SCU Development at LBNL
Soren Prestemon
Lawrence Berkeley National Laboratory
Superconducting Undulator R&D
Review
Jan. 31, 2014
Outline
Background
Areas of contribution to the proposal
Status of technology in each area and proposed R&D
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Test cryostat for tuning development
Tuning concepts
Nb3Sn SCU prototyping
SCU testing
Cost estimate: LBNL contribution
Project schedule: LBNL contribution
Infrastructure and resource availability
Conclusions
SCU R&D Review, Jan. 31, 2014
Background
Long history in undulator development at LBNL
– ~1985: Halbach initiated development of PM technology
– ~1991-: Development, fabrication, and implementation of large
number of plane-polarizing and elliptically-polarizing undulators for
the ALS
– ~1995-1996: Studies of NbTi helical SCU’s for SLAC FEL
– 2002-: Development of Nb3Sn SCU’s
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*First LDRD, ALS-motivated: 2003 – Prototype 1
*Continuation LDRD, ALS-motivated: 2004 – Prototype 2
*WFO funding from ANL: 2006 – Prototype 3
LDRD, Variable-polarizing undulator, NGLS-motivated: 2011
*NGLS R&D funds: 2011-2012
*Continued funding via LDRD:mid-2013, 2014
– 2012-: Responsible for the LCLS-II hybrid PM baseline undulators
SCU R&D Review, Jan. 31, 2014
Areas of contribution
Tuning system scale-up
– Scale-up existing tuning concept and test off-line
Tuning test cryostat
– “Simple” extension of existing cryogen free cryostat: 1m => 1.5m
– Primary purpose: will allow testing of tuning system in parallel with main cryostat fabrication
⇒avoid risk of commissioning tuning system late in project
Nb3Sn 1.5m prototype
– 18.5mm period, end corrections
– Potential for significant performance enhancement or significantly increased performance
margin (e.g. temperature) vs NbTi
Testing
– Participate in testing and tuning of SCU prototype in the ANL Test Cryostat
SCU R&D Review, Jan. 31, 2014
Tuning concepts
Guidelines:
– Want method that provides sufficient degree-of-freedom
correction
– Want to minimize cool-down => warm-up cycles
– Want minimal complexity
Approach:
– Single active electrical circuit drives multiple correctors in series
– Initially large selection of possible corrector locations
• At each location +Icor,0,-Icor are allowed
– Optimize distribution of active correctors to minimize trajectory
and phase-shake errors.
SCU R&D Review, Jan. 31, 2014
Tuning concept scale-up
General approach to field-errors:
– Minimize errors via tight machining tolerances, assembly
– Eliminate “global” steering and displacement via end correction
coils
– But… also provide a mechanism for local field error correction
Use detailed error analysis to develop algorithm for
tuning concept scale-up
– Many poles (N) can have correction loop carrying current ±Icor
– Icor can be varied with main coil current I0
– N varies from undulator to undulator
• selected based on measurements
SCU R&D Review, Jan. 31, 2014
Tuning concept: basics
SCU R&D Review, Jan. 31, 2014
Tuning concept - improvements
SCU R&D Review, Jan. 31, 2014
Tuning concept scale-up: proposed R&D
Scale up tuning concept for application to 1.5m undulators
Demonstrate concept off-line (no undulator) in advance of NbTi
and Nb3Sn undulator readiness
Develop algorithms to optimize corrections based on measured
field and/or first and second integrals
SCU R&D Review, Jan. 31, 2014
Existing Test Cryostat: features
A cryogen-free test cryostat has been fabricated
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Currently compatible with 1m prototypes
Uses 2 pulsed-tube cryocoolers
500A HTS leads for main coil
250A HTS leads for end correctors
250A HTS leads for tuning system
Large number of possible diagnostics (thermal, voltage,…)
SCU R&D Review, Jan. 31, 2014
Test cryostat: details
SCU R&D Review, Jan. 31, 2014
Test cryostat modifications for tuning development:
proposed R&D
Extend existing cryostat ends to allow 1.5m testing
– Need additional spools with flanges
– Need appropriate cryogenic shielding
Modify existing pulsed wire system to accommodate new length
Commission modifications via demonstration of cryogenic
performance
Use test cryostat to demonstrate scale-up of tuning concept in
advance of undulator prototype readiness
⇒ minimize schedule risk
SCU R&D Review, Jan. 31, 2014
Nb3Sn SCU development at LBNL: background
Motivated by performance potential
SCU R&D Review, Jan. 31, 2014
Nb3Sn superconductor options
SCU R&D Review, Jan. 31, 2014
Nb3Sn prototyping: history (1)
Prototype 1 (2003):
– Demonstrated that superconducting undulators operating at very high
current densities (JE>1500A/mm2, resulting in Jcu>6000 A/mm2 during a
quench) can be passively protected without damage
PRESTEMON et al.: DESIGN, FABRICATION, AND TEST RESULTS OF UNDULATORS
besides requiring that the temperatures stay below the melting
point of Sn, the wires cannot be rolled into tape (e.g. made rectangular) without a reduction in critical current [9]. This is most
likely due to the nonuniform tin distribution that results from
rolling a twisted wire. Recent progress in powder-in-tube (PIT)
manufacturing, which has the potential to allow for very small
filament diameters and wire rolling, is particularly appealing for
future SCU devices. Such wires were successfully used in recent
high-field dipole prototypes [10].
The danger of flux-jump limitations with state of the art
can be partially alleviated by providing dynamic stability [11], i.e. providing high RRR copper in the conductor
matrix. Experience at LBNL shows that appropriate tailoring
of the heat treatment cycle can provide significant increases in
RRR with nominal decrease in critical current [8].
1237
Fig. 1.
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MAGNET
DESIGN ANDJan.
FABRICATION
SCU III.
R&D
Review,
31, 2014
Cross-section of the first prototype coilpack, on the beam side.
does not require splices, and minimizes fabrication
complexity.
Design of a (scalable) protection system capable of
protecting the conductor during a quench, despite
copper current densities approaching 4–5
.
Nb3Sn prototyping: history (2)
Prototype 2 (2004):
1238
– Demonstrated that simple current loop on a pole can
provide adequate field perturbation to serve as tuning
mechanism
IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 15, NO. 2, JUNE 2005
0.0225
B [T]
0.0175
0.0125
0.0075
0.0025
-0.0025
0
25
50
75
100
125
150
175
200
Position [mm]
Fig. 2. Beam side of one of the undulator halves, showing the five trim coils
installed in the prototype.
SCU R&D Review,
Jan. 31, 2014
IV. MAGNET PERFORMANCE
Fig. 3.
Low-field instability measurements. Field sweeps at the specified
Nb3Sn prototyping: history (3)
Prototype 3 (ANL funded; 2006)
one- yoke only
Demonstrated field performance
consistent with predicted B(λ,gm)
curves, as used by Paul Emma
SCU R&D Review, Jan. 31, 2014
SCU development for FEL’s - ongoing
Systematic R&D undertaken to address key technological
issues with high-performance superconducting
undulators
– Development of an SCU short model to
=> demonstrate field performance
– Development of a magnet measurement system to
=> evaluate field quality
– Development of a shimming concept to
=> correct trajectory and phase-shake errors
SCU R&D Review, Jan. 31, 2014
Nb3Sn prototyping: ongoing…
Nb3Sn prototype for FEL applications:
– λ=20mm, gm=7.5mm, 50cm device
– Optimized end design
– Tight fabrication tolerances
Detailed tolerance and tuning analysis
SCU R&D Review, Jan. 31, 2014
End design (1)
Odd number of poles chosen for prototype
– 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
As field is ramped:
Pole 2 saturates before 1
SCU R&D Review, Jan. 31, 2014
End design (2)
Odd number of poles
Ideal end design is used for the main coil (1/8, 1/2, 7/8)
Kick corrector + field clamps placed at each end (only generates a kick)
Dipole corrector is co-wound with the main coil in the first pocket (generates both kick
and dipole)
Strength of both correctors is varied as a function of the undulator field (look-up table)
SCU R&D Review, Jan. 31, 2014
Nb3Sn prototyping: ongoing - fabrication
SCU R&D Review, Jan. 31, 2014
Status
SCU R&D Review, Jan. 31, 2014
Nb3Sn prototype: proposed R&D
Design and fabricate a Nb3Sn prototype
– λ=18.5mm, gm=7.5mm, 1.5m
Document all design choices
Document all fabrication tolerances
Identify issues associated with future scale-up to
industrial fabrication level
SCU R&D Review, Jan. 31, 2014
SCU testing: capabilities
Pulsed wire development
– Demonstrated accuracy on SLAC ECHO undulator
– Will be incorporated in tuning test cryostat for use during tuning scale-up
testing at LBNL
– Will be incorporated into ANL test cryostat for SCU testing and tuning
SCU R&D Review, Jan. 31, 2014
SCU testing: proposed R&D
Implement pulsed-wire in tuning cryostat for tuning scale-up
testing
Implement pulsed-wire system in ANL test cryostat
Demonstrate tuning on NbTi undulator in ANL test cryostat
Demonstrate tuning on Nb3Sn undulator in ANL test cryostat
SCU R&D Review, Jan. 31, 2014
Summary: proposed LBNL contributions
Modifications of an existing cryocooler-based, cryogen-free test cryostat
to allow development of a tuning system commensurate with the 1.5m
SCU prototypes
Development of a 1.5m scale tuning system, based on concepts already
tested and proven in previous work at LBNL.
Nb3Sn SCU design and fabrication. The Nb3Sn SCU prototype will have a
period λ=18.5mm.
Contribute to prototype testing in the ANL test cryostat
SCU R&D Review, Jan. 31, 2014
Schedule and Cost for LBNL effort
Sept Octo Nov Dece Janu Febr Marc April May June July
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Aug Sept Octo Nov Dece Janu Febr Marc April May June July
Aug Sept Octo Nov
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LCLS- II- proposal- LBNL- v2
LBNL- contributions
Test Cryostat mods
Design
1m ?
D.; S.M.; D.2.; H.P.
Design review
procure components
1.5m
Assembly
Commissioning
Tuner scale- up
3w
R.O.; H.P.
1.5m
H.P.; T.K.
8.05 months
T.K.; R.O.; D.A.; D.2.; H.P.
Nb3Sn 1.5m prototype
Design
3.55 months
D.D.; S.M.; D.A.; D.
NOTE: This estimate does not include contingency
Integrated design review
Final documentation
Fabrication
1m
D.A.
9.9 months
R.O.; B.C.; S.M.; D.D.; T.2.; R.A.
Testing
Testing I
2.35 months
Testing II
H.P.; D.A.; R.O.; B.C.; S.P.; R.A.; T.2.
1.6m
Summarize results
H.P.; D.A.; R.A.; B.C.; S.P.; R.O.; T.2.
1.5m
Final review
SCU R&D Review, Jan. 31, 2014
D.A.
Infrastructure
SCU R&D Review, Jan. 31, 2014
Resources
Engineering Division:
– Magnetic Systems group
Accelerator and Fusion Research Division:
– Superconducting Magnet Group
Together we have a strong team with expertise in:
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Magnetics and magnetic systems
Undulators: design, fabrication, and implementation
Superconducting magnets
Cryogenics
Ample resources are available to perform the proposed R&D
Work will not be limited by resource availability
SCU R&D Review, Jan. 31, 2014
Summary
We have designed, fabricated and tested multiple
prototypes that provide credibility to the proposed
design point, and have invested in significant analysis to
support the tuning concept.
We have infrastructure and resources available to
perform the proposed work.
The proposed LBNL contributions: tuning system
development and 1.5m Nb3Sn design and fabrication,
complement the ANL part of the proposal and are
critical to minimize risk for the project so as to achieve
LCLS-II undulator specifications
SCU R&D Review, Jan. 31, 2014