OPERATIONAL PERFORMANCE OF THE LHC PROTON BEAMS WITH THE SPS LOW TRANSITION ENERGY OPTICS

Abstract An optics in the SPS with lower integer tunes (20 versus 26) was proposed and introduced in machine studies since 2010, as a measure for increasing transverse and longitudinal instability thresholds, especially at low energy, for the LHC proton beams. After two years of machine studies and careful optimisation, the new Q20 optics became operational in September 2012 and steadily delivered beam to the LHC until the end of the run. This paper reviews the operational performance of the Q20 optics with respect to transverse and longitudinal beam characteristics in the SPS, enabling high brightness beams injected into the LHC. Aspects of longitudinal beam stability, transmission, high-energy orbit control and beam transfer are discussed

OPERATIONAL PERFORMANCE OF THE LHC PROTON BEAMS WITH THE SPS LOW TRANSITION ENERGY OPTICS

Abstract An optics in the SPS with lower integer tunes (20 versus 26) was proposed and introduced in machine studies since 2010, as a measure for increasing transverse and longitudinal instability thresholds, especially at low energy, for the LHC proton beams. After two years of machine studies and careful optimisation, the new Q20 optics became operational in September 2012 and steadily delivered beam to the LHC until the end of the run. This paper reviews the operational performance of the Q20 optics with respect to transverse and longitudinal beam characteristics in the SPS, enabling high brightness beams injected into the LHC. Aspects of longitudinal beam stability, transmission, high-energy orbit control and beam transfer are discussed

SHORT HIGH-INTENSITY BUNCHES FOR PLASMA WAKEFIELD EXPERIMENT AWAKE IN THE CERN SPS

Abstract Obtaining the shortest possible bunch length in combination with the smallest transverse emittances and highest bunch intensity -this is the wish list of the proton-bunch driven, plasma wakefield acceleration experiment AWAKE currently under feasibility study at CERN. A few measurement sessions were conducted to determine the achievable bunch properties and their reproducibility. To obtain a short bunch length, the bunches were rotated in longitudinal phase space using the maximum available RF voltage prior to extraction. Measurements were carried out in two optics with different transition energies. The main performance limitation is longitudinal beam instability that develops during the acceleration ramp. With lower transition energy, beam stability is improved, but the bucket area is smaller for the same voltage. Based on the results obtained, we shall discuss the choice of optics, the impact of longitudinal instabilities, the importance of reproducibility, as well as options for improving the bunch parameters

LOW GAMMA TRANSITION OPTICS FOR THE SPS: SIMULATION AND EXPERIMENTAL RESULTS FOR HIGH BRIGHTNESS BEAMS

Abstract The single bunch transverse mode coupling instability (TMCI) at injection is presently one of the main intensity limitation for LHC beams in the SPS. A new optics for the SPS with lower transition energy yields an almost 3-fold increase of the slip factor at injection energy and thus a significantly higher TMCI threshold, as demonstrated both in simulations and in experimental studies. It is observed furthermore that the low gamma transition optics yields better longitudinal stability throughout the entire acceleration cycle. In addition, simulations predict a higher threshold for the electron cloud driven single bunch instability, which might become an important limitation for high intensity LHC beams with the nominal 25 ns bunch spacing. This contribution gives a summary of the experimental and simulation studies, addressing also space charge effects and the achievable brightness with high intensity single bunch beams