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SRF DEVELOPMENT AT DARESBURY LABORATORY
A. WheelhouseASTeC, STFC Daresbury Laboratory
2nd PASI Workshop, RAL 3rd – 5th April 2013
Outline
• Mini PIPSS / IPS Programme– Aims & Objectives– Progress & Results
• SRF Cryomodule Development– Aims & Objectives– Progress
• Summary
4th April 2013 PASI Workshop A Wheelhouse
Mini PIPSS & IPS Programme
4th April 2013 PASI Workshop A Wheelhouse
Aims
4th April 2013 PASI Workshop A Wheelhouse
• The fundamental remit of the Mini PIPSS & IPS, Industry Partnership Schemes is to develop the capability of UK industry in the manufacturing of superconducting RF cavities
• Mini PIPSS– Fabrication of a single cell niobium cavity (1-year)
• IPS– Fabrication of a bulk niobium 9-cell accelerating structure (3-year)
• Cell to cell alignment• Tuning robustness and uniformity• Tolerance management• Cleaning/processing compliance • RF surface integrity management
• Technology directly applicable to future large scale accelerator facilities. Opportunity for Daresbury Laboratory and Shakespeare Engineering Ltd to
develop unique capabilities in the UK Enable Shakespeare Engineering Ltd to exploit the large SRF commercial
opportunity
Objectives
4th April 2013 PASI Workshop A Wheelhouse
• Mini PIPSS– Fabrication of a single cell TESLA SRF cavity– Acceleration gradient > 15 MV/m at a Qo better than 1 x 1010
• IPS– Fabrication of a 9-cell TESLA SRF cavity which will be qualified in 2 ways:-– Accelerating gradient > 20 MV/m at a Qo better than 1 x 1010 after
conventional Buffer Chemical Polishing (BCP) is performed– Accelerating gradient > 30 MV/m at a Qo better than 1 x 1010 when Electro-
Polishing (EP) chemical processing is performed
Aim to provide a clear indication of Shakespeare’s capability and assist in qualifying them as a potential supplier
Cell and Beampipe Forming• Cavity half cells and beampipes fabricated by
Shakespeare Engineering • Half cells pressed on a 60 t hydraulic press
– Pressing performed in 3 operations
• Beampipes were spun using a CNC spinning machine– Eliminates additional welded seam joint– Spinning of cones performed with intermediate
heat-treatments – Beam tube finally formed on a mandrel
3 single cell cavities welded at JLab
4th April 2013 PASI Workshop A Wheelhouse
PIPSS #01 (JLab)
4th April 2013 PASI Workshop A Wheelhouse
Multipactor
Target
• Achieved 15.7 MV/m with a Q0 of 1.15 x 1010
• CW and pulsed conditioning
• Gradient - 17.6 MV/m with a Q0 of 2.17 x 109
PIPSS #01 (JLab)
4th April 2013 PASI Workshop A Wheelhouse
• Additional BCP etch − Approximately 41µm removed
PIPSS #01 (JLab)
4th April 2013 PASI Workshop A Wheelhouse
• Vac furnace run at 600ºC for 10 hours• Plus an additional BCP etch
− Approximately 28µm removed− Further high pressure rinses
PIPSS #01 (JLab)
4th April 2013 PASI Workshop A Wheelhouse
• Further high pressure rinses
PIPSS #02 (Daresbury)
4th April 2013 PASI Workshop A Wheelhouse
• Acid fume cupboard used to perform the BCP etch• Thickness removed measured on a sample piece
which doubled as a stirrer• Acid temperature monitored 85µm removed in 2 etch runs
– Cavity turned up the other way for the 2nd run• HPR performed for 1 hour• Cavity sealed in a ISO4 class cleanroom
PIPSS #02 Evaluation
4th April 2013 PASI Workshop A Wheelhouse
• VTF manually filled from a 1000lt dewar
• Reduced performance achieved on second cavity processed at DL
Ineffective temperature control on the BCP etch
• Improvements to BCP processing is underway– Further testing to be performed
PIPSS #03 (FNAL)
• EB weld good– Some inclusions
EB weld inspection
Electro-polishing monitoring
4th April 2013 PASI Workshop A Wheelhouse
Electro-polish - 150µm
Ultrasonic Clean
High Pressure Rinse
Vacuum Bake - 800ºC 2 hrs, <5x10-07 mBar
Electro-polish - 30µm
Ultrasonic Clean and Rinse
High Pressure Rinse
Vertical Test Assembly
High Pressure Rinse
Slow evacuation and leak check
Vacuum Bake - 120ºC 2 hrs, <5x10-07 mBar
Vertical Test
FERMI Lab Standard Preparation
PIPSS #03 TestsFermiLab Tests• Cavity tested at 2K• Maximum accelerating gradient 25 MV/m with Q0=1.5x1010
• Gradient limited by a quench– First quench at 18 MV/m– Quenched twice at 21 MV/m– Finally quenched at 25 MV/m– Limited by repetitive quenches at 25 MV/m which showed no sign of
conditioning after 20 mins• No field emission above background was observed • Some multipacting was noted at around 18 MV/m
– Instabilities in Ptransmitted signal were observed
– Common ILC-shape multipacting range – Multipacting processed
Successfully met target
4th April 2013 PASI Workshop A Wheelhouse
PIPSS #03 Tests
4th April 2013 PASI Workshop A Wheelhouse
Target
PIPSS #03 - Further Qualification
4th April 2013 PASI Workshop A Wheelhouse
CBP
• Further processing performed• Cavity has been CBP
– Removing ~180µm• Light 30µm electro-polish to remove
a weld inclusion• Vacuum bake at 800ºC• Cavity to be tested 5/4/13
Typical before and after CBP
IPS Programme• 3-year programme on-going• Cavity drawings complete• Tooling has been manufactured• Pressing trials being completed with
Copper– Assessing repeatability and
reproducibility Niobium half cells to be pressed soon• Further beampipe spinning trials
– Thicker sheets• SRF infrastructure development
– Automated BCP process– Automated HPR
• It is hoped that FNAL can continue to assist in qualifying Shakespeare with this structure.
9-cell cavity drawings
BCP facility HPR stand
4th April 2013 PASI Workshop A Wheelhouse
ALICE
SRF Cryomodule Development
4th April 2013 PASI Workshop A Wheelhouse
Aims & Objectives• To lead the design of a new, high current and
world leading cryomodule.• To educate and demonstrate effective:
– Processing, – Handling, – Assembly,– Testing,– QA processes.
• To integrate the new cryomodule onto ALICE• Commission cryomodule + cryogenics systems• To validate cryomodule performance with beam
4th April 2013 PASI Workshop A Wheelhouse
SRF Cryomodule
Existing Cryomodule on ALICE
ERL (New) Cryomodule
• International collaboration initiated in early 2006:– ASTeC (STFC)– Cornell University– DESY– FZD-Rossendorf– LBNL– Stanford University– TRIUMF (2009)
• Fabricate new cryomodule and validate with beam.
• Dimensioned to fit on ALICE:– Same CM footprint– Same cryo/RF interconnects– ‘Plug Compatible’
4th April 2013 PASI Workshop A Wheelhouse
SRF Cryomodule
Existing Cryomodule on ALICE
ERL (New) Cryomodule
4th April 2013 PASI Workshop A Wheelhouse
Parameter ALICE Target
Frequency (GHz) 1.3 1.3
Number of cavities 2 2
Number of Cells per Cavity
9 7
Cavity Length (m) 1.038 0.807
Cryomodule Length (m) 3.6 3.6
R/Q (Ω) 1036 762
Eacc (MV/m) 12 - 15 >20
CM Energy Gain (MeV) 27 >32
Qo <5 x109 >1x1010
Qext 4 x 106 4x106 - 108
Max Cavity Fwd Power (kW)
10 SW 20 SW
Coupler Conditioning• High power conditioning of
the CPI input couplers:– Up to 30 kW (pulsed)– Up to 10 kW (CW)
• For these tests, couplers water/air cooled only
• No vacuum activity seen
Pulsed Conditioning
4th April 2013 PASI Workshop A Wheelhouse
Coupler Conditioning• High power conditioning of
the CPI input couplers:– Up to 30 kW (pulsed)– Up to 10 kW (CW)
• For these tests, couplers water/air cooled only
• No vacuum activity seen
CW Conditioning
4th April 2013 PASI Workshop A Wheelhouse
Cryomodule Assembly
4th April 2013 PASI Workshop A Wheelhouse
HOM assembly
µ metal installation
Cavity string
Cavity wiring
Cold Tests (Off-line)• Check the cryogenic performance • Understand the processes and establish
commissioning and operating procedures • Validate instrumentation• Cavity frequency verification
• Issue with tuner sticking had to be resolved
• Identify and resolve any unknown issues• 80K tests successfully completed• Attempted to cool-down to 4K however:
• Large temperature gradient between the two cavities• Helium reservoirs did not fill completely
• Result of blockage between cavity bottom fill connection and excessive heat load at the input transfer line
4th April 2013 PASI Workshop A Wheelhouse
Parameters Measured Specification
Static Heat Load at 80K ~ 7 W 20W
Static heat losses for the cavities at 80K
~ 3.5 W 15 W at 4K
Delta T across thermal shield at equilibrium
< 5K <10K
Delta T across the two cavities during cool-down
< 5K< 5K
Currently 50-60K for ALICE
Cryomodule Evaluation• Cryomodule installed and cooled to 2K• Optimisation presently being performed on the
cryogenic system
Evaluation Programme:-• Establish gradient and Q0
• Measure Lorentz force detuning at high gradient • Performance measurements with piezo tuners • Determine DLLRF control limitations wrt Qext
• Evaluate the effect of beam loading with DLLRF, piezo control for various Qext levels under pulsed and CW conditions
• Characterise cavities in CW mode at high gradient:– Evaluate thermal transients across cavity string and
2-phase line
• Synergies with PXIE operational requirements to be evaluated
Cryomodule installed on ALICE
4th April 2013 PASI Workshop A Wheelhouse
Summary Verified the fabrication of a single cell SRF cavity 9-cell SRF cavity and infrastructure development
progressing UK SRF capability in a stronger position thanks to
FNAL collaboration
Cavity string integrated into the cryomodule Cryogenically commissioned cryomodule off-line Cryomodule now installed in ALICE Cryomodule characterisation about to commence
4th April 2013 PASI Workshop A Wheelhouse
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