Evaluation of Excitation Conditions of ITG Modes in the PANTA

Abstract

To study the nonlinear saturation mechanism in turbulent plasmas, we plan to obseve ion temperature gradient (ITG) modes in the Plasma Assembly for Nonlinear Turbulence Analysis (PANTA). Linear growth rates of ITG modes in the linear device are analyzed to determine their excitation conditions using a three-field fluid model to describe the ion motion. Parameter scans of the linear growth rate show the threshold for ITG mode excitation, and the typical plasma parameters of the PANTA are found in the unstable domain.

Ion temperature measurement by laser‐induced fluorescence spectroscopy in panta

“…The assumption of T i / T e ∼0.1 in the previous experimental studies (such as the resistive drift wave and D'Angelo mode ) were verified. These assumptions in nonlinear simulations were also confirmed. Our experimental result provides valuable information for the evaluation of nonlinear processes of the plasma turbulence.…”

“…More detailed experimental verifications are required for further progress. Some of the instabilities that excite plasma turbulence are ion temperature gradient (ITG) mode , resistive drift wave and D'Angelo mode . Linear growth rates, dispersion relations and dumping rates of these modes depend on ion temperature .…”

“…The ion temperature is difficult to measure in laboratory plasmas and is often assumed to be much smaller than the electron temperature on the basis of a limited number of spectroscopic measurements. The absolute value of the ion temperature significantly affects the instabilities, such as the drift waves , and the ITG mode . Despite this, in our turbulence experiment for linear magnetized plasma at Kyushu university (LMD, LMD‐U and PANTA), we have assumed that T i / T e ∼0.1 , where T i is the ion temperature, and T e is the electron temperature.…”

“…The effect of Zeeman splitting is evaluated for a more accurate assessment of the ion temperature measurement by changing the direction of the polarization axis on a linearly polarized laser beam. In PANTA, many nonlinear turbulence phenomena have been identified . The accurate measurement of ion temperature allows us to more precisely compare observed fundamental processes of turbulence with models.…”

Finite Larmor Radius Effect on Ion-Temperature-Gradient Instability in Cylindrical Plasmas

“…In basic experimental devices, the typical spatial scales of the device and gyro-motion of ions are close to each other, so the finite Larmor radius (FLR) effect is not negligible. A mode with the wave length comparable to the effective ion Larmor radius can become unstable even in low ion temperature plasmas [12]. For the first step, linear characteristic of the ITG instability has been investigated using the parameter set of PANTA linear device [13].…”