Diagnostic Instrumentation for the Fermilab Vertical Cavity Test Facility C'M' Ginsburg , R' Carcagn

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Diagnostic Instrumentation for the Fermilab
Vertical Cavity Test Facility C.M. Ginsburg , R.
Carcagno, M. Champion, N. Dhanaraj, A. Lunin,
W.-D. Moeller, A. Mukherjee, R. Nehring, D.
Orris, J. Ozelis, V. Poloubotko, D.A.
SergatskovAll Fermilab except (DESY)

• The Fermilab vertical cavity test facility
  (VCTF), for CW RF vertical testing of bare ILC
  1.3 GHz 9-cell SRF cavities, was completed in
  July 2007.
• Primary purpose of VCTF is to assess cavity
  performance
• Study cavity production and processing
• Perform acceptance test prior to insertion in a
  cryomodule
• VCTF diagnostic instrumentation and measurements
  are required to understand cavity performance

• Quench Location on AES01 Cavity
• Mode measurements indicate the poorly performing
  cell is 3 or 7
• Initial Fast thermometry test (8 sensors on
  each equator) implicates 45o region of cell 7
  near equator
• Comprehensive Fast thermometry test pinpoints
  quench on AES01 cell 7

• AES01 quench location
  using Fast thermometry
• Eight Cernox sensors
• Temperature (K) vs. time (sec) over 4
  quench-recovery cycles input power constant
• Temperature rise 0.1 K over 2 sec seen in
  sensors 3 and 4 before quench
• Quench seen in all 8 sensors

• Fast thermometry - hot spot detection
• Cernox RTD (resistive thermometry device) sensors
  
• Calibrated, absolute temperature measurement
• Flexible sensor placement, depending on test
  requirements
• Wired in series with 1 mA current source and
  shunt resistor for measuring current
• G10 band or nylon thread, plus Apiezon grease,
  used for mounting
• Fast 10 kHz sampling rate suitable for quench
  detection and temperature rises
• Status well tested and reliable system
• Successfully and repeatedly used in other test
  systems since 2002
• Used to pinpoint quench in AES01 cell 7

AES01 cell 7
3
4

• Mode measurements determine cavity performance
  limiting cell(s)
• Determine limitation to within one (cell 5) or
  two cells
• Measure frequencies of 8 out of 9 TM010 passband
  modes on network analyzer (the p/9 was not
  measurable)
• Determine total cavity stored energy at maximum
  input power just before quench for each
  measurable passband mode
• Maximum gradient for each cell extrapolated from
  measurement using Superfish simulation by Haipeng
  Wang (JLab)
• Cell 3 7 had the lowest maximum gradient, and
  cause the performance limitation
• Field emission observed for 7p/9 mode only

• 9-cell thermometry - hot spot detection
• System requirements
• Measure temperature rise, not absolute
  temperature, in a comprehensive pattern around
  each of the 9 cells, all 9 cells tested in a
  single step
• Fast installation use for every 9 cell test
• Design
• Diode sensors 1mm x 1mm sense area, 1cm
  spacing
• Diodes allow multiplexing without active
  multiplexer
• 1N4148 diode in a SOD523 package
• 960 diodes per cell 60 cards x 16 diodes/card
• 8640 diodes for a 9-cell cavity
• Cards G10 boards, Kapton printed circuit, Kapton
  flex loop provides spring to hold diodes against
  surface
• Cage Cards installed once on two half-shells
  which bolt together
• Status Single-cell prototype being built test
  CY07

R
Completed card
z
G10 boards
Kapton printed circuit

• Variable RF input coupler
• Keeps cavity critically coupled
• Facilitates mode measurements useful for cavity
  diagnostics
• Mounts to standard input coupler port
• Movement range DR15 mm (equiv. 2109 . Qext .
  41010)
• Status Parts arriving test CY07

Diode sensor
Flex shown in compressed state as if contacting
cavity