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The Engineering Test Facility for nLC

The Engineering Test Facility for nLC. ALCPG Victoria, BC July 30, 2004. Introduction. Linear collider project goals: Construct a collider with an initial energy of 500 GeV that can be upgraded to 1 TeV later Deliver 500 fb -1 in the first four years of physics operation

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The Engineering Test Facility for nLC

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  1. The Engineering Test Facility for nLC ALCPG Victoria, BC July 30, 2004

  2. Introduction • Linear collider project goals: • Construct a collider with an initial energy of 500 GeV that can be upgraded to 1 TeV later • Deliver 500 fb-1 in the first four years of physics operation • Begin physics operation in 2016 (one year commissioning) to ensure concurrent operation with LHC • Discussion of project risk earlier this morning • R&D program should be focused on reducing project risk • Different stages of development process • Fundamental R&D – technology development or beam physics understanding • System engineering/integration – can it go together and does it work together • Industrialization and mass production – can components be produced

  3. The Engineering Test Facility(s) • Critical elements that the ETF must address: • E+ source target/capture • Damping ring beam physics • Main linac rf system production • Main linac emittance/jitter control • BDS collimators/stabilization/machine-detector interface • Some additional long-lead time or difficult components • Cannot and do not want to do this in a single test facility • Final configuration is subject to constraints due to resources and schedule and must be chosen with a goal of reducing the project risk

  4. Damping Ring Test Facilities • Beams are stored in the rings for a long time • Small (subtle) effects can have a large impact • Many novel effects will be important due to small emittances and tight stability requirements • Rings are quite different from other operating accelerators • ATF has been a very important test facility • Probably not possible to duplicate for cold design  adds some risk but how much and what can be done in other studies?

  5. Main Linac e-control • Given tolerance specs, instrumentation, and algorithms, the emittance performance is similar in warm and cold • Dge ~ 10nm over 5 to 10 km • Very hard to measure in a small facility • Complicated source – ATF is the only source that comes close • Not simple to scale to lower energies or amplify the effects • Real issue is performance/interaction of diagnostics and controls • Most algorithms are local  use dedicated tests of local systems • Rf structure girder alignment test • Cryomodule alignment study

  6. Main Linac RF Systems • Need to produce some number of complete rf sub-units • Rf subunit has 5-m of structures in X-band • Rf subunit has 36-m of structures in L-band • Demonstrate stable operation of a few units • With/without beam? • Beam is desired to verify rf operation stability and gradients • Forces a more rigorous approach • Be nice to use beam for centroid studies of trajectory control and verify instrumentation • Need engineering studies to optimize fabrication and lifetime • Don’t need to produce every component though

  7. Possible Examples of a big RF ETF

  8. e-control: Wakefield Effects • Primary tolerance is set by short-range wakefields • Girder of 4 structures must be aligned at 3 um level for NLC • In the ETF with a 300 um bunch length and 7.5e9, the kick of the beam tail is roughly 80 V * sqrt(Nrf) • At 1 GeV, this is ~0.1 urad as compared to the beam angular divergence >1urad for an emittance of 2e-8 • Very difficult to verify performance from emittance growth alone • Ways to increase the sensitivity: • Increase bunch length or bunch charge by ~5x • Use long-range wakes with 4- and 8-bucket spacing • This is a dedicated test of an rf-girder not a test in a long (or short) linac

  9. ETF Luminosity Study Implications • Even with nominal GLC/NLC emittances and 50-meter ETF cannot verify tolerances with emittance • ATF-III is still factors of five too insensitive to verify GLC/NLC performance requirements • Jitter measurements are best done with accelerometers • Alignment tolerance verification: • Bunch centroid or beam tilt for wakes and dispersion • Beam tilt: • 1.7 mrad in 300 um bunch  close to desired tolerances • Beam centroid • Works fine for dispersion • Use dedicated facility to verify wakefields and e-control

  10. The Engineering Test Facility(s) • Small scale (~1 GeV) rf test facility with multiple rf units • Include beam to verify low-level rf control and gradients • Include good (but not nLC) beam for e-control studies • Many other test facilities of smaller but similar scale • Dedicated studies of most relevant systems • Focused test can yield scientifically relevant information • Do NOT try to focus all effort (and resources) on one large showpiece which demonstrates little (but an ability to spend money – important but not essential at this time) • Caveat: major schedule delay would increase the importance of a large showpiece for political reasons

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