Spoke Cryomodules
Sébastien BOUSSON (IPNO), Christine DARVE (ESS)
On behalf of the CNRS/IPNOrsay and ESS teams
www.europeanspallationsource.se
April , 2016
Spoke cryomodule overview:
Executive summary
• IPN Orsay is taking in charge the design of the ESS spoke cryomodules. The design activity is 99%
achieved, up to a very high level of details. The only remaining design work to perform is to
implement DC Bias capacity of the power coupler doorknob (for margins...).
• WP4 is in the design validation phase: prototypes of all sub-components have been fabricated and
are under test to have an experimental validation of their performances before starting series
productions.
• Excellent performances, well above specifications have been already reached on the spoke cavities
prototypes allowing to start the procurements for the cavity mass production (niobium supply and
cavity fabrication).
• Other validation steps, also on prototypes, are planned for the coming months: power coupler
conditioning, tests at Uppsala University of cavity+coupler and of the prototype cryomodule at full
power.
• Collaboration with UU well in place, with many technical exchanges and already common
experiments performed on HNOSS (UU horizontal cryostat) with spoke cavities.
• IPN Orsay Infrastructure is being adapted to be ready for the mass production and tests of the spoke
cryomodule components.
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Schedule: main blocks
• Main objective: deliver to ESS the last (#13) spoke cryomodule for Xmas 2018
Achieved or estimated dates for
Reference milestones for the production phase:
the call for tender publication
Cavity production start : May/June 2016 (2 months delay, no further consequences)
Cryomodule production start : December 2016
First cryomodule shipped to Uppsala: 14 Aug 2017
RFI date (ready for installation): January 2018
Last cryomodule tested & validated in Uppsala: 20 Dec 2018
i.e. cryomodule production rate = 1 cryomodule every 5 weeks
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Spoke cryomodule requirements &
technical performances
Warm linac
The 13 spoke cryomodule composing the first
superconducting acceleration stage.
SCRF linac (T=2K)
The cryogenic distribution system for the spoke
section (valve boxes, cryolines, cryo end box)
The IPNO task includes all activities linked to the design, prototyping, series production, preparation, assembly and
then testing of the spoke cryomodule components (cavities, power couplers, cold tuning systems, cryostat). The 13
cryomodule validation tests at nominal RF power will be done by the Uppsala University team, already strongly involved
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in the project, in their newly built and operational FREIA facility.
Spoke cryomodule requirements &
technical performances
Double Spoke
SRF Cavities
• Double spoke cavity (3-gaps), 352.2 MHz, b=0.50
• Goal: Eacc = 9 MV/m [Bp= 62 mT ; Ep = 39 MV/m]
• 4.2 mm (nominal) Niobium thickness
• Titanium Helium tank and stiffeners
• Lorentz detuning coeff. : ~-5.5 Hz/(MV/m)2
• Tuning sentivity Df/Dz = 130 kHz/mm
Cold Tuning System
Power Coupler
• Ceramic disk, 100 mm diameter
• 400 kW peak power (335 kW nominal)
• Antenna & window water cooling
• Outer conductor cooled with SHe
• Doorknob transition from coaxial
to ½ height WR2300 waveguide
• Slow tuning (stepper motor):
Max stroke: ~ 1.3 mm
Tuning range: ~ 170 kHz
Tuning resolution: 1.1 Hz
• Fast tuning (piezo-actuator):
Applied voltage up to +/- 120V
Tuning range at 2K: 675 Hz (min)
Spoke Cavities design & prototype
performances 1/2
DOUBLE-SPOKE CAVITY
Frequency [MHz]
Beta_optimum
Operating gradient [MV/m]
Temperature (K)
Bpk [mT]
Epk [MV/m]
G [Ohm]
r/Q [Ohm]
Lacc (=beta optimal x nb of gaps x λ /2) [m]
Bpk/Eacc [mT/MV/m]
Epk/Eacc
P max [kW]
352.21
0.50
9.0
2
61
38
133
427
0.639
6.8
4.3
335
3 spoke cavity prototypes have been
fabricated and tested in vertical cryostat:
#1 fabricated by SDMS (Fr), #2 and #3
fabricated by ZANON (It)
Niobium is from Tokyo Denkai (Japan)
ZA 01
Romea
ZA 02
Giulietta
SD 01
Germaine 6
Spoke Cavities design & prototype
performances 2/2
Spoke cavity prototype test results (Jan15 – Feb16):
• Excellent performances, well within specifications (both on Eacc & Qo)
Pcav<0.5W
Chemical etching
Ultra pure water
high pressure rinsing
Cold tuning system design &
prototype performances 1/2
Design features:
• Double lever arm tuner (“Saclay-type”).
• Actuators : one stepper motor and two
piezos per tuner (one for redundancy).
CTS parameters / design results
Cavity sensitivity
128 kHz/mm
Cavity stiffness
20 kN/mm
Max cavity deformation
1.28 mm
Course / Tuning range
1.28 mm / 160 kHz
Resolution
1 Hz/step
Piezo tuning range
@ RT
@2 K
~ 1.5 kHz
~ 800 Hz (tbc)
Cold tuning system design &
prototype performances 2/2
4 prototypes tuners fabricated by ESIM (Fr) and tested (Cryo, VT)
• With 50 mm piezos length  All specifications reached
• With 90 mm piezos length (purpose: extra margin  Bad
performances. Analysis in progress: pre-load? high stress
(differential thermal shrink)?...
Cavity ID
VT date
Piezo #1
Piezo #2
Tuner sensitivity @2K
Tuner sensitivity @4K
Tuner sensitivity @300K
Cavity sensitivity @300K
Detuning range Piezo #1 @2K
Detuning range Piezo #2 @2K
Frequency @4K (w/o tuner)
Frequency @2K (w/ tuner)
Pressure sensitivity (w/o tuner)
Pressure sensitivity (w/ tuner)
Static Lorentz coefficient
ZA01
ZA02
SD01
ZA01
Romea
Giulietta
Germaine
Romea
janv-15
feb-15
apr-15
juin-15
Noliac 50 mm Noliac 50 mm PI 36 mm PiezoMec. 90 mm
Noliac 50 mm Noliac 50 mm Noliac 50 mm
PI 90 mm
kHz/mm
78
88
68
kHz/mm
79
92
73
82
kHz/mm
67
kHz/mm
144
Hz
930
953
542
306 (+/- 120V)
Hz
680
717
791
0 (issue)
MHz
352.453
352.123
352.038
352.409
MHz
352.429
352.100
352.032
352.419
Hz/mbar
25.5
23.3
5.5
Hz/mbar
28.8
28.8
14.5
Hz/(MV/m²)
-8.5
-6.8
-8.1
-
Coarse tuning range
Power coupler & prototype
performances 1/2
Design features:
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



Coaxial geometry, capacitive coupling.
Ceramic: disk, 6 mm thick, TiN coated
Designed for 400 kW peak (25 kW CW)
Eq. average power : 25 kW CW.
3 cooling channels:
• water for ceramic window & antenna
• 5 K SC He for outer conductor
4 power coupler prototypes have been fabricated:
#1 and #2 fabricated by SCT company (Fr)
#3 and #4 fabricated by PMB Company (Fr)
Power coupler port
100 mm diameter
Power coupler & prototype
performances 2/2
First conditioning happened in end January 2016, at CEA premises (availability of RF source )
Due to an accidental disabling of all securities,
the conditioning went on without any
protection/interlock on…
… and at ~100 kW,
vacuum was too high, an
arc discharge occurred
and one of the coupler
ceramic cracked.
The second power coupler test is now
being prepared.
Cryomodule design & prototyping
1/2
Thermal shield
All cryomodule parts are fabricated and delivered
Gate valves
Vacuum vessel & its
Mechanical support
Cold/warm transition
Blankassembly of some parts
Inter-cavity belows
Coupler/vacuum
vessel interface
Cryomodule design & prototyping
1/2
First test at 80 K in the
cryomodule (without
the cavity package) in
February 2016
Spoke cryomodule components
Integration and Verification
Several test results are validation of components ability to perform as required by
ESS and thus are mandatory before launching series production:
• Cavity test in vertical cryostat (achieve 9MV/m and nominal Qo)
 Required prior tendering for niobium production for series (December 2015)
 i.e. one successful test to be achieved in October 2015 at the latest
Done !
• Cavity with coupler test in HNOSS (RF coupling successful, achieve 9MV/m and CTS)
 The test requires around 100 kW of RF power
 Required prior tendering for the power coupler mass production (Dec. 2016)
 i.e. one successful test to be achieved in Dec 2016 at the latest
On time
(Summer 2016)
• Prototype cryomodule test (validate cryo, assembly, overall results)
 Required prior tendering for the series production of spoke cryomodules (Dec. 2016)
 i.e. one successful test to be achieved in Dec. 2016 (ideally), or March 2017 (at the latest)
On time
(Nov. 2016 – few margin)
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Organization at IPN Orsay
2015: an average of 12
FTE has worked on ESS
WP4 (spoke)
(it was 9 in 2014, 7 in
2012 & 2013)
Projected for 2016, 2017
& 2018 is 14 FTE/year
In total, in 2015, about 24 IPN Orsay persons have been working for ESS 15WP4
Spoke cryomodule Major
Procurements 1/2
1.
Niobium procurement & lead time
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2.
In progress - Cost estimated to ~ 2.0 M€
2 good offers received
Order all niobium for spokes in one single procurement
Supplier strategy: only 1 (for the ~ 4 tons of Nb)
Performance mitigation strategy: buy niobium equivalent to 3 more cavities.
Spoke cavities procurement & lead time
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In progress - Cost estimated to ~ 4.0 M€
3 good offers received
Order the 26 spoke cavities in one single procurement
Supplier strategy: only 1 – it’s cost effective & less required work for fabrication
follow-up (2 contractors is of course possible, but no clear advantages, not
necessary for schedule reasons for instance)
• Performance mitigation strategy : buy 3 more if within allocated budget
• Allocated production lead time will allow 2 phases:
- a pre-production (4 units) to check production processes and quality,
constituting a Go/NoGo for phase 2.
- a series production for the remaining 22 units
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Spoke cryomodule Major
Procurements 2/2
3.
Spoke power couplers procurement & lead time
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4.
Scheduled between June 2016 and June 2018 - Cost estimate: ~ 1.1 M€
Several companies worldwide & Europe – Prototypes: SCT (Fr) and PMB (Fr)
Order the 26 power couplers in one single procurement, to a single supplier
Spare strategy: no spare (ESS guideline), but with option for 1 or 2 spares
Allocated production lead time will allow 2 phases:
- a pre-production (2 to 4 units) to check production processes and
quality, constituting a Go/NoGo for phase 2.
- a series production for the remaining (22 or 24)
Spoke cold tuning systems procurement & lead time
• Scheduled between June 2016 and June 2018 - Cost estimate: ~ 0.5 M€
5.
Cryomodule parts procurement/assembly & lead time
• Scheduled between July 2016 and Sept. 2018 - Cost estimate: ~ 4.0 M€
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Top risks
• #1 (Main risk): success-oriented schedule: no room for a failure
– Typically: a cavity VT failure, a cryomodule assembly failure implying a partial or
full disassembly/re-assembly of a cryomodule.
– Mitigation: anticipate as much as possible the series production, to give schedule
margin during series production, without taking additional risk: this is the followed
scenario with the intermediate validation tests.
• #2: No spare: neither for sub-components nor for a complete module
– A failure during production of a sub-component, or a lower performing component
(cavity, power coupler, cryomodule...).
– Mitigation: integrate options in procurement for additional production (yield) and
use whenever possible the prototype cryomodule parts (except for cavities).
• #3: Failure of a test/preparation facility: RF source, vertical cryostat,...
– Cavity, coupler or cryomodule tests and preparations rely on heavy infrastructure
that might have failures
– Mitigation: have fallback solutions: for RF, several sources will be available at UU
(FREIA) and 1 at IPNO; for cryo test, 2 VC will be available at IPNO,...
Next Six Months
• Conditioning of the 2 sets of power coupler pairs
• Develop and validate several cavity procedures:
• Cavity H degassing at 550 °C to cure from Q-disease
• Cavity venting procedure without inducing particle contamination
• Achieve the prototype valve box fabrication
• Perform a test of a cavity + power coupler in HNOSS before
sept. 2016
• Achieve preparation and assembly of the spoke cryomodule
for Oct. 2016
• Start niobium and cavity mass production within 2 months
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Summary
• All 3 cavity prototypes already tested in VT and showed excellent
performances, with important margins w.r.t. specifications
• Design of all components for the spoke cryomodule is 99 %
achieved
• Fabrication and assembly of the spoke cryomodule prototype and
valve box, close to completion; the prototype cryomodule
should be ready for test in Oct. 2016.
• The actual schedule allows us to deliver the last spoke
cryomodule to ESS on time (Dec. 2018), with realistic time
allocated for the different activities…but only little (no ?) margin
to cover for potential failures.
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