No abstract

No abstract

We have succeeded in canceling longitudinal space charge effects using the 'impedance tuner' [7] which has large permeability over the beam spectrum region. A frequency shift of coherent quadrupole mode is measured to infer the modified impedance. It turns out that nonlinearity unavoidable in a longitudinal rf bucket has to be treated carefully in order to digest observed beam signals. We will describe how to measure the impedance from the beam signal, how to analyze the effect of impedance tuner, and how to succeed in canceling space charge effects.

We designed an impedance tuner consisting of an inductive material, FINEMET, to cancel the space charge impedance in the longitudinal direction. It was installed in the KEK Proton Synchrotron (PS) main ring. We observed the frequency shift of the coherent quadrupole oscillations and inferred the shift of the incoherent synchrotron oscillation. The total reactive impedance can be estimated as the coefficient between the shift and the beam intensity. The measured impedance is reduced from −j2475Ω to −j1182Ω by the impedance tuner which consists of 12 pieces of FINEMET cores. We demonstrated that the space charge impedance is compensated by the impedance tuner. This is the first time for FINEMET to be equipped with an accelerator component. One may think that the characteristics of FINEMET deteriorate under an environment with strong radiation generated by unavoidable beam loss. We have proved that the radiation dose not affect FINEMET even with a total neutron dose of 1.83×1012(n cm−2), which is considered to be the highest dose of the main ring.

No abstract