The FRIB Accelerator Project Challenges Progresses Vacuum Aspects

The FRIB Accelerator Project – Challenges, Progresses, Vacuum Aspects J. Wei (speaker), M. Leitner, F. Marti, E. Pozdeyev, D. Sanderson, Y. Zhang For the FRIB Accelerator Team Presented at the Operation of Large Vacuum Systems Workshop (OLAVIII), ORNL, July 11 – 14, 2011

FRIB Project at MSU Project of $614. 5 M ($520 M DOE, $94. 5 M MSU) § § Dec. 2008: DOE selects MSU to establish FRIB June 2009: DOE and MSU sign corresponding cooperative agreement Sept. 2010: CD-1 granted; conceptual design complete & preferred alternatives decided June 2012: CD 2/3 A pursued; performance baseline & start of conventional facility construction Growth from more than 400 employees today at NSCL, MSU More than 700 registered user at NSCL user group and at FRIB user organization J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 2

Outline § Project overview § Accelerator challenges § Vacuum related aspects • • • Beam loss due to charge exchange (e. g. capture of electron) Control of vacuum pressure near front end Control of vacuum pressure near target/fragment seperator Gas desorption and mitigation Charge stripping section consideration » Plasma window & differential pumping • Machine protection • Maintenance § Summary J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 3

Goal – A DOE National User Facility J. Wei et al, OLAVIII, 11 July 2011, Oakridge , Slide 4

Building Blocks of a Rare Isotope Beam Facility A heavy-ion driver can also accelerate light ions needed for an ISOL facility J. Wei et al, OLAVIII, 11 July 2011, Oakridge

FRIB Complex Layout Uranium beam example J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 6

FRIB Driver Accelerator Layout § Delivers FRIB accelerator as part of a DOE-SC national user facility with high reliability & availability § Accelerate ion species up to 238 U with energies of no less than 200 Me. V/u § Provide beam power up to 400 k. W § Satisfy beam-on-target requirements § Energy upgrade by filling vacant slots with 12 SRF cryomodules § Maintain ISOL option § Upgradable to multiuser simultaneous operation of light/heavy ions with addition of a light-ion injector J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 7

Baseline Requirements & Upgrade Goals § Baseline requirements • Energy and ion species » Up to 238 U with energies of no less than 200 Me. V/u • Beam power: up to 400 k. W • Beam on target interface § Science driven upgrade options • Energy upgrade by filling vacant slots with 12 SRF cryomodules » Reaching 400 Me. V/u for 238 U, e. g. when the HWR gradients are raised by 35% • ISOL option » Allow for addition of beam delivery to future ISOL target • Multiuser simultaneous operation of light/heavy ions with light-ion injector » Simultaneous 3 He and 238 U operations J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 8

Primary Technical Challenges § FRIB combines the technical features of a heavy ion accelerator (like RHIC) and a high power accelerator (like SNS/ESS), becoming uniquely challenging in several aspects • Solid charge stripper can no longer sustain the high-power heavy ion beam; developing liquid stripping and alternative gas/plasma stripping • Multiple charge states of heavy ions need to be accelerated simultaneously to the target; demanding sophisticated optics and diagnostics • Superconducting RF acceleration for a cw beam from very low to intermediate velocity • Ability to simultaneously accelerate heavy ion and light ion beams • Low uncontrolled beam loss demanding appropriate low-loss accelerator design, beam collimation and shielding • Stringent beam-on-target requirements demanding strategic staging planning J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 9

FRIB Accelerator Design Philosophy § Deliver FRIB Accelerator as part of a DOE-SC national user facility • Meet Experimental System’s requirements with optimized designs • Use proven technology as much as reasonably achievable (AMARA) • Use commercial fabrication as much as reasonably achievable (AMARA) § Meet Accelerator Systems challenges • High intensity & power, diverse scenarios, largest cw hadron SRF linac § Support Conventional Facilities CD-3 A; deliver CD-2 • Team & culture readiness; design readiness; technical R&D readiness; acquisition plan readiness • Proceed long-lead procurement items (cryoplant) § Seek collaboration & best value practices • Engage national laboratories for the best value & collaborate worldwide § Preserve upgrade paths • Energy upgradability; ISOL option; multiuser operation of light/heavy ions J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 10

Accelerator Design & Requirements Support Multiple Operational Scenarios § Proposed baseline scenario • Operating liquid Li stripper for U 78+ § Alternative scenario • Operating He gas stripper for U 71+; adding 3 cryomodules to reach 200 Me. V/u § Fault scenario • Tolerate cavity failure for U 63+; higher availability at reduced energy & power 238 U beam Scenario Proposed Baseline Alternative Fault Charge state (average) 78+ 71+ 63+ Energy [Me. V/u] (baseline) (baseline + 12 C. M. ) + 3 C. M. ) + 12 C. M. ) (35% gradient enh. for b=0. 29 & 0. 53) 201 179 155 228 202 176 306 275 247 413 375 342 J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 11

Accelerator Layout Optimized Accommodate Both Baseline & Alternative Stripping Schemes § Adjusted accelerator layout to allow open cutting of the tunnel, resulting in significant savings in construction Preliminary configuration § Folding Segment 1 buncher layout optimized • Accommodates energy spread caused by straggling due to He stripping • Improves performance with Li stripping Preferred new configuration § Linac Segment 1 extended • Accommodate multiple user options (20 MHz spacing scenario) & extra pumping J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 12

Design Efforts to Improve Accelerator Availability LS 1 Cold BPM for On-line Tuning § CD-1 lattice design doesn’t allow tuning of whole machine at once • Lattice only allows one-at-a-time steering making tuning operationally impractical (warm BPM at unfavorable phase-advance locations) § Implement 44 “cold” beam position monitors (BPM) – allowing practical beam steering for increased accelerator availability • Cold BPM facilitates response-matrix-based on-line tuning for greatly improved machine availability QWR cryomodule with 3 solenoids and 3 BPMs Dual-plane BPM J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 13

ASD Key Collaborators § ANL • Liquid lithium stripper • Beam dynamics verification • β=0. 285 HWR design and prototype* § BNL • Plasma window & charge stripper, physics modeling, database § FNAL • Diagnostics § JLab • Cryogenics systems design • QWR & HWR Hydrogen degassing • PANSOPHY e-traveler • HWR processing & certification* § LBNL • ECR ion source; beam dynamics** § ORNL • Diagnostics, controls § SLAC** • Cryogenics**, SRF multipacting**, physics modeling § RIKEN • Helium gas charge stripper § TRIUMF • Beam dynamics design, SRF, physics modeling § INFN • SRF technology § IMP • Magnets* § COSYLAB • Machine protection controls § Budker Institute, INR Institute • Diagnostics § Tsinghua Univ. & CAS • RFQ* * Under discussion or in preparation ** Completed , Slide 14

Systematic Approaches to SRF Issues Started in November 2010 § Lessons learned; culture adjustments in progress to meet FRIB demands § Sept 2010: major reorganization in MSU/FRIB accelerator division § Nov 2011: systematic approaches started to be implemented § Managerial approach • Recruiting top SRF experts from the world • Closely collaborating with world experts in defining mitigation strategy § Technical approach • Detailed planning and execution of each of 4 types of SRF cavities • Enhancement in diagnostics to understand malfunction mechanisms • Systematic engineering to correct design flaws • Timely engineering re-design to meet FRIB requirements • Infrastructure upgrade to sustain long-term growth § Acquisition strategy • Growing vendor base and encouraging competition • Working closely with vendors on technology transfer and readiness • Working closely with vendors to share the risks and optimize the cost J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 15

Aug 2010 July 2011 § Aggressive recruiting key team members • Latest recruitment 1: Sheng Peng as Controls Department Head • Latest recruitment 2: Tom Russo as ASD Project EE, Electrical Department and Diagnostics Group Head § Strengthened SRF department • A. Facco (LNFN) on sabbatical heading SRF Group • Weekly SRF teleconference: P. Kneisel (JLab), B. Laxdal (TRIUMF), C. Crawford (Cornell), K. Saito (KEK) § Top experts on FRIB part time • J. Nolen (ANL); J. Stovall, L. Young J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 16

Re. A 3 as FRIB Technology “Prototype” Installed or close to final installation (EBIT) Q/A Pilot source MHB RT RFQ 0. 041 modules 0. 085 module FY 12 § Re. A 3 is a MSU contribution to FRIB § Re. A 3 shares similar technologies as the FRIB driver LINAC § Re. A 3 provides data for the FRIB engineering, commissioning and installation planning, beam physics, and development of the control system J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 17

β=0. 041 SRF Cavity Successfully Accelerates Beam at Re. A 3; Tested for FRIB Gradients § Apr 2011: Beam acceleration achieved for the 1 st time at MSU using an SRF cavity § May 2011: β=0. 041 cryomodule accelerated beam as designed § Some cavity performing at world record accelerating gradient § Lessons learned with β=0. 041 cryomodule tests • Installation, multipacting & controls, cleanness, tuner design, interlock transients J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 18

β=0. 53 SRF HWR Performance Demonstrated with Vendor-built Cavities § FRIB prototype cryomodule in fabrication with 2 cavities & 1 solenoid • Existing 5 cavities: 3 tested; 3 shipped to JLab for degassing § Preparation of full pre-production cryomodule (8 cavities) with optimized design; request for proposal ready to be released J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 19

β=0. 53 SRF HWR Performance Summary with Vendor-built Cavities § Test history • July 2010: Test of MSU-built cavity (A) • March 2011: Tests of cavities partially built by vendors (C, D) • Typically 3 rounds of processing § Work to be done • Test with He vessel • Test in prototype cryomodule MSU-built cavity Partly built by vendor C, D J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 20

β=0. 085 SRF QWR Cavity Performing at Both 4 K and 2 K Temperatures J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 21

Leading Vacuum Related Aspects § Beam loss due to charge exchange (e. g. capture of electron) • Hands-on maintenance requiring average uncontrolled beam loss < 1 W/m § Control of vacuum pressure near front end • J-PARC: insufficient pumping and hydrogen saturation at LEBT causes stripping in RFQ. Need to replace ion pump and TMP with cryopump § Control of vacuum pressure near target/fragment separator • Target area (400 k. W beam) vacuum ~ 104 worse than accelerator side § Gas desorption and mitigation • Severe for high charge state at low energy; coating? Collimation? § Charge stripping section consideration • Liquid lithium, or He gas with plasma window & differential pumping § Machine protection § Maintenance J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 22

Initial Success on Charge Stripper R&D [1] Progress on Liquid Lithium R&D § Stripped charge state determines cryomodules needed to reach energy § FRIB can accommodate switchable stripper assemblies • Liquid lithium stripper: project baseline; FRIB supported R&D Phase 1 successfully completed at ANL » Established Li film stable with time; thickness controllable » Need to confirm integrity of film with FRIB-equivalent beam power deposited • Intense proton beam ion source on loan from LANL » Need to confirm stripped electron effects Liquid Li stripper system under development at ANL

Initial Success on Charge Stripper R&D [2] Progress on Helium Gas & Plasma Window R&D • Helium gas stripper: alternative to baseline; partly demonstrated at RIKEN » RIKEN beam test at lower (11 Me. V/u) energy and gas density » Cross section measured at 14 and 15 Me. V/u, closer to FRIB design energy of 17 Me. V/u » Need to increase the gas density – plasma window / differential pumping » Need to confirm performance at FRIB beam energy » Requires 3 additional cryomodules • Plasma window for He stripper & plasma stripper: FRIB supported R&D at BNL » Plasma window initial firing performed at BNL verifying vacuum performance » Need to optimize assembly geometry for beam threading Beam out MIT plasma window recently fired at BNL Beam in Plasma window test setup at BNL J. Wei et al, OLAVIII, 11 July 2011, Oakridge

Gas stripper contained by plasma windows L~ 30 cm Differential pumping Plasma Window Gas cell Plasma Window Differential pumping P~ 1/3 atmosphere 2 mm hole in plasma window between gas cell and differential pumping station A. Hershcovitch and P. Thieberger (BNL) J. Wei et al, OLAVIII, 11 July 2011, Oakridge , Slide 25

Pressure Versus He Concentration § Pressures as function of He concentrations for ½ atmosphere of He-Ar mixtures maintained in the gas cell and 12 A per cathode in the plasma window J. Wei et al, OLAVIII, 11 July 2011, Oakridge , Slide 26

Plasma Window Conductance Reduction Factor § Helium pressure in the chamber adjacent to the gas cell as function of the gas cell pressure with the PW off. The red curve is a parabolic fit to the data. The value of 2. 42 Torr in the chamber with 380 Torr in the gas cell was used to calculate the Plasma Window Conductance Reduction Factors(PWCRF) shown on the figure MIT PW Conductance Reduction Factor (PWCRF) as function of average cathode current and total PW power input. The line is a linear least squares fit to the data J. Wei et al, OLAVIII, 11 July 2011, Oakridge , Slide 27

Vacuum Induced Beam Loss Mechanism in FRIB Front End § Main beam loss mechanism in the Front End is the charge exchange (charge pickup): Xi + N 0 = Xi-1 + N+. § Charge pickup cross section at low energy (Salzborn, q-charge, Iionization potential): § Charge pickup cross section was measured in ARTEMIS line for Ar 7+, Ar 11+, Xe 14+, Xe 20+ (MSU, G. Machicoane, E. Pozdeyev, L. Sun, 2010) Ion Species Ar 7 Ar 11 Xe 14 Xe 20 Cross section (Salzborn, m 2) (Experiment, m 2) 8. 63471 E-19 1. 71 E-18 1. 46525 E-18 2. 40 E-18 1. 94291 E-18 3. 56 E-18 2. 94909 E-18 4. 58 E-18 Ratio Exp/Calc 1. 98 1. 64 1. 83 1. 55 J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 28

Front End Vacuum and Pumping Requirements § ECR area base vacuum: 1 e-8 Torr • Operational pressure <1 e-7 § The rest of the LEBT base vacuum: 5 e-9 Torr • Operational pressure 5 e-9 to 5 e-8 Torr § RFQ area base vacuum 1 e-8 Torr • Operational pressure <1 e-7 § MEBT base vacuum 5 e-9 Torr § Vacuum turbo-pumps with scroll-pumps • Ion pumps produce magnetic field, require shielding § Beam pipe size increased to 6” to facilitate pumping and satisfy beam dynamics requirements § Pumps every 10’, increased pumping next to ECRs, collimators, RFQ § Most systems compatible with low-temperature bake (120 C) J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 29

Linac Segments Dominated by Cold Surfaces § Cryomodule – separate vacuum system • Beam vacuum • Insulation vacuum § Warm section Gate valve Beam pipe Cavity (2 K) Solenoid (4 K) Diagnostics box Linac segments include cryomodules and warm sections between cryomodules. Beam vacuum 5 E-9 torr for room temperature or equivalent particle density, limit fractional beam loss due to charge exchange <1 E-4. Warm section length 38 cm, need to prevent backflow of vacuum pump. J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 30

Vacuum Level and Constraints § Front End: < 3 E-07 Torr § Charge selection section; RFQ: <5 E-08 Torr § LEBT; MEBT: < 1 E-08 Torr § Linac superconducting segments: 5. 0 E-09 Torr § Charge stripper section: 1 E-06 Torr (liquid Li); 3 E+02 Torr (He gas) § Target and fragment separator section: ~ 1 E-04 Torr § Re. Accelerator: ~ 1 E-08 Torr (similar to driver linac) § Constraints on the vacuum hardware • No city water cooling in the linac tunnel • All hardware must be UHV compatible and bakable to > 100 deg C • Near the cryomodules, the installation must be low-particulate with clean room operations J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 31

Machine Protection and Beam Permits § Machine protection response time is about 35 ms • Detection: beam diagnostics system like fast beam loss monitor and current monitor (~ 15 ms) • MPS system processing (~ 10 ms) • Mitigation: electrostatic deflector near RFQ (to empty residual beam ~10 ms) § Fast valves (~ms) to protect cryomodules from contamination • Beam permit with magnet and cavity power supply, fast valves, etc. 43 CSS FD 1 SS 6 2 LS 3 RC 5 1 FE LS 1 LS 2 FD 2 J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 32

Separate Cryostats to Allow Maintenances § Two gate valves for each cryomodule, allowing independent installation, commissioning, and maintenance A rebuncher cryomodule with two gate valves at the two ends J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 33

Gas Desorption & Mitigation § Electron cloud effects do not seem to be an issue for FRIB • Single-pass cw linac, low average current § Gas desorption is severe for beams of high charge state at low energy § Vacuum chamber surface coating with Non Evaporative Getter is likely to saturate quickly § Consider using collimator to localize beam loss to regions with fast pumping Beam dump Charge stripping Collimation & shielding J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 34

FRIB Is On Track Towards CD 2/CD 3 A FY FY FY GOVERNMENT FISCAL YEAR Schedule range Manage to early completion in 2018 Rev. 4/29/2011 Paced by Funding Profile Paced by Facilities Paced by Installation & Test J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 35

Summary § The FRIB Project is moving forward at accelerated speed – progresses are made to meet the challenges § Vacuum aspects are challenging and exciting § We desire a close collaboration with the community § We are looking for motivated colleagues to join FRIB! § THANK YOU! § This material is based upon work supported by the U. S. Department of Energy Office of Science under Cooperative Agreement DE-SC 0000661 J. Wei et al, OLAVIII, 11 July 2011, Oakridge, Slide 36