In the SPS the LHC type high intensity beam can be kept stable longitudinally during acceleration to 450 GeV/c by using the 800 MHz higher harmonic system and, in addition, by making a longitudinal controlled emittance increase by a factor of about 1.5. This latter is obtained by applying band-limited RF phase noise via the main RF system. In LHC itself, which does not have a higher harmonic system, an emittance increase by a factor 2.5 is required. This was attempted in the SPS, as a test-bed for LHC, with shaped RF phase noise and with the 800 MHz system switched off - limiting the maximum stable beam intensity. The emittance of a single (LHC-) pilot bunch has been blown up to a factor 2.5 in coast at 270 GeV/c with a final âgoodâ bunch shape. It remains to be demonstrated that this technique can also be applied successfully for many high intensity bunches with differing synchrotron frequency profiles along the batches. Also a first very quick test to create hollow bunches was done
