Recent Work on Insertion Devices at the ALS
Transcript of Recent Work on Insertion Devices at the ALS
Berkeley LabBerkeley Lab
Recent Work on Insertion Devices at the ALS
Soren Prestemon, Steve Marks, Ross Schlueter, M. Coleman
Input from:
ALS Accelerator Physics groupD. Robin, C. Steier, W. Wan
AFRD SuperconD. Dietderich, A. Godeke, H. Higley, N. Liggins, and others
Lawrence Berkeley National Laboratory
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 2
Berkeley LabBerkeley Lab
Outline
1. Review of existing insertion devices at the ALS• Planned insertion devices - applications and specifications
• Near term (reasonably well known)• Longer term (likely to change…)
2. Details of a device under construction – MERLIN• Quasi-periodic magnetic structure• Anticipated spectral performance
3. EPU modifications to accommodate top-off operation• Dynamic multipoles and compensating shims
4. R&D results on superconducting undulator prototypes
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 3
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ALS beamline diagram1234 Review of existing IDs…
Now W11
( IVID)
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 4
Berkeley LabBerkeley Lab 1234 Review of existing IDs…
Review of existing and future insertion devices at the ALSWave 1*Wave 2**
Wave 3: SCU’s, ultra-fast,…
Beamline Application Period, LengthMERLIN - meV resolution spectroscopy 90mm; 1.8m
50mm; 1.8m
110mm; 3.5m
30mm; 1.5m
50mm; 4.5m
34mm, 1.8m
70mm, 1.8m
50mm; 4.5m
100mm, 4.5m
100mm, 4.5m
50mm, 1.8m
50mm, 1.8m
12.0.1,2 EUV, ARPES, Coherent x-ray science Undulator 80mm, 4.5 60-1000eV 1993
10.0.1** Photoemission HERS EPU
10.1.1** Atomic / molecular physics EPU
2.?** QUERLIN – Q-res.Inelastic scattering SCU ~1keV
80mm, 3m
Magnetic spectroscopy (MCD, MLD)
Protein crys.; femto modulator
Femto radiator – ultrafast science
Surface & materials science
COSMIC – coh. scattering & imaging
MAESTRO – microscopy & elect. Struct.
Imaging, x-ray fluorescence
Coh. Scattering; Chem. Dynamics
Photoemission
PEEM
Molecular environmental science
ARPES; coherent science
4.0.1
4.0.2
5.0.1
6.0.1,2
7.0.1
7.0.1*
7.0.2*
8.0.1
9.0.1,2
10.0.1
11.0.1
11.0.2
12.0.1,2**
Type Energy range* StatusQEPU 8-300eV Being fabricated
EPU 50-1900eV 1998
Wiggler 2004
IVID 200-1800 (U)2keV-10keV (W)
2005
Undulator 60-1200eV 1993
EPU 250-1300eV ~2008
EPU 20-600eV ~2008
Undulator 65-1400eV 1993
Undulator 5-800eV 1995
Undulator 17-340eV 1997
EPU 100-2000eV 2003
EPU 95-2000eV 2001
Undulator * Typically reflects beamline, not ID, energy range
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 5
Berkeley LabBerkeley Lab
ALS storage ring parameters(Thanks to David Robin)
1234 Review of existing IDs…
Present Operation
• Injection at 1.5 GeV and then ramp
• Inject with insertion devices open
• Average beam current is 250 mA
• Vertical emittance is 150 pm rad
• Lifetime is 8 hours at 400 mA
• Injection period every 2 to 8 hours– 1 Hz injection for 4 minutes
• From 200 to 400 mA
• Photon shutters are closed during injection
After Top-Off
• Full energy injection (1.9 GeV)
• Inject with insertion devices closed
• Average beam current is 500 mA
• Vertical emittance is 30 pm rad
• Lifetime is about 3 hours at 500 mA
• Injection period about every 30 seconds
– 1 pulse• From 498.5 to 500 mA
• Photon shutters remain open during injection
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 6
Berkeley LabBerkeley Lab 1234 Review of existing IDs…
Top-Off upgrade and ID’s linked
• Can no longer open ID’s for injection– Inject every ~30s– Beam dynamics concerns
• Injection efficiency limitations imposed by EPU’s
• Minimum aperture must be set by scrapers – Avoid radiation damage to ID’s– Safety considerations
• Possible fault scenario of electrons sent down beamlinesmust be eliminated
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 7
Berkeley LabBerkeley Lab 1234 Review of existing IDs…
Installed EPUs
Three EPU50s of sameDesign:• 4.0.2: MCD, 1998
– First in a 3rd Gen. ring!• 11.0.2: MES, 2002• 11.0.1: PEEM3, 2005
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 8
Berkeley LabBerkeley Lab 1234 Review of existing IDs…
W11: Femto-Slicing Modulator
• Installed 2004• Replaces W16• Meets ongoing PX needs• ~790nm fundamental for
femto-slicing• Re-uses W16 structure and
vacuum chamber designs
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 9
Berkeley LabBerkeley Lab 1234 Review of existing IDs…
IVID30: Femto-Slicing Radiator
• Installed 2005• Purchased from
Neomax (formerly Sumitomo Special Metals)
• Collaboration with Spring8
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 10
Berkeley LabBerkeley Lab 1234 Review of existing IDs…
Permanent Magnet ChicaneJ. Y. Jung et al., PAC03
m =1
m =0
m =2
m =3
m =4 m =5
• Installed in center of chicaned ID straights• Objective: eliminate magnetic hysteresis
characteristic of iron-core electro-magnets• Design based upon PM corrector ring concept• Uses PM rotors to set main field• Uses air-core coils for fast horizontal and
vertical dipole correction
Concept proposed in:R. Schlueter et al, NIM Phys Res. A, Vol 395, 1997
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 11
Berkeley LabBerkeley Lab 1234 Review of existing IDs…
Merlin EPU• To be installed Spring 2007• Longer period
– Higher forces– Increased impact on beam dynamics– Larger photon fan, increased power
• Quasi periodic– Reduce flux from higher harmonics
• New Design Features– Stiffer/stronger structure to deal with
higher forces– New drive system to improve
performance– Modified magnetic mounting to
eliminate systematic relative motion with quadrant shifts
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 12
Berkeley LabBerkeley Lab 1234 Review of existing IDs…
EPU34: Concept for CosmicFull Polarization Control Ep > 250 eV
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 13
Berkeley LabBerkeley Lab 1234 Review of existing IDs…
EPU70: Concept for Maestro
• Horizontal Polarization Ep > 20 eV
• Vacuum chamber heating limitation:– Vertical Polarization
Ep > 60 eV– Circular Polarization
Ep > 80 eV
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 14
Berkeley LabBerkeley Lab 1234 Details of MERLIN QEPU…
Some details of the MERLIN EPU
• Quasi periodic EPU– S. Sasaki, NIM Phys. Res. A, 1994; B. Diviacco et al, epac98; J.
Chavanne et al, EPAC 1998– Optimized spectral properties by varying parameters
• (e.g. interlattice ratio, block strength) – Varying vertical blocks rather than horizontal
• More effective at generating anharmonic spectrum• Individual block perturbations are not self-compensating (steering)
• Blocks mounted on individual keepers – Avoid ALS experience with modules (Marks et al, “Shift-dependent
Skew Quadrupole…”, MT19, 2005)• Ends optimized for minimal shift-dependent first integrals
– Schlueter et al, MT19, 2005; Chavanne et al, PAC 1999
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 15
Berkeley LabBerkeley Lab
Quasi-periodic synchrotron radiation
1234 Details of MERLIN QEPU…
• Idea (introduced by Sasaki): by breaking the periodic magnetic structure in a specific manner, the harmonic structure of the undulatorradiation can be modified, yielding “harmonics” at non-integer multiples of the fundamental which are then stopped by the monochrometer
– Should be particularly useful for low photon energies, where harmonics can excite unwanted electron states;
– Has been tested on linear undulators at the ESRF, EPU at ELETTRA– Currently being investigated by others (Soleil, …) in the case of EPUs
Polarization EPU90Fundamental [eV]
QEPU90Fundamental [eV]
Linear horizontal
8 9
Linear vertical 13 14.7
circular 10.7 12.2
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 16
Berkeley LabBerkeley Lab
-400 -200 0 200 400
-0.75
-0.5
-0.25
0
0.25
0.5
0.75 1234 Details of MERLIN QEPU…
Field components for different polarization
modes
VerticalPolarizationmode
Bx(z)
• The reduced-strength blocks, when phase-shifted, generate
– Bz fields– By fields even in vertical polarization mode– Field-amplitude fluctuations even in
“circular” polarization mode, resulting in harmonic content
-400 -200 0 200 400
-0.1
-0.05
0
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0.1
-400 -200 0 200 400
-0.06
-0.04
-0.02
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0.06
By(z)
Bz(z)
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 17
Berkeley LabBerkeley Lab
Flux density in horizontal polarizationComparison with baseline EPU90
80x1012
60
40
20
0
Ph/s
/0.1
%bw
/mm
2
72eV6354453627189Photon Energy
1234 Details of MERLIN QEPU…
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 18
Berkeley LabBerkeley Lab 1234 Details of MERLIN QEPU…
Radiation spectra on axis
-0.4
-0.2
0.0
0.2
0.4
70605040302010
Ellip
tical
Var
iabl
e lin
ear
Fundamental 3rd harmonic
Modes resulting in reduced dynamic aperture
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 19
Berkeley LabBerkeley Lab 1234 Details of MERLIN QEPU…
Radiation spectra for a (0.6mrad x 0.6mrad) aperture
-0.4
-0.2
0.0
0.2
0.4
70605040302010
Ellip
tical
Var
iabl
e lin
ear
Fundamental 3rd harmonic
Modes resulting in reduced dynamic aperture
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 20
Berkeley LabBerkeley Lab 1234 Details of MERLIN QEPU…
~Circularly polarized radiation (ds=0.3λ)
- 1000 - 500 0 500 1000z @mmD0
0.1
0.2
0.3
0.4
BX2 +
By2
Quasi-periodic EPU
80x1012
60
40
20
0
Ph/s
/0.1
%bw
/mm
2
74.90eV64.2053.5042.8032.1021.4010.70Photon Energy
QEPU90EPU90
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 21
Berkeley LabBerkeley Lab 1234 EPU modifications for top-off…
Dynamic compensation shims for top-off operation
• Insertion devices typically exhibit natural vertical focusing
– “Dynamic”, i.e. due to particle trajectory coupled to off-axis longitudinal fields (not seen with multipole measurements on the bench)
– Further “dynamic” defocusing due to field roll-off (see Safranek et al., PAC 2000)
• EPU’s have special characteristics:– Focus/defocus depending on polarization mode– Exhibit strong nonlinear behavior, i.e. (de)focus strength
varies with offset– Introduces focus/defocus in horizontal plane, where beam
dynamics are typically more sensitive
⇒ Serious impact on lifetime / injection efficiency – tune shift scales with (λ/E)2, so problem is worst for low energy rings and long-period EPU’s
⇒ Nonlinear effects cannot be compensated with other optics; have significant impact on dynamic aperture
Idea (Chavanne et al., EPAC 2000.;): introduce magnetic shims to compensate for nonlinearity
Currently implemented at Bessy (J. Barhdt et al
- 20 - 10 0 10 20x@mmD- 0.2
- 0.1
0
0.1
0.2
xp@darmD
Dynamic aperture needed for top-off
Uncorrected EPU90Linear defocusing region limited
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 22
Berkeley LabBerkeley Lab 1234 EPU modifications for top-off…
Shim perturbation By(x,y=0)
B
M
B
B
III
21
4 3x
y
IV III
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 23
Berkeley LabBerkeley Lab 1234 EPU modifications for top-off…
Integrated shim fields and effective focusing
-20 -10 0 10 20-0.0025
0
0.0025
0.005
0.0075
0.01
0.0125
0.01521
4 3 -20 -10 0 10 20-0.01
-0.005
0
0.005
0.01
Ix(x) Iy(x)
-20 -10 0 10 20
-1.5 ´ 10-6
-1´ 10-6
-5´ 10-7
0
5´ 10-7
1´ 10-6
1.5 ´ 10-6
Quadrant Block orientation
Q1 Up
Q2 Down
Q3 Down
Q4 Uppx(x)
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 24
Berkeley LabBerkeley LabBaseline EPU90
Note: p1 controls variable linear polarization modes, p2 controls variable elliptical modes (p2=0.3~circular)
1234 EPU modifications for top-off…
Horizontal kick at different polarizations
-0.0002
-0.00015
-0.0001
-0.00005
0
0.00005
0.0001
0.00015
0.0002
-20 -15 -10 -5 0 5 10 15 20
x [mm]
px [r
ad]
1) p1=-0.5, p2=02) p1=-0.3, p2=03) p1=-0.2, p2=04) p1=0, p2=05) p1=0, p2=0.26) p1=0, p2=0.37) p1=0, p2=0.5
1
2
3
4
5
6
7
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 25
Berkeley LabBerkeley Lab 1234 EPU modifications for top-off…
Shimmed EPU90(Calculated with Radia)
Horizontal kick at different polarizations
-0.0002
-0.00015
-0.0001
-0.00005
0
0.00005
0.0001
0.00015
0.0002
-20 -15 -10 -5 0 5 10 15 20
x [mm]
px [r
ad]
1) p1=-0.5, p2=02) p1=-0.3, p2=03) p1=-0.2, p2=04) p1=0, p2=05) p1=0, p2=0.26) p1=0, p2=0.37) p1=0, p2=0.5
1
2
34
5 6
7
Variable linear modes still problematic;All others appear OK
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 26
Berkeley LabBerkeley Lab
Shimmed Merlin, vertical polarization(calculated, before and after shimming)
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 27
Berkeley LabBerkeley Lab 1234 EPU modifications for top-off…
Shimmed Merlin, circular polarization(calculated)
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 28
Berkeley LabBerkeley Lab 1234 EPU modifications for top-off…
Shimmed Merlin, linear (~45degrees) polarization(calculated)
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 29
Berkeley LabBerkeley Lab 1234 EPU modifications for top-off…
Other scenarios evaluated• Tracking performed at g=14, nominal minimum gap• Checked that the dynamic aperture remains
acceptable at g=18, 22 – Tracking was performed for linear horizontal and linear
vertical– Tracking also performed for elliptical mode, g=22– Kick map evaluated for g=18, elliptical mode – appears OK
-0.00015
-0.0001
-0.00005
0
0.00005
0.0001
0.00015
-25 -20 -15 -10 -5 0 5 10 15 20 25
x [mm]
px [r
ad]
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 30
Berkeley LabBerkeley Lab
Combining dynamic multipole correction shims and quasi-periodicity
-0.00025
-0.0002
-0.00015
-0.0001
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0.00025
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px [r
ad]
shim4+QP, hor. pol.shim4+QP, vert. pol.shim4, hor. pol.shim4, vert. pol.
1234 EPU modifications for top-off…
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 31
Berkeley LabBerkeley Lab
LBNL Nb3Sn superconductor Undulator R&D
Collaboration of AFRD & Engineering Div.
Considered for ALS applications:• Radiator for femto-slicing experiment• Source for protein crystallography
LDRD results (2003-04):• Two prototypes using 6-strand cable • 30mm period prototype; 80% of Jc • 14.5mm period prototype: ~75% Jc
WFO (2005-06, for Argonne Nat. Lab):• Test single strand conductor• Design and fabrication improvements• Reached short sample Jc in 4 quenches
1234 Superconducting undulator R&D…
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 32
Berkeley LabBerkeley LabLow-temperature superconductors of interest:
Nb3Sn, NbTi with Artificial Pinning (APC)
2015
1015
10
20
5103
5
104
105
106
107
temperature(K)
current density(A/cm )2
Nb Sn3
Nb-Ti
magnetic field(T)
critical J-H-Tsurface
See Thesis of Arno Godekefor an excellent review of Nb3Sn
Oxford MJR strand used for LBNL Nb3Sn prototypes
Peter Lee et al, Applied Superconductivity Center, NHMFL, Florida
1234 Superconducting undulator R&D…
Best commercially available APC NbTi
See R. Scanlan and D. Dietderich, IEEE Trans. Applied Supercond., Vol. 13, No 2, June 2003 for review of recent improvements in Jc of Nb3Sn
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 33
Berkeley LabBerkeley Lab 1234 Superconducting undulator R&D…
Superconducting undulator R&D at LBNL
• Issues addressed:– Conductor stability and magnet protection under extremely high current
operation– Demonstrated ability to provide field kick for phase-error correction– Demonstrated fabrication techniques to yield peak conductor
performance in a real magnet configuration• Remaining issues
– Field measurement system for phase-error determination– Full phase-error correction scheme– Calorimetric measurements of beam-based heating on real rings– For SC-EPU:
• demonstrate reasonable ramp-rates for field (photon energy) variation• Demonstrate switching network for period-doubling operation
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 34
Berkeley LabBerkeley Lab 1234 Superconducting undulator R&D…
Prototype III undulator quench performance• Five quenches:
– 585A, 585A, 635A, 717A, 714A– At 717A:
• Jsc=8250A/mm2• Jcu (quench)=7600A (self-protected)• Jav = 1760A/mm2 (using full pocket size)
0
100
200
300
400
500
600
700
800
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0 1 2 3 4 5 6 7 8Bcoil
Ic, I
[A]
Load-lineShort-sample, corrected (1mT/A)Test quench data
Record performance
Jc (12T, 4.2K)Old generation ~2000A/mm2
(This was used for all of the LBL prototypes)
New generation ~3000A/mm2
(just need to get the filament size down…)
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 35
Berkeley LabBerkeley Lab 1234 Superconducting undulator R&D…
Magnetic gaps and lengths for future insertion devices at the ALS
• Gaps, assuming 5mm vacuum aperture:– PM, PM-EPU: 7.3mm (1mm wall thickness, existing controls spacings; could be
reduced, but risk increases – no hard stops, chance of hitting chamber…)– IV, IV-EPU: 5.4mm (0.4mm needed for controls, RF foil)– SCU, SC-EPU: 6.6mm (0.75mm wall thickness)
• Lengths:– PM: 2m (extend devices from current 1.85m by eliminating end chicanes & chambers)– IV: 1.62m (lose 360mm compared to PM on each side due to RF transitions)– SCU, SC-EPU: 1.6m (“cold-bore” operation; RF transitions do not move, but need
space for thermal transitions; this is a reasonable estimate)– IV-EPU: 1.55m (RF transitions are a definite concern; this is an optimistic guess)
• To avoid heating vacuum chamber/magnets with SR, the estimated peak vertical K value for a 2m device is ~4.5. For PM, PM-EPU one could consider cooling the vacuum chamber, but the risks/issues have not been evaluated.
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 36
Berkeley LabBerkeley Lab
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
10 15 20 25 30
period [mm]
field
[T]
g=6mm
g=8mm
g=10mm
g=12mm
K=1
g=4mm
K=2
K=4
K=3
K=5
g=14mm
Nb3Sn SCU performance curves 24% superconductor in coilpack, Jc(4.2K,6T)=6800A/mm2
g=magnetic gap
Review of LBNL interest/effort in superconducting undulatorsALS upgrade parameters
U50: 50mm period, 4.5m length, K=3.97
SCU22: 22mm period, 1.5m/4.5m length, K=6.49
1234 Superconducting undulator R&D…
Papers:• Prestemon, S. et al. Proceedings, PAC2003• M. A. Green, D. R. Dietderich, S. Marks, S. O. Prestemon, Advances in
Cryogenic Engineering, AIP, Vol. 49, p 783-790., 2004• Prestemon, S.; Dietderich, D.;Marks, S. ; Schlueter, R. Synchrotron
Radiation Instrumentation, AIP, vol. 705, p 294, 2004.• Ross Schlueter, Steve Marks, Soren Prestemon, and Daniel Dietderich,
Synchrotron Radiation News, January/February 2004, Vol. 17, No. 1.• S. O. Prestemon et al., IEEE Transactions on Applied Superconductivity,
June 2005 • S. Prestemon, R. Schlueter, S. Marks, D. Dietderich, presented at MT19,
Sep. 18-23, 2005, Genoa, Italy• D. R. Dietderich et al., Presented at ASC2006, Seattle, Wa.
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 37
Berkeley LabBerkeley Lab
1014
1015
1016
1017
1018
1019
1020
1021
Bri
ghtn
ess
[Pho
t/s/0
.1%
bw/m
m2 /m
r2 ]
1keV2 3 4 5 6 7 8 9
10keV2 3
Photon energy [eV]
ALS performance enhancement,Application Protein Crystallography
Device Fig. of meritSCU13 39.0×1012
IVU17 3.09×1012
SCW70 6.7×1012
W11 1.2×1012
Sbend 0.34×1012
Figure of merit: flux at 12.6keV accepted into 50µm x 50 µm x .25mrad x .25mrad phase space [photons/sec/0.1% bw] . Undulator values assume 4.5m lengths.
ALS SCU13, L=1.5m and 4.5m
IVU17
SCW70
W114, pre/post upgrade
Superbends
12.6keVSe K-edge
1234 Superconducting undulator R&D…
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 38
Berkeley LabBerkeley Lab 1234 Superconducting undulator R&D…
Polarization controlGenerating variable linear polarization
I
x
y• A coil as shown generates antisymmetric
Bx and By field profiles in z about the coil. The fields are largely on a plane of angle ψ that is a function of the coil gap and x-offset.
• A series of such coils in z, separated by λ/2 with alternating current directions, generates Bx(z) and By(z) fields that are periodic with equal phase shift.
z
Bx,y
Beam ψ
Beam
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 39
Berkeley LabBerkeley Lab
Polarization controlGenerating variable linear polarization
1234 Superconducting undulator R&D…
IB IA
IC ID
Beam
ABur
BBur
CBur
DBur
For IA=IB=IC=ID:
ψ
• Consider a 4-quadrant array of such coil-series.
– If IC=-IA, Coils A and C generate additive fields.
– Set IC=-IA, ID=-IB; Independent control of IA and IB provides full linear polarization control.
BA
Independent control of IA and IB provides variable linear polarization control
- If IA=IB, vertical field, horizontal polarization- If IA=-IB, horizontal field, vertical polarization
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 40
Berkeley LabBerkeley Lab
0
1
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3
4
-2
-1
0
-2
-1
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1
Polarization controlGenerating variable elliptic polarization
• Add a second 4-quadrant array of such coil-series, offset in z by λ/4 (coil series α and β)
• With the following constraints the eight currents are reduced to four independent degrees of freedom:
,
,C A D B
C A D B
I I I I
I I I I
α α α α
β β β β
= − = −
= − = −
• The α and β fields are 90° phase shifted, providing full elliptic polarization control via
( , ; ), ( , ; ) :A B A BB I I z B I I zα α α β β βr r
( ) ( )( ) ( )
( ) ( )( ) ( )
Cos Cos 2SinSin Sin
Cos Cos 2Sin2Sin Sin
x A
y B
x A
y B
B I zB I
B I zB I
α α
α α
β α
β α
ψ ψ πηλψ ψ
ψ ψ π πηλψ ψ
⎧ ⎫⎛ ⎞ −⎛ ⎞⎛ ⎞⎪ ⎪ ⎛ ⎞=⎜ ⎟ ⎜ ⎟⎜ ⎟⎨ ⎬ ⎜ ⎟⎜ ⎟⎜ ⎟⎜ ⎟ ⎝ ⎠⎪ ⎪⎝ ⎠⎝ ⎠⎝ ⎠ ⎩ ⎭
⎧ ⎫⎛ ⎞ −⎛ ⎞⎛ ⎞⎪ ⎪ ⎛ ⎞= −⎜ ⎟ ⎜ ⎟⎜ ⎟⎨ ⎬ ⎜ ⎟⎜ ⎟⎜ ⎟⎜ ⎟ ⎝ ⎠⎪ ⎪⎝ ⎠⎝ ⎠⎝ ⎠ ⎩ ⎭
A
B
C
D
3, ; ,
1
2Note: sin ; typically 2%x y n x yn
anxB aa
α πλ
⎛ ⎞= <⎜ ⎟⎝ ⎠
∑
1234 Superconducting undulator R&D…
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 41
Berkeley LabBerkeley Lab
1017
2
3
456
1018
2
3
456
1019
2
3
45
Ph/s/
0.1%
bw/m
m2 /m
r2
2 3 4 5 6 7 8 9100
2 3 4 5 6 7 8 91000
2 3 4 5
Photon Energy
λ=28mm horiz. pol. SC-EPU λ=56mm horiz. pol. (28mm period-doubled) SC-EPU λ=28mm circ. pol. SC-EPU λ=56mm (28mm period-doubled) circ. pol. SC-EPU λ=32mm horiz. pol. PM-EPU λ=32mm circ. pol. PM-EPU
Spectral range and Brightness of example SC-EPU λ=28mm device and PM-EPU λ=32mm
Circular
λ linear polarization
2λ linear polarization
2λ
λ
Beam Parameters:I=0.5Aβx/y=13.65 / 2.25mεx/y=6.3 / 0.03nm0.06 disp. in xEnergy spread not included
Limited by aperture
1234 Superconducting undulator R&D…
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 42
Berkeley LabBerkeley Lab 1234 Superconducting undulator R&D…
A conceptual design for the LBNL SC-EPU with minimal joints
• Four-quadrant, iron-free design• Cryocooled using heat-pipe approach• Performance limited by AC losses (dB/dt-induced heating) of coil• Period halving/doubling requires “switchyard” – superconducting switch needs to be demonstrated
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 43
Berkeley LabBerkeley LabNb3Sn superconductors
Highest (Jc, Tc) of all commercially available superconductors in the field range of interest to SCU’s
• These are intermetallic compounds, in an A15 structure; A15 is a brittle crystal structure
• Requires a fabrication process providing the appropriate composition and A15 development
• Process must not jeopardize quality of stabilizer in conductor (typically Cu)
• Requires heat treatment to ~650C
=> Have significant impact on magnet design and fabrication!
See Thesis of Arno Godekefor an excellent review of Nb3Sn
(source of these plots)
1234 Superconducting undulator R&D…
Nov. 21, 2006 Elettra: New Frontiers in Insertion Devices Soren Prestemon, LBNL 44
Berkeley LabBerkeley Lab 1234 Details of MERLIN QEPU…
Comparison of QEPU and EPU700x109
600
500
400
300
200
100
0
Ph/s
/0.1
%bw
/mm
2
63eV544536271890Photon energy [eV]
700x109
600
500
400
300
200
100
0
Ph/s
/0.1
%bw
/mm
2
63eV544536271890Photon energy [eV]
EPU90QEPU90PerformanceAt minimum gapALS upgrade parameters