Abstract
During the first phase of the ITER Pre-Fusion Power Operations (PFPO-1), the Electron Cyclotron Radio Frequency system will be the main heating and current drive source [1]. Evaluations of the L-H power threshold [2] have shown that H-mode is unlikely to be achieved in PFPO-1 scenarios at half-field (B0=2.65T). For this reason, the use of one-third field scenarios in an early phase might help to access H-mode. This means that the EC Heating (ECH) system, with gyrotrons operating at 170 GHz, would then rely on n=3 harmonic resonance. Using a lower frequency, namely 104 GHz, could allow the exploitation of n=2 harmonic resonance, improving heating efficiency and facilitating EC-assisted breakdown which has not been demonstrated yet for n=3 harmonic. This work presents a preliminary evaluation of the performances of an EC system using the two frequencies in a B0=1.8T scenario (obtained by adequately rescaling a reference half-field scenario [3]) via a parametric scan of density/temperature profiles, to cover the range of possible values expected to occur during the operations and provide an estimation of the parameter space region where the use of each frequency allows a good absorption efficiency.
Highlights
The initial phase of the ITER research plan, after the First Plasma and before the D and DT operations, consists of non-activated H/He plasmas in which the Lto-H-mode transition power thresholds will be investigated [1]
During the Pre-Fusion Power Operation 1 (PFPO-1) the magnetic field will start at half the nominal field strength, that is B0 = 2.65 T, and proceed towards full-field (B0 = 5.3 T)
The analysis presented is based on the ITER half-field scenario (B0 = 2.65 T, Ip = 7.5 MA, He plasma, H-mode) [3] rescaled to one-third field (B0 = 1.8 T, Ip = 5 MA), keeping constant safety factor q and Greenwald density fraction
Summary
The initial phase of the ITER research plan, after the First Plasma and before the D and DT operations, consists of non-activated H/He plasmas in which the Lto-H-mode transition power thresholds will be investigated [1]. During the PFPO-1 the magnetic field will start at half the nominal field strength, that is B0 = 2.65 T, and proceed towards full-field (B0 = 5.3 T) It has been shown [2] that H-mode access at half-field in this scenario is unlikely due to the high power threshold. The ITER gyrotrons will operate at f = 170 GHz, taking advantage of n=1 harmonic resonance at the nominal field and n=2 harmonic resonance at half-field. Using a magnetic field at one-third strength means that the heating system would rely on the lower efficiency of n=3 harmonic resonance absorption. The present work aims at presenting a preliminary evaluation of the performances of an EC system operating at the two frequencies (170/104 GHz) in a onethird magnetic field scenario.
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