Laser spectroscopy for measuring the parameters of a plasma containing helium and argon
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MA DIAGNOSTICS
Laser Spectroscopy for Measuring the Parameters of a Plasma Containing Helium and Argon D. A. Shcheglov, S. I. Vetrov, I. V. Moskalenko, A. A. Skovoroda, and D. A. Shuvaev Nuclear Fusion Institute, Russian Research Centre Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123182 Russia Received July 5, 2005
Abstract—Laser spectroscopy diagnostics used in experiments on the PNX-U facility are described. The working gas was argon with an additive of helium. The 23P 33D transition was excited by means of optical pumping, and helium fluorescence at wavelengths of 388 and 706.5 nm was observed. The Doppler temperature of helium atoms was determined by scanning the profile of the absorption line with the help of a tunable laser. The sum of the signals so obtained provides information on the local density of helium atoms. It was proposed to determine the local value of the electron density Ne(R) from the ratio between the fluorescence intensities at wavelengths of 388 and 706.5 nm. The ratio of these intensities as a function of Ne for He I was calculated in the collisional–radiative model, and relevant measurements of Ne in the PNX-U facility were performed. When diagnosing the argon component, the main attention was paid to measurements of the ion temperature Ti (R, t). In the course these measurements, anomalous heating of Ar II ions was revealed. The concentration of singly charged argon ions was estimated. PACS numbers: 52.70.–m DOI: 10.1134/S1063780X06020061
1. INTRODUCTION Injection of noble gases into plasma is widely used for diagnostic purposes in various facilities. In recent years, a series of experiments aimed at obtaining the socalled radiatively improved confinement mode by means of injecting neon or argon into tokamak plasma have been performed (see, e.g., [1, 2]). Such discharges are to be produced in ITER, the injection of argon being considered more preferable. Therefore, when designing diagnostics for the divertor plasma of ITER, it is necessary to take into account the presence of both helium (the “ash” of fusion reactions) and argon.
2. SPECTROSCOPIC SCHEME FOR PROBING HELIUM ATOMS In our experiments, we measured the local Doppler temperature TD(He I) and evaluated the density of helium atoms. It was also demonstrated for the first time that the local electron density can be determined by measuring the intensity ratio between the triplet fluorescence lines. The diagram of the He I energy levels used in our measurements is shown in Fig. 1. The profile of the 587.6-nm absorption line was scanned by
Laser spectroscopy measurements were performed in the PNX-U plasma neutralizer intended to study the stripping of high-energy D– ion beams. The term “laser spectroscopy” is used to emphasize that, in those experiments, a tunable laser served as a high-resolution spectrometer. The PNX-U facility is a multicusp trap in which an argon plasma is ionized and heated with the help of two klystrons (PMW = 4–50 kW) [3]. Helium was either added to argon or injected into a discharge with the hel
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