Intensity Upgrade Plans for CERN-LHC Injectors

With LHC coming into operation very soon an upgrade plan for the whole CERN accelerator complex has been proposed to allow full exploitation of the LHC potential in the future as well as giving increased support to traditional and possible new experiments at lower beam energies. This plan foresees replacing during the period 2011 - 2017 all the accelerators in the LHC injector chain (Linac2,Booster, PS) by new machines (Linac4, SPL and PS2) except for the last - the SPS. In this scenario the SPS should be able to reliably accelerate twice higher beam intensity than achieved so far and therefore significant improvements to the machine performance, in addition to the increased injection energy due to PS2, should be found and implemented at the same time scale. The present status of proposals and ongoing studies for all accelerator injector chain is described with main emphasis on the SPS challenges and upgrade plans

Analysis of coupled bunch instability spectra

Beam spectra observed during the development of a coupled bunch instability contains information about the coupled bunch mode n, which describes the phase shift between adjacent bunch oscillations. This number indicates the possible frequency of the guilty impedance with accuracy up to an integer multiple of the bunch spacing frequency. When there are many possible candidates with imprecisely known frequencies this can be insufficient. In this paper we discuss what additional information about the frequency of the source of instability can be obtained from the analysis of the unstable beam spectra envelope. This is applied to the measurements in the CERN SPS

Nonlinear bunch motion in an accelerator with reactive impedance

Closed form solutions have been found for single particle and bunch motion in an accelerator with reactive (space charge or inductive wall) impedance. The problem is solved for the particular initial longitudinal distribution corresponding to a parabolic line density. In the case with RF off the system of equations in phase space is the same as that describing motion of a body under a gravitational force with integrals of motion similar to Kepler's laws. With RF on this model allows the amplitude and frequency of coherent bunch shape oscillations to be calculated for a bunch of any intensity far away from equilibrium. The results have been used to estimate the low-frequency impedance of the CERN SPS

Signatures of microwaves instability

The microwave instability is probably one of the most well known manifestations of collective effects in accelerators. However the theory describing this instability for bunched beams is still under development. The result of the instability is a significant increase in longitudinal emittance of the beam, leading to a serious performance limitation in many machines. In this lecture we first discuss what is the phenomenon that one calls the microwave instability and then describe measurements of instability threshold, momentum spread and spectrum of the unstable bunch

Bunch motion in the presence of the self-induced voltage due to a reactive impedance; 1, RF off

Analytic self-consistent solutions have been found for the nonlinear Vlasov equation describing different types of behaviour with time of an intense bunch under the influence of voltage induced due to a reactive part of broad band impedance. The problem is solved for the particular type of the initial distribution function in longitudinal phase space which is elliptic and corresponds to parabolic line density. The first part of the paper is devoted to the consideration of the effects in the machine with RF off. In this case induced voltage is changing with time and, as in the case with RF on, can have a significant effect on bunch motion. Numerical estimations for the SPS show that this effect can be important for manipulations with beam at 26GeV. Measurements of the change in the rate of debunching with intensity can also be used to estimate the value of the impedance. The same method is applied in the second part of the paper to analyse time dependent effects of potential well distortion when RF is on

High brillance and closer bunches from the LHC injectors

The challenges for increasing intensity and reducing bunch spacing in the present LHC injectors are discussed together with requirements for new machines to replace them for a future luminosity upgrade of LHC