Toroidal plasma rotation in the PLT tokamak with neutral-beam injection

Abstract

Toroidal plasma rotation in the Princeton Large Torus, PLT, has been measured for various plasma and neutral beam injection conditions. Measurements of the plasma rotational velocities were made from Doppler shifts of appropriate spectral lines and include data from both hydrogen and deuterium beams and co-and counter-injection at several electron densities. Without injection, a small but consistent toroidal rotation exists in a direction opposite to the plasma current (counter-direction) in the plasma center but parallel to the current (co-direction) in the plasma periphery. Using these measured velocities and the plasma density and temperature gradients, radial electron fields can be determined from theory, giving E r » 40 V/cm near tne plasma center and E r » 10 V/cm near the plasma edge. Insertion of a local, 2.5 percent magnetic well produced no observable effect on the beam driven rotation. Modeling of the time evolution and radial distribution of the rotation allows one to deduce an effective viscosi..; of the order of (1-5) x 10 4 cm 2 /sec.

Observations of central toroidal rotation in ICRF heated Alcator C-Mod plasmas

“…Toroidal impurity rotation in ohmic plasmas (no net momentum input) is consistent with neoclassical predictions [24,33,34]; in ohmic L-mode discharges, impurities rotate in the direction opposite to the plasma current, so in general the assumption that the majority ions and impurities (which are most often measured) rotate in the same way might be questionable [34]. In neutral beam heated plasmas, which have substantial direct momentum input, the toroidal momentum confinement time is much shorter than the neoclassical predictions [8][9][10][11]. Toroidal rotation profiles have been used to infer E, [8,11].…”

“…This is in the direction opposite to the rotation of impurities in ohmic L-mode plasmas [8,24,33,34]. The magnitude of the shift is -.…”

“…Counter-current toroidal rotation associated with ion orbit loss in neutral beam and ICRF heated plasmas has been observed [26,31], and the effects of electron loss in LHCD plasmas have been seen [29]. It is difficult to separate the contribution to the rotation from the direct momentum input of the neutral beams and the rotation that may be associated with (or induced by) Hmodes, although some information has been gleaned from balanced or perpendicular beam injection [8,11]. ICRF-only heated discharges provide the opportunity for the study of toroidal rotation in plasmas with no direct momentum input.…”

Toroidal rotation and momentum transport in Alcator C-Mod plasmas with no momentum input

“…Even so, there has been considerably less effort addressing momentum transport compared to energy and particle transport. In a majority of tokamak plasmas, the observed toroidal rotation is generated externally by neutral beam injection [8][9][10][11][12][13][14][15]. Momentum confinement is generally found to be anomalous, with a diffusivity, χ φ , similar to the ion thermal conductivity, χ i [8][9][10][11][12][13][14][15], but much larger than the neo-classical diffusivity (viscosity).…”

Measurements of the toroidal plasma rotation velocity in TFTR major-radius compression experiments with auxiliary neutral beam heating

“…Also observed was a sudden increase of the beam-induced toroidal rotation of the bulk plasma during compression. The toroidal rotation of tokamak plasmas with intense neutral beam injection has been a subject of research in recent years [2][3][4][5].…”