Transcript FELs and X band

FEL X band issues
M. Dehler, BE/RF & PSI
• SwissFEL project at PSI
• FEL specific RF issues
• The CLIC/PSI/ST X band structure
PSI Ost
PSI West
Large research facilities
Proton
Accelerator
Spallation Neutron
Source SINQ
Swiss Light Source
SLS
SwissFEL – the next big Facility at PSI
Slides courtesy H. Braun
SwissFEL, the next large facility at PSI
SwissFEL parameters
FEL principle
Electrons interact with periodic magnetic field
of undulator magnet to build up an
extremely short and intense X-ray pulse.
Wavelength from
1 Å - 70 Å
Pulse duration
1 fs - 20 fs
e- Energy
5.8 GeV
e- Bunch charge
10-200 pC
Repetition rate
100 Hz
Time- and length scales of the nano world
SwissFEL
pulselength
SwissFEL wavelength range
Understand dynamics of fundamental processses
for chemistry, biology, condensed matter physics and material science
Basic Considerations
SwissFEL is build as a national facility in a small country
Total cost have to fit in a limited framework
$
U  K
1 
2 2 
2

N  
4
 
2



 N  1 μm qB nC
• Lowest beam energy technically possible
• Small period undulators with low K values
• Low qB charge
• Normal conducting linac technology
SwissFEL baseline
S-band & X-band
C-band
C-band
C-band
715 m
Aramis:
1-7 Å hard X-ray SASE FEL,
In-vacuum , planar undulators with variable gap.
Athos:
7-70 Å soft X-ray FEL for SASE & Seeded operation .
APPLE II undulators with variable gap and full polarization control.
D’Artagnan:
FEL for wavelengths above Athos, seeded with an HHG source. Besides
covering the longer wavelength range, the FEL is used as the initial
stage of a High Gain Harmonic Generation (HGHG) with Athos as the
final radiator.
SwissFEL key parameters
Parameters for lasing at 1Å
Operation Mode
Long Pulses
Short Pulses
Charge per Bunch (pC)
200
10
Beam energy for 1 Å (GeV)
5.8
5.8
Core Slice Emittance (mm.mrad)
0.43
0.18
Peak Current at Undulator (kA)
2.7
0.7
Repetition Rate (Hz)
100
100
Undulator Period (mm)
15
15
Effective Saturation Power (GW)
2
0.6
Photon Pulse Length at 1 Å (fs, rms)
13
2.1
The Operation Modes
Wakefield
Limited
•
•
•
•
Diagnostic
Limit
Charge
•
•
•
•
Standard operation
200 pC
Maximum FEL pulse energy
Longest FEL pulse length
Lowest charge operation
10 pC
Short FEL pulse length
Single-spike in soft X-ray
Special Cases
•
•
•
Strong residual energy chirp
200 pC
Large FEL Bandwidth (>1%) for
single short Absorption
spectroscopy.
•
•
•
•
Attosecond FEL pulse
10 pC
Strongest compression
Single-spike in hard X-ray
Bolko Beutner - FLAC 15.11.2010
SwissFEL in comparison with the other hard X-ray FEL projects
Beam
energy
min
GeV
Å
April 10
2009 !
13.6
1.5
SCSS, Japan
2011
8
1.0
European X –FEL, Hamburg
2014
17.5
1.0
SwissFEL
2016
5.8
1.0
Project
LCLS, USA
Start of
operation
SwissFEL has lowest beam energy
Advantages: Compact and affordable on national scale
Challenges : More stringent requirements for beam quality,
mechanical and electronic tolerances
First existing part of SwissFEL: 250 MeV Injector
715m
#3
First beam to dump 9.8.2010
#2
Cavity #1
RF-gun
Inauguration SwissFEL first stage, 24.8.2010
SwissFEL Milestones
Gun laser
2010
250 MeV Injector facility
2014
Building completed
Gun laser
2.1 GeV
3.4 GeV
5.8 GeV
ARAMIS FEL 1-7 Å
Exp2
2016
Gun laser
SwissFEL Phase I
Accelerator and hard X ray FEL
2.1 GeV
Laser
pump
3.4 GeV
5.8 GeV
ARAMIS FEL 1-7 Å
Exp2
2018
SwissFEL Phase II
Soft X-ray FEL
ATHOS FEL 7-70 Å
Seed laser
Exp2
Laser
pump
THz pump
RF issues
•RF systems with three different frequencies at
S-band, C-band and X-band
•Development of C-band linac module
optimized for space and power economy
•Extreme phase tolerance specs require
sophisticated synchronization and LLRF
Frequencies
SwissFEL Injektor
2998.8 MHz
11995.2 MHz
Main C-band LINAC
5712 MHz
Why (not) C Band?
Active length S-band acceleration
24 m
Active length C-band acceleration
208 m
ARAMIS string of undulators
60 m
Other beam line elements
273 m
Photon beam transport
100 m
Experiment halls
50 m
Total facility length
715 m
 No strong motivation for very high gradients !
Why (not) C Band: the Compression Schemes
BC 2
Linac 1
Linac 2+3
Collimator
wakes remove chirp
double dogleg
(slight decompression)
over-compression
wakes add to chirp
double dogleg
(slight compression)
compression
wakes partially remove chirp
chicane
(compression)
•
Normal:
•
Large Bandwidth:
•
Attosecond:
compression
Actively making use of single bunch wakes:
RF frequency → Aperture → Active length → Gradient
Bolko Beutner - FLAC 15.11.2010
C-band LINAC Module
Modulator LLRF
116 MW
Main LINAC
#
LINAC modules
26
Modulator
26
Klystron
26
Pulse compressor
26
Accelerating structures
104
Waveguide splitter
78
Waveguide loads
104
50 MW, 3.0 µs max.
40 MW, 3.0 µs for operation
BOC PulseCompressor
120 MW, 0.5 µs
30.8 MV/m
30.8 MV/m
30.8 MV/m
30.8 MV/m
2m
Courtesy Hansruedi Fitze
C-band development
Linac
structure
Short structure
2011
Full scale structure
Series production
2012
2013
2012
2013
Power
tests
BOC
Design
2011
Fabrication
Tests
2012
2013
Courtesy Hansruedi Fitze
Klystron
Two Klystrons ordered from Toshiba
E37202
E37210
Peak Power
50 MW
50 MW
RF Pulse Width
3 us
3 us
Repetition Rate
60 Hz
100 Hz
Avg. RF Power
7.7 kW
15 kW
Collector Power
35 kW
78 kW
Delivery Date
May 2011
Feb 2012
•
•
•
•
One E37202 is orderd for startup of test stand
Delivery May 2011
Upgrade Programm in Execution
E37210 to be delivered early 2012
Courtesy Jürgen Alex
Longitudinal phase space manipulations
SwissFEL Injektor
2998.8 MHz
11995.2 MHz
Main C-band LINAC
5712 MHz
X-Band Structure Tasks
1.
Removal of quadratic component
from RF curvature:
with x-band on-crest – this can
be changed for fine tuning of
compression.
2.
Compensation of the quadratic
contribution to the path length
through the chicane
Court.: B. Beutner
S-band
X-band
1
2
3
4
BC
Chicane
1
2
tail
head
First compression
stage of SwissFEL
3
4
Court.: B. Beutner
The Compression Scheme
Linac 1
•
BC 2
•
Collimator
Normal:
wakes remove chirp
double dogleg
(slight decompression)
over-compression
wakes add to chirp
double dogleg
(slight compression)
compression
wakes partially remove chirp
chicane
(compression)
compression
•
Linac 2+3
Large Bandwidth:
Attosecond:
Bolko Beutner - FLAC 15.11.2010
200 pC std mode
Booster 2:
X-Band:
-17 deg
16 MV/m
180.13 deg
16.98 MV/m
Linac 1:
Linac 2/3:
-20.9 deg
26.5 MV/m
0 deg
26.5 MV/m
200pC Mode
2.15 deg
4.2 deg
355MeV 150A
3.2kA
2.04GeV 3.2kA
head
head
tail
tail
head
tail
Bolko Beutner - FLAC 15.11.2010
FEL Performance @ 200 pC
200pC
Saturation
32 m
Esat
0.11 mJ
sp
20 fs
<Psat>
2.1GW
BW
0.065 %
Bolko Beutner - FLAC 15.11.2010
200pC Tolerances
arrival time
peak current
energy
goals:
20 fs
5%
0.05 %
S-Band Phase [deg]
0.19
0.23
0.32
S-Band Voltage [rel]
0.001
0.00026
0.0011
X-Band Phase [deg]
30
0.061
0.86
X-Band Voltage [rel]
0.0051
0.0017
0.0058
Linac 1 Phase [deg]
0.15
0.084
0.43
Linac 1 Voltage [rel]
0.001
0.0041
0.0046
Linac 2 Phase [deg]
5.2e+003
1.6e+002
2.2e+003
Linac 2 Voltage [rel]
0.15
0.87
0.0051
Linac 3 Phase [deg]
4.6e+003
1.8e+002
2.9e+003
Linac 3 Voltage [rel]
0.12
0.19
0.0041
19
1.9
47
6.2e+002
68
2.9e+003
0.00097
0.00031
0.0011
BC1 angle [rel]
0.052
0.0011
0.014
BC2 angle [rel]
0.19
0.0011
0.015
Charge [pC]
initial arrival time [fs]
Initial Energy [rel]
Bolko Beutner - FLAC 15.11.2010
200pC Performance
Expected Perfromance
S-Band Phase [deg]
0.015
S-Band Voltage [rel]
1.2 * 1e-004
X-Band Phase [deg]
0.06
X-Band Voltage [rel]
1.2 * 1e-004
Linac 1 Phase [deg]
0.03
Linac 1 Voltage [rel]
1.2 * 1e-004
Linac 2 Phase [deg]
0.03
Linac 2 Voltage [rel]
1.2 * 1e-004
Linac 3 Phase [deg]
0.03
Linac 3 Voltage [rel]
1.2 * 1e-004
Charge
1%
initial arrival time [fs]
30
Initial Energy [rel]
1e-004
BC1 angle [rel]
5 * 1e-005
BC2 angle [rel]
5 * 1e-005
Tolerance
Goal for
Arrival
Time [fs]
Peak
Current
[%]
200pC
20
5
Energy
Jitter
[%]
0.05
Bolko Beutner - FLAC 15.11.2010
10pC – Attosecond Pulse
Modification of 10pC mode:
•
•
•
•
Fully upright compression
BC1 bending angle: 3.82 deg  4.2 deg
Linac 1 Phase: -16.7 deg  -20.8 deg
Reconfiguration of bunch collimator for
additional compression
head
tail
Bolko Beutner - FLAC 15.11.2010
head
tail
10 pC Performance
•
•
Significant enhancement of the current and
thus increase of the FEL parameter.
Single spike operation at one 1 Angstrom
with an RMS pulse length of 60 as!
Bolko Beutner - FLAC 15.11.2010
10pC Tolerances
arrival time
goals:
peak current
energy
5 fs
15 %
0.05 %
S-Band Phase [deg]
0.027
0.027
0.43
S-Band Voltage [rel]
0.00011
0.0003
0.0018
X-Band Phase [deg]
0.12
0.027
0.25
X-Band Voltage [rel]
0.00054
0.0021
0.0099
Linac 1 Phase [deg]
0.13
0.3
1.4
Linac 1 Voltage [rel]
0.00024
0.0065
0.0045
Linac 2 Phase [deg]
2.8e+002
35
5.3e+002
Linac 2 Voltage [rel]
0.0052
0.25
0.0052
Linac 3 Phase [deg]
1.5e+002
36
4.3e+002
Linac 3 Voltage [rel]
0.0041
0.25
0.0041
0.92
0.28
4.3
81
17
2.8e+002
0.00011
0.0012
0.0022
BC1 angle [rel]
0.0015
0.00029
0.0033
BC2 angle [rel]
0.0076
0.001
0.015
Charge [pC]
initial arrival time [fs]
Initial Energy [rel]
Bolko Beutner - FLAC 15.11.2010
32
10pC Performance
Expected Perfromance
S-Band Phase [deg]
0.015
S-Band Voltage [rel]
1.2 * 1e-004
X-Band Phase [deg]
0.06
X-Band Voltage [rel]
1.2 * 1e-004
Linac 1 Phase [deg]
0.03
Linac 1 Voltage [rel]
1.2 * 1e-004
Linac 2 Phase [deg]
0.03
Linac 2 Voltage [rel]
1.2 * 1e-004
Linac 3 Phase [deg]
0.03
Linac 3 Voltage [rel]
1.2 * 1e-004
Charge
1%
initial arrival time [fs]
30
Initial Energy [rel]
1e-004
BC1 angle [rel]
5 * 1e-005
BC2 angle [rel]
5 * 1e-005
Tolerance
Goal for
Arrival
Time [fs]
Peak
Current
[%]
100pC
5
15
Energy
Jitter
[%]
0.05
Bolko Beutner - FLAC 15.11.2010
33
Ultra-stable Sync System Requirements
•
Most critical issues for sync system:
Jitter (RMS, 10Hz..10MHz) between two clients and long term drift (hours)
•
•
Typical FEL client is using ref. (RF, opt.) directly or for locking a PLL
Gun laser:
≈30fs expected (goal: towards 10fs), measure with BAM
(beam arrival time monitor)
Most critical RF stations:
goal is “0.02° phase jitter at 3GHz“ for SwissFEL
RF system contributes >10fs (far out) intrinsic jitter, <5fs (diff.
mode) req. from sync
Experiment (pump-probe) lasers:
<10fs (optical sync combined w. BAM for sorting of jittery
experimental data)
Seeding laser:
<10fs (optical sync combined w. BAM for drift FB)
E/O sampling:
<50fs
BAM (opt. sync only):
approx. 6fs timing resolution/stability (down to 10pC)
“Differential mode jitter“ betw. stations is critical, “common mode jitter“ (all clients jittering w.
ref.) is less critical.
Actual injector drift requirement:
some 100fs over hours, will be tightened in the future
probably down to <10fs.
•
•
•
•
•
•
•
10fs is equivalent to 3um in air!
Courtesy Stefan Hunziker
FEL phase reference: generic layout
Hybrid Layout: High Flexibility, Reasonable Cost
electron beam
pulsed
laser
…
multiple
fibers
opt. sync
front-end
(pulsed)
opt. sync
front-end
(pulsed)
pulsed
cw
uncrit.
uncrit.
uncrit. RF
(el. subdistribution)
optical sync
front-end (cw)
optical reference signals (pulsed and cw)
distrib.
Want ultimate performance for critical clients  pulsed optical ref. signal
RF generation
RF master
oscillator
…
optical sync
front-end
moderately
crit. RF
dir. harm.
extraction
…
extremely
crit. RF
bal. o-W
detector
laser
crit.
…
clients:
beamlines
…
electron gun
mod.
mod.
Courtesy Stefan Hunziker
cw
cw
lasers
lasers
Don‘t need ultimate performance everywhere  (sub-)distributions with
lower cost technologies
Challenges for FELs
( as opposed to linear colliders?)
• Synchronization with electrooptical methods
• Photon diagnostics (partially real time, suitable
for feedback and stabilization)
• Push for real time 6D phase space diagnostics
for FB
• Push for high rep rate NC RF linacs
• New RF structures (see next part ...)
Multi purpose X band structure
A CERN/PSI/ST collaboration
• Motivation for CLIC:
• Another data point in high gradient test program
• Validation of design and fabrication procedures
• A true long term test in another accelerator facility
• Motivation for the FEL projects:
• An X band structure to compensate long. phase space nonlinearities
• High gradient/power requirements of CLIC = a design for safe
operation at the more relaxed parameters of the PSI X-FEL
• RF design (mostly) by PSI, engineering design, fabrication,
assembly & LL RF test at CERN, mechanical support & other
parts by FERMI
…. Possibly create a general purpose structure for other applications …
Special considerations for FEL
• Operating structure at relatively low beam
energies (PSI injector: 250 MeV)
• High sensitivity to transverse wakefields!
• Strategy:
– Passive: Try to have open structure while
maintaining good efficiency and breakdown
resilience
– Active: Wake field monitors
• See offsets before they show up as emittance dilution
• Possibly measure higher order/internal misalignments
(tilts, bends ….)
A priori specifications
•
•
•
•
•
•
•
•
Beam voltage 30 MeV at a max. power of 45 MW
Mechanical length <1017 mm
Iris diameter > 9 mm
Wake field monitors
Operating temperature 40 deg. C
Constant gradient design, no HOM damping
Fill time < 1 usec
Cooling assuming 1 usec/100 Hz RF pulse
The strategy
•
•
•
•
Use 5π/6 phase advance:
– Longer cells: smaller transverse
wake
– Intrinsically lower group velocity:
Good gradient even for open
design with large iris
– Needs better mechanical precision
Long constant gradient design
(efficiency!)
No HOM damping
Wake field monitors to insure optimum
structure alignment
• Do a castrated NLC type H75
without damping manifolds!
NLC type H75
• Well optimized design (iris
aperture, thickness and ellipticity
varying along structure)
• Original design gives 65 MV/m for
80 MW input power
• Sucessfully tested up to 100
MV/m with SLAC mode launcher
(below)
|E|
r
z
|B|
r
z
Constant gradient design
• 72 cells, active length 750 mm
• Relatively open structure: mean
aperture 9.1 mm
• Average gradient 40 MV/m (30 MeV
voltage) with 29 MW input power
• Group velocity variation: 1.6-3.7%
• Fill time: 100 nsec
• Average Q: 7150
HOM coupler a la NLC DDS
• TE type coupling minimizes
spurious signals from
fundamental mode and
longitudinal wakes
• Need only small coupling
(Qext<1000) for sufficient signal
• Minor loss in fundamental performance: 10% in Q, <2% in
R/Q
• Output wave guides with coaxial
transition connecting to
measurement electronics
• Two monitors replacing cells 36
and 63 for up- and downstream
signals
Electric short on one side
Axial signal output wave guides
Output signal spectra
Signal envelopes of wake monitors
Signal at time t is correlated with frequency – is correlated with cell number…..
Can we learn something about internal misalignments?
Structure tilt
Beam axis
Tilted
Ref. - offset
Eigenvalues with ACE 3P
The accelerating mode
• 66 cell substructure:
• Omit power couplers, matching
cells
• 500’000 elements, 10’000’000
unknowns (3rd order approach
required)
• Computed resonance
frequency:
• F = 11.99235 GHz (w/o losses)
• ~ F=11.9912 GHz (including
losses)
• Design: F=11.991648 GHz
Accuracy of design approach
exceeds mechanical
precision!
|E| of 5 π/6 mode
Below: monitor at cell 36
(more to come in an up coming CLIC structures meeting ..)
Mechanical model
Each two structures for structures for PSI (SwissFEL) and ST
(Sincrotone Trieste) with wakefield monitors under fabrication
Wakefield
monitor details
48
(court. D. Gudkov)
Short test stack done with diffusion bonding
Bonding at 1040°C for 90 minutes under H2
Metallurgical polishing + etching 75 s in Ammonium peroxodisulfate (NH4)2S2O8
49
(Court.: Markus AICHLER)
Site of Interest 1: Outer side of disc stack
• Grains grew down across the joining plane
Joining plane
50
RF check of assembled structure
(court. J. Shi)
Assembly structure before bonding
(court. S. Lebet)
Sub stack ready for bonding
(court. S. Lebet)
Straightness check after bonding
(court. S. Lebet)
Big thanks to:
• Design work: A. Citterio, G. D‘Auria, M. Dehler, A. Grudiev, J.-Y.
Raguin, G. Riddone, I. Syratchev, W. Wuensch, R. Zennaro
• Mechanical design and production team of G. Riddone: M.
Filipova, D. Gudkov, S. Lebet, A. Samoshkine, J. Shi & ... & ... & ...
• Access & support for ACE3P: A. Candel, K. Ko, R. Lee, Z. Li