Low magnetic field helicon plasma sources for compact fusion reactor concept

Low magnetic field helicon plasma sources (LF-HPS), which may have great potential application in high-δ, advanced fuel compact fusion reactor (AF-CFR) design [1] –[3], can fundamentally determine the performance and operating characteristics of advanced fuel compact fusion reactor. As the pre-ionization stage aimed for seed plasma production, the performance of this LF-HPS may have fundamentally impact on AF-CFR concept, such as the rotating magnetic field (RMF) driven field reversed configuration (FRC) [4–5]. By employing the warm plasma dielectric tensor model with considering the plasma temperature anisotropy effect, influence of key parameters (plasma radius, neutral gas pressure, axial static magnetic field et al.) of LF-HPS system on RMF-FRC performance (in terms of time evolution process of RMF and RF power deposition intensity) are theoretically and numerically investigated. Detailed analysis shows that, for typical helicon plasma electron temperature T
e
<10 eV and low magnetic field B
0
<100 G, mode coupling between helicon and Trivelpiece-Gould (TG) waves may play a significant role in determining the amplitude of the plasma density, which further determines the degree of penetration of the rotating magnetic field into the core plasma region; a fully formed field reversed configuration can be obtained with very low amplitude of RMF (less than 5% of the axial static magnetic field intensity) in several RMF periods (results are shown in Figure 1 below); parameters such as plasma density, electron/ion temperature and neutral gas pressure all have direct and significant impact on the RMF-FRC performance; finally, theoretical analysis implies that each harmonic contributes differently during the RMF penetration process (FRC formation process), further analysis show that the n=1 harmonic may be the main contributor for initial RMF penetration.