ACIS Instrument Support - Monthly Progress Report for September 2000


1. ACIS Characterization

1.1 Characterize and model radiation damage in ACIS CCDs

  ...  Continued quantum efficiency calibration of radiation damaged CCD, w457c1.  Final results will be used to characterize the uniformity of CCD QE after radiation damage.

  ...  Conducted tests in the command load for the 16-row squeegee mode with no initial flushing frames.  Bias frames will be used to measure trap time constants.  Results indicate less initial charge than expected - analysis on-going.

       * 02 September - Ran 16-row squeegee with no initial flush frames on I0 (L10, ObsID 61946)
       * 07 September - Same on S0 (L11, ObsID 61938)
       * 10 September - Same on I2 (L12, ObsID 61932)
       * 13 September - Same on S2 (L13, ObsID 61927)

  ...  Conducted real-time test of squeegee readout mode on flight device I0.

       * 15 September - Ran 16-row squeegee in raw mode.  Results will be used to characterize the trap time constants and densities.

  ...  Continued characterization of column to column variation of radiation-damaged lab CCD, w459c1.  Without squeegee, general effect is still present, but source flux seems to become more of an issue.  Gain versus row fits look better, but performance isn't improved substantially.

1.2 Define and characterize alternative CCD readout modes

  ...  Conducted real-time tests of squeegee readout mode on flight device S1.

       * 05 September - First test of a squeegee mode (16-row simple squeegee) on a BI CCD.  As expected, small improvement in parallel and serial CTI, little to no improvement in FWHM.

  ...   Analysis of flight squeegee results on-going.  Preliminary results can be found at http://space.mit.edu/~cgrant/squeegee/squeegee.html.  Results for both S0 and I0 are as expected based on lab results.


1.3 Monitor scientific on-orbit performance of ACIS

  ...  Continued monitoring of ACIS CTI.

1.4 Update and improve CCD simulation

  ...  Continued re-calibration of S3 QE using sub-assembly and XRCF data and more accurate source/detector models.  New XRCF source model with more accurate continuum and filter transmission improves both S2 and S3 spectral fits.

 [...] Created simulated eventlist for the external calibration source on S3.  Disregarding soft continuum component (see next point), comparison to flight data shows good agreement. 

 [...] Identified soft continuum component in emission from flight spare external calibration source (aluminum target).  The spectral flux density is very roughly described as a power law with number index E**-1.5 to E**-2 and a high-energy cutoff about 4.5 keV. The total rate of emission in the continuum is comparable (with a factor of 2) to the number of Al X-rays detected. Experiments with a BI CCD partially covered by a 12-micron thick parylene membrane suggest the the soft continuum is not due to X-ray emission. Rough order of magnitude estimates suggest it could be due to photoelectric emission from the Al target.  An experiment with magnets is planned to confirm this interpretation. If confirmed, this observation implies that we should NOT interpret the low-energy continuum observed in the BI spectrum of the ACIS external calibration source as entirely due to a (currently unmodelled) tail in the BI detector response function. 

  ...  Continued effort to model the electron concentration in the CCD channel as a function of Fermi potential in the channel.  The CCD model and the flight software CTI corrector requires this relationship for accurate results.

 [...] A measurement of the charge clouds formed in the neutral bulk was made, results were compared to a model in order to improve the response simulator.  Some of the results are described in a paper submitted to "Nuclear Instruments and Methods in Physics Research".

  ...  Continued work on introducing FI CCD CTI effects in the CCD model.


2. Engineering

2.1 Instrument science performance

  ...  Continued daily quick-look processing of ACIS telemetry.

  ...  Continued to publish the "annotated DOT" timeline reports.

  ...  Continued testing of flight S/W algorithms to estimate correction for charge lost to medium time-constant CCD charge traps.

  ...  Continued to test the Web interface to ACIS real-time data.

2.2 Participate in Chandra activities

 [...] Supported squeegee readout mode tests on 02 September, 05 September, 07 September, 10 September, 13 September, and 15 September including load and CAP review and real-time data analysis support.


3. CXC Support

3.1 Provide user support

  ...  Updated ACIS memo listing calibration ObsIDs and observation characteristics (ACIS Memo #165).


4. OCC Support

4.1 Use of MIT/ACIS EGSE at OCC

  ...  Continued support and maintenance of ACIS EGSE software and hardware at the OCC.

Outreach:

"Characterization of the radiation damage in the Chandra x-ray CCDs" presented by Gregory Prigozhin (8/2/00, SPIE, San Diego)