37 research outputs found

    On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

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    A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

    Identification of the ubiquitous Coriolis momentum pinch in JET tokamak plasmas

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    High-resolution gamma ray spectroscopy measurements of the fast ion energy distribution in JET He-4 plasmas

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    Analysis of damping rate measurements of toroidal Alfven eigenmodes as a function of n: part II (vol 52, 023014, 2012)

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    Wave-particle resonances and redistribution/losses of fast ions in tokamaks

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    Study of fast-ion transport induced by fishbones on JET

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    The impact of fishbone oscillations onto a confined fast-ion population is simulated for a JET plasma and benchmarked against experiment quantitatively with the help of neutron rate measurements. The transient drops in volume integrated neutron emission are found to be mainly caused by the spatial redistribution of the (neutral beam injected) fast-ion population confined in the plasma rather than by fast-ion loss. The simulations yield a quadratic dependence of the neutron drop on the fishbone amplitude. It is found that the simulations are able to correctly reproduce the magnitude of the experimentally observed drop in volume integrated neutron emission to within a factor 2. Furthermore, frequency chirping is found to be important. Omitting the fishbone frequency chirp in the simulations reduces the magnitude of the neutron rate drop (and hence fast-ion redistribution) to about half its original value

    Non-resonant magnetic braking on JET and TEXTOR

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    The non-resonant magnetic braking effect induced by a non-axisymmetric magnetic perturbation is investigated on JET and TEXTOR. The collisionality dependence of the torque induced by the n = 1, where n is the toroidal mode number, magnetic perturbation generated by the error field correction coils on JET is observed. The observed torque is located mainly in the plasma core (normalized radius

    COREDIV and SOLPS Numerical Simulations of the Nitrogen Seeded JET ILW L-mode Discharges

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    In this paper we present the comparison of simulations with the numerical codes COREDIV and SOLPS5.0 for JET L-mode discharges with ITER like wall (ILW). The simulations have been performed for L-mode shots with and without nitrogen seeding (#82291 - 9) which are characterised by relatively low auxiliary heating power (PNBI = 1.1 MW) and low electron density (ne = 2.35 × 1019 m–3). Comparisons are made to the experimental measurements (e.g. radiation levels, plasma profiles) and the differences between the results from the two codes (e.g. temperature and density profiles at the outer divertor plate) are shown and discussed

    An FPGA-based bolometer for the MAST-U Super-X divertor

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    A new resistive bolometer system has been developed for MAST-Upgrade. It will measure radiated power in the new Super-X divertor, with millisecond time resolution, along 16 vertical and 16 horizontal lines of sight. The system uses a Xilinx Zynq-7000 series Field-Programmable Gate Array (FPGA) in the D-TACQ ACQ2106 carrier to perform real time data acquisition and signal processing. The FPGA enables AC-synchronous detection using high performance digital filtering to achieve a high signal-to-noise ratio and will be able to output processed data in real time with millisecond latency. The system has been installed on 8 previously unused channels of the JET vertical bolometer system. Initial results suggest good agreement with data from existing vertical channels but with higher bandwidth and signal-to-noise ratio

    Plasma turbulence measured with fast frequency swept reflectometry in JET H-mode plasmas

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