# Presentation: 499863

## Instabilities in Critical Current Measurement of Nb3Sn Rutherford-type cables in Different Magnetic Fields

- OUTLINE:
-  Sample holder:
- - design, FEM and modifications
-  1st sample: MJR
-  2nd and 3rd samples
-         - (short tests because of lead failure)
-  Conclusions

- Giorgio Ambrosio
*FNAL – Technical Division*

***Acknowledgement: Arup Ghosh for testing all these cables at BNL***

## Features:

2 cables in magnet-like environment 

BNL and NHMFL versions

** **
**2 cables in magnet-like environment **
**BNL and NHMFL versions**

_***Sample holder design***_

- The original sample holder was designed by:  P. Bauer, K. Ewald and J. Ozelis

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## BNL and NHMFL versions

_***BNL and NHMFL versions***_

- NHMFL test facility

- NHMFL version
- with copper leads

- BNL version
- with NbTi leads

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Ic measurement of straight and bent cables at NHMFL

_***Ic measurement of straight and bent cables at NHMFL***_

- †P. Bauer et al. *“Fabrication and Testing of Rutherford-type Cables for React and Wind Accelerator Magnets”*  ASC 2000, to be published in IEEE Trans. On Applied Superconductivity.

*Courtesy of Pierre Bauer*

**Samples without bending**
**Expected cabling degr.**
**Samples with bending**
**Expected cabling + bending degradation**
**Samples with bending**
**Excessive cabling + bending degradation**
**  ****0.7 mm ITER strands**

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Modifications for testing 28 x 1-mm cables 

**Parts:**
**Thinner splice boxes, thinner pusher bar**
**Fabrication procedure:**
**Less pre-stress before impregnation**
**Pre-stress after impregnation (by inserting a Kapton film)**
**Instrumentation:**
**Voltage taps soldered to the edge of the cable**

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## FEM analysis

**Magnetic analysis to compute forces at I****Max**** (25 kA), B****Max**** (7 T) and in self-field **
**B****ext**** transverse, parallel and anti-parallel to the self-field**
**Mechanical analysis to compute stresses (********x****, ********y****, ********xy****)**
**Pre-stress, cool-down, Fmagn.  **

- Anti-parallel orientation

- Parallel orientation

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## FEM analysis - results

**Results:**
**B****ext**** transverse gives large shear stress (****12 MPa****)**
**B****ext ****anti-parallel is mechanically the safest orientation**
**Minimum pre-stress optimized for field orientation **
**12 MPa pre-stress is sufficient to keep cables under compression with anti-parallel orientation**
**23 MPa pre-stress is sufficient to keep cables under compression with parallel orientation**

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Sample assembly

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Sample assembly

**The sample is impregnated in the same holder used for test**
**After impregnation the top is removed and a Kapton layer is added on the pressure bar **

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## 1st sample: 28 x 1-mm MJR strands

**Sample:**** **
**Cable: 28 strands 1 mm diameter (standard Cos-theta cable)**
**Cable dim.: (bare cable) 14.23 mm x 1.687 – 1.913 mm**
**Sample length: 1220 mm (splices included)**
**Strand: OST-MJR**
**Insulation: ceramic tape with ceramic binder**
**Standard OST HT: 100h @ 210 °C, 48h @ 340 °C, 180h @ 650 °C **
** **
**Instrumentation:****  **
** **
**Test facility (BNL):**
**Max field: 7 T @ 4.2 K**
**Max current: ~25 kA (Max I for leads 20 kA steady state)**
**Uniform field region: 600 mm**
**Acquisition: two dual-channel oscilloscopes **

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Quench history

_***Quench history***_

- Field (T) and Ramp rate (A/s)

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Quench current vs. background field

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Quench current vs. ramp rate @ 7 T

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Data analysis

**The oscilloscopes were set to read the signal of a ****voltage tap pair (NM or BC)**** and the signal of the ****whole sample (AL)**
**The AL signal was used **_**to synchronize**_** the oscilloscopes in the data analysis**
**The other signals (NM and BC) were compared with the AL signal in order to check if the **_**quench started inside a pair of voltage taps or not**_

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Data

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Quench between VTs

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Quench outside VTs

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Results of data analysis

**    ****In 12 quenches **_**both BC and LM**_** could be synchronized with AL:**
**Without field: **_**Two quenches out of 7 started within the voltage tap pair BC**_**.**
- When the quench didn’t start from BC, the time delay for the propagation within the first voltage tap pair was in the range from 2 to 12 ms. In quench #44 the quench propagated first into NM and then into BC.
**In 7 T field: **_**None of the 5 quenches started within any voltage tap pair**_**. **
- The time delay for quench propagation within the first voltage tap pair was in the range from 1 to 4 ms.

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Results of data analysis

**    ****In 11 quenches **_**BC**_** could be compared with AL:**
**In 7 and 3 T field: **_**No quenches out of 5 started within the voltage tap pair BC**_**.**
- The time delay for the propagation within BC was in the range from 1 to 6 ms.
**In 1 T field: **_**1 quench out of 3 started within BC**_**. **
- The time delay for quench propagation within BC was in the range from 10 to 45 ms.
**Without field: **_**1 quench out of 3 started within BC**_**. **
- The time delay for quench propagation within BC was in the range from 2 to 10 ms.

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Conclusions for 1st test

**Quench current: 15010 ± 578 A  **
**Quench current ~**_**independent of background field**_
**Erratic quench start location (i.e. NO damage)**
**History effect:**
**The first quench after a reduction of the background field (i.e. from 7 to 3, from 3 to 1 and from 1 to 0 tesla) occurred at a current significantly lower than the current of all other quenches at the same field.**
**In 7 and 3 T: **_**No quenches started within recorded VT pairs**_
**In 1 and 0 T: **_**Four quenches started within VT pairs**_
_**Conductor instability**_** is the only **
**	****simple explanation for this behavior**

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## 2nd and 3rd sample

**2****nd**** sample: PIT cable**
**Cable: 28 strands 1 mm diameter (Rectangular X-section)**
**Strand: SMI-PIT**
**Insulation: ceramic tape with ceramic binder**
**Heat treatment: ramp at 25 oC/h up to 655 oC, hold for 170 h**
**Prestress: 35 MPa**
**3****rd**** sample: MJR in field region only**
**Cables: 28 strands 1 mm diameter**
**Bottom: PIT (Rectangular X-section)**
**Top in field: MJR (Keystoned)**
**Top out of field: PIT (Keystoned)**
**MJR cable length: 640 mm (splices included)**
**MJR heat treatment: 100h @ 210 °C, 50h @ 340 °C, **_**72h @ 650 °C**_** **
**Total sample length: 935 mm (splices included)**
**Insulation: ceramic tape with ceramic binder**
**Prestress: 12 MPa  **

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## 2nd sample:  PIT cable

**Iq (0T) > 18 kA**
**Iq (7T) > 19 kA**

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## 3rd sample: MJR in field region only

**We tried to prevent the lead-quench failure by doubling the leads**
**In the first quench the current reached 19877 A**
**Without background field at 150 A/s **
**	**
**but the quench **
**	****started in a lead **
**	****and...**

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## 1st and 3rd cable test comparison

**CABLE 1**
**54 subelements**
**d****eff**** ~ 110 ********m**
**Cu: 47.8%**
**Ic (12 T) = 700 A**
**ceramic tape & binder**
**RRR = 5**
** **
**CABLE 3**
**54 & 60 subelem.**
**d****eff**** ~ 110 ********m**
**Cu: 46.7%**
**Ic (12 T) = 730 A**
**ss core**
**ceramic tape & binder (small)**
**RRR = 50**

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Cable resistance and RRR

**RRR of 1****st**** MJR tested (5.5) is consistent with strand measurement (~5)**
**Cable resistance of MJR samples at room temperature is higher than expected **
**1****st**** sample: 13%**
**2****nd**** sample: 6%**
**Cable resistance of PIT samples at room temperature is consistent with strand parameters**

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Conclusions

**Three high-Jc Nb****3****Sn cable samples have been assembled at FNAL and tested at BNL**
**All samples had cables made of 28 1-mm strands**
**Insulated with ceramic tape & binder**
**1****st**** sample (MJR) showed limited Iq ~15000 A **
**Because of instabilities in the low field part of the cables**
**2****nd**** and 3****rd**** samples showed that PIT conductor is more stable**
**Iq > 20 kA**
**3****rd**** sample showed that MJR after short heat-treatment (******** higher RRR) may be more stable**
**Iq > 20 kA**
**There is a discrepancy between the measured resistance of MJR cables and the expected value**

- Very close to the quench current of our Cos-theta magnets and mirrors

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Addendum

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004

## Cable resistance and RRR

- G. Ambrosio - Instabilities in Nb3Sn Rutherford-type cables

- April 28, 2004