The SPS as a Damping Ring Test Facility for CLIC March 6 th, 2013 Yannis PAPAPHILIPPOU CERN CLIC Collaboration Working meeting

Dream Damping Ring Test Facility Ring achieving lowest possible emittances in all three dimensions, in the range of few GeV  Vertical and longitudinal easier than horizontal Short bunch train structure similar to damping rings  Bunch spacing of 0.67ns (1.5GHz RF system) should be a good compromise Space for installing wigglers, kickers (and extraction line), vacuum test areas, RF, instrumentation Beam conditions for studying IBS, space-charge, low emittance tuning, e-cloud (positrons), fast ion instability, CSR…  High brightness single bunches/trains, small bunch length Available beam time for experimental tests Y.P., 06/03/2013 SPS DR Test facility2

SPS Already proposed as damping ring for CLIC and lately LHeC Low energies (4-10 GeV) in coasting mode Need wigglers (~300m) to get low horizontal emittance (3microns) and fast damping (a few tens of ms)  May gain by lattice modification Evans and Schmidt, 1988 Papaphilippou 2011 RF system upgrade  Total voltage needed (Energy loss/turn of a few tens of MeV)  Different RF frequency (the higher the better) Need to revive lepton injector (now CTF) and transfer lines Y.P., 06/03/2013 SPS DR Test facility

SPS low emittance optics SPS is an all FODO cell lattice (6 sextants), with missing dipole Usually tuned to 90 deg. phase advance for fixed target beams (Q26) and since 2012 to 67.5 deg (Q20) for LHC beams Move horizontal phase advance to 135 deg. (Q40) Normalized emittance with nominal 4GeV of 35 μ m drops to 13 μ m (mainly due to dispersion decrease) Damping times of 6s Y.P., 06/03/2013 SPS DR Test facility

Parameterisation Based on classical formulas, find connection between emittance, wiggler length and damping times Consider wiggler parameters as the ones of the CLIC damping ring prototypes (50mm wavelength and 3T peak field) Y.P., 06/03/2013 SPS DR Test facility

Emittance vs Energy Very low emittances can be achieved for energies of few GeV Y.P., 06/03/2013 SPS DR Test facility

Emittance vs damping time Linear dependence of emittance with damping time for fixed energy (here 4GeV) Y.P., 06/03/2013 SPS DR Test facility

Damping wiggler length Very large number of wigglers for getting low damping time Y.P., 06/03/2013 SPS DR Test facility

Damping wiggler length For moderate total wiggler length (10m), damping times of a 100s of ms can be achieved In particular for 4GeV, damping time of 200ms Y.P., 06/03/2013 SPS DR Test facility

Energy loss per turn Energy loss per turn proportional to energy and inversely proportional to damping time In particular for 4GeV, ~1MeV, i.e. enough RF voltage available Y.P., 06/03/2013 SPS DR Test facility

Energy spread Energy spread depends weakly on damping time for lower energies In particular for 4GeV, energy spread of ~0.16% Y.P., 06/03/2013 SPS DR Test facility

Bunch length Bunch length has very similar behaviour as energy spread for fixed voltage (5MV in this example) In particular for 4GeV, bunch length of <2mm Y.P., 06/03/2013 SPS DR Test facility

SPS Beam energy [GeV]4 Bunch charge [10 9 ]4 Bunches/pulse<=9221 Bunch spacing [ns]5 Hor. norm. emittance [nm]400 Ver. Norm. emittance [nm] 5 Damping time (x,y) [ms]0.2 Bunch length [mm]1.7 Energy spread [%]0.16 Repetition rate [Hz]1 Improvements High repetition rate electron/positron injector complex Damping wigglers (3T, 10m total length) Y.P., 06/03/2013 SPS DR Test facility13

Next step Establish injector parameters  Positrons may be easier, as there is no transferline for electrons any longer Estimate of parameters including IBS Check the possibility to run with these optics in MD (use protons) Y.P., 06/03/2013 SPS DR Test facility14