Abstract
A kicker magnet and a pulse modulator with a low charging voltage and a short rise time are designed and fabricated for an extraction instrument of an 1GeV electron synchrotron of Mitsubishi Electric Corp. The kicker magnet is a lumped type one with a C type ferrite yoke. The gap height of the magnet is 15mm and the yoke width is 30mm. Total length of the magnet is 0.6m and the inductance is about 1.5μH.
The effect of the residual magnetic field of the magnet on the low energy electron beam is studied by a beam tracking method. The results show the residual field must be lower than 1 G to obtain enough dynamic aperture of the low energy beam.
The modulator consists of two Blumlein line modulators, whose inpedance are 75Ω, and is switched by a single thyratron. At the magnet, the lines are connected in series such that the inner conductor of one line is connected to the outer conductor of the other line. Then, the current in each line are added at the kicker magnet. In our system, the magnet is connected to the modulators with a mismatched resistor. Therefore the current has a damping oscillation waveform.
The rise time of the current is about 40ns and the charging voltage of the modulator at the extraction from the synchrotron is no more than 40kV and which is a quarter of the voltage when a conventional P. F. N type modulator is used. The flatness of the waveform is less than ±1% and the stability is no more than 0.1%. The restriction of the residual field is satisfied by using the damping oscillation waveform of the current. The measured value of the residual field is reduced by factor 4 (0.5G) compared with the one by a rectangular waveform.
At the extraction operation, successful extraction of eight bunches from fifteen bunches in the synchrotron are measured by a wall current monitor at the extraction transport line.
