Experimental Studies of Controlled Longitudinal Emittance Blow-up in the SPS as LHC Injector and LHC Test-Bed

The longitudinal emittance of the LHC beam must be increased in a controlled way in both the SPS and the LHC itself. In the first case a small increase is sufficient to help prevent coupled-bunch instabilities but in the second a factor three is required to also reduce intra-beam scattering effects. This has been achieved in the SPS by exciting the beam at the synchrotron frequency through the phase loop of the main RF system using bandwidthlimited noise, a method that is particularly suitable for the LHC which will have only one RF system. We describe the tests that have been done in the SPS both for low- and high-intensity beams, the hardware used and the influence of parameters such as time of excitation, bandwidth, frequency and amplitude on the resulting blow-up. After taking into account intensity effects it was possible to achieve a controlled emittance increase by a factor of about 2.5 without particle loss or the creation of visible tails in the distribution.