Abstract
In the present work, an ECRH scenario with reduced magnetic field 1.75 T is considered. For 140 GHz, this field corresponds to X3 heating. The high mirror-ratio magnetic configuration, B01/B00 ≃ 0.24, was considered as one from most attractive for long-pulse operation with low bootstrap current. Since X3 wave mode can be effectively absorbed only in sufficiently hot plasmas, a preheating stage is necessary, and the requirements for target plasmas suitable for starting X3 have been studied. Different ways to establish target plasmas are also discussed, in particular, augmenting X3 heating with X2 beams at 105 GHz.
Highlights
At the near-term focus of the W7-X scientific program are experiments to help assess stellarator optimization in view of economic operation of a stellarator fusion power plant [1]
Applications of the X3-mode in W7-X was considered for different goals already; see, for example, the references [3] and [9]
The main conclusion from this consideration is the following: for the high-mirror magnetic configuration (UEM) with reduced magnetic field, B0 = 1.75 T, target plasmas suited for X3 heating must be preheated up to temperatures higher than 0.7 keV
Summary
At the near-term focus of the W7-X scientific program are experiments to help assess stellarator optimization in view of economic operation of a stellarator fusion power plant [1]. The possibility of heating with a pure multipass O2-mode scenario was demonstrated. Applications of the X3-mode in W7-X was considered for different goals already; see, for example, the references [3] and [9] (in the last, X3 at 140 GHz launched near the minimum of B in high-mirror configuration was investigated with respect to selective heating of trapped/passing electrons). Three possible methods are under consideration for the role of creating the target-plasma: NBI, ICRH and ECRH with X2 at the frequency 105 GHz. The assessment of plasma start-up with pure NBI in W7-X was investigated already in detail in Ref. In this paper we analyze the conditions necessary for stable operation of X3 heating in the magnetic configurations with very high mirror ratios and consider the mixed X2 (105 GHz) and X3 (140 GHz) ECRH scenarios. All simulations are performed with the ray-tracing code TRAVIS [10] coupled to the transport code NTSS [11]
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