DEVELOPMENT OF HIGH-SPEED DIFFERENTIAL CURRENT- TRANSFORMER MONITOR

A new current-transformer (CT) monitor for the XFEL/SPring-8, called “SACLA”, was developed. In the SACLA, the bunch length of an electron beam is compressed from 1 ns to 30 fs, and the beam charge decreases to obtain a genuine electron beam from 1 nC to 0.3 nC along with acceleration. Tis new CT monitor must be able to measure the charge of the electron beam and monitor bunch length in velocity bunching. To satisfy this requirement, the CT has two advantageous properties. One is a differential output signal that suppresses common-mode noise from the thyratron of a klystron modulator by a factor of ten. The other property is a highspeed signal output that makes it possible to measure the bunch length and time-of-flight at the injector part of the SACLA. The output signal has 200 ps rise-time and a pulse width of 400 ps (FWHM) for an impulse beam. Bunch length between 1 ns and 400 ps was measured around a 238 MHz buncher cavity. Moreover, the TOF of a low energy beam between two CTs was measured with a few picoseconds resolution. It was thus confirmed, the performance of the new CT is sufficient for the SACLA.