Laser induced fluorescence measurements of ion velocity and temperature of drift turbulence driven sheared plasma flow in a linear helicon plasma device

Abstract

Using laser induced fluorescence (LIF), radial profiles of azimuthal ion fluid velocity and ion temperature are measured in the controlled shear de-correlation experiment (CSDX) linear helicon plasma device. Ion velocities and temperatures are derived from the measured Doppler broadened velocity distribution functions of argon ions. The LIF system employs a portable, high power (>300 mW), narrowband (∼1 MHz) tunable diode laser-based system operating at 668.614 nm. Previous studies in CSDX have shown the existence of a radially sheared azimuthal flow as measured with time delay estimation methods and Mach probes. Here, we report the first LIF measurements of sheared plasma fluid flow in CSDX. Above a critical magnetic field, the ion fluid flow profile evolves from radially uniform to peaked on axis with a distinct reversed flow region at the boundary, indicating the development of a sheared azimuthal flow. Simultaneously, the ion temperature also evolves from a radially uniform profile to a profile with a gradient. Measurements in turbulent and coherent drift wave mode dominated plasmas are compared.

Helicon discharges and sources: a review

“…According to P Diamond [125], this should drive a poloidal flow, which was indeed seen and measured [126]. In collaboration with Scime (see section 10), laser induced fluorescence was brought to the experiment, and this sheared poloidal flow was directly measured, along with the perpendicular ion temperature [127]. This brief summary cannot do justice to the sophistication of this experiment.…”

Development of core ion temperature gradients and edge sheared flows in a helicon plasma device investigated by laser induced fluorescence measurements

“…1(b), similar to the configuration used in a previous campaign of LIF experiment on the original CSDX with an m ¼ 0 antenna, smaller source diameter (10 cm), and reduced magnetic fields. 26,27 The laser light was injected perpendicular to the background magnetic field using a rectangular glass window at the top of the plasma vacuum chamber, located 75 cm downstream from the helicon antenna. The argon ions are Doppler shifted along the path of the injected light, and hence this yields the perpendicular ion temperature and the azimuthal ion fluid velocities.…”

Direct measurements of classical and enhanced gradient-aligned cross-field ion flows in a helicon plasma source using laser-induced fluorescence

“…4 Recently, turbulence-driven sheared flow has been shown to mitigate enhanced radial ion transport, triggering high-confinement modes in both helicon devices and tokamaks. [28][29][30] Externally driven sheared flows have also been shown to mitigate cross-field ion transport. 31 There is a substantial and growing body of theoretical and experimental studies on drift wave turbulence and transport.…”