The use of atomic hydrogen line emission to determine the particle confinement time τp of a tokamak plasma is a well-known diagnostic technique. Using such a method, for any one of the emission lines, be it from Lyman, Balmer, or Paschen series, the same (i.e., unique) value of τp must be obtained. Furthermore, this measurement is directly related to the local values of the electron temperature and density. We have developed a method based on the Hα, Hβ, and Hγ hydrogen line emissions and on the concept of τp uniqueness for a tokamak plasma, to determine the local electron density and temperature. The technique has been applied to plasma discharges generated in the NOVA-UNICAMP tokamak. The results show good agreement with measurements from multichannel Thomson scattering and Langmuir probe. A procedure to simulate the Hα emissivity radial profile using the obtained results is also discussed.

Electron density and temperature determination using the concept of particle confinement time uniqueness

A new modified branching ratio (MBR) method for the absolute intensity calibration of a vacuum ultraviolet (VUV) spectrometer is presented. The spectrometer is equipped with a multichannel detector, consisting of an open microchannel plate coupled to a charge-coupled device (CCD), or with a single channel photomultiplier. This technique extends the number of calibration points available from those provided by the branching ratio (BR) calibration technique. The MBR method is a variation of the conventional BR method, where we relax the condition that the two spectral emissions, in the visible and VUV spectra, come from the same excited level, to include transitions from different sublevels of the same energy level. However, a critical study of the statistical equilibrium of sublevels from the same ion energy level was necessary. As a result, we have more than doubled the number of calibration points for our spectrometer used in tokamak plasma diagnostics. The appropriate identification of new spectral line pairs for absolute calibration here presented opens the path for future works in other devices with similar plasma conditions or impurities content.

Modified branching ratio method for absolute intensity calibration in VUV spectroscopy

A vacuum ultraviolet spectrometer equipped with a charge coupled device and an open multichannel plate has been used to analyze the temperature of carbon and oxygen ions in the NOVA-UNICAMP tokamak. The detection system was optimized and aligned to minimize the instrumental broadening. Also, higher order diffractions of the emissions were analyzed, resulting in lower experimental errors. The ion temperature was monitored during the tokamak discharge, presenting values between 30 and 70 eV.

Multichannel detector for ion temperature determination in vacuum ultraviolet spectrum.

In this article, the use of an 8×8-matrix independent 10-stage dynode multichannel photomultiplier for multipass Thomson scattering is described. Light from a pulsed ruby laser is irradiated 12 times in the central region of plasma using the resonator cavity of a multipass system, and integrated scattered light is detected for the first time using the multichannel photomultiplier XP1752 from Philips. The simultaneous measurements of electron temperature and density at four spatial positions, which can be extended by increasing the numbers of Analog-to-Digital Converter (ADC) channels and signal output windows, have been performed throughout full discharge by a shot-to-shot procedure. An electron temperature Te of 50 eV and a density ne of 5×1012 cm-3 were measured for the tokamak NOVA-UNICAMP. Because of the use of a low-power ruby laser (typically 1 J) and scattered light amplification using a multipass system, the level of stray light was kept low and absolute density measurements were made possible by nitrogen Rayleigh scattering.

https://iopscience.iop.org/article/10.1143/JJAP.44.383/pdf

Marcelo de Jesus Rangel Monteiro

Papers

Multiposition Multipass Thomson Scattering Diagnostic for Tokamak NOVA-UNICAMP