Experimental demonstration of the plasma electron density diagnostics using the single-shot THz detection method

Abstract

We report the first experimental demonstration of a novel plasma diagnostics method using the single-shot THz detection method. In this experiment, a broadband single THz pulse is generated by focusing two-color (400 nm and 800 nm in wavelength) laser pulses in air and the THz pulse is sent through an inductively-coupled plasma with a density of 1013–1014 cm−3 which is in the modern tokamak plasma density range. Phase shift of the THz pulse is measured by the single-shot THz detection method and the instant plasma density information is obtained from the phase shift. The result is compared with that of the existing THz time domain spectroscopy method and it is found that both results are in good agreement. It implies that the proposed method in this paper can provide a new plasma diagnostics tool which can be used for dynamically changing plasmas.

Noninvasive THz-TDS measurements of plasma bounded and optically shielded by Hall thruster wall material

“…A relatively novel plasma diagnostic technique with the potential to perform Hall thruster channel measurements is terahertz time-domain spectroscopy (THz-TDS) [16][17][18][19][20][21][22][23]. THz-TDS probes plasma with broadband pulsed THz radiation to measure line-integrated electron density and collision frequency.…”

“…THz-TDS probes plasma with broadband pulsed THz radiation to measure line-integrated electron density and collision frequency. Previous work has demonstrated the capability of THz-TDS to achieve mm-scale spatial resolution [17] and psscale temporal resolution [16,23]. Pulsed THz radiation has also been shown to transmit through various grades of BN and BN-SiO 2 composite, and the pulsed nature of the radiation can enable measurements in bounded plasma without interference from Fabry-Pérot (FP) reflections [24][25][26].…”