The Front-End System Study of Project X Derun Li Center for Beam Physics Lawrence Berkeley National Laboratory March 16, 2010 Fermi National Accelerator Laboratory

Summary In collaboration with Fermilab, we (LBNL) propose to take responsibility of the complete front-end system (warm) of Project X through CD3 and for the construction and commissioning: Design study, engineering, construct, integration, deliver and commission of the complete front-end system Design study, engineering, construct, integration, deliver and commission of the complete front-end system – Ion source (DC H - ) and LEBT – RFQ accelerator (CW) – MEBT, narrow-band chopper and rebuncher cavities – Ancillary components to produce a fully integrated system Experience in front-end system and multi-lab collaborations Experience in front-end system and multi-lab collaborations R&D on ion sources, RFQ, chopper, rebuncher cavity R&D on ion sources, RFQ, chopper, rebuncher cavity Developed an R&D plan (proposal) Developed an R&D plan (proposal) 2 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

Front-End System Studies – Project X configuration has been evolving (determined by physics programs), so does the Front-End (FE) system – FE scenario has not been finalized (requirement parameters, configuration and space) – However, key elements remain H- ion sources (10 mA, DC) and LEBT H- ion sources (10 mA, DC) and LEBT CW RFQ accelerators (162 MHz or 325 MHz) CW RFQ accelerators (162 MHz or 325 MHz) CW Rebuncher cavity CW Rebuncher cavity Conceptual preliminary chopper schemes and CW RFQ accelerator designs have been presented before (J. Staples) Conceptual preliminary chopper schemes and CW RFQ accelerator designs have been presented before (J. Staples) – Recent progress, development and plans H- ion source (DC 10 mA and pulsed mode with modulated intensity) H- ion source (DC 10 mA and pulsed mode with modulated intensity) Normal conducting CW rebuncher cavity Normal conducting CW rebuncher cavity Preliminary physics/engineering studies on thermal management of CW RFQ accelerators and rebuncher cavity Preliminary physics/engineering studies on thermal management of CW RFQ accelerators and rebuncher cavity 3 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

Study of Ion Sources and LEBT Physics study of ion sources and low energy beam transport (LEBT) Physics study of ion sources and low energy beam transport (LEBT) – Develop an ion source and LEBT system that meet the requirements for the FE system of Project X – From design study or test to construction Identify a feasible solution of H - ion source and LEBT system that can provide two operation modes (suggested by S. Nagaitsev at last visit to LBNL) Identify a feasible solution of H - ion source and LEBT system that can provide two operation modes (suggested by S. Nagaitsev at last visit to LBNL) – 10 mA of DC H - beam (baseline) – Pulsed H - beam at 10 Hz with 5 ms pulse width, 0.5 ms pulse ramping up and down time, with variable beam intensities of adjacent pulses from 1.7 mA to 10 mA 4 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

Possible solutions Two ion sources and two LEBT systems with a bending magnet to select between two beams Two ion sources and two LEBT systems with a bending magnet to select between two beams One hybrid H - ion source One hybrid H - ion source – A hybrid filament discharge and RF-driven H - ion source – Or a hybrid of volume- and surface-production H - ion source – Vary H - ion beam extracted from the source by changing operation conditions DC H - ion source and LEBT with a limiting aperture DC H - ion source and LEBT with a limiting aperture – The H - ion beam extracted from the ion source stays constant – By varying the setting of the Einzel lens in the LEBT, the H- ion beam current passing through the downstream limiting aperture will change accordingly 5 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

H - Ion Source Options Option A: D-Pace ion source Option A: D-Pace ion source – DC filament discharge – No RF drive and no cesium – 10  15 mA DC of H - – Normalized 4 rms emittance < 1  -mm-mrad All previously delivered D-Pace units were used in cyclotrons for isotope productions All previously delivered D-Pace units were used in cyclotrons for isotope productions – Electron to H - ratio unknown, need to be checked – Electron leakage may limit its capability – Emittance needs to be verified The D-Pace unit comes with beam extraction system and electron dump, but not a full LEBT The D-Pace unit comes with beam extraction system and electron dump, but not a full LEBT 6 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

D-Pace H - Ion Source (TRIUMF-type) DC-filament discharge DC-filament discharge 10  15 mA DC H - beam 10  15 mA DC H - beam Lifetime > 350 hours Lifetime > 350 hours Output energy: 25  30 keV Output energy: 25  30 keV Normalized 4 rms emittance less than 1  -mm-mrad Normalized 4 rms emittance less than 1  -mm-mrad Electron dump Electron dump Extraction system, not full LEBT Extraction system, not full LEBT Need power supply and vacuum pumps Need power supply and vacuum pumps 7 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

D-Pace H - Source Emittance Measurement (10 mA) in 2005 Normalized 4 rms Emittance:  -mm-mrad 8 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

D-Pace H - Source Emittance Measurement (15 mA) Normalized 4 rms Emittance: 0.76  -mm-mrad 9 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

Low Energy Beam Transport (LEBT) The choice of magnetic or electrostatic LEBT depends chopping scenarios The choice of magnetic or electrostatic LEBT depends chopping scenarios Pros and cons of electrostatic versus magnetic LEBT Pros and cons of electrostatic versus magnetic LEBT – Electrostatic LEBT SNS source:  60 mA, 6 % duty factor  3.6 mA average beam current, lower than 10 mA for Project X SNS source:  60 mA, 6 % duty factor  3.6 mA average beam current, lower than 10 mA for Project X Experience from SNS indicates short electrostatic LEBT seems marginal Experience from SNS indicates short electrostatic LEBT seems marginal Power management Power management High voltage breakdown High voltage breakdown  Not a good bid (depending on chopping scheme) – Magnetic LEBT Longer in space, good for multiple stage electron dumping Longer in space, good for multiple stage electron dumping May suffer from emittance growth May suffer from emittance growth More studies needed More studies needed – Available study/simulation tools at LBNL: PBGun, IGUN, WARP 3D 10 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

DC H - Source and LEBT with a Limiting Aperture Potential risks: Potential risks: – Power management  90% H - ion dump at limiting aperture  90% H - ion dump at limiting aperture High duty factor of 5% High duty factor of 5% – Emittance growth During beam level transition During beam level transition Beam scattering in the aperture Beam scattering in the aperture 11 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

Hybrid Ion Source Option B: Hybrid of filament discharge and RF driven Option B: Hybrid of filament discharge and RF driven – Add filament to a pulsed RF-driven H - source – Filament discharge provides the baseline of H - beam – Pulsed RF boosts the H - level to higher intensity/amplitude – Longer filament lifetime The H - ion beam extracted from the source can be varied by changing the ion source operation condition The H - ion beam extracted from the source can be varied by changing the ion source operation condition – LEBT parameter settings need to be synchronized with source operation Potential risks: Potential risks: – Pulsed RF with a high duty factor of 50% 12 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

RFQ Accelerators and Choppers Conceptual preliminary designs of two CW RFQ accelerators, LEBT and MEBT chopping schemes have been presented before (J. Staples) Conceptual preliminary designs of two CW RFQ accelerators, LEBT and MEBT chopping schemes have been presented before (J. Staples) Two choices of RF frequencies: MHz and 325 MHz Two choices of RF frequencies: MHz and 325 MHz ☺ Good beam dynamics (preliminary, kick-bunch RFQ design) – Need more studies on RF and engineering designs of NC CW RFQ structures Mechanical design Mechanical design Thermal management Thermal management – MHz CW RFQ is easier for thermal management Successful experience relevant to CW RFQ design and engineering Successful experience relevant to CW RFQ design and engineering – PEP-II HOM damped NC CW RF cavity (476 MHz) – SNS RFQ (6% duty factor) – LBNL VHF photo-injector NC CW RF gun 13 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

MHz RFQ Beam Traces The un-captured beam, shown here eliminated at cell 58, actually continues to the end. Input current is 6 mA, acceptance to full energy is greater than 93%. to the end. Input current is 6 mA, acceptance to full energy is greater than 93%. Energy Spread vs cell number rms energy spread = 10 keV Phase vs. cell number rms phase spread = 5.0 deg x vs. cell number normalized emittance = 0.30 mm-mrad 14

15 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/ Example of MEBT Design As simple as possible Two 0.5 meter TW choppers and Two 0.5 meter TW choppers and placed near each other placed near each other Two rebuncher cavities Two rebuncher cavities Four quads at each end, trim quad Four quads at each end, trim quad in the middle in the middle “Ribbon” beam shape in choppers “Ribbon” beam shape in choppers and chopping slit and chopping slit No diagnostic boxes, etc. included yet No diagnostic boxes, etc. included yet Deflection 9.5 sigma at the chopper slit with 500 volt peak, each meander line Deflection 9.5 sigma at the chopper slit with 500 volt peak, each meander line Space charge important, even at 2.5 MeV Space charge important, even at 2.5 MeV 15

More on NC CW RFQ Design In addition to beam dynamics design, RFQ accelerator is an RF structure with EM fields weakly coupled between quadrants In addition to beam dynamics design, RFQ accelerator is an RF structure with EM fields weakly coupled between quadrants – Vane modulation (cell table) generated from beam dynamics design – Mode stabilization in RFQ (structure) – RF coupler and tuners – Common engineering challenge for any normal conducting CW RF structures Thermal management Thermal management Mechanical (structure) design Mechanical (structure) design – Two examples: an improved SNS RFQ and a CW RF gun designs 16 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

17 Relevant Experience in NC CW RF Design Example of an improved SNS RFQ Design Exploded View the improved SNS RFQ Design (single module)

The Improved SNS RFQ Design Combined 25 years of successful RFQ design experience and recent ADNS RFQ design Combined 25 years of successful RFQ design experience and recent ADNS RFQ design The same beam dynamics design The same beam dynamics design Areas of improvements Areas of improvements – Simplified fabrication, assembly and more cost effective – Get rid of the Glidcop completely – Stainless steel back-skeleton to provide strong mechanical support for RF and vacuum seals – Gun drill cooling channels in vanes – Two RF coupling loops Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/

Cavity geometry optimized to maximize the shunt impedance, to minimize the wall power density, to reduce the mechanical stress, simplify fabrication and facilitate photocathode replacement. Re-entrant geometry: desired frequency with a reasonably small size Total length35.0 cm Diameter69.4 cm Accelerating gap4 cm Frequency187 MHz Q0Q Operation modeCW Gap voltage750 kV Field at the cathode19.47 MV/m Peak surface field24.1 MV/m Stored energy2.3 J Shunt impedance6.5 MW RF Power87.5 kW Peak wall power density25.0 W/cm 2 CW RF Gun Cavity (example) at LBNL 19 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

NC CW Rebuncher Cavity A TM 010 pillbox-like rebuncher (SNS design) for a 2.5 MeV proton beam operating at 325 MHz is compared to a TE 210 RFQ-type rebuncher operating on the same beam. The peak energy gain at on crest is 75 keV A TM 010 pillbox-like rebuncher (SNS design) for a 2.5 MeV proton beam operating at 325 MHz is compared to a TE 210 RFQ-type rebuncher operating on the same beam. The peak energy gain at on crest is 75 keV Bead dynamics through the two rebuncher cavities is similar, new simulation code has been developed. Bead dynamics through the two rebuncher cavities is similar, new simulation code has been developed. 20 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

NC CW Rebuncher Cavity Comparisons 21 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010 Almost identical beam dynamics for 4-cell and 6-cell RFQ rebuncher cavities Almost identical beam dynamics for 4-cell and 6-cell RFQ rebuncher cavities RFQ rebuncher needs less RF power and lower wall power density RFQ rebuncher needs less RF power and lower wall power density

Preliminary Simulation Studies of the RFQ Rebuncher 22 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010 Strongly coupled RFQ structure, good mode separation  41 MHz; Does not need mode stabilization.

R&D Plans – Ion source and LEBT D-Pace H - Ion Source as baseline D-Pace H - Ion Source as baseline Emittance measurements Emittance measurements Electron filtering and dumping study Electron filtering and dumping study Study of other ion source and LEBT options Study of other ion source and LEBT options Beam dynamics study of LEBT Beam dynamics study of LEBT – RFQs ☺ Preliminary conceptual designs in beam dynamics and RF 162-MHz RFQ (mechanically easier) and 325-MHz RFQ (doable) 162-MHz RFQ (mechanically easier) and 325-MHz RFQ (doable) – Continue beam dynamics, RF structure design studies and cost estimate – Rebuncher cavity: NC CW RFQ rebuncher – MEBT and choppers studies in collaboration with Fermilab – Scenario, space and requirements 23 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010

Acknowledgements Special thanks to John Staples, Qing Ji, Steve Virostek, Thomas Schenkel, Joe Kwan, Ji Qiang, John Byrd, John Corlett, Steve Gourlay and colleagues at Center for Beam Physics of LBNL for their contributions and suggestions to this presentation 24 Front-End System of Project X, D. Li, Lawrence Berkeley National Lab, 3/16/2010