Elena Shaposhnikova

AWAKE, The Advanced Proton Driven Plasma Wakefield Acceleration Experiment at CERN

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) aims at studying plasma wakefield generation and electron acceleration driven by proton bunches. It is a proof-of-principle R&D experiment at CERN and the world׳s first proton driven plasma wakefield acceleration experiment. The AWAKE experiment will be installed in the former CNGS facility and uses the 400 GeV/c proton beam bunches from the SPS. The first experiments will focus on the self-modulation instability of the long (rms ~12 cm) proton bunch in the plasma. These experiments are planned for the end of 2016. Later, in 2017/2018, low energy (~15 MeV) electrons will be externally injected into the sample wakefields and be accelerated beyond 1 GeV. The main goals of the experiment will be summarized. A summary of the AWAKE design and construction status will be presented.

Beam echoes in the CERN SPS

Longitudinal echo signals have been produced in the CERN SPS by exciting a proton beam at 120 GeV/c with two short RF pulses separated by a suitable time-delay. The aim of the experiments was to confirm the analytical predictions for beam echoes in the SPS and to probe the applicability of beam echoes for a measurement of the energy distribution and diffusion coefficients in the accelerator. We summarise here the results obtained with bunched and unbunched beams. For an unbunched beam, the excitation frequencies are at different harmonics of the revolution frequency and result in an echo response at the difference frequency of the two RF kicks. For the case of a bunched beam, the RF kicks are adjusted to excite the quadrupole mode of the bunch motion and the beam echo response can also be observed as a quadrupole mode.

Measuring diffusion coefficients and distribution functions using a longitudinal beam echo

Longitudinal echo signals can be produced in the CERN-SPS by exciting a coasting proton beam at 120 GeV/c with two short RF pulses at different harmonics of the revolution frequency, separated by a suitable time-delay. We show here how one can measure energy distributions and longitudinal diffusion coefficients by using longitudinal beam echoes. The energy spread measured in this manner is in an excellent agreement with the data obtained from the Schottky signal.

Lower-Harmonic RF System in the CERN SPS

Significant beam losses increasing with intensity are observed at capture and along the SPS flat bottom for the LHCtype proton beams. The intensity should be doubled for High-Luminosity LHC and high losses may be a major performance limitation. Bunches extracted from the PS, the SPS injector, are produced in a 40 MHz RF system applying a bunch rotation at the end of the cycle and therefore cannot be perfectly matched to the 200 MHz SPS RF bucket. The possibility of using a lower-harmonic, additional RF capture system in the SPS was already proposed after the LEP era in preparation for transfer of the nominal LHC beam but the bunch rotation was the preferred solution, since the induced voltage in the SPS 200 MHz RF system would be too large to ensure stability in a low harmonic system without mitigation measures. However, the use of the upgraded one-turn delay feedback and the 200 MHz RF system as a Landau cavity could help to improve beam stability. The feasibility of this scenario to reduce capture losses in the SPS is analysed and presented in this paper. The beam transfer to the main 200 MHz RF system is simulated using a realistic bunch distribution.