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A U.S. Department of EnergyOffice of Science LaboratoryOperated by The University of Chicago
Argonne National Laboratory
Office of ScienceU.S. Department of Energy
Beam Source Requirements forHigh Beam Power Accelerators
John W. LewellenAccelerator Systems DivisionAdvanced Photon Source
2
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
Acknowledgements
Charles Brau (Vanderbilt)Jym Clendennin (SLAC)Dave Dowell (SLAC/LCLS)Klaus Flöttmann (DESY)Fred Kiewit (Eindhoven)Yuelin Li (ANL)Kwang-Je Kim (ANL)John Noonan (ANL)
John Petillo (SAIC)John Power (ANL)John Schmerge (SLAC)Charles Sinclair (Cornell)Frank Stephan (DESY-PITZ)Todd Smith (Stanford)Alan Todd (AES)
and many others for interesting discussions ongun design & improvement
Katherine Harkay (ANL) – ongoing discussions & support
3
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
Overview of the Talk
• Acknowledgements & Introduction
- What this talk is not about
- Accelerator Taxonomy
- What drives the requirements?
• Source requirements
- Storage-ring replacements
- X-FELs
- MW-class IR-FEL facilities
• Conclusions
4
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
What am I not talking about?
• Injector & linac technology specifics
- DC vs. RF
- NC vs SRF
- recirculation
• Particular proposed future sources in any detail
- provide broad brush strokes
- generalization of performance figures & concepts
• “Operational” performance (i.e. uptime, MTBF, MTBM, etc.)
“User Perspective” (from machine builder’s standpoint)
5
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
Accelerator Taxonomy
• “Big Iron” accelerators
- Linear colliders
- Next-generation x-ray lightsources
• “Desktop” accelerators
- Electron microscopy
- Electron beam lithography
- Small laboratory experiments
• “Mini-Me” accelerators
- Radioisotope generation
- High-power free-electron lasers
- Slow positron production
- Pulse radiography
Courtesy S
LAC
/LCLS
Courtesy LLNL
6
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
What drives the requirements?
• Linac-based light sources
- bifurcation between high-flux and high-brightness
- minimum performance enhancement to be worthwhile
- our ability to make magnetic structures
• “Mini-Me MW” FELs
- wavelength
- maximum desired electron beam power
- size requirements
7
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
Sense of Scale: X-ray Facility
AdvancedPhotonSource
APS: 3rd-generation storage-ring light source
Circumference: ~ 1 km
Beamlines: ~ 35 bending magnet ~ 40 undulator/ID
Local user group offices
Users per year: thousands
Scheduled run hours per year: thousands
8
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
What improvements can be made?
• Increase the x-ray beam flux (photons / sec unit bandwidth)
• Increase the x-ray beam brightness (peak or average)
- more “useful photons” per unit flux delivered
• Increase the temporal resolution (shorter x-ray pulses)
- time-resolved phenomena
- pump-probe experiments
• Coherent light production
- “light bulb-to-laser” transition
9
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
Storage Rings vs. Linac-Based Light Sources
• Electrons circulatemany times
• Beam power delivery =γ losses
• Electron beamproperties set by thering (injector irrelevant)
• Electrons make onepass
• Beam power delivery =Ebeam·Ibeam + γ losses
• Electron beamproperties set by thelinac (injector iseverything)
Storage Ring Light Sources Linac-Based Light Sources
10
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
Storage-Ring Replacements & X-FELs
“1st-generation” Linac Based Light Sources
Storage-RingReplacement
(SRR):
Higher Peak Brightness
Improved TemporalResolution
X-ray Free ElectronLaser (X-FEL):
Coherence
Temporal Resolution
11
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
SRR – Performance Requirements
• >102 peak brightness improvement over existing SR sources
• < ps temporal resolution (i.e. bunch length)
y,nx,n
22 INB
εε
γ∝ωωΔ
0.1
0.1
1.0
3 – 18
BunchCharge
[nC]
New Gun (II)
New Gun (I)
S-band Gun
APS
Source
13.5‡1351000† 0.1 0.1 x 0.1
135*1351000† 0.1 0.1 x 0.1
45*453000† 0.331 x 1
1*1300 20 - 4043 x 0.5
Avg.Brightness
Enhancement
PeakBrightness
Enhancement
PeakCurrent
[A]
BunchLength
[ps]
Norm.Transverse
Emittance [µm]
† With linac-based bunch compressor‡ Assuming 10 mA average beam current* Assuming 100 mA average beam current
12
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
But here’s the kicker…Imean = Qb / Δt
where:
Imean = average beam current Δt = bunch-to-bunch interval
Qb = single-bunch charge
Δt: as large as possible fortiming exp.
Qb: as small as possible for εn
define SRR in terms ofbrightness, not flux
1 10 1000.1
1
10
100
1?103
1 nC100 pC10 pC
Bunch spacing [ns]
Average current [mA]
13
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
The Pierce Parameter and X-FEL Performance
3
x,n2p
x2
2b
22u
A
332
x
bu
A
p I
64
fK
I
1
2
1
22
Kf
I
I
εγ⋅
βπ
λ⋅=
γ
πσ
λ=ρ
The larger the Pierce parameter…• the smaller the gain length• the shorter the X-FEL undulator• the less expensive the facility is
0
25
50
75
100
125
150
175
200
225
0.1 0.6 1.1 1.6 2.1
Norm. emittance [µm]
Satu
rati
on
len
gth
[m
]
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
η/(η
d+η
+η
)
LCLS OperatingPoint
Emittance too big? Pump up K andλu … but there’s a price.
γ-2 λu for fixed λ, so slow progress
14
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
X-FEL – Performance Requirements
• Maintain LCLS wavelength performance
• Minimize overall systems cost
+=2
12
2
2
Ku
γλ
λ
Fixed Parameterλ = x-ray wavelength = 1.5 Å
Parameters we can adjustλu = undulator period > 1_ cmK = undulator strength ~ 1
Parameter to Minimizeγ = electron beam Lorentz factor
With existing undulatortechnology, need abouta 4 GeV beam to make1.5 Å x-rays … assumingwe can get the gain.
15
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
SCALE: 1 in = 100 m
100 m
APS Linac
PAR
Storage Ring
Booster Synchrotron
APS VUV-FEL
N
10 2.400
1.000
Primary Linac SecondaryLinac
UndulatorFarm
Storage RingInjection Branchline
Interleaving Dipole Energy Separator
X-FEL Design Optimization…
Parameter LCLS High -Energy Low -? design #1 Low -? design #2 Beam Energy 13.35 GeV 7 GeV
(APS beam energy) 4 GeV
(alternate params) ?n 1.2 ?m 0.1 ?m 0.1 ?m (0.15 ?m) Ipeak 3400 A 1000 A 500 A (1000 A) ? E/E 0.01 % 0.025 % 0.025 %
Undulator period 3.0 cm 3.0 cm 1.25 cm K 3.7 1.3 1.0 Optimized beta fcn. 7.5 m 3 m 2 m Saturation length 91 m 31 m 24 m
Assume:• Existing undulator technology• Existing linac technology• “Classic” SASE design
16
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
Summary: SRR and X-FEL sources
• Single-bunch parameters for X-FEL and SRRsources are remarkably similar:~ 0.1 µm normalized emittance (or better)
~ 1 kA peak beam current (post-compressor)
• SRR will need 10 – 100 mA beam current to maintainreasonable average brightness
• X-FELs might want long inter-pulse spacing tochange out samples
17
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
A Word on Linear Collider Guns…
• Why are these desired?
- Damping rings are expensive as well as challenging
- Makes most sense when LC combined with X-FEL
• Basic parameters not dissimilar from X-FEL guns
• Additional requirements:
- flat-beam production (100:1 emittance ratios)
- polarized electron beam production
• A positron gun would be nice…
18
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
IR-FEL – Driving Parameters• “1-ish” µm operating wavelength
• ~ 100 MeV max. beam energy
• 1 MW optical power output
• Notional FEL extraction efficiency: ~ 1%
⇒1-A average beam current
⇒100 MW circulating e-beam power
• Large outcoupling (50-ish %)
⇒ reduce circulating optical power (save the mirrors)
⇒high gain per pass
⇒ fairly high beam quality
19
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
High-power IR and UV FELs
Injector
7 MeV 50 MeV 100 - 150 MeV
Beam ParametersIpeak ~ 500 – 1000 Aεn ~ 5 – 10 µm
δE/E ~ 0.1 – 0.25%
Electron beam power: 100 MWOptical beam power: 1 - 2 MW
RF power used: 7 MW (to dump)Average beam current: 1A
Wallplug efficiency: ~ 10 – 20%: 2 MW (FEL)
20
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
Source Parameter Estimation
• For the moment, assume no “exotic” designs
- no tapered undulator
- no linac/wiggler combinations
- etc.
• Assume some “reasonable” undulator parameters- λu ~ 3 cm
- K ~ 2− β ~ 10 m
• Assume some “bulk” beam properties
- Ebeam ~ 100 MeV- ΔE/E ~ 0.25% (rms)
21
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
What do we get…?
geometr ic beam emit tance
?x0 . 7 1 5m m? beam size in the undulator (average)
aw1 . 4 1 4? wiggler parameter the rest of the known universe uses
?r1 . 1 7 5?m? l a s e r w a v e l e n g t h
fB0 . 8 0 8? helical undulator Pierce parameter reduction factor
? 3 . 8 4 81 03?
??Pierce parameter
L1D0 . 3 5 8m?one-d imens iona l ga in length
Lg0 . 6 1 6m? three-dimensional gain length
Pbeam1 0 0G W? peak particle beam power
Pn0 . 0 6 1W? peak noise power at startup
Psat2 0 7 . 9 4MW? peak optical power at saturation
Lsat1 4 . 8 8 7m? saturation length of the device
ps 1 012?sec???Particle beam properties Undulator propert ies
particle beam energy:Eb1 0 0MeV??? wiggler parameter
(NOT rms):K 2??
normalized electron beam emit tance: ?n1 0?? m m? mrad???
undulator per iod: ?w3cm???rms relative energy spread on the beam:??0 . 2 5%?? average design undulator
beta function:?f1 0m??
peak current: Ip1 n C?1 ps?
??
Ip1 1 03? A?
Calcu la ted proper t ies
? 1 9 5 . 6 9 5? Lorentz factor for the beam
? 5 1 . 1n mrad??
σx = 0.715 mmSpot size in undulator isreasonable; no exoticfocusing schemes needed
λr = 1.175 µmLaser wavelength is in thedesired range
Lg = 0.616 mGain length (1 e-foldinglength) is a reasonable matchfor a few-m undulator in ahigh-loss cavity.
εnx = 10 µm, Ip = 1 kAAdjust to get reasonable Lg
22
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
Summary – MW-class ERL-FEL Sources
• 1-A average beam current; Qb = 1 amp / frf
• Transverse emittance: ~ 10 µm (rms norm) @ ~ 1.5nC / bunch
• Longitudinal emittance: ~ 100 keV ps (rms)
23
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
LCLS gun
TESLA X-FEL Gun
IR/UV ERL
MicroscopeGun
X-FEL, SRR Gun
0.0001
0.001
0.01
0.1
1
10
0.0001 0.001 0.01 0.1 1 10 100
Bunch charge [nC]
Tra
ns.
em
itta
nce
[u
m]
Specified Guns
New Gun Designs
TESLA X-FEL GunLCLS gun
new X-FEL gun
MicroscopeGun
SRR Gun
IR/UV ERL
0.0001
0.001
0.01
0.1
1
10
0.0001 0.001 0.01 0.1 1 10 100 1000
Average beam current [mA]
Tra
ns
. e
mit
tan
ce
[u
m]
Specified Guns
New Gun Designs
General Source Requirements
TESLA X-FEL Gun
LCLS gun
New X-FEL gun
MicroscopeGun
SRR Gun
IR/UV ERL
0.0001
0.001
0.01
0.1
1
10
100
1000
0.0001 0.001 0.01 0.1 1 10 100
Bunch charge [nC]
Ave
rag
e b
eam
cu
rren
t [m
A]
Specified Guns
New Gun Designs
24
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
A Word on Recirculation Losses…
• Megawatt-class IR FEL
- 1 A x 100 MeV = 100 MW
- 1 kW losses = Pbeam x 10-5 = 0.001%
- 1 W loss = 10-8 ≈ 90 electrons / bunch (from 1.4 nC)
• Storage-Ring Replacement X-ray Source
- 100 mA x 5 GeV = 500 MW
- 1 kW losses = 0.0002% beam loss
- 1 W loss = 2·10-9 ≈ 1_ electrons / bunch (from 100 pC)
• Controlling halo no longer means winning an X-Box game.
• Source parameters must be consistent with zero-lossoperation.
25
PioneeringScience andTechnology
Office of Science U.S. Department
of EnergyJohn Lewellen8 – 10 November 2004 Workshop on High-Power Beams
Summary
• X-FEL wants:
- order-of-magnitude improvement in emittance
• MW IR-FEL wants:
- true CW operation
- high beam currents (ca. 1 A) at modest energy
- ~ 10-8 recirculation losses
• SRR wants:
- true CW operation
- high beam currents (ca. 10 – 100 mA) at 7-ish GeV
- order-of-magnitude improvement in emittance
- True zero-loss recirculation
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