Effect of changes in viewing window transmission on high-temperature Thomson scattering data

Abstract

Unmonitored changes in the transmission of viewing windows owing to deposited films can produce errors in Thomson scattering temperature measurements. This effect is illustrated by a recent run on the Tokamak Fusion Test Reactor (TFTR) where apparent errors of over 25% in peak temperatures of 9 keV owing to carbon films were noted. Since coatings can also be removed by hydrogen discharges, the transmission of a window may change with time, resulting in variable errors in the temperature. It is proposed that these changes be monitored by calibration in situ with the aid of a low-pressure hydrogen glow discharge.

First mirrors for diagnostic systems of an experimental fusion reactor I. Simulation mirror tests under neutron and ion bombardment

“…The experimental data on the transmissivity of the films deposited on the windows of the Tokamak Fusion Test Reactor (TFTR) and the JT-60 under carbonization have been given in [69,70]. In both cases, the vessel walls were regularly coated by a carbon film.…”

Diagnostics for steady state plasmas

“…The measured spectral transmission losses of a TFTR window [238] were found to be very similar to samples coated in laboratory glow [253] and ECR discharges in H 2 /CH 4 gas mixtures. Based on windows used in JT60-U during 1992-1995, a simple polynomial description for the wavelength dependent attenuation by a film of thickness d has empirically been derived [246].…”

“…Detailed investigations particularly into the chromatic transmission of predominantly hydrocarbon coated windows have been undertaken in the field of Thomson-scattering diagnostics since the wavelength dependence leads to significant errors in derived temperatures, but of course also density measurements [238,246]. The measured spectral transmission losses of a TFTR window [238] were found to be very similar to samples coated in laboratory glow [253] and ECR discharges in H 2 /CH 4 gas mixtures.…”

“…In fusion machines with high heat load carbon components, the build-up of brownish hydrocarbon films on the windows is regarded as having the more detrimental effect on window transmissivity [238]. Physical sputtering, chemical erosion and chemical sputtering of carbon by hydrogen isotopes lead to a release of hydrocarbons which are redeposited all around the machine, even in shaded regions [239].…”

Emission Spectroscopy Application for Changes Evaluation of the Optical Path Transmission Due to Degradation of the Plasma Facilities in-Vessel Elements

“…Для настройки многоканальных систем регистрации ТР применялись современные источники излучения, например, оптический параметрический генератор (ОПГ), перестраиваемый в широком диапазоне длины волны [4]. В работе [5] для определения пропускания оптического окна, используемого при измерении электронной температуры методом ТР, в качестве источника калибровочного излучения был применён тлеющий разряд в водороде при фиксированных условиях (рабочее давление газа, магнитное поле, напряжение разряда и др.). Применимость такого метода калибровки связана с воспроизводимостью спектра излучения используемого разряда.…”