|Brought to you by the ACIS team.||Flagstone Apartment Information||Last modified: 3/97 - psh|
|ACIS - PSU||TRW XTC||ASC-Cal Expander||ASC Cal||Project Science|
|TMA/TOGA||MST||ASC at MIT||dsd calibration||LETG (MPE)|
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.
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.
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.
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.
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:
These readout modes are controlled by code loaded into the L-boxes sequencer(?), Steve Kissel is the clocking guru.
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:
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.
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.
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:
Eric Kintner, MIT, firstname.lastname@example.org, 617 258-8391 Mark Bautz, MIT, email@example.com, 617 253-0023 Steve Jones, MIT, firstname.lastname@example.org, 617 253-0320 Steve Kissel, MIT, email@example.com, 617 353-7242 Takashi Isobe, MIT, firstname.lastname@example.org, 617 253-7396 Beverly Fergason, MIT, email@example.com, 617 258-8153 Patrick Hindle, MIT, firstname.lastname@example.org, 617 253-8764 Pamela Hollis, Luxel, 360 378-4137
This web page is: http://space.mit.edu/HETG/acis2c.html.
Please send any comments and updates to: email@example.com.