1. At ICFA Mini-Workshop on High Field Magnets for pp Colliders,
High Field Superconducting Magnet Program at Fermilab: R&D for magnets at the 16 T dipole frontier Tengming Shen for Alexander Zlobin and High Field Magnet Program at Fermilab
At ICFA Mini-Workshop on High Field Magnets for pp Colliders,
June 14-17, 2015, Shanghai

2. Present record – 13.8 T in ~35 mm aperture (HD2, LBNL, 2008)
Magnet target parameters for 100-Tev class proton-proton colliders: FCC and SppC
FCC
B / G
(T) / (T/m)
Bpeak
(T)
Bore
(mm)
Length
(units x m) MB 16
16.4 50
4500 x 14.3 MQ
450 13
800 x 6
MQX
225
100 D1 12 60
4x2 x 12 D2 10
10.5
4x3 x 10
Inter-aperture distance ≈ 250 mm; Yoke diameter ≤ 700 mm; Stray field ≤ 100 mT
SppC
Collision
energy
B (T)
Bore
(mm)
Circumference
(km)
71.2 TeV 12
40-50 80 20 50
Present record – 13.8 T in ~35 mm aperture (HD2, LBNL, 2008)

3. FNAL HFM Program
FNAL HFM R&D plan was coordinated with recent P5 recommendations and updated DOE-HEP GARD program
Recommendation 24: “Participate in global conceptual design studies and critical path R&D for future very high-energy proton-proton colliders. Continue to play a leadership role in superconducting magnet technology focused on the dual goals of increasing performance and decreasing costs.”
In collaboration with the U.S. National laboratories, universities and industry
Develop accelerator magnets with world record parameters
Small-aperture 15 T Nb3Sn dipole, suitable for FCC, and 2 T HTS insert
Large-aperture 15 T Nb3Sn dipole and 5+ T HTS insert with stress management
Small-aperture 20 T accelerator dipole based on LTS (Nb3Sn) and HTS (Bi-2212 or YBCO) coils
Perform magnet cost optimization studies.
Continue superconductor and structural material R&D for T accelerator magnets.

4. FNAL HFM Program Timeline
VLHC
HL-LHC
LARP
FCC
Record field 13.8 T
HFDA HFDM-LM mm Dipole mirror
10 T dipole
TQC TQM-LQM
90 mm 200 T/m Quadrupole quadrupole mirror
HFDC (R&W)
40 mm 10 T dipole
MBHDP
60 mm 11 T dipole
MBHSP MBHSM
60 mm 11 T dipole Dipole mirror
FY15-17:
Focus on 15 T Nb3Sn dipole demonstrator

5. Magnet Design Choice Coil design: Technology: W&R, R&W
RD3c (LBNL),
10 T, W&R, 2003
DCC017 (BNL),
10 T, R&W, 2007
HFDC (FNAL),
~6 T, R&W, 2004
Coil design:
cos-theta
block-type
common coil
Technology: W&R, R&W
Mechanical structure:
with and w/o collar
Stainless Steel or Al shell
stress management
Field range: T
13.8 T - record since 2008
Focus on the cos-theta (shell-type) design w/o collar
MBHSP (FNAL)
11.6 T,
MBHDP (FNAL)
11.5 T, 2015
HFDA (FNAL)
10 T,
D20 (LBNL),
13.4 T, 1997
HD2 (LBNL),
13.8 T, 2008

6. General considerations
1.9 K
Magnet field B ~ λJ×w
Bmax~λJc(Bmax,T,…)×w
Small aperture dipole (~50 mm)
Quench protection: Coil enthalpy can absorb the stored energy in <50% of the coil volume with Tmax=250 K
Coil maximum azimuthal stress is ~150 Mpa

7. Strand and Cable Strand Cable R&D RRP 127, 169 or 217
Strand ID – 1 and 0.7 mm
Jc(12T, 4.2K) ~2700 A/mm2
Cable
N=28 (HFDA)
N=40 (MBH)
Ic degradation ~5%
stainless steel core
cable prototypes are available
R&D
increase Jc(15 T, 4.2 K)
increase strand D, cable width
reduce filament size
RRP RRP RRP-217
Parameter
28-strand
40-strand
Number of strands 28 40
Mid-thickness, mm
1.870
1.319
Width, mm
15.10
Keystone angle, deg
0.805

8. Coil Design Study Coil aperture: 60 mm
Coil cross-section: 4 layers, graded
Design parameters: Bmax, field quality, coil volume, az. stress
Design choice: 4L-5 – minimal coil size and stress

9. 15 T Dipole Demonstrator Design concept: Design fields:
Coil bore: 60-mm
Coil length: 1 m
Optimized design: 4-layer graded coil
Interim design: with 11 T coil
Cold iron yoke
Design fields:
Jc(15T, 4.2K)=1.35 kA/mm2
Coil Bmax= 16.3/15.2 T at 4.3 K
Bore Bmax= 15.6/14.6 T at 4.3 K
+ ~1.5 T at 1.9 K
Additional margin – higher Jc
Optimized graded coil
Interim coil design

10. Mechanical Design Lorentz forces Structure: Protection heaters:
Horizontal support
Structure:
Thin stainless steel coil-yoke spacer
Vertically split yoke
Stainless steel clamps
Bolted skin (from 11 T dipole)
Cold mass length: 1 m
Cold mass OD<610 mm (VMTF)
Protection heaters:
Outer-layer
Inter-layer (2-3)
Up to 80% of coil volume

11. Demonstration of 15-16 T field level Study and optimization of
Test goals
Demonstration of T field level
Study and optimization of
magnet quench performance
training, degradation, memory, effect of coil pre-load
ramp rate sensitivity
operation margin
quench protection
heater efficiency, radial quench propagation, coil quench temperature
field quality
geometrical harmonics, coil magnetization, iron saturation, dynamic effects

12. FNAL 15 T 2-in-1 Demonstrator Parameters
Number of apertures 2
Aperture(mm) 60
Aperture spacing (mm)
250
Coil current (A)
11100
Operating temperature (K)
4.3
Max bore field at 4.3 K (T)
16.48
Max coil field at 4.3 K (T)
16.96
Margin along the load line
Stored energy (MJ/m)
TBD
Inductance (mH/m)
Yoke ID (mm)
190.8
Yoke OD (mm)
650
1 m diameter “cryostat” envelope

13. Cost reduction strategy:
Magnet Cost Reduction
B. Palmer (BNL), 2014
Cost reduction strategy:
Reduce magnet cross-section
cold mass (coil, structure)
cryostat
Increase magnet length
15 m => 20 m
Reduce component cost
superconductor (use NbTi in low fields)
structural components
Reduce labor
number of coil layers
Improve performance
Bop, Top

14. Conclusion
Future p-p colliders needs cost-effective main dipole magnets with nominal operation fields of ~16 T based on Nb3Sn technology
Special magnets with operation fields up to 20+ T based on HTS/LTS coils
By 2018, demonstration of 16-T-class accelerator quality dipole is a key milestone
FNAL has a promising dipole design and a plan to achieve this milestone by 2018
Design Bmax is above 17 with conservative Jc
Accelerator quality features
Issues to be understood and resolved
demonstration of T nominal field and accelerator class parameters, improvement of magnet training, reduction of conductor degradation, magnet cost optimization

15. Infrastructure
Use the 11 T dipole components, tooling, and FNAL fabrication and test infrastructure => R&D cost and time reduction