Operation of CEBAF with heavy beam loading

CEBAF is a 4 GeV, 200 μA five-pass recirculating superconducting electron accelerator that has been operating for nuclear physics research at full energy since November 95. The beam current has been increased to over 180 μA at 4 GeV with the maximum current in the linac over 900 μA. The superconducting cavities operate in a regime where the beam-induced voltage is comparable to the accelerating gradient. The operational limits and the issues required to maintain stable operation of the 1497 MHz superconducting cavities will be discussed, together with the implications for the other accelerator systems. There are three experimental Halls which can run simultaneously with three interleaved 499 MHz bunch trains and RF separators. Operation with simultaneous beams to two Halls is now routine, and simultaneous three beam operation has been demonstrated. The maximum design current per bunch train (120 μA) has been achieved. Hall B eventually requires beam currents as low as 1 nA (200 pA has been delivered) simultaneous with delivery of up to 200 μA to the other Halls. The required beam current ratio of 10,000 has been achieved; development of 1 nA beam position monitors continues