a recirculating linac synchrotron light source for ......a. zholents, august 21, 2001 • this...

A. Zholents, August 21, 2001

A Recirculating Linac Synchrotron Light Source for Ultrafast X-Ray Science

J. Corlett, S. DeSantis, N. Hartman, P. Heimann, R.LaFever, D. Li, H. Padmore, R. Rimmer, K. Robinson, R. Schoenlein, J. Tanabe, S. Wang, LBNL, Berkeley

D. Kairan, BINP, Novosibirsk

A. Zholents


• Goal: A dedicated ultra-fast x-ray user facility with characteristics driven scientific needs in Physics, Chemistry and Biology:

– High time resolution: 50 fs (FWHM)– High flux: 1011 photon /s 0.1% bw– Wide photon energy range: 1 keV to 10 keV, tunable– Synchronized to optical lasers– Many undulator and bend magnet photon beamlines

• Constraints– Must be based on proven, robust technology

• A user facility, not an accelerator development project


• This project is an extension of the Berkeley fsec x-ray program

– 300 fsec Thompson scattering• R.W.Schoenlien et al., Science 274, 1996; A.H.Chin, et al. PRL 83, 1999

– psec streak camera detection using synchrotron x-rays• A.M.Lindenberg, et al., PRL 84, 2000

– laser induced 100 fsec beam slicing in a synchrotron• R.W.Schoenlien et al., Science 287, 2000

– proposed slicing using an undulator source• R.W.Schoenlien, R.W.Falcone, proposal to DOE, 2000

– parallel development of atto-second laser driven electron beam source• A.A.Zholents. et al., PAC 2001

– Linac driven ultra-fast x-ray source• A.A.Zholents. et al., PAC 2001; H.Padmore et al., SRN 2001

• This project is driven by a very strong local fsec optical spectroscopy community


Bright electron beams from a photocathode gun:

Q=1nC, transv. emit. = 2x10-4 cm, long. emit.=8x10-3 cm (10 ps, 15 keV) Brightness = 2x1019 electrons/cm3

Compare with the ALS beam:Q=1nC, transv. emit. = 1.5x10-3 cm / 3x10-5 cm , long. emit.=1.5 cm (15 ps, 1900 keV)Brightness = 1x1017 electrons/cm3

(BNL, SLAC, LANL, UCLA, FNAL, Boeing, CERN, DESY, …)

Single pass accelerator


10.0 m

50.0 m 33.7 m

6 0 0 Me V Linac

1 4 0 Me V Linac 1 0 Me V

2 .5 Ge V

Recirculat ing Linac X-ray Source for Ultra Fas t Scie nce

Sp re a d e r

B0B2

B1

B4B3

Q11Q12Q13Q14Ba1Ba1

Ba1Sa 1 1

Qa11Sa1 2

Qa12Sa1 3

Qa13Ba1

Ba1

Ba1

Sa 1 1Qa11

Sa 12Sa1 2

Sa1 3Sa1 3

Ba 1Ba1

Ba 1

QS1 1 QS1 2

inject ion chicane

Q21Q22Q23Q24Ba2

Ba2Ba2

Ba 2Sa2 1

Qa21Sa2 2

Qa22Sa 23

Qa23Ba2

Ba2

Ba2

Ba2

Ba2

Ba2Sa2 1

Qa21Sa 2 2

Qa2 2Sa2 3

Qa2 3Ba 2

Ba2

Ba 2Ba 2

Q31Q32Q31Q32

Ba3Ba 3Ba3

Ba 3Ba 3

Ba3

Q41Q42Ba 4Ba 4Ba 4Ba 4

Ba4

Spreader

Isochronous arc

600 MeV

Superconducting linac

Photocathode gun

Crab cavityUndulator farm

Flat-beam optics

A schematic of the machine


60 m 28.6 m

39.

6 m

6 0 0 Me V Linac

1 1 0 MeV Linac 1 0 Me V

6 undulator, 2m long6 magnets, 2 T, 8 keV, 60 mrad

A layout of the 2.5 GeV recirculating linac


Energy 10 MeVCharge 1 nCNormalized rms horizontal emittance 20 mm-mradNormalized rms vertical emittance 0.4 mm-mradEnergy spread at 10 MeV 15 keVPulse length (uniform distribution) 10 psThe RF gun parameters:RF frequency 1.3 GHzPeak electric field on a cathode 70 MV/mRepetition rate of injection pulses 1 - 10 kHz

Electron beam parameters from the injector

Laser parameters:Wavelength (3-rd harmonic of Ti:sapphire laser) 267 nmPulse energy 100 µJPulse length (FWHM) 10 psRepetition rate 1-10 kHz


Proposed by Brinkmann, Derbenev, Flötmann

Flat beam from the electron gun

LBNL is collaborating with FNAL in future experiments

A0 photocatode accelerator (FNAL)

Edwards and co-workers obtained 50 to 1 ratio of the horizontal to vertical emittance


RF gun designAccelerating voltage at cathode needs to be ~ 40+ MVm-1 to achieve good beam quality

Gun repetition rate then limited by cavity wall heating

Design cavity for optimal voltage, and wall power density < 100 Wcm-2

Field calculations for 1.3 GHz cavity

1.3 GHz cavity with cooling

Temperature profile

Von Mises stress

gun freq Eocath ..

reprate

MaxPdens

(MHz) MV/m kHz W/cm 2

1300 1300 13.8 CW 99.01300 62.0 10 99.91300 40.1 100 99.5

2600 2600 11.0 CW 99.72600 82.6 10 99.82600 53.5 100 99.7

pillbox 1300 13.8 CW 2071300 37.8 10 1001300 24.6 100 100

ANSYS model of RF gun design

E H

Maximum 68° above ambient temperature

Maximum stress 5500 psi safely below “limit” of 18000 psi for 10,000 cycles in Cu


Sp re a d e r

B0B2

B1

B4 B3

Q11Q12Q13Q14Ba1Ba1

Ba1Sa1 1

Qa11Sa1 2

Qa12Sa1 3

Qa13Ba1

Ba1

Ba1

Sa1 1Qa11

Sa1 2Sa1 2

Sa1 3Sa1 3

Ba1Ba1

Ba1

QS1 1 QS12

inje ct ion chicane

Q21Q22Q23Q24Ba2

Ba2Ba2

Ba2Sa2 1

Qa21Sa2 2

Qa22Sa2 3

Qa23Ba2

Ba2

Ba2

Ba2

Ba2

Ba2Sa2 1

Qa21Sa2 2

Qa22Sa2 3

Qa23Ba2

Ba2

Ba2Ba2

Q31Q32Q31Q32

Ba3Ba3Ba3

Ba3Ba3

Ba3

Q41Q42Ba4Ba4Ba4Ba4

Ba4


Spreader

B2 B3B4 Q42Q41 Ba4 Ba4Q34Q33Q32Q31

Ba3 Ba3 Ba3

Q24Q23Q22Q21 Ba2Ba2

Ba2

Ba2

B1

B0

Q14Q13Q12Q11 Ba1Ba1

Ba1Sa1 1

Qa11Sa1 2

Qa12Sa1 3

Qa13


Septum magnet, J=50A/mm2Septum quadrupole, J=20A/mm2


Spreader


LINAC Technology

• superconducting linac developed for DESY Linear Collider TESLA with industry

- 42 MV / m accelerating gradient achieved in a single cavity

TESLA superconducting RF modules


SC 600 MeV Linac

9-cell superconducting cavity for TESLA: gradient Eacc=23 MV/mEacc 20 MV/m

Frequency 1.3 GHzOperation mode CWQuality factor 1x1010

RF power loss/cavity 42 WCavity length 1.038 mModule length 12 mCavities/module 8Beam current 0.04 mABeam power/cavity 800 WQbeam 6x108

Bandwidth 200 HzQexternal 6.5x106

RF power/4 modules 540 kWRF power loss/4 modules 1.3 kW


Specify cryosystem 50% above expected load

2 MW wall-plug power for cryosystem

Superconducting RF and cryogenic systemsRF power requirement for CW operation, five cryomodules at 20 MVm-1 (including injector module)

1.7 kW to wall currents , 25.4 kW to beam power

To maintain feedback control of cavity resonance need bandwidth ~ 200 Hz

Cavities must be strongly over-coupled: Qexternal ~ 6.5 x 106

Klystron power required 670 kW

1 MW wall-plug power for RF

Investigate recirculating RF power. Efficiencies from recirculating beam small.

Thermal losses in cavity dominated by BCS resistivity, plus static heat load

BCS losses increase by a factor of 50 at 4K compared with 2K

RBCS ~ 2x10-4 1T

f1.5

2 e-17.67T

Pcompressor - Prefrigeration 300 - TT η=


Transverse instabilities in a recirculating linac

• Single bunch, multi pass-cumulative beam break up:

Average current = 40 µµµµAPeak current = 200 AAverage linac beta-function = 35 m

1

2

3

4

5

6

7

8

9

10

�2 �1.5 �1 �0.5

20

40

60

80

100

120

Transverse wake field, V/pC/m

z, cm

z, cm�0.4 �0.2 0.2 0.4

1

2

3

4

5

6

7

ρ(z)

y/ σyAlignment rmserror = 0.5 mm


First pass

Second pass

Third pass

Fourth pass

Mitigation of BBU through the four linac passes

Linac cavities align with errors


The effect of the misalignmentcan be compensated by an appropriate initial displacement y0

�0.3 �0.2 �0.1 0.1 0.2 0.3

0.1

0.2

0.3

0.4

0.5

0.6

z, cm

y/ σy

Compensation by orbit off-set∫

∑ ∑∞

⊥⊥

⊥

′′′+∆

=

∆+∆

′+

++

∆+−∆+=

02

200

0

0

00

00000

)()()(

),,(

1lnLˆˆ1ln),,()(

zdzWzzLrzWF

yddyzWFyzy jjii

ργ

γγ

γγ

γγ

γγ

γγγ ff

y0 = −f i di + ˆ f i ˆ d i∑∑

∆γγ 0

− ln 1 +∆γγ 0

initial displacementinitial angle

RF cavities misalignments

cryomodules misalignments

At the end of the linac:


magnet

σθ is the natural openingangle of undulator radiation

Asymmetrically cut Bragg crystal

RF RF

Compression of x-ray pulsesis possible due to a correlation between the longitudinal and transverse positions of electrons inside the electron bunch created by the RF orbit deflection in a cavity in the beginning of the final straight section.

( ) ( )zkE

eUzy RFundRFb

RF Sinββδ =

yσδ >>y2d

2by σσσ +=

Diffraction limited size of a source at λŸ1Å: ~3 µmdσBeam size at εn=0.4 mm-mrad: ~14 µmbσ


Undulator place holders

Optical functions

½ Linac ½ LinacArc4 Arc4Undulator farm


2 4 6 8 10 12keV

255075

100125150175200

undulatorbend magnet

X-ray pulse length, fs (FWHM)

Flat beam with normalized emittances: vertical = 0.4 mm-mrad; horizontal = 20 mm-mrad

X-ray pulse length

Needs Urf=8 MV at frf=1.3 GHz


RF RF

LASER OSCILLATOR(passively modelocked)

Laser/X-ray Timing Jitter

∆t ∆t1.3 GHz(RF Kick)

electron bunch

laser pulse

x-rays

aperture

MASTER OSCILLATOR

LASER OSCILLATOR GUN + LASER DRIVER LINAC

LASER AMPLIFIER “CRAB” CAVITY

Synchronization of optical and x-ray pulses


photon energy (eV)

flux

(ph/

s/0.

1% B

W)

106

108

1010

1012

103 104

Flux Comparison – Femtosecond X-rays (10 kHz)

undulator(14 mm period, 2 m length, 1.5 T field)60 fs

Recirculating LINAC (2.5 GeV)

undulator(20 mm period, 1 m length, 1T field)200 fs

ALS BL6.0 (1.9 GeV)

bend magnet (2 T, 3 mrad)60 fs

Recirculating LINAC (2.5 GeV)

a recirculating linac synchrotron light source for ......a. zholents, august 21, 2001 • this...

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