Page 3 - Hybrid MHD Model for a Driven, Ion-Current FRC

broad power deposition region in the SOL and heating directly in front of the launcher. The position of power damping is far away (about 25 cm) from the second fce harmonic layer.
Simulations with 5 GHz and 8 GHz cases show similar good results: both scenarios have up to 90% mode conversion and power absorption efficiency. The 8 GHz case seems better because the location of its power dumping is slightly deeper and more close to the separatrix layer even though this scenario is slightly sensitive to angular mismatch. The typical process of the O-X-B mode conversion can be clearly seen in Fig. 4 (a) and (b) that the O-mode (8 GHz) launched from external antenna propagates from edge into plasma; the O-mode reflects back at its cut-off layer and meanwhile it converts to the X-mode, which propagates outwards to low plasma density; at the UHR layer, the X-mode converts to the electrostatic Bernstein wave (EBW) which propagates inward and its power is absorbed at the 4th fce harmonic layer as shown in Fig. 4 (c), where it is around 6 cm behind the mode conversion layer and about 1 cm outside the separatrix.
(a) (b)
FIGURE 3. (a) Mode conversion and power absorption along the distance of ray propagation; (b) the tracing of rays propagation in X-Z plane for 2.45 GHz.
(a) (b) (c)
FIGURE 4. (a) The zoom-in tracing of ray propagation in X-Z plane; (b) the variation of (ɷpe/ɷ) 2 and (c) the variation of
(ɷ/ɷce) along the distance of ray propagation for 8 GHz.
(a) (b) (c)
FIGURE 5. (a) The zoom-in tracing of ray propagation in X-Z plane; (b) the variation of (ɷpe/ɷ) 2 and (c) the variation of
(ɷ/ɷce) along the distance of ray propagation for 28 GHz.
For the cases of 18 GHz and 28 GHz, simulation results indicate that the sensitivity on injection angle is more pronounced because the normalized density gradient length k0Ln becomes larger with the increase of microwave frequency. Meanwhile, the mode conversion and power absorption efficiencies are gradually reduced with frequency even at an optimal launch angle. The injected microwave power is damped with a maximum 75% efficiency at the
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