ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 1

Performance characteristics of

Nb3Sn block-coil dipoles

for a 100 TeV hadron collider

G. Sabbi, L.Bottura, D. Dietderich, D. Cheng, P. Ferracin,

A. Godeke, S. Gourlay, M. Martchevskii, E. Todesco, X. Wang

2014 Applied Superconductivity Conference

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 2

Collider Parameters (M. Benedikt)

Parameter Unit Baseline Alt.

CM Energy TeV 100

Circumference km 100 80

Dipole Field (Coll.) T 16 20

Dipole Field (Inj.) T 1-1.2

Aperture mm 40-50

Top (magnet) K 4.5-1.9

Top (beam screen) K 40-60

“Main focus is the 16 T Nb3Sn program as hadron collider baseline,representing a natural continuation of HL-LHC developments”

We discuss the Nb3Sn block-dipole characteristics in this context

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 3

Design Features

190MPa

0 MPa

Coil Stress @ B0 = 16 T

Flared coil ends

Winding Pole

Central support tube(tested with/without)

Bore structural support

Magnetic Field @ B0 = 16 T

0T

16.9 T

16.9 T

0T

0 MPa

190MPa

200 MPa (0T)

200 MPa (0T)

36 mm

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 4

Experimental Reference

1. Coils assembled around a central tube for bore support (36 mm clear bore)

• HD2a & HD2b (coil 1&2); HD2c (coil 2&3)• Highest B0 on record for an accelerator dipole: 13.8 T (87% SSL)

2. Same coils 2&3 assembled without the central tube (43.3 mm clear bore)

• HD2d & HD2e: 13.4 T maximum field (-3%) but slower training

3. Coil design & process iteration aimed at correcting observed limitations

• HD3: similar quench patterns and slightly lower field than HD2

HD Models: 5 Coils, 6 Tests in 3 Phases:

• This study uses the HD experience as a basis to the extent possible

• We also incorporate feedback from the LARP models (TQ, HQ)

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 5

Reference Design (single aperture)

Performance parameters at B1=16 T

Operating current kA 18.6

Peak field T 16.9

Peak coil stress (0T) MPa 200

Peak coil stress (16T) MPa 190

Stored energy MJ/m 0.77

Main geometrical parameters

Strand diameter mm 0.8

Number of strands 51

Cable width mm 22.0

Clear aperture mm 36-43

No. turns (1 quadrant) 54

Coil width at mid-plane mm 39

Minimum bending radius mm 12.78

Magnet cross-section

• Vertical aperture linked to cable width and strand diameter (cable aspect ratio) • Coil stresses within the limits established by HD1, LARP TQ and HQ models

Al shell(40 mm)

Axialrods

Loadkeys

Iron Yoke

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 6

Quench Performance and Margin

Quench Locations

(HD2a)

• All HD models limited to ~87% by localized quenches at the end of the straight section• Need to incorporate a longitudinal pole gap to prevent excessive strain at reaction

HD1Coil

Split-island with straincontrol gap

1

1

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 7

Quench Performance and Margin (2)

0

100

200

300

400

500

600

700

800

900

1000

12 13 14 15 16 17 18 19 20

Magnetic field [ T ]

Str

an

d c

riti

cal

cu

rren

t [

A ]

10/25/07 - Brl-R03 - RW

Parameterization RW

10/16/07 - XS-8

10/17/07 - XS-10

Parameterization XS

Parameterization XS at 4.5 K

Parameterization XS at 1.9 K

Loadline layer 2 peak field

1.9K

Strand design: RRP 54/61Jc (12T,4.2K)= 3419 A/mm2

Jc (15T,4.2K)= 1880 A/mm2

Cu/Sc ratio = 0.82 Ic data corrected for self field

4.5K

4.2K (RW)

4.2K (XS)

T= 1.9 KBpk= 18.1 TB1 =17.1 T

T= 4.5 KBpk= 16.4 TB1 = 15.5 T

*HD2cBpk=14.5 TB1 =13.8T

Magnetic Field [T]

+1.7 T (12%)(optimization)

+1.6 T (10%)(temperature)

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 8

Coil Grading

Benefits: higher field than HD2 with same conductor area (13.8 cm2/quadrant)Challenges:

• High Field cable: thickness +0.35 mm, winding radius -1 mm (should be ok)• Low Field cable: (further) increased aspect ratio (may be beyond limits)• Fabrication and splicing of the two sub-coils (a long list…)

Cable Parameters HF LF

Strand diameter [mm] 1.0 0.65

No. Strands 41 64

No. turns (L1+L2) 6+2 28+25

Conductor area [cm2] 2.57 11.25

B1 (SSL) [ T ] 4.5K 1.9K

Reference (HD2) 15.52 17.15

Graded (*) 16.67 18.42

Dipole field increase

+1.15 +1.27

11.76 mm

(*) Ic scaled with strand area from HD2

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 9

Two-in-one Configuration

• Geometrically the two coils can be brought in contact: 126 mm separation • Field actually increases but field quality degrades due to left-right asymmetry

• This can be corrected with an asymmetric coil (same concept as for HiLumi D2)• Satisfactory solution found for 150 mm separation:

+75-75

3 mm

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 10

Compactness

• Compact arrangement has significant cost benefits• 150 mm separation smaller than 194 mm in LHC• Small beam separation allows small yoke OD• 60 cm yoke OD to be compared with 55 cm LHC• May be further reduced, need mechanical analysis• Mechanical envelope will still be larger (shell)• Short sample field is identical to single aperture:

• However, also need to consider other systems• IR dipoles, RF etc.

Short sample performance Iss B1ss

Temperature 4.5K 1.9K 4.5K 1.9K

Single aperture (HD2) 18.0 20.1 15.52 17.15

Double aperture (2HD) 17.8 19.7 15.49 17.12

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 11

Aperture Considerations

HD2 bore design:

• Coil 45 x 47.2 mm• Pole cutout OD 43.3 mm• Bore tube ID 36 mm

R21.65

Y=23.6

X=22.5

• HD2d/e & HD3 w/o bore tube: 13.4 T (-3%) but slower training• A thin support tube may be assumed as an optimal solution

• 50 mm aperture would require 1 mm strand (same aspect ratio)• Same cable development as for grading (but cannot do both)

• Conductor scaling for this design is about linear with aperture• +25% aperture will have a very significant impact on cost

• For same reason, optimization of internal bore structure is essential• Integrate bore structural design with vacuum, cooling etc.

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 12

Field Quality Considerations

• All cases optimized for low geometric harmonics (<1 unit at R=13 mm) • As required in order to make meaningful comparisons

• HD2 was also optimized for low saturation (will work also for graded)• For 2-in-1, we need some further improvement for low orders (n=2,3)

• Should be done together with mechanical analysis

Large persistent current harmonics will require magnetic shim correction:

HQ calculation and correctionHD2 calculation

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 13

Conductor Properties

• Three cases representing actual wires used in HD and HQ models

• One set representing a possible FCC target (under discussion)• Assumes shift of flux pinning curve

with improved grain refinement• Small Deff and increased Cu fraction

Wire Parameter Unit 54/61 60/61 108/127 Target

Deff mm 77 77 53 < 20

Non-Cu Fraction 55 61 50 42

Heat Treatment C/h 665/48 665/48 665/48 TBD

RRR 287 230 70 >200

Jc (12T, 4.2K) (*) kA/mm2 3419 3552 2776 3552

Jc (15T, 4.2K) (*) kA/mm2 1880 1935 1499 2772

Ic (15T, 4.2K) (*) A 520 588 376 585

(*) From extracted strands; self-field corrected

4.2K

ASC 2014 Nb3Sn Block Coil Dipoles for a 100 TeV Hadron Collider – G. Sabbi 14

Strategies for 16 T

• At 1.9K: 16 T goal requires improved conductor or graded coil• At 4.5K: 16 T goal required improved conductor and graded coil

B1 (SSL) [ T ] 4.5K 1.9K

54/61 15.5 17.160/61 15.8 17.5108/127 14.5 16.0Target 17.5 >19

• Step 1: model magnet performance optimization • Understand & remove 87% limitation - incorporate pole gap• Optimize bore design for maximum aperture and fast training

• Based on this, we set an operating point at 85% of SSL• Short sample target for 16 T at 85% is 18.8 T• Assume graded coil will give +1 T

• Conductor options: