Abstract
For a toroidal plasma facility to realize fusion energy, researching the transport of fast ions is important not only due to its close relation to the heating and current drive efficiencies but also to determine the heat load on the plasma-facing components. We present a theoretical analysis and orbit simulation for the origin of lost fast-ions during neutral beam injection (NBI) heating in Korea Superconducting Tokamak Advanced Research (KSTAR) device. We adopted a two-dimensional phase diagram of the toroidal momentum and magnetic moment and describe detectable momentums at the fast-ion loss detector (FILD) position as a quadratic line. This simple method was used to model birth ions deposited by NBI and drawn as points in the momentum phase space. A Lorentz orbit code was used to calculate the fast-ion orbits and present the prompt loss characteristics of the KSTAR NBI. The scrape-off layer deposition of fast ions produces a significant prompt loss, and the model and experimental results closely agreed on the pitch-angle range of the NBI prompt loss. Our approach can provide wall load information from the fast ion loss.
Highlights
The physics of fast ions in tokamak plasmas has been widely investigated because of its importance to ion heating, which is relevant to fusion performance.[1,2] Neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH), which are auxiliary ion heating methods for current tokamaks, accelerate the ion speed from several keV to hundreds keV or MeV
To study the characteristics of the prompt loss of beam ions detected by fast ion loss detector (FILD), the NBI birth profile was calculated with two tools: NUBEAM and our developed minimal model
We studied the fast ion prompt loss in Korea Superconducting Tokamak Advanced Research (KSTAR) of plasma produced by NBI from three ion sources having different directions and energy levels
Summary
The physics of fast ions in tokamak plasmas has been widely investigated because of its importance to ion heating, which is relevant to fusion performance.[1,2] Neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH), which are auxiliary ion heating methods for current tokamaks, accelerate the ion speed from several keV to hundreds keV or MeV. In various tokamak devices, including KSTAR, the fast ion loss detector (FILD) has been used to study fast ion transport.[5,6,7,8,9] A FILD measures the energetic ions bombarding a scintillator in the vicinity of a plasma-facing component. It has been used to investigate fast ion loss and the correlation with magnetic perturbations like Alfven eigenmodes,[8] tearing modes,[10] and external magnetic perturbations.[11] It has the benefit of enhancing the reliability of analytical predictions for the loss particle energy and pitch-angle information by allowing direct comparison with measurements. We evaluated a fast ion loss model and compared it with the FILD measurements. We used analytical modelling and numerical simulation for phase space analysis and straightforward fast-ion orbit calculation. Lorentz orbit (LORBIT) code[13] analysis provides specific fast ion loss and orbit information.
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