Observation of relativistic runaway electrons with a wide-angle infrared periscope system in HL-2A

To gauge synchrotron radiation from relativistic runaway electrons during plasma disruptions, a novel wide-angle infrared periscope system has been installed and commissioned on the HL-2A tokamak. Observed along the tangent to the plasma, along the orientation of electron movement on the equatorial plane, the spectral characteristics of synchrotron radiation under typical HL-2A parameters were investigated, and the pitch angle and energy of the runaway electrons were deduced. This technique has been verified to be well suited for monitoring beams of runaway electrons with energies around 20 MeV during disruptions on the HL-2A tokamak, particularly in dedicated experiments on runaway current mitigation using supersonic molecular beam injection (SMBI) during plasma disruptions. The system is employed to track the temporal evolution of the runaway electron beam, providing direct insight into the mitigation mechanism of runaway electrons following SMBI.