Flat bunches in the LHC

A high-harmonic RF system that could serve multiple purposes was proposed for the LHC. Possible applications of the second harmonic RF system include beam stabilisation in the longitudinal plane in the absence of wide-band longitudinal feedback and reduction of bunch peak line-density. Apart from other useful features, flat bunches are expected to produce less beam-induced heating at frequencies below 1 GHz, the frequency region critical for some LHC equipment. The latter, however, can also be achieved by de-populating the bunch centre. This was demonstrated during the dedicated machine development session in the LHC using RF phase modulation. In this paper the results of tests with single bunches and nominal LHC beams are presented and the possible use of this technique in LHC operation is discussed.
Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany