FIRST TESTS OF A TRAVELING-WAVE CHOPPER FOR THE ATLAS POSITIVE ION LINAC

A ten segment traveling-wave chopper has been constructed and successfully tested at 5 % of the design 12 MHz repetition rate. The chopper must remove unbunched tails from a partially bunched heavy-ion beam in order to avoid undue emittance growth in the linac and the production of undesirable satellite beam bunches. When poorly bunched beams traverse a chopper, the traditional sine wave chopper produces unacceptable transverse emittance growth and unnecessary beam loss. Emittance growth and unnecessary beam losses are expected to be much reduced in the traveling wave chopper. These first tests have confirmed the validity of these claims, clearly showing much reduced transverse emittance growth as compared to the original sine wave chopper and excellent selectivity for the desired beam. Details of these tests will be presented and compared to calculations. Operation of the new chopper at the full 12 MHz rate is the next goal. Development of a driver power supply capable of full CW operation will also be described.