Cures for Beam Instabilities in the CERN SPS and their Limitations

The LHC beam in the SPS is unstable with a threshold almost an order of magnitude below the nominal intensity. The cures used to stabilise this beam against coupled bunch instabilities apart from RF feedback, feed-forward and longitudinal damping, include a fourth harmonic RF system and controlled emittance blow-up. The limitations of the two last methods were studied experimentally and are analysed here from the point of view of beam quality requirements at extraction and future intensity increases up to ultimate value

RF scenarios and longitudinal dynamics in SPS and LHC for 12.5 and 75 NS bunch spacings

Beams with proton bunches spaced at 12.5 ns and twice shorter than nominal, or spaced at 75 ns and twice longer than nominal, are the key ingredients for two main scenarios considered for an LHC upgrade. These two options are analysed from the point of view of the choice of both RF systems and beam parameters in the SPS and LHC and the corresponding longitudinal beam stability

Analysis of the maximum potential proton flux to CNGS

In this note we investigate the limitations to the proton flux which can be sent to the CNGS facility and estimate the maximum that can be attained. In the first part, the injector chain remains unchanged and the limitations are reviewed for operation up to the so called ultimate CNGS intensity, 7x10^13 protons per CNGS cycle. In the second part, the limitations of the SPS accelerator and CNGS facility are described in the scenario of operating with the new injectors - LINAC4, SPL and PS2, as proposed by the PAF working group (PAF)

An RF System for Landau Damping in the LHC

A Landau system in the LHC could significantly increase the longitudinal stability of the LHC beams in the absence of wide-band longitudinal feedback and provide more freedom to define the bunch parameters even during the initial stages of LHC operation. This technique for stabilizing beams, used already in many accelerators, has proven to be very useful in the SPS, raising the instability thresholds by a factor five. One of the luminosity upgrade paths for LHC requires an RF system at 1.2 GHz with ~ 60 MV per beam for bunch shortening. A much smaller RF system at this frequency with ~3 MV per beam would be sufficient to provide Landau damping. This Note analyses the possible benefits and recommends that an R & D programme, leading to one prototype cryostat per ring to be installed in the LHC machine, be launched as soon as possible

SPS performance with PS2

The upgrade of the PS to the PS2 would allow injection into the SPS at higher energy (up to 70 GeV/c). Possible advantages deriving from a higher injection energy into the SPS include the improvement of space charge at flat bottom, absence of transition crossing for all proton beams and a higher threshold for the horizontal electron cloud coupled bunch instability. Transverse Mode Coupling Instability (TMCI) and vertical Electron Cloud Instability (ECI) thresholds are studied in greater detail. Their dependence on energy is defined in simulations with the HEADTAIL code and the results of this study are presented

Simulation study on the energy dependence of the TMCI threshold in the CERN-SPS

This paper concentrates on theoretical studies of Transverse Mode Coupling Instability (TMCI) at the SPS. It shows the expected thresholds based on the HEADTAIL tracking model and on impedance values estimated from previous measurements. First, the effect of space charge is addressed as an important ingredient at the low energies. Subsequently, the change of TMCI threshold possibly induced by a higher injection energy into the SPS (plausible according to the upgrade studies) is investigated and a scaling law with energy is derived

Longitudinal Schottky Spectrum of the Peak Bunch Amplitude Signal

Diagnostic techniques based on the Schottky spectrum of the peak detected signal have been used at CERN for a long time to study the behaviour of bunched beams. In this paper it is shown how the measured spectrum is related to the particle distribution in synchrotron frequency. The experimental set-up used and its limitations are also presented together with examples of beam measurements in the SPS and LHC