cooler injector synchrotron (cis) at iucf v.s. morozov meic collaboration meeting march 30-31, 2015

Cooler Injector Synchrotron (CIS)at IUCF

V.S. Morozov

MEIC Collaboration Meeting

March 30-31, 2015

MEIC Collaboration Meeting 3/30-31/15 2

Current MEIC baseline injector– Single 285 MeV 220 s pulse of 2.751012 H- with low emittance

IUCF Cooler Ring injector complex

Introduction

Optimum stripping energy: 13 MeV/u

10 cryostats4 cryostats 2Ion Sources

QWRQWR HWR

IH

RFQ

MEBT

10 cryos4 cryos 2 cryos


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

Main Goals


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

Indiana University Cyclotron Facility


0.5 mA (peak) unpolarized duoplasmatron source later replaced by high-intensity (>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

Pre-Accelerator


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

– Strip injection equipment

– Fast extraction equipment

– RF cavity

– Five vertical correctors (four dipoletrim 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

CIS Ring


Weak-focusing synchrotron

Optics control– Dipole-straight length ratio

– Dipole edge angles

– Trim quadrupoles

CIS Lattice


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

Tune Diagram


Nominal transition energy is 256 MeV

Trim quadrupoles provide the possibility of imaginary transition energy

Transition Energy


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

Main Dipoles


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

Nonlinear Effects


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

Compensation of Sextupole Component


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

RF Cavity


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 injectionIntensity gain of ~80 achieved (~81010 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

Strip Injection


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 < 21010 protons – Well below space charge limit of ~ 21010 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 ~1.11010 – All losses occur in the first 200 ms of the ramp due to gas scattering

Acceleration


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 extraction1.3 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

1.11010 out of 1.31010 protons have been extracted at 200 MeV (85% efficiency)Extracted beam has emittance of ~10 m and momentum spread of about 210-3

Injection efficiency into the Cooler Ring of ~50% for both stacking and bucket to bucket transfer probably due to large emittance

Fast Extraction


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 51010 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– 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

Conclusions

cooler injector synchrotron (cis) at iucf v.s. morozov meic collaboration meeting march 30-31, 2015

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