Runaway electron imaging spectrometry (REIS) system

Abstract

A portable Runaway Electron Imaging and Spectrometry System (REIS) was developed in ENEA-Frascati to measure synchrotron radiation spectra from in-flight runaway electrons in tokamaks. The REIS is a wide-angle optical system collecting simultaneously visible and infrared emission spectra using an incoherent bundle of fibers, in a spectral range that spans from 500 nm to 2500 nm, and visible images using a CCD color microcamera at a rate of 25 frames/s. The REIS system is supervised and managed using a dedicated LabVIEW program to acquire data simultaneously from three spectrometers every 20 ms (configurable down to 10 ms). An overview of the REIS architecture and acquisition system and resulting experimental data obtained in FTU are presented and discussed in this paper.

Overview of the FTU results

“…An upgrade of the REIS [32] system has been carried out recently. The range of the measured synchrotron radiation spectra emitted by REs is now from 0.4 up to 5 μm.…”

Fast dynamics of radiofrequency emission in FTU plasmas with runaway electrons

“…Hard x-ray (HXR) emission from in-flight RE collisions with plasma ions is measured by a collimated fast electron bremsstrahlung (FEB) camera with 5 ms time resolution and 20-200 keV energy range. High energy RE are detected by imaging and spectral analysis (REIS) of synchrotron emission in the visible/infrared range [18]. REIS spectra fits give energies up to 20-30 MeV and pitch angles of about 0.1 rad [19].…”

Results on quiescent and post-disruption runaway electrons studies at Frascati Tokamak Upgrade: RE mitigation via solid deuterium pellets and anomalous Doppler instability

“…Indeed, it is possible to employ the difference of signals NE213 and BF3 to define γ = NE213 − BF3 ≈ γ that may be considered as rough estimate of the number/energy of RE seed. In FTU, the critical electric field E r in (1) is at least 5 (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) times lower than the normalized electric field V loop = V loop /2πR 0 , with R 0 = 0.96 m, above which RE are seen to form in FTU i.e. γ > 0 (possibly increasing in time) when V loop σE r and σ 5 in FTU (B T ∈ [4 T, 8.1 T]).…”

“…fast RE energy dissipation by heavy-Z material injection is often accompanied by fast current decay leading to uncontrollable VDEs: the result is a competition among vertical displacement and energy dissipation rates that may not have ITER feasible solutions. Research is seeking further techniques that may be used in combination with MGI/SPI, such as a dedicated control strategy [3,4] that, 3D stochastic fields by resonant magnetic perturbation [7] and generating other instabilities [9]. It has to be pointed out that in [33] Dina simulations have been performed showing that stabilization of a 10 MA RE beam (15 MA discharge), during the initial CQ, can be achieved in ITER if the disruption is detected 1 s head in order to move vertically the plasma column before the CQ onset to the optimum position.…”