Update on a Proposed Bakeout

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Update on a Proposed Bakeout CXC SOT
FOT, ACIS Instrument Team and MSFC Project
Science
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Contributors to the Bakeout Effort
TheACIS Contamination Working Group has been
studying the ACIS contamination issue for the
last two years. This presentation is a summary
of that work. Those contributing directly to this
presentation CXC P. Plucinsky, A. Vikhilin, H.
Marshall, N. Schulz, R. Edgar, D. Schwartz, S.
Wolk, H. Tananbaum, J. DePasquale, S. Virani, D.
Dewey, L. David MIT M. Bautz, C. Grant, W.
Mayer, R. Goeke, P. Ford, B. LaMarr, G Prigozhin,
S. Kissel, E. Boughan PSU G. Garmire, L.
Townsley, G. Chartas, D. Sanwal, M. Teter, G.
Pavlov MSFC S. ODell, D. Swartz, M. Weisskopf,
A. Tennant, R. Elsner NGST M. Mach, P.
Knollenberg, D. Shropshire, L. McKendrick, R.
Logan, R. Giordano, T. Trinh, K. Chen, K.
Henderson, F. Cottrell, J. Lamb, D. McGregor, H.
Tran, D. Lindemann, L. Harper, L. Ryan, A.
Tao LMA N. Tice
McMaster University A. Hitchcock
Many others have contributed directly or
indirectly.
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New Items since Last CUC Briefing (June 2004)

• Tests on spare OBFs at NGST are complete and the
  project is convinced that OBFs will not be
  damaged during the bakeout
• Chandra FOT determined that it is not safe to use
  the additional heaters on the SIM to heat the
  ACIS collimator/SIM interface
• Project decided to postpone bakeout decision
  until the impact of not using the heaters was
  understood
• MSFC Project Science generated new simulations
  with these colder surfaces and not surprisingly,
  the contaminant does not vent as effectively.
  The recommendation is to keep the OBF warmer than
  any of the surrounding surfaces during the
  bakeout.
• Calibration team continues to work on the
  characterization of the contaminant (see Herman
  Marshalls talk)
• ACIS team is planning new irradiation tests to
  better understand the mechanism for the CTI
  increase from the room temperature bakeout in Sep
  1999

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Chandra X-Ray Observatory
ACIS Location
OBA Vent Locations
Contaminate Migration Path
Optical Bench Assembly (OBA)
Integrated Science Instrument Module (ISIM)
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(No Transcript)
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Geometric model
OBA vent
SIM focus structure
SIM translation table
Optical bench (OBA)
ACIS collimator
Snoot
OBA stove pipe
ACIS camera top
ACIS OBF
TRASYS model by NGST/ H. Tran et al.
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10.DOP de-rated TOBF Mass column
ODell Swartz (MSFC)
1 ACIS OBF 2 Camera top 3 ACIS snoot 4 ACIS
collimator 5 SIM trans table 6 SIM focus
struc 7 OBA stove pipe 8 Optical bench 9 OBA
vent
NOMINAL
DE-RATED
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1.0DOP de-rated TOBF Mass column
ODell Swartz (MSFC)
NOMINAL
DE-RATED
1 ACIS OBF 2 Camera top 3 ACIS snoot 4 ACIS
collimator 5 SIM trans table 6 SIM focus
struc 7 OBA stove pipe 8 Optical bench 9 OBA
vent
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Limits on vaporization rates
ODell Swartz (MSFC)
Min to vent 0.2 g in 1 orb5?10-3 mg cm-2 s-1 _at_
Tcoldest
Min to clean OBF in 1 orb2?10-3 mg cm-2 s-1 _at_
TOBF-bake
Upper limit at OBF center1?10-7 mg cm-2 s-1 _at_
TOBF-ops
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Conclusions From New Simulations

• If the contaminant has a volatility of less than
  0.1 X DOPs volatility, a one orbit 30 C bakeout
  will not move a significant amount of the
  contaminant
• If the contaminant volatility is within an order
  of magnitude of DOPs volatility, a significant
  amount of the contaminant will vaporize and
  migrate to the cold surfaces at the top of the
  ACIS collimator and the SIM. The contaminant
  will then migrate very slowly back to the OBF and
  it may be years before a significant amount
  re-accumulates on the OBF
• If the contaminant volatility is an order of
  magnitude higher than that of DOP, a significant
  amount of the contaminant will vaporize and
  migrate to the cold ACIS collimator and SIM
  surfaces. The contaminant will then migrate back
  to the OBF such that after 1 year, the thickness
  will be 1/3 of the original thickness.

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Work Still to be Done (January 2004)

• ACIS team will conduct irradiation tests,
  analyze the results, and refine the prediction
  for the effect of another room temperature
  bakeout on the CTI
• The working group will prepare another briefing
  for the Chandra project and seek approval for the
  bakeout