NLC - The Next Linear Collider Project JLC/NLC Baseline Design and TRC Report Tor Raubenheimer & Kaoru Yokoya ISG9 KEK, December 10 th, 2002

X-band Linear Collider Goals Stage 1: Initial operation (length ~ 18 km) 500 GeV cms (650 GeV at lower luminosity) L = 25 ~ 20x10 33 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 ~ 30x10 33 in JLC and NLC Higher Energy Upgrades: –1.5 TeV with upgrade of linac rf system or length increase NLC injector and beam delivery built for >1.5 TeV –3 TeV+ with advanced rf system and upgraded injector See CLIC parameters: “A 3-TeV e+e- Linear Collider Based on CLIC Technology,” CERN Beam delivery sized for 3 to 5 TeV collisions

Beam Parameters Stage 2 has ~5x10 33 at 1.3 TeV Trade cms energy for beam current Parameters also exist for operation at the Z, W, low-mass Higgs, and top

Change to Baseline Design Initial NLC design presented to the TRC was too difficult (3.2  s klystrons and 8x DLDS pulse compression) –3.2  s klystrons were not on the horizon –DLDS demonstration was years away –TESLA has been making rapid progress both technically and politically However 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 TESLA –1.6  s klystrons were making great progress at KEK –SLED-II only requires 2 klystrons rather than 8 klystrons for DLDS –Concept was already demonstrated with NLCTA operation –At 4x pulse compression, compression efficiency is still quite good

Stolen from Nobu Toge!

JLC/NLC RF System Tests SLED-II Demonstration Spring MW in 400 ns JLC/NLC SLED-II Rf System Layout Delay line in tunnel or gallery

Desired Energy Range Would 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 known –Opinions 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 schemes –Current TESLA scheme does not work between cms 200 ~ 300 GeV Highest energy reach can be attained by trading beam loading for energy –TESLA 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 2 Trade cms energy for beam current Luminosity (10 34 ) Bunches 192 Bunches Both designs can trade luminosity for energy in Stage I TESLA reaches ~ 750 GeV NLC reaches ~ 650 GeV NLC can do the same in Stage II to reach 1.3 TeV NLC trades tighter tolerances for a greater energy reach

Upgrade Routes and Costs NLC and TESLA costs are similar in value for 500 GeV –FNAL review of TESLA costing methods estimated 6.1 B$ with US accounting and 20% contingency –NLC (and JLC?) costs are estimated at ~7 B$ with 30% contingency –The error on the costs is much greater than any differences! JLC/NLC upgrade requires adding structures, klystrons, etc. in the 2 nd half of the linac tunnel –Cost 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-plant –Assuming initial installation of 35 MV/m cavities, cost to upgrade to 800 GeV cms is 20% of initial project cost –Upgrade from 800 GeV to 1 TeV is another 25% for a total of 45% of the initial project cost

SLED-II Implications Changing 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 structures Depends on final modulator configuration –Doubled number of klystrons, modulators, and PC systems and increased the linac length by 8% Obvious cost impact; perhaps some advantage in reliability –Decreased unloaded gradient by 7% Reduced breakdown rate –Very small effect on tolerances and emittance preservation Tolerances scale with the square root of the gradient –Makes 8-pack failure slightly more invasive to beam operation With 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 cryostats –Entering new regime with massive superconducting facility—will limiting effects be found that cannot be seen in TTF? –Many sub-systems are very different from anything demonstrated Particularly true for damping ring complex –Are 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 collider –The technology exists and the tolerances are attainable Present prototypes are better than tolerances Directly use knowledge from SLC: “It’s 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 testing X-band klystron sources took 10 years to develop and can now reliably deliver 500 MW in 150ns CLIC just recently delivered 200 MW in 40ns at 30 GHz in CTF-II but lots of jitter and breakdown even with 40 MW This will change with time, making higher f more attractive however it will take years to develop the suite of rf components –Pulsed heating becomes a severe limitation 900°C pulsed rise calculated in CLIC heavily damped structure Cracking in copper observed with 80°C rise –Do 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 klystrons—TBA drive beam is quite difficult Beam must be steered but beam halo makes diagnostics difficult Drive beam is basically unstable with BBU and large energy spread Operational issues associated with TBA are very difficult –TBA is years from being tested as a system CTF-II is demonstration of concept but not feasibility –Cost 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 collisions –X-band provides essential knowledge base for continued progress in e+/e- colliders

LC Technical Review Committee Energy & Technology Daniel Boussard (Chair) Chris Adolphsen, SLAC Hans Braun, CERN Yong-Ho Chin, KEK Helen 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, SLAC Luminosity Gerald Dugan (Chair) Ralph Assmann, CERN Winnie Decking, DESY Jacques 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, DESY Andy Wolski, LBNL Two working groups (plus reliability)

LC Technical Review Committee The Technical Review Committee (TRC) has led to extensive review of many JLC/NLC and TESLA subsystems –Many 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 studies Benchmarking simulation codes against each other Pushing to include ‘all’ relevant effects –Static alignment procedures –Vibration and stability effects with feedback systems –Beam-beam effects at IP –Integrated luminosity performance very difficult to evaluate –Reliability Group: pushing everybody to arrive at realistic reliability goals with necessary changes to designs –Leading to improvements in all designs: TESLA and JLC/NLC

TRC Conclusions Greg Loew reported at ICFA Seminar –Four levels of R&D priority: R1 = feasibility; R2 = required for design; R3 = before final engineering; R4 = optimization. Energy and technology issues were not unexpected Lots of work on luminosity issues –Conclusions not very sharp –Two unexpected items found in JLC/NLC design Importance of collimator wakefields Jitter amplification of parasitic crossings –Many unexpected items found in TESLA 10x better vacuum and BPM resolution required in TESLA DR Wigglers severely limit dynamic aperture in TESLA DR 100 ~ 150% emittance growth in TESLA linac versus 3% in TDR Large difficulties with head-on collisions –Also learned of things that work in TESLA design  apply to NLC?

TRC Energy & Technology Conclusions Test of complete accelerator structure at design gradient with detuning and damping, including study of breakdown and dark current Demonstration 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 beam Full test of KEK 75 MW, 1.6 µs PPM klystron at 150 or 120 Hz Full 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 beam Testing of several cryomodules at nominal field (23.4 MV/m) over long enough periods to verify breakdown and quench rates, and measure dark current Test of RF components at higher powers for 800 GeV operation R1 R2 R1 R2 JLC/NLC TESLA

TRC Luminosity Conclusions Electron cloud and ion instabilities need study Additional simulations and experiments on  correction are needed for damping rings Demonstrate extraction kicker with better than 0.1% stability Complete static DR  IP tuning simulations with dynamic effects Develop most critical beam instrumentation, including intra- train diagnostics Develop sufficiently detailed prototype of linac girder/cryostat to provide information on vibration Further optimization of damping ring dynamic aperture Study tighter alignment and electron cloud and ion instability requirements for 800 GeV upgrade Development of TESLA DR kicker Review trade-offs between head-on and crossing-angle collisions Detailed analysis of the tradeoffs between one and two-tunnel layouts Detailed evaluation of critical sub-system reliability R2 Common (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 3.5x10 10 NLC: 120 Hz x x10 10  200x Generation of uniform multi-bunch trains sets source requirements Control of long-range wakefields is essential to prevent BBU –Larger beam cross-sectional densities: N / (  x  y ) SLC: 3.5x10 10 x 1.6  m x 0.7  m (FFTB: 0.6x10 10 x 1.7  m x 0.06  m) NLC: 0.75x10 10 x 250 nm x 3.0 nm  330x SLC Factor 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 FY03 Concentrate on improving source designs –Evaluate undulator-based e+ source –Improve energy spectrum at damping ring injection and review multi-bunch limitations Improve damping ring designs –Evaluate e-cloud and ion instabilities and improve wiggler models –Consider alternate ring designs for better stability Improve linac (LET) emittance preservation simulations –Aim towards evaluating integrated luminosity –Must understand reliability issues –Experiments? Continue BDS optimization –More inclusive background/collimation studies Stabilization studies

Polarized Electron Sources JLC/NLC e- source based on successful SLC injector design Emittance estimates reasonable from SLC operation Charge Limit limited current from SLC polarized photocathode Demonstrated charge and polarization during E158 run 14 mm spot in 100ns 20 mm spot in 100 ns SLC photocathode in 300 ns NLC requires ~100 nC per 100 ns Greatly exceeded in E-158 tests Polarization was ~85% NLC Req.

Positron Source Targets SLC 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 investigate SLC e+ target Beam direction SLC target studied at LANL and modeled at LLNL Problem due to embrittlement from radiation damage

Positron Source Concepts Baseline design uses a brute force solution to e+ target limitations –Need to investigate other conventional concepts Studying a variation of TESLA undulator source for polarized positron production –Studies of e+ yield as well as helical undulator and targets –150 GeV location eases operational limitations –Possible test in FFTB line at SLAC

Damping Ring Issues Beam is stored for a relatively long time in the rings (ms) –More accelerator physics in the rings than elsewhere in LC –Stability is essential for collider performance –JLC/NLC rings are similar to the ATF and the 3 rd generation SRS Damping rings have beam currents and bunch trains similar to the high operating luminosity factories –However they have much smaller beam sizes (higher densities) and are much more sensitive to weak instabilities –Tougher dynamic aperture and stability requirements –They also require much better alignment to get flat beams ~ 40 um High beam density pushes frontier in electron machines –Space charge tune depression and microwave instabilities –Ion trapping and electron cloud effects –Intrabeam scattering and short Touschek lifetime

Operating Ring Comparisons Compare random alignment and jitter ‘tolerances’ –Uncorrelated misalignments or jitter that would lead to equilibrium emittance, jitter equal to the beam size, or  = These are not specs. on alignment but they are measures of the sensitivity Looking for significantly better alignment and stability than has been previously attained

Dynamic Aperture Studies Dynamic aperture in rings is difficult for three reasons: –Strong focusing for small emittance –Long wigglers for damping time –Large 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   E Need to improve wiggler model and add field errors –Recent work by Marco Venturini looks like a good start

Impedance Issues Calculated chamber impedance model using MAFIA and Omega3P in 1995 and again in 1998 –Ring layout and components have not changed much Used Oide-san Vlasov code to calculate thresholds –Close to weak threshold and factor of 3 or below strong –Very similar results in 1996 ZDR Recently started calculating CSR impedance from bends and wigglers (Juhao Wu) –Thresholds look similar to that of chamber impedance –Need to combine all sources of impedance and update threshold calculations Also need to consider methods of increasing  p –Increases bunch length and increases threshold

Electron Cloud and Ion Instabilities Electron cloud and ion instabilities are important concerns –Designed ring for 1 nTorr vacuum pressure to reduce ion instability growth times Analytic 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 Preservation Improved optics to avoid known SLC problems BBU from short- and long-range wakefields must be controlled –Measurements at ASSET verify wakefield reduction procedures Tight alignment tolerances –NLC alignment and jitter tolerances are ~10x and 100x tighter than SLC TESLA alignment and jitter tolerances are ~1x and 10x tighter than SLC –Sets tight requirements on diagnostics and controls NLC design includes more controls and diagnostics than FFTB TESLA design include less control and diagnostics than SLC –Demonstrated NLC-level alignment at FFTB –Demonstrated emittance tuning and BNS damping at SLC Will require excellent stability (both vibration and drift) –Need to understand limitations Requires improved simulation tools  integrated luminosity

Coolant Vibration Studies Vibration of accelerating structure caused by turbulent water flow –Measured 300 nm on structure << tolerance –Coupling to quadrupole was measured at about ~3 nm – tolerance is ~10 nm! –Direct coolant induced quad vibration ~2 nm –Direct effect from rf pulse is negligible! –Next step: model complete girder with quad 300 nm at nominal flow

Stabilization Studies Final doublet tol. ~ 1nm Inertial system with 6 d.o.f. tested at SLAC –Limitation due to sensors –Reduced vibration >10x Other inertial studies at CERN Optical anchor system studied at UBC Developing new non-magnetic sensor with better noise characteristics –Working on details before considering a ‘real’ implementation Inertial Stabilization Test Block

FONT: Feedback On ns Timescales Magnet assembly and X-band BPM installed onto NLCTA latency of ~40 ns + cable delay Measured 10x reduction of beam motion Feedback loop Beam direction

Conclusions SLED-II demonstration and Gradient R&D are 1 st priority Luminosity R&D has been very broad and addressed most issues –This is a real strength of the JLC/NLC design –Many test facilities, R&D, and simulation studies –Most sub-systems and diagnostics are modest extrapolations from operating accelerators or demonstrations at test facilities –Collider is designed with an energy reach from 92 GeV to 1.3 TeV Continue to develop models to evaluate reliability and integrated luminosity –Think about next-generation simulation tools Work on multi-bunch issues in source studies Improve damping ring designs and beam injection systems Continue to work on stability issues and BDS optimization

WG1 (Luminosity Issues) Schedule