Anomalous transport and multi-scale drift turbulence dynamics in tokamak ohmic discharge as measured by high resolution diagnostics and modeled by full-fgyrokinetic code

Abstract

The complex interaction between large-scale mean EB flows, meso-scale zonal flows and fine-scale micro-turbulence excited due to specific profiles of plasma parameters and leading to anomalous transport is an important area of experimental and theoretical research in magnetically confined plasmas. In this paper the global gyrokinetic full particle distribution particle-in-cell simulations performed for Ohmic discharge of small research FT-2 limiter tokamak are for the first time validated against experimental data obtained both with a set of standard tokamak diagnostics and by sophisticated microwave backscattering techniques characterizing the tokamak turbulent dynamics and transport phenomena at micro, macro and intermediate scales. As a result of the simulation carried out with the ELMFIRE code an overall reasonable agreement between the numerical expectations and the experimental estimations of the electron and ion effective heat conductivity profiles obtained from the primary experimental profiles is achieved. The agreement obtained at the macro-level was strengthen at the microlevel and for intermediate turbulent scales using the Doppler reflectometry (DR), radial correlation reflectometry (RCR) and Doppler Enhanced Scattering (ES) microwave diagnostics. The turbulence dynamics at the micro-scale measured by DR at FT-2 were compared to the ELMFIRE predictions using synthetic DR diagnostics. As a result, not only the experimental DR spectra frequency shift, but its width and even the shape of the spectra was well reproduced by synthetic diagnostic indicating comparable rotation and spreading of the selected turbulent density fluctuations. The turbulence radial correlation length dependence on its frequency provided by the modeling appears to be in reasonable agreement to that given by RCR. The fluctuation poloidal rotation velocity profile obtained by the DR is very close to that obtained from the synthesized DR spectrum and also close to that given by ES and to the value produced by ELMFIRE for plasma EB drift velocity. The large spectral width of the DR and ES spectra is explained by fast and strong variation of radial electric field observed in the modeling. Giant oscillations of the field at a frequency of approximately 30-50 kHz much smaller than the typical drift wave frequency, but much larger than the inverse energy confinement time, observed by DR and ES as well, are attributed to the geodesic acoustic mode (GAM). This attribution is supported by comparison of the oscillation frequency dependence on the radial position with analytical prediction for the GAM frequency accounting for the impurity contribution. The dispersion of radial electric field estimated from the ES is found to be comparable to the huge E r dispersion provided by the gyrokinetic modeling. Moreover the GAM correlation length and phase velocity determined using ES technique appears to be close to those obtained by the ELMFIRE. The interrelations of GAM and drift wave turbulence in experiment and gyrokinetic modeling are compared....

Fast synthetic X-mode Doppler reflectometry diagnostics for the full-f global gyrokinetic modeling of the FT-2 tokamak

“…The massively parallelized particle-in-cell simulations of the gyrokinetic (GK) distribution function and the electric field 5,6 provide an efficient theoretical tool for studying the nonlinear turbulent plasma dynamics, which, however, needs a validation and comprehensive benchmarking against the experimental data. [7][8][9] In the recent papers, 10,11 such simulations of the electron and ion distribution functions from the first principles were performed for the small research tokamak FT-2 with a limiter configuration. The complex interplay of different turbulence components was studied in the simulations, and the successful quantitative comparison with the measurements carried out mostly at the low magnetic field side of the machine, where the turbulence is excited, was presented.…”

“…Development of a synthetic diagnostics, allowing the DR signal computation based on the results of GK modeling, could be helpful in this case both for the interpretation of the experimental results and for the code benchmarking. 10,11,[15][16][17][18][19][20][21] The linear version of the DR synthetic diagnostics, based on the computation of the probing microwave spatial distribution in the background plasma and evaluation of the DR signal in the Born approximation, was developed and used in Refs. 10, 11, and 15 for the O-mode and in Refs.…”

Capabilities of Spectroscopic Diagnostics CXRS in T-10 Tokamak

“…Детальные измерения параметров плазмы с помощью CXRS необходимы при проведении исследований свойств геодезических акустических мод (ГАМ) плазменных колебаний. ГАМ могут оказывать значительное влияние на аномальный транспорт в плазме токамака [28], при этом закономерности их возникновения и развития, а также их основные свойства напрямую связаны с профилями ионной температуры и концентрации примесей в плазме [29][30][31].…”

Multichannel Measurements of Effective Plasma Charge in T-10 Tokamak Using Visible Bremsstrahlung Intensity Under High Spectral Resolution

“…Радиальный профиль концентрации ионов примесей, а также их компонентный состав и распределение по зарядовым состояниям оказывают влияние на различные плазменные процессы, в том числе на закономерности возникновения и развития геодезических акустических мод колебаний в плазме токамака [10][11]. В частности, на Т-10 было обнаружено существенное изменение амплитуды и частоты ГАМ при импульсном напуске примесей [12].…”