Technical aspects of the ATLAS efficiency & intensity upgrade

1. Technical aspects of the ATLASefficiency & intensity upgrade Peter N. Ostroumov ATLAS Users Workshop, August 8-9, 2009

2. Content • Limitations of the current ATLAS configuration • Efficiency of CARIBU beams • High-intensity ion beams (~0.1 mA) • ATLAS, >10x intensity upgrade • Phase I & II • Phase I: ARRA funding • New CW RFQ • New G=0.075 cryomodule • Upgrade of LHe distribution system • Current technical developments related to AIP and ARRA • Linac design optimization • Prototyping the cavity sub-systems • Development of new QWR, G=0.075 • RFQ: hardware development and test • SC cavity EM optimization and mechanical design • Initial studies of EBIS charge breeder for CARIBU

3. The goal PHASE I, ARRA, $9.86M project • Increase overall transmission of any ion beam including CARIBU radioactive beams to 80% as compared to the intensity of DC beam from the ion source or charge breeder • Deliver ~5 MeV/u medium-intensity (~10 pA), medium-mass ion beams for experiments related to the synthesis of superheavy elements • Increase reliability and efficiency of the LHe distribution system • Deliver full ATLAS energies at beam intensities of 1 pA PHASE II, additional $35M • Increase efficiency of charge breeding by using EBIS • For low intensity CARIBU beams (≤107 ions/sec) the efficiency can reach ~15% • Produce and accelerate stable ions to 6-16 MeV/u (depending on Q/A) with intensity up to 10 pA • Increase existing ATLAS capabilities for low-intensity ion beams with improved acceleration efficiency (beam energies from 10.2 to 26 MeV/u)

4. Efficiency and Intensity Limitations of the current ATLAS • Previous generation ECR • Low Energy Beam Transport • Multi-Harmonic Buncher • Low voltage, strong space charge effects • As a result not efficient for high current beams (>10 pA) • Low transverse acceptance of the first PII cryostat • The aperture diameter of the first cavity is 15 mm, the second cavity – 19 mm • The transverse acceptance is ~0.6  mm-mrad, normalized • Strong transverse-longitudinal coupling in the first cavities at high field – emittance growth • Longitudinal emittance growth • Non-adiabatic motion in the phase space, low acceptance, emittance growth for high-intensity beams and beam losses • Beam steering in the split-ring cavities, especially for light ions • RF system was not designed to compensate beam loading • Cryogenics, Radiation Shielding, Control system, Beam diagnostics,….

5. Current ATLAS Layout New cryomodule Tandem CARIBU

6. Feasible solutions • ECR: Upgrade existing ECR • EBIS: Increase efficiency of CARIBU beams by factor of 2 and higher • Low Energy Beam Transport: Re-design, more frequent focusing, possibly electrostatic • Multi-Harmonic Buncher • Increase voltage (water cooling), move closer to the RF accelerator • Low transverse acceptance of the first PII cryostat • Replace with the normal conducting RFQ accelerator • Longitudinal emittance growth due to high accelerating fields • Adiabatic acceleration in the RFQ up to ~250 keV/u, no emittance growth • Beam steering: Replace two Booster cryostats with new cryostat with 6 or 7 /4 cavities • RF system was not designed to compensate beam loading: New couplers, new RF system • Cryogenics, Shielding, Controls, Diagnostics,….Upgrade

7. Beam time structure and intensities • Maintain 12.125 MHz beam time structure – 80 ns between bunches In the following discussions: Low intensity ion beams (CARIBU) ≤ 0.1 pA Medium intensity ion beams ~1.0 pA (current ATLAS performance) High intensity ion beams ~10 pA

8. ATLAS High-Intensity Upgrade, PHASE II (Total $45M) • 14 QWR, G=0.075, f=72.75 MHz • EBIS charge breeder • Upgraded ECR • Gas cell and Mass Separator Gas cell + Mass Separator Available space for future experiments 2 Booster and 2 ATLAS cryomodules EBIS CARIBU MHB RFQ MEBT 2 new cryomodules Energy upgrade cryomodule

9. Phase I: Beam energies as function of Q/A • 2 PII Cryo.  12 cavities (existing) • 1 New Cryo.  6 QWR @ 72.75 MHz for β ~ 0.075 (new) • 3 Booster Cryo.  16 cavities (existing) • 2 ATLAS Cryo.  12 cavities (existing) • 1 Upgrade Cryo.  7 QWR @ 109.125 MHz for β ~ 0.15 (existing) Note: High intensity energy is before the booster Low intensity energy is the full energy

10. Phase I: Example Beams Note: High intensity energy is before the booster Low intensity energy is the full energy

11. Phase I: Q/A = 1/7 - Cavity Voltage Profile 2 PII 1 New 3 Booster 2 ATLAS 1 Upgrade

12. 2 PII Cryo.  12 cavities (existing) 2 New Cryo.  14 QWR @ 72.75 MHz for β ~ 0.075 (new) 2 Booster Cryo.  12 cavities (existing) 2 ATLAS Cryo.  12 cavities (existing) 1 Upgrade Cryo.  7 QWR @ 109.125 MHz for β ~ 0.15 (existing) Phase II Note: High intensity energy is before the booster Low intensity energy is the full energy

13. Phase II: Example Beams Note: High intensity energy is before the booster Low intensity energy is the full energy

14. ATLAS Efficiency and Intensity Upgrade schedule (PHASE II)

15. ATLAS High-Intensity Upgrade: PHASE I (ARRA) • Modify PII-1, install RFQ • G=0.075, f=72.75 MHz – one cryomodule • LHe system upgrade CARIBU MHB RFQ MEBT New cryomodule Energy upgrade cryomodule

16. PHASE I – ARRA • Build new RFQ to boost beam energy to ~250 keV/u for q/A=1/7 • 80% efficiency of bunching and acceleration, upgrade MHB • Capable to accelerate 1 mA beams • Build a new cryomodule with ~6 SC cavities, G =0.075 • Capable to accelerate 1 mA beams • New high-power coupler • Based on design of the Energy Upgrade Cryomodule • Modify the first cryomodule of the PII • Remove the first 2 cryomodules of the Booster (G=0.06 cavities) • Upgrade LHe distribution system: higher efficiency and reliability

17. Multi-Harmonic Buncher, 58Ni15+ , 35.7 keV/u ATLAS: 10 meters between the MHB and the RF LinacAfter the MHB Low current (<1 pmA) 0.5 mA MHB - RF Linac distance is 3.5 m

18. RFQ • 1/7≤q/A≤ 1 • Injection energy = 30 keV/u • 60.625 MHz, 5th harmonic, ~3.0-meter length • 80% efficiency of beam capture for acceleration • Voltage ~90 kV, R0=7.5 mm • High-temperature furnace brazing • ~100 kW RF power • 2 circuits of temperature-stabilized water-cooling systems

19. 60.625 MHz RFQ will be very similar to the FRIB prototype • Stable operation in wide dynamic range of RF power • The highest voltage is 91 kV (limited by available RF power) • Q-factor: Simulation = 9300, Measured = 8860 • 3-meter long RFQ will provide ~250 keV/u ion beams, Q/A1/7 Pre-brazed assembly Prototype RFQ Fabrication technology: High-T furnace brazing, OFE copper

20. 80.65% captured to the central bunch

21. 25 cm 109.8 cm 3 cm ARRA: new cryomodule with QWR @ 72.75 MHz, βG=0.075 • Electromagnetic optimization is complete • Reduced BPEAK/EACC • Reduced EPEAK/EACC • Expected performance • VMAX= 2.5 MV • BPEAK = 600 Gs • EPEAK = 45 MV/m About 50% better performance than the ATLAS Upgrade Cryomodule 14 cm

22. Couplers • Existing ATLAS couplers (≤ 1 kW) • Proposed high-power (~10 kW) capacitive coupler

23. Tuners • AEU pneumatic slow tuner: excellent performance • Replace VCX with piezoelectric tuner • Can handle higher accelerating gradients Piezoelectric fast tuner, tested on spoke cavities

24. Current activities on new ARRA-RFQ project • Project documentation • WBS • Schedule – off-line commissioning in June 2012 • Implementation Plan • Study of the transmission of high-intensity beams through the PII, beam steering, transverse acceptance. • Design optimization of the accelerator • LEBT, RFQ, matching to the PII cryostat • RFQ prototype • Modify RF coupler with additional cooling and test • Build slug tuners, install and test • EM simulations of the RFQ resonator • Accurate frequency calculation • Minimize length and RF power

25. Frequency verification: Simulations vs Experiment

26. RFQ • Test high-power coupler (~120 kW) with an additional cooling • Build and test slug tuners

27. Current activities on new ARRA: Booster replacement project • Develop and prototype QWR, f=72.75 MHz cavity. The following features will be implemented: • Highly optimized EM design • SC cavities with “beam steering compensation” • New approach for electropolishing of QWRs • Develop and test adjustable (1-1/2”) capacitive coupler to handle ~10 kW RF power. • Develop piezoelectric tuner • Apply the vast experience gained during the ATLAS Energy Upgrade cryomodule

28. ATLAS Energy Upgrade Cryomodule

29. ATLAS Energy Upgrade Cavities are ready to drop into the box cryostat

30. (cm) New coupler Double window: cold and warm

31. Prototyping • Fast piezoelectric tuner • Capacitive coupler • Use the existing half-wave resonator and new test cryostat

32. 60 MHz 20 kW CW amplifier is available both for the test of the RFQ segments and can be retuned to 72 MHz for conditioning of SC QWRs • Was purchased for testing of the prototype RFQ

33. Charge Breeder based on EBIS for CARIBU beams • Low intensity of CARIBU beams allows us to efficiently apply EBIS for charge breeding. Compared to ECR: • Factor of 2-3 higher efficiency • Significantly higher purity • EBIS parameters are less demanding than the BNL EBIS • Major challenges are • precise alignment of electron and ion beam required • achieve high acceptance and short breeding times Q/A1/7 A=80-160 From CARIBU To ATLAS B EBIS LEBT Q+ 1+ (2+) Mass-Separator Post- Accelerator EBIS charge breeder design is based on BNL Test-EBIS: Double e-gun approach: 2A/5 kV and 0.2A/2 kV Electron beam current density – 300 A/cm2(BNL –575 A/cm2) Breeding time – 30 – 40 ms Efficiency ~ 15%, can be higher by factor of 2-3 when shell closure effect is applicable B: RFQ Buncher EBIS: Electron Beam Ion Source LEBT: Low Energy Beam Transport

34. EBIS R&D for the CARIBU beams • In collaboration with BNL • Build low-emittance 1+ injector, beam diagnostics for breeding efficiency measurements for low-intensity beams • Study shell closure effects at the BNL test-EBIS. For this purpose ANL will build low-current, high-perveance electron gun

35. Summary of upgraded ATLAS ion beams and future activities (no stripping is assumed)

36. Conclusion • The Physics Division has developed detailed plan for future ATLAS upgrade • PHASE I – two ARRA projects • ARRA-funded ATLAS upgrade is based on R&D results performed for FRIB, ATLAS AIP • We are in the stage of preliminary design for both ARRA projects • Schedule: • Commissioning of the RFQ – efficiency upgrade – September 2012 • Commissioning of the Booster replacement cryomodule – high-intensity medium mass beams – December 2012. • PHASE II is not funded yet, can be completed by the end of 2013 if the funds become available in FY10.