scu development at lbnl soren prestemon lawrence berkeley national laboratory superconducting...
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SCU Development at LBNL
Soren PrestemonLawrence Berkeley National Laboratory
Superconducting Undulator R&D ReviewJan. 31, 2014
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SCU R&D Review, Jan. 31, 2014
Outline
BackgroundAreas of contribution to the proposalStatus of technology in each area and proposed R&D– Test cryostat for tuning development– Tuning concepts– Nb3Sn SCU prototyping– SCU testing
Cost estimate: LBNL contributionProject schedule: LBNL contributionInfrastructure and resource availabilityConclusions
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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
• *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
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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
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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.
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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
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SCU R&D Review, Jan. 31, 2014
Tuning concept: basics
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SCU R&D Review, Jan. 31, 2014
Tuning concept - improvements
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SCU R&D Review, Jan. 31, 2014
Tuning concept scale-up: proposed R&D
Scale up tuning concept for application to 1.5m undulatorsDemonstrate 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
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SCU R&D Review, Jan. 31, 2014
Existing Test Cryostat: features
A cryogen-free test cryostat has been fabricated– 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,…)
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SCU R&D Review, Jan. 31, 2014
Test cryostat: details
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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 lengthCommission modifications via demonstration of cryogenic performanceUse test cryostat to demonstrate scale-up of tuning concept in advance of undulator prototype readiness
⇒ minimize schedule risk
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SCU R&D Review, Jan. 31, 2014
Nb3Sn SCU development at LBNL: background
Motivated by performance potential
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SCU R&D Review, Jan. 31, 2014
Nb3Sn superconductor options
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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
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SCU R&D Review, Jan. 31, 2014
Nb3Sn prototyping: history (2)
Prototype 2 (2004):– Demonstrated that simple current loop on a pole can
provide adequate field perturbation to serve as tuning mechanism
-0.0025
0.0025
0.0075
0.0125
0.0175
0.0225
0 25 50 75 100 125 150 175 200
Position [mm]
B [
T]
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SCU R&D Review, Jan. 31, 2014
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
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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
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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
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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
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End design (2)Odd number of polesIdeal 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)
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Nb3Sn prototyping: ongoing - fabrication
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SCU R&D Review, Jan. 31, 2014
Status
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Nb3Sn prototype: proposed R&D
Design and fabricate a Nb3Sn prototype– λ=18.5mm, gm=7.5mm, 1.5m
Document all design choicesDocument all fabrication tolerancesIdentify issues associated with future scale-up to industrial fabrication level
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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
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SCU R&D Review, Jan. 31, 2014
SCU testing: proposed R&D
Implement pulsed-wire in tuning cryostat for tuning scale-up testingImplement pulsed-wire system in ANL test cryostatDemonstrate tuning on NbTi undulator in ANL test cryostatDemonstrate tuning on Nb3Sn undulator in ANL test cryostat
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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
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SCU R&D Review, Jan. 31, 2014
Schedule and Cost for LBNL effort
NOTE: This estimate does not include contingency
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SCU R&D Review, Jan. 31, 2014
Infrastructure
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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:– Magnetics and magnetic systems– Undulators: design, fabrication, and implementation– Superconducting magnets– Cryogenics
Ample resources are available to perform the proposed R&DWork will not be limited by resource availability
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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