Development of multichord ion Doppler spectroscopy system for toroidal flow measurement of field-reversed configuration

Abstract

A double-chord ion Doppler spectroscopy (IDS) system was developed to measure the ion temperature and flow velocity of field-reversed configuration (FRC) plasmas in the FRC amplification via a translation-collisional merging (FAT-CM) device. Adopting a Czerny–Turner mount monochromator and 16-channel photomultiplier tube array, the developed IDS system achieves high wavelength resolution and fast time response. In addition, two vertically aligned optical paths share the optical system up to the monochromator and then branch just before the detector, successfully reducing crosstalk to <1%. The Doppler broadening was measured at two measurement points in the FAT-CM device, simultaneously, and ion temperatures of ∼50 eV were measured. Toroidal spin-up from 7 to 15 km/s and a steady flow velocity of ∼10 km/s were estimated from the Doppler shift obtained by the developed system. The observation of the toroidal flow velocity and the spatial profile of the ion temperature of the FRC plasma in the FAT-CM device were realized. These spectroscopic diagnostic’s double chord capabilities will aid in understanding and improving the FRC plasmas.

Observation of rapid flux coalescence in merging field-reversed configurations

“…In this investigation, Doppler spectroscopy of impurity carbon spectra (C III and C V ) is used to estimate ion temperature. 21 Here, the relaxation times of deuterium with carbon (C III ) is approximately 2.5 ls and with C V is 0.6 ls. Subsequently, the temperature decreases relatively quickly, while the magnetic flux and total energy gradually decrease but remain twice as high compared to the case without the second merging.…”

Suppression of radial motion in translated field-reversed configuration plasma via global gyro-effect

“…Two interferometers for electron density measurement were installed at the formation section (z ∼ 2.1 m) and the confinement section (z ∼ −0.6 m) [25]. Ion temperature and toroidal flow were measured using the ion Doppler spectroscopy (IDS) system [26] at the formation section (z ∼ 2.1 m). Radial motion was observed by a set of two tomography cameras (T-cams) that we have developed [27,28].…”

Refueling of field-reversed configuration core via axial plasmoids injection

“…The line-integrated electron density is measured using a quadrature interferometer [17]. In addition, the ion temperature (T i ) is assessed using ion Doppler spectrometry [18], whereas the total temperature (T t = T i + T e ) is derived from radial pressure balance: B z 2 /2µ 0 + p = B e 2 /2µ 0 . We obtained the volume-averaged beta <β⩾ 1−(r s /r w ) 2 /2 from the equation…”