HRC-S u,v to LSI Coordinate Mapping

Introduction

The HRC-S crossed-grid charge detector (CGCD) provides a 2-dimensional readout of event positions. However, the HRC-S MCPs and CGCD do not form a single plane; the two outer MCP segments are tilted so that the three segments approximate the circumference of the OTG Rowland circle. X-rays will interact with the MCPs at some location in 3-dimensions for which we receive only two numbers. In addition, discontinuities in the linear mapping of the location of an event on the MCP surfaces and the v-axis coordinate observed, caused by the tilts in the segments, must be accounted for. Some mapping between HRC-S u,v coordinates and x,y,z coordinates in the reference frame of the detector are needed. The CXCDS uses a Local Science Instrument (LSI) coordinate system to describe the 3-dimensional geometry of the detector (see Jonathan McDowell's Coordinates Memo for a description).

HRC-S V-axis MCP Segment Locations

Mapping of the locations of the ends of MCP segments and other fiducial points along the v-axis can be determined from flat-field illuminations done in the HRC lab. The following table lists these v-axis locations as well as the linear distance (6.4294 microns/pixel) along the MCP surfaces of the locations, taking into account the discontinuities between the MCP segments. Between the +Y and center segment a 0.1022 mm (15.9 pixels) discontinuity was removed; while between the -Y and center segment a discontinuity of 0.0874 mm (13.6 pixels) was removed. Also included in the table are descriptions and some general comments about the locations. The projection histograms of the flat-fields tend to have peaks at the ends of the MCP segments as if the region were brighter than over most of the segment. In some cases this may be caused by mis-located events. Note in particular that there are problems in determining the locations of the events at the inner end of the +Y segment (v > 16384) due to the lack of information from "left-most" of the three taps.

MCP Segment HRC v-coordinateLinearized Y (mm)Notes
+Y ~1190154.255Apparent physical end of +Y MCP segment
Exact location difficult to asses due to uncertainty in degapping
~1616151.516Edge of CsI photocathode
Exact location difficult to asses due to uncertainty in degapping
1664151.207Outer edge of first full 1/2 tap of CsI coated region
1638456.567Inner edge of last full 1/2 tap on the +Y segment
~1643556.239Edge of region with counts from the +Y segment
Events from v=16384 to here have incorrectly assign positions due to the lack of a "right-hand" tap amplifier
Center ~1696052.965Apparent physical edge of central segment
1702452.554Outer edge of first full 1/2 tap on the central segment
Still the brightened region at the end of the segment
~1706052.322Just off the bright end-region
245764.000Detector readout center
251980.000Nominal optic axis location (4 mm from detector center)
32128-44.556Outer edge of last full 1/2 tap on the central segment
~32165-44.794Start of brightened region at end of detector segment
~32250-45.340Apparent physical edge of central segment
-Y ~32930-49.625Apparent physical edge of -Y segment
Many events have zero signal on the "left-hand" tap
32960-49.818Just off the bright end-region
33024-50.229Inner egde of first full 1/2 tap on the -Y segment
47616-144.047Outer edge of last full 1/2 tap on -Y segment
~47632-144.150Edge of CsI photocathode coating
Exact location difficult to asses due to uncertainty in degapping
~48112-147.236Apparent physical edge of -Y segment

Adding Another Dimension

If we assume that the tilts of the +Y and -Y segments are due to rotations only about the Z-axis and that the planes of the tops of the MCPs intersect as designed (i.e. the +Y and center planes intersect at 55.905 mm and the -Y and center planes intersect at -47.904 mm), then the X and Y locations, relative to the optic axis, of the points listed above can be determined.

MCP Segment HRC v-coordinateY (mm)X (mm)
+Y ~1190154.2242.454
~1616151.4862.386
1664151.1772.378
1638456.5670.017
~1643556.2390.008
Center ~1696052.9650.0
1702452.5540.0
~1706052.3220.0
245764.0000.0
251980.0000.0
32128-44.5560.0
~32165-44.7940.0
~32250-45.3400.0
-Y ~32930-49.6250.037
32960-49.8180.041
33024-50.2290.050
47616-144.0252.047
~47632-144.1282.049
~48112-147.2132.115

Adding the Last Dimension

The u-axis of the HRC-S is aligned with the spacecraft Z-axis. Because of the need to shield the High-Energy Suppression Filter during the flat-field illuminations, to prevent reflections from compromising the measurements, the low u-axis edge of the HRC-S is not readily determined from the data. The lower edge of the active area is roughly at a u of ~560; the upper edge is at ~3536. However, since the SIM motion allows us to place the aim-point of the HRMA at any u-coordinate we are free to choose the detector readout center of u = 2048 as the Z = 0.0 mm line. Using this assignment and the pixel scale (6.4294 microns/pixel), the Z-locations of the edges are at -9.567 mm (for u = 560) and 9.567 mm (for u = 3536). The nominal optic axis location, (Y,Z) = (0.0,0.0) is at u,v = (2048, 25198).

The table below gives the (u, v) and LSI (X, Y, Z) coordinates of the corners of the "active" area of each of the MCP segments, where the active areas are the regions coated by CsI but are outside the "bright" regions near the ends of the segments or where the the events locations may be piled up due to mis-location.

SegmentuvLSI X (mm)LSI Y (mm)LSI Z (mm)
+Y 56016162.386151.486-9.567
353616162.386151.4869.567
560163840.01756.567-9.567
3536163840.01756.5679.567
Center 560170600.00052.322-9.567
3536170600.00052.3229.567
560321650.000-44.794-9.567
3536321650.000-44.7949.567
-Y 560329600.041-49.818-9.567
3536329600.041-49.8189.567
560476322.049-144.128-9.567
3536476322.049-144.1289.567

For more information send mail to
CXC Calibration(cxccal@cfa.harvard.edu) or
Dr. Michael Juda(mjuda@cfa.harvard.edu)