Glenn B Christian

Abstract: To achieve the design luminosity at future linear colliders, control of beam stability at the sub-nanometre level at the interaction point will be necessary. Any source of beam motion which results in relative vertical offsets of the two beams at the interaction point may significantly reduce the luminosity from the nominal value. Beam-based intra-train feedback systems located in the interaction region are foreseen to correct the relative beam-beam offset and thus to steer the two beams into collision. These feedback systems must be capable of acting within the bunch train. In addition, these feedback systems might considerably help to relax the tight stability tolerances required for the final doublet magnets. For the Compact Linear Collider (CLIC), the extremely short nominal bunch spacing (0.5 ns) and very short nominal pulse duration (156 ns) make the intra-train feedback implementation technically very challenging. In this paper the conceptual design of an intra-train feedback system for the CLIC interaction point is described. Results of luminosity performance simulations are presented and discussed for different scenarios of ground motion. We also show how the intra-train feedback system can help to relax the very tight tolerances of the vertical vibration on the CLIC final doublet quadrupoles.

Abstract:

Abstract: In­sta­bil­i­ties as­so­ci­at­ed with beam-size blow-up have pre­vi­ous­ly been ob­served with mul­ti-bunch beam in the damp­ing ring (DR) of the KEK Ac­cel­er­a­tor Test Fa­cil­i­ty (ATF). A sys­tem has been de­vel­oped to mon­i­tor such in­sta­bil­i­ties, util­is­ing an ATF stripline beam po­si­tion mon­i­tor (BPM) in the DR, and BPM pro­ces­sor hard­ware de­signed for the FONT up­stream feed­back sys­tem in the ATF ex­trac­tion line. The sys­tem is de­signed to record the hor­i­zon­tal and/or ver­ti­cal po­si­tions of up to three bunch­es in the DR in sin­gle-bunch mul­ti-train mode or the head bunch of up to three trains in mul­ti-bunch mode, with a bunch spac­ing of 5.6 ns. The FPGA firmware and data ac­qui­si­tion soft­ware were mod­i­fied to record turn-by-turn data for up to six chan­nels and 1–3 bunch­es in the DR. The max­i­mum mem­o­ry con­fig­u­ra­tion on the FPGA al­lows 131071 bunch-turn-chan­nels of data to be record­ed from a par­tic­u­lar ma­chine pulse, and the sys­tem has the ca­pa­bil­i­ty to se­lect only cer­tain turns at a reg­u­lar in­ter­val in which to record data, in order to zoom out and cover the en­tire pe­ri­od of the damp­ing cycle at the ATF. An overview of the sys­tem and ini­tial re­sults will be pre­sent­ed.