High Electron Cyclotron Resonance Heating Research Articles

Transport transitions at high electron cyclotron resonance heating powers at the L-2M stellarator

The experimental results are presented from the experiments on the high-power electron cyclotron resonance heating (ECRH) of the current-free plasma with the power 200–500 kW (the specific power was 0.8–2 MW/m3). The spontaneous transport transitions were observed that resulted in an increase in the plasma density and energy. At the ECRH powers exceeding 150 kW, the processes are observed accompanied by the abrupt changes in the plasma edge parameters, while the core plasma parameters change only slightly. At the ECRH powers exceeding 400 kW, a jump-like increase in the plasma density and energy is observed. At a power of approximately 500 kW, the regime was obtained, in which at time of transition, the plasma energy and lifetime increase by 20%, despite a decrease in the electron temperature. At the same time, at heating powers up to 700 kW, the energy lifetime corresponds on average to the L-2M single-machine stellarator scaling.

Understanding helium transport: experimental and theoretical investigations of low-Z impurity transport at ASDEX Upgrade

The presence of helium is fundamentally connected to the performance of a fusion reactor, as fusion-produced helium is expected to heat the plasma bulk, while He ‘ash’ accumulation dilutes the fusion fuel. An understanding of helium transport via experimentally validated theoretical models of the low-Z impurity turbulent transport is indispensable to predict the helium density profile in future fusion devices. At ASDEX Upgrade, detailed, multi-species investigations of low-Z impurity transport have been undertaken in dedicated experiments, resulting in an extensive database of helium and boron density profiles over a wide range of parameters relevant for turbulent transport (normalised gradients of the electron density, the ion temperature, and the toroidal rotation profiles, the collisionality and the electron to ion temperature ratio). Helium is not found to accumulate in the parameter space investigated, as the shape of the helium density profile follows largely that of the electron density. Helium is observed to be as peaked as the electron density at high electron cyclotron resonance heating fraction, and less peaked than the electron density at high neutral beam heating fraction. The boron density profile is found to be consistently less peaked than the electron density profile. Detailed comparisons of the experimental density gradients of both impurities with quasilinear gyrokinetic simulations have shown that a qualitative agreement between experiment and theory cannot always be obtained, with strong discrepancies observed in some cases.

Testing of the spectroscopic method for location of water microleakages in ITER at the L-2M stellarator

Results of testing of a possible method for location of water microleakages in the cooling system of the first wall and vacuum chamber of ITER are presented. The method consists in spectroscopic detection of the emission lines of atoms and ions of the Xe additive dissolved in water. These lines are excited when the water with dissolved Xe contacts the plasma. The high electron cyclotron resonance heating (ECRH) power deposited in a relatively small plasma volume in the L-2M stellarator (P = 0.5 MW, V = 0.24 m3, and the specific heating power ∼2 MW/m3) makes it possible to achieve plasma parameters close to those in the edge plasma of ITER for different operating modes, including the H-mode with an edge transport barrier. In test experiments, several lines of Xe ions were revealed suitable for detection of xenon in plasma with parameters close to those in the edge plasma of ITER at leakage rates at a level of ∼10−6 Pa m3 s−1 and spatial resolution of ∼0.5 cm.