Cos superconducting magnets Soren Prestemon Lawrence Berkeley National

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 Shiltsev, http: //arxiv. org/pdf/1205. 3087 v 2. pdf 2

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

Working examples from colliders: many things different, yet in many respects similar 0. 008 T/s 0. 06 T/s 4

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 SIS 300… 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. 5

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 6 T, 1 T/s version o Initial estimates suggest ~50% increase in cold-mass cost from 4. 5 T to 6 T Note: this is a curved, fast ramping magnet that has been built and tested, meeting design requirements 6

Design parameter trade-offs - selection influences conductor and magnet design • Main parameters: Bmin, Bmax, r, d. B/dt, duty factor o Forces and energy • E ∝ r 2 B 2 ; losses scale with r. B (or greater) • σθ ∝ JBr ⇒ midplane stresses scale with field and radius o Ramping: d. B/dt strongly impacts design • Results in “AC” losses – impacts cryogenics – impacts magnet performance • Introduces issues with field quality 7

AC losses impact conductor, magnet and cryostat design • • 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 • • Hysteresis: o Reduce deff o Increases with I/Ic Coupling: o Minimize twist pitch o Modify inter-filament resistance Eddy currents: o laminations 8

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 9

Interaction region quadrupoles: LARP developments • Final design of the Hi. Lumi LHC interaction region quadrupoles • A “short” version, MQXFS, has been built: length~1. 5 m 10

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