1. Cooling for Hadron Beams Yaroslav Derbenev Thomas Jefferson National Accelerator Facility The 4 th EIC Workshop Hampton, May 19-23, 2008

2. Cooling for HB Introduction Stacking positive ions Electron Cooling for eRHIC EC for ELIC Optical Stochastic Cooling Coherent Electron Cooling Thinking on prioritizing the cooling techniques Conclusions Outline Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

3. Preamble: Interaction Region as a Microscope Small transverse and longitudinal beam emittance allows one to design and use a strong final focus:  * about 5 mm or even shorter can be designed! Chromaticity can be an obstacle, but it can be compensated (we know exactly how to do so!) Luminosity (p-e round beams): Beam emittance: Requirement to bunch length: The (6D) emittance is a subject to change by cooling! Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008 --invariant Beam-beam tune shift:

4. What is Beam Cooling? One needs a media with which the beam should interact incoherently An individual charged particle creates an effective charge polarization of the media (image charge) In response, particle motion is effected by the image field, that decelerates the particle relatively the beam frame - this is cooling! Feedback with the right receiver - kicker phasing can be used in order to amplify the response Influence of image fields from particle neighbors can only decrease the cooling effect (shield effect) The achievable cooling rate and equilibrium is limited by noise in the media and amplifier Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

5. What cooling does for luminosity? Decrease of beam emittances (up to reaching the beam-beam or intra-beam space charge limit) Preventing the beam blow-up by IBS and other slow heaters Small transverse emittance allows one to design a tight star-focus (more beam extension is available in final quadrupoles) Short bunches allow one to: - use the designed low beta-star (no “hour glass”) - implement the crab-crossing beams – hence, increase the bunch collision rate Beam stacking after linac (works for all species!) Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

6. Cooling techniques and ideas Radiation Cooling (RC) Maxwell-Lorentz demon 1950 th works in e± colliders, can be used in LHC.. Ionization Cooling (IC) Shrinking before plague (muons…) 1966/1981 under development towards the Neutrino Factory and Muon Collider! Electron Cooling (EC) Thermostat of the relativistic engineer 1966 -used at low and medium energies - under development for colliders Stochastic Cooling (SC) van der Meer’s demon (RF feedback) 1968 used Coherent Electron Cooling (CEC) Spoiled hybrid of EC and SC 1980 development just started… Optical Stochastic Cooling (OSC) Max’s demon 1993 (RC+optical feedback) development to start… Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

7. Electron Cooling: The thermostat of a relativistic engineer Landau liked to call me “The relativistic engineer”, I am very proud of that. Gersh Budker Do not renounce from prison and money bag Kinetic equation (plasma relaxation) was derived by Landau in 1937. But… can it work for beams? It does! Yet very interesting and important phenomena have been discovered (magnetized cooling, super-deep cooling, christaline beams…) Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

8. Stochastic cooling “Is n’t it the Maxwell’s demon?” (G.Budker) The van der Meer’s demon It works!! Works well for a coasted low current, large emittance beams. Can it work for bunched beams? Hardly… but demonstrated by M.Blaskewitz for lead at RHIC! May help ELIC (eRHIC?) (stacking and pre- cooling of the coasted beam)…? Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

9. A 1/N-like dependence is clearly visible for the 2-4 GHz system but not for the other two systems (although the 1-2 GHz system shows some dependence on the # of pbars) Stochastic Cooling rate as function of # pbars (‘Fast Schottky’) Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May

10. EC in Fermilab’s Recycler ring Electron cooling is used at the Recycler for cooling 8 GeV pbars 4.34 MeV, 0.1 A DC electron beam Primarily longitudinal cooling To free space for the next antiproton injection from Accumulator ring Cooling strength is regulated by a vertical offset of the electron beam in the cooling section Most of the time, e- beam is shifted by ~2 mm to maximize the life time Moved on axis before extraction to minimize emittances of the extracted beam Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May

11. Forming high current ion beams (agenda in general) 3-9 GeV electrons 3-9 GeV positrons 30-225 GeV protons 15-100 GeV/n ions prebooster 1.Stacking in pre-booster or an accumulator ring 2. Accelerating in the pre-booster and large booster 3. Pre-cooling in collider ring at injection energy 4. Continuous cooling in collider mode Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

12. Stacking ions 1A ion current is required for high luminosity Stripping injection into pre-booster can be used for proton and deuteron beam Accumulation of He and other ions only is possible at use of beam cooling Stochastic cooling of 1A beam is too slow The DC EC (or CEC) is promising! There is an experience: - Accumulating polarized protons from positive source in IUCF Proton Cooler Ring - Electron cooling of 3.10^12 pbar’s in Recycler ring of FNAL An issue for beam accumulation in pre-booster at 200 MeV/n: large emittance caused by the space charge… This emittance cannot be “managed” by Electron pre-Cooling in collider ring A solution seems to exist… Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

13. Stochastic Cooling and Stacking of Ions An optimistic scenario  Multi-turn (10 – 20) injection from 285 MeV SRF linac to pre-booster  Stochastic damping of injected beam  Accumulation of 1 A coasted beam at space charge limited emittance  RF bunching and accelerating to 3 GeV  Inject into large booster  Fill large booster, accelerate to 30 GeV  Inject into collider ring  Transverse stochastic cooling of 1 A coasted ion beam in collider ring At this stage, Ion beam is ready for electron cooling Beam EnergyMeV200 Momentum Spread%1 Pulse current from linacmA20 Cooling timemin1.5 Accumulated currentA1 Stacking cycle /fill LB duration min4/60 Beam emittance, norm.μm12 Laslett tune shift0.03 Stacking proton beam in pre- booster with stochastic cooling Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

14. Stacking positive ions by use of DC EC Accumulator Ring with DC EC Design advancements : Circumference m 50 Beam stacking in one o f two Arc radius m 3 circular modes matched with Crossing straights length m 2 x 15 solenoid of cooling section Energy/u MeV 200 Electron current A 1 This concept allows one to Electron energy KeV 100 overcome space charge Cooling time for protons ms 10 limit on 4D emittance, Stacked ion current A 1 hence, increase EC pre- Large norm.emittance cooling rate in collider ring after stacking µm 16 Accumulation time s 10 Stacking of positive fully stripped polarized and unpolarized ions can be realized in the accumulator-cooler ring (ACR) with electron cooling. Such method has been successfully used for accumulating of polarized beam in Proton Cooler Ring of IUCF Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

15. Requirements for eRHIC 1. Protons (250 GeV): 2. Au ions (100 GeV): Bunch intensity: 2e11 Bunch intensity: 1.1e9 95%, normalized emittance: 6  m 95%, normalized emittance: 2.4  m Rms bunch length: 0.2 m Rms bunch length: 0.2 m Peak luminosity: 2.6e33 Peak luminosity: 2.9e 33 Requires pre-cooling: Au ions: factor of 6 reduction in initial emittance Protons: factor of 3-2 reduction in initial emittance Such electron cooling is possible based on RHIC-II electron cooler with 703 MHz SRF gun. Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

16. Pre-cooling of Au ions (N=1e9) Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

17. Pre-cooling of protons (N=2e11) Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

18. Electron cooling section at RHIC 2 o’clock IP Each electron beam cools ions in Yellow ring of RHIC then the same beam is turned around and cools ions in Blue ring of RHIC. ` 100 m IP 2 ERL helical wigglers e-e- e-e- e-e- RHIC triplet 10 m solenoids Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

19. Energy Recovery Linac (ERL) for RHIC-II Cooling of Au ions at 100 GeV/n: 54.3 MeV electron beam 5nC per bunch rms normalized emittance < 4  m rms momentum spread < 5×10 -4 Courtesy D. Kayran D. Kayran, PAC07 Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

20. R&D ERL at BNL 5 cell cavity successfully processed 0.5 ampere SRF gun – under construction 703 MHz 5 cell SRF cavity designed by BNL and fabricated by Advanced Energy Systems. The cavity has reached its specification of 20 MV/m at a Q of 1×10 10. Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

21. EC Test bed for RHIC-II and eRHIC Commissioning starts February 2009 Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

22. Circulated Electron Cooling of ELIC ion bunch electron bunch circulator cooler ring (CCR) Cooling section solenoid kicke r SRF Linac dum p electron injector energy recovery path Max/min energy of e-beamMeV125/8 Electrons/bunch10 1 Number of bunch revolutions in CCR100 Current in CCR/ERLA3/0.03 Bunch repetition rate in CCR/ERLMHz1500/15 CCR circumferencem80 Cooling section lengthm20 Circulation duration ss 27 Bunch lengthcm1-3 Energy spread10 -4 1-3 Solenoid field in cooling sectionT2 Beam radius in solenoidmm1 Cyclotron beta-functionm0.6 Thermal cyclotron radius mm 2 Beam radius at cathodemm3 Solenoid field at cathodeKG2 Laslett’s tune shift in CCR at 10 MeV0.03 Time of longitudinal inter/intra beam heating ss 200 CCR makes 100 time reduction of beam current from injector/ERL Fast kickers operated at 15 MHz repetition rate and 2 GHz frequency bend width are required Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

23. Cooling Time and Ion Equilibrium * max.amplitude ** norm.,rms Cooling rates and equilibrium of proton be am ParameterUnitValu e EnergyGeV/MeV30/1 5 225/123 Particles/bunch10 0.2/1 Initial energy spread*10 -4 30/31/2 Bunch length*cm20/31 Proton emittance, norm* mm 11 Cooling timemin11 Equilibrium emittance, ** mm 1/11/0.04 Equilibrium bunch length** cm20.5 Cooling time at equilibrium min0.10.3 Laslett’s tune shift (equil.) 0.040.02 Multi-stage cooling scenario: 1 st stage: longitudinal cooling at injection energy (after transverses stochastic cooling) 2 nd stage: initial cooling after acceleration to high energy 3 rd stage: continuous cooling in collider mode Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

24. Electron Cooling of Ions in ELIC Staged cooling  Start electron cooling (longitudinal) in collider ring at injection energy,  Continue electron cooling (in all dimension) after acceleration to high energy F(v ) v 0 Dispersive cooling Compensates for lack of transverse cooling rate at high energies Flat beam cooling Based on flattening ion beam by reduction of coupling IBS rate at equilibrium becomes reduced compared to cooling rate Sweep cooling After transverse stochastic cooling, ion beam has a small transverse temperature but large longitudinal one. Use sweep cooling to gain a factor of longitudinal cooling time Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

25. Injector and ERL for EC in ELIC ELIC CCR driving injector  30 mA@15 MHz, up to 125 MeV energy, 1 nC bunch charge, magnetized Challenges  Source life time: 2.6 kC/day (state-of-art is 0.2 kC/day)  source R&D, & exploiting possibility of increasing evolutions in CCR  High beam power: 3.75 MW  Energy Recovery Conceptual design  High current/brightness source/injector is a key issue of ERL based light source applications, much R&D has been done  We adopt light source injector as initial baseline design of ELIC CCR driving injector Beam qualities should satisfy electron cooling requirements (based on previous computer simulations/optimization) 500keV DC gun solenoids buncher SRF modules quads Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

26. Fast Kicker for Circulator Cooling Ring Sub-ns pulses of 20 kW and 15 MHz are needed to insert/extract individual bunches. RF chirp techniques hold the best promise of generating ultra-short pulses. State-of-Art pulse systems are able to produce ~2 ns, 11 kW RF pulses at a 12 MHz repetition rate. This is very close to our requirement, and appears to be technically achievable. Helically-corrugated waveguide (HCW) exhibits dispersive qualities, and serves to further compress the output pulse without excessive loss. Powers ranging from up10 kW have been created with such a device. Estimated parameters for the kicker Beam energyMeV125 Kick angle10 -4 3 Integrated BdLGM1.25 Frequency BWGHz2 Kicker ApertureCm2 Peak kicker fieldG3 Kicker Repetition Rate MHz15 Peak power/cellKW10 Average power/cellW15 Number of cells20 kicker Collaborative development plans include studies of HCW, optimization of chirp techniques, and generation of 1-2 kW peak output powers as proof of concept. Kicker cavity design will be considered Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

27. Coherent Electron Cooling or how the van der Meer’s demon can spoil thermostat of the relativistic engineer Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

28. History of CEC idea (1980-91-95-2007) Coherent electron cooling (CEC) was proposed 27 years ago What changed in last 10 years? Relativistic DC EC realized (FNAL) ERL realized (JLab) SASE FEL realized (UCLA - DESY) ERL-based HEEC on the way (BNL) And more… CEC advantages/disadvantages compared to: EC : Gain in cooling rate Complicate BT SC : Very large FB (30 GHz – optics) Precise phasing required OSC : Effective in a wide energy range Small signal delay Intense e-beam required Signal gain is limited General idea: amplify response of e- beam to an ion by a micro-wave instability of the beam A few instabilities have been shown Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

29. FELs and HEEC And so, my fellow Americans, ask not what your country can do for you; ask what you can do for your country. And so, my fellow FELers, ask not what storage ring can do for FELs: Ask what FELs can do for your storage rings ! Vladimilr Litvinenko 29th International FEL Conference August 26-31, 2007, BINP, Novosibirsk Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

30. Optical stochastic cooling (OSC) Max’s demon (by Max Zolotorev, 1993) ---- Proton radiates light in undulator (“receiver”) ----optical amplifier---- ---“proton interacts with the amplified light in the end undulator “kicker”) Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008 2000 - OSC considered for cooling of halo particles in the VLHC, by Barletta, Chattopadhyay, Zholents, Zolotorev

31. Why we need OSC if we have electron cooling Cooling rate Optical stochastic cooling can effectively reduce number of the particles in the beam tails. This will increase lifetime of the beam and reduce detectors background. Custom beam shaping might be possible. OSC Electron cooling Beam profile Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

32. Optical Stochastic Cooling Amplified signal ss pp Pump laser  i =  p -  s ; k p = k s + k i Gold beam ss pp Horizontal and longitudinal cooling time 1hr for the full gold beam requires 16W of power = 12  m Bandwidth ~ 3 THz Optical amplifier on 3.5 cm CdGeAs 2 crystal with d 14 =236 pV/m LDRD test at ATF for Optical Parametric Amplification Freshly grown crystals at Lockheed Sanders, NH Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

33. Optical Parametric Amplifier OPA Parametric process is photon interaction in which one high frequency photon is annihilated and two lower frequency photons are created, i.e.:  (pump) =  (signal) +  (idler) where photon energy is conserved. In addition, photon momentum is conserved by the wave vectors: k(pump) =k(signal) +k(idler). 3 cm length crystal → intensity gain 3 10 5 Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

34. Critical studies on Cooling for Hadrons Pre-cooling for eRHIC: Non-magnetized, space charge dominated e-beam transport CEC for eRHIC: all physics and design EC for ELIC: ERL - CCR super-fast kicker for e-beam OSC (of “beam halo”): Parametric optical amplifier SC for beam stacking and pre-cooling (ELIC): Limits for coasted beams DC EC (and CEC) for beam stacking (alternative to SC): Accumulator-cooler design and all beam physics Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

35. My view of Current prioritization of potential employment of cooling techniques at EIC by taking into account : Potential efficiency + Conceptual readiness + Proximity to realization Service: I II III IV Stacking DC EC DC CEC SC Pre-cooling HE EC CR EC SC HE CEC Core Cooling CR EC HE CEC Tail cooling OSC HE CEC HE EC EC – electron cooling; DC - direct current; HE - high energy (ERL based) CR – cirulator ring; CEC - coherent EC; SC - stochastic cooling; OSC - optical stochastic cooling Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

36. Conclusions The studies and designs of cooling for EIC are getting mature. The projects are well profiled in the goals and expected performance. The engineering works and test studies for 1 hundred MeV scale ERL started at BNL. A prototype of ERL will be built, which, as minimum, will serve pre-cooling of ions to reach luminosity in eRHIC. Conceptual development of 125 MeV ERL + Circulator Ring scheme of electron cooling for ELIC will finalize soon (in 1-1.5 year) at JLab. Could such scheme also be implemented in eRHIC to raise the cooler efficiency? Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

37. Conclusions (cont-d) Recent development of Optical Stochastic Cooling brings a realistic promise to extend luminosity lifetime and ease the EC design, by cooling beam tail. The OSC, however, can work only in a relatively narrow beam energy region of the collider ring. The new perspectives for cooling hadron beams in colliders seem to be open with development of the Coherent Electron Cooling, which starts at BNL. It invites SASE FEL amplifier to cooling section of a collider. The efficiency of colliders can be frequently increased by stacking positive ions in a small ring after linac. Here, the EC or CEC on a non-relativistic DC e-beam could be employed to accumulate 1 A level of ion current. Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

38. We entering an exciting era of the new generation of high luminosity colliding beams provided by the Advanced cooling techniques! Thank you! Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008

39. Making sense of the different cooling techniques Optical SC: Similar to SC, but at optical wavelength Not limited by amplifier bandwidth ~3THz Can cool whole RHIC beam in one hour with16W of optical power Favors large amplitudes, Greatly reduces requirements on electron current if used with EC Works only over limited ~5-10% range of the ion beam energies Requires challenging RHIC lattice modifications No demo, yet Stochastic Cooling: beam error signal is measured by a pickup, amplified by RF amplifier and corrected in the kicker Works over wide range of the ion beam energies Can be used for stacking Limited by amplifier bandwidth ~5GHz Possibly can cool only tails of the RHIC beam Electron cooling: ion beam “heat” transferred to “cold” electron beam Works over wide energy range Effective for the beam core and against IBS (faster cooling for the colder beam) Complimentary with OSC as it effective against IBS (main growth in RHIC) Requires ERL and long solenoid High e-efficiency in the ERL+CCR advance scheme Can be used for stacking Was not demonstrated at high energies Coherent Electron Cooling: response of e-beam to an ion is amplified by a micro- wave instability of the e-beam (SASE FEL) Strong image interaction Very large FB (30 GHz – optics) Effective in a wide energy range Small signal delay Requires high current ERL Signal gain is limited Needs more study, no demo yet Ya. Derbenev /TJNAF/. 4 th EIC Workshop, Hampton, May 2008