Upgrade Capabilities

of the JLab FEL DriverChris Tennant

Jefferson LaboratoryMarch 15, 2013

“Workshop to Explore Physics Opportunities with Intense, Polarized Electron Beams up to 300 MeV”

Outline Review of the Jefferson Lab FEL Driver Upgrade scenarios

• Flexible machine, many options available

Present capabilities• DarkLight experiment

Preliminary S2E for low charge• understanding low-charge operation

Experimental hall transport line• Fixed-target experimental program

Capabilities of RF drive Incorporating a polarized injector

• Maintain high-charge gun capabilities

Key Components Summary

Jefferson Lab FEL Driver: 2 ERLsDC Gun

SRF

Linac

UV FEL

Tran

spor

t Lin

e

Dump

IR W

iggl

er

Bunch

ing

Chica

ne

THz L

ine

350 keV DC photocathode gun, 9 MeV booster, Penner bend merge 3-cryomodule linac Bates-bend arcs longitudinal matching/bunch compression in

chicane for IR arc/bypass for UV (“chicaneless”)

energy compression during recovery nonlinear compaction management

IR FEL: 14+ kW at 1.6 microns, several kW at multiple wavelengthsUV FEL: High power (100+ W) at 70 and 400 nm, coherent harmonics into VUV (10 eV)THz Beamline: 10s of W at (0.2-1.5) THz

Upgrade Scenarios

DL Upgrade

100 MV Cryomodule

Two 100 MV Cryomodules

Polarized e- Injector

RF Drive (300 kW)

Experimental Hall

Transport Line

Energy (MeV)

1-pass

2-pass

Repetition Freq. (MHz)

Linac RF Power (kW)

Polarization

75

120

No

260

750

300

130180

360

Yes

300

600

DarkLight Experiment 450 kW (4.5 mA CW at 100 MeV) through 2 mm

aperture for 8 hours Clean transmission, low beam loss (6 ppm) Achieved small beam size (50 μm rms) (Note: performed at 60 pC/bunch)

1 mm

1 mm

sx = 50 mmsy = 52 mm

(courtesy P. Evtushenko)

DarkLight with 20 pC 20 pC injector solution, optimized for beam brightness (courtesy Fay Hannon) Transverse emittance preserved (< 1 mm-mrad)

DarkLight with 20 pC

sx,y = 11.5 um

Physical phase space at the location of the DarkLight cube

Longitudinal Match

30 ps

1.9

MeV

A B C D

B CD

A B C D

Beam Quality Issues at Low Charge Coherent Synchrotron Radiation

should not be an issue; reduced charge, no bunch compression Space charge

charge density may be comparable Halo

Due to flexibility of machine, have some level of control

Low-charge operation Beam can become very bright,

care must be taken with longitudinal phase space which can become “spindly/thready”

Transport Line to Experimental Hall Avoid interferences with lab

infrastructure for new (fixed-target) experimental hall

Need a spectrometer to phase linac for 1-pass operation

Preserve beam quality

(courtesy D. Douglas)

Capabilities: 120 kW RF Drive

20 pC at 75 MHz2 pC at 750 MHz

2.7 pC at 75 MHz0.27 pC at 750 MHz

Capabilities: 300 kW RF Drive

50 pC at 75 MHz5 pC at 750 MHz

6.7 pC at 75 MHz0.67 pC at 750 MHz

Polarized Electron Injector Want to retain functionality of current gun – which is optimized for

high charge• install gun within FEL “ring” and use 180° arc to merge to linac

200 kV

350 kV

(under construction)

Polarized Injector: Merger 4-quad matching section + 4-period FODO arc

Polarized Injector: Merger Push 100K particles through with PARMELA

• Suffers no significant transverse emittance degradation• The arc has M56 = 0.25 m; with initial chirp on bunch from booster,

beam gets compressed a good thing

Longitudinal MatchA B C D

10 ps

B C D

0.4

MeV

A

BCD

Energy Spread at Linac Exit

DEfull = 1.8 x 10-3

DEfull = 1.5 x 10-2

Current mergerArc merger (polarized source)

Key Components to Upgrade(s)

Polarized Gun: new generation gun design (350 kV) DC Power Supply: Drive Laser: Buncher: reuse from FEL injector (soon to be replaced) Booster: reuse from FEL injector (soon to be replaced)

Merger Design: FODO arc to allow placement of gun within FEL ring

Inje

ctor

Mer

ger

Currently, the machine can provide unpolarized beam for internal target experiments (e.g. DarkLight)

To support a fixed-target program with polarized beam requires:

Key Components to Upgrade(s) Cryomodules: 100 MV module by end of 2013; increase

energy further by adding two more refurbished cryomodules RF Power: installing 12 GeV klystrons would increase our

capacity from 120 kW (8 kW klystrons) to 300 kW (12 kW klystrons)

Recirculator: though specified for 80-210 MeV operation, with modification to the temperature of the cooling water, the hardware is capable of operating at 300 MeV

Experimental Hall: civil construction Transport Line: new dipole magnet design required, vacuum

chamber

RFRe

circ

ulat

orEn

d St

ation

SummaryCurrent Fall 2013 Full Capability

ERL External* ERL External* ERL External*

E (MeV) 80-135 80-260 80-165 80-320 80-310 80-610

Pmax (kW) 1350 120 1650 120 3100 300

I (mA) 10 1.25-0.38 10 1.25-0.31 10 3.75-0.5

fbunch (MHz) 75 75/750 75/750

Qbunch (pC) 135 16.7-5 135/13.5 16.7-4/1.67-0.4 135-13.5 50-6.7/5-0.67

etransverse(mm-mrad)

10 ~3 10/~3 ~3/~1 10/~3 ~5/~2

elongitudinal(keV-psec)

50 ~15 50/~15 ~15/~5 50/~15 ~25/~10

75 MHz drive laser;RF drive and gradient

limited

750 MHz drive laser; single 100 MV module

12 GeV RF drive; three 100 MV modules

(courtesy D. Douglas)

*assumes transport line and experimental hall in place