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An EBIS-based RHIC Preinjector - Overview

An EBIS-based RHIC Preinjector - Overview. Jim Alessi Preinjector Group Collider-Accelerator Department. Motivation Requirements Intensity, species, q/m, energy, operating modes, … General comments on design choices Project status. EBIS - Overview.

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An EBIS-based RHIC Preinjector - Overview

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  1. An EBIS-based RHIC Preinjector - Overview Jim Alessi Preinjector Group Collider-Accelerator Department Motivation Requirements Intensity, species, q/m, energy, operating modes, … General comments on design choices Project status EBIS Project Technical Review 1/27/05

  2. EBIS - Overview Presently, one or two ~35-year old Tandem Van de Graaff accelerators are used for RHIC pre-injection, but the recent advances in the state of the art in EBIS performance by more than an order of magnitude now make it possible to meet RHIC requirements with a modern linac-based preinjector. BNL now has DOE CD0 approval for new pre-injector for RHIC based on the Laboratory’s development of an advanced Electron Beam Ion Source (EBIS). The new preinjector would consist of an EBIS high charge state ion source, a Radio Frequency Quadrupole (RFQ) accelerator, and a short linac. EBIS Project Technical Review 1/27/05

  3. Two Tandems presently serve as RHIC preinjectors EBIS Project Technical Review 1/27/05

  4. EBIS Project Technical Review 1/27/05

  5. EBIS Tandem to Booster transport line is 860 m long. 44 quadrupoles 71 steering dipoles 6 large dipoles 25 multiwires 20 Faraday cups Dozens each of pumps, vacuum valves, vacuum gauges, etc. The transport from the EBIS to the Booster will be only 30 m long! EBIS Project Technical Review 1/27/05

  6. Heavy Ion Preinjector for RHIC • The Tandem Van de Graaff is the present RHIC preinjector. Until our recent EBIS development, it was the only option which could meet RHIC requirements, and while presently it is quite reliable, it has disadvantages - • 860 m transport line to Booster • Stripping foils at terminal and high energy • lead to intensity & energy spread variations • Injection over > 40 turns is required • Limitations on ion species (must start with • negative ions) • High maintenance, manpower • Obsolete equipment requires upgrading EBIS Project Technical Review 1/27/05

  7. REQUIREMENTS To improve upon the present Tandem performance, it is desirable for the preinjector to be able to switch both species and transport line rigidity in ~1 second, so that there are no restrictions on compatibility between RHIC and NSRL operations. Requirement for RHIC (one example) : 1.7 emA of Au 32+, 10 µs; 5 Hz plus….NSRL (NASA Space Radiation Laboratory) – interleaved second beam at 5 Hz: He 2+, C 6+, O 8+, Si 14+, Ti 18+, Fe 21+, Cu 22+, all at ~2-3 emA, ~ 10 µs --- short pulses, fast beam changes, any species EBIS Project Technical Review 1/27/05

  8. The present control system supports “pulse-to-pulse modulation” The setpoint of any device can be changed pulse-to-pulse, depending on the “user”. So, within 1 second: the source (EBIS) has to change species, the RFQ and linac have to change gradient (amplitude) transport line elements have to switch to new values EBIS Project Technical Review 1/27/05

  9. Intensity required at injection into the Booster, for RHIC: Au32+ : 2.7 x 109 ions per pulse. (8.6 x 1010 charges/pulse). Sufficient to achieve 1.2 x 109 ions per bunch in RHIC. D: 2.5 x 1011 ions/pulse. (will be produced from a plasma source, for convenience). Cu11+ : 1.4 x 1010 ions/pulse. (1.5 x 1011 charges/pulse) Beams for NSRL With a present efficiency from Booster injection to extraction of ≥ 60% (EBIS should be better), one needs ≤ 1011 charges/pulse in all cases for NSRL. With a trap capacity in the EBIS of 1012 charges, these intensities should be readily achievable. EBIS Project Technical Review 1/27/05

  10. Summary of Performance Specifications Injection energy: 2 MeV/amu. Present tandem injection is at 0.92 MeV/amu for Au. At this energy, there is a significant beam loss due to electron capture during Booster injection. By raising the injection energy to 2 MeV/amu, the capture cross section is reduced by a factor of 20-40. In addition, the higher energy reduces the space charge tune shift at injection, which might be important at these higher peak currents. At even higher injection energies one would approach the voltage limit of the inflector, and losses due to ionization would begin to become important. EBIS Project Technical Review 1/27/05

  11. The EBIS preinjector offers the following benefits: • Improvements in reliability, setup time, and stability should lead to increased integrated luminosity in RHIC • Reduced operating costs, and avoidance of ~ 9 M$ in reliability-driven investments in the tandems • Elimination of two stripping stages and an 860 m long transport line, leading to improved performance • Simplification of Booster injection (few turn vs. present 40 turn) • Increased flexibility to handle the multiple simultaneous needs of RHIC, NSRL, and AGS • Capability to provide ions not presently available, such as noble gas ions (for NSRL), uranium (RHIC), or, with additional enhancements, polarized 3He (eRHIC) (the Tandems must start with negative ions) • Simpler technology, robust, more modern (Tandem replacement parts becoming difficult to get) 12 MV LINAC EBIS Project Technical Review 1/27/05

  12. Proposed Linac–Based RHIC Preinjector 4 m 4.3 m RFQ: 17 - 300 keV/u; 100 MHz Linac: 0.3 - 2.0 MeV/u; 100 MHz EBIS Project Technical Review 1/27/05

  13. Linac-based Preinjector - Source “requirements” 1. Intensity for 1 x 109 Au ions/bunch in RHIC : ~ 3.4 x 109 Au32+ ions/pulse from the source 2. No stripping before Booster injection : q/m > 0.16 (Au32+, Si14+, Fe21+) 3. 1-4 turn injection into Booster : pulse width 10-40 s (Note - 1 & 3 result in a Au32+ current of 1.6 - 0.4 mA) 4. Rep rate : ~ 5 Hz 5. Emittance :  0.2  mm mrad, normalized, rms (for low loss at Booster injection) EBIS Project Technical Review 1/27/05

  14. EBIS Radial trapping of ions by the space charge of the electron beam. Axial trapping by applied electrode electrostatic potentials. Ion output per pulse is proportional to the trap length and electron current. Ion charge state increases with increasing confinement time. Charge per pulse (or electrical current) ~ independent of species or charge state! EBIS Project Technical Review 1/27/05

  15. Charge state is selected by choosing the confinement time of ions in the trap Ions are extracted from an EBIS in pulses of constant charge; one has control over the pulse width EBIS Project Technical Review 1/27/05

  16. EBIS Test Stand EBIS Project Technical Review 1/27/05

  17. EBIS Project Technical Review 1/27/05

  18. RHIC EBIS Design changes relative to the Test EBIS, needed to meet RHIC requirements: 1. Longer SC solenoid and ion trap region 2. Collector design for higher average power Improvements to increase operational reliability and safety margin: 3. Collector design for higher peak power 4. Electron gun capable of 20 A operation 5. Increases to the solenoid bore and maximum field EBIS Project Technical Review 1/27/05

  19. EBIS Project Technical Review 1/27/05

  20. ECR Features, advantages ~ the only choice for high current, high Q, dc applications Reliable; lots of operating ECRs, lots of experience Technologies SC magnets; At high freq's, need SC sol and SC hexapole 28 GHz VENUS - 4 T injection field, 2 T hexapole at plasma chamber RF power source - 28 GHz gyrotron, 10-15 kW; plus sometimes multiple frequencies Questions, issues? Broad charge state distribution, so one has to extract & transport a high total current Performance depends on species, favoring gases and low melting point solids “Memory” effects, slower beam switching times EBIS Project Technical Review 1/27/05

  21. LIS Features, advantages Produces high currents, short pulses Technologies High power laser – 100 J, CO2, 15-30 ns Optics Targets – 3 x 1013 W/cm2 on the target Questions, issues? Laser reliability, rep rate Pulse-to-pulse current fluctuations Target erosion; coating of optics by target material Species ~ limited to solid targets, high melting point solids are best EBIS Project Technical Review 1/27/05

  22. Comment (qualitative) …. LIS, short pulses ECR EBIS at different pulse widths EBIS Project Technical Review 1/27/05

  23. RFQ: 100 MHz, 4 rod design is conventional. Very similar to GSI, CERN, etc. Deepak’s talk – 17 keV/u injection energy chosen to reduce space charge problems in LEBT. LINAC: IH structure chosen, very similar to CERN Pb linac. (conventional baseline design). SCL was considered, but abandoned since it is not required to meet design requirements, it has higher cost, and the technology is less familiar in Collider-Accelerator, so would increase operational burden. EBIS Project Technical Review 1/27/05

  24. Planned location at the end of the 200 MeV linac EBIS Project Technical Review 1/27/05

  25. The EBIS, operating with a 10 A electron beam, will produce in excess of 5 x 1011 charges/pulse, for any desired species. For heavy ions, ~20% of these ions will be in the desired single charge state, while for light ions this fraction can reach ~ 50%. In addition, key components (electron gun and collector) will be designed with the capability of operating at up to 20 A electron beam current, so one will have the potential of a factor of 1.6 improvement with further developments. EBIS Project Technical Review 1/27/05

  26. EBIS Au32+ 17 keV/u 3.4 x 109 ions RFQ 90% Au32+ 300 keV/u 3.0 x 109 ions LINAC 90% Au32+ 2 MeV/u 2.7 x 109 ions BOOSTER 85% 70 MeV/u 2.3 x 109 ions Au32+ STRIPPER FOIL 60% Au77+ 70 MeV/u 1.4 x 109 ions AGS 90% 9 GeV/u 1.2 x 109 ions Au77+ STRIPPER FOIL 100% Au79+ 9 GeV/u 1.2 x 109 ions RHIC (=1e11 charges) (=8.6e10 charges) EBIS Project Technical Review 1/27/05

  27. Intensity required at injection into the Booster, for RHIC: Au32+ : 2.7 x 109 ions per pulse. (8.6 x 1010 charges/pulse). Sufficient to achieve 1.2 x 109 ions per bunch in RHIC. (met, asshown in previous slide) D: 2.5 x 1011 ions/pulse. (4 x 1011 charges = 4 x 1011 ions/pulse from EBIS, but will be produced from a plasma source, for convenience). Cu11+ : 1.4 x 1010 ions/pulse. (1.5 x 1011 charges/pulse) 5e11 charges x 81% x 27% in Cu11+ = 1.1e11 charges/pulse  need 70% neutralization, or ~15A electron beam Beams for NSRL All NSRL requirements can be met. Note – assumption is 10A electron beam, 80% EBIS to Booster input, 85% Booster input to output. EBIS Project Technical Review 1/27/05

  28. Project Status • DOE gave CD0 approval (“mission need”) in August, 2004. • Preparing all documents required for CD1 – (“alternative selection and cost range”) EBIS Project Technical Review 1/27/05

  29. We are here! “Begin operations” EBIS Project Technical Review 1/27/05

  30. EBIS Project Technical Review 1/27/05

  31. SUMMARY • The EBIS initiative, a linac-based preinjector, is based on a modern technology, which will be simpler to operate and easier to maintain than the Tandems and will have the potential for future performance improvements. • It will provide a robust and stable preinjector, which is important for the successful operation of the injectors. • The RHIC EBIS design has been verified by the present EBIS operating at BNL (next talk). • No significant improvement in performance is required, other than the straightforward scaling of ion output with an increase in trap length. The RFQ and linac are very similar to devices already operating at other labs. EBIS Project Technical Review 1/27/05

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