July LEReC Review July 2014 Low Energy RHIC electron Cooling Jorg Kewisch, Dmitri Kayran Electron Beam Transport and System specifications July LEReC beam structure in cooling section Example for = 4.1 (E ke =1.6 MeV) 110 nsec, f=9.1 MHz 1.42 nsec 30 electron bunches Electrons: f_SRF= MHz Rms length=3 cm, I_peak=0.4 A Q_e=100 pC 9 MHz RHIC RF July Electron Beam Energies Gun Energy [MeV] GammaCharge per bunch [pC] Beam Power [kW] July Low-Energy RHIC electron Cooler (LEReC), 2018 Cooling sections Beam transport lines Beam dump 704 MHz cavity 704 MHz SRF gun e-e- e-e- e-e- e-e- e-e- IP2 DX 2.1 GHz cavity July Oclock Interaction region 5 July Merging Electrons and Ions (Dog Leg) 6 July Cooling section Use two solenoids at the start of the section to match the beam size to 4.3 mm Continuous weak focusing to keep the divergence of the beam small and the radius constant Use two solenoids to reduce the beam size at the end to avoid over-focusing by the weak focusing of the U-turn dipoles July Lattice : cooling section blue, turn around, cooling section yellow July Beam Transport in the low energy cooler No acceleration to high energies, space charge is an issue for the whole accelerator Long transport Strong focusing elements produce continuous emittance compensation Space charge pushes head and tail of the bunch in opposite direction. Energy spread increases continually 9 July What to do about it? Longitudinal bunch shaping: The energy spread growth depends on the longitudinal density distribution: Beer can is best, Gaussian is mediocre, Triangular is bad Longitudinal profile after the 3 rd harmonic cavity (energy spread is small): 10 Starting with beer can Starting with trapezoid July What else to do about it? Make the bunch long as quickly as possible Adjust the phase of the gun to create energy chirp Bunch length increases due to velocity spread Remove linear chirp in the 5 cell cavity Remove non-linear chirp in the 2100 MHz cavity Does not work if bunch is too long Too much energy spread hurts transverse emittance 11 July Bunch length and minimum energy spread after the 3 rd harmonic Cavity 12 July Emittance degradation through Chromaticity in Solenoids between Gun and 5 cell Cavity 13 July What else to do about it? Hot particles dont cool, but dont do harm either Put 10% more charge into the bunch Ignore the 10% hottest particles 14 July Simulations All simulations were made using the code PARMELA PARMELA assumes for the space charge calculations that the beam is round. If the aspect ratio is large the space charge in the smaller direction is underestimated For this simulations we used solenoid focusing only. If quadrupoles are used a 3-D program like ImpactT must be used. A multi-threaded optimizing program (written at BNL) was used which launches PARMELA for the function evaluation. The WINE program was used to allow running PARMELA, which is closed source and MICROSOFT only, in an UNIX environment A typical optimization run with 5 parameters takes 36 hours. 15 July Orientation All calculations are done at 1.6 MeV. Higher energies are easier. 16 July Envelope 17 July Maximum Envelopes and Beam Pipe Dimensions 18 July Transverse Temperature after 10% cut 19 July Longitudinal Phase Space at the Cathode 20 July Longitudinal Phase Space at the Gun Exit 21 July Longitudinal Phase Space at the 5 cell Entrance 22 July Longitudinal Phase Space at the 5 cell Exit 23 July Longitudinal Phase Space at the 5 cell Exit 24 July Longitudinal Phase Space at the 3 rd Harmonic Exit 25 July Longitudinal Phase Space at minimum energy spread 26 July Energy Spread Disclaimer: The parameters for this calculation are different from ones above 27 July Energy Spread in the cooling sections 28 July Summary Getting required electron beam parameters (transverse angular spread and momentum spread) is most challenging for lowest energy of LEReC operation. A scheme with RF manipulation was developed which produced satisfactory beam quality. Beam lattice and dynamics can be further optimized. Complete gun-to-dump calculations are planned to Find optimal focusing in the transport section Match flat envelope in cooling section Optimize dispersion matching 29 July Backup slides 30 July Cooling sections U-turn dump 2.1 GHz warm cavity 704 MHz SRF cavity 704 MHz SRF gun Focusing Solenoids Dipoles quadrupoles v Layout not to scale, not showing all magnets in their locations Transport quadrupoles