Capture solenoid discussion a look at operating margins in the sc coils
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Capture Solenoid Discussion A look at Operating Margins in the SC Coils. Peter Loveridge [email protected] Rutherford Appleton Laboratory UKNF Meeting, Lancaster April-2009. Introduction. Would like to define a realistic operating surface (J,B,T) for SC capture solenoid coils

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Capture Solenoid Discussion A look at Operating Margins in the SC Coils

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Capture solenoid discussion a look at operating margins in the sc coils

Capture Solenoid DiscussionA look at Operating Margins in the SC Coils

Peter Loveridge

[email protected]

Rutherford Appleton Laboratory

UKNF Meeting, Lancaster

April-2009


Introduction

Introduction

Would like to define a realistic operating surface (J,B,T) for SC capture solenoid coils

To understand operating margins

To enable study of alternative coil configurations

Strategy:

Performance of Nb3Sn strands developed for ITER

Define a “Neutrino Factory” cable

Extrapolate cable performance from strand data


Study 2 capture solenoid

Study-2 Capture Solenoid

Hybrid 20 Tesla Solenoid Magnet

NC insert generates ~6 Tesla

SC “Outsert” generates ~14 Tesla, Nb3Sn

Combination of high field, large bore, presents a real challenge

Pion capture is related to B x R

Huge inter-coil forces >10,000 Tonnes

Lorentz forces are related to B2 x R

Magnet optimisation?

Study-2 capture solenoid


Iter central solenoid model coil

ITER Central Solenoid Model Coil

In Study-2 (2001), Capture Solenoid performance “Based on” ITER CSMC

Taken as “State-of-the Art”

Nb3Sn strands

5 stage cable = 3 x 3 x 4 x 5 x 6 = 1080 strands

Conduit dimensions 50 mm x 50 mm

ITER Central Solenoid Model Coil (CSMC) tested 19 Apr 2000

Achieved 46 kA @ 13 Tesla

ITER Central Solenoid Model Coil (CSMC) Conductor

ITER Central Solenoid Model Coil Assembly in Test Facility


A critical surface definition for nf solenoid

A Critical Surface Definition for NF Solenoid

190 A @ 4.2K, 12 T

Data scaled from ITER VAC strand measurements

[Courtesy Durham, Supercond. Sci. Technol. 18 (2005) S241-S252]

STRAND

Assume ITER strand specification (TF cable)

190 A @ 4.2 K and 12 Tesla

0.82 mm diameter strand

Cu:Non-Cu ratio = 1

CABLE

Assume a “CSMC like” Cable

Strand Diameter = 0.82 mm

Strand Area = 0.528 mm2

Total Strands = 1080

No. SC strands = 720 (2/3)

No. Cu strands = 360 (1/3)

Conduit Dims: 50 mm x 50 mm

Conduit Area = 2500 mm2


Strain degrades nb3sn strand performance

Strain Degrades Nb3Sn Strand Performance!

Nb3Sn Strand performance is very sensitive to applied strain!

Sources of strain:

Cabling

Jacketing

Thermal strain (650˚C to 4.2 K)

Lorentz Forces

ITER experience:

Operating strain in the strand of the order -0.75 %

Cable degradation is large (50% not unheard of…)

Difficult to predict cable performance from strand data!

Illustration of Strain Degradation in Modern Nb3Sn Strands

(Courtesy ITER Organisation)


Coil operating conditions

Coil Operating Conditions

Cable degradation

Study-2 SC Coil

23.4 A/mm2

ITER CSMC

Achieved 46 kA @ 13 T

Note: 5 % margin on load-line ~ 0.7 Kelvin temp margin


Coil shielding issues temperature margin

Coil Shielding Issues – Temperature Margin

Shielding designed to mitigate beam heating of SC coils

Steady-state

Instantaneous (pulsed)

Note: a reasonable temperature margin to aim for ~ 1K

~ 1 mJ/cc could cause a quench!

Link with FLUKA power deposition studies

Note: Bmax at Rmin

Material Properties at 4 Kelvin

Specific heat of coil materials is dramatically reduced at low temperature


Summary

Summary

Would like to define a realistic operating surface (J,B,T) for the SC capture solenoid coils

But… strain degradation in cable is large, and not easy to quantify!

Difficult to extrapolate cable performance from strand data

In any case, Study-2 magnet performance already looks optimistic compared to ITER technology

Questions & Next Steps

  • Need to understand what level of strain degradation to expect!

    • Look at “whole cable” test data

    • Interpret SULTAN (PSI) short-sample tests

  • Is the coil shielding sufficient?

    • Small heat capacity in SC coil

    • Space constraints for shielding in magnet bore


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