Extraction Electrons from a Helical Device for Utilization as an Electron Source

For the purpose of making use a torus type magnetic confinement device as a high current electron source by extracting runaway electrons, we investigated magnetic fields' configuration and calculated electron orbits by numerical simulation. Extraction coils which generate field to lead electrons to outside of the device, also strongly disturbed magnetic field in partly installed case. We propose new cancellation coil setups. The numerical calculation shows influence of extraction coils are reduced, and as a results, the maximum radius of magnetic surface is almost the same as the case of setting up extraction coils all around device.

We also traced the electron acceleration and extraction orbits from low energy in confinement area. Through that, we estimated the extraction ratio of the runaway electrons and their averaged energy. The results show that 70% of the runaway electrons can be extracted and the averaged energy of those electrons is 4 keV in case of all direction extraction.