Uniformity scan of the 6cm tubes. Jingbo Wang Argonne National Laboratory, Lemont, IL

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1 Uniformity scan of the 6cm tubes Jingbo Wang Argonne National Laboratory, Lemont, IL

2 Update of the test system Realized the computer control for the multi-channel HV supply, the 2D translation stage and the keysight oscilloscope. Integrated all the codes into a single python script. Two testing options enabled: 1) Usual data acquisition and offline analysis. 2) Immediate measurements using the scope functions 2

3 2D scan All the strips are chained one by one. Signals are readout from two ends. 2D translation stage (Newport ESP300 motor) has a 5 cm scanning range in both x and y directions. Step size: 2 mm in both directions Scanning area: 5 cm 5 cm Left Grid spacer Right 3

4 Gain uniformity: Tube#44 In single-pe mode, the signal of the direct incident photon is contaminated by the scattered photons. No matter where the laser spot is, the tube is always able to detect the scattered photons, which makes the gain look more uniform. For example, even the laser spot is on the spacer, the tube gives a good pulse due to the scattered photon somewhere else. In this case, the spacer is indistinguishable in the 2D gain map. In multi-pe mode, the pulses produced by the main laser beam is much higher than that produced by the scattered photons, which reveals the spacers in the 2D map. Left Random scattered photon Main laser beam Right 4

5 Uniformity: Tube#44 Left figure is the absolute gain map measured in single PE mode, but the result is contaminated by the scattered photons. Right figure is a map of the number of the collected electrons, measured in multi-pe mode. It shows the overall uniformity of the tube. It is a combination of the QE and gain uniformities. Multi-PE 5

6 Uniformity: Tube#45 and Tube#47 Tube#47 was measured to have a decent QE (%14) and a low gain (2e6). Even in multi-pe mode, the spacers are barely distinguishable in the 2D map. Increasing the light level should help to reveal the spacers. 2e6 gain and 100 ps time resolution of Tube#47 were measured with the laser spot on the upper-left quadrant. The same measurements should be done for other quadrants. Multi-PE Multi-PE 6

7 Is there any way to measure the absolute gain? Option 1: multi-pe measurment Assume the number of collected electrons N e responses linearly to the number of input photons as: where G is gain. If N photon and QE are known, gain G can be calculated. N photon can be calibrated by a device (silicon photomultiplier for instance) with a known QE. QE can be measured separately in the optical table. Option 2: single-pe measurement In single PE mode, the total number of collected electrons N e consists of two parts: First, block the laser beam just in front of the tube and measure the number of collected electrons (G*N scatterred ) produced by the scattered photons. Then, unblock the laser and measure the total number of collected electrons (N e ). Then the gain G can be calculated. Option 3: single-pe measurement using a fiber 7

8 Conclusion The bule laser test facility has been updated from a manual system to a automatically computer control system. Uniformity scan is available in multi-pe mode. This can be a routine test for every new tube. It is difficult to measure the uniformity of the absolute gain due to the contamination from the scattered photons. Overall uniformity can be scanned in multi-photoelectron mode. There are two possible options for measuring the absolute gain uniformity with the current setup. A better solution is using a fiber. Next Try to measure the absolute gain uniformity. Redo the performance tests for all three working tubes. Write a documentation for the laser system. 8