Longitudinal impedance tuner using new material FINEMET

We designed an impedance tuner consisting of an inductive material, FINEMET , to cancel the space charge impedance in the longitudinal direction. It wa s installed in the KEK Proton Synchrotron (PS) main ring. We observed the f requency shift of the coherent quadrupole oscillations and inferred the shi ft of the incoherent synchrotron oscillation. The total reactive impedance can be estimated as the coefficient between the shift and the beam intensit y. The measured impedance is reduced from -j2475 Omega to -j1182 Omega by t he impedance tuner which consists of 12 pieces of FINEMET cores. We demonst rated that the space charge impedance is compensated by the impedance tuner . This is the first time for FINEMET to be equipped with an accelerator com ponent. One may think that the characteristics of FINEMET deteriorate under an environment with strong radiation generated by unavoidable beam loss. W e have proved that the radiation dose not affect FINEMET even with a total neutron dose of 1.83x10(12)(n cm(-2)), which is considered to be the highes t dose of the main ring. (C) 1999 American Institute of Physics. [S0034-674 8(99)04606-7].