Electron Gyro-scale Fluctuation Measurements in National Spherical Torus Experiment H-mode Plasmas

Abstract

A collective scattering system has measured electron gyro-scale fluctuations in National Spher-

Quantitative comparisons of electron-scale turbulence measurements in NSTX via synthetic diagnostics for high-k scattering

“…Turbulence in the tokamak core can live at ion gyro radius scales (k ⊥ ρ s < 1) and at electron gyro radius scales (k ⊥ ρ s > 1), where k ⊥ is the perpendicular wavenumber of the turbulence and ρ s = c s /Ω c,i is the ion sound gyro radius evaluated at the ion sound speed c s = T e /m i , and Ω c,i = eB/m i is the ion gyro-frequency. Experimentally, coherent scattering techniques implemented through Doppler backscattering (DBS) [8][9][10][11][12][13][14][15][16] and high-k scattering [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] can probe turbulent density fluctuations at electron-scales (k ⊥ ρ s > 1). These can be of special importance in spherical tokamak plasmas where electron thermal transport dominates heat transport losses in H-mode scenarios [34][35][36][37][38][39], and electron-scale turbulence can be the main heat loss mechanism in some operating regimes [40,41].…”

“…In this section we highlight the importance of geometric effects, such as the normali zing B-field, the effect of plasma elongation and Shafranov shift, which can strongly affect the interpretation of the measured wavenumber components from scattering measurements (by up to factors of ∼5 for the present NSTX case). In section 4 we apply the synthetic diagnostic to compute numerically generated synthetic spectra for the high-k scattering system in NSTX [26][27][28], using realistic electronscale gyrokinetic simulations based on a modest-β NSTX NBI heated H-mode plasma. Finally, we compare synthetic high-k frequency and wavenumber spectra with experimental spectrum measurements.…”