Issues for Formation of MEIC Ion Beam

Thomas Jefferson National Accelerator Facility

Operated by the Southeastern Universities Research Association for the U.S. Department of Energy

Issues for Formation of MEIC Ion Beam

MEIC Ion Complex Design Mini-Workshop

JLab, January 27-28, 2011

Ya. Derbenev



O u t l I n e

• Concept of high luminosity• Required parameters, concepts and problems of :

- High energy EC for EIC

-Synchronization for EC-

- Beam emittance injected in collider ring (required)

- Luminosity lifetime (due to IBS and other) - Crab Crossing

- Acceleration/rebunching in collider ring

- Synchronization for collisions-

- Emittance vs space charge at stacking

- Beam loss at re-bunching

- Microwave beam stability (wakes in SRF cavities and other)

- Electron cloud

- Gaps



Luminosity in colliders with Electron Cooling

Decrease the bunch length design low beta-star

Decrease transverse emittances design low beta-star

Raise the beam-beam tune shift limit: large Qs (exceeding bb tune shift)

Raise repetition rate by arrangement for crab crossing to eliminate the parasitic bb

-Crab crossing is effective at HF- matches short bunches !

Decrease charge/bunch- receive MW stability, reduce IBS

Diminish the IBS using flat beams (non-coupled optics)

EC in cooperation with strong HF SC field allows one to obtain:

•Very short ion bunches (1cm or even shorter)

•Small transverse emittances



Forming the ion beamMain issues: •Initial cooling time•Bunch charge & spacing

General recommendations:•Prevent the emittance increase at beam transport (introducing a fast feedback)•Use staged cooling •Start cooling at possibly lowest energy•Use the continuous cooling during acceleration in collider ring, if necessary

Beam bunching, cooling and ramp agenda:•After stacking in collider ring, the beam under cooling can be re-bunched by high frequency SC resonators, then re-injected for coalescence (if needed), more cooling and final acceleration & cooling •The final focus could be switched on during the energy ramp, keeping the Q-values constant



Lifetime due to Intrabeam Scattering

IBS heating mechanism: Energy exchange at intra-beam collisions leads to x-emittance increase due to energy-orbit coupling, and y-emittance increase due to x-y coupling

Electron cooling is introduced to suppress beam blow up due to IBS, and maintain emittances near limits determined by beam-beam interaction.

Since L 1/ xy , reduction of transverse coupling while conserving beam area, would result in decrease of impact of IBS on luminosity

Electron cooling then leads to a flat equilibrium with aspect ratio of 100:1.

Touschek effect: IBS at large momentum transfer (single scattering) drives particles out of the core, limiting luminosity lifetime.

A phenomenological model which includes single scattering and cooling time of the scattered particles has been used to estimate an optimum set of parameters for maximum luminosity, at a given luminosity lifetime.



High Energy Electron Cooling

ion bunch

electron bunch

Electron circulator

ring

Cooling section

solenoid

Fast beam kicker

Fast beam kicker

SRF Linac

dumpelectron injector

energy recovery path

Circulator ring by-pass

Path length adjustment

ERL based circulator electron cooler

Initial cooling

After bunching

Colliding mode

Momentum GeV/MeV 12/6.6 60/33 60/33

Beam current A 0.6/3 0.6/3 0.6/3

Particle/bunch 1010 0.7/3.8 0.7/3.8 0.7/3.8

Bunch length mm200/20

010/30 5/15

Energy spread 10-4 5/1 5/1 3/1Hori. Emit.

norm.mm 4 1 0.56

Vert. emtt. norm. mm 4 1 0.11

Laslett tune shift 0.002 0.006 0.1

Cooling length m 15 15 15

Cooling time s 92 162 0.2

IBS growth time (longitudinal)

s 0.9

ERL/CR based staged EC in collider ring



Feasibility of High Energy Electron Cooling

Beam adapters•Allows one to flatten the e-beam area in order to reach the optimum cooling effect

Advances on electron beam

SRF energy recovering linac (ERL)•Removes the linac power show-stopper•Allows for two stages cooling or even cooling while accelerating•Allows for fast varying the e-beam parameters and optics when optimizing the cooling in real time•Delivers a low longitudinal emittance of e-beam

Electron circulator-cooling ring•Eases drastically the high current and energy exposition issues of electron source and ERL

Beam transport with discontinuous solenoid•Solves the problem of combining the magnetized beam transport (necessary for efficient EC) with effective acceleration



Beam-beam kicker for EC

Kicker beam is not accelerated after the DC gun

Both beams are flat in the kick section

Flat beams can be obtained from magnetized sources (grid operated).

•Kicker beam is maintained in solenoid. It can be flatten by imposing constant quadrupole field

•Flat cooling beam is obtained applying round-to- flat beam adapters

Circulating beam energy MeV 33

Kicking beam energy MeV ~0.3

Kicking frequency MHz 5 – 15

Kicking angle mrad 0.2

Kicking bunch length cm 15 – 50

Kicking bunch width Cm 0.5

Kicking bunch charge nC 2

Design parameters for beam-beam kicker

A schematic of beam-beam fast kicker



Synchronization for EC

Injector 5 MeVx25 mA

ERL 75 MeV

Fast kicker

arcarc

Fast kicker

Cooling section

Dumper 125 KWt

ii



Short bunches make feasible the Crab Crossing

SRF deflectors 1.5 GHz can be used to create a proper bunch tilt

SRF dipole

Final lens FF

Crab Crossing

Parasitic collisions are avoided without loss of luminosity

R. Palmer 1988, general idea



Crab Crossing for EIC• Short bunches also make feasible the Crab Crossing:• SRF deflectors 1.5 GHz can be used to create a proper bunch tilt

E

leB

F

ttt

tfcr

22

mm

ml

mMVGB

GHzcm

mF

GeVE

f

t

t

1

4

)/20(600

5.1(20

3

100

4105

1.0

t

cr

2

l



Preliminary IP layout for ion beam

CCB with inserted SRF for bunching and dispersive crabbing

• Dipoles bending the beam in addition to arcs• Inserted SRF resonators are sufficient for required

bunching and dispersive crabbing

Issues for Formation of MEIC Ion Beam

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