Measurement of ICRF wave propagation using a microwave reflectometer with fast antenna switching on GAMMA 10

A fast visible light measurement system was installed on GAMMA 10/PDX to measure plasma light fluctuations induced by ion cyclotron range of frequency (ICRF) (6360 kHz) waves. Time evolution and power spectrum were obtained and the relative amplitude of the fluctuations was the order of 0.1%. The difference of measured wavelength region was investigated by using three interference filters, but obtained time evolutions and the relative amplitudes were similar when we neglect a factor of difference. The RF pick-up noise is about two orders of magnitude smaller than the ICRF wave induced plasma signal, and the broad frequency band component is about an order of magnitude smaller than the signal. The latter arises from the shot-noise of the photon detection Poisson process, and an expression of the shot-noise, in which the effects of the frequency response of the system and the detector property are included, was obtained. The expression is confirmed experimentally using a stable light source.

Section: Measurement Resultssupporting

confidence: 63%

Section: Introductionmentioning

confidence: 97%

Development of a Fast Visible Light Measurement System for the Study of Ion Cyclotron Range of Frequency Waves in GAMMA 10/PDX Plasmas

Ejiri

Hirata

Ichimura

et al. 2021

“…Furthermore, an ECR plasma with the density of about 1 × 10 19 m −3 was produced by using a 28 GHz gyrotron although it was still transient, and thus, found to be difficult for ion heating experiments at present. As for (ii), a two-channel microwave reflectometer for wave studies was developed, which provides an antenna switching for a multipoint detection in the axial direction and a simultaneous two-point measurement for wavenumber detection [11,12]. This paper corresponds to (iii), describing the first investigation on the density dependence of a slow wave excitation in the GAMMA 10/PDX central cell configuration based on a full wave calculation using TASK/WF3D code, which is developed in Kyoto University by one of the authors (A. Fukuyama) [13].…”

Section: Introductionmentioning

confidence: 99%

A Full Wave Simulation on the Density Dependence of a Slow Wave Excitation in the GAMMA 10/PDX Central Cell with TASK/WF3D

Ikezoe

Kubota

Ichimura

et al. 2019

Beach heating using a slow Alfvén wave in ion cyclotron range of frequencies would be the first candidate for ion heating in a DEMO-relevant divertor testing linear plasma device if it is applicable to a high-density regime. To clarify its availability, the density dependence of a slow wave excitation is investigated using a full wave simulation with TASK/WF3D code in the GAMMA 10/PDX central cell configuration, where there is an extensive track record of a beach heating. A shielding effect is successfully demonstrated and well understood under a three-dimensional configuration in the limit of cold plasma approximation. As the density increases, excitable left-handed electric field, which contributes to ion cyclotron heating, degrades more and more from a core region, and resultantly the ion absorption region goes outwards with reducing its power. For core densities above 10 20 m −3 , the wave field exists only at a very edge, and ion heating becomes negligible unless the wave frequency is much increased with a correspondent magnetic field enhancement.

“…Although the wave measurements using a reflectometer and magnetic probe in the central region could not be conducted during the DF wave heating experiment, this result strongly indicates the difference between the radial profiles of the DF and external-antennas-excited waves. The extant microwave reflectometry measurements indicated that the normal slow wave excited by the external DHT antenna exhibited significant amplitude in the peripheral region rather than in the central region [22,23].…”

Section: Difference-frequency Wave Heating Experimentsmentioning

confidence: 99%

High-Energy Ion Generation During Difference-Frequency ICRF Wave Heating in GAMMA 10/PDX

SUGIMOTO,

HIRATA,

NAKASHIMA

et al. 2023

One of the greatest challenges of simulating the high heat flux on the divertor in linear plasma devices is the achievement of ion temperatures of > 100 eV under high densities (≥ 10 19 m −3 ). The slow wave in the ion cyclotron range of frequency has been employed for ion heating in GAMMA 10/PDX and demonstrated its high efficiency at middle densities of 10 18 m −3 . However, at high densities (≥ 10 19 m −3 ), exciting the slow wave in the center of the plasma by external antennas becomes challenging. Alternatively, we have demonstrated the excitation of the difference-frequency (DF) slow wave using two high-density-applicable fast waves. In this study, we first applied the charge-exchange neutral particle analyzer (CX-NPA) to a DF wave heating experiment. Even when the bulk temperature did not increase significantly, the high-energy ions in the > 0.5 keV range were measured during the experiment. Such high-energy ions were only measured in the central line of sight of CX-NPA, indicating that the power deposition from the DF wave was largely centered and differed greatly from the normal heating scheme using external antennas. This result will motivate further pursue of exploiting nonlinearity of plasma media to produce different heating accessibilities.