Abstract
A historical perspective on key discoveries which contributed to understanding the properties of coupling both slow and fast waves and the effects on plasma heating and current drive will be presented. Important steps made include the demonstration that the Alfven resonance was in fact a mode conversion on the C-stellarator, that toroidal m = -1 eigenmodes were excited in toroidal geometry and impurity influx caused the Z mode on the ST tokamak, that the H minority regime provided strong heating and that 3 He minority could be used as well on PLT, that the 2nd harmonic majority tritium regime was viable on TFTR, and that high harmonic fast wave heating was efficient when the SOL losses were avoided on NSTX.
Highlights
Understanding of ICRF coupling and heating physics has evolved through the combination of experiments, modeling, and technology over several decades
The C stellarator was configured in a race track geometry with the ICRF four strap antenna located in one straight section and a toroidal limiter located in the other straight section [1]
This comparison clearly verifies the cold plasma theory with the Alfven mode conversion. This modeling was extended to a two step density profile that accounted for the density drop-off in the C stellarator toroidal divertor and used to explain the two peak loading profile versus Ω observed at higher density (Fig. 2) [6]. This comparison further revealed that the peak closest to Ω = 1 was due to power coupled to the scrape off layer (SOL) as shown in Fig.3, and such coupling can be a major effect in the fast-wave regime on NSTX as will be discussed later
Summary
Understanding of ICRF coupling and heating physics has evolved through the combination of experiments, modeling, and technology over several decades. At PPPL this has involved experiments and modeling for a line of experimental devices including – C stellarator, ST tokamak, PLT tokamak, TFTR tokamak, and NSTX/NSTX-U spherical tokamak – and employing critical hardware and diagnostics for achieving high power operation and observing the RF effects on the core and scrape off layer (SOL) plasmas. It is informative to track the historical evolution of advances in understanding on these devices and a selection of these advances is given here
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