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A single ASIC (v2) has been attached to the carrier board and a small sensor (48x48 pixels). The sensor has a standard entrance window, i.e., not the thin entrance window intended for the final detectors. The requirements that the detector was designed for and the measured results stated by TID for (Matrix+ADC) can be seen below:

Table 1. Design requirements and measured performance of key characteristics.

Gain modes

As stated in Table 1., the detector has a 100um pixel pitch and can be configured in 5 different gain modes; 3 fixed gain modes and 2 auto-ranging gain modes. In the same way as for the ePix10k ASIC, the gain mode is selected using the tr_bit register and the pixel map settings. The combinations to get to the specific gain modes can be seen in table 3.

Table 2. Tr_bit and pixel config file combinations are required to get a specific gain mode.

Readout channel, timing diagram, and targeted machine rates

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Figure 5. Machine operation rep rates and targeted detectors.

Add section on running Run and DAQ triggers differently or the same:

The machine base rates, and the resulting frequencies that can be hit if the Run trigger is kept set when changing the DAQ trigger, can be seen in the Excel file below.

Allowed ACQ trigger rates for set Run trigger rate LCLS-II

Quantum Efficiency

For the prototype detector, a small 500 um thick Si sensor was used with the standard entrance window (1um Al, 1 um non-sensitive Si) was used. For the final detector, a full-size 500 um thick Si sensor with a thin entrance window (Sintef - 100nm Al, 100nm non-sensitive Si) will be used. A first-order estimate of the resulting detection efficiency as a function of photon energy for the two types of sensors can be seen in Figure 6. It should be noted that the non-sensitive region and the Al thickness have not been measured and are best estimates. For the plots stating "with shield" the detection efficiency has been calculated assuming a 25 um thick Polyimide shield located in front of the sensor. An excel sheet containing the values for both sensors can be found under the Figure.

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Figure 6. First-order estimate for the detection efficiency for the standard sensor and the thin entrance window sensor.

QE ePixHR - thin entrance window and standard.xlsx

Initial testing

Gains

A first evaluation of the gains for the high and low gains, as well as the ratio between the two, can be seen in Table 3, while figure 7 show the gain maps (fitted peal position for 22.1 keV photons). It should be noted that this was measured using v2 of the ASIC, the original single trigger firmware, 262MHz Serdes clock, symmetrical ACQ/RO widths (24us), and a 4kHz frame rate. This measurement has to be redone and validated for v4 of the ASIC, with the final settings and firmware.

Table 3. Initial measurements for the FH and FM gains.

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Figure 7. Pixel map and histograms for the fitted peal position (Ag fluorescence - 22.1 keV), and the gain ratio map.

Pedestals

The pedestals shown below in figure 8 and summarised in Table 4, were taken under the same detector settings as the gain maps.

Table 4. Pedestal values observed for the different gain modes.

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Figure 8. Pedestal distributions and maps for the ePixHR5kHz detector.

Noise

The noise shown below in figure 9 and summarised in Table 5, were taken under the same detector settings as the gain maps.

Table 5. Noise values observed for the different gain modes.

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Figure 9. Pedestal distributions and maps for the ePixHR5kHz detector.