Superconducting Ultimate-Storage-Ring Design Weiming Guo, Animesh Jain NSLS-II FLS workshop, March 5, 2012, J-Lab

Outline Introduction to the existing designs: prospects and difficulties Lattice-structure study: reasons for superconducting A design with superconducting magnets Approaches to chromaticity correction

The Basic Idea ε~θ3~(1/N)3 Increase the number of cells; Or, split the dipole and add focusing Elements. To go from 2nm to 8pm: 6 slices Experimental Hall ESRF Multi-bend lattice with 0.3nm emittance *A. Ropert, EPAC’2000 >10 girders installed

Existing Designs US7-Michael Borland SLAC, PEP-x design Type I: qudrupole triplet + a dipole SLAC, PEP-x design Type II: a focusing quadrupole + a defocusing dipole

Why Superconducting US7: Cx=-1.25, ~6m per dipole Normal magnets QC: QUAD,L=0.4,K1=2.1 DC: DRIF,L=2.080831419590222 BH: CSBEND,L=0.2,ANGLE=0.00965,K1=-1.911 Beamline: (BH,DC,QC,DC,BH) Superconducting magnets QC: QUAD,L=0.4,K1=12.55 DC: DRIF,L=0.1 BH: CSBEND,L=0.2,ANGLE=0.00965,K1=-8.21 Beamline: (BH,DC,QC,DC,BH)

Limitations of Superconducting Magnets Strength: 6T, 30mm bore radius QUAD: 180 T/m, Sextupole: 1500-3000 T/m2 Magnet length: the longer the better, ~0.5m Magnetic field: coil dominated, combined function magnets are possible Magnet to magnet separation: 0.1m Precision alignment: difficult Cryogenic module: 5-8m, 0.5 m separation

A Compact Design On-momentum dynamic aperture Sextupole scheme: Combined quadrupole and sextupole BC: K2=-6551.7 QC: K2=3638.9 Circumference: 828m Emittance: 6.4 pm Number of straights: 60 straight length: 6m Chromaticity: 336/ 222 Momentum spread: 7x10-4 All quadrupole, no dipoles; emittance reduction: >63

Alternative Sextupole Scheme The long straight One-third of the ring, and the parameters Requirements to the long straight: large βx , βy , ηx ; βx , βy variation; >2π phase advance for nonlinear correction Negative effects Emittance is mostly produced in the long straights; nonlinear terms become large due to large beta functions.

Other Long-Straight Schemes 2π-transformer Dispersion flips signsextupole flip sign nonlinearity adds up Mini-DBA Very difficult to obtain large dispersion due to small H

Summary Advantages of using superconducting magnets for the ultimate-storage-ring design: less chromatic, more compact Showed a preliminary design Using long straights to correct chromaticity looks promising.