Study of runaway electron dynamics at the ASDEX Upgrade tokamak during impurity injection using fast hard x-ray spectrometry

Abstract

To study the runaway electron (RE) dynamics during plasma discharge and develop scenarios for disruption mitigation, a hard x-ray (HXR) spectrometric system has been developed and commissioned at the ASDEX Upgrade tokamak (AUG). The diagnostic system consists of two high-performance spectrometers based on LaBr3(Ce) scintillation detectors supplied with advanced electronics and analysis algorithms. These spectrometers view the AUG tokamak chamber quasi-radially at the equatorial plane. The measurements were carried out in the RE beam generation regimes by injecting argon into a deuterium plasma. In the interaction of a developed RE beam with a heavy gas target, powerful bremsstrahlung flux is induced, reaching energy close to 20 MeV. The electron energy distributions were reconstructed from the measured HXR spectra by deconvolution methods. The experimentally obtained maximum RE energies at different discharge stages were compared with relativistic test particle simulations that include the effect of toroidal electric field, plasma collisional drag force, synchrotron deceleration force. It was observed that the electrons attain their maximum energies within 50-100 ms after the gas injection. It gradually decreases due to the drop in loop voltage, energy loss due to synchrotron radiation emission and collisions dissipation of energy with the background plasma. HXR measurements at the discharge with multiple deuterium pellet injections allowed observing the effects of plasma cooling and argon ion

Characterization of vacuum HV microdischarges at HVPTF through X-ray bremsstrahlung spectroscopy

“…The analysis revealed a drastic drop in the number of X-ray produced during microdischarges: this is likely not being due to detector paralysis (as was the case with previous X-ray detectors [5]) but instead to a temporary stop to the electron acceleration process caused by the drop of the potential between the electrodes. This might be confirmed in the future by irradiating the scintillator with a LED and verify the correct detection of the light during microdischarges, similarly to what was done in other works [18,19].…”

A new hard x-ray spectrometer for runaway electron measurements in tokamaks

“…Information like the one presented in figure 12 is the only way, besides synchrotron radiation measurements in some cases [23], to of the RE energies and the impact that alternative mitigation techniques have on them. For a more detailed analysis of the AUG discharges see [24].…”

Длительность Пучка Убегающих Электронов При Субнаносекундном Фронте Импульса Напряжения

“…Только за последние годы опубликованы сотни работ. Наибольшее число статей в последние два года были посвящены изучению влияния УЭ на нагрев плазмы в установках для получения управляемого термоядерного синтеза, см., например, [1][2][3]. В установках типа ТОКАМАК подробно изучаются разряды, генерирующие УЭ, которые приводят к повреждению стенок вакуумной камеры.…”