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Tor Raubenheimer
CLIC and Other Optionsfor Multi-TeV Lepton Physics
Tor Raubenheimer
Accelerator Research Division Head, SLAC
P5 Meeting
Fermilab
February 1st, 2008
February 1st, 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
February 1st, 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
February 1st, 2008 Page 4 Tor Raubenheimer
Two-Beam Accelerator Concept(from R. Corsini; 2006 parameters)
February 1st, 2008 Page 5 Tor Raubenheimer
CLIC RF Module ~ 2 metersMain Beam ~1 ADrive 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
February 1st, 2008 Page 6 Tor Raubenheimer
CLIC Schematic (2007 Parameters for 3 TeV)
Injector systems similarto other LC concepts
Drive beam complex efficientlygenerates 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 klystronsas 500 GeV ILC
February 1st, 2008 Page 7 Tor Raubenheimer
CLIC Linear Collider Parameters
February 1st, 2008 Page 8 Tor Raubenheimer
Possible CLIC Siting Option
IP under CERN Prevessin sitePhase 1: 1 TEV extension 19.5 kmPhase 2: 3 TeV extension 48.5 km
Detectors and Interaction Point
CERN sitePrevessin
February 1st, 2008 Page 9 Tor Raubenheimer
Proposed Timescale(from JPD presentation to CERN SPC)
February 1st, 2008 Page 10 Tor Raubenheimer
0
50
100
150
200
250
300
350
400
450
0 500 1000 1500 2000 2500 3000
% o
f 50
0 G
eV N
LC
NLC
TBLC
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 comparisonof 1996 NLC versus X-band TBA costs by G. Loew
Cms GeV
February 1st, 2008 Page 11 Tor Raubenheimer
GLC/NLC >50 MV/m Operation
Unloaded Gradient (MV/m)
Bre
akd
ow
n R
ate
at
60
Hz
(#/h
r)w
ith
40
0 n
s Pu
lses
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
February 1st, 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
February 1st, 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 techniquesDifficulties• Full scale structures are complex and expensiveSolution• 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.
0.1
1
10
100
1000
90 100 110 120 130 140
75 ns150 ns300 ns
Gradient [MV/m]
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
February 1st, 2008 Page 14 Tor Raubenheimer
CTF3 – CLIC Test Facility
• Large-scale LC test facility to demonstrate TBA concept
DL
CLEX 2007-2009building in 2006/7
2004 2005Thermionic gun
CR
TL2 2007-2008
30 GHz production(PETS line)and test stand
Photo injector / lasertests from 2008
D FFD
D F D
D F D D F D
D F D
DF DF DF DF DF DF DF DF DF
D F D
F DF D
D FFFDD
D F DD F D
D F DD F D D F DD F D
D F DD F D
DF DF DF DF DF DF DF DF DF DFDF DF DF DF DF DF DF DF DF DF DF DF DF DF DF DF
D F DD F D
F DF DF DF D
Linac
Beam up to here
2007
Major milestones in 2007:Combiner Ring (CR) installedCLEX building finished, equipment installation started
150 MeV 30 A - 140 ns
February 1st, 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
February 1st, 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
February 1st, 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 powercost per MW by 2x or double shunt imped. to increase G by 40%
Unloaded Gradient (MV/m)
Rel
ativ
e T
PC
At low gradient, cost increases due to larger length costs
At high gradient, cost increases due to higherrf power costs
GLC/NLC X-band
February 1st, 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 whatdrives the frequencyscaling but the basicform makes sense
– Believe that there isan assumption thatabove 10 GHz, thegradient is independentof frequency
– Main point: very highgradients don’t make cost sense
PreviousNewOptimum
Cost
February 1st, 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
February 1st, 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
February 1st, 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 2020 2040 20502030Timescale (personal guess)
Plasma Acc
Superconducting RF
Normal conducting - Two-Beam-based
Normal conducting – Klystron-based
Multi-TeV LC
4th GenerationSR Sources
5th Generation SR Sources?
The LC roadmap illustrates options and connections between them. Selecting a path requires additional information suchas LHC results and technology status
February 1st, 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 2020 2040 20502030Timescale (personal guess)
Plasma Acc
Superconducting RF
Normal conducting - Two-Beam-based
Normal conducting – Klystron-based
Multi-TeV LC
4th GenerationSR Sources
5th Generation SR Sources?
February 1st, 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
February 1st, 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)
February 1st, 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.
February 1st, 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 2020 2040 20502030Timescale (personal guess)
Plasma Acc
Superconducting RF
Normal conducting - Two-Beam-based
Normal conducting – Klystron-based
Multi-TeV LC
4th GenerationSR Sources
5th Generation SR Sources?
February 1st, 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 RF Superconducting 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
February 1st, 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
February 1st, 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 2020 2040 20502030Timescale (personal guess)
Plasma Acc
Superconducting RF
Normal conducting - Two-Beam-based
Normal conducting – Klystron-based
Multi-TeV LC
4th GenerationSR Sources
5th Generation SR Sources?
PWFA accelerator couldlikely work with either SCor NC driver linacs – SCoption illustrated here.
February 1st, 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
February 1st, 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
February 1st, 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
February 1st, 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
Recommended