bnl r&d erl and coherent electron cooling test at rhic

4th Electron-Ion Collider Workshop, 4th Electron-Ion Collider Workshop, Hampton University, May 2008 19-23Hampton University, May 2008 19-23

BNL R&D ERL and Coherent Electron Cooling test at RHIC

OutlineOutline• Goals of R&D ERL at BNL• ERL general layout and main components• Coherent electron cooling test at RHIC• Plans & Conclusions


PHENIX

STAR

e-cooling (RHIC II)

Four e-beam passes

e+ storage ring 5 GeV - 1/4 RHIC circumference

Main ERL (3.9 GeV per pass)

IntroductionIntroduction

R&D ERL will serve as a test-bed for future RHIC projects:• ERL-based electron cooling (conventional or coherent),• 10-to-20 GeV ERL for lepton-ion collider eRHIC.

It will also address general issues expanding capabilities of ERLs:

• novel SRF injector,• high current and high brightness beam ERL operation,• flexible lattice to enable covering a vast operational parameter space.


Goals for ERL R&D at BNL

• Test the key components of the High Current Energy Recovery Linac based solely on SRF technology– 703.75 MHz SRF gun test with 500 mA – high current 5-cell SRF linac test with HOM absorbers

• Single turn - 500 mA – test the beam current stability criteria for CW beam currents – Demonstrate beam quality close to that required for high energy

electron cooling• Test the attainable ranges of electron beam parameters in SRF ERL


50 kW 703.75 MHzsystem

Control room

Cryo-module

SRF cavity

1 MW 703.75 MHzKlystron

e- 2.5MeV

Laser

SC RF Gun e- 2.5 MeV

Beam dump

Cryo-module

e- 15-20 MeV

Schematic Layout of the ERL

Merger system

Return loop


Half cell SRF Gun

SuperFish File Gun 5cm Iris NO transition Section F = 703.68713 MHz

C:\DOCUMENTS AND SETTINGS\KAYRAN\MY DOCUMENTS\ERL\SCGUN_DESIGN\FROM_RAM\RGUN51.AM 4-25-2005 10:50:06

0

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18

0

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0 5 10 15 20 25

Electromagnetic field data from file GUN4MM.AMProblem title line 1: SuperFish File Gun 5cm Iris

GUN4MM01.TBL 8-31-2005 15:13:54

Z (cm)

0

.5

1

1.5

2

2.5

3

0 2 4 6 8 10 12 14 16 18 20 22 24Er

A. M. M. Todd et al., “State-of-the-Art Electron Guns and Injector Designs for Energy Recovery Linacs”,PAC2005

SC RF Gun: shape and axial electric field profile (SUPERFISH result)

fRF= 703.75 MHzEnergy=2.5-3 MeV

Average Current: 0.5 ATwo fundamental power couplers: 0.5 MW each

1.9

1.95

2

2.05

2.1

0 10 20 30 40 50 60

Launch Phase, deg

Ene

rgy,

MeV

Electron beam energy gain at the exit of the gun versus initial phase

Electromagnetic field data from file RGUN6.AMProblem title line 1: SuperFish File Gun 6cm Iris NO transition Section

RGUN601.TBL 4-25-2005 11:49:52

Z (cm)

0

.5

1

1.5

2

2.5

3

0 2 4 6 8 10 12 14 16 18 20 22 24

Ez

Er

SC RF Gun: axial electric field profile for different cathode insertion depth (SUPERFISH result)


BNL R&D ERL SRF Injector layoutBNL R&D ERL SRF Injector layout

SRF GunSRF Linac

Z-merger Dipoles

Solenoids

ERL Loop

Dipole


Evolution of normalized beam emittances in the BNL R&D ERL injector

15º

-15º-30º

99.5 cm

70 cm

70 cm

30º

SC RF Gun5 cell SC RF cavity

0 2 4 6 8 100

5

10

15

Length, m

Rm

s N

orm

aliz

ed E

mitt

ance

s, m

m m

rad

12.075

0

xn0

xn1

xn2

8.3120 s0 s0 s1 s1 s2 s2 s3 s3

0 2 4 6 8 100

20

40

60

80

100

120

Length, m R

ms

Nor

mal

ized

Em

ittan

ces,

mm

mra

d

101.925

0

yn0

yn1

yn2

8.3120 s0 s0 s1 s1 s2 s2 s3 s3

Blue 5 nC Red 1.4 nC Green 0.7 nC

4.8/5.3 um 2.2/2.3 um 1.4/1.4um

Horizontal Vertical

BNL ERL Injector: beam dynamics simulation results


ERL: loop layoutERL: loop layout

2-3 MeV

2-3 MeV

20 MeV

20 MeV

20 MeV

2-3 MeV

SC RF GunSC 5 Cell cavity

Beam dump

Modes of operation Critical parameters

High energy acceptance Low dispersion, large aperture

Beam break up instability study Adjustable transverse phase advance

Longitudinal motion study Adjustable longitudinal dispersion

Two pass acceleration Changeable path length


ERL loop lattice is very flexibleERL loop lattice is very flexibleLattice and D functions of the ERL for the different cases longitudinal dispersions

(Ds=M56):

Positive longitudinal dispersion

Negative longitudinal dispersion

Zero longitudinal dispersion

No dispersion

Dis

pers

ion,

m

, m

Transverse normalized emittances from cathode to dump Q=0.7 nC

(PARMELA simulation)


BNL 5 Cell SRF Cavity Design

F = 703.75 MHz, E = 20 MeVQ0 ~ 1010, QHOM ~ 103

•The 5-cell cavity was specifically designed for high current, high bunch charge applications such as eRHIC and high energy electron cooling. •The loss factor of the cavity was minimized. •The number of cells was limited to 5 to avoid HOM trapping. •Additionally, HOM power is effectively evacuated from the cavity via an enlarged beam pipe piece 24 cm diameter.

Build: AES

Processed: JLAB

Arrived at BNL


Cavity VTA testsThe cavity was processed at JLab. After BCP, Rinsing, and low temp. bake low temp. bake (120 C)(120 C) cavity reached 19 MeV/m at Q0=1010.

19 MeV/m

Ebeam,max 20 MeV


HOM measurements

The damping of the Q-values is 2 orders of magnitude. Results well agree with simulations.

Several dipole modes at frequencies below 1 GHz were measured and could be identified by comparison with simulation results

The simulated BBU threshold is of the order of 20 Afor the nominal designed ERL lattice and simulated HOM parameters.GBBU and TDBBU codes were used.Dipole resonances in the RHIC ERL cavity fcu

[MHz] Qcu R/Qcu

[Ω] fFRT

[MHz] QFRT R/QFRT

[Ω] fData [Ω]

QData R/QData [kΩ]

805.1 29,700 0.0 803.4 588 0.1 0.08 810.2 34,000 0.4 808.4 150 1.1 807.8 900 0.17 817.9 34,500 1.2 816.1 136 0.7 0.10 829.2 32,000 0.3 827.0 265 0.2 825.18 370 0.06 851.6 31,000 13.7 849.5 493 11.8 848.99 130 5.8 874.6 31,100 55.1 872.6 379 49.3 18.7 890.2 32,800 43.0 888.1 163 42.0 6.8 897.1 31,900 21.2 895.0 201 22.8 4.6 929.0 42,800 10.1 926.2 104 6.7 0.79 943.8 46,000 5.8 940.7 79 8.6 0.68 957.6 38,500 0.1 956.1 40,370 0.0 958.34 9,500 1.6 963.7 40,700 2.6 962.2 6410 2.6 964.76 3,350 17.0 975.4 45,800 7.9 973.7 2132 8.1 977.15 830 17.2 991.8 54,200 2.4 989.8 1644 2.4 995.46 205 3.9


R&D ERL beam parameters

High Current

High Current

High charge

Charge per bunch, nC 0.7 1.4 5

Numbers of passes 1 1 1

Energy maximum/injection, MeV 20/2.5 20/2.5 20/3.0

Bunch rep-rate, MHz 700 350 9.383

Average current, mA 500 500 50

Injected/ejected beam power, MW 1.0 1.0 0.15

R.m.s. Normalized emittances ex/ey, mm*mrad 1.4/1.4 2.2/2.3 4.8/5.3

R.m.s. Energy spread, E/E 3.5x10-3 5x10-3 1x10-2

R.m.s. Bunch length, ps 18 21 31

Operation regimeParameter


2-3 MeV

2-3 MeV

20 MeV

20 MeV

20 MeV

2-3 MeV

SC RF GunSC 5 Cell cavity

Beam dump

BPM

DCCT

1MW Klystron

SRF Linac50 kW Transmitter ready to operate

Arc assembly

Quadrupole

Dipole

Tested in

BLD912

Arrived, test this summer

Measured, ready to be

installed

• ERL Enclosure (Vault) was constructed• 5-cell Cavity is being processed and tested at JLAB, arrived in

March, 2008• The dumping of HOM Q-values measured 2 orders of magnitude • 1 MW Gun klystron and 50 kW 5-cell cavity transmitter are installed • Recirculation loop magnets and vacuum system components have

arrived• Injection dipoles are under magnetic measurements• Gun drive laser is been procured • Gun is under construction at AES

BNL R&D ERL: Status


R&D ERL Commissioning Milestones and beyond

Coherent Electron Cooling Proof of Principal Test around 2012


Modifications from R&D ERL to P-o-P CEC

• Move SRF Gun, 5cell cavity, loop arcs and injection line from 912 to IR2

• Stretch straight line in order to accommodate cooling section (modulator-undulator-kicker ) ~15 m

• Build and install 7 m undulator

Bldg 912

IR2


SC 5 Cell cavity

IR-2 for proof-of-principle for CEC19.6 m

RHIC Beam RHIC Beam

RHIC lattice functions IR2

7 m4 m4 m

electron and ion beams


Electron beam lattice functions for CEC PoP test at RHIC

UNDULATOR

Modulator region

Kicker region


16.2 16.3 16.4 16.5 16.6 16.7 16.80

0.2

0.4

0.6

0.8

1

7.813 10 4

HistKE1 1

max HistKE1 1 HistKE11 1

max HistKE11 1

16.76416.254 HistKE1 0 HistKE11 0

20 10 0 10 2016.2

16.4

16.6

16.816.765

16.249

KE1

KE11

16.62213.389 Phi1 Phi11

Q=1.4 nC,

100% : dE/E=4.8x10-3, ex/ey=5.6/6.7 um

80% : dE/E=1.3x10-3, ex/ey=5.4/5.6 um

BNL R&D ERL electron beam longitudinal profile

The electron bunch is +/-15 degrees of RF

For CEC: emittance requirements are relax

The energy spread is important

Some injection line modification may be applied


CEC proof of principal at RHIC setup

Au bunch intensity 1E09

Z/A 79/197

Energy 40 GeV/n

RMS normalized emittances

2.5 mm-mrad

RMS energy Spread 4E-04

RMS bunch length 66 cm

Beta* 10 m

Electron bunch charge 5 nC (4x1.4nC)

Energy 21.7 MeV

RMS normalized emittances

5 mm-mrad

RMS Energy Spread 0.15 %

Beta* 5 m

pe, CMF 5.0 E09 Hz

Modulator length L1,m 4 m

Number of plasma oscillations

0.256

Ion bunch parameters Electron bunch parameters


CEC proof of principal at RHIC setup (cont.)

w 5 cm

Undulator length 7 m

B 1.2 kGauss

Beta_und 1 m

aw 0.555

FEL 18 m

Amplitude gain G =150, Lw 7 m

IBS rate 9 min

Cooling time, beam, 2.6 minutes

FEL parameters Cooling parameters

CEC 2Grp

nL2

Z 2

A

Electron bunches are usually much shorter that the hadron bunches and cooling time for the entire bunch is proportional to the bunch-lengths ratios

bunch CEC ,e

,hThe formula gives very encouraged result

More simulations and accurate studies are under way

Ion bunch: 2.5E-09 secElectron bunch: 50E-12 sec

Kicker length, L2 3 m

Cooling time, local, minimum 0.05 minutes


Plans & ConclusionsPlans & ConclusionsDesign of major ERL components is completed. Hardware components are being manufactured and/or procured.We plan to start commissioning of the R&D ERL in 2009

•First, we develop the straight pass (gun -- 5 cell cavity -- beam stop) test for the SRF Gun performance studies.

•Next, a novel concept of emittance preservation in a beam merger at the lower energy will be tested

•After recirculation loop completed, demonstrate energy recovery of high charge and high current beam

The prototype will serve as a test bed for studying issues relevant for very high current ERLs (since 2010)Proof of principle coherent electron cooling ions in RHIC at ~ 40 GeV/n is feasible with existing R&D ERL parameter and should be demonstrate around 2012

bnl r&d erl and coherent electron cooling test at rhic

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