Helium partial pressure measurement in a deuterium environment

Abstract

To study the removal of helium ash in present day, medium sized tokamaks, experiments with deuterium plasmas and helium puffs are conducted. Because D2 and He have almost the same mass, a spectroscopic method had been developed at TEXTOR where the He partial pressure in the exhaust line was measured by exciting the neutral gas in a Penning gauge and observing the characteristic emission lines of helium and deuterium. This method was limited to low pressures and concentrations because broad spectral lines from the deuterium molecules superimpose the He lines. By using a spectrometer and an intensified charge coupled device camera instead of optical filters and photomultipliers, it is now possible to record the interesting part of the spectrum with a time resolution of 20 ms. By subtracting the molecular spectrum of deuterium, helium concentrations from 2% on can be detected over about three orders of magnitude in pressure down to 2×10−6 mbar. He and D2 pressures are measured simultaneously. By another method the 58 nm resonance line of helium is observed and the crosstalk of the deuterium gas could be eliminated. Pressure measurements as low as 5×10−8 mbar and 1% He concentration are possible. A detection system utilizing a vacuum ultraviolet monochromator in combination with a channeltron has been tested.

Applicability of the dielectric barrier discharge for helium ash measurements in the divertor region

“…an amount of helium in the mixture), the intensities of both selected lines are of the same order of magnitude. One of the problems described in the Denner paper [2] was a very large difference between intensities of hydrogen and helium line (more than one order of magnitude) registered in the Penning discharge. The registered spectra show also that the hydrogen molecular spectra are negligibly small (again unlike in the case of Penning source).…”

“…It could be applied only for very low pressures, due to conditions required by Penning discharge. Another diffi culty that is observed in this discharge is the overlapping of the helium line and the hydrogen molecular spectrum [2].…”

“…In order to register such radiation, one needs to apply a proper excitation source. The study of different discharge sources was performed by Finken and Denner [1,2] with the conclusion that the best is the Penning discharge associated with the operation of the Penning-type gauge. Unfortunately, this method has some serious disadvantages.…”

The Toroidal Pump Limiter ALT-II in TEXTOR

“…The first generation of Penning detectors was equipped with interference filters and photo multipliers 41 while later versions used a spectrometer plus a charge-coupled device camera. 42,43 The Penning discharges are robust and operate reliably; because of the intrinsic magnetic field, they are practically insensitive to the magnetic field of the discharge. An example of the Penning calibration curve is shown in Fig.…”

Development of miniaturized, spectroscopically assisted Penning gauges for fractional helium and hydrogen neutral pressure measurements

“…This approach was shown to be a very versatile method for partial pressure measurement of neutral He and molecular D 2 , which is challenging because they have almost identical masses. It has been used on plasma devices including TEXTOR, JET and DIII-D [2,3,4]. The measurements on these devices have all been done with large commercial Penning gauges, the Alcatel CF2P, that use permanent magnets to sustain the Penning discharge.…”