major azimuthal angles of the torus, respectively). As m decreases, the intensity of the disruptive instability increases, until following m = 2, the disruptive instability dominates the tokamak discharge. In fact, the m -2 oscillations are observed to precede the violent disruptive instabilities at both the low fast heating of thermal electrons is desired. . Note that in this work the wavelengths were not measured, and the thresholds were not compared with theory. 9 M. Porkolab, Nucl. Fusion JL2, 329 (1972). 10 O. A. Anderson et al., Bull. Amer. Phys. Soc. _17, 997 (1972). n M. Porkolab, V. Arunasalam, and R. A. Ellis, Jr., Phys. Rev. Lett. 29, 1438. safety factor q(a) and high-pressure (plasma density) limits to useful tokamak operation [q(r) -rB^^/RB^r),where r and R are the minor and major toroidal radii, respectively, and a is the plasma limiter radius]. Apparently, the disruptive instability occurs when the radial current distribution j^r) is such that the q-m singular magnetic surface location is favorable to the enhanced growth of the m-mode oscillation. 1 (Runaway electrons do not appear to cause the instability. 3 ) When the q = 2 singular surface is moved toward the plasma surface by lowering q(a) or by causing the current channel to shrink by increasing pressure as evidenced by a constriction of the electron temperature profile, 1 ' 4 the m-2 mode grows to an amplitude of B e (d)/B e (d)~ 6% at Low-frequency oscillations, which can lead into the violent disruptive instability which sets the q (current) limit of tokamak operat...

Electron Temperature Measurement by Floating Probe Method Using AC Voltage

“…Conventional methods to measure plasma parameters include the use of electrostatic probes (Langmuir probe method) [13] , high-frequency probes [14,15] , neutral analysis [16] , and laser spectroscopy [17] . In particular, the Langmuir probe method, shown in Fig.…”

Radial Electric Fields and Transport Barriers

“…The possible importance of radial electric fields for transport was in the past repeatedly established [10,11,12,13]. Since the early days the plasma potential has been measured in tokamaks such as ST [14], TM-4 [15] and ISX-B [16], but because no significant effects of the radial electric field E r on plasma transport were observed under the machine conditions at that time, no further research was conducted in tokamaks.…”

Locking of Small Magnetic Islands by Error Field in T-10 Tokamak

“…where  R = 1/ R is the inverse resistive time,  R =  0 a 2 /,  is the plasma resistivity and  p is the plasma pressure normalized by the poloidal magnetic field pressure at r = r S . In (10), (11) [6,7,12,20,25,26]. In the TEAR code, the equations of the resonant layer angular motion in the toroidal and poloidal directions are used to calculate the V θ and V φ time variations due to the interaction between the RMP and magnetic island structure (see [14]):…”