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.

Interpretation of measurements of the global momentum and energy confinement times in strongly rotating tokamak plasmas

“…While this assertion is true in the usual neoclassical ordering of Hsu and Sigmar, it is not in their 'strong impurity' ordering, where A =~ 0 (1) for a = n I Z 2 /n i ~ 0(1). Thus, the arguments which Connor et al [28] present to support their contention that the solution of Stacey et al [13b] for Kj is 'unphysical' and that the numerical result (no ordering approximations) that \d%/dd\ -|eO 0 | is 'flawed' are themselves invalid in the strong impurity limit of Hsu and Sigmar.…”

“…We use a right hand (^, p, <f>) flux surface co-ordinate system (e.g. [9]) with differential length elements, d£ x = h x dx, and a differential volume element, = 2TT dip B P (1) where B p is the 'poloidaT magnetic field. The flux surface average of a quantity A is (A) = 2TT Ad j (2) in this co-ordinate system, and the volume integral of a quantity A is (A) V'…”

“…When unbalanced neutral beam injection (NBI) is used to heat a tokamak plasma, the resulting torque causes the plasma to rotate. Rotation speeds comparable to the thermal speeds of impurity ions present in the plasma and well within a factor of ten of the thermal speed of the main plasma ion species are routinely achieved (see, for example, Refs [1][2][3][4][5][6][7]). In rotating plasmas there are new transport effects associated with the viscous radial transfer of momentum and with the plasma inertia which are not found in non-rotating plasmas.…”

Stability of a tokamak plasma with diffuse toroidal rotation

“…For example, a deuterium plasma has reached toroidal velocities of approximately 40 % the sound speed in the DIII-D tokamak (Baylor et al 2004, figure 9) and the National Spherical Torus Experiment (NSTX) has reported toroidal velocities of approximately half the Alfvén speed (Sabbagh et al 2006, p. 641). Rotation is typically induced by neutral beam injection (known as NBI) or radio-frequency (known as RF) heating (Suckewer et al 1981;Eriksson, Righi & Zastrow 1997).…”

“…Rotation is typically induced by neutral beam injection (known as NBI) or radio-frequency (known as RF) heating (Suckewer et al. 1981; Eriksson, Righi & Zastrow 1997).…”