Reconstruction of superthermal electron velocity distribution function from electron cyclotron spectra at down-shifted frequencies in tokamak T-10

Abstract

Abstract.A model is developed to quantitatively interpret the electron cyclotron (EC) spectra in tokamak T-10 at frequencies lower than the first EC harmonic at the plasma edge. The model is based on the almost free propagation and isotropy of EC radiation in between the vacuum chamber wall and the cut-off zone in plasma. The inverse problem for the reconstruction of the velocity distribution function of superthermal electrons (in parallel and perpendicular momenta, and magnetiс flux surfaces at the plasma edge) is formulated and solved. It is shown that in the Ohmic discharges in the tokamak T-10 the superthermal electrons are the trapped particles at the low magnetic field side of toroid. Their mean kinetic energy lies in the range ~ 150-200 keV, and the density fraction is about ~ 10 -4 relative to the main plasma.

Review of Recent Advances in the Analytical Theory of Stark Broadening of Hydrogenic Spectral Lines in Plasmas: Applications to Laboratory Discharges and Astrophysical Objects

“…In some discharges in tokamaks, the plasma current decays and it is partly replaced by runaway electrons that reach relativistic energies: this poses danger to the mission of the next generation tokamak ITER-see, e.g., papers [76][77][78] and references therein. At various discharges at different tokamaks, such as, e.g., those presented in papers [79][80][81], the energy of the runaway electrons was measured in the range~(0.2-10) MeV and the ratio of their density to the density of the bulk plasma electrons was measured in the range~(10 −1 -10 −4 ).…”

Stark Broadening of Spectral Lines in Plasmas

“…In some discharges in tokamaks, the plasma current decays and it is partly replaced by runaway electrons that reach relativistic energies: this poses danger to the mission of the next generation tokamak ITER-see, e.g., papers [76][77][78] and references therein. At various discharges at different tokamaks, such as, e.g., those presented in papers [79][80][81], the energy of the runaway electrons was measured in the range~(0.2-10) MeV and the ratio of their density to the density of the bulk plasma electrons was measured in the range~(10 −1 -10 −4 ).…”

Spectroscopic diagnostics of superthermal electrons with high-number harmonic EC radiation in tokamak reactor plasmas

“…The proposed spectroscopic diagnostics is based on the solution of an inverse problem for reconstruction of the EVD in parallel and perpendicular-to-magnetic-field components of electron momentum at high and moderate energies responsible for the emission of the high-numberharmonic EC radiation (similarly to the inverse problem solved in [3]). In such a formulation we assume that x parameters of the EVD of the bulk Maxwellian plasma are known from other diagnostics, presumably, Thomson scattering, and x we can determine parameters of the EVD only at high enough energy of electrons and actually only in the central plasma.…”

“…An example of treating these effects for the reconstruction of an essentially non-Maxwellian EVD may be found in [3], [4] for interpretation of the data from tokamak T-10. However, the use of this effect for diagnostics of the edge plasma in fusion reactors is possible only in regimes with low plasma density at the plasma edge.…”