Abstract
For the first time it is experimentally demonstrated on the JET tokamak that a combination of a low impurity concentration bulk plasma and large magnetohydrodynamic instabilities is able to suppress relativistic electron beams without measurable heat loads onto the plasma facing components. Magnetohydrodynamic simulations of the instability and modeling of the postinstability plasma confirm the prompt loss of runaways and the absence of regeneration during the final current collapse. These surprising findings motivate a new approach to dissipate runaway electrons generated during tokamak plasma disruptions.
Highlights
Magnetohydrodynamic simulations of the instability and modeling of the postinstability plasma confirm the prompt loss of runaways and the absence of regeneration during the final current collapse
RE beams with currents up to 1.27 MA were mitigated at JET with no measurable energy deposition to the plasma facing components. This level of RE current is well in excess of levels previously found to lead to significant damage to the first wall in JET [29]. This result is achieved through a combination of the excitation of a large magnetohydrodynamic (MHD) instability followed by the absence of regeneration of REs
The avalanche amplification γREt ≈ Ip=1⁄2IAlfven lnðΛÞ [21] is predicted to be larger for ITER than for JET, this mitigation scenario opens a new approach to dissipate REs generated during tokamak plasma disruptions
Summary
(Received 19 September 2020; revised 19 February 2021; accepted 16 March 2021; published 30 April 2021). Magnetohydrodynamic simulations of the instability and modeling of the postinstability plasma confirm the prompt loss of runaways and the absence of regeneration during the final current collapse These surprising findings motivate a new approach to dissipate runaway electrons generated during tokamak plasma disruptions. This level of RE current is well in excess of levels previously found to lead to significant damage to the first wall in JET [29] This result is achieved through a combination of the excitation of a large magnetohydrodynamic (MHD) instability followed by the absence of regeneration of REs. Qualitatively similar RE terminations were observed at DIII-D [30]. The avalanche amplification γREt ≈ Ip=1⁄2IAlfven lnðΛÞ [21] is predicted to be larger for ITER than for JET, this mitigation scenario opens a new approach to dissipate REs generated during tokamak plasma disruptions. The impact at beam termination is characterized by infrared [MA]
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