1. Tor Raubenheimer CLIC and Other Options for Multi-TeV Lepton Physics Tor Raubenheimer Accelerator Research Division Head, SLAC P5 Meeting Fermilab February 1 st, 2008

2. February 1 st, 2008 Page 2 Tor Raubenheimer Introduction Outline –CLIC concept (X-band Two-Beam Accelerator) –Technology status –Outstanding issues –LC roadmap and other options Assumptions –Believe that the motivation for TeV-scale LC remains the same but timescale is slower, motivating a broad look at LC technology Caveats –Evaluation of outstanding issues for CLIC design is my opinion –Suggestions for ‘other options’ is also my opinion These views are not endorsed by SLAC, the GDE, or … I (and SLAC) are committed to developing the ILC as the near-term solution for a 500 GeV LC

3. February 1 st, 2008 Page 3 Tor Raubenheimer What is CLIC? CLIC = Compact LInear Collider –Developed by CERN originally as a 30 GHz and 150 MV/m that is based on a two-beam accelerator concept Two-beam concept is an efficient way to transform rf frequency from long-pulse low-frequency  short-pulse high-frequency and thereby drive high gradients Concept is elegant but still waiting for demonstrations and detailed costs illustrating the benefits – Developed parameters from 500 GeV  3TeV Recently changed parameters to 12 GHz and 100 MV/m to reduce cost and better utilize GLC/NLC R&D –Development program to demonstrate ~100 MV/m by 2010 –CTF3 test facility should demonstrate TBA concept on a similar timescale

4. February 1 st, 2008 Page 4 Tor Raubenheimer Two-Beam Accelerator Concept (from R. Corsini; 2006 parameters)

5. February 1 st, 2008 Page 5 Tor Raubenheimer CLIC RF Module ~ 2 meters Main Beam ~1 A Drive Beam 100 A Accelerating structure, +100 MV/m, 64 MW, 229 mm Power Extraction Structures: -6.5 MV/m, 136 MW, 210 mm rf distribution

6. February 1 st, 2008 Page 6 Tor Raubenheimer CLIC Schematic (2007 Parameters for 3 TeV) Injector systems similar to other LC concepts Drive beam complex efficiently generates high power beam Main linacs have deccelerator struct- ures adjacent to accelerator structures in single tunnel – all LLRF and complicated electronics are elsewhere Similar number of klystrons as 500 GeV ILC

7. February 1 st, 2008 Page 7 Tor Raubenheimer CLIC Linear Collider Parameters

8. February 1 st, 2008 Page 8 Tor Raubenheimer Possible CLIC Siting Option IP under CERN Prevessin site Phase 1: 1 TEV extension 19.5 km Phase 2: 3 TeV extension 48.5 km Detectors and Interaction Point CERN site Prevessin

9. February 1 st, 2008 Page 9 Tor Raubenheimer Proposed Timescale (from JPD presentation to CERN SPC)

10. February 1 st, 2008 Page 10 Tor Raubenheimer Cost for TBA versus Conventional LC Major study needed as part of CLIC CDR but characteristics can be understood. The TBA has a large central infrastructure that generates drive beam  –Cost per GeV of TBA is likely cheaper than that of a conventional klystron-based linear collider –Initial cost of the TBA is higher than that of a klystron-based collider –Location of cross-over and slopes is unknown for present technologies From 1998 comparison of 1996 NLC versus X-band TBA costs by G. Loew Cms GeV

11. February 1 st, 2008 Page 11 Tor Raubenheimer GLC/NLC >50 MV/m Operation Unloaded Gradient (MV/m) Breakdown Rate at 60 Hz (#/hr) with 400 ns Pulses NLC/GLC Rate Limit Eight Structure Average Single Structures Breakdown performance continued to improve with time BDR ~ exp(- t / 400 hrs) over the 2000 hrs operation

12. February 1 st, 2008 Page 12 Tor Raubenheimer 100 MV/m Structure testing at NLCTA (Structures from GLC/NLC program in early 2000’s) Run slotted, a/ = 0.18, 75 cm NLC structure (H75vg4S18) with 150 ns pulses - at 102 MV/m, breakdown rate = 6 10 -6 Run early NLC, non-slotted, 53 cm, smaller aperture (a/ = 0.13) structure (T53vg3MC) at short pulses – unloaded gradient at a 10 -6 breakdown rate with 100 ns pulses is 105 MV/m and more recently it achieved similar gradient with 200ns ramped pulse. Building CERN-designed structures for future tests at SLAC and KEK

13. February 1 st, 2008 Page 13 Tor Raubenheimer Single Cell Accelerator Structure Testing (Understand Fundamental Breakdown Limits) Goals Study rf breakdown in practical accelerating structures: dependence on circuit parameters, materials, cell shapes and surface processing techniques Difficulties Full scale structures are complex and expensive Solution Single cell Traveling wave (TW) and single cell standing wave (SW) structures with properties close to that of full scale structures This program, now, has a strong participation from both KEK and CERN. Time of flat pulse after filling time Variety of Single Cell Accelerator Structures Manufactured at KEK SW accelerator structure test with a/ ~0.21. In this type of structures loaded and unloaded gradients are the same

14. February 1 st, 2008 Page 14 Tor Raubenheimer CTF3 – CLIC Test Facility Large-scale LC test facility to demonstrate TBA concept DL CLEX 2007-2009 building in 2006/7 2004 2005 Thermionic gun CR TL2 2007-2008 30 GHz production (PETS line) and test stand Photo injector / laser tests from 2008 Linac Beam up to here 2007 Major milestones in 2007: Combiner Ring (CR) installed CLEX building finished, equipment installation started 150 MeV 30 A - 140 ns

15. February 1 st, 2008 Page 15 Tor Raubenheimer RF Unit Demonstrations (What is necessary before construction?) The ‘RF Unit’ is the acceleration element that is replicated through the main linacs –Usually thought of as the minimal element that needs demonstration before construction -- CLIC is different –In GLC/NLC: two 75-MW klystrons, SLED-II rf pulse compression system and 4.8 meters of accelerator structure operating at 50 MV/m loaded  ~250 MeV per rf unit Pieces demonstrated in 2004; System demo canceled –In ILC: a modulator and klystron, an rf distribution system, and 3 cryomodules with 26 1-meter rf cavities operating at 31.5 MV/m  ~1 GeV per rf unit Pieces to be demonstrated in 2010; System demo in ~2012 –In CLIC: a 2.5 GeV 100 Amp drive beam is fed into ~600 meters of decellerator structures that accelerate the primary by ~60 GeV Pieces demonstrated in ~2012 in CTF3 but no RF Unit demo

16. February 1 st, 2008 Page 16 Tor Raubenheimer Outstanding Issues for CLIC Program to develop high-gradient accelerator structures by 2010 –May not achieve 100 MV/m at desired breakdown rate but, given present results, will probably be close Systematic cost estimate needed –Working with GDE to develop costs using same methodology as applied to ILC – aiming for 2010-timescale Tighter alignment and jitter tolerances –Aiming to demonstrate stabilization techniques by 2010 Program to demonstrated TBA-concept in CTF3 by 2012 and accelerate beams to ~1 GeV –Concept demonstrated but drive beam parameters quite different from CLIC and will not demonstrate an ‘RF Unit’ Not clear what is necessary to launch construction and the collaboration is discussing options

17. February 1 st, 2008 Page 17 Tor Raubenheimer Understanding the Gradient Choice Cost optimum is a balance between costs proportional to length, i.e. tunnel & structures and costs proportional to the rf power sources G = A sqrt(P * Rs) P = rf power / meter Rs = shunt imp. / m Have to reduce rf power cost per MW by 2x or double shunt imped. to increase G by 40% Unloaded Gradient (MV/m) Relative TPC At low gradient, cost increases due to larger length costs At high gradient, cost increases due to higher rf power costs GLC/NLC X-band

18. February 1 st, 2008 Page 18 Tor Raubenheimer CLIC Gradient Optimization CERN developed a detailed cost estimate using the TESLA estimate and the US Technical Options Study (2003) costing –Not entirely clear what is included and what drives the frequency scaling but the basic form makes sense –Believe that there is an assumption that above 10 GHz, the gradient is independent of frequency –Main point: very high gradients don’t make cost sense Previous New Optimum Cost

19. February 1 st, 2008 Page 19 Tor Raubenheimer Approaches to a Linear Collider (Four Options) Superconducting rf (1.3 GHz) –Strong international support through ILC collaboration –Gradients of 30 MV/m in cavities yielding 20 MV/m average –Technology well advanced (1 GeV test facilities under construction at Fermilab and KEK  2011 or 2012) –Can be stretched to ~1 TeV energy Normal conducting rf (11 ~ 12 GHz) –Strong international support through CLIC collaboration CLIC recently adopted 12 GHz down from 30 GHz –Gradients of 100 MV/m yielding 80 MV/m average –Technology fairly well advanced (test facility at SLAC demonstrated 300 MeV at 50 MV/m in 2004 and CTF3 at CERN aiming for 1 GeV at 100 MV/m in 2012 - 2014) –Certainly reach 1 TeV and maybe multi-TeV energies

20. February 1 st, 2008 Page 20 Tor Raubenheimer Approaches to a Linear Collider (2) (Four Options) Normal Conducting rf (cont.) –Two NC rf source concepts have been considered: Klystron-based linacs with klystrons along accelerator Two-Beam accelerator with drive beam powering linac Possible to consider a staged implementation using first klystron-based and then TBA-based rf power to reduce risk Advanced concepts (laser and plasma) –Small lab and university-based collaborations –Gradients of many GeV per meter have been demonstrated –Technology has many challenges – working to develop roadmap illustrating development of acceleration concept and beam quality concepts –Some concepts (PWFA) use conventional rf linacs as drivers or injectors

21. February 1 st, 2008 Page 21 Tor Raubenheimer A Roadmap for Multi-TeV Lepton Colliders 500 GeV LC Neutrino source Neutrino ring Muon collider (few TeV) 350 GeV LC Multi-TeV LC 2010 2020204020502030 Timescale (personal guess) Plasma Acc Superconducting RF Normal conducting - Two-Beam-based Normal conducting – Klystron-based Multi-TeV LC 4 th Generation SR Sources 5 th Generation SR Sources? The LC roadmap illustrates options and connections between them. Selecting a path requires additional information such as LHC results and technology status

22. February 1 st, 2008 Page 22 Tor Raubenheimer One Possible Path to Multi-TeV Lepton Physics 500 GeV LC Neutrino source Neutrino ring Muon collider (few TeV) 350 GeV LC Multi-TeV LC 2010 2020204020502030 Timescale (personal guess) Plasma Acc Superconducting RF Normal conducting - Two-Beam-based Normal conducting – Klystron-based Multi-TeV LC 4 th Generation SR Sources 5 th Generation SR Sources?

23. February 1 st, 2008 Page 23 Tor Raubenheimer RF Power Source R&D Developing rf power sources for ILC: –Marx solid state modulator – broad applicability of technology –Sheet beam klystron – broad applicability of SBK concept Developed rf power source for GLC/NLC: –SLED-II system delivered >500 MW –Two-Pac modulator fabricated but never tested – halted in 2004 –X-band klystrons operated at 75 MW and 1.5 us but limited by breakdowns →Consider new output structures or reduced power levels using knowledge from high gradient studies Future program to complete X-band rf source program –Could provide a more conservative option to CLIC design –Power sources for compact radiation sources and other compact installations

24. February 1 st, 2008 Page 24 Tor Raubenheimer GLC/NLC RF Power Sources Good success with modulator, pulse compression and rf distribution development. Klystrons achieved peak power and pulse length specs but BDR was too high Combined Klystron Power Output Power (Gain = 3.1, Goal = 3.25)

25. February 1 st, 2008 Page 25 Tor Raubenheimer Staged Approach to TBA Should re-optimize the NC rf source but as a start: Use the (nearly developed) GLC/NLC power source to power the CLIC accelerator structures at a loaded gradient of ~60 MV/m –Need to solve klystron BDR problem but assuming success Increase gradient by ~20% for same cost per meter Easy to perform systems demonstration of an rf unit Simple improvements in pulse compression could increase power per meter  10% cost reduction Build lowest reasonable energy LC with klystrons –Commission X-band main linac, BDS, sources and detectors –Use infrastructure to start testing TBA drive beam dynamics while operating klystron-based collider and then move to TBA.

26. February 1 st, 2008 Page 26 Tor Raubenheimer Another Possible Path to Multi-TeV Lepton Physics 500 GeV LC Neutrino source Neutrino ring Muon collider (few TeV) 350 GeV LC Multi-TeV LC 2010 2020204020502030 Timescale (personal guess) Plasma Acc Superconducting RF Normal conducting - Two-Beam-based Normal conducting – Klystron-based Multi-TeV LC 4 th Generation SR Sources 5 th Generation SR Sources?

27. February 1 st, 2008 Page 27 Tor Raubenheimer Comment on Spin-off Applications Compact high gain FELs Storage ring injectors Medical linacs Industrial radiation sources High gain FELs Recirculating linacs and CW applications Industrial accelerators (no present applications) Both NC and SC rf technology have many additional applications Normal conducting RFSuperconducting RF To date, NC technology has been simpler and cheaper to implement (at least for small-scale applications) SC technology is better suited for CW applications and NC is better suited to short high-current beam pulses Both technologies can have comparable efficiencies and deliver comparable beam power

28. February 1 st, 2008 Page 28 Tor Raubenheimer Applications Example: High Gain FELs Roughly equal number of normal conducting and superconducting– based FEL sources Many FELs use higher harmonics for bunch compressions; SLAC was asked to build 12 GHz klystrons for Trieste, Frascati and PSI

29. February 1 st, 2008 Page 29 Tor Raubenheimer Yet Another Possible Path to Multi-TeV Lepton Physics 500 GeV LC Neutrino source Neutrino ring Muon collider (few TeV) 350 GeV LC Multi-TeV LC 2010 2020204020502030 Timescale (personal guess) Plasma Acc Superconducting RF Normal conducting - Two-Beam-based Normal conducting – Klystron-based Multi-TeV LC 4 th Generation SR Sources 5 th Generation SR Sources? PWFA accelerator could likely work with either SC or NC driver linacs – SC option illustrated here.

30. February 1 st, 2008 Page 30 Tor Raubenheimer Example: Plasma Wakefield Acceleration (PWFA) Acceleration gradients of ~50 GV/m (3000 x SLAC) –Doubled energy of 45 GeV beam in 1 meter plasma Major questions remain –Beam acceleration –Emittance preservation –New facilities being developed

31. February 1 st, 2008 Page 31 Tor Raubenheimer Future PWFA Opportunities A TeV Plasma Wakefield Accelerator based Linear Collider … or optimized design using low energy bunch train to accelerate single high energy bunch Single stage afterburner… Other applications: Apply MT/m focusing gradients in plasma ion column to radiation production (Ion Channel Laser) New phenomena (trapped electrons) may offer high brightness sources

32. February 1 st, 2008 Page 32 Tor Raubenheimer X-band R&D Funding Requirements X-band R&D was cut from ~20M$ / year to ~3M$ per year after 2004 ITRP decision –3M$ / year funds US High Gradient Collaboration pursuing fundamental R&D on structure gradient limitations –US and KEK are working with CERN testing high-gradient structure prototypes. Need additional funds to support this. Also urge funding for X-band power source R&D in US –Complete GLC/NLC rf power source development to facilitate a staged approach to CLIC while pursuing fundamental R&D on alternate rf power sources –Infrastructure is already in place  relatively inexpensive to use; however it will be difficult to maintain capability without a program Complete R&D program would ramp to ~10 M$ / year –Roughly 20% of projected FY10 US SCRF and ILC programs

33. February 1 st, 2008 Page 33 Tor Raubenheimer Summary Critical time for linear collider R&D program –Science case for a TeV-scale collider remains strong Need to consider what we as a community need to do to maintain options for energy frontier lepton probes –Options exist with different reaches, timescales, risks and costs ILC is the most developed but X-band options also exist Don’t really know the costs and risks of the different paths –Should have much more information in 2010 ~ 2012 Develop multiple linear collider technologies: need R&D on SC, NC and advanced acceleration concepts –Great potential & many applications of the technology across science –Strong collaborations with ILC GDE as well as CERN and KEK –Extensive infrastructure exists to support X-band and plasma R&D