Transcript Slides - Indico

Introduction to Accelerators
Part 4
M W Poole
Past Director and Honorary Scientist
ASTeC
Cockcroft Education Lectures
M W Poole
Remaining Topics
•
•
•
•
•
•
Undulator sources
Periodic magnet technologies
3rd Generation Light Sources (DIAMOND)
Energy recovery linac (ALICE)
Free Electron Laser
4th Generation Light Sources (NLS)
• Overview remarks
Cockcroft Education Lectures
M W Poole
Multiple Source ID Concept
12
Horizontal Position (mm)
B Field (T)
10
8
Position
Several successive wigglers
6
4
2
0
-2
Field
-4
-6
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
6
Longitudinal Position (m)
Combined wiggles
Magnetic Field (T)
4
2
0
-2
-4
-6
Multipole Wiggler =
Cockcroft Education Lectures
MPW
-1
-0.5
0
0.5
1
Longitudinal Position (m)
M W Poole
Trajectory in Multipole Wiggler
Sinusoidal field with period lu and peak value B0:
 2s 

B(s)  B0 sin 
 lu 
Electron also has a sinusoidal trajectory.
Electron angle and displacement will be:
Maximum angle is equal to K/
 2s  K
 2s 
dx B0e l u
  cos


cos
ds mc 2  l u  
l
 u 
x
 2s 
K lu

sin 
 2  l u 
B0e l u
K
 93.4B0l u
mc 2
Cockcroft Education Lectures
M W Poole
Trajectory in Multipole Wiggler
The radiation opening angle is typically 1/ so there is
little overlap between radiation from different poles
Multipole Wiggler
K >> 1
K/
2/
But what if K ~ 1 ?
2/
Interference effects can occur
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M W Poole
Interference
Condition for interference
d  nl 
lu
 l u cos q
s
d
q
lu
Electron
Cockcroft Education Lectures
M W Poole
Undulator Equation
Substituting in for the average longitudinal velocity of the
electron, s :
lu  K
2 2


l
1


q

2 

2n 
2

2
For a 3 GeV electron passing through a 50 mm period
undulator with K = 3, the wavelength of the first
harmonic (n = 1) on axis (q = 0) is ~ 4 nm
Cockcroft Education Lectures
M W Poole
Line Shape (q=0)
Similar behaviour
as diffraction
grating with N slits
Width ~ 1/nNl
Angular spread of harmonic
 r' 
Cockcroft Education Lectures
l
l

N l lu
L
For l ~ 1nm and L ~
5m, r’ ~ 14 mrad
M W Poole
K<1
Observer ‘sees’ the electron continuously as it oscillates by
less than ~1/. The electric field due to this electron is then
a pure sinusoidal and so there is only one harmonic.
1.5
1.4
1.2
0.5
Intensity
(Arb. Units)
Electric Field
(Arb. Units)
1.0
0.0
-0.5
1.0
0.8
0.6
0.4
-1.0
0.2
-1.5
0
10
20
Cockcroft Education Lectures
30
40
Time (Arb. Units)
50
60
70
0.0
0
10
20
30
40
Frequency (Arb. Units)
50
60
M W Poole
K > 1 (on axis)
Observer ‘sees’ the electron briefly as it oscillates by more
than ~1/. The electric field due to this electron is then a
series of spikes of alternating polarity.
If the observer is on axis the spikes are equally spaced.
The Fourier Transform of these spikes only contains odd
harmonics (n = 1, 3, 5, …)
15.0
1.4
Angle
1.2
5.0
+1/
Intensity
(Arb. Units)
Electric Field
(Arb. Units)
10.0
0.0
-1/
-5.0
1.0
0.8
0.6
0.4
-10.0
Field
0.2
0.0
-15.0
0
10
20
Cockcroft Education Lectures
30
40
Time (Arb. Units)
50
60
70
0
10
20
30
40
Frequency (Arb. Units)
50
60
M W Poole
Different Kinds of SR Sources
Cockcroft Education Lectures
M W Poole
Insertion Device Technologies
Electromagnets
Superconducting magnets
Permanent magnets
Typical periods required
~ 20 - 500 mm
Typical fields required
~ 0.5 - 10 T
Cockcroft Education Lectures
M W Poole
Electromagnets
Separate coils wound around iron poles. Difficult to
have small periods without excessive heat.
Ophelie (France) - 250 mm period, 0.11 T in both planes
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Restrictions on Specification
• Not free choice of periodicity
• Period/gap ratio is critical parameter (Maxwell !)
• Rarely < 2
• Gap set by aperture needs of beam, including tolerances
• Periodicity must incorporate coil space (if present)
• Permanent magnet systems optimise period
Cockcroft Education Lectures
M W Poole
Permanent Magnets
Most undulators and MPWs are built with permanent
magnets
High fields in short periods - no power supplies or cooling
Combined with iron poles : ‘hybrid’ configuration
otherwise: ‘pure permanent magnet’ devices (PPMs)
Modern permanent magnet materials are very
powerful - SmCo or NdFeB (1 - 1.5 T remanence)
Cockcroft Education Lectures
M W Poole
PPM Undulators or MPWs
  g 

B0  2.2 exp 
 lu 
g = gap between the two arrays
With 4 blocks per period the
field is quite sinusoidal
Cockcroft Education Lectures
M W Poole
Hybrid Undulators or MPWs
Iron poles increase the magnetic
field - but can make it less
sinsoidal
eg SRS 2.4 T MPW, 220 mm period
3.0
2.0
B Field (T)
1.0
0.0
-1.0
-2.0
-3.0
0
200
400
600
800
1000
Distance (mm)
Cockcroft Education Lectures
M W Poole
Periodic Magnet Engineering
Daresbury
Solutions
Cockcroft Education Lectures
M W Poole
In-Vacuum Undulators
In a storage ring the minimum gap is
typically 10 - 20 mm
It usually has to leave space for the
electron beam vacuum chamber
The latest generation of undulators put
the complete magnet inside the vacuum
chamber to save a few mm on the magnet
gap
Spring-8 (Japan)
Cockcroft Education Lectures
M W Poole
Modern World of Synchrotron Light Sources
Cockcroft Education Lectures
M W Poole
Storage Ring Brightness Scaling
Flux
BRIGHTNESS 
Emittance
(Emittance is phase space area)
 k
E
3
N cell
SRS: 2 GeV 16 cell 100 nm-rads
Cockcroft Education Lectures
2
ESRF: 6 GeV 32 cell 4 nm-rads
M W Poole
Third Generation Light Source Brightness
Comparison of 3rd Generation Synchrotrons
20
Diamond Main Parameters
Circumference 561.6 m
Energy
3 GeV
Current
300 mA
Lifetime
20 h
Emittance
- horizontal
2.7 nm
- vertical
2.5–50 pm
Min. ID gap
5-7 mm
Canadian Light Source
18
SPEAR3 (USA)
Emittance / nm rad
16
14
PLS (Korea)
12
10
MAX-II (Sweden)
ELETTRA (Italy)
8
ALS (USA)
6
Australian Synchrotron
BESSY II (Germany)
Swiss Light Source
4
ESRF
SPring-8 (Japan)
ALBA/CELLS (Spain)
SOLEIL (France)
Diamond
APS (USA)
2
PETRA III (Germany)
0
0
1
2
3
4
5
6
7
8
9
Energy / GeV
Cockcroft Education Lectures
M W Poole
Established Third Generation Light Sources
ESRF
6 GeV
Undulator
Sources
Grenoble
Cockcroft Education Lectures
M W Poole
The DIAMOND Project
3rd Generation Light Source
Conceived 1994 !
BOOSTER 3 GeV
Transfer line
Transfer line
LINAC
100 MeV
STORAGE RING
3 GeV 24 cells
300 mA
Circumference = 560 m
Instrument
Cockcroft Education Lectures
5 m and 8 m straights
M W Poole
Schematic of DIAMOND DBA Cell
Dipole Magnets
48
Quadrupole Magnets
240
Sextupoles
168
Cockcroft Education Lectures
Beta functions (m)
i
Dispersion (m)
Insertion Device
M W Poole
Linac and Booster
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Storage Ring Installation
Cockcroft Education Lectures
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DIAMOND SRF Cavity
Cockcroft Education Lectures
(Cornell ring)
M W Poole
DIAMOND Experimental Hall (2005)
Cockcroft Education Lectures
M W Poole
DIAMOND sited on Harwell Campus
Cockcroft Education Lectures
M W Poole
Accelerator Physics R&D Programme at DLS
•
Top-up and low-alpha modes
83 h of uninterrupted beam (Apr. ’09)
• Reduced coupling
coupling ~0.08% achieved
→ vertical emittance ~ 2.2 pm
• Nonlinear dynamics
• Collective effects
Measurements
Simulations
• Insertion devices
Cockcroft Education Lectures
M W Poole
Storage Ring Problems as Light Sources
•Equilibrium beam dimensions set by radiation emission
•Beam lifetime limits bunch density
(1011 turns)
•Demanding UHV environment
•Undulators restricted by cell structure and apertures
•Most issues worse at low energies (eg < 1 GeV)
FUNDAMENTAL 3GLS LIMITATIONS
Cockcroft Education Lectures
M W Poole
Energy Recovery Linac Principle
Converts linac to high current capability
Courtesy G Neil
Cockcroft Education Lectures
M W Poole
Testing Next Generation Ideas – ALICE at Daresbury
Chirped beam compression
~100 fs
FEL included
‘Green’ machine: energy recovery
ALICE = Accelerators and Lasers in Combined Experiments
Cockcroft Education Lectures
M W Poole
ALICE Photo-Gun Scheme
Cathode ball
Ceramic
SF6
Cathode
Vessel removed
Electrons
laser
XHV
Stem
Anode Plate
Courtesy: David Holder
Cockcroft Education Lectures
350 keV
M W Poole
ALICE Accelerating Modules
•
2 x Stanford/Rossendorf
cryomodules
– cryomodule = 2 x 9-cell (TESLAtype 1.3 GHz)
•
0.35-8.35 MeV booster module
– 4 MV/m gradient
– ~50 kW RF power
•
8.35-35.0 MeV linac module
– 14 MV/m gradient
– 16 kW RF power
Delivered April/July 2006
Commissioned September 2007
Operating at reduced levels
Cockcroft Education Lectures
M W Poole
ALICE Layout in Tower Building
Cockcroft Education Lectures
M W Poole
ALICE at Daresbury
Displaced linac now in line
Cockcroft Education Lectures
M W Poole
Elements of a Laser
Pump
Optics
Gain medium
All lasers contain a medium in which optical gain can be
induced and a source of energy which pumps this medium
Light Amplification by Stimulated Emission of Radiation
Cockcroft Education Lectures
M W Poole
Novel Laser Alternatives ?
• Lasers are very bright sources of radiation
• Lasing media include solids, liquids and gases
• Extremely high powers and ultra-short pulses
• Mainly limited to IR-UV output (some exceptions)
• Tunability severely limited (in general)
• Power limited by thermal effects
Cockcroft Education Lectures
M W Poole
The Free Electron Laser
• Exploit electron-wave energy exchange (Lorentz)
• Transverse beam modulation
• Magnet couples TEM field to particle (weakly)
• Axial velocity modulation causes bunching
• Relative phasing controls energy gain/loss
Electron Decelerator
Cockcroft Education Lectures
M W Poole
Next Generation Solution: Coherence
Incoherent emission:
Synchrotron Radiation
Intensity ~ Ne
electron
s
light
Coherent emission:
Free-Electron Laser (FEL)
Intensity ~ Ne2
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M W Poole
Gain Curve
Cockcroft Education Lectures
M W Poole
Free Electron Laser (FEL) Principle
Oscillator illustrated
λ
λn  u 2
2nγ
 K2
2 2
1


γ
θ 

2


where :
• relativistic electron beam passes through
periodic magnetic field - radiates
• mirror feeds spontaneous emission back
onto the beam
• spontaneous emission enhanced by stimulated
emission
Cockcroft Education Lectures
n  1,2,3 ...
E
γ
, K  0.934B0 λ u
m 0c 2
λ u is the undulator period
(B 0 is in Tesla and λ u is in cm)
M W Poole
FEL Oscillators
• Infra-red FELs operated since 1977
• Tunable and high power
• User facilities highly successful (eg FELIX in Nieuwegein)
• Short wavelength limited by mirrors (EUFELE <200nm)
• Mainly linacs but storage ring versions tried
• 4th Generation Sources need to employ alternative FELs
Cockcroft Education Lectures
M W Poole
FEL User Facilities
Stanford
Cockcroft Education Lectures
M W Poole
FELIX – Dutch IRFEL Facility
New high quality linac
UK undulator(s)
Lased August 1991
UK Agreement 1993 ….
Cockcroft Education Lectures
M W Poole
FELIX Characteristics
Fourier transform limited
Mirror scan
Cockcroft Education Lectures
M W Poole
FEL Tunability Example
(CLIO was French Project)
No table top laser can achieve
such a tuning range
Cockcroft Education Lectures
M W Poole
FEL Output Power Record
Energy Recovery Linac
2500
Laser Power (W)
2000
4.6 mA
1500
3.8 mA
1000
500
4.8 mA
Fundamental Lasing
Third Harmonic Lasing
Achieved Power
0
1
10
Wavelength(µm)
Courtesy G Neil – Jefferson Laboratory, Virginia
Cockcroft Education Lectures
M W Poole
UV/VUV Experiments
• Energy range (GeV) suggests storage ring (SRFEL)
• Small number of active centres
• Synergy with 3rd generation light sources
• Mirror problems - normal incidence
• User doubts - but pump/probe attractive
Cockcroft Education Lectures
M W Poole
High Energy EU-Funded FEL Project
Power (mW)
300
200
100
medium T @ 34 mA
high T @ 32 mA
0
235
240
245
250
255
260
265
270
Wavelength (nm)
Very limited tuning
200
250
300
350
Wavelength (nm)
Wavelength
Lased at 190 nm in 2001
World record !
350 - 356 nm
Lasing
Ta2O5/SiO2
yes
235 - 265 nm
HfO2/ SiO2
yes
218 - 224 nm
Al2O3/ SiO2
yes
189.7 - 200.3 nm
Al2O3/ SiO2
yes
LaF3/MgF2
no
186 nm
Cockcroft Education Lectures
Multilayer mirror type
M W Poole
FEL Oscillators - Summary
• Infra-red FEL operated 1977 – few sources before 1990
• Tunable and high power
• User facilities highly successful
(eg FELIX in Nieuwegein)
• Short wavelength limited by mirrors
(EUFELE <200nm)
• Mainly electron linacs but storage ring versions tried
• 4th Generation Sources need to employ alternative FELs
Cockcroft Education Lectures
M W Poole
FELs for XUV and X-rays ?
• Major electron accelerators (GeV +)
• Remove mirrors - new regime (demo 1985)
• Integrated USA R&D programme
• European and Japanese projects
• Enormous challenges - high brightness beams
• Particle Physics technologies - Linear Collider synergy
Cockcroft Education Lectures
M W Poole
High Gain FEL - Single Pass
No Mirrors !
•
•
•
•
•
Self Amplified
Spontaneous
Emission
(SASE)
electrons start emitting incoherent radiation
radiation from the tail of the bunch interacts with electrons nearer the front, causing the
electrons to bunch on the scale of the radiation wavelength
due to the bunching, the electrons emit more coherently
more radiation  more bunching  more radiation … an instability !
radiation power grows exponentially
Need for very high peak currents ~ kA
Cockcroft Education Lectures
M W Poole
High Peak Currents by Bunch Compression



sz0
z
z
z
sz
sE/E
RF Acceleration
Bunch Compression
Compress (shorten) bunch to increase peak current
(but at cost of energy spread from chirp)
Cockcroft Education Lectures
M W Poole
FLASH: Illustrating a High Gain FEL Light Source
Previously called TESLA Test Facility (TTF) at DESY
bunch compressor
Early configuration before upgrades
J. Rossbach/DESY Nov. 2001
Cockcroft Education Lectures
M W Poole
First TTF-FEL (FLASH) Lasing (2000)
J. Rossbach/DESY Nov. 2001
Cockcroft Education Lectures
June 2010 achieved 4.5 nm at 1.2 GeV
M W Poole
New World Record - LCLS 2009
Linac Coherent Light Source
1.5 Å
(25 of 33 undulators installed)
Use of 1/3 SLAC Linac
14 GeV
x,y = 0.4 mm (slice)
Ipk = 3.0 kA
E/E = 0.01% (slice)
courtesy of P. Emma, SLAC
Cockcroft Education Lectures
M W Poole
Europe’s Answer: XFEL in 2015
20 GeV
0.1 nm
UK unable to join !
1 G euro project
Cockcroft Education
Lectures
DESY X-FEL Parameters
~1 kA peak currents
Cockcroft Education Lectures
M W Poole
meanwhile in Japan …
The Next X-Ray Project - Japan
Start of User operation: end 2011
Cockcroft Education Lectures
M W Poole
Comparison 3rd and 4th Generation Sources
Cockcroft Education Lectures
M W Poole
SASE Issues – Seeding Alternative
SASE spectra are very noisy (in time and frequency)
seeded
SASE
FLASH, LCLS, XFEL are all SASE machines
Seeding improves beam quality enormously
Cockcroft Education Lectures
M W Poole
4GLS Concept - Multiple Sources and ERL
Proposed 4th generation light source
Incorporating advanced accelerator technology
beam splitter
high average
current loop
Abandoned 2007
Cockcroft Education Lectures
M W Poole
NLS Design Studies: Baseline Specification
•
Free-Electron Lasers to cover the range 50 eV to 1 keV :
FEL1: 50 - 300 eV
FEL3: 430 - 1000 eV
-
harmonics up to 5 keV
-
independently tunable via undulator gap variation
-
variable polarization using APPLE-II undulators
seeded in order to provide longitudinal coherence, in 20 fs
pulses, and better synchronisation to conventional lasers
-
•
•
FEL2: 250 - 850 eV
Conventional lasers + HHG: 60 meV (20 mm) – 50 eV
IR/THz source: e- beam generated and synchronised to the FELs
20 – 500 mm
Cockcroft Education Lectures
M W Poole
Start-to-End Simulations
Astra
Gun
A01
GENESIS
Elegant
A39
BC0
A02
A03
BC1
A04
A05
A06
A07
A08
BC2
A09
A10
A11
A12
A13
A14
DL
undulators
• Astra - optimise the injector, including space-charge effects
• Elegant - optimise beam quality delivered to the undulators, including CSR, longitudinal
space charge, wake-fields, ...
• GENESIS - validate the optimisation with full start-to-end time dependent FEL simulations
Operating in a seeded mode adds a vital factor to the optimisation:
the need for a relatively long region with constant beam parameters to tolerate
jitter between the seed laser and the electron beam pulses
Cockcroft Education Lectures
M W Poole
Baseline Optimisation (0.2 nC)
150 fs
before FEL
energy
Cockcroft Education Lectures
M W Poole
FEL Systems
Modulator 1
HHG 75-100eV λw = 44 mm
e- @ 2.25 GeV
Modulator 1
HHG 75-100eV λw = 44 mm
e- @ 2.25 GeV
HHG 50-100eV
Modulator
λw = 49 mm
e- @ 2.25 GeV
Modulator 2
λw = 44 mm
Modulator 2
λw = 44 mm
APPLE-II Radiator
λw = 56.2 mm
APPLE-II Radiator
λw = 32.2 mm
APPLE-II Radiator
λw = 38.6 mm
FEL3
430 - 1000eV
FEL2
250-850eV
FEL1
50-300eV
- common electron energy for all 3 FELs, allows simultaneous operation
- HHG seeding with realistic laser parameters, up to 100 eV
- harmonic cascade scheme to reach up to 1 keV
Cockcroft Education Lectures
M W Poole
Proposed New Light Source (NLS) for the UK
experimental stations
gas filters
IR/THz undulators
photoinjector
3rd harmonic cavity
diagnostics
accelerating modules
laser heater
BC1
BC2
BC3
spreader
collimation
FELs
IR undulators
synchronised to
FELs
Superconducting linac
2.2 GeV
Electron gun
3 FELs
50 eV–1 keV
Active STFC/DLS design team producing CDR for March 2010
Cockcroft Education Lectures
M W Poole
Recirculating Linac Layout
Laser
Heater
Linac
(2 modules)
Gun
Collimation + beam switchyard
(same as single-pass)
BC1
3w
Injection
dogleg
Linac
(8 modules)
Extraction/spreader
BC3
Merger
BC2
~30m
180˚ arc
180˚ arc
FODO + possible path length corrector
0m
50m
100m
150m
200m
Inject at ~200 MeV, two passes through 1 GeV
Total 10 SC modules
Cockcroft Education Lectures
-- compared with 18 in single pass
M W Poole
The UK Skill Base: STFC and the HEIs
• Accelerator Science and Technology Centre (ASTeC) created 2001
•
•
•
•
Response to decline of R&D in UK
DL and RAL
Centre of excellence in specialised science and technology
Strong HEI links
• Cockcroft + John Adams Institutes created 2004
• Multi-HEI collaborations grant funded 2004-2008 (LC-ABD and UK-NF)
• Healthy programmes but major technology infrastructure lacking
• STFC accelerator R&D strategy under review
• Next Major UK project ?
Cockcroft Education Lectures
M W Poole
Cockcroft/ASTeC Programmes
• Particle Physics:
LC NF
• Photon Sources:
ALICE
• Neutron Sources: ESS
LHC/Super-B/HIE-ISOLDE ?
NLS
ISIS
• Novel:
FFAG
• Technology:
Magnetics SRF Vacuum Diagnostics
Plasma Wake
KE ?
All with varying degrees of certainty !!
STFC prioritisation reviews under way
Cockcroft Education Lectures
M W Poole
Laser Plasma R&D
•
Substantial UK activity – RAL and Strathclyde experiments
•
Astra-Gemini upgrades at RAL
•
ALPHA-X consortium – 7 HEIs + RAL/DL + international
•
Theory modelling too
•
Also target foil proton/ion projects (LIBRA)

 0.8%

Number of electrons / MeV [a.u.]
1.0
0.5
0.0
79
80
81
82
83
84
85
86
87
88
89
90
91
Energy [MeV]
Cockcroft Education Lectures
M W Poole
Sir John Douglas Cockcroft FRS
(1897-1967)
The Nobel Prize in Physics 1951
Cockcroft Education Lectures
M W Poole