Speaker
Description
The coherent THz facility developed at NSRRC delivers superradiant radiation with wavelengths ranging from 100 – 500 um from a gap tuneable U100 planar undulator. An S-band laser-driven photocathode rf gun has been used in its 25 MeV linac system to generate a sub-picosecond high brightness relativistic electron beam via velocity bunching for emission of coherent THz radiations. However, the high accelerating field in the gun cavity is found to be the main cause of electron field emission that generates the non-negligible background current (dark current) in the system. A portion of the field emission (FE) electrons with launching conditions close to that of the main beam can be accelerated to high energies by the booster linac structure located downstream. The primary cause of excessive radiation dosage stems from the collision of these unwanted high-energy electrons with the system's vacuum vessel. In order to limit the transportation of FE electrons from rf gun to the booster linac, a collimation system will be implemented at upstream of the booster linac. In this work, the drive linac system has been modeled with 3D space charge tracking code – IMPACT-T for both main beam as well as dark current simulation. Particle transmission and energy distribution of dark current after collimation has been simulated. Trajectories of electrons at various initial positions and particle loss mechanism have also been analyzed.
| Region represented | Asia |
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