1. HIGH LUMINOSITY LHC: MAGNETS
HI LUMI and LARP collaboration meeting
FNAL, 7th May 2012
HIGH LUMINOSITY LHC: MAGNETS
E. Todesco
CERN, Geneva Switzerland
With contributions from
G. Ambrosio, M. Bajko, L. Bottura, H. Felice, P. Fessia, P. Ferracin, L. Fiscarelli,
G. Kirby, T. Nakamoto, J. M. Rifflet, L. Rossi, S. Russenschuck,
G. L. Sabbi, T. Salmi, M. Segreti, P. Wanderer, R. Van Weelderen, Q. Xu, …

2. CONTENTS Inner triplet quadrupoles
Layouts
Where are we today?
HQ test [LARP collaboration, S. Caspi and G. Sabbi]
MQXC assembly [CERN, G. Kirby]
The 140 mm option
Some highlights on the other magnets
Separation dipole D1 [KEK, Q. Xu, T. Nakamoto, A. Yamamoto]
Two-in-one quadrupole MQZ [CEA, M. Segreti, J. M. Rifflet]
Future steps, decisions and open issues

3. THE INNER TRIPLET: First lay-out
Two technologies / two apertures
Guidelines
20% margin on the loadline (~2 K for Nb-Ti, ~5 K for Nb3Sn)
1.9 K operational temperature
For Nb3Sn 140 mm a first X-section with a 0.8 mm strand, 40 strands
Four gradients: 100 – T/m
Operational gradients and lengths of the four options [S. Fartoukh, R. De Maria, B. Holzer, P. Ferracin]

4. THE INNER TRIPLET: APERTURE
Aperture of the triplet versus time

5. THE INNER TRIPLET: A FEW WORDS ABOUT FIELD QUALITY
Critical issues
These magnets are become important at 7 TeV after squeeze
At injection energy they are in the shadow of the main dipoles
Transfer function is the most important quantity
Reproducibility is required, within a fraction of unit at 7 TeV
Multipoles are an issues only at 7 TeV
Very relaxed limits at injection  I would not worry too much about magnetization
Comparison in strength between main dipoles and IT quadrupoles

6. CONTENTS Inner triplet quadrupoles
Layouts
Where are we today?
HQ test [LARP collaboration, S. Caspi and G. Sabbi]
MQXC assembly [CERN, G. Kirby]
The 140 mm option
Some highlights on the other magnets
Separation dipole D1 [KEK, Q. Xu, T. Nakamoto, A. Yamamoto]
Two-in-one quadrupole MQZ [CEA, M. Segreti, J. M. Rifflet]
Future steps, decisions and open issues

7. THE INNER TRIPLET: HQ RESULTS
First results of HQ tested at 1.9 K [talk by H. Bajas]
 Operational value (14.6 kA) with one quench
 91% of design short sample reached with some gymnastic 
Operational current
90% of short sample
HQ training at 1.9 K [H. Bajas, M. Bajko, et al.]

8. THE INNER TRIPLET: HQ RESULTS
First results of HQ tested at 1.9 K [talk by X. Wang]
 Spikes in the transfer function of ~10 units
Origin not understood, much larger at 4.2 K (100 units)
Lower at higher field where the magnet becomes critical for optics –not an issue for operation
HQ transfer function at 1.9 K [L. Fiscarelli, S. Russenschuck]

9. THE INNER TRIPLET: HQ RESULTS
First results of HQ tested at 1.9 K [talk by X. Wang]
Significant decay induced by ramp rate effects
Exponential in time, time constants around 30 s
Amplitude: 130 units at injection, but 10 units at 7 TeV
Not nice but not critical for operation (when squeeze starts, decay is well over)
Decay of HQ transfer function at injection, 1.9 K
Decay amplitude versus current at 1.9 K

10. THE INNER TRIPLET: HQ RESULTS
First results of HQ tested at 1.9 K [talk by X. Wang]
Not bad geometric harmonics at 7 TeV within 1.5 units
Except a large a3 (4.6 units) due to the two different conductors
Dc magnetization of b6 : 20 units at injection
It will be better with coil of 108/127 but looks not critical (simulations ongoing)
Geometric harmonics at 7 TeV
b6 versus current at 1.9 K [L. Fiscarelli, S. Russenschuck]

11. THE INNER TRIPLET: MQXC
Magnet 0 assembled in January-April [G. Kirby talk]
Now yoked
Field quality
Good geometric nearly within targets
Test at 1.9 K in May-June
MQXC field quality measured at room temperature
[P. Galbraith, J. Garcia Perez, S. Russenschuck]
MQXC yoked [G. Kirby, J. Perez, et al]

12. CONTENTS Inner triplet quadrupoles
Layouts
Where are we today?
HQ test [LARP collaboration, S. Caspi and G. Sabbi]
MQXC assembly [CERN, G. Kirby]
The 140 mm option
Some highlights on the other magnets
Separation dipole D1 [KEK, Q. Xu, T. Nakamoto, A. Yamamoto]
Two-in-one quadrupole MQZ [CEA, M. Segreti, J. M. Rifflet]
Future steps, decisions and open issues

13. THE INNER TRIPLET: THE Nb3SN OPTION MQXF
120 mm does not give the maximum performance
We are making a first iteration on the design of a larger aperture Nb3Sn quadrupole
Aperture, strand and cable optimization – most critical aspects to be fixed to start as soon as possible [P. Fessia talk]
Critical aspects: stress, protection
Strategy: MQXF should be a simple scaling of HQ
The magnet should not be more challenging
140/150 mm considered
Cable with 40 strands
To have more coil, less stress
Strand of 0.8 to 0.9 mm

14. THE INNER TRIPLET: THE Nb3SN OPTION MQXF - MARGIN
To have a more fair comparison we fix the gradient for each aperture:
150 T/m with 140 mm
140 T/m with 150 mm
Larger strand gives slightly more margin (up to +3%)
Operational currents from 15 to 17.5 kA
Short sample at 22 kA in some cases can be annoying (limit of test stations ?)

15. THE INNER TRIPLET: THE Nb3SN OPTION MQXF - STRESS
Larger cable  smaller stress (10-15%)
Notwithstanding larger apertures, one can manage to stay on the same level of HQ (already pretty high)

16. THE INNER TRIPLET: THE Nb3SN OPTION MQXF - PROTECTION
One has three phases
Detection time – you take all the Io2
- Open switch, quench heater firing
Delay to quench coil – only resistance is the dump resistor
Coil is quenched
Resistance is dump resistor plus the coil resistance which is increasing with temperature

17. THE INNER TRIPLET: THE Nb3SN OPTION MQXF - PROTECTION
Present case of HQ (total available 17 MIITS at 300 K)
Example of a typical quench at 1.9 K and 15 kA
10 ms of detection time plus 2 ms switch opening: 3 MIITS
10 ms (?) to quench all the coil 1.5 MIITS
9 MIITS taken by the coil all quenched + dump resistor
We are tight ! - and this is not short sample …
Going to 140/150 mm we should try to gain ...
Fit of quench data at 15.1 kA with simple model, 0.01 s delay to quench all HQ
[test data from H. Bajas and M. Bajko]

18. THE INNER TRIPLET: THE Nb3SN OPTION MQXF - PROTECTION
First case: detection time
MIITS scales with square of cable cross-sectional area S2
Detection time scales with S/Io
Quality factor proportional to fraction of MIITS used by detection: Io/S
This today is eating 20% of the budget in HQ (3 MIITS out of 17)
Larger strand gives a bit larger margin (+20%)
Nearly in the shadow, but at least is not worse

19. THE INNER TRIPLET: THE Nb3SN OPTION MQXF - PROTECTION
Third case: magnet totally quenched (no dump resistor)
This happens after firing of quench heaters
We assume all magnet resistive at 1.9 K,  magnet heats  resistance increases  decay faster and faster
We estimate the MIITS for this case, and compare of the cable MIITS
All cases are rather similar (larger strand does not change the picture)
The totally quenched coil eats 40% of the budget
The only way to improve this aspect is to add more copper

20. THE INNER TRIPLET: THE Nb3SN OPTION MQXF
Choice of the cable: ~0.85 mm diameter strand, 40 strands
For the 140 mm
2% percent more margin on loadline
20% more margin on detection time
Same stress as HQ
For 150 mm 0.85 or 0.9 mm strand is marginal
1% percent difference in margin
5 MPa less
Disadvantages of larger strand
Larger filament
Self field instabilities

21. THE INNER TRIPLET: THE Nb3SN OPTION MQXF
First planning with share between CERN and LARP [P. Fessia, G. L. Sabbi]
Conceptual design ended with 2012,
Tooling and structure in 2013, first half 2014
12 coils wound in 2014 and first half 2015,
two structures, two magnets, three test in mid 2015

22. THE INNER TRIPLET: THE Nb3SN OPTION MQXF - DESIGN
First design of cold mass accounting for cooling and stainless steel He vessel [P. Ferracin]
HQ cross-section
MQXF 140 mm cross-section (same scale)

23. CONTENTS Inner triplet quadrupoles
Layouts
Where are we today?
HQ test [LARP collaboration, S. Caspi and G. Sabbi]
MQXC assembly [CERN, G. Kirby]
The 140 mm option
Some highlights on the other magnets
Separation dipole D1 [KEK, Q. Xu, T. Nakamoto, A. Yamamoto]
Two-in-one quadrupole MQZ [CEA, M. Segreti, J. M. Rifflet]
Future steps, decisions and open issues

24. THE SEPARATION DIPOLE
Main guidelines [talk by T. Nakamoto, Q. Xu, A. Yamamoto]
Aperture 10 mm larger than quadrupole
Nb-Ti conductor
Large aperture  large stress  thick coil to reduce stress
2 layer 15 mm cable as in the LHC dipoles
Heavy radiation  larger margin
 30% on the loadline
Operational field of 6.3 T
40 Tm needed  length of 6-7 m
As in the triplet, field quality
critical only at 7 TeV
Problem: LHC cable not enough
long for 150 mm case
D1 150 mm aperture cross-section
[Q. Xu, T. Nakamoto, A. Yamamoto]

25. THE SEPARATION DIPOLE Fringe field
Fringe field is large (~0.15 T on th cryostat) – but no spec available
Methods to compensate
Larger iron yoke (cost, doubles the weight)
Thicker cryostat (from 10 to 60 mm)
Correction coils (5-10 turns needed)
D1 in the cryostat
[Q. Xu, T. Nakamoto, A. Yamamoto]
Fringe field on the cryostat versus turns of correcting coil
[Q. Xu, T. Nakamoto, A. Yamamoto]

26. THE MATCHING SECTION QUARUPOLE
Two-in-one quadrupole replacing Q4 [talk by M. Segreti]
Larger aperture: from 70 mm today to mm
Guidelines
Nb-Ti
Strength not critical one can
make it longer (thin coil)
Reduce as much as possible
magnetic coupling
Main issue
Magnetic field quality b3 at 7 TeV
Iron is saturated, aperture are close,
cross-talk difficult to avoid
A possible Q4 cross-section
[M. Segreti, J. M. Rifflet]

27. STRATEGY AND NEXT DEADLINES
Decide now the cable for 140/150 mm
Wait for a first estimate of energy deposition (June) to choose aperture
Shielding for the coil, and final performance
Heat loads, energy map for the cooling conditions
Powering scheme and protection estimates for final layou-outs
Estimate of vacuum conditions
Is it possible to have no beam screen?
Specs on b6 at injection for the triplet coming soon
Impact on filament size
Provide field quality estimates to WP2 to have a guess of correctors

28. THE INNER TRIPLET: TENTATIVE SUMMARY OF HQ RESULTS
Performance
The additional performance given by 1.9 K is there (91% reached)
Even with 54/61conductor !
But signs of ramp rate effects – heating ?
Magnetic measurements made at 14 kA, just 4% below nominal
Field quality – magnet is ver close to be OK
Transfer function
Spikes to be understood
Large ramp rate effects with decay – could be cured by cored cable - do we neded it ?
Both effects not a showstopper but should be addressed
Multipoles: Geometric rather close to target
b6 mgnetization of 20 units at injection probably not an issue – better with 108/127
Congratulations to the LARP team !

29. THE INNER TRIPLET: TENTATIVE SUMMARY OF HQ RESULTS
Most emphasis put up to now on
Performance (quench)
Field quality
Very close to targets in both cases
Next challenges
Protection
Cooling
Energy deposition

30. D1, Q4 and COOOLING - SUMMARY
Notwithstanding the large aperture, with a lot of coil the stress is as in the LHC dipoles
Length of 6 m, 6 T operational field
Fringe field is an issue
Active correction could be an interesting technological development Q4
Here we need very thin coil
Separate as much as possible magnetically the two apertures
Cooling
All steps to be taken to remove the heat in the most effective way
Heat loads give a higher temperature on the coil – is temperature margin enough ?