Proper IPC operation is critical to meeting the scientific objectives of the SXRP. In this section, we describe the specific requirements placed on the IPCs and the results of the testing program devised to compare IPC operation to these requirements. This section has three parts. In the first part, we discuss the environmental testing the IPCs underwent to test their durability to vibration, temperature cycling, and pressure cycling. The environmental testing was designed to simulate the conditions the IPCs will encounter during testing, launch, and on-orbit operation of the SXRP. In the second part, the measurements that were made to check that the IPCs meet the mechanical specifications are presented. These mechanical specifications directly influence the IPC performance, particularly the uniformity of Gas Gain. The third part contains a description of the functional requirements and the results of the functional testing. The functional testing is designed to check that the critical IPC parameters, such as X-ray Efficiency, Energy Resolution, and Position Resolution, are acceptable to meet the SXRP's scientific objectives.

IPC testing was conducted both at Metorex and Columbia University to compare IPC performance to the requirements which are specified in this section. Here, we state each requirement placed on the IPCs, describe the tests conducted to measure IPC performance, and report the results of these tests. A set of environmental and functional tests were performed on the IPCs while at Metorex. The Metorex environmental testing is described below. Although functional tests were performed at Metorex, they are superseded by the ones done during the Columbia University IPC calibration. Thus, only the functional testing performed at Columbia University is described here.

4.1 Environmental Testing

Thermal cycling and Vibration/shock testing were performed according to acceptance levels specified in the document "Operational Requirements for the Scientific Equipment Operation and Adaptation with the SPECTRUM-X-Gamma Spacecraft - ISSUE 4" (Moscow, 1991). The environmental tests were performed before the welding of the IPCs' back plates. After completion of the environmental testing, tests were conducted to check that the IPCs satisfy the following requirements:

1. The electrical resistance between each feedthrough and the IPC body must be in excess of 10 gigaohms.

2. The capacitances between the electrodes in the W&S plane (WS, WZ, SZ, WSa, SSa, ZSa where W, S, Z, and Sa refer to the Wedge, Strip, Zee, and Sideanti electrodes respectively) measured after environmental testing must agree to within 10% or within 5 pF (the larger of the two) with the measurements made before testing. This test verifies that no breaks formed in the W&S electrodes.

3. The detector interior must be visually inspected for damage such as breakage of wires or wire frames.

4. The beryllium window must pass a helium leak test. Specifically, when the detector is filled to a pressure in excess of 1 Bar and the region in front of the window is placed under vacuum, the partial pressure of helium in the vacuum region must be less than 2 x 10^-9 torr.

Tests were performed at Metorex to check that these four requirements are satisfied, and the results show that the IPCs satisfy the specifications in each case.

4.2 Mechanical Specifications

In the following table, the "Specification" column contains the specifications for the distances between IPC planes (see Figure 3.1-2 and Table 1). The other four columns are the measured distances between planes for each IPC. The measurements were performed at Metorex using a calibrated micrometer caliper or a caliper rule and a microscope (10 times magnification) with an x-y-z table. The measurement given in the table for each dimension is the mean of four or nine separate measurements. The measurements are made at different points on the IPC planes providing a check that the planes are parallel. The error given on the measurement for each dimension is the standard deviation of the separate measurements divided by the square root of the number of separate measurements. It should be noted that a small error is an indication that the planes are nearly parallel. It can be assumed that the error given in the table is an upper limit on the random error on the measurement. The measurements given for distances between wire planes are from the wires of one plane to wires of the other plane.

Table 4: Specified and Measured Distances Between IPC Planes

The measurements indicate that the distances between the planes are within the specifications.

4.3 Functional Requirements

4.3.1 Spatial Uniformity

It is important that the IPC response to x-rays is uniform over the face of the IPC. Here, three parameters are used to quantify the IPC response to x-rays at different positions on the IPC: Gas Gain, Efficiency, and Energy Resolution. During the uniformity tests, a collimated 55Fe source is put in 50 different positions over the IPC face. At each position, data is acquired for 30 seconds resulting in the collection of about 4000 events per position. The collimated 55Fe source is designed to produce an x-ray spot size less than 3 mm in diameter. A more detailed explanation of the setup for this testing is given in section 5.6. The data taken as described here and in section 5.6 is recorded in section 5.9.2. The specifications for the uniformity of Gas Gain, Efficiency, and Energy Resolution over the face of the IPC follow:

1. Gas Gain Specification: None of the 50 positions where data was taken should have a Gas Gain which is different from the mean Gas Gain for all 50 positions by more than 10%.

2. Efficiency Specification: None of the 50 positions where data was taken should have an Efficiency which is different from the mean Efficiency for all 50 positions by more than 5%.

3. Energy Resolution Specifications:

a. None of the 50 positions where data was taken should have an Energy Resolution greater than 20% where the Energy Resolution is defined as the FWHM of the x-ray energy distribution divided by the mean x-ray energy.

b. When the full face of the IPC is illuminated, the Energy Resolution must be less than 25% at 6 keV.

The results addressing each of the above specifications are presented below.

1. Gas Gain Results

For each IPC, the following table gives the deviation of the individual positions with the highest and lowest Gas Gain from the mean Gas Gain for all 50 positions. There is a linear relationship between Anode pulse height and Gas Gain which is given in section 5.4.1. Thus, the Gas Gain deviations can be calculated from the mean Anode pulse heights for each position. The values given below indicate by what percent the individual positions with the highest and lowest mean Anode pulse heights deviate from the mean Anode pulse height for all 50 positions.

Table 5: Measurements of Spatial Deviation of Gas Gain

LE2, HE1, and HE2 meet the specified requirements. For LE1, the individual position with the highest Gas Gain is 11% above the mean Gas Gain for all 50 positions. This individual position is the only one above the specification.

2. Efficiency Results

For each IPC, the following table gives the deviation of the individual positions with the highest and lowest Efficiency from the mean Efficiency for all 50 positions. The Efficiency for a given position is defined as the number of 55Fe x-rays detected in 30 seconds of data acquisition. In this way, the Efficiency is actually a measure of "differential efficiency" from position to position on the detector rather than an absolute measure of IPC efficiency. The values given below indicate by what percent the individual positions with the highest and lowest Efficiencies deviate from the mean Efficiency for all 50 positions.

Table 6: Measurements of Spatial Deviation of Efficiency

Each IPC meets the specified requirement.

3a. Individual Position Energy Resolution Results

For each IPC, the following table gives the Energy Resolution at the individual position with the highest Energy Resolution. The Energy Resolution is defined as the FWHM of the x-ray energy distribution divided by the mean x-ray energy.

Table 7: Energy Resolution Measured at the Highest Individual Position

Each IPC meets the specified requirement.

3b. Full Face Illumination Energy Resolution Results

For each IPC, the following table gives the measured Energy Resolution when the entire face of the IPC is illuminated with an 55Fe source at Gas Gains of 5000 and 10000. At least 50,000 x-rays were used for each Energy Resolution measurement. The Energy Resolution is defined as described previously.

Table 8: Measurements of Full Face Illumination Energy Resolution at Two Gas Gains

Each IPC meets the specified requirement.

4.3.2 Position Resolution

Our design goal is a Position Resolution of 4 mm at 2.6 keV (see part 2). The Position Resolution is defined as the FWHM of the resultant position distribution when x-rays strike the same location on the IPC. The methods for measuring and calculating the Position Resolution are discussed in detail in section 5.5.2. For each IPC, the following table gives the X and Y Position Resolution measurement averaged over the face of the IPC. The Position Resolution measurements given here are calculated from data taken when the IPCs are set to a Gas Gain of 10000 and are illuminated by 2.84 keV x-rays.

Table 9: X and Y Position Resolution

Each IPC meets the specified requirement.

4.3.3 Spark Testing

The IPCs are tested to check that they can sustain operating Gas Gains over time without sparking. Spark testing is performed by turning on the Anode or Anti high voltage for a given IPC to attain a specific Gas Gain and looking for sparks while the IPC is set to this Gas Gain. The procedure for Spark Testing and the method used to detect sparks are described in section 5.7. The spark testing requirements follow. The Low Energy IPCs must not spark in 10 hours of operation at a Gas Gain of at least 10,000 and in 2 hours of operation at a Gas Gain of at least 20,000 for both the Anode and Anti. The High Energy IPCs must not spark in 10 hours of operation at a Gas Gain of at least 5,000 and in 2 hours of operation at a Gas Gain of at least 10,000 for both the Anode and Anti.

Tables 33 to 36 in section 5.7 summarize the results of the spark tests performed at Columbia. During the tests reported in the tables, no sparks were observed. Tables 33 to 36 show that the IPCs were spark tested for the requisite time.

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