Cooler Injector Synchrotron (CIS)
at IUCF
V.S. Morozov
MEIC Collaboration Meeting
March 30-31, 2015
Introduction
Current MEIC baseline injector
– Single 285 MeV 220 s pulse of 2.751012 H- with low emittance
QWR
RFQ
Ion Sources
IH 4 cryostats
4 cryos
MEBT
HWR
2
2 cryos
1010
cryostats
cryos
Optimum stripping energy: 13 MeV/u
IUCF Cooler Ring injector complex
MEIC Collaboration Meeting 3/30-31/15
QWR
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Main Goals
Put things in perspective
– Get a feeling for parameter scales
Compare CIS parameters to MEIC requirements
Try to identify what the limitations are
See if the performance can be improved
Try to decide whether CIS or a similar system may be suitable
for MEIC
– Hardware may be available
Learn from operational experience
– Literature, particularly, X. Kang’s thesis and papers by D.L. Friesel et al.
– Personal experience limited because there seemed to be no issues
Request input from the audience on heavy ions
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Indiana University Cyclotron Facility
Wide range of research: fundamental, material and medical science
New injector complex replaced the 15 and 200 MeV cyclotron chain
– Improve experimental luminosity
– Simplify the injection process to increase the experimental duty factor
Modest budget from NSF and IU of $3.5M in 1994
– New Linac, RF cavity, and ring magnetic, diagnostic and extraction systems
– Surplus ion source, injection and extraction beam lines, and vacuum system
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Pre-Accelerator
0.5 mA (peak) unpolarized duoplasmatron source later replaced by highintensity (>1 mA peak) Cooler Injector Polarized IOn Source (CIPIOS)
Commercial 7 MeV 425 MHz H-/D- linac
– 3 MeV RFQ with replaceable vanes to accelerate D- to 4 MeV
– 4 MeV DTL
Debuncher rotating longitudinal phase space to reduce momentum spread
200 s 300 A (peak) 7 MeV H- beam pulse at 4 Hz with 1 m normalized
emittance and 150 keV FWHM energy spread
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CIS Ring
Compact 17.36 m 2.4 Tm ring with four-fold symmetry
– One of the smallest and least expensive accelerators of this type
Four 2 m 90 dipoles
Four 2.34 m straights housing
– Trim quadrupoles
• Tune and transition energy control
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Strip injection equipment
Fast extraction equipment
RF cavity
Five vertical correctors (four dipole
trim coils for horizontal steering)
– Diagnostics
• x/y BPM pair at the entrance and
exit of each dipole
• Large bandwidth wall gap monitor
• Ping tune kicker
• Removable wire Harp
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CIS Lattice
Weak-focusing synchrotron
Optics control
– Dipole-straight length ratio
– Dipole edge angles
– Trim quadrupoles
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Tune Diagram
Working point chosen by adjusting dipole length and edge angles to avoid
beam and spin resonances
Trim quadrupoles can be used to control the betatron tunes
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Transition Energy
Nominal transition energy is 256 MeV
Trim quadrupoles provide the possibility of imaginary transition energy
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Main Dipoles
Fabricated from 1.5 mm modified 1006 steel laminations pre-coated with a
B-stage epoxy resin (Remisol EB-540)
– ~4-6 m resin layer serves as an insulator and bonding agent
– Sufficient to overcome the eddy currents at up to 5 Hz cycling rate
Each dipole is made of 5 wedge-shaped and 2 endpack modules
– Each module individually stacked, baked and machined
– The modules mounted on a precision base plate assembly
– Pole ends shaped to minimize the integrated sextupole component
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Nonlinear Effects
Nominal natural chromaticities are low and do not require compensation
The main sources of nonlinearity are sextupole fields
– Sextupole component of the dipole field
• Minimized by endpack design
– Sextupole component due to the eddy currents in the vacuum chamber wall
• Compensation using correcting coils
• Limiting the ramp rate
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Compensation of Sextupole Component
Correcting coils around the vacuum chamber inside the dipole
– Correct the nonlinear field at the source
Residual dipole field compensated using main dipole trim coils
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RF Cavity
Frequency change from 1.3 to 10.1 MHz when accelerating from 7 to
200 MeV at h = 1
Support accelerator cycle rates of up to 5 Hz
Non-uniform ferrite biasing: external magnetic field changes effective ferrite
permeability
– Wide tuning range
– Small size
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Strip Injection
200 s 300 A (peak) H- beam strip injected using 6 mm  25 mm
4.5 gm/cm2 carbon foil
– ~400 turns at 0.48 s revolution period
Three DC chicane dipoles produce a closed orbit bump near the foil and two
bumper magnets kick the beam onto the foil during injection
Intensity gain of ~80 achieved (~81010 accumulated protons)
Factors limiting the intensity
– Scattering in the foil
– Scattering on the residual gas of 10-7 Torr
– Slow fall time of ~200 s of the bumper magnets
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Acceleration
Beam adiabatically captured by ramping the RF cavity to 250 V in 2 ms
Acceleration starts within a few s of RF capture
By the start of acceleration, due to short lifetime, stored beam reduced to
< 21010 protons
– Well below space charge limit of ~ 21010 protons
Beam accelerated to 50-240 MeV in 0.5 s
– Dipole current and RF cavity frequency ramped using 96-step waveforms
– No beam position feedback
– Bunching factor varies from 3 at injection to about 5 at 225 MeV
~75% ramp transmission efficiency with a flattop intensity of ~1.11010
– All losses occur in the first 200 ms of the ramp due to gas scattering
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Fast Extraction
Bumper magnets and dipole trim coils used to locally bump the beam away from
septum by -7 mm during acceleration and close to septum by +17 mm for extraction
1.3 m parallel-plate Blumlein kicker magnet supplies a 55 kV 300 ns voltage pulse
across a 4 cm gap with a rise time of about 35 ns
– 20 mm beam displacement at the Lambertson septum entrance
1.11010 out of 1.31010 protons have been extracted at 200 MeV (85% efficiency)
Extracted beam has emittance of ~10 m and momentum spread of about 210-3
Injection efficiency into the Cooler Ring of ~50% for both stacking and bucket to
bucket transfer probably due to large emittance
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Conclusions
With the demonstrated parameters of 1 Hz repetition rate and 1010 particles
per pulse, assuming no injection losses, it would take about 4 and a half
minutes to fill the MEIC booster, which is probably not practical
On the other hand, assuming a 5 Hz ramp rate and an intensity closer to
the space charge limit of 51010 particles per pulse, filling the booster would
take 11 s, which may be reasonable as long as this is a small fraction of the
complete collider cycle
Factors limiting the intensity
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Vacuum pressure
Strip injection parameters, particularly, slow bumper fall time
Low RF cavity voltage
RFQ performance (from private communication with S.Y. Lee)
Possibly beam dynamics (need to look carefully at sextupole resonances)
Need to think how to deal with heavy ions
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