After finishing the assembly of the T3B cassette, the preamplifier and the photosensor need to be supplied with the correct voltage, the resistance of the temperature sensor needs to be monitored and the signals of the 15 SiPMs need to be recorded. We will highlight some key aspects of the operational hardware used for the T3B experiment in the following.
Picoscopes
Up to five USB-Oscilloscopes of the type PS6403 [73] (see Figure 4.5, right) were used to acquire the data of the experiment. They record the SiPM signals of the T3B cells, digitize them, buffer the data and transfer it via USB to a PC which stores it to the hard drive. The PS6403 series has a couple of specifications that make it the ideal choice for a test beam experiment that focuses on the time resolved recording of fast signals. For one, the oscilloscope can sample four signals with a rate of 1.25GSamples/sec simultaneously. The delivered driver can handle oscilloscope requests and callbacks in a multithreaded way such that multiple units can be operated from the same PC at the same time. In contrast to most regular oscilloscopes, the PS6403 have a very large internal buffer of 1GB and a so-called rapid block mode. This means that the user can specify the number of signals he wants to acquire, store them in the buffer and transfer all of them to the PC only afterwards. By this, the PS6403 can achieve a signal acquisition rate of up to1MHz until the buffer is filled. The data transfer takes then up to 40seconds provided the whole buffer was filled. Additionally, it can check the number of signals that are in the buffer and trigger the transfer to the PC upon request. This is extremely useful for test beam experiments in which the particles arrive in short spills. During the spill there is no time for the data transfer of individual signals as it takes orders of magnitude longer than the time available till the next spill particle arrives at the calorimeter (details on the spill structure at the different accelerators will
Figure 4.5: Picture of the Picoscope PS2203 (left) and PS6403 (right).
be explained later in Section 4.3.1). Using the rapid block mode, the user can record all events within a spill, trigger the data transfer once the spill is finished and be ready for the next spill on time. This guarantees a maximal efficiency in recording the particle events the accelerator can deliver.
Concerning its functionality, the PS6403 is a normal oscilloscope. One can configure the vertical range and analog offset of the recorded waveform, adjust the sampling rate and configure various trigger options. For the test beam operation the external trigger option is of major relevance. An external trigger signal can be fed to the back plane of the oscilloscope and the trigger threshold can be adjusted correspondingly. This way all five oscilloscopes can be triggered simultaneously provided one splits a trigger signal and chooses an identical trigger cable length.
The PS2203 oscilloscope series (see Figure 4.5, left) has a low maximum sampling rate of 40MSamples (when operating one of the two channels) and a buffer depth of only 8000 samples [73]. This suffices to record the spill signal that is delivered by the accelerator to indicate when the particle spill starts and stops. The PS2203 can trigger the initialisation of the rapid block mode of the five PS6403 oscilloscopes via the data acquisition software (see Section 4.2.4) after the start of the spill signal, and their data transfer to the PC after the spill has finished. A PS2203 oscilloscope is therefore vital for the successful test beam operation of T3B. One PS2203 device was used for that purpose.
Power Distribution System
Two power distribution boxes (PDB) have been assembled to supply the signal pream- plifier and the SiPMs with their respective voltages. They consist of a breadboard which hosts the circuitry and a plastic box for protection. The preamplifier needs an operating voltage of 5V. An external power supply feeds this voltage into the first PDB which simply parallelizes it 15 times so that it can be wired to the T3B cells.
R1 R1 R1 RP,14 RP,1 RP,0 S0 S1 S14 U R1=56kΩ RP=0-2kΩ
Figure 4.6: Electronic circuit of the power distribution box for the SiPM bias voltage. Each SiPM has its own circuitry to adjust to its device specific bias voltage (shown by red circles) consisting of a resistor in parallel to the SiPM and an adjustable potentiometer positioned in series to those two components.
of the used SiPMs vary in a range from 70.9V to 72V. The supply voltage U (see Figure 4.6) is fed into the PDB by an external power supply and has a value of e.g. 73V (this varies depending on the test beam phase). Each SiPM has its own circuitry which reduces this voltage to its individual bias voltage. The resistance of the potentiometer
RP,i can be manually adjusted in a range of0−2kΩ and the ratio of the resistanceR1
(fixed to56kΩ) to the total resistance Rtot determines the voltage US,i that is applied
to the respective SiPM:
US,i≈ R1 Rtot ×U = R1 R1+RP,i ×U (4.1)
where i is the index of the SiPM Si ranging from 0 to 14.
Note that the resistance ofR1 andRP,i have been chosen low enough that the resistance
of the SiPM can be assumed as infinite and high enough that the overall power consumption is small. The applied voltage can be adjusted in a range of70.5V−73V which covers the needed range with a convenient tolerance. This PDB represents a very simple and easy realizable way to power multiple SiPM with their specific bias voltages.
Temperature Monitoring System
15 PT-1000 sensors attached to the T3B cells and up to 6 PT-1000 sensors positioned in the test beam area are read out by a temperature board designed and constructed at the MPI. It measures the temperature values periodically and transfers them via USB to the PC which stores them to disk. It is beyond this thesis to explain every detail of the board design. We will only highlight some key aspects relevant for its operation. The heart of the board is an integrated circuit (IC) from Texas Instruments of the type ADS1248IPW [74] which is a 24-bit analog to digital converter specifically designed to measure the resistance values of temperature sensors with high precision. One chip can read out three PT-1000 sensors and takes ∼2 seconds for it. Up to 21
UTC Time 02h 08h 14h 20h 02h 08h 14h 20h C] ° Temperature [ 24 25 26 27 28 29 30 All Sensors Standalone Sensor 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Area 0 Area 1 Area 2 Area 3 Area 4 Area 5
Figure 4.7: Temperature development of the T3B cells as measured by the temperature monitoring system for two days at the test beam. 15 PT-1000 (black to turquoise, labeled 0-14) and one standalone PT-100 sensor (red) were attached to the T3B cells. 2 PT-1000 sensors (yellow) were monitoring the temperature of the test beam area. Up to 6 area sensors can be connected (labeled Area 0 to Area 5). The day-night cycle can be clearly identified.
temperature sensors can be wired to the board. They are read out one after another, so one whole measurement sequence takes up to ∼15 seconds. This is fast enough because temperature changes occur at the test beam on a timescale of hours. The day-night cycle is the main source of variations (see Figure 4.7). Due to systematics in the board design every third channel shows a higher measurement error. A relative precision of
±0.015◦C could be achieved for the 14 good channels and a precision of ±0.25◦C for the other 7 channels. These channels were used to monitor the temperature of the test beam area and for the outermost T3B cell. Measurement outliers that occur from time to time can be easily rejected in the analysis.
Additionally, one independent layer sensor of the type PT-100 was read out by a digital multimeter of the type Agilent 34411A [75]. Its measured temperatures are about
2◦C lower than for the cell sensors since the main source of waste heat is the used preamplifier located underneath the center of the cell board and the standalone sensor was positioned between T3B cell number 7 and 8 (see Figure 4.4). The standalone sensor achieves a relative precision of ±0.01◦C. Due to the large number of sensors and the high measurement precision, the T3B temperature monitoring system allows for a good cross check of the stability of the SiPM performance over time and for an accurate determination of the temperature sensitivity of every SiPM individually.