Fluctuation measurements at c/ω_pe spatial scales in a tokamak

Magnetic and electrostatic fluctuations have been measured at the short scale length of the collisionless skin depth (c/ω_pe) using small magnetic and electrostatic probes in the Tokapole II tokamak [Nucl. Fusion 9, 1509 (1979)]. For certain conditions and at high frequency (the MHZ range), fluctuations are present at the c/ω_pe scale, with significant amplitude variation in the range between c/ω_pe and the ion gyroradius scale. Wavelength dependence is inferred from measurements with probes of varying sizes. The amplitude of the turbulence at the c/ω_pe scale is smaller than the dominant low-frequency turbulence, and is thus not relevant to transport in Tokapole II. Comparison with theoretical treatments of c/ω_pe turbulence is discussed.