J. AlessiOverview
EBIS Project Technical Review1/27/05
An EBIS-based RHIC Preinjector - Overview
Jim Alessi
Preinjector GroupCollider-Accelerator Department
MotivationRequirements
Intensity, species, q/m, energy, operating modes, …General comments on design choicesProject status
J. AlessiOverview
EBIS Project Technical Review1/27/05
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.
J. AlessiOverview
EBIS Project Technical Review1/27/05
Two Tandems presently serve as RHIC preinjectors
J. AlessiOverview
EBIS Project Technical Review1/27/05
J. AlessiOverview
EBIS Project Technical Review1/27/05
EBIS
Tandem to Booster transport line is 860 m long.44 quadrupoles71 steering dipoles6 large dipoles25 multiwires20 Faraday cupsDozens each of pumps, vacuum valves, vacuum gauges, etc.
The transport from the EBIS to the Booster will be only 30 m long!
J. AlessiOverview
EBIS Project Technical Review1/27/05
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
J. AlessiOverview
EBIS Project Technical Review1/27/05
MODE PREINJECTOR OPERATION
Dedicated RHIC running; same species in both rings
5 Hz, 4 pulses every ~3 seconds; single Tandem
Dedicated RHIC running; two species 5 Hz, 4 pulses every ~3 seconds; 2 minute switching time between species; two Tandems
Dedicated NSRL running ~0.3 Hz; single Tandem
RHIC single species & NSRL same species, energy, charge state
5 Hz, 4+1 pulses every ~3 seconds; single Tandem
RHIC single species; NSRL different species of same magnetic rigidity
4 pulses at 5 Hz, ~1.5 second switching, then 1 NSRL pulse; two Tandems
RHIC single species; NSRL different species of different rigidity
~2 minute switching; two Tandems
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.
REQUIREMENTS
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
J. AlessiOverview
EBIS Project Technical Review1/27/05
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
J. AlessiOverview
EBIS Project Technical Review1/27/05
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)
Species Q Ions/pulse Charges/pulse(Booster output)
C 5+ 1.2 x 1010 6 x 1010
O 8+ 4 x 109 3.2 x 1010
Si 13+ 3 x 109 5.2 x 1010
Ti 18+ 8 x 108 1.4 x 1010
Fe 20+ 1 x 109 2 x 1010
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.
J. AlessiOverview
EBIS Project Technical Review1/27/05
Species He to U
Intensity in desired charge state ≥ 1 x 1011 charges/pulse
Charge-to-mass ratio, Q/m ≥ 1/6
Repetition rate 5 Hz
Pulse width 10 – 40 µs
Switching time between species 1 second
Output energy 2 MeV/amu
Emittance (full beam, normalized) ≤ 1.4 π mm mrad
Momentum spread, dp/p ≤ ± 0.05%
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.
J. AlessiOverview
EBIS Project Technical Review1/27/05
12 MVLINAC
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)
J. AlessiOverview
EBIS Project Technical Review1/27/05
4 m 4.3 m
RFQ: 17 - 300 keV/u; 100 MHz
Linac: 0.3 - 2.0 MeV/u; 100 MHz
Proposed Linac–Based RHIC Preinjector
J. AlessiOverview
EBIS Project Technical Review1/27/05
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)
J. AlessiOverview
EBIS Project Technical Review1/27/05
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
J. AlessiOverview
EBIS Project Technical Review1/27/05
Ions are extracted from an EBIS in pulses of constant charge; one has control over the pulse width
Charge state is selected by choosing theconfinement time of ions in the trap
J. AlessiOverview
EBIS Project Technical Review1/27/05
EBIS Test Stand
J. AlessiOverview
EBIS Project Technical Review1/27/05
J. AlessiOverview
EBIS Project Technical Review1/27/05
RHIC EBIS
Design changes relative to the Test EBIS, needed to meet RHIC requirements:
1. Longer SC solenoid and ion trap region2. Collector design for higher average power
Improvements to increase operational reliability and safety margin:
3. Collector design for higher peak power4. Electron gun capable of 20 A operation5. Increases to the solenoid bore and maximum field
J. AlessiOverview
EBIS Project Technical Review1/27/05
Advantages of an EBIS (vs. LIS, ECR) An EBIS can produce any type ions – from gas, metals, etc., and
is easy to switch species (pulse-to-pulse!)
One has control over the charge state produced (easy to get intermediate charge states, such as Au32+ or U45+)
One has control over pulse width, extracting a fixed charge – can better match to synchrotron requirements
EBIS produces a narrow charge state distribution ( ≥ 20% in the desired charge state), so there is less of a space charge problem in the extraction and transport of the total current
The scaling laws are understood
The source is reliable, and has excellent pulse-to-pulse stability, long life
Our R&D now shows that an EBIS meeting the RHIC requirements can be built. (mA’s of Au32+ !)
J. AlessiOverview
EBIS Project Technical Review1/27/05
ECRFeatures, advantages
~ the only choice for high current, high Q, dc applications
Reliable; lots of operating ECRs, lots of experience
TechnologiesSC magnets; At high freq's, need SC sol and SC hexapole 28 GHz VENUS - 4 T injection field, 2 T hexapole at plasma chamberRF 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
J. AlessiOverview
EBIS Project Technical Review1/27/05
LISFeatures, advantages
Produces high currents, short pulses
TechnologiesHigh power laser – 100 J, CO2, 15-30 nsOpticsTargets – 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
J. AlessiOverview
EBIS Project Technical Review1/27/05
EBIS at different pulse widthsECR
LIS, short pulses
Comment (qualitative) ….
J. AlessiOverview
EBIS Project Technical Review1/27/05
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.
J. AlessiOverview
EBIS Project Technical Review1/27/05
Planned location at the end of the 200 MeV linac
J. AlessiOverview
EBIS Project Technical Review1/27/05
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.
J. AlessiOverview
EBIS Project Technical Review1/27/05
EBIS
RFQ
LINAC
BOOSTER
STRIPPER FOIL
AGS
Au32+
Au32+
Au32+
Au32+
Au77+
17 keV/u 3.4 x 109 ions
300 keV/u 3.0 x 109 ions
2 MeV/u 2.7 x 109 ions
70 MeV/u 2.3 x 109 ions
70 MeV/u 1.4 x 109 ions
9 GeV/u 1.2 x 109 ions
STRIPPER FOIL
RHIC
Au77+
Au79+
90%
90%
85%
60%
90%
100%
9 GeV/u 1.2 x 109 ions
(=8.6e10 charges)
(=1e11 charges)
J. AlessiOverview
EBIS Project Technical Review1/27/05
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, as shown 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
Species Q Ions/pulse(Booster output)as run
EBIS(see note)
C 5+ 12 x 109 27 x 109
O 8+ 4 x 109 12 x 109
Si 13+ 3 x 109 5.3 x 109
Ti 18+ 0.8 x 109 3.8 x 109
Fe 20+ 1 x 109 3.4 x 109
He 2+ 172 x 109
Beams for NSRL
Note – assumption is 10A electron beam, 80% EBIS to Booster input, 85% Booster input to output.
All NSRL requirements can be met.
J. AlessiOverview
EBIS Project Technical Review1/27/05
Project Status• DOE gave CD0 approval (“mission need”) in August, 2004.• Preparing all documents required for CD1 – (“alternative selection
and cost range”)
J. AlessiOverview
EBIS Project Technical Review1/27/05
We are here! “Begin operations”
J. AlessiOverview
EBIS Project Technical Review1/27/05
J. AlessiOverview
EBIS Project Technical Review1/27/05
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.