chris tennant jefferson laboratory march 15, 2013 “workshop to explore physics opportunities with...
TRANSCRIPT
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)
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)
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 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
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