Modification of tokamak edge plasma turbulence and transport by biasing and resonant helical magnetic field

Abstract

In this paper, both Resonant Helical magnetic Field (RHF) and limiter biasing have been applied to the tokamak. We have investigated their effects on the turbulence and transport of the particles at the edge of the plasma. The biased limiter voltage has been fixed at 200 V and RHF has L = 2 and L = 3. Also, the effects of the time order of the application of RHF and biasing to the tokamak have been explored. The experiment has been performed under three conditions. At first, the biasing and RHF were applied at t = 15 ms and at t = 20 ms. In the next step, RHF and biasing were applied at t = 15 ms and t = 20 ms, respectively. Finally, both of them were turned on at t = 15 ms until the end of the shot. For this purpose, the ion saturation current (I(sat)) and the floating potential (V(f)) have been measured by the Langmuir probe at r/a = 0.9. Moreover, the power spectra of I(sat) and floating potential gradient (∇V(f)), the coherency, the phase between them, and the particle diffusion coefficient have been calculated. The density fluctuations of the particles have been measured by the Rake probe and they have been analyzed with the Probability Distribution Function (PDF) technique. Also the particle diffusion coefficient has been determined by the Fick's law. The results show that, when RHF and biasing were applied at the same time to the plasma (during flatness region of plasma current), the radial particle density gradient, the radial particle flux, and the particle diffusion coefficient decrease about 50%, 60%, and 55%, respectively, compared to the other conditions. For more precision, the average values of the particle flux and the particle density gradient were calculated in the work. When the time is less than 15 ms, the average values of the particle flux and the particle density gradient are identical under all conditions, but in the other time interval they change. They reduce with the simultaneous application of biasing and RHF. The same results obtain from the histogram of the particle flux and the gradient of the particle density and the particle diffusion coefficient. Consequently, the simultaneous application of biasing and RHF is more effective for the plasma confinement.

The Study of Surface Properties of Tokamak First Wall Using TiN Coated on Stainless Steel

“…This device consists of a vacuum vessel with circular cross-section that was made from a stainless steel welding structure with two toroidal breaks and a minor radius b = 15 cm [13][14][15]. IR-T1 Tokamak chamber has been made of the stainless steel 316L (S.S.316L).…”

“…The plasma current and loop voltage are measured by Rogowski coil and loop voltage coil. Electron temperature is calculated by Langmuir-Ball Pen Probe (LBPP) using the method mentioned in earlier researches of IR-T1 group [13][14][15].…”

MF-DFA Analysis of Turbulent Transport Measured by a Multipurpose Probe

“…The effect of the amount of biasing voltage has been investigated in the previous work. [11] In the present work the effect of time of applied bias has been analyzed. For this purpose the bias with fixed voltage (𝑉 bias = 200 V) was applied to the plasma at different times.…”

“…[10] The amount of bias is a factor which can reduce turbulent transport. [11] In this work, we apply bias at different times to the plasma and investigate its effect on turbulent transport, using the multifractal detrended fluctuation analysis (MFDFA) method. For nonstationary time series, it is important to correctly separate fluctuations from average behavior (trend).…”