1. Naoyuki Amemiya Kyoto University
The 3rd Workshop on Accelerator Magnets in HTS (WAMHTS-3)
September 10 – 11, 2015
Lyon, France
(September 11, 2015)
Report from WAMHTS-2
Naoyuki Amemiya
Kyoto University

2. 55 participants: 21 (Asia, pacific) +20 (Europe) +14 (US)
Focusing on magnet technology, whereas the WAMHTS-1 in Hamburg focusing on conductors
WAMHTS-3 Amemiya

3. Key topics in the workshop on magnet technology
Magnet designs using assembled HTSs
Stability and protection
Coated-conductor magnetization and field quality
WAMHTS-3 Amemiya

4. Magnet designs using assembled HTSs
Various designs have been made in Europe (EuCARD2) as well as in US.
CCT design with BSCCO Rutherford cable
Cosine theta design with BSCCO Rutherford cable
YBCO stacked tapes cable block design
Aligned block design with YBCO Roebel cable
Cosine theta design with YBCO Roebel cable
WAMHTS-3 Amemiya

5. Stability and protection
Tiina Salmi (Tampere) “Modeling quench propagation in a protection heater covered YBCO coil”
Justin Schwartz (NCSU) “Key issues for advancing high field superconducting magnets: quench detection & degradation limits”
Massimo Sorbi (INFN) “Quench & protection: modelling and review of toolings”
Andrzej SIEMKO (CERN) “State-of-the-art and future challenges for the quench detection and protection of accelerator superconducting magnet circuits”
WAMHTS-3 Amemiya

6. Modeling quench propagation in a protection heater covered YBCO coil
Tiina Salmi (Tampere)
Modeling quench propagation in a protection heater covered YBCO coil
WAMHTS-3 Amemiya

7. Justin Schwartz (NCSU)
Optical fiber based quench detection
Quench degradation limits: in terms of mechanical / stress aspect Q T J
Jc(B,θ,T) Fm
Electric
(Superconductivity)
Thermal
Magnetostatic
Structural Mechanics
WAMHTS-3 Amemiya

8. Review of modelling tools for quench & protection
Massimo Sorbi (INFN)
Review of modelling tools for quench & protection
Many labs. have their own developed code
Need to pick the right code fitting the user’s goals
Need the validation with experimental data for HTS
WAMHTS-3 Amemiya

9. Andrzej SIEMKO (CERN)
LHC quench detection technologies as an example of the state-of-the-art
Resolution < 20 μV @ +/-10V
Minimum reaction time tEVAL = 20 ms
Modern voltage detection schemes seems to be capable to detect “on time” a normal zone developed within HTS magnets. Challenging limitations in real environment is EMC.
WAMHTS-3 Amemiya

10. Coated-conductor magnetization and field quality
A couple of numerical studies reported
Simulation of Feather – 2 at its straight section
2D simulation to compare the experimental results
Development of 3D model for cosine theta dipole magnets
Experimental studies reported from Kyoto U.
Small dipole magnets consisting of racetrack coils wound with coated conductors
Bath-cooled in liquid nitrogen
Conduction-cooled by GM cryocooler
WAMHTS-3 Amemiya

11. Simulation of Feather – M2
Harmonics at 2/3 aperture less than 10 units
WAMHTS-3 Amemiya

12. Focusing on drifts of harmonics
Field measurements in dipole magnet consisting of four racetrack coils bath-cooled in LN2
Focusing on drifts of harmonics
In 50 min., dipole drifts 7.4 10-4; sextupole drifts 1.4 10-4
Measurements agree with 2D calculation qualitatively.
SUST28(2015)035003
WAMHTS-3 Amemiya

13. 3D modelling (reported in WAMHTS-2 but more progress toward MT-24)
layer
2nd
3rd
4th
5th
6th
Last turn in the 6th layer
Straight section
Coil end
50 A/line
t = 50 s
WAMHTS-3 Amemiya

14. Summary of the report Magnet designs using assembled HTSs
The applicability of assembled coated conductors (Roebel, stack) should be verified in test coils.
Rutherford cables of Bi-2212 are attractive, but the fabrication process of (long) coils should be established.
Coated-conductor magnetization and field quality
It looks possible to manage: considering it when designing; prediction
More experiments as well as analyses are needed.
Stability and protection
A big concern; to be focused in WAMHTS-3
WAMHTS-3 Amemiya

15. Back-up slides
WAMHTS-3 Amemiya

16. BSCCO Rutherford cable CCT designs
5 T at 3 kA
12-strand BSCCO Rutherford cable
4 layers
Je = 510 A/mm2 (80% Jc)
18 T
4 layers of Bi-2212
8 layers of Nb3Sn
WAMHTS-3 Amemiya

17. YBCO stacked tapes cable Block design
Six pancake coils
3 pancakes are flat
3 pancakes have twist-and-bend heads
In each pancake, 4-turn bundles are distributed to allow reinforcement and twisting
“Twist and bend” test with dummy cable was carried out.
WAMHTS-3 Amemiya

18. YBCO Roebel cable aligned block design
Tapes oriented in the direction of the field lines to maximize critical currents
Baseline YBCO Roebel cable, 12 mm x 1.2 mm
Feather – M2 test magnet will be fabricated
WAMHTS-3 Amemiya

19. How to manage this issue?
We have to accept the existence of the large magnetization in coated conductors: their influence on field harmonics ~ mostly less than 10 units
Good news: reproducible magnetization
3D modeling will enable us the magnetic field design considering the magnetization: we can design a coil, not assuming uniform current but considering the non-uniform current distribution.
Drift in harmonics caused by the decay of magnetization is another concern, but,
not very large drift: at the order of unit, most possibly less than 10 units
dipole drifting more but higher harmonics drifting less
WAMHTS-3 Amemiya