SPECTROSCOPIC MEASUREMENTS OF THE IMPURITY CONTENT OF JET PLASMAS WITH OHMIC AND RF HEATING
Knowledge of the impurity concentrations in the JET plasmas is based mainly on the analysis of resonance line intensities in the VUV, with additional information coming from measurements of soft x-ray spectra. The plasma impurity content is monitored routinely by a McPherson Model 251 VUV broadband spectrometer, covering the wavelength range 100-1700 ANGSTROEM by means of two interchangeable gratings and equipped with a multichannel detector. The spectrometer views a horizontal central chord in the torus midplane. Up to 128 spectra are recorded during a plasma discharge, allowing the study of the time evolutions of various spectral line intensities. A relative calibration of the spectrometer sensitivity has been obtained by studying transitions between charge exchange populated, excited levels in C VI and O VIII during neutral beam injection on the ASDEX tokamak. The absolute sensitivity is derived from the H-alpha L-beta branching ratio using a special H-alpha monitor along the same line-of-sight. The soft x-ray spectra over the range 4-30 keV are recorded by a HgI-2 detector viewing the plasma in the horizontal midplane through Al, Be and air absorbers. The detector has an energy resolution of 0.6 keV at 6 keV, which is sufficient to separate the groups of He-like metal impurities in the plasma. The spectra show both continuous emission and the characteristic K lines of Ni and Cr. The latter are used to calculate the nickel concentrations in the centre of the plasma.
Bibliographic Reference: 12TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA PHYSICS, BUDAPEST (HUNGARY), SEPT. 2-6, 1985 PP. 45-48 WRITE TO THE PUBLICATIONS OFFICER, JET JOINT UNDERTAKING, ABINGDON, OXON, OX14 3EA (UK), MENTIONING REPORT JET-P(85)10, 1985
Record Number: 1989124056600 / Last updated on: 1987-01-01
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