X-band Linear Collider GoalsStage 1:Initial operation (length ~ 18 km)500 GeV cms (650 GeV at lower luminosity)L = 25 ~ 20x1033 in JLC and NLC

Stage 2:Add additional X-band rf components (length ~ 32 km)1 TeV cms (1.3 TeV at lower luminosity)L = 25 ~ 30x1033 in JLC and NLC

Higher Energy Upgrades:1.5 TeV with upgrade of linac rf system or length increaseNLC injector and beam delivery built for >1.5 TeV3 TeV+ with advanced rf system and upgraded injectorSee CLIC parameters: A 3-TeV e+e- Linear Collider Based on CLIC Technology, CERN-2000-008Beam delivery sized for 3 to 5 TeV collisions

Beam Parameters Stage 2 has ~5x1033 at 1.3 TeVTrade cms energy for beam current Parameters also exist for operation at the Z, W, low-mass Higgs, and top

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#REF!

CMS Energy (GeV)

Luminosity (1033)

Repetition Rate (Hz)

Bunch Charge (1010)

Sheet1

High Energy IP Parameters

Stage 1Stage 2

CMS Energy (GeV)5001000

SiteUSJapanUSJapan

Luminosity (1033)20253025

Repetition Rate (Hz)120150120100

Bunch Charge (1010)0.750.75

Bunches/RF Pulse192192

Bunch Separation (ns)1.41.4

Loaded Gradient (MV/m)5050

Injected gex / gey (10-8)300 / 2300 / 2

gex at IP (10-8 m-rad)360360

gey at IP (10-8 m-rad)44

bx / by at IP (mm)8 / 0.1113 / 0.11

sx / sy at IP (nm)243 / 3.0219 / 2.1

qx / qy at IP (nm)32 / 2817 / 20

sz at IP (um)110110

Uave0.140.29

Pinch Enhancement1.511.47

Beamstrahlung dB (%)5.48.9

Photons per e+/e-1.31.3

Two Linac Length (km)13.827.6

Change to Baseline DesignInitial NLC design presented to the TRC was too difficult (3.2 ms klystrons and 8x DLDS pulse compression)3.2 ms klystrons were not on the horizonDLDS demonstration was years awayTESLA has been making rapid progress both technically and politicallyHowever with progress on the structure gradient, the potential for X-band was clearer than it had been for years!

Needed an rf configuration that could be conclusively demonstrated in ~1 year timescale to compete with TESLA1.6 ms klystrons were making great progress at KEKSLED-II only requires 2 klystrons rather than 8 klystrons for DLDSConcept was already demonstrated with NLCTA operationAt 4x pulse compression, compression efficiency is still quite good

Stolen from Nobu Toge!

JLC/NLC RF System TestsSLED-II Demonstration Spring 2003 500 MW in 400 nsJLC/NLC SLED-II Rf System LayoutDelay line in tunnel or gallery

Desired Energy RangeWould like to cover the Z-pole and W-production and then have continuous energy coverage at energies above LEP (>220 GeV)Upper energy reach needs are not knownOpinions vary around the world (HEPAP and ACFA specify 1 ~ 1.5 TeV while ECFA calls for 400 ~ 800 GeV)

Lower energy operation is limited by e+ production schemesCurrent TESLA scheme does not work between cms 200 ~ 300 GeV

Highest energy reach can be attained by trading beam loading for energyTESLA has 50% loading 50% greater energy reach (providing cavity limits are not exceeded)NLC has 30% beam loading cavities are qualified at unloaded gradients

Energy Reach NLC Stage 2Trade cms energy for beam currentLuminosity (1034)00.511.522.53100011001200130025 Bunches192 BunchesBoth designs can trade luminosity for energy in Stage I TESLA reaches ~ 750 GeV NLC reaches ~ 650 GeV

NLC can do the same in Stage IIto reach 1.3 TeVNLC trades tighter tolerances for a greater energy reach

Upgrade Routes and CostsNLC and TESLA costs are similar in value for 500 GeVFNAL review of TESLA costing methods estimated 6.1 B$ with US accounting and 20% contingencyNLC (and JLC?) costs are estimated at ~7 B$ with 30% contingencyThe error on the costs is much greater than any differences!

JLC/NLC upgrade requires adding structures, klystrons, etc. in the 2nd half of the linac tunnelCost to upgrade to 1 TeV is roughly 30% of initial TPC

TESLA upgrade route: install 35 MV/m cavities at onset, double rf system, upgrade cryo-plantAssuming initial installation of 35 MV/m cavities, cost to upgrade to 800 GeV cms is 20% of initial project costUpgrade from 800 GeV to 1 TeV is another 25% for a total of 45% of the initial project cost

SLED-II ImplicationsChanging the baseline rf system to SLED-II:Faster demonstration of both power source and later a full rf sub-unit, i.e. 1, 2, or 4 klystron pairs powering structuresDepends on final modulator configurationDoubled number of klystrons, modulators, and PC systems and increased the linac length by 8%Obvious cost impact; perhaps some advantage in reliabilityDecreased unloaded gradient by 7%Reduced breakdown rate Very small effect on tolerances and emittance preservationTolerances scale with the square root of the gradientMakes 8-pack failure slightly more invasive to beam operationWith DLDS 8-pack failure probably did not have to scale quadrupole lattice (LEM) with SLED-II almost certainly will

Why X-Band?Why X-band instead of superconducting?Superconducting has loose tolerances and stability however these are not necessary nor are they necessarily easier to achieve in cryostatsEntering new regime with massive superconducting facilitywill limiting effects be found that cannot be seen in TTF?Many sub-systems are very different from anything demonstrated Particularly true for damping ring complexAre the cost of TESLA and NLC similar for comparable energy reach?

Why X-band instead of lower rf frequencies?Support higher gradients: 70 100 MV/m for cheaper colliderThe technology exists and the tolerances are attainablePresent prototypes are better than tolerancesDirectly use knowledge from SLC: Its the diagnostics, stupid!X-band provides essential knowledge-base for continued progress in e+/e- colliders at higher gradients and possibly higher rf frequencies

Why X-Band? (2)Why not higher rf frequencies?Power sources are not available for component testingX-band klystron sources took 10 years to develop and can now reliably deliver 500 MW in 150nsCLIC just recently delivered 200 MW in 40ns at 30 GHz in CTF-II but lots of jitter and breakdown even with 40 MWThis will change with time, making higher f more attractive however it will take years to develop the suite of rf componentsPulsed heating becomes a severe limitation900C pulsed rise calculated in CLIC heavily damped structureCracking in copper observed with 80C riseDo not understand breakdown limits well enough but cannot expect a linear gradient rise with f

Why X-Band? (2)Why klystrons instead of Two-Beam Accelerator at X-band?Experience building reliable repeatable klystronsTBA drive beam is quite difficultBeam must be steered but beam halo makes diagnostics difficultDrive beam is basically unstable with BBU and large energy spreadOperational issues associated with TBA are very difficult

TBA is years from being tested as a systemCTF-II is demonstration of concept but not feasibilityCost is not significantly different at 1 TeV: higher initial value for drive beam complex but lower slope with increasing energy

However, higher frequency normal conducting is probably the only route to higher energy collisionsX-band provides essential knowledge base for continued progress in e+/e- colliders

LC Technical Review CommitteeEnergy & TechnologyDaniel Boussard (Chair)

Chris Adolphsen, SLAC Hans Braun, CERNYong-Ho Chin, KEKHelen Edwards, FNAL Kurt Hubner, CERN Lutz Lilje, DESY (Pavel Logatchov, BINP) Ralph Pasquinelli, FNAL Marc Ross, SLAC (Tsumoru Shintake, KEK) Nobu Toge, KEK Hans Weise, DESY Perry Wilson, SLACLuminosityGerald Dugan (Chair)

Ralph Assmann, CERN Winnie Decking, DESYJacques Gareyte, CERN Witold Kozanecki, Saclay Kiyoshi Kubo, KEK Nan Phinney, SLAC Joe Rogers, Cornell Daniel Schulte, CERN Andrei Seryi, SLAC Ron Settles, MPI Peter Tenenbaum, SLAC Nick Walker, DESYAndy Wolski, LBNLTwo working groups (plus reliability)

LC Technical Review CommitteeThe Technical Review Committee (TRC) has led to extensive review of many JLC/NLC and TESLA subsystemsMany JLC/NLC people are involved directly or indirectly

Energy/technology Group: present status is being studied (compared)Luminosity Group: breaking new ground (collaborative effort)Mainly damping ring studies and DR IP luminosity studiesBenchmarking simulation codes against each otherPushing to include all relevant effectsStatic alignment proceduresVibration and stability effects with feedback systemsBeam-beam effects at IPIntegrated luminosity performance very difficult to evaluateReliability Group: pushing everybody to arrive at realistic reliability goals with necessary changes to designsLeading to improvements in all designs: TESLA and JLC/NLC

TRC ConclusionsGreg Loew reported at ICFA SeminarFour levels of R&D priority: R1 = feasibility; R2 = required for design; R3 = before final engineering; R4 = optimization.Energy and technology issues were not unexpectedLots of work on luminosity issuesConclusions not very sharpTwo unexpected items found in JLC/NLC designImportance of collimator wakefieldsJitter amplification of parasitic crossingsMany unexpected items found in TESLA10x better vacuum and BPM resolution required in TESLA DRWigglers severely limit dynamic aperture in TESLA DR100 ~ 150% emittance growth in TESLA linac versus 3% in TDRLarge difficulties with head-on collisionsAlso learned of things that work in TESLA design apply to NLC?

TRC Energy & Technology ConclusionsTest of complete accelerator structure at design gradient with detuning and damping, including study of breakdown and dark currentDemonstration of SLED II pulse compression system at design power level

Test of a complete main linac RF sub-unit (as identified in machine description) with beamFull test of KEK 75 MW, 1.6 s PPM klystron at 150 or 120 HzFull test of SLAC induction mod. Building and testing of a cryomodule at 35 MV/m and measurement of dark current

Test of a complete main linac RF sub-unit (as identified in machine description) with beamTesting of several cryomodules at nominal field (23.4 MV/m) over long enough periods to verify breakdown and quench rates, and measure dark currentTest of RF components at higher powers for 800 GeV operation R1R2R1R2JLC/NLCTESLA

TRC Luminosity ConclusionsElectron cloud and ion instabilities need study Additional simulations and experiments on e correction are needed for damping ringsDemonstrate extraction kicker with better than 0.1% stabilityComplete static DRIP tuning simulations with dynamic effectsDevelop most critical beam instrumentation, including intra-train diagnosticsDevelop sufficiently detailed prototype of linac girder/cryostat to provide information on vibration Further optimization of damping ring dynamic apertureStudy tighter alignment and electron cloud and ion instability requirements for 800 GeV upgradeDevelopment of TESLA DR kickerReview trade-offs between head-on and crossing-angle collisionsDetailed analysis of the tradeoffs between one and two-tunnel layouts

Detailed evaluation of critical sub-system reliability R2R2Common (JLC/NLC and TESLA)TESLA Only

Luminosity Issues Only few x 10,000 larger than SLC!

Increased beam power from long bunch trains SLC: 120 Hz x 1 bunch @ 3.5x1010NLC: 120 Hz x 192 bunches @ 0.75x1010 200xGeneration of uniform multi-bunch trains sets source requirementsControl of long-range wakefields is essential to prevent BBU

Larger beam cross-sectional densities: N / (sx sy)SLC: 3.5x1010 x 1.6 mm x 0.7 mm (FFTB: 0.6x1010 x 1.7 mm x 0.06 mm)NLC: 0.75x1010 x 250 nm x 3.0 nm 330x SLCFactor of 5 from energy (adiabatic damping) and factor of 4 from stronger focusing (similar to Final Focus Test Beam)Factor of 15 ~ 30 from decrease in beam normalized emittances at IP

Luminosity Issues for FY03Concentrate on improving source designsEvaluate undulator-based e+ sourceImprove energy spectrum at damping ring injection and review multi-bunch limitationsImprove damping ring designsEvaluate e-cloud and ion instabilities and improve wiggler modelsConsider alternate ring designs for better stabilityImprove linac (LET) emittance preservation simulationsAim towards evaluating integrated luminosityMust understand reliability issuesExperiments?Continue BDS optimizationMore inclusive background/collimation studiesStabilization studies

Polarized Electron SourcesJLC/NLC e- source based on successful SLC injector designEmittance estimates reasonable from SLC operationCharge Limit limited current from SLC polarized photocathodeDemonstrated charge and polarization during E158 run

14 mm spot in 100ns20 mm spot in 100 nsSLC photocathode in 300 ns NLC requires ~100 nC per 100 ns

Greatly exceeded in E-158 tests

Polarization was ~85%NLC Req.

Positron Source TargetsSLC e+ target failed after 5 years at stress levels ~2x lower than previously measured and predicted for WRe targets

Radiation damage problem may be worse in Ti targets starting R&D program to investigateSLC e+ targetBeam direction SLC target studied at LANL and modeled at LLNL

Problem due to embrittlement from radiation damage

Positron Source ConceptsBaseline design uses a brute force solution to e+ target limitationsNeed to investigate other conventional concepts

Studying a variation of TESLA undulator source for polarized positron productionStudies of e+ yield as well as helical undulator and targets150 GeV location eases operational limitationsPossible test in FFTB line at SLAC

Damping Ring IssuesBeam is stored for a relatively long time in the rings (ms)More accelerator physics in the rings than elsewhere in LCStability is essential for collider performanceJLC/NLC rings are similar to the ATF and the 3rd generation SRS

Damping rings have beam currents and bunch trains similar to the high operating luminosity factoriesHowever they have much smaller beam sizes (higher densities) and are much more sensitive to weak instabilitiesTougher dynamic aperture and stability requirementsThey also require much better alignment to get flat beams ~ 40 um

High beam density pushes frontier in electron machinesSpace charge tune depression and microwave instabilitiesIon trapping and electron cloud effectsIntrabeam scattering and short Touschek lifetime

Operating Ring ComparisonsCompare random alignment and jitter tolerancesUncorrelated misalignments or jitter that would lead to equilibrium emittance, jitter equal to the beam size, or Dn = 0.001These are not specs. on alignment but they are measures of the sensitivityLooking for significantly better alignment and stability than has been previously attained

Sheet1

ALSAPSATFSLSNLC DRTESLA DR

Energy1.971.32.425

Circ200100014028830017,000

gex [mm-mrad]24342.81538

gey [nm-rad]500140281501314

Yalign [mm]1357487993813

Roll align [mr]860240147553040045

Yjitter [nm]8502803203379391

DK/K [0.01%]1.51.42.11.51.81.1

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Dynamic Aperture StudiesDynamic aperture in rings is difficult for three reasons:Strong focusing for small emittanceLong wigglers for damping timeLarge injected beam size from high-power injector (60 kW)Current calculations look good but have narrow energy acceptance

Want to improve model of incoming beam and reduce sDE

Need to improve wiggler model and add field errorsRecent work by Marco Venturini looks like a good start

Impedance IssuesCalculated chamber impedance model using MAFIA and Omega3P in 1995 and again in 1998Ring layout and components have not changed muchUsed Oide-san Vlasov code to calculate thresholdsClose to weak threshold and factor of 3 or below strongVery similar results in 1996 ZDRRecently started calculating CSR impedance from bends and wigglers (Juhao Wu)Thresholds look similar to that of chamber impedanceNeed to combine all sources of impedance and update threshold calculationsAlso need to consider methods of increasing ap Increases bunch length and increases threshold

Electron Cloud and Ion InstabilitiesElectron cloud and ion instabilities are important concernsDesigned ring for 1 nTorr vacuum pressure to reduce ion instability growth timesAnalytic estimates still give 100 us

Will need to reduce SEY to handle electron cloud

Experiments planned at LBNL to study methods of reducing SEY

Need to understand e- lifetime

Need full simulations: ions are easy; electron cloud more difficult.Calculation by Mauro Pivi

Linac Emittance PreservationImproved optics to avoid known SLC problemsBBU from short- and long-range wakefields must be controlledMeasurements at ASSET verify wakefield reduction procedures

Tight alignment tolerancesNLC alignment and jitter tolerances are ~10x and 100x tighter than SLC TESLA alignment and jitter tolerances are ~1x and 10x tighter than SLCSets tight requirements on diagnostics and controlsNLC design includes more controls and diagnostics than FFTB TESLA design include less control and diagnostics than SLCDemonstrated NLC-level alignment at FFTBDemonstrated emittance tuning and BNS damping at SLCWill require excellent stability (both vibration and drift)Need to understand limitationsRequires improved simulation tools integrated luminosity

Coolant Vibration StudiesVibration of accelerating structure caused by turbulent water flowMeasured 300 nm on structure

Stabilization StudiesFinal doublet tol. ~ 1nm

Inertial system with 6 d.o.f. tested at SLACLimitation due to sensorsReduced vibration >10x

Other inertial studies at CERN

Optical anchor system studied at UBC Developing new non-magnetic sensor with better noise characteristicsWorking on details before considering a real implementationInertial Stabilization Test Block

FONT: Feedback On ns TimescalesMagnet assembly and X-band BPM installed onto NLCTA

latency of ~40 ns + cable delay

Measured 10x reduction of beam motionFeedback loopBeam direction

ConclusionsSLED-II demonstration and Gradient R&D are 1st priorityLuminosity R&D has been very broad and addressed most issuesThis is a real strength of the JLC/NLC designMany test facilities, R&D, and simulation studiesMost sub-systems and diagnostics are modest extrapolations from operating accelerators or demonstrations at test facilitiesCollider is designed with an energy reach from 92 GeV to 1.3 TeV

Continue to develop models to evaluate reliability and integrated luminosityThink about next-generation simulation toolsWork on multi-bunch issues in source studiesImprove damping ring designs and beam injection systemsContinue to work on stability issues and BDS optimization

WG1 (Luminosity Issues) Schedule