ACIS Two Chip, ACIS-2C

cute ACIS-2C image
 Brought to you by the ACIS team.  Flagstone Apartment Information  Last modified: 3/97 - psh

Other pages related to XRCF and Chandra:
ACIS - PSU  TRW XTC  ASC-Cal Expander  ASC Cal  Project Science


TMA/TOGA  MST  ASC at MIT  dsd calibration  LETG (MPE)


ACIS-2C Status:

8/7 picture: ACIS-2C at MSFC
8/12: ACIS-2C operating at MSFC (MIT) - COMPLETE
8/14: ACIS-2C pre-1238 cleaning (MSFC) - COMPLETE
8/23: ACIS-2C 1238 bakeout verification complete (MSFC) - COMPLETE
8/30: ACIS-2C staged to cleanroom - COMPLETE
9/16-19: ACIS-2C integrated to SIM/Cable connection - COMPLETE
9/20-24: ACIS-2C ambient verification - COMPLETE
9/24-26: Close chamber/pre-vac checkout - COMPLETE
9/27-10/4: ACIS-2C rehearsal operations - COMPLETE
10/5-1/97: ACIS-2C calibration CCD chips installed-COMPLETE
2/20/97-3/15/97: Phase 2 Calibration w/ACIS-2C-COMPLETE
3/15/97-4/30/97: Phase 2 Calibration w/ACIS flight instrument-COMPLETE

Table of Contents

  • Introduction
  • General Design
  • ACIS-2C CCDs
  • Readout modes
  • Data acquisition
  • Source Optical Blocking Filter, SOBF
  • Engineering details
  • ACIS-2C people
  • Introduction to ACIS-2C

    To support the ground calibration rehearsal at MSFC's X-Ray Calibration Facility, XRCF, a two chip ACIS system, ACIS-2C, is being provided by MIT and SAO. The complete Source-TMA-TOGA-ACIS-2C system will be a good model for flight ACIS and grating-ACIS operation. Data from this system will be important for proving the calibration methods and software to be used in the Phase 2 XRCF calibration. The ACIS-2C will also be present at the start of the real Phase 2 calibration and be swapped out when the ACIS flight instrument arrives.

    A great deal of ACIS-2C documentation exists internally; the purpose of this page is not to replace it but to document those ACIS-2C essentials that are most relevant to AXAF scientists, especially for measurement planning.

    General Design

    This section summarizes the general characteristics of the ACIS-2C up to the surface of the CCDs. As shown in the figure below the ACIS-2C has a finite entrance aperture (NO optical blocking filter, OBF), two CCD chips, and electronics support. Note that the electronics are housed in ambient air close to the CCD chips.

    diagram of ACIS-2C optical arrangement

    Given the distance of 15 inches (381 mm) from the entrance aperture to the chip plane, the converging TMA beam will have a diameter of 0.0705 * 381 mm = 26.9 mm at the aperture. Adding in the ~2.5 inch chip-centers spacing and ~1 inch chip size, a minimum clear aperture diameter of ~5 inches is required to allow unvignetted access to all active chip area. This has been provided.

    The drawing below shows a source's eye view of the CCDs. The drawing has been oriented so that "up" on the page is" up" at XRCF and left is North at XRCF. [Drawing in readable orientation.] The rows of the CCD are clocked "up" to the frame store areas under metal covers.

    diagram of ACIS-2C optical arrangement

    ACIS-2C CCDs

    The ACIS-2C has installed in it the following two CCD chips:

      ACIS-2C location        Chip ID         Comments
          CCD-x                w202C2         Frontside, ~< 4 e noise
          CCD-x                w198C3         Frontside, ~< 4 e noise

    These CCDs have not been through extensive laboratory calibration. Detection efficiency vs. E and Resolution vs. E can be predicted based on data from other CCDs tested. An extensive set of papers have ben presented on ACIS calibration at the 1996 SPIE meeting. In addition, some plots are available below of CCD-L-box data sets. Note that the resolution varies depending on which quadrant is being readout, among other effects.


    Readout modes

    A single chip can be operated at one time. The readout modes are currently being defined and input now is needed if other modes are needed. The planned modes at this time are:

    Timed exposure
    Cycle time: 7 s, standard full frame readout.
    Continuous readout
    Cycle time: ~10 mS/row, image and frame store continously clocked. Creates output "image" file of N rows.
    Windowed readout
    Cycle time: 2 s, full frame transfer from image to frame store region but only 100 (TBR) rows read out.
    Continous window mode, aka "Fast mode"
    Cycle time: 0.1 s Frame store area shifted by 20-30 rows every 0.1 s; after ~1-3 seconds (TBR) the image is moved to the frame store area and a full frame readout of the multiply-exposed image occurs.

    These readout modes are controlled by code loaded into the L-boxes sequencer(?), Steve Kissel is the clocking guru.

    Data acquisition

    The raw data from the ACIS-2C hardware are images captured by the MIT acquisition machine (sparc 20, glenfiddich). ACIS-2C software on an MIT processing machine will analyze the images to produce event lists. Details are available in Dave Plummer's 8/7/96 report. A simplified block diagram of the setup is shown below:

    diagram of ACIS-2C processing machines

    As of 8/12/96, there are two minor problems with the data acquisition hardware in place at MSFC: i) the bias voltage is fluctuating more than desired (lbox) and ii) the GSE data collection program only records for about 15 min before shuting off (it just has to be re-started to continue). These may have been related to a LN2 solenoid and controller producing voltage spikes into the acquisition hardware, suggests the unflapable Steve Kissel.

    Source Optical Blocking Filters, SOBF

    The ACIS-2C has no optical blocking filters and the only optical light in the chamber is expected from the X-ray source (and maybe the MDS?) so filters have been provided for inclusion on the XSS filter wheel(s) to allow minimal X-ray attenuation and yet block visible light. The optical blocking filters are made by Luxel (e.g., R/N 6370) and are a sandwich of Al/Lexan/Al with thicknesses like 810A/1975A/890A, and have an active diameter of 0.497". The Al layers have 1% Si as well to help with the grain size. Lexan is a poly carbonate with formula C16 H14 O3 and density of 1.2 g/cm3. The X-ray transmission plot and an ASCII table are available below.


    Engineering details

    The installation and optical/mechanical alignment of the ACIS-2C will be carried out by SAO with assistance from MIT. Besides measuring the physical location of the CCD chips in Y-Z, it will be important to measure the tip and tilt of the chips w.r.t. the facility axes.

    Some useful diagrams:

    Some useful pictures of ACIS2C at XRCF:

    ACIS-2C People

    Eric Kintner, MIT,, 617 258-8391
    Mark Bautz, MIT,, 617 253-0023
    Steve Jones, MIT,, 617 253-0320
    Steve Kissel, MIT,, 617 353-7242
    Takashi Isobe, MIT,, 617 253-7396
    Beverly Fergason, MIT,, 617 258-8153
    Patrick Hindle, MIT,, 617 253-8764
    Pamela Hollis, Luxel, 360 378-4137

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