1. Cos(θ) superconducting magnets
Soren Prestemon
Lawrence Berkeley National Laboratory
JLEIC Collaboration Meeting Spring 2016
March 31, 2016

2. Outline Review of working examples
Trade-offs associated with major parameters
Other considerations
Next steps
Firs I would like to point out that as of Tuesday we have a new Director, Michael Witherell, who is well known to your offive having been Director of Fermilab in the past. For the last ten years he has been Vice Chancellor for Research at UC Santa Barbara which has prepared him well I believe to be the Director of a multi-purpose lab like ours. From our persepective, the bar may have been raised a little in terms of review from the Director’s Office.
The lab is divided now into 6 areas including Physical Sciences which contains ATAP, Physics, NSD and Engineering. You interact directly with ATAP and Physics but Engineering plays an important behind the scenes role in supporting R&D and Projects.
Shiltsev,

3. All major superconducting colliders to-date use Cos(θ) superconducting magnets
Wilson
Isabelle
Cos(θ) design lends itself to…
well-understood field quality
“Roman arch” mechanical support of azimuthal forces
Various structures have been designed
“Collar” approach has become the standard for NbTi designs
Compatible with laminations
Cost-effective assembly
RHIC
SSC
L. Bottura, S. A. Gourlay, A. Yamamoto, and A. V. Zlobin, IEEE Trans. Nucl. Sci., vol. PP, no. 99, pp. 1–26, 2015.
Ferracin, USPAS

4. Working examples from colliders:
many things different, yet in many respects similar
0.008T/s
0.06T/s

5. Fast ramping Cos(θ) magnets - many designed, a few built
Courtesy P. Fabbricatore
RHIC magnets known for their cost-effectiveness
RHIC magnets adapted for fast ramp? First versions of SIS300…
M. N. Wilson et al. “Design studies on superconducting Cos(θ) magnets for a fast pulsed synchrotron,” IEEE Trans. Appl. Supercond, vol. 12, no. 1, pp. 313–316, Mar

6. Demonstrated example of fast ramping Cos(θ) magnet –good starting point for a baseline
Courtesy P. Fabbricatore
Magnet reached operating current after 1 quench
There has been preliminary investigations into a 6T, 1T/s version
Initial estimates suggest ~50% increase in cold-mass cost from 4.5T to 6T
Note: this is a curved, fast ramping magnet that has been built and tested, meeting design requirements

7. Design parameter trade-offs - selection influences conductor and magnet design
Main parameters: Bmin, Bmax, r, dB/dt, duty factor
Forces and energy
E ∝ r2B2 ; losses scale with rB (or greater)
σθ ∝ JBr ⇒ midplane stresses scale with field and radius
Ramping: dB/dt strongly impacts design
Results in “AC” losses
impacts cryogenics
impacts magnet performance
Introduces issues with field quality

8. AC losses impact conductor, magnet and cryostat design
Hysteresis:
Reduce deff
Increases with I/Ic
Coupling:
Minimize twist pitch
Modify inter-filament resistance
Eddy currents:
laminations
Loss estimates are further complicated by field regime, operational current, etc.
Final design is a balance between heat capacity, losses, heat transfer and duty cycle resulting in conductor temperature excursions and hence performance limitations

9. Other considerations in design and operation
Iron magnetization and saturation induces multipoles and hysteresis
Boundary-induced coupling currents (BICCs) in the Rutherford cable introduce ramp-dependent transient field effects
Markus Haverkamp Ph.D. thesis
Regime complicated by hysteresis

10. Interaction region quadrupoles: LARP developments
Final design of the HiLumi LHC interaction region quadrupoles
A “short” version, MQXFS, has been built: length~1.5m

11. Next steps Map out existing magnet designs:
Identify major performance drivers
Identify major cost drivers
Develop cost estimates with caveats (tooling, uncertainties)
Downselect:
Develop baseline options for 3T and 6T Cos(θ) magnets
Provides reference points for alternatives
Need iterative feedback between magnet designers and accelerator physicists to identify best (cost & performance) regime