Giovanni Volpini, IHEP, Russia, 19 March 2009 low loss superconducting Rutherford Cable for DiscoRap v. 1

Giovanni Volpini, IHEP, Russia, 19 March 2009

low loss superconducting Rutherford Cable for

DiscoRap

v. 1


1 introduction & first trials2 superconductor design3 specifications & manufacture status4 qualification

OverviewOverview




““historicalhistorical”” background background

Our work started from the first developments, performed in 2002-2004 by GSI, for the Rutherford cable design for the SIS-300 dipoles.

The Rutherford cable layout, its dimensions and the number of strands, were taken from the LHC dipole outer cable, with the insertion of a stainless steel core to increase Rc.

This decision was taken immediately after the change from the SIS 200 to SIS 300 synchrotron design; GSI 001 (SIS200) Rutherford cable design was based on RHIC dipole, with 30 x 0.648 mm strands. To reach a 1 K temperature margin it would have been necessary to have more than 48 0.648 mm strands. Therefore the dimensions of the existing LHC dipole outer layer conductor were chosen.

The preliminary magnetic analyses of the 4.5 T, single layer, INFN design have shown that an analogous margin could be achieved by using the same Rutherford cable, which was therefore adopted.


Frascati ECOMAG meetingFrascati ECOMAG meeting

...At the Oct 2005 ECOMAG meeting in Frascati, (...) we came to some important conclusions about this wire:

a) Single stacking produces the lowest filament distortion but stacking the enormous numbers of rods required (23 000 for 3.5 m filaments and 45 000 for 2.5 m) is not a practical process. So we probably have to accept the distortion of a double stack process and make the filaments proportionately finer.

b) Cu-0.5%Mn is good for suppressing proximity coupling and has a resistivity which is much higher than pure Cu, but not too high (in my view Cu-15%Ni has a too high resistance – and too low thermal conductivity).

c) Cu-0.5%Mn is much better matched to Cu in deformation characteristics than is Cu-15%Ni.

d) Only the minimum amount of CuMn needed to minimize coupling should be used in the wire, elsewhere pure Cu should be used because it improves stability and quench protection.

From M. N. Wilson GSI Report no. 29:


Prototype wirePrototype wire

Geometrical filament diameter 2.52 μm

Small apparent deformation

The “prototype wire” is based on cold drawing of seven elements of Luvata OK3900 wire already in stock.

Although significantly different from the final wire, it has allowed to show that reasonably high Jc and short twist pitch lengths can be realistically achieved on wires with NbTi fine filaments embedded in a CuMn matrix, with a diameter around 2 - 3 μm (see next slide).

NbTi/CuMn Cu


JJcc and n-index as a function of and n-index as a function of the twist pitchthe twist pitch

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0 2 4 6 8 10

Magnetic Field [T]

Jc

[A

/mm

2]

3 mm

4 mm

5 mm

6 mm

7 mm

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10

Magnetic Field [T]

n-i

nd

ex

[-]

3 mm

4 mm

5 mm

6 mm

7 mm

Jc @ 5 T, 4.2 K2,500 A/mm²

Heat treatments were not optimized for the final filament diameter, further improvment may be expected




Filament Coupling LossesFilament Coupling LossesProblem statementProblem statement

zx

y

dB/dt

Eddy currents (z)

E.C. term

])()([/ 22222 yxxBjQ

22

2

L

Q

Bt

0),(2 yx

Therefore we use the term transverse resistivity in a wider meaning; it describes both the transverse current and the EC losses.

The EC’s contribute to 10-15% of the total losses

)cos(2

),(

RLBR

Laplace Equation

Boundary conditionaround the filamentary areas

“effective” transverseresistivity

Interfil. term

Interfilamentary coupling


Solving the problem:Solving the problem:analytical approachanalytical approach

Duchateau, J.L. Turck, B. & Ciazynski, D. have developed a model, based on a simplified geometry, with cylindrical symmetry. In this model, the above-seen equations may be solved analytically.

Duchateau, J.L. Turck, B. Ciazynski, D. “Coupling current losses in composites and cables: analytical calculations” Ch. B4.3 in “Handbook of Applied Superconductivity”, IoP 1998

We have improved their approach, to better suit our geometry, increasing the number of annular regions. The Laplace equation has then been solved.

Outer Cu Sheath

(CuMn Barrier)

Filamentary area

Cu area

Cu core

(CuMn Barrier)

Filamentary area


Solving the problem:Solving the problem:FEM solutionFEM solution

Given the geometry and the BC’s, the Laplace solution can be solved with FEM as well.

Here we show the potential φ (colour map), and the in-plane x-y (i.e. related to the

interfilament coupling) current density.The total power dissipation Q is again found by numerical integration of E², and adding the EC term.

From Q we compute the effective transverse resistivity.


0.0E+00

2.0E-10

4.0E-10

6.0E-10

8.0E-10

1.0E-09

1.2E-09

1.4E-09

1.6E-09

1.8E-09

2.0E-09

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Magnetic Field [B]

Tra

ns

ve

rse

Re

sis

tiv

ity

[o

hm

*m]

Transverse resistivity from Transverse resistivity from Analytical & FEM methodsAnalytical & FEM methods

1st generation◊ 2nd generation

Green good couplingRed poor coupling

Full FEMEmpty analytical

Black line: specification value

Good agreement, 15% or better, between FEM and analytical computations


Dynamic stabilityDynamic stability

The stability criterion appears to be satisfied:

Thermal conductivityWeighed average beteween NbTi and CuMn 1.87 W/mKApproach “à la Carr” 1.14 W/mK

(NbTi fill factor in the bundle) 0.526Jc @ 4.2 K, 5 T 2700 A/mm2

Cu @ 4.2 K, 5 T 3.5 · 10-10 ohm·m

Characteristic length 22 mRound filament factor form 4√2 “ 120 m

Equivalent macrofilament diameterInner, Outer 25 m

So the margin for stability seems comparable or better to the layouts envisaged by MNW in Rep 29.

equivalent diameter <<

0.1 W/mK4.4 W/mK




Table I. Wire Main Characteristics. Wire Notes

Diameter after surface coating 0.825 ± 0.003 mm Filament twist pitch 5 +0.5 -0 mm Effective Filament Diameter for 1st Generation wire

3.5 m a)

Effective Filament Diameter for 2nd Generation wire

2.5 m a)

Interfilament matrix material Cu-0.5 wt% Mn Filament twist direction right handed screw

(clockwise)

Ic @ 5 T, 4.22 K > 541 A b) n-index @ 5 T, 4.22 K > 30 Stabilization matrix Pure Cu Strand transverse resistivity at 4.22 K 0.4 + 0.09 B [T] n∙m Cu+CuMn:NbTi ratio (ratio >1.5 ratio tolerance ± 0.1

c)

Surface coating material Staybrite (Sn-5 wt% Ag) d) Surface coating thickness d 0.5 m e)

Notes:

a) As measured from magnetization. b) This is the primary value for virgin wire. It is 5% higher than the cabled values, to

take into account degradation during cabling. It amounts, e.g., to 2.529 A/mm² for =1.5 or 2.832 A/mm² for =1.8 , @ 5 T, 4.22 K.

c) The supplier may propose an alpha value, provided it is larger than 1.5. Tolerance during the production must remain between ± 0.1 from the nominal value.

d) Same coating material used for LHC dipoles. e) This is a preliminary value, to be better defined later.

Wire specificationsWire specifications


Table II. Cable Main Characteristics.

Geometrical Notes Strand Number 36 Width 15.10 +0 -0.020

mm

Thickness, thin edge 1.362 ± 0.006 mm Thickness, thick edge 1.598 ± 0.006 mm Mid-thickness at 50 MPa 1.480 ± 0.006 mm Edge radius ≥ 0.30 mm

a)

Core material AISI 316 L stainless steel, annealed Core width 13 mm Core thickness 25 m Transposition pitch 100 ± 5 mm Cable transposition direction left-handed screw thread

Electrical Ic @ 5 T, 4.22 K >18,540 A b) Stabilization matrix RRR >70

Notes: a) The geometrical layout is the same as that of the LHC dipole outer cable design.

Dimensions are specified at 20 °C. b) Ic @ 5 T, 4.22 K for the extracted strand must be equal to or above 515 A.

Rutherford cable specificationsRutherford cable specifications


A first contract for superconducting Rutherford cable for magnet winding has been awarded to Luvata Superconductors, through its Fornaci di Barga (Italy) Businness Unit. The following material will be supplied:

1080 m (3 unit lenghts) of 1st generation Cable. Two units will be used for winding each of the two poles composing the 4 m long prototype magnet, while the third will serve as a spare.720 m (2 unit lenghts) of 2nd generation Cable. These units will be used to wind future model magnets.

The same basic geometry will be used for both the first and the second generation, with a filament geometrical diameter 2.65 μm.

The two designs will involve different lay outs to achieve different values of ρt.

Delivery of 1st generation is expected in June 2009

SC Rutherford Cable for Magnet Winding:SC Rutherford Cable for Magnet Winding:The ContractThe Contract

Giovanni Volpini, IHEP, Russia, 19 March 2009 18

The same basic geometry will be used for both the first and the second generation. Design filament geometrical diameter 2.65 μm.

The design involves sub-elements with Cu outer sheath and sub-elements with CuMn outer sheath. Both have CuMn interfilamentary matrix.

The number of Cu-sheath and CuMn-sheath elements differ between 1 st and 2 nd generation, to achieve different values of ρt.

SC Rutherford Cable for Magnet Winding:SC Rutherford Cable for Magnet Winding:Wire DesignWire Design

Wire Component Volume Fractions.

Generation I Generation II

(Cu+CuMn)/NbTi 1.56

NbTi 39.0% 39.0%

Cu 42.3% 36.3%

CuMn 18.7% 24.7%

Min. Jc @ 5 T , 4.2 K before cabling 2,600 A/mm²Target Jc “ “ 2,700 A/mm²Expected cabling degradation ≤ 5%


ρt(B=0) dρt /dB nΩ∙m nΩ∙m/T Contact type Good Bad Good Bad 1st generation 0.496 0.530 0.109 0.134 2nd generation 0.771 0.855 0.138 0.188

Values adopted in the computations

Alpha wire 1.70 Cu RRR=100 resistivity at 4.2 K 1.53∙10-10@ 0 T

3.53∙10-10@ 5 T nΩ∙m

CuMn resistivity at 4.2 K 2.5∙10-8 nΩ∙m Alpha wire used in computations is slightly higher than the target value, 1.6, in order to get conservative results. An higher value of alpha with a comparable geometry gives lower transverse resistivity values.

SC Rutherford Cable for Magnet Winding:SC Rutherford Cable for Magnet Winding:Wire Transverse ResistivityWire Transverse Resistivity


INFN believes that it is important to qualify a second supplier, also in order to test different technical solutions

An order has been awarded to Bruker EAS for the manufacture of:

80 km of SC wire, small filament, CuMn barriers

It must be emphasized that only wiredouble stack extrusiononly one design64,000 filament (wrt 38,000 in Luvata order), 2 m filaments geometrical (wrt 2.65 m in Luvata order)

Delivery: 12 months (March 2010)

Contract for a second wire Contract for a second wire developmentdevelopment




Magnetization, Magnetization, CuMn contributionCuMn contribution

-0,015

-0,01

-0,005

0

0,005

0,01

0,015

-4 -2 0 2 4 6 8 10

M(B)_totale_analisi

M (emu)

M (

emu

)

Campo (T)

-0,005

0

0,005

-5 0 5

M(B)_fondo

m(emu)

m(e

mu

)

B(T) 4.2 K

10 KΔm

The CuMn paramagnetism has an effect on the harmonic content of the field within the magnet bore.In our case, the largest effect is < 10-4 for sextupole.


Magnetization, Magnetization, effective diametereffective diameter

0

200

400

600

800

1000

1200

0 2 4 6 8 10

0 2 4 6 8 10

Ic MagnetizationIc Trasport

Crit

ical

Cur

rent

(A)

B(T)

sampleceff lI

md

04

3

@ 5T

Ic = 295 AΔm = 2.2·10-12 Wb·mLsample = 4.7 mm

deff = 3.0 μmdgeo = 2.5 μm


RRaa & R & Rcc measurement measurement

1 5 10 15 18

36 30 25 20 19

I+I-

1 5 10

5

2

11121520

36193 35

Rc >> Ra

Voltage was measured with:

1) a Agilent scanner with a µV sensitivity on 20 channels.

2) a high-resolution HP34420 nanovoltmeter + 8 channel scanner (red numbers in the upper sketch).

NOTE: in our mea’s voltages are w.r.t. current output (wire#19), here are w.r.t. wire #1


RRaa & R & Rcc measurement measurement

In order to test the measuring apparatus, we have measured Ra on the “superdummy” Rutherford cable used for winding the test poles;

The sample was “as provided”, i.e. no curing was done;

The force applied on the sample cooled at 4.2 K was controlled precisely by an mechanical test machine;

The force was changed during the same thermal cycle;


first results: voltage dropfirst results: voltage drop

33.3333 M P a

5. A

R un no. 17

5 10 15 20 25 30 35S tr a n d

50

100

150

200

V o lta g e V Ra 325 µΩRc is assumed to >> Ra


from voltage drop to Rfrom voltage drop to Raa

33.3333 M P a

5. A

17

5 1 0 1 5S tra n d

5 0

1 0 0

1 5 0

2 0 0

2 5 0

3 0 0

R e s is ta n c e Ra 325 µΩ


conclusionsconclusions

-the Rutherford cable manufacture at Luvata is running smoothly;

-a second contract for the SC wire has been awarded to Bruker EAS;

-soon we shall know the performances of these demanding Rutherford Cables

Documents

Giovanni Volpini, IHEP, Russia, 19 March 2009 low loss superconducting Rutherford Cable for DiscoRap v. 1