potential CERN facilities to study proton-driven plasma acceleration Frank Zimmermann Munich MPI, 9 December 2008

CTF-3

existing accelerator chain (LHC beam) PS booster PS SPS LHC final momentum [GeV/c] 2.1 26 450 7000 protons/bunch [1011] 17 1.3 1.15 rms longitudinal emittance [eVs] 0.11 0.03 0.06 0.2 (0.08*) rms bunch length [ns] 143 1 <0.5 0.25 (0.16*) relative rms energy spread [10-3] 0.32 0.3 0.11 (0.07*) rms transverse emittance [mm] 2.5 3.0 3.5 3.75 bunch spacing [ns] N/A 25 # bunches / cycle 4 (4 rings) 72 288 2808 cycle time 1.2 s 3.6 s ~22 s 5-10 h? * w/o longitudinal blow up in the LHC 1 ns = 30 cm, 3x10-4 ns = 100 mm

present and future LHC injectors Proton flux / Beam power Linac2 Linac4 50 MeV 160 MeV PSB (LP)SPL 1.4 GeV 4 GeV (LP)SPL: (Low Power) Superconducting Proton Linac (4-5 GeV) PS2: High Energy PS (~ 5 to 50 GeV – 0.3 Hz) SPS+: Superconducting SPS (50 to1000 GeV) SLHC: “Superluminosity” LHC (up to 1035 cm-2s-1) DLHC: “Double energy” LHC (1 to ~14 TeV) PS 26 GeV PS2 50 GeV Output energy SPS 450 GeV SPS+ 1 TeV LHC / SLHC DLHC 7 TeV ~ 14 TeV Roland Garoby, LHCC 1July ‘08

layout of new LHC injectors SPS PS2, ~2017 SPL,~2017 PS Linac4 ~2012 R. Garoby, CARE-HHH BEAM07, October’07; L. Evans, LHCC, 20 Feb ‘08

injector upgrade schedule synchronized with LHC IR upgrades R. Garoby, LHCC 1 July 2008 LHC IR phase 1 2013: PSB with linac4 LHC IR phase 2 2017: SPL+PS2

upgraded accelerator chain (LHC beam) SPL PS2 SPS LHC final momentum [GeV/c] 5 50 450 7000 protons/bunch [1011] 2.5x10-4 4 rms longitudinal emittance [eVs] 7.3x10-7 0.05 0.06 0.2 (0.08*) rms bunch length [ns] 1.9x10-4 1 <0.5 0.25 (0.16*) relative rms energy spread [10-3] 0.18 0.3 0.11 (0.07*) rms transverse emittance [mm] 0.35 3.0 3.5 3.75 bunch spacing [ns] 2.8 25 # bunches / cycle 200,000 144 288 2808 cycle time 20 ms 2.4 s ~13 s 5-10 h? * w/o longitudinal blow up in the LHC 1 ns = 30 cm, 3x10-4 ns = 100 mm

phase space at SPL exit M. Eshraqi A. Lombardi

intermediate conclusions the only proton beam which is naturally “short” is the one from the SPL, ~60 micron rms length, with 2.5x107 protons / bunch and available at the earliest in 2017 the beam from the SPS must be compressed by a factor 10,000 to obtain rms bunch lengths of 100-200 mm equilibrium bunch length scales with the inverse 4th root of RF voltage and with the 4th root of the momentum compaction factor four other possibilities come to mind: rapid change in momentum compaction factor followed by bunch rotation in mismatched bucket or transverse deflecting cavity?! damping by intrabeam scattering below transition?! coherent electron cooling?!

mismatch d bunch pulse fast quadrupoles to change momentum compaction, and quickly raise RF voltage shape of linear rf bucket z extract after ¼ synchrotron oscillation when bunch length is minimum bunch length scales with the square root of pulsed momentum compaction factor

→ expect compression by factor 2 x 10-2 /Sqrt(10) ~ 0.006 ~ 1/160 initial momentum compaction ac,initial ~ 0.01 we may hope for ac,new ~ 10-6 initial RF voltage ~ few MV we may hope for final RF voltage ~ 10x higher → expect compression by factor 2 x 10-2 /Sqrt(10) ~ 0.006 ~ 1/160

transverse deflecting cavity+ bending system can the plasma wave excited by crabbed beam be used for e- acceleration? drift bending system? transverse deflecting cavity can something like this work? short bunch! idea is to convert transverse size into longitudinal size (above schematic ignores x-dependent energy change from crab cavity) or transverse crab cavity followed by “slit”?

coherent e- cooling CeC proof-of- V. Litvinenko, Y. Derbenev damping times in hours: CeC proof-of- Principle experiment at RHIC in 2012 V. Litvinenko, Y. Derbenev promise of 1-hr damping time at 7 TeV! interesting, but still too small for our purpose

final conclusion to get “high-energy” proton bunch lengths below 1 mm, we can use the beam from the SPL, or we need strong cooling or bunch compression or an x(y)-z 4/6-D emittance exchange transformation or a combination thereof

appendix: thoughts on scattering limits and chances scattering limits and maximum energy reach of plasma accelerators the return of fixed target experiments?

scattering limits and energy reach at the plasma-acceleration WG of CLIC08 Andrei Seryi and Tor Raubenheimer reported that 500 GeV acceleration in a plasma was possible, but that 1.5 TeV was excluded by Coulomb scattering – this seemed odd at first glance since Coulomb scattering gets weaker at higher energy scattering limits were previously looked at by Montague & Schnell (1985) and Katsouleas & Dawson (1987)

A. Seryi CLIC08 workshop, Plasma wakefield acceleration working group, CERN, Oct. 2008 B.W. Montague, W. Schnell Multiple scattering and synchrotron radiation in the plasma beat wave accelerator. 2nd Int. Workshop on Laser Acceleration of Particles, Los Angeles, CA, Jan 7-18 Jan 1985, AIP Conf.Proc.130:146-155,1985. T. Katsouleas, J.M. Dawson Plasma acceleration of particle beams. 1987. AIP Conf.Proc.184:1798-1828,1989.

scaling of the multiple scattering limit multiple scattering from my memory indeed the normalized emittance grows as the square root of the final energy, but no hard limit in energy reach to avoid this limit the b function must increase less than with the the square root of energy (e.g. tapered plasma density)

bremsstrahlung most important vacuum limit at high energy e+ or e- machines this effect would suggest that the total distance travelled through the plasma cannot be more than one or a few radiation lengths for example X0~10 m for 4x1022 e/cm3 using the rough estimate of 30 GV/m for 1x1017e/cm3 this gives an ultimate energy of ~200 TeV

nuclear interaction of protons with plasma? similar magnitude as radiation length variation with beam energy?

return of fixed target experiments since extremely high gradients are feasible with plasmas but the collision of two such beams may be difficult to achieve, could fixed target experiments become attractive again? Pantaleo Raimondi in particular they could be interesting for proton driven plasma accelerators with a single proton beam, a single stage, and very high proton and electron energy; possibly high luminosity experiment might be different from present colliders