Tohoku University, School of Scinece, Sendai
Generation of high brilliance beam using an RF gun is very attractive for advanced use of electron linacs. Beam dynamics in the RF gun has been studied theoretically so far, and many simulation codes have been developed. The stage in which the beam is extracted and accelerated to relativistic momentum is crucial for understanding of space charge dominated beams. In this sense, actual measurement of the beam phase space is highly desired to examine the validity of the simulation codes. However, for the low energy electrons, such measurement is difficult because the phase space is easily distorted due to space charge effect during travel through drift space. Accordingly, we have considered employing the energy dependent angular distribution of Cherenkov radiation. Though the emission angle of Cherenkov radiation decreases rapidly with increasing beam energy, it is still 25 deg/MeV at an energy around 2 MeV when we use a radiator that has a refractive index of 1.035. Thus the energy distribution can be measured by observing the Cherenkov ring with sufficient angular resolution. Since this method needs only a thin radiator, the drift space length can be minimized.
STFC/RAL/ISIS, Chilton, Didcot, Oxon
The gas ionisation beam profile monitor is a well established piece of diagnostic hardware. The use of active devices such as micro-channel plates (MCP’s) and channeltrons within such a diagnostic can present problems with gain differences between channels. At the Rutherford Appleton laboratory we have produced a beam profile monitor that uses an array of 40 individually powered channeltrons; these devices were chosen over the MCP for their robustness and longer lifetimes. These channeltron devices (like MCP’s across their surface) can suffer from large variations in gain at the desired operating voltage. We have successfully shown that an additional in-built calibration system using a single, motorised , channeltron can overcome these issues. We report on the work to build the calibration system, and the 40 channeltron array. The PXI (National Instruments) system used to control the motor drive and provide the all data acquisition is also covered. Also we report the new high voltage drift field to reduce space charge effects on the beam profile. Ongoing work on understanding how the drift field as well the beam field affects the measured profile is also discussed.
