electron cooling of the rhic - overview - … · s booster ags rhic ip#4- optional ip#2 ... rank,...

Electron Cooling of the Relativistic Heavy Ion Collider:

Overview

Ilan Ben-ZviCollider-Accelerator DepartmentBrookhaven National Laboratory

I. Ben-Zvi, 2nd EIC Workshop, March 15-17, 2004

Motivation• The motivation for electron

cooling of RHIC is to increase luminosity by reducing emittance and overcoming IBS.– Increase the integrated

luminosity for gold on gold collisions by an order of magnitude, also higher P-P luminosity (RHIC II).

– Increase the luminosity of protons and ions on electrons and shorten ion bunches (eRHIC)

• Both RHIC II and eRHIC are on the DOE’s 20 years facilities plan. RHIC luminosity decay (3.5 hours)



Linac

EBIS Booster

AGS

RHIC

IP#4- optional

IP#2 - optional

IP#12 - main

IP#10 - optional

Electro

n

cooling

Place for doubling energy linac

Luminosity up to 1 x 1034 cm-2 sec-1 per nucleon

Linac-ring eRHIC:Main-stream - 5-10 GeV e-

Up-gradable to 20+ GeV e-

What is special about cooling RHICThe cooling takes place in the co-moving frame, where the ions and electrons experience only their relative motion.

RHIC ion are ~100 times more energetic than a typical cooler ring. Relativistic factors slow the cooling by at least factor of γ2. So, first and foremost, we must provide a factor of γ2 more cooling power than typical.

Other points: Cooling of a bunched beam, cooling of a collider, recombination and disintegration, use of a high-temperature electron beam. Transport of a magnetized (angular momentum dominated) beam without a continuous solenoid.

We cannot use conventional accelerator techniques. We require a high-energy (54 MeV), high-current (0.1 to 0.3 A) electron beam for the cooler, based on an Energy Recovery Linac.


R&D issues• High current, energetic, magnetized, cold

electron beam. Not done before– Photoinjector (inc. photocathode, laser, etc.) – ERL, at x100 the current of current JLAB ERL– Beam dynamics study (magnetized beam AND

space-charge AND discontinuous solenoid)• Understanding the cooling physics in a new

regime, must reduce uncertainty – bunched beam, recombination, IBS, disintegration– electron cooling simulations with some precision

• A very long, super-precise solenoid (30 m long, 1-2 Tesla, 8x10-6 error)


Structure of theRHIC Electron Cooling R&D

Electron cooling R&D

Experimental R&D Theory / simulations

ERL Linac cavity

Guns Laser, photocathodes

Beam dynamics Electron cooling

Friction, IBS

DynamicsBenchmarkingexperiments Also: Cost and schedule.

Work in progress.


Electron cooling group (Reporting to

Thomas Roser) and collaborators.Ilan Ben-Zvi, Vladimir Litvinenko, Andrew Burrill, Rama Calaga, Xiangyun

Chang, Alexei Fedotov, Dmitry Kairan, Joerg Kewisch, David Pate, Mike Blaskiewicz, Yuri Eidelman, Harald Hahn, Ady Hershcovitch, Gary

McIntyre, Christoph Montag, Anthony Nicoletti, George Parzen, James Rank, Joseph Scaduto, Alex Zaltsman,

Animesh Jain, Triveni Rao, Kuo-Chen Wu, Vitaly Yakimenko, Yongxiang Zhao.GSI/INTAS collaboration: O. Boine-Frankenheim, others. JLAB: J. Delayen, Ya. Derbenev, P. Kneisel, L. Merminga. JINR (Dubna), Russia: I. Meshkov, A. Sidorin, A. Smirnov, G. TrubnikovBINP, Russia: V. Parkhomchuk, A. Skrinsky, many others.FNAL: A. Burov, S. Nagaitsev.SLAC: D. Dowell.Advanced Energy Systems: M. Cole, A. Burger, A. Favale, D. Holmes, A. Todd, J. Rathke, T. Schultheiss.Tech-X, Colorado: D. Abell, D. Bruhwiler, R. Busby, J. Cary.


Electron cooling theory, simulations and benchmarking experiments

• Lead – Alexei FedotovObjective: Reduce the extremely large

uncertainty in calculating cooling rates, develop new software tools and benchmark them.

Status: Three software tools in various stages of development. Expect solid results in FY05.


Outstanding issues

1. Complete development of code and benchmarking, obtain accurate estimates for cooling times.

2. Cooling with bunched electron beam.3. Cooling with “hot” electrons: RHIC Typical coolers

transverse : 1000 eV 0.1-1 eVlongitudinal : 50 meV 0.1 meV

4. Do we have sufficient magnetized cooling?5. What are the optimum parameters for electron beam?6. Detailed IBS. 7. Dynamics of the cooled ion beam, such as the impact on

threshold of collective instabilities.


Cooling gold at 100 GeV/A

Transverseprofile

Luminosity increase Longitudinalprofile


Two-stage cooling

0.5 1 1.5 2 2.5 3 3.5 4time hours

0.5

1

1.5

2

2.5

norm

aliz

edrm

sem

ittan

ceum

0.5 1 1.5 2 2.5time hours

5

10

15

20

25

30

35

rms

bu

nch

lem

gth

cm

2 4 6 8 10time hours

0.25

0.5

0.75

1

1.25

1.5

1.75

2

norm

aliz

edrm

sem

itta

nce

um

Pre-cooling protons at 27 GeV, Np=1x1011, Betacool with Derbenev-Skrinsky formula.

Ne=5x1010 and 1x1011 Ne=1x1011

Subsequent emittance growthat 250 GeV of initiallypre-cooled protons


Electron dynamics R&D• Lead - Joerg KewischThe objective is a complete design of the electron

accelerator, including start-to-end simulation. Understanding emittance growth under high space-charge forces is important as well transport and matching of magnetized electrons.

Status: Basic simulation tools at hand, initial start-to-end simulation done, new understanding of physics gained. To be completed in FY2006 with a test.


Layout of RHIC electron cooler

Gun

Solenoid

ERL cavities

Beam dump

Stretcher

I. Ben-Zvi, 2nd EIC Workshop, March 15-17, 2004Each electron bunch is used just once.


Layout

ParametersCooling Section:

Energy: 55 MevEnergy spread: 1· 10-4

Bunch length: 15 cmBunch radius: 1mmEmittance: 50 mm mradSolenoid: 1

Tesla Linac:

700 MHz Cavities: 4Gradient: 15 MV/m2100 MHz Cavities: 3Gradient: 7.5 MV/mPower amplifiers: 50 kW

Arcs:Max.Dispersion: 6 mMax. Beam Size (rms): 5 cmStretch factor: 33 m

Gun:Normal Conducting700 MHz 2½ CellBunch charge: 10 nCBunch frequency: 9.8 MHzBeam Energy: 2.5 MeVPower: 1MW


Front to End Simulation: Beam Size

alpha=6,Mag.Cath.100G,Fld=9Mv/m,Charge=10nc,phs=30,R=15mm,FWHM=4deg,B1=2.1

-10.00

-5.00

0.

5.00

10.00

0. 1600.00 3200.00 4800.00 6400.00 8000.00 9600.00 11200.0012800.0014400.0016000.00

x vs distance

-10.0

-5.0

0.

5.0

10.0

0 1600 3200 4800 6400 8000 9600 11200 12800 14400 16000

y vs distance


Front to End Simulation: Emittance

Method:

•Track electrons using PARMELA including space charge

•Apply linear transformation to make transport axial symmetric, remove dispersion

•Apply solenoid fringe field matrix

•Measure emittance

22

22 .])[(*511.0][ mradmmcmeVT n

ne ⋅=⋅=⊥ ε

σε


Development of complete ERL

• Lead - Vladimir LitvinenkoThe objective is to build an ERL comprising

a CW photoinjector, superconducting cavity and beam transport and test it for the RHIC/eRHIC current limits.

Status: Basic beam optics design done for up to 0.5 amperes. Testing system in 2006.



Cryo-module

e- 15-20 MeV

e- 30-40 MeV

Gun

e-

2.5MeV e-

2.5MeV

Beam dump

1 MW 700 MHzKlystron

50 kW 700 MHz

SRF cavity

Magnets, vacuum

Vacuum system

Controls &Diagnostics

Laser

ERL - Bldg. 912

Klystron PS

Goals for ERLse-cooler prototype


• Generate and accelerate bright (εn < 50 µmrad)intense (i.e. 150+ mA)magnetized (i.e. with angular momentum)electron beam to the energy of 54.677 MeV

• Cool the ion beam(s)• Decelerated the electron

beam to few MeV and to recover its energy back into the RF field

• Generate and accelerate bright (εn < 50 µmrad)intense (i.e. 150+ mA)electron beam with energy ~ 20-40 MeV

• Decelerated the electron beam to few MeV and to recover its energy back into the RF field

• Test the concepts and stability criteria for very high current ERLs

Photocathode and laser

• Lead – Triveni RaoThe objective: Develop a photocathode

material that has a high quantum efficiency in the green and long life. Develop suitable laser technology.

Status: UHV deposition chamber operational, CsK2Sb cathode depositions started. Cathode will be provided for photoinjector in FY05.


CW - Photoinjector -Glidcop, 703.75 MHz

New 703 MHzCW PhotoinjectorUnder construction

Solenoid

RF input coupler

LANL and Advanced Energy Systems


Superconducting gun

(1) Niobium Cavity(2) Choke Flange Filter(3) Cooling Insert (4) Liquid Nitrogen Tube

(5) Ceramic Insulation(6) Thermal Insulation(7) 3 Stage Coaxial Filter(8) Cathode Stem

Beamline Preparation Chamber

68 7

1 2 3 4

5

AES – BNL – JLAB gun Possible direction?Rossendorf like gun with CsK2Sb or similar cathode


CsK2Sb Photocathode

UHV photocathode preparation system


Q.E. as a function of Cs deposition

0

2

4

6

8

10

12

14

16

18

20

0 50 100 150 200 250 300 350 400

time (sec)

Cur

rent

(uA

)

0

0.5

1

1.5

2

2.5

3

QE

(%)

Current

QE %


High current ERL SRF cavitySee presentation by Ram Calaga in WG

• Lead – Ilan Ben-ZviObjective: Develop a cavity for high average

current (about 100 times the JLAB ERL), with large-charge bunches (difficult HOM power handling)

Status: Design successfully finished, contract for manufacturing in place. Cold test June 2004, cavity delivered for tests in May 2005.


HOM calculated By MAFIA.All HOMs are extremely well damped.

E_2

E_4

E_5

E_6

E_7

E_8

E_9

E_13

FerriteHOM damper

Cryomodule

Copper cavity parts


Low impedance: 6 times smaller than TESLA cavity


Cavity quality:• Ep / Ea ~2• R/Q = 807 Ω• Γ = 225 Ω• Hp/Ea = 5.8 mT/MV/mQualities important for ERL service:• Loss factor 1.2 V/pC (less HOM power)• BBU threshold about 1.5 to 2 amperes• Mechanically very stiff cavity, lowest mechanical

resonance over 100 Hz


Superconducting solenoid

• Lead –Animesh JainObjective: Develop a prototype superconducting

solenoid and its measurement system, demonstrate ability to deliver ultra-high precision in two 13 m long sections, 1 T superconducting solenoid.

Status: Solenoid principles established, Prototype design under way. Correction system under tests.


Conceptual Design of Solenoid

Copper Solenoid20 mT; 1.83 m longDipole Corrector



Simulated Correction

-1.0E-05

-8.0E-06

-6.0E-06

-4.0E-06

-2.0E-06

0.0E+00

2.0E-06

4.0E-06

6.0E-06

8.0E-06

1.0E-05

-4000 -3000 -2000 -1000 0 1000 2000 3000 4000

Z Position (mm)

Res

idua

l By

(Tes

la)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

B_y Error data;20 harmonics; Lambda=100mm to 2 meters; 6.5m long solenoid; ~6.6m long corrector 2 families; Dipole06a;b; 150mm patterns. 160mm spacing; 80mm offset for second layer; No extra gaps. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Net Field after correction from 10-4 initial error

Conclusions

• High energy electron cooling looks feasible, but requires R&D.

• An aggressive and comprehensive R&D program is in place.

• We recognize the challenges, but we are confident that cooling RHIC will work well.

• In about three years we expect to resolve all outstanding R&D issues.


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