ACIS Instrument Support - Monthly Progress Report for February 2000


1. ACIS Characterization

1.1 Characterize and model radiation damage in ACIS CCDs

 [...  Started a series of faint mode observations of the ext. cal. source with a frame time of 9.9 seconds which replaced one set of standard CTI measurements around the radiation belts.  This tests the utility of sacrificial charge to decrease measured CTI.

  ...  Continued analysis of raw mode flight data trying to determine electron trap characteristics.  Better determined time constant for the millisecond trap using charge re-emitted into pixels trailing behind large cosmic ray events.  Better determined time constant for fast trap using charge trailing behind X-ray events.

  ... Continued characterization of CCDs damaged in January irradiation tests.

      * w459c1 (damaged with 100 keV protons)

      ...  Acquired data over temperatures of -50 C to -150 C and a range of calibration lines with and without a robust Cobalt_60 "cosmic ray simulator".

     [...  Retested the squeegee readout with the "cosmic ray simulator" and as expected showed better results. The squeegee technique has clearly some merit but is not optimized - 2 rows does not save enough total charge.

     [...  Compared charge trailing characteristics for Mn and Al emission lines with those from the flight devices and found them to be identical.
In general all the results look like the flight devices.

     [...  Studied the effect of radiation damage on the quantum efficiency as a function of photon energy and row number.

     * ccdid7 (cold tested by Penn State)

      ...] Returned to MIT.  It shows a problem - some sort of substrate crack or separation.  It doesn't work and after several attempts is being abandoned.


 [...] Installed, registered and hooked up all software able to make simulations of the volume occupied by a charge packet as a function of signal charge in the CCD channel.  The flight software CTI corrector requires this relationship for accurate results.

 [...  Prepared paper on the ACIS characterization efforts for SPIE conference 'Radiation damage in the Chandra X-ray CCDs'.

1.2 Define and characterize alternative CCD readout modes

 [...  Retested squeegee readout mode in lab (see above)

1.3 Monitor scientific on-orbit performance of ACIS

  ... Continued monitoring of ACIS CTI.  No additional radiation damage detected in either FI or BI CCDs.

 [...] Created web page for internal CTI monitoring and continuing analysis of anti-correlation of CTI and high energy rejected events.

 [...] Studied the appearance of anomalously low pixels in a few bias maps.

 [...] Examined corner pixel values for flight calibration data to assess accuracy of bias subtraction.  Results look nominal.

 [...] Analyzed ACIS pre-CTI (OBSID 62705) and post-CTI (OBSID 536) data to compare the background event grade distributions as a function of temperature and CTI.  The focal plane temperature was -90C for OBSID 62705 and -110C for OBSID 536.  The results of this analysis showed that the grade distribution from OAC Phase 1 remains valid for GTO and GO phase observations, despite the decrease in temperature, increase in CTI, and inclusion of the cosmic X-ray background.


2. Engineering

2.1 Flight software maintenance

  ...  Continued work on flight software patch to telemeter additional data with each X-ray event that would ameliorate the effects of CTI.  Tests of the algorithm show better results than a simple linear correction of pulseheights.

2.2 Instrument science performance

  ...  Continued quick-look processing of all ACIS science runs, using EHS telemetry supplied by the GOT.

  ...  Monitored performance of new ACIS Flight Software patches including FEP bias parity error fix.  FEP bias parity errors never exceeded trigger value, otherwise patch functioned properly.

 [...  Examined possible software patches to report more information about rejected events

3. ASC Support

  ...  Continued to assist the CXC MTA in automating ACIS CTI monitoring

 [...] Supported discussions of decreasing the 'pad' time during the radiation belt passage with improved CTI results.

 [...] Assisted in preparation of ACIS chapter of the Proposer's Guide for AO-2 including sections on the background event grade distribution, bias subtraction validity, and general comments and corrections.

 [...] Provided summed -120C external cal source spectra to Norbert

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

  ...  Updated memo listing calibration ObsIDs