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Upgrade of the CEBAF Accelerator to 12 GeV L. Harwood

Upgrade of the CEBAF Accelerator to 12 GeV L. Harwood. What’s the Point?. The 12 GeV Upgrade at Jefferson Lab aims at answering two core questions: 1) What is the nature of quark confinement?

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Upgrade of the CEBAF Accelerator to 12 GeV L. Harwood

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  1. Upgrade of the CEBAF Accelerator to 12 GeVL. Harwood Harwood; AccDiv retreat; 10/3

  2. What’s the Point? • The 12 GeV Upgrade at Jefferson Lab aims at answering two core questions: • 1) What is the nature of quark confinement? • Differently put: why are quarks (the most fundamental building blocks of matter that has been observed) the only particles known in nature that do not exist as individuals, but rather only in close company with other quarks. This question has been identified in a National Academy of Sciences report as one of the ten most important questions for physics in the 21st century. • 2) What is the fundamental nature of the nuclear force in terms of quark and gluon interactions? • Measurements made possible by the 12 GeV Upgrade will provide a major leap forward in the transition from the present phenomenological model of the nucleon-nucleon force to an analytical model based on QCD. This question includes investigation of whether quarks behave differently when bound in a nucleus vs when in the near-free condition explored by elementary particle investigators and explained so elegantly by QCD. Quark Confinement Hall D Analytical model (based on QCD) of nuclei as groups of quarks Halls A, B, & C Harwood; AccDiv retreat; 10/3

  3. Quark Confinement • Quarks are the only particles known that cannot be observed as individuals. They always occur in groups. • This is known as quark confinement. Harwood; AccDiv retreat; 10/3

  4. 1 GeV/fm No radial dependence Mass of 2 quarks Energy in the field Separation distance Quark Confinement (cont’d) • Current “wisdom”: Fq-q = k • Uq-q = kr Implication: Field energy always increases as the quarks separate Quark Confinement There is some separation distance at which field energy: • Exceeds the mass of 2 quarks. • Can be reduced by creating quark-antiquark pair. Never find an isolated quark. Harwood; AccDiv retreat; 10/3

  5. q q Mass of 2 quarks (~600 MeV) q q Energyinthefield Flux tube (many gluons) Separationdistance Quark Confinement (cont’d) Harwood; AccDiv retreat; 10/3

  6. “String” analog Can make mesons with “forbidden” quantum numbers How to “see” the flux tubes Flux tube 2 quarks = 1 meson Spectrum is known. Exotic Mesons Flux tube has it’s own quantum numbers Harwood; AccDiv retreat; 10/3

  7. Observation of exotic mesons • Need a way to create the exotic mesons and distinguish them from the background of normal mesons. • 8-9 GeV polarized photons will do it. • Can use 12 GeV electrons to create the photons. Harwood; AccDiv retreat; 10/3

  8. High-level Parameters • Beam energy 12 GeV • Beam power 1 MW • Beam current (Hall D) 5 µA • Emittance 10 nm-rad • Energy spread 0.02% Harwood; AccDiv retreat; 10/3

  9. Upgrade magnets and power supplies CHL-2 12 11 6 GeV CEBAF Harwood; AccDiv retreat; 10/3

  10. Emittance/energy-spread/optics • Optics in first 5 passes need not be changed • Synchrotron radiation increases the emittance above 6 GeV . Approved by UG-BoD Beam Physics • BBU & HOM damping • 4 GeV needed HOM’s below Q = 1x105 • 12 GeV needs 2x106(easier than 4 GeV specification) Harwood; AccDiv retreat; 10/3

  11. SRF • What is needed? • Present: 6 GeV / 5 passes = 1.2 GeV/pass = 0.6 GeV/linac • 12 GeV: 12 GeV / 5.5 passes = 2.2 GeV/pass = 1.1 GeV/linac • Need to add 0.5 GV/linac • Adding 0.5 GV/linac • There are 5 empty zones at the end of each linac • We’re “there” if we install a 100 MV cryomodule in each zone. Present cryomodules operate at 30 MV on average. What can be done to achieve 100 MV? Harwood; AccDiv retreat; 10/3

  12. Prototype 7-cell cavity 19.2 MV/m 100 MV cryomodules • Simplest change would be to add more cells. • Present 8.5m-long cryomodules have 4.0m of active length. • 7-cell cavities would use 5.6m - OK • Gives 40% more voltage with the same gradient. • 40% helps but is not enough -- Need more gradient • How much gradient is needed? • 100 MV / 5.6 m = 17.5 MV/m • Add 10% for cavities that might be off-line Harwood; AccDiv retreat; 10/3

  13. 19.2 MV/m 250 W Q0 = 8 x 109 100 MV cryomodules - Q0 • Will use one 5 kW cryo plant per linac (details to come) • Each plant must support: • Present needs of each linac • 5 new cryomodules (static and dynamic loads) • 250 W available at 2.05K for each new cryomodule Harwood; AccDiv retreat; 10/3

  14. Goal, ‘01 Cavity Performance (‘01) Ran out of RF power KEK/JLab/DESY collaboration Harwood; AccDiv retreat; 10/3

  15. SRF development Translating cavity performance to performance in full cryomodules • Cryomodule design has been improved • Fewer joints and bellows (reduces particulates) • Magnetic shielding (reduces surface resistance) • Procedures & conditions have been improved • All cavity string assembly is done in the clean room • Helium processing (to deal with any particulates that sneak in) • Need to try it all out: Build test/developmental cryomodules • Two for 6 GeV performance/reliability • One for FEL UV upgrade Harwood; AccDiv retreat; 10/3

  16. Space- frame for 8-cavity string Tuner with helium vessel Prototype 7-cell cavity Space- frame in vacuum vessel Cavity in helium vessel Cryomodule prototyping Harwood; AccDiv retreat; 10/3

  17. SRF development - cell shapes • Cryogenics load and RF power are each linear with the stored energy (U). • Heat load  U/Q0 • Powerdetuning  U fdetuning •  Decreasing U (increasing R/Q) is a very good thing. • Have developed a shape with 16% lower stored energy • Prototype in FY02 • Can we do better? Harwood; AccDiv retreat; 10/3

  18. SRF development (cont’d) • Electropolishing may have eliminated field emission as an issue. • Can reduce concern about surface electric fields • More flexible design-parameter space for cavity shape • New overall optimization possible • Reduce cryo and rf requirements. Should be pursued Harwood; AccDiv retreat; 10/3

  19. Cryogenics • Existing plant is at full capacity with 6 GeV configuration. • New load means we must build a new plant. • We have the major components for a second 5 kW plant. • Spare 2k cold-box • MFTF-B 4K plant • Need to: • Add compressors and oil skids • Add 80K cold-box • Put it all together in a building • Make it all work together Harwood; AccDiv retreat; 10/3

  20. RF Power requirements • Gradient (affects beam power and detuning power) • Cavity performance goal is 19.2 MV/m • Some cavities will be better, some will be worse. • Should be able to use the full potential of the best ones • Plan for 19.2 MV/m + 10% = 21.2 MV/m • RF power requirement is set by: • Beam loading, gradient, R/Q, Qloaded , and cavity’s frequency error. Harwood; AccDiv retreat; 10/3

  21. Actual Qexternal is 70% of optimum (use stub tuners) • 25 Hz of detuning • 4 Hz (2x the tuner resolution of 2 Hz) • 21 Hz (6x the standard deviation of the existing cavities’ noise spectrum) • Need gain.  Don’t run the klystron into saturation. 6.8 kW 12.5 kW RF Power requirements (cont’d) • Beam power per cavity: 6.8 kW at 21 MV/m 13 kW klystrons Harwood; AccDiv retreat; 10/3

  22. Could reach 27 MV/m if microphonics are reduced. Operating envelope with a 13 kW klystron • Presentgoal Allowance for tuner Harwood; AccDiv retreat; 10/3

  23. ~All the power is used to overcome detuning. RF Power (cont’d) • Almost 50% of the rf power is “wasted” dealing with detuning. • Microphonics is the largest contributing source. • Elimination/reduction of detuning  Cost savings. • Reduce the size klystrons that are needed. • Reduce power consumption • Increase klystron lifetime • AND / OR • Operate at higher gradients. • Potential benefit to: JLab, RIA, a neutrino-factory, and ERL’s. Harwood; AccDiv retreat; 10/3

  24. RF Power (cont’d) • New control algorithm (J. Delayen) • Uses small gradient oscillations to damp the microphonics • 0.01% amplitude oscillation results in a 50% reduction in microphonics • If uncorrelated between cavities, effect on energy spread is 5x10-6. • Residual energy error may be correctable with energy feedback system. • “Simple” to implement in a digital system. • The algorithm works on paper; it needs to be tried on a real system. • Development work in FY02 Harwood; AccDiv retreat; 10/3

  25. RF control • Technology choice • Existing systems at JLab are analog (ca. 1990) • “Standard” technology now is digital (flexibility) • May do an analog/digital hybrid (need to review bandwidth) • Algorithm choice • Large Lorentz forces • Narrow bandwidth • Detuning curve is VERY different. • Overall performance requirements are the same as 6 GeV • Amplitude: 1x10-4 • Phase: 0.1º Harwood; AccDiv retreat; 10/3

  26. Peak moves as (gradient)2 -200 0 +200 +400 +600 +800 Frequency relative to master oscillator (Hz) Resonant frequency relative to that at low field (Hz) Lorentz Detuning Effects Tuner must run  slow Is there an alternative? Harwood; AccDiv retreat; 10/3

  27. RF control (cont’d) • Self-excited-loop (SEL) solves the problem. • SEL drives the cavity at its resonant frequency if the external frequency reference is “disconnected”. • Permits quick recovery if a cavity trips off. • SEL’s are already in use for SRF applications, e.g. ATLAS. • International workshop on rf control was held at JLab (April, 2001) • Examined the needs of many machines • Endorsed our plan to use SEL’s. • Also recommended SEL’s for RIA and ERL’s. Harwood; AccDiv retreat; 10/3

  28. RF control (cont’d) • Plans • Conceptual design for rf control module in FY02 • Prototype and debug in FY03 • Pilot run (for testing on full cryomodule) in FY04-05 Harwood; AccDiv retreat; 10/3

  29. Arc 10 Beam Transport • Existing recirculation and transport to halls • 367 Dipoles • 730 Quads • Power supplies • Arc 10 • Transport to Hall D Harwood; AccDiv retreat; 10/3

  30. Saturation occurs in the return leg. • Power would double (beyond that needed if there is no saturation). “CH” magnet New iron Saturation “C” dipole Dipoles • Need more field • Simplest solution is to turn up the current • There is a simple and cheap way to add return iron. Greatly Reduced “CH”dipole Harwood; AccDiv retreat; 10/3

  31. Quads • Present system of 730 magnets (plus power supplies) “works” up to 7.2 GeV. • Samples have been tested at 180% of design current • Field quality acceptable • Do not overheat Changes • 19 replacements in Hall B line • 57 get 20A/50V supplies • 7 get moved Harwood; AccDiv retreat; 10/3

  32. Power pack s Current regulator Magnets Dipole Magnet Power Supplies • The system will use 32 large supplies of varying sizes up to 750kW • 23 can be re-used from the present inventory • 9 new ones must be added • Will use a modular approach Harwood; AccDiv retreat; 10/3

  33. Spreader/recombiner • Original’s were a nightmare • New ones aren’t better • At least they’re perturbations. • Issues: • Hall D beam (6 beams in NE spreader) • Double the dipole fields (saturation….again) Harwood; AccDiv retreat; 10/3

  34. East spreader layout 2.0m 1.5m 1.0m 0.5m 0.0m 0m 5m 10m 15m 20m 25m Harwood; AccDiv retreat; 10/3

  35. S/R dipoles • Problem: Saturation worse than in arcs (return + pole) • Solution: • Add iron where possible • Add turns • Use BIG shunts to deal with lack of tracking between arc and S/R. Harwood; AccDiv retreat; 10/3

  36. Extraction - Upgrade plans • 3-way split is eliminated • RF separators: Add more cavities and run at higher power/cavity • Currently operate the cavities at < 1 kW • Cavities were designed for 5 kW • Have been tested to 2.5 kW • Magnets • Passes 1 and 2: No changes • Pass 3: Add another septum • Passes 4 and 5 • Use Lambertson dipoles instead of “thin” septa • RF separators kick vertically instead of horizontally. • Chao has done a proof-of-principle Harwood; AccDiv retreat; 10/3

  37. Max-min Pathlength - Doglegs Deal with spread using doglegs and orbit shifts Deal with “centroid” by shifting MO frequency Harwood; AccDiv retreat; 10/3

  38. I&C: Network, Diagnostics, Safety • No new development required. • Add stuff for Arc 10 and Hall D line Harwood; AccDiv retreat; 10/3

  39. Civil - Power, Water, & Space • AC power additional loads • RF system: 2 MVA • Magnet power supplies: 10 MVA • Second 5 kW cryogenics plant: 6 MVA • ICW/LCW additional loads • Magnet & RF systems 12 MW • Cryogenics plant 6 MW • Space • Building for CHL-2 • Tunnel to Hall D Harwood; AccDiv retreat; 10/3

  40. Major shutdown. No beam. DOE approves mission need Tech. scope (CDR) and cost envelope Preliminary design complete Cost baseline validation Final design complete. Ready for construction start. Proposed Schedule CHL Magnets, RF, Cryomodules Harwood; AccDiv retreat; 10/3

  41. $213.5M “Down” year Cost Profile Harwood; AccDiv retreat; 10/3

  42. Funding dependent Open questions • Lots of details • Finalized optics and magnets • New klystron • New rf control module • CHL-2 control algorithm • etc, etc, etc Schedule Harwood; AccDiv retreat; 10/3

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