Electron lens studies in support of RHIC / LHC Wolfram Fischer 28 July 2010 Fermilab Accelerator Advisory Committee Meeting

Content Head-on beam-beam compensation for RHIC / LHC RHIC luminosity goals and electron lenses LHC beam-beam compensation Proposed Tevatron studies Electron lenses with Gaussian transverse profile Parametric scans to investigate tolerance to errors Pbar tune footprint compression Pbar lifetime without BB / with BB / with BB+lens Test of instrumentation (bremsstrahlung monitor) Wolfram Fischer2

3 2 superconducting 3.8 km rings 2 large experiments 100 GeV/nucleon Au 250 GeV polarized protons Performance defined by 1. Luminosity L 2. Proton polarization P 3. Versatility Au-Au, d-Au, Cu-Cu, polarized p-p (so far) 12 different energies (so far) Relativistic Heavy Ion Collider 1 of 2 ion colliders (other is LHC), only polarized p-p collider

RHIC polarized protons – luminosity and polarization Wolfram Fischer4 L peak = 85x10 30 cm -2 s -1 L peak = 50x10 30 cm -2 s -1 FOM = LP 4 (longitudinally polarized beams)

Wolfram Fischer5 RHIC luminosity and polarization goals ParameterUnit AchievedEnhanced design Next L upgrade Au-Au operation (2010)(>=2012) Energy GeV/nucleon 100 No of bunches … 111 Bunch intensity Average L cm -2 s p  - p  operation (2009)(>=2011/12)(>=2014) Energy GeV 100 / No of bunches … 109 Bunch intensity / / Average L cm -2 s / 5530 / / 300 Polarization P % 55 / 3470 Source upgrade (N b increase) and electron lens (  )

Electron lenses in RHIC – under construction Wolfram Fischer6 IP8 -IP10  y = 10.9  IP6-IP10  x = 19.1  Basic idea: In addition to 2 beam-beam collisions with positively charged beam have another collision with a negatively charged beam with the same amplitude dependence. 2 electron lenses installed in Tevatron, not used for head-on beam-beam compensation Exact compensation possible for: short bunches  x,y = k  between p-p and p-e collision no nonlinearities between p-p and p-e same amplitude dependent kick from p-p, p-e Only approximate realization possible IPAC2010 papers: MOPEC026 (overview), THPE100 (long bunches), Y. Luo TUPEC082 (SimTrack), THPE102 (simulations), C. Montag MOPEC035 (beam alignment with bremsstrahlung), C. Montag TUPEB050 (e-lens for e-beam)

Electron lenses in RHIC – under construction Wolfram Fischer7 e-beam p-beam partial compensation of head-on beam-beam goal of 2x luminosity increase together with source upgrade (allowing for higher bunch intensity with good polarization) critical: relative beam alignment (Tevatron experience) requires straight solenoid field lines, good instrumentation (bremsstrahlung monitor – C. Montag MOPEC035) DC gun: 7 kV, 0.6 A 6 T solenoid, straightness ~0.1 rms beam size collector

Electron lenses in RHIC – under construction Wolfram Fischer 8 6D beam lifetime simulation of electron lens (Y. Luo, THPE102) N b = 3x10 11 without and with e-lens Simulations show full benefit of e-lens for N b > 2x10 11 (i.e. with source upgrade) Beam lifetime simulations are challenging – require good model and supercomputer

Beam-beam compensation in LHC Beam-beam in LHC Total beam-beam parameter in LHC:  = 0.01 (3 IPs, design) 3 head-on collisions, 18 or 19 long-range collision on each side of every IP Long-range compensation Space is reserved for long-range wire compensators (about 100 m from IP, location with  x =  y ) Wire experiments done in SPS, RHIC; wire compensation in DA  NE Head-on compensation Could use same space as wire location Would allow increase in bunch intensity as a possible upgrade Wolfram Fischer9 Ph.D. Thesis, G. Sterbini, 2009

Location for beam-beam compensators in LHC Wolfram Fischer10 IP s = m  x = 0.55 m  x = [2  ]  y = 0.55 m  y = [2  ] BBLR or e-lens s = m  x = 1925 m  x = [2  ]  y = 1784 m  y = [2  ]  x = 91   y = 91 

Simulation for LHC (LARP Collaboration Meeting, April 2010) Wolfram Fischer 11

Wolfram Fischer 12 A. Valishev, LARP CM14

Tevatron electron lens studies Gaussian transverse electron beam profile for all measurements (Gaussian gun to be removed next week, may ask for reinstallation) Quantify tolerances for a number of quantities: Beam offset Crossing angle (Spurious) dispersion Electron beam current Electron size Tolerances: Within tolerance pbar beam lifetime acceptable Static or time-dependent (harmonic, noise) excursions of above quantities [All studies provide input for benchmark simulations.] Wolfram Fischer13

Tevatron electron lens studies 2 Golden experiments: 1.Demonstrate reduction in pbar footprint with electron lens 2.Measure pbar lifetime Without beam-beam interaction (large) With beam-beam interaction (small) With beam-beam interaction and electron lens (large again?) (Measuring pbar tune distribution with protons present difficult – 21 MHz Schottky not gated for bunches.) Some experiments done already – not all fully analyzed. Wolfram Fischer14

Gaussian Gun Up to 1A current with the new modulator (N e =2 x ) Installed in TEL-2 on June 20 (Tevatron shutdown 6/15 – 9/11) A.Va lishe v, Tev Acc Stud ies Wks hp Collector current Courtesy A. Valishev, CM14

BPM Readout Old LabView program slow New Java program faster (response time ~20 s), uses simpler algorithm Shorter e- pulse with new generator – closer calibrations and offsets for electrons and protons/pbars 1/13/2010A.Va lishe v, Tev Acc Stud ies Wks hp 16 Courtesy A. Valishev, CM14

Wolfram Fischer17 Courtesy A. Valishev, CM14

Wolfram Fischer18 Courtesy A. Valishev, CM14

Wolfram Fischer19 Courtesy A. Valishev, CM14

Test of bremsstrahlung monitor Wolfram Fischer 20 Plan to use bremsstrahlung to align p and e beams in RHIC C. Montag, D. Gassner et al. IPAC2010 Would like to test detectors Tevatron Waiting for opportunity to install

Test of bremsstrahlung monitor in Tevatron Wolfram Fischer 21 Micro Channel Plate Tectra MCP-18-D-R-A MCP (assembly diameter = 30mm) Diameter MCP sensitive area = 18mm Number of MCP's = D = Double Mount type = S = Short Readout = A = Anode Options = Ring or Grid

Tevatron studies Also interested in: Studies with hollow electron beam (different e-beam edge) Coherent beam-beam modes Wolfram Fischer22

Wolfram Fischer 23

Wolfram Fischer 24

Summary RHIC electron lenses under construction for head-on beam-beam compensation Head-on beam-beam compensation is a possible upgrade for the LHC (location available, some simulations done) Tevatron studies with electron lenses for RHIC / LHC Until RHIC lenses are completed (end of 2012), TELs are the only available test devices for head-on beam-beam compensation Primarily interested in Gaussian profile (  reinstallation) After quantitativ analysis of experiments done, may ask for further test (parametric scans to investigate tolerance to errors; Pbar tune footprint compression, lifetime without BB / with BB / with BB+lens) Test of bremsstrahlung monitor (profile not critical) Wolfram Fischer25

Acknowledgment Wolfram Fischer 26 Fermilab staff is extremely helpful in the RHIC electron lens design, collaboration on beam-beam simulations, and electron lens experiments in the Tevatron. V. Shiltsev, A. Valishev, H.J. Kim, G. Kuznetsov, A. Romanov, G. Saewert, T. Sen, G. Stancari, X. Zhang Also: A. Kabel (SLAC), J. Qiang (LBNL)