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Transcript of Progress in Superconducting Undulator Development at LBNL · PDF fileProgress in...
Progress in Superconducting Undulator Development at LBNL
Soren Prestemon Lawrence Berkeley National Laboratory
D. Arbelaez, E. Rochepault, H. Pan, T. Ki, S. Myers, T. Seyler, M. Morsch, R. Oort, C. Swenson, R. Schlueter
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Outline
• Motivation • Main areas of development • Progress and status • Future outlook
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Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Motivation• SCU’s can provide the best performance characteristics for X-ray facilities
• High-field, short-period devices provide spectral range with shortest FEL footprint, lowest beam energy • Fine trajectory and phase-shake correction provides requisite field quality and access to harmonics
• SCU design is focused on performance and cost • Anticipate lower fabrication costs versus competing technologies • Anticipate faster commissioning time / undulator section
• Need to clearly demonstrate technology for applications to storage rings and FEL’s
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LCLS, most storage rings!SACLA, many storage rings!a few storage rings!New capability!!
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Main areas of R&D focus at LBNL
• Superconducting undulator technology using Nb3Sn ✓ Choice and specification of superconductor ✓ Materials compatibility ✓ Fabrication: processes, tooling
• Field trajectory correction and phase tuning ✓ End design and correction ✓ Internal trajectory wander reduction and phase error tuning
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Part of a collaboration between ANL, LBNL and SLAC
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Conductor options• Using 0.48mm diameter OST MJR • Working with OST to investigate RRP 217 strand
✓ Dia: 0.6mm, Deff: 30 microns, RRR: ~50-100?, ✓ Jc: ~2000-2400?, Cu:SC: 1.1:1
• Working with SupraMagnetics, Inc on PIT
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Nb3Sn
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Undulator components
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Single'Wire'Winding'
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Number of layers
Num
ber o
f turns per layers
Design optimization
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Load Line Margin
8 turns per layer
Load Lines
3.65 3.7 3.75 3.8 3.85 3.9 3.95700
750
800
850
900
Peak Magnetic Field on Conductor [T]
Ope
ratin
g Cu
rrent
[A]
Operating current for B0 = 1.86 T
8 by 7
8 by 9Design Point Peak Conductor Field
On-‐Axis Field
Cur
rent
[A]
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Motivations to consider Nb3Sn
• Nb3Sn prototype example design: ✓ λ=20mm, gm=7.5mm
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Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Beam steering considerations• Ideal condition consists of…
✓ Beam arrival on axis ➡ parallel to nominal path (NP), and with no offset
✓ Undulator entry results in electron transverse oscillation about NP ✓ Periodic section results in identical transverse oscillations ✓ Beam exit results in beam on NP (parallel, no offset)
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Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
End Design options and selection• Want zero net displacement and steering due to the ends • Even or Odd number of poles
✓ Even – zero net steering, non-zero net displacement ✓ Odd – zero net displacement, non-zero net steering
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2δ
Even number of poles
δ+K
-‐K
Odd number of poles
+K +K
+δ -‐δ
Steering + Displacement
Displacement Only
Ideal
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
End design optimization• Odd poles/even coils • Binomial expansion pattern
✓ Poles: 0, +1/4, -3/4, +1, -1,… ✓ Coils: +1/8, -4/8, +7/8, -1, +1,…
• 7 x 8 turns/pocket: ✓ Turns/coil: 7, 28, 49, 56, 56,…
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+1/8 -‐1/2 +7/8 -‐1
Yoke
Poles Coils
• Example requirements: • I1 (end) < 40 μT•m, I2 (end) < 50 μT•m2
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Permeability effects• Non-ideal effects due to finite permeability and differential saturation of end poles
✓ End kick is dependent on the undulator field ✓ Dipole field is generated by unbalanced yoke field
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x x x
xx x
x x x
xx x
1 2
Second Field Integral
End Kick
Curvature due to dipole field
End Kick
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
End correctors for compensation: Correction of distributed dipole
• Wound on top of the main coil in the remaining pocket on each end • Adds both a dipole and end kicks
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Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
End correctors for compensation: Correction of end kicks
• Wound in a separate yoke on each end • Decoupled from the main yoke
• => adds only end kicks
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Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Tuning for internal trajectory and phase errors
• Concept of in-situ tuning of undulators ✓ Selectable correction locations ✓ Corrections at all locations have the same strength ✓ Strength can be varied with a single power supply as a
function of the undulator field strength
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Once correction locations and current calibration are known, hardwire with final system
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Scaling of Trajectory and Phase Errors (random)
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RMS value of second integral error
[µm]
[µT•
m2 ]
LCLS-II requirement
RMS value of phase shake
[o ]
[µm]
σ I2=
23λu
Lu3/2I1(σ err ) σ I2
=2λuLu1/2I 2 (σ err )
Pole Errors Coil Errors
Trajectory errors scale with the undulator length to the power of 3/2
Trajectory and phase error scaling with respect to fabrication tolerances
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Switch-Based Tuning Concept
• One superconducting path - with heater • One resistive path (low resistance) • When heater is on the superconducting path becomes resistive (high resistance)
174/21/14
Superconducting path
Heaters
CurrentResistive path (high resistance)
Resistive solder joint (low resistance)
Heaters ON
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Current path via lithography on YBCO Tapes• Commercial tape from SuperPower Inc. • Masks designed for photolithography process • Chemical etching used to remove Copper, Silver, and YBCO layers where desired
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Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Possible tuning layouts
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Example: • Icorr = 50 A • Max operating field
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Strength of single-loop corrections• Corrector strength approximately varies linearly with corrector current • For a given current the corrector strength varies with the undulator field
strength due to saturation of the poles
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Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Sensitivity to longitudinal position• Misalignment from
✓ fabrication ✓ differential thermal contraction
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∆z#
Signature#(not#to#scale)#shi4ed#longitudinally#
By I1 I2 Phase advance
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Full Length Layout Concept• Correctors are placed on both sides of the vacuum chamber • Top and bottom correctors are used together • Drive current on each side of the vacuum chamber
✓ Allows for loops with positive and negative orientation ✓ Return current line is directly below the drive current
224/21/14
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Correction Configurations• Various configurations allow for:
✓ Increase and decrease in the phase error without introducing a net kick ✓ Positive and negative net kicks without net changes in the phase ✓ Individual correctors give both a kick and phase change
234/21/14
Net phase increase No net kick
Net phase decrease No net kick
Net kick No net phase change
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Testing capabilities• Test cryostat for superconducting undulators • Being extended to allow for testing of 1.5m tuning system
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Cold%mass%support%(ver0cal)%
Cold%mass%support%(horizontal)%
Thermal%shields%supports%
Instrumenta0on%port%
Instrumenta0on%port%
PT415%Cryocooler%
Plus%wire%feed@in%
Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Pulsed wire measurements complement Hall-probe systems• Dispersion correction algorithm provides high-accuracy • End-damping allows averaging with wire in vacuum • System has been successfully used on PM EPU’s
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Soren Prestemon, Workshop on Superconducting Undulators, April 28, 2014
Looking forward
• Our plans for the next year include: ✓ Fabrication of a 1.5m Nb3Sn prototype meeting FEL requirements ✓ Develop tuning concepts and test off-line
➡ Critical for FEL and higher-harmonic applications ✓ Demonstrate tuning of NbTi and Nb3Sn prototypes
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