Induction synchrotron. VI. Beam loading

When a steep beam bunch comes into the induction unit, it conceivably causes voltage modification and/or beam instability in the induction synchrotron. The effect may depend not only on the impedance of the driving circuit but also the non-linearity of the magnetization characteristics of the core material. Using induction modules with FET (Field Effect Transistor) switches, the effect of beam loading on the acceleration voltage was experimentally estimated. The tested cores were nano-crystalline alloy (Finemet) and Co-amorphous alloy. The beam was simulated by a resistive secondary source and the loading effect was measured as functions of ΔB and current rise of the secondary loop (dI/dt), up-to 100A/μsec. Experimentally observed values of the voltage modification did not depend on the ΔB (as far as being used at not-saturation region of the core) and were almost proportional to di/dt. However, they depended on the bias voltage for Co-amorphous alloy. These results indicate that the response of the core material depend on the magnetic-domain shape. Based on those results, voltage modification caused by the effect of the beam on the module in the induction synchrotron at KEK-PS was evaluated