85 research outputs found
Evidence for Alfvén eigenmodes driven by alpha particles in D-3He fusion experiments on JET
Alfvén eigenmodes (AEs) driven by energetic alpha particles can lead to enhanced fast ion transport and losses, thereby degrading the plasma performance in ITER and future magnetic confinement fusion reactors. Unexpectedly, AEs with negative toroidal mode numbers, which are currently not considered for ITER, were observed in dedicated experiments with fusion-born alpha particles on the tokamak Joint European Torus (JET). The paper provides evidence for a complex interplay between fast ions, monster sawtooth crashes and AEs. Our results highlight the need for an improved description of the synergies between different fast ion phenomena in future burning plasmas
Comparison of runaway electron generation parameters in small, medium-sized and large tokamaks-A survey of experiments in COMPASS, TCV, ASDEX-Upgrade and JET
This paper presents a survey of the experiments on runaway electrons (RE) carried out
recently in frames of EUROFusion Consortium in different tokamaks: COMPASS, ASDEXUpgrade, TCV and JET. Massive gas injection (MGI) has been used in different scenarios for RE generation in small and medium-sized tokamaks to elaborate the most efficient and reliable ones for future RE experiments. New data on RE generated at disruptions in COMPASS
and ASDEX-Upgrade was collected and added to the JET database. Different accessible
parameters of disruptions, such as current quench rate, conversion rate of plasma current into runaways, etc have been analysed for each tokamak and compared to JET data. It was shown,
that tokamaks with larger geometrical sizes provide the wider limits for spatial and temporal
variation of plasma parameters during disruptions, thus extending the parameter space for
RE generation. The second part of experiments was dedicated to study of RE generation in
stationary discharges in COMPASS, TCV and JET. Injection of Ne/Ar have been used to
mock-up the JET MGI runaway suppression experiments. Secondary RE avalanching was
identified and quantified for the first time in the TCV tokamak in RE generating discharges
after massive Ne injection. Simulations of the primary RE generation and secondary
avalanching dynamics in stationary discharges has demonstrated that RE current fraction
created via avalanching could achieve up to 70â75% of the total plasma current in TCV.
Relaxations which are reminiscent the phenomena associated to the kinetic instability
driven by RE have been detected in RE discharges in TCV. Macroscopic parameters of RE
dominating discharges in TCV before and after onset of the instability fit well to the empirical
instability criterion, which was established in the early tokamaks and examined by results of
recent numerical simulations.EURATOM 633053Fundação para a CiĂȘncia e Tecnologia UID/FIS/50010/2013Ministry of Education and Science of the Russian Federation 14.619.21.0001, 15.08.2014, RFMEFI61914X000
Fusion product losses due to fishbone instabilities in deuterium JET plasmas
During development of a high-performance hybrid scenario for future deuteriumtritium experiments on the Joint European Torus, an increased level of fast ion losses in the
MeV energy range was observed during the instability of high-frequency n=1 fishbones. The
fishbones are excited during deuterium neutral beam injection combined with ion cyclotron
heating. The frequency range of the fishbones, 10 â 25 kHz, indicates that they are driven by
a resonant interaction with the NBI-produced D beam ions in the energy range â€120 keV.
The fast particle losses in a much higher energy range are measured with a fast ion loss
detector, and the data show an expulsion of deuterium plasma fusion products, 1 MeV tritons
and 3 MeV protons, during the fishbone bursts. An MHD mode analysis with the MISHKA
code combined with the nonlinear wave-particle interaction code HAGIS shows that the loss
of toroidal symmetry caused by the n=1 fishbones affects strongly the confinement of nonresonant high energy fusion-born tritons and protons by perturbing their orbits and expelling
them. This modelling is in a good agreement with the experimental data.EURATOM 633053RCUK Energy Programme EP/P012450/
Fusion product losses due to fishbone instabilities in deuterium JET plasmas
During development of a high-performance hybrid scenario for future deuteriumâtritium experiments on the Joint European Torus, an increased level of fast ion losses in the MeV energy range was observed during the instability of high-frequency nââ=ââ1 fishbones. The fishbones are excited during deuterium neutral beam injection combined with ion cyclotron heating. The frequency range of the fishbones, 10â25âkHz, indicates that they are driven by a resonant interaction with the NBI-produced deuterium beam ions in the energy rangeâââ€120âkeV. The fast particle losses in a much higher energy range are measured with a fast ion loss detector, and the data show an expulsion of deuterium plasma fusion products, 1 MeV tritons and 3 MeV protons, during the fishbone bursts. An MHD mode analysis with the MISHKA code combined with the nonlinear wave-particle interaction code HAGIS shows that the loss of toroidal symmetry caused by the nââ=ââ1 fishbones affects strongly the confinement of non-resonant high energy fusion-born tritons and protons by perturbing their orbits and expelling them. This modelling is in a good agreement with the experimental data.This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053 and from the RCUK Energy Programme [grant No EP/P012450/1]. To obtain further information on the data and models underlying this paper please contact [email protected] . The views and opinions expressed herein do not necessarily reflect those of the European CommissionPeer ReviewedPostprint (author's final draft
Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating
We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed âthree-ionâ scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of 3He ions to high energies in dedicated hydrogenâdeuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast 3He ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular, 3He-rich solar flares.This paper is dedicated to the late P. E. M. Vandenplas, founder and first director of
LPP-ERM/KMS, in recognition of his lifelong outstanding commitment to fusion research, in particular to ICRH. The support from the JET and Alcator C-Mod Teams is warmly acknowledged. We are grateful to A. Cardinali, C. Castaldo, R. Dumont, J. Eriksson, T. FĂŒlöp, C. Giroud, C. Hellesen, S. Menmuir and M. Schneider for fruitful discussions. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014â2018 under grant agreement no. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. This work was also supported by the US DoE, Office of Science, Office of Fusion Energy Sciences, SciDAC Center for Simulation of Wave Plasma Interactions under DE-FC02-01ER54648 and the User Facility Alcator C-Mod under DE-FC02-99ER54512. The Alcator C-Mod Team author list is reproduced from ref. 12. The JET Contributors author list is reproduced from ref. 33.Peer ReviewedPostprint (author's final draft
MeV-range velocity-space tomography from gamma-ray and neutron emission spectrometry measurements at JET
We demonstrate the measurement of a 2D MeV-range ion velocity distribution function by velocity-space tomography at JET. Deuterium ions were accelerated into the MeV-range by third harmonic ion cyclotron resonance heating. We made measurements with three neutron emission spectrometers and a high-resolution Îł-ray spectrometer detecting the Îł-rays released in two reactions. The tomographic inversion based on these five spectra is in excellent agreement with numerical simulations with the ASCOT-RFOF and the SPOT-RFOF codes. The length of the measured fast-ion tail corroborates the prediction that very few particles are accelerated above 2 MeV due to the weak wave-particle interaction at higher energies
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