Speaker
Dr
Andrej Lizunov
(Budker Institute of nuclear physics)
Description
The method of measurement of magnetic fields in plasmas based on the motional Stark effect (MSE) was first developed in 1989 [1]. Since the first implementation, diagnostics based on this approach became a premier instrument for measurements of magnetic and electric fields in magnetically confined plasmas. In the gas dynamic trap mirror device (GDT) [2], a spectral MSE diagnostics deliver information on spatial distributions of magnetic field and pressure in the plasma with fusion deuteron population. Calculation of transverse pressure deduced from the MSE data, yielded β approaching 0.6 in recent experiments [3]. After precise tuning of the diagnostic deuterium beam, the spectral MSE system on GDT is capable of measuring of magnetic fields as low as 0.29 T [4]. Further study of high-beta plasma equilibrium in GDT and the projected experiment for creation of a plasmoid with a reversed magnetic field, require a challenging extension of detectable fields down to few millitesla. This task can be solved combining a laser-induced fluorescence (LIF) approach with analysis of atomic beam light emission. The proof-of-principle for the combined MSE-LIF method was successfully demonstrated [5]. Our paper describes the project of development of the MSE-LIF diagnostic for simultaneous measurements of spatial profiles of the magnetic field magnitude and direction in a plasma. An upgraded ion source produces the 50 keV focused deuterium beam with the 1-ampere atomic current and the ultra-small energy spread. For excitation of upper energy levels for the Balmer-alpha optical transition, the specially designed dye laser is used. Fast scanning of the laser wavelength over spectrum emitted by beam atoms, resolves individual lines enabling the calculation of the magnetic field magnitude. At the same time, a photoelastic modulator sweeps the laser ray polarization to detect the magnetic field direction. The optical registration system does not include a spectrometer or polarimetry instrument, which makes it relatively simple and inexpensive. Each line of sight uses a single large area avalanche photodiode to detect the optical signal.
1. F.M. Levinton et al., Phys. Rev. Lett., vol. 63, p. 2060, 1989.
2. A.A. Ivanov et al., Plasma Phys. Control. Fusion, vol. 55, p. 063001, 2013.
3. P.A. Bagryansky et al., Fusion science and technology, vol. 59, no. 1T, pp. 31-35, 2011.
4. A. Lizunov at al., Rev. Sci. Instrum., vol. 84, p. 086104, 2013.
5. E.L. Foley and F.M. Levinton, Rev. Sci. Instrum., vol. 84, p. 043110, 2013.
Primary author
Dr
Andrej Lizunov
(Budker Institute of nuclear physics)
Co-authors
Dr
Alexander Khilchenko
(Budker Institute of nuclear physics)
Mr
Denis Moiseev
(Budker Institute of nuclear physics)
Mr
Peter Zubarev
(Budker Institute of nuclear physics)
Ms
Tatyana Berbasova
(Budker Institute of nuclear physics)
Dr
Valery Savkin
(Budker Institute of nuclear physics)
