Fast ion relaxation and confinement in the gas dynamic trap

Abstract

Studies of the relaxation and confinement of hot anisotropic ions are considered to be the key elements of the gas dynamic trap (GDT) experimental research programme. The method of confinement study described consists essentially in the comparison of measured ion parameters with those predicted by computer simulations. To realize this approach a set of diagnostics for the measurements of local and global parameters of the fast ions has been developed. In particular, this set includes diagnostics to measure the local energy and the angular distribution functions. For numerical studies of the fast ion dynamics a Monte Carlo code based on the theory of two body Coulomb collisions has been elaborated. Comparison of the experimental data with the results of the simulation clearly demonstrates that the fast ion characteristic relaxation times in the warm target plasma are close to those determined by binary Coulomb collisions. Significant anomalous energy losses or scattering of fast ions have not been observed as yet. The measurements provide a maximum density of the fast ions with mean energy of about 8 keV up to 1013 cm-3, in good agreement with computer simulations. The increase of the neutral beam power and improved vacuum conditions of GDT made possible the access to plasma β of as high as 30%.

Experimental Evidence of High-Beta Plasma Confinement in an Axially Symmetric Gas Dynamic Trap

“…We estimated the average energy of the beam-produced deuterons to be about 10 keV. The measured angular width of fast ion distribution and their energy distribution well correspond to the results of numerical simulations [7]. We also found that the heated target plasma losses are dominated by the axial ones through the mirrors, as predicted.…”

“…At the end of beam injection pulse, the ion temperature was close to that of the electrons. The parameters of the fast ions were measured by using an artificial target method [7], neutral particle analyzers, and an array of diamagnetic loops installed at different axial locations inside the solenoid [8]. We estimated the average energy of the beam-produced deuterons to be about 10 keV.…”

Electron cyclotron emission at the fundamental harmonic in GDT magnetic mirror

“…Neutrons are born as a result of thermonuclear reactions between energetic deuterium ions driven by neutral beam injection (NBI); the energy confinement time of fast ions is determined by the electron-ion Coulomb collisions, 2 / 3 e h T   . For this reason, the electron temperature is the main factor limiting the confinement time of fast ions and, thus, the power efficiency of a beam-driven fusion reactor 13 . Success in ECRH experiments at GDT is convincing enough to consider the prospects of simple axially symmetric open magnetic traps as a high-power neutron source for a number of fusion applications 14 , including material testing, a hybrid fusion-fission reactor and nuclear waste processing 12,[15][16][17][18] .…”

Parameters optimization in a hybrid system with a gas dynamic trap based neutron source

“…The GENESYS calculation results have been compared with the results presented in [15,16]. Particularly, comparison with the warm plasma components temperature, angular width of the fast ions distribution function, the fast plasma energy content and the 1D neutron emission rate depending on the machine axis position was carried out.…”