Ion cyclotron emission (ICE) excited by collective instability of fusion a particles has been observed during deuterium-tritium experiments with radio-frequency heating and neutral beam injection (NBI) in the Joint European Torus. A model based on classical a-particle confinement is broadly consistent with this data. ICE spectra from discharges with high-power NBI also show evidence of ion hybrid wave excitation by beam ions, relevant to a channeling. [S0031-9007(99)08608-1] PACS numbers: 52.55.Pi, 52.20.Dq, 52.35.Hr, 52.55.Fa Collective effects driven by fusion a particles in deuterium-tritium (D-T) plasmas have been a primary research objective of JET [1] (the Joint European Torus) and TFTR [2,3] (the Tokamak Fusion Test Reactor). The most easily excited phenomenon is spectrally structured, suprathermal ion cyclotron emission (ICE): this was observed from the outer edge regions of the earliest D-T plasmas, in JET hot ion H-modes [1], and TFTR supershots [2] (indeed, ICE driven by fusion products was observed in JET before the use of T [4], and ICE driven by beam ions has been observed in TFTR [5]). Because of the crucial role played by confined a particles in sustaining a thermonuclear plasma, and the difficulty of detecting such particles by other means, the mechanism and diagnostic implications of a-particle-driven ICE have been subjects of considerable theoretical interest [6][7][8]. The consensus is that emission of a-particle-driven ICE is due to the magnetoacoustic cyclotron instability (MCI) [9], involving fast Alfvén wave excitation at a-particle cyclotron harmonics; MCI is also successful in interpreting related phenomena observed in space [10] and astrophysical [11] plasmas. In tokamaks MCI is driven by centrally born, marginally trapped fusion products undergoing radial drift excursions to the outer edge plasma. Since the radial excursion increases as the cube root of energy [12], the velocity distribution of fusion products in the ICE source region has a local maximum at finite speed and pitch angle, which can drive the MCI.ICE data from JET D-T plasmas were obtained with a fast wave antenna at the outer plasma edge, used primarily as a source of ion cyclotron resonance heating (ICRH) but also as a receiver [1]. Prior to 1997, energetic particle-driven ICE was observed only in JET plasmas heated Ohmically and by neutral beam injection (NBI) [1,4]. ICE spectra from ICRH discharges contained peaks at harmonics and half harmonics of the ICRH frequency, but no emission which could be attributed to energetic particles [13]. The ICE diagnostic was not available in the highest performance 1997 D-T discharges, but clear evidence was obtained of energetic particle-driven ICE during ICRH. Figure 1 shows neutron flux S n in optimized shear pulse 42697, with combined ICRH (6 MW) and NBI (8-20 MW). The spectra in Fig. 2 were obtained by sweeping through the range 0-100 MHz over 0.6 s intervals. The 25 and 95 MHz peaks are calibration markers. In the first spectrum the 50 MHz peak is due mainly to the ICRH sou...

Recent high-power electron-cyclotron resonance heating (ECRH) H-mode experiments on COMPASS-D have used fundamental high-power ECRH to access high densities. Within the operating range set by the H-mode density threshold and ECRH accessibility, H-mode power thresholds are significantly higher than expected from ITER scalings, and show a contrary dependence on density. Energy confinement is somewhat lower than that suggested by the present ITER scalings, but correction for incomplete RF absorption may be needed. Complex H-mode and ELM behaviour is observed.

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