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

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, http://arxiv.org/pdf/1205.3087v2.pdf

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

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

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. 2002.

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

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

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

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

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

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