WIR SCHAFFEN WISSEN – HEUTE FÜR MORGEN

PSI High-Field Magnet Design for the FCC

B. Auchmann (CERN/PSI), L. Brouwer (LBNL), S. Caspi (LBNL), J. Gao (PSI), G. Montenero (PSI),

M. Negrazus (PSI), G. Rolando (CERN), S. Sanfilippo (PSI)

24.08.2017, Swiss and Austrian Physical Society Annual Meeting, Geneva, CH.

Work supported by the Swiss State Secretariat for Education, Research and Innovation SERI.

• Canted Cosine Theta (CCT) Magnets for FCC

• The PSI CCT Program

Overview

Page 2

• Canted Cosine Theta (CCT) Magnets for FCC

• The PSI CCT Program

Overview

Page 3

• FCC, Future Circular Collider.

100 km, 100 TeV center of mass.

• Magnet requirements:

16-T, i.e., the limit of Nb3Sn technology.

Motivation

Page 4

Magnet Types

Page 5

Cosine Theta Coil Block Coil

Common Coil Canted Cosine Theta (Tilted Helices)

On paper simpler mechanics.

Difficult transition in ends.

Slightly lower efficiency.

Highest efficiency. Difficult stress

management and coil end design.

Simple manufacturing, low coil stress.

Reduced efficiency.Simple coil ends.

Difficult horizontal

force containment.

More energy, less efficiency.

Preliminary Designs

Page 6

Common coilsCos-theta

Block coil Canted Cosine Theta

Mechanics Challenge

• Keep coils under compression at all stages

of operation avoid stick-slip motion. Forces scale quadratically with field.

For 16 T, dipole forces of 1.5 kt/m

pull coil apart.

10 µm abrupt movement is enough

to cause quench.

• Minimize stress on

stress-sensitive Nb3Sn. Limit is of the order of 150 to 200 MPa.

7

Example: Cos-theta

option of 16-T FCC

dipole.

Mechanics Challenge

8

• Canted Cosine Theta program for HFM started at LBNL (US).

• Promises a decisive reduction of coil transverse stress through individual

support of turns.

• Many challenges ahead: efficiency

former manufacturing

impregnation scheme and training performance

135 MPa @ 16 T

Courtesy: C. Senatore

Efficient CCT Design for FCC

• Keys to an efficient CCT design:1. Thin spars

(+ external mech. structure)

2. Wide cable, large strands

3. Thin ribs.

Increase Je.Spar

Ribs

Comparison of Designs Variants 1/2

10

9.2 ktons

All designs stable and optimized (recall initial estimate of 9000 tons)

7.4 ktons

7.4 ktons 9.7 ktons

Blocks

Cos-theta

Common

coils

Canted

cos-theta

C. Lorin, CEA

V. Marinozzi, INFN

F. Toral, CIEMAT

B. Auchmann, PSI

Courtesy, L. Bottura

Comparison of Designs Variants 2/2

11

10-cm Al shell 7.5-cm Al shell

Structures with Al shell require an additional 1-cm stainless steel shell for He tightness.

200 MPa 200 MPa 155 MPa 135 MPa

2.5-cm steel shell

coil stress:

7-cm Al shellSpace

efficiency:

• Canted Cosine Theta (CCT) Magnets for FCC

• The PSI CCT Program

Overview

Page 12

PSI Goals towards FCC Requirements

• Thin spars

• Exterior Bladder and Key structure

• Impregnation system (NHMFL resin, etc.).

• Fast quench detection and CLIQ protection.

• Wide Rutherford cable.

• Inclined channels manufacturing.

13

CD1

CD2

Conceptual Design Review and Initial Hardware Tests

• International conceptual design review of CD1 on June

26 at CERN (http://indico.cern.ch/e/cd1cdr).

• Green light to start procurement of a short mechanical

structure for test purposes.

• First machining-, winding-, and reaction-trials under

way. Impregnation trials to start shortly.

14Test formers delivered. Test winding completed. Preparation for heat treatment.

CC

T P

rogra

m Te

am

http://indico.cern.ch/e/cd1cdr)

First Planning (Feb. ‘17)

15

Summary

• The CCT option was established as a valid contender in the FCC

design study.

• The PSI program has been designed to be complementary to and

closely coordinated with the LBNL program, pushing towards

specific features needed in an FCC magnet.

• Applied superconductivity in CH is organized under the CHART

umbrella (Swiss Accelerator Research and Technology).

• Support by LBNL and CERN, but also FNAL are essential

for our program. We are grateful for the generosity.

16

Page 17

END

PSI’s CCT Design for FCC

18

• Current: 18055 A

• FCC-wide conductor use

• Total: 9.77 kt (~ +30% wrt. CT)

• NonCu: 3.75 kt

• Cu: 6.02 kt

• Total inductance: 19.2 mH/m

• Total energy: 3.2 MJ/m

Layer # nS cuNc loadlinemarg. [%]

current marg. [%]

Tpeak[K]

Vgrnd[V]

Jcu[A/mm2]

1 29 0.8 14.2 111 292 1133 1237

2 25 1.1 14.4 95 342 1264 1217

3 22 1.95 14.4 74 310 1156 1096

4 20 2.6 15.7 70 338 1144 1103

Winding Tests

• Improve windability through inclined channels.

• Winding tests at LBNL and PSI.

• Successful tests with LD1 cable (@LBNL),

LBNL CCT cable, and 11-T cable (@PSI).

19

inclined channel: successful

radial channel: de-cabeling

Mechanical Structure

• CCT does not require azimuthal prestress.

• Radial prestress on the midplane provided by “scissor” laminations.

20

Mechanical Structure

21

Al shell 25 mm

Vertically split yoke, OR 250 mmVertically split steel pad

Protective Al shell 5 mm

Vertical and horizontal keys

Bladder locationsClosed pad gap

Open yoke gapAl-bronze former

Bladder and Key technology chosen for tuneability and relative simplicity.

Closed and pre-loaded pad gap for maximum-rigidity cage around coils.

Steel pads to better match coil differential contraction.

Manufacturability and Cost• Deep channels, aspect-ratio ~10 with inclined, tapered channels.

Machining trials started – limited room for cost reduction.

Selective Laser Melting (3-D printing) not successful in keeping tolerances.

Thin-lamination formers, R&D in

collaboration with IWS Fraunhofer.

Laser “weld-cutting”.

Goal: improve scalability and cost.

22

Trial C: weld-cutting two discs.

Trial B: laser cutting, laser spot welding.

Trial A: SLS.

CD1 Magnetic Design

• At 4.2 K: ISS = 20 kA, ~11 T bore field.

• At 1.9 K: ISS = 21.6 kA, ~11.7 T bore field (NB: CERN Imax = 20 kA)

• With iron pads at 4.2 K: ISS = 19 kA, ~11.35 T bore field

• With iron pads at 1.9 K: ISS = 20 kA, ~12 T bore field

23

Jc(B, 4.2 K)

Selected for mechanical design

ultimate load.

Movement Cryo to 16 T

24

• Tool : Mechanical APDL (ANSYS Parametric Design Language)

A scripting language to build models & analyses

Features : design optimization & adaptive meshing

Quench Simulation

Electric

Electro-thermal

Electro

magnetic

Quench Simulation

• Model I : Helical Propagation

Determination of propagation velocity per layer and per excitation level.

Quantification of detection problem.

CD1 Layer1 3-turn model results, working at Iss = 20kA, IC : T = 20K for 1st turn

3-D modeling results:• Yoke cut-back not needed (20 mT peak-field enhancement in ends).

• Magnetic length with yoke equal to that of bare coil.

• Physical length minus magn. length = 53 cm; equal to 11 T magnet.

• Peak field minus main field at 16-T bore field: 0.14 T excluding self field. comparable or lower than cos-theta due to continuous current distribution.

27Courtesy M. Negrazus

3-D Magnetic Design

3-D Periodic Simulation

28

• Generalized plane stress condition applied (following D. Arbelaez, L. Brouwer, LBNL)

• Initial 3-D results confirm 2D, but show distinct imprint of scissors lams

increase protective shell thickness, change its material to iron

decrease lamination thickness.

135 MPa on conductor