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

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

3. 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

4. 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

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

6. Limitations of Superconducting Magnets
Strength: 6T, 30mm bore radius
QUAD: 180 T/m, Sextupole: 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

7. A Compact Design On-momentum dynamic aperture Sextupole scheme:
Combined quadrupole and sextupole
BC: K2=
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

8. 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.

9. 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

10. 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.