Superconducting wiggler magnets for CLIC damping rings

Superconducting wiggler magnets for CLIC damping rings
Laura García Fajardo CERN TE Magnet Seminar 4th November, CERN

TE Magnet Seminar. SC wiggler magnets for CLIC damping rings
Outline Overview CLIC emittance requirements, wigglers winding configurations Nb-Ti full magnet Magnet design, cryogenic system, bath test, factory acceptance test, status Nb3Sn prototype Background, main issues and challenges of the previous prototype, selection of the main parameters of the next prototype Design of the impregnation mould for the Nb3Sn prototype Conclusions TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Overview - CLIC layout at 3TeV
CLIC Conceptual Design Report, 2012 TE Magnet Seminar. SC wiggler magnets for CLIC damping rings Paolo Ferracin

Overview - CLIC emittance requirements
For the luminosity performance of the collider, CLIC damping rings (DRs) should produce the necessary ultra-low emittance with high bunch charge CLIC emittance requirements driving the DRs design Horizontal normalized emittance [nm·rad] 500 Vertical normalized emittance [nm·rad] 5 Longitudinal normalized emittance [keV·m] 6 Mechanism enabling to reach such small emittances: Natural synchrotron radiation damping of the beam A total wiggler length of 26m is foreseen per each straight section of the DRs (52m per DR, 104m in total for CLIC) Insertion devices for CLIC DRs: Superconducting wiggler magnets CLIC Conceptual Design Report, 2012 Antoniou, F., 2012 The synchrotron radiation damping mechanism CLIC damping rings TE Magnet Seminar. SC wiggler magnets for CLIC damping rings Paolo Ferracin

Overview - Wigglers winding configurations
A superconducting wiggler is a multipole magnet with alternating high magnetic field along movement of particles in the storage ring Vertical design advantages Period length not limited by the bending radius Possibility of continuous winding Lower forces at the end coils … but is a less efficient design Options for winding the magnet Superconducting material The baseline design foresees Nb-Ti Nb3Sn technology has some advantages: Larger parameter space available Higher T and enthalpy margin Nb3Sn could be used to increase the magnetic flux density amplitude in the gap and reduce the total length of wigglers in the DRs … but is a very brittle material (R+D required) Schoerling, D., 2012 Vertical racetrack Horizontal racetrack TE Magnet Seminar. SC wiggler magnets for CLIC damping rings Paolo Ferracin

Nb-Ti full magnet - Introduction
Designed and built at BINP, Novosibirsk, Russia, in the frame of BINP/KIT/CERN collaboration This wiggler is intended for two operation modes: As light source at ANKA-IMAGE beamline Like test facility for CLIC damping wiggler prototype Current design includes only the horizontal racetrack coils magnetic system, but cryostat design permits the future quick replacement of the magnetic system to another type The magnet is not immersed into a special liquid helium cryostat. The cooling of the magnet is provided by the special indirect cooling system, which is a main feature of this project TE Magnet Seminar. SC wiggler magnets for CLIC damping rings Paolo Ferracin

Nb-Ti full magnet - Magnet design
Mezentsev, N.A., 2012 Coils SC strand produced by Bochvar Institute of Inorganic Materials in Moscow for superconducting wigglers Each coil has two sections of the winding to optimize current‐magnetic field dependence Working points at 4.2 K on the load lines for inner and outer sections of the SC coils: 81% and 86 % respectively Operating current values: 487 A for the inner section and 974 A for the outer section Works as a yoke for magnetic flux closing, and like heat conductor of big cross‐section One piece iron pole (ARMCO) Coil layout Strand cross section Real coils Superconducting wire parameters Diameter (mm) 0.85 (0.90 with insulation) Ratio of Nb-Ti : Cu 1.1 Number of Nb-Ti filaments 312 Critical current of SC wire (A) ~520 (at 7 Tesla, 4.2K) Model for the magnetic field calculations TE Magnet Seminar. SC wiggler magnets for CLIC damping rings Paolo Ferracin

Nb-Ti full magnet - Magnet design
Mezentsev, N.A., 2012 Photo taken during bath test at BINP Main superconducting magnet parameters Total number of poles 72 Number of main poles 68 Number of additional poles 4 Period length [mm] 56 Magnetic gap [mm] 18 Nominal operational bore field [T] 3 Conductor peak field [T] 5.4 Currents of the power suppliers [A] 243.5 x 4 Magnetic system assembly TE Magnet Seminar. SC wiggler magnets for CLIC damping rings Paolo Ferracin

Nb-Ti full magnet - Cryogenic system
Cooling system based on indirect cooling of the wiggler by LHe boiling in two copper tubes attached to the copper plate of the upper half of the wiggler The lower half is cooled via copper links Liquid helium is stored in the LHe vessel positioned above the wiggler Mezentsev, N.A., 2012 Photo taken during FAT at BINP Cross‐section of the assembled wiggler cryostat Wiggler in its cryostat during the Factory Acceptance Test TE Magnet Seminar. SC wiggler magnets for CLIC damping rings Paolo Ferracin

Nb-Ti full magnet - Bath test
The magnet was tested at BINP, Russia, in liquid He bath in March, 2014 It reached a bore field of 3.2 T (91% of short-sample field) Quench history during the bath test Photo taken during bath test at BINP Zolotarev, K., 2014 Longitudinal scans with 5 Hall probes TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb-Ti full magnet - Factory acceptance test (FAT)
The magnet was tested in its own cryostat at BINP, Russia, in May, 2014 Cooling down to a temperature <=4.2K (minimum achieved temperature was 3.2K) Maximum bore field reached = 3.1T It was possible to hold the current for more than 1 hour only up to a field of 2.6 T, with the magnet quenching at 2.7 T after about 10 minutes Photo taken during FAT at BINP Holding quenches suspected to be due to excessive heat generated in the splice region Data analysis was done to identify which area of the magnet presents a high-resistance splice TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb-Ti full magnet - Status
Instability at ~ 2.8 T filed with significant time delay (the cause of the holding quenches is still not clear) Quenches in the higher, coldest half in new coils have appeared after training in higher field Mechanical movements of the coils could be the reason of such degradation Quench history of the latest test (Oct, 2014) during ramping In horizontal position the centre of the wiggler is bended down 23 microns if it is supported at its ends. This may give 18 microns of the void for the movements of the coils New spacers of titanium alloy with less relative contraction than stainless steel are being produced to be place between the halves of the wiggler TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype - Background
First vertical racetrack magnet (5 coils) tested in 2011 Strand: OST, RRP Period length: 41.8mm Strand’s diameter [mm] 0.81 Jc SC [A/mm2] at B=12T and T=4.3K 2963 Schoerling, D., 2012 Magnet test interrupted after reaching 75% of max. current because of short circuit between the conductor and the iron parts (shorts to ground) Short model sample Short model sample inside the impregnation mould Manufacturing process TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype - Main issues and challenges
All the coils featured a short to ground, with resistance ranging from Ω to 1 kΩ Infrared image of the model at 1 A - Heating of one coil due to conductor damage To investigate the coils, #1 and #5 were cut along the winding poles, and the others, perpendicularly End region Ferracin, P., 2012 Straight section TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

In the straight section, the position of the cables was good but very thin wire to pole insulation was observed Ferracin, P., 2012 TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

The transition wire was in the centre of the groove, with enough space from the iron part Also in the end region, the position of the cables was good but the wire to pole insulation was very thin Ferracin, P., 2012 TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

A large quantity of epoxy on top of the conductor block was observed, not fully filled with fiberglass Ferracin, P., 2012 Longitudinal cut of the coil block Cross section of the coil with a layer of fiberglass on top TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Epoxy leaks were observed during impregnation - Need to modify the design of the impregnation mould Schoerling, D., 2012 Regions where most of the epoxy leaks were observed TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype - Strategies adopted
An additional coil with fiberglass insulation (0.2 mm) instead of plasma coating between turns and winding and side poles, was built and tested Ferracin, P., 2012 TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Strategies envisaged for the next prototype: Put both plasma spray and fiberglass on the winding and side poles (0.5 mm in total) Increase the radius of the transition groove to put fiberglass Round all the sharp edges and increase the radius of the grooves of the side poles to put more fiberglass Ferracin, P., 2012 TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Change the design of the impregnation mould to assure its tightness and avoid epoxy leaks Change the shape of the mould to a prismatic box to ease the manufacturing Cover the corners where the current leads are located to avoid leaks of epoxy during impregnation Schoerling, D., 2012 TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype. Redesign - New features that change the magnetic design Strand options Increasing the insulation thickness between the poles and the cables implies either increasing the period length or using a more efficient strand Strand specification d [mm] 0.70 # of filaments 132/169 Sub-element size [µm] 41 Jc SC [A/mm2] at B=10T and T=4.3K 3421 Jc SC [A/mm2] at B=12T and T=4.3K 2176 SC fraction 44.44% Need to repeat the magnetic design Technology: RRP Provider: OST Price: ≈5€/m d [mm] 0.85 # of filaments 132/169 Sub-element size [µm] 48 Jc SC [A/mm2] at B=12T and T=4.3K 2450 Jc SC [A/mm2] at B=15T and T=4.3K 1400 SC fraction 45.45% Strand insulation: Fiberglass braiding, 0.07mm thick Strand cross section d: Strand diameter Jc SC: Critical current density of the superconducting material TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Important wiggler’s parameters
Nb3Sn prototype. Redesign - Starting point: CLIC damping rings requirements From the point of view of the magnet design, to get low emittances we should reach the highest Bw at the lowest possible λw, considering the IBS effect Important wiggler’s parameters Schoerling, D., 2012 Plots by F. Antoniou Bw: Maximum mag. field dens. in the gap Bp: Mag. field dens. in the pole tip Bs: Maximum mag. field dens. in the conductor’s surface By: Vertical component of the mag. field dens. Bmod: Norm of the mag. field dens. λw: Period length g: Magnetic gap zc: Width of the square aperture Lw: Total length of wigglers in the damping rings; εr: Intra-beam scattering effect TE Magnet Seminar. SC wiggler magnets for CLIC damping rings Paolo Ferracin

Winding configuration of the short model:
Nb3Sn prototype. 2D optimization - Selection of the winding configuration Goal: Finding the most efficient way to wind the magnet It means: the winding configuration with the highest packing factor It means: the highest ration between the area occupied by the cables and the area of the square aperture Winding configuration of the short model: Odd number of layers that have the same number of turns Insulation layers will be added between the wire bundle and the iron poles Plasma coating + fiberglass = 0.5mm Cross section of the short model Square aperture of the short model TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype. 2D optimization - Selection of the winding configuration
Comparing the packing factor (f) of different winding configurations f(1) is greater than f(2) if n < 2m+1 It means that the winding configuration #1 has the highest packing factor if the height and width of the square aperture meet the following relation: * Note that the number of layers must be odd in order to wind the coils continuously n: number of layers m: number of turns of the lowest layer a: height of the square aperture b: width of the square aperture D: diameter of the insulated strand Winding configuration selection (1) Centred layers – odd number (2) Displaced layers – odd number TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

One period of the wiggler
Nb3Sn prototype. 2D optimization - Selection of the wire bundle thickness Cable saving. Comparing the maximum Bw for R=0.30 and R=0.27 (R=zc/λw): Schoerling, D., 2012 R=0.30 R=0.27 Bw gain ≈1% Cable unit length saving ≈19% Ratio of Bp achieved with a cross-section yc and zc to the maximum Bp* for a given period length λw One period of the wiggler Previous studies (Schoerling, 2012) have shown that the optimal cross-section dimension in terms of maximum Bp* is yc ≈ zc ≈ 0.30*λw Period length vs. maximum Bw for R=0.27 and R=0.30. Strand diameter=0.70mm TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype. 2D optimization - Selection of the magnetic gap
Fix ratio: R=0.27 As zc has to be an integer multiplier of the cable’s diameter, for different strand diameters we get different period lengths Magnetic gap selection: g=15mm (clear bore gap=10mm) 1-period Bwy profile for different period lengths Strand diameter 0.70mm 1-period Bwy profile for different period lengths Strand diameter 0.85mm TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype. 2D optimization - Selection of the max. magnetic field density in the gap Magnetic gap: 15mm Working point: 80% Nb3Sn strand Diameter: 0.85mm Jc SC at B=12T and T=4.3K: 2450 A/mm2 NbTi Bochvar strand Jc SC at B=5T and T=4.3K: 3088A/mm2 2 possible options using Nb3Sn: Bw=3.5T Bw=4.0T TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Period length selection: Cable unit length saving
Nb3Sn prototype. 2D optimization - Selection of the period length and the strand Period length selection: λw=44mm for Bw ≈3.5T λw=48mm for Bw ≈4.0T Period length: λw=40, 42, 44, 46, 48, 50mm Ratio: 0.27 ≤ R ≤ 0.30 λw [mm] Bw [T] Cable unit length [m] d-strand: 0.70mm 0.85mm 44 3.63 3.58 99 69 48 4.06 119 93 λw [mm] Bw gain Cable unit length saving d-strand: 0.70mm d-strand: 0.85mm 44 ≈1% ≈30% 48 0% ≈22% Strand selection: Diameter=0.85mm TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype. 2D optimization - By profile in one period of the wiggler λw=44mm λw=48mm Air Iron yoke Coil Winding pole Side pole Half gap TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype. 2D optimization - Parameters of the selected options CS: Critical surface; WP: Working point; L: Cable unit length; CC: Critical current Parameters of the selected options λw [mm] L [m] R % of CC I-strand [A] J-strand [A/mm2] Bs [T] Bw [T] Bw/Bs 44 69 0.27 100 % 1365 2406 7.81 4.32 55 % 80 % 1092 1925 6.26 3.58 57 % 48 93 0.29 1232 2172 8.40 4.92 59 % 986 1737 6.73 4.06 60 % TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype. 2D optimization - Behaviour of the maximum field in the gap (Bw) respect to λw Red plots: R=0.27 Blue plots: 0.27 ≤ R ≤ 0.30 *Remember that zc has to be an integer multiplier of the insulated strand’s diameter TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype. 2D optimization - Selection of the iron yoke thickness λw=44mm λw=48mm Air region Iron yoke region Iron yoke thickness selection: 25mm TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Nb3Sn prototype. 2D optimization - Flux density profiles for iron yoke thickness=25mm λw=44mm λw=48mm TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Design of the impregnation mould
Drawings by Javier Parrilla Leal This piece does not compress the cables Wiggler prototype on the bottom piece of the mould Assembly of the top piece of the mould Assembly of the side pieces of the mould Assembly of the front and back pieces of the mould Previous wiggler prototype inside its impregnation mould, 2011 Wiggler prototype inside its impregnation mould TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

Conclusions The Nb-Ti wiggler magnet, built and tested at BINP, reached 3.1T during FAT, but only at 2.6 was possible to hold the current for more than 1h Analysis and modifications are ongoing in order to repeat the FAT Based on preliminary computation, building a wiggler magnet using Nb3Sn strand would reduce the size of CLIC DRs and the IBS effect Two possible scenarios were selected for constructing the Nb3Sn wiggler prototype: Period length=44mm for a maximum field density in gap ≈3.5T (better choice for total wiggler length decrease) Period length=48mm for a maximum field density in gap ≈4.0T (better choice for IBS effect decrease) Manufacture of 1 test coil of the Nb3Sn wiggler prototype is foreseen by the end of the present year TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

References A Multi-TeV linear collider based on CLIC technology: CLIC Conceptual Design Report, edited by M. Aicheler, P. Burrows, M. Draper, T. Garvey, P. Lebrun, K. Peach, N. Phinney, H. Schmickler, D. Schulte and N. Toge, CERN Antoniou, F. Optics design of intrabeam scattering dominated damping rings. Ph.D. Thesis. CERN, 2012. Ferracin, P. et al. Report on CLIC Nb3Sn wiggler magnet. Local report, CERN, 2012. Mezentsev N.A. et al. Final Design Report on Superconducting Wiggler Serving as CLIC Damping Wiggler Test Device and Light Source for ANKA‐IMAGE‐Beamline at KIT. BINP, 2012. Schoerling, D. Superconducting wiggler magnets for beam-emittance damping rings. Ph.D. Thesis, CERN, 2012. Zolotarev, K. The results of Hall probes measurements of the ANKA/CLIC wiggler. BINP, 2014. TE Magnet Seminar. SC wiggler magnets for CLIC damping rings

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Superconducting wiggler magnets for CLIC damping rings

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