1. Front-End System: Ion Source and RFQ Accelerator
Derun Li
Center for Beam Physics
Lawrence Berkeley National Laboratory
September 11-12, 2009
Fermi National Accelerator Laboratory

2. Acknowledgments
Special thanks to John Staples, Qing Ji, Steve Virostek, John Byrd, John Corlett, Steve Gourlay and colleagues at Center for Beam Physics of LBNL for their contributions and suggestions to this presentation and Sergei Nagaitsev and colleagues at FNAL for collaboration studies of the front-end system
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

3. Front-End System of Project X
Ion source
(H- CW 10 mA)
LEBT
RFQ
2.5 MeV
MEBT
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

4. Contents LBNL’s ion source experience and the state-of-art ion sources
Proton sources
Negative ion sources
Proposal of CW H- ion source for Project X
RFQ accelerator experience & history
Five RFQs have been built so far
Recent RFQ research
A 6 MeV deuteron RFQ for neutron source (as an example)
Innovative beam dynamics design
Improved RF structure design
3 D E&M simulations
Mechanical design and fabrication
CW RFQ studies for Project X (John Staples’ presentation)
Summary
We propose to design, construct, deliver and commission complete front- end system for Project X
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

5. LBNL’s Ion Source Experience
Extensive experience and highly successful history in ion source and injector development.
Past examples include the positive and negative ion sources for neutral beam injectors for Fusion research programs, and the H- ion source for SSC and SNS.
Proton sources
Extensive experience in RF-driven proton source (in both CW and pulsed mode) development
Two types of H- ion sources developed at LBNL:
Surface-conversion type H- sources (LANSCE, KEK ….)
Volume-production type H- sources (SSC, SNS ….)
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

6. Proton Source Mature technology for producing 10s mA CW proton beams.
We propose to use RF-driven Multicusp Proton Source
Permanent Magnets
Antenna
Cylindrical chamber wall
Quartz RF window
Back streaming electron dump
10 cm
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

7. Surface Conversion H- Ion Source
Employed in LANSCE Upgrade*
1 ms pulse at 120 Hz
Extracted peak current versus Arc power
* M. Williams et al, “Ion Source Development for LANSCE Upgrade”, 19th International Linear Accelerator Conference, Chicago, IL, USA, August 23-28, 1998.
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

8. Status of LANSCE Ion Source
Current LANSCE H- ion source (operational)*
Two filaments (250 mm long, 1.6 mm thick, high purity tungsten)
4-11 kW discharge power
Beam current mA through a 9.8 mm aperture
Emittance < 0.2 π mm-mrad (95%, normalized, 1-rms)
Duty factor 6-12 %
Current R&D on RF (13.56 MHz) helicon-driven converter source at LANL
Beam current mA through a 9.8 mm aperture
Duty factor 1-3.7% demonstrated
* R. Keller et al, “H- ion source development for the LANSCE Accelerator Systems”, 1st International Symposium on Negative Ions, beams, and Sources, Aix-en-Provence, France, September 9-12, 2008.
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

9. Volume-production H- Ion Source
RF-driven H- Source with Porcelain Antenna (currently been used in the SNS at Oakridge National Laboratory)
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

10. SNS Electrostatic LEBT
The ion source with outlet and dumping electrode is tilted by 3 degree with respect to
the LEBT axis.
Some magnet orientations are rotated into the viewing plane of this illustration.
The shape of the beam envelope is exaggerated for emphasis.
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

11. Status of SNS H- Ion Source
Current SNS H- ion source*
RF-driven with internal antenna
Routinely delivering 32 mA
0.67 ms, 60Hz, ~ 4% duty-factor
Development of RF-driven external antenna ion source at SNS
Demonstrated maximum beam current of 95 mA at 52 kW RF power, with Ni elemental collar
1 ms pulse at 60 Hz
* R. F. Welton et al, “Next Generation H- Ion Sources for the SNS”, 1st International Symposium on Negative Ions, beams, and Sources, Aix-en-Provence, France, September 9-12, 2008.
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

12. Status of CW H- Sources Operational CW H- ion source in accelerators
Multicusp filament
TRIUMF 1-5mA (0.5 π mm mrad)
Jyvaskyla-LIISA: 3 mA (0.6 π mm mrad)
D-Pace : 15-mA, 30 kV DC H- (< 1 π mm mrad, 4 rms)
The state-of-art CW H- ion source*
Reported by Yu. Belchenko et al
Technology: Penning discharge, surface-plasma source
Current: 15 mA
Normalized 1-rms emittance < 0.2 π mm mrad
* Yu. Belchenko et al, “A 15 mA CW H- source for accelerators”, 1st International Symposium on Negative Ions, beams, and Sources, Aix-en-Provence, France, September 9-12, 2008.
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

13. RF-driven Volume H- Ion Source with External Antenna (pulsed)
H- Sources for Project X
RF-driven Volume H- Ion Source with External Antenna (pulsed)
RF-driven Surface Conversion H- Ion Source (CW)
Cesium collar
Cesium oven and injector
Antenna
Cylindrical Quartz wall
Converter
Repeller
H- beam
Cylindrical chamber wall
Antenna
Quartz RF window
Filter magnets
Permanent Magnets
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

14. CW H- Sources for Project X
We propose to use the surface conversion ion sources for CW operation:
Switching from filament discharge to RF-driven
Long lifetime
Cleanliness
Emittance optimization
Flat converter or concave converter
Less extracted electron beam
Low risk for CW operation
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

15. LBNL has designed and built five RFQs
LBNL RFQ Experience & History
LBNL has designed and built five RFQs
RFQ1 - Bevatron
RFQ2 – CERN
RFQ3 – BNL Injector
Accelerator Handbook RFQ Article
US Particle Accelerator School
RFQ4 – LBNL Proton
RFQ5 - SNS
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

16. Most Recent RFQ Research
A 6 MeV Deuteron RFQ for Cargo-Screening
Evaluating two beam dynamics approaches (John Staples’s presentation)
Modified “conventional” design (LANL method)
Like SNS RFQ, but significantly shortened
Kick-buncher+drift design (LBNL method)
IUCF RFQ for cyclotron injector based on this design
Length in the 5 meter range, kV injector voltage
Similar in beam characteristics, each will satisfy requirements
Fabrication techniques slightly different
We have developed many mechanical concepts over the 28 year history of LBNL RFQ development
Best ideas from the last two RFQs and combine them for this and future designs
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

17. Two Representative RFQ Models
RFQ 4 (BNL) – 750 keV proton
Bolt-together construction
Copper-plated aluminum
Vane coupling rings
~ 1 meter long
RFQ 5 (SNS) – 2.5 MeV proton
6% duty factor
Cu/Glidcop brazeup
Pi-mode stabilizers
4 segments, 3.7 m long
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

18. Cavity Construction
The SNS segmented structure with pi-mode stabilizers works well, but is expensive to manufacture
Developed for very long life, high duty factor
The 750 keV proton structure with vane coupling rings is efficient and compact
Developed for low-cost manufacturing techniques
Take the best aspects of each and combine them into a structure with good thermal characteristics, good field stability and good thermal properties, as well as easy to fabricate
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

19. RFQ Beam Dynamics Designs
We use three independent codes to design
Parmteq-h (LBNL)
Toutatis (CEA-Saclay)
Parmteq-M (LANL)
The innovative kick-buncher to beam dynamics design has been thoroughly checked with independent codes
Beam dynamics extensions include
Dynamic tapering of parameters along z
Stepping physical parameters in each module for ease of construction
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

20. Parmteq Beam Dynamics Simulation
- RFQ length: 5.05 m
- Tracking of 5000 particles
- Total # of cells: 225
- The RFQ parameters (focusing and m) are adjusted to give the best transmission and exit beam parameters
- Low peak surface field
- Evolution of the transverse beam sizes
- Phase and energy spread along the structure
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

21. Runs slowly, but has more detailed physics model
Toutatis Beam Dynamics Calculation
Runs slowly, but has more detailed physics model
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

22. Better E&M Modelling Tools Now
More powerful 3 D Electromagnetic codes available now
Extensive experience in CST Microwave Studio
Much better mesh with adaptive techniques
Benchmarked the code against the SNS RFQ*
Excellent agreement, even with complex end sections
Good enough to skip cold modelling stage
Still need to do a final tune with bead pull
RFQTUNE program facilitates setting tuners
Get frequency within klystron power bandwidth
* D. Li, J. Staples and S. Virostek, DETAILED MODELING OF THE SNS RFQ STRUCTURE WITH CST MICROWAVE STUDIO, Linac-2006, Knoxville, TN
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

23. SNS RFQ with Microwave Studio
Frequency to 0.5%
Field profile correct
Complex end tuner geometry
Pi-mode stabilizers
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

24. RFQ Structure Simulations
Parameterized 3D CST MW model
RFQ with -mode stabilizers
A 3D RFQ slice for quick frequency search, cross-section optimization and RF parameter calculations
A 3D 1.28 m long RFQ model to study
-mode stabilization and mode separation
Simulations with radial matcher, cut-backs and ends
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

25. RFQ Structure Simulations
Frequency domain simulations
Field distributions and mode separations
Mode separation ~ 20 MHz
Quadrupole mode
f = MHz
Dipole mode
fH = MHz
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

26. RFQ Detailed 3D CAD Model
Sensing loop
-mode rods
Slug tuners
Module joint
bolt pockets
Minor vane
Vane-vane
RF seal
3D O-ring
Module-module
RF seal
Major vane
Vacuum
port
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

27. 3D CAD Model Details
Detailed geometry of vanes for all four modules and the associated components are included in the model
Modulation information is included in a separate data file to generate the input program to the computer controlled milling machine
Layout developed to include even spacing of pi-mode rods, tuners and sensing loops along entire RFQ
Other design details to be incorporated in the model are: final vane cutback geometry, vacuum port grill and vane- vane bolting, …
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

28. RFQ fabrication (BNL RFQ)
Assembly
Cavity and vane fabrication
Bead-pull measurement
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

29. CW RFQ Studies for Project X
More details in John Staples’s presentation
Overview of CW RFQs
Frequency choices
Beam dynamics designs
Comparison between “conventional” and innovative “kick-buncher” designs
CW RF cavity/structure and mode stabilization
Thermal management
Mechanical stability
Minimize required RF power
MEBT considerations …
We do collaboration better than anyone
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory

30. Summary
LBNL has extensive experience in ion source development and RFQ design and fabrications
Expertise in beam dynamics, engineering, fabrication and commissioning
We are willing to collaborate with FNAL on Project X and propose to design, construct, deliver and commission whole front-end system
Ion source (CW H-) and LEBT
RFQ accelerator (CW) and MEBT
Ancillary components to produce a fully integrated system
Experience in multi-lab collaborations
Started detailed RFQ studies for Project X front-end
We do collaboration better than anyone
September 11-12, Front-End System: D. Li, Lawrence Berkeley National Laboratory