Abstract
In the ion cyclotron range of frequency (ICRF), the presence of a lower hybrid (LH) resonance can appear in the edge of a tokamak plasma and lead to deleterious edge power depositions. An analytic formula for these losses is derived in the cold plasma approximation and for a slab geometry using an asymptotic approach and an analytical continuation near the LH resonance. The way to minimize these losses in a large machine like ITER is discussed. An internal verification between the power loss computed with the semi-analytical code ANTITER IV for ion cyclotron resonance heating (ICRH) and the analytic result is performed. This allows us to check the precision of the numerical integration of the singular set of cold plasma wave differential equations. The set of cold plasma equations used is general and can be applied in other parameters domain.
Highlights
A potentially important edge power loss mechanism for ion cyclotron resonance heating (ICRH) arising in the presence of a lower hybrid (LH) resonance in the edge of a tokamak plasma has gained renewed interest in view of ICRH application to future large fusion machines like ITER and DEMO as it will likely be present in their scrape-off layer (SOL).Historically, ion heating at the LH frequency range was expected to take place near the LH resonance through mode conversion from a fast electromagnetic wave to a slow electrostatic one or through the direct launch of a slow wave (Stix 1965; Hooke & Bernabei 1972; Bellan & Porkolab 1974)
The Alfvén resonance is an approximation (Stix 1992; Bellan 1994) in the limit me → 0) and corresponds to the fast wave power lost at the confluence with the slow wave while the LH resonance corresponds to the power lost by the slow wave through mode conversion
This paper presents an analytical derivation of the power loss arising in the presence of the singular point 1 = 0 in the differential system of (2.1) describing an inhomogeneous cold plasma in a slab geometry
Summary
A potentially important edge power loss mechanism for ion cyclotron resonance heating (ICRH) arising in the presence of a lower hybrid (LH) resonance in the edge of a tokamak plasma has gained renewed interest in view of ICRH application to future large fusion machines like ITER and DEMO as it will likely be present in their scrape-off layer (SOL). Ion heating at the LH frequency range was expected to take place near the LH resonance through mode conversion from a fast electromagnetic wave to a slow electrostatic one or through the direct launch of a slow wave (Stix 1965; Hooke & Bernabei 1972; Bellan & Porkolab 1974). The presence of a LH resonance appears at low densities, in non-inverted heating scenarios (i.e. f > fci where fci is the cyclotron frequency of the majority ions and f is the frequency of the radio-frequency (rf) waves launched by the antenna) In these conditions, for a toroidal wavenumber |kz| which is smaller than the propagation constant in vacuum k0, the fast wave undergoes a confluence with the slow wave.
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