In 2007 a prototype of an analog Sum-Trigger for air Cherenkov telescopes was installed in the MAGIC I telescope lowering the trigger threshold from 55 GeV to 25 GeV and led to the detection of pulsed gamma-radiation from the Crab pulsar. However, that first prototype requires intensive maintenance and manual adjustment of each trigger channel and thus strongly limits its applicability for new high-resolution cameras comprising a larger number of pixels in the trigger area. Hence, a new setup with fully automatic setting of the trigger parameters has recently been designed. To minimize system costs and complexity, the improved version utilizes a sequential rate counting procedure to determine and compensate the gain and delay shifts of all channels caused by aging and changing operation conditions of the camera's photomultipliers (PMTs). The key element of the new system is a continuously tunable, passive delay line for fast analog signals enabling precise equalization of the PMT's signal transit times. When only a few small signals form the trigger, as in low energy air showers, precise temporal overlap in the analog sum is particularly essential for efficient detection. Unlike current commercial devices with bandwidths below 200 MHz and discrete delay setting, this new delay line allows smooth variation of each channel's delay within a range of 6 ns while maintaining a bandwidth of above 300 MHz, thus preserving the system's minimal pulse width of 2.6 ns. In 2010 a fully working new Sum-Trigger test setup comprising eight pixels has been built and temporarily installed at the MAGIC I telescope. It has been shown that the new design meets or even surpasses the requirements of a new analog trigger system with an anticipated energy threshold below 25 GeV.

A Tunable Delay Line for Fast Analog Pulses as Key Element of a New Sum-Trigger for Cherenkov Telescopes

Fiber optic smart structures have been developed over several decades by the recent fiber optic sensor technology. Optical intensity-based sensors, which use LD or LEDs, can be suitable for the monitor system to be simple and cost effective. In this paper, a novel fiber optic smart structure with human-like perception has been demonstrated by using intensity-based hetero-core optical fiber sensors system with the CMOS detector. The optical intensity from the hetero-core optical fiber bend sensor is obtained as luminance spots indicated by the optical power distributions. A number of optical intensity spots are simultaneously readout by taking a picture of luminance pattern. To recognize the state of fiber optic smart structure with the hetero-core optical fibers, the template matching process is employed with Sum of Absolute Differences (SAD). A fiber optic smart glove having five optic fiber nerves have been employed to monitor hand postures. Three kinds of hand postures have been recognized by means of the template matching process. A body posture monitoring has also been developed by placing the wearable hetero-core optical fiber bend sensors on the body segments. In order for the CMOS system to be a human brain-like, the luminescent spots in the obtained picture were arranged to make the pattern corresponding to the position of body segments. As a result, it was successfully demonstrated that the proposed fiber optic smart structure could recognize eight kinds of body postures. The developed system will give a capability of human brain-like processing to the existing fiber optic smart structures.

Multi-channel measurement for hetero-core optical fiber sensor by using CMOS camera

Various spurious effects limit the effectiveness of Photomultipliers when used in low-light-level coincidence counting experiments. One of these effects is afterpulses from light emission in the Photomultiplier. Here we present a study on the light emission in Photomultipliers using a variety of methods. First we image the light emission directly. Second we characterize the light emission spectrum. Finally we investigate the time resolved light emission. In particular we find that, not only the dynodes “glow,” but also the support structure emits light. A fluorescent effect is found. The experiments performed help to understand the fundamental effects of light emission and afterpulses in Photomultipliers.

Light Induced Afterpulses in Photomultipliers

This thesis deals with the development and characterisation of a novel silicon photomultiplier concept with bulk-integrated quench resistors. The approach allows the realisation of a free entrance window and high fill factors, which leads to an improvement of the detection efficiency. With first prototype productions a proof of concept was possible. A full characterisation provided promising results, in particular with respect to the photon detection efficiency. By customising the simulation tools, a reliable description of the devices was achieved. In addition, conceptual studies of the next device generation demonstrated the possibility of single cell readout, expanding the application range of those detectors to particle tracking.

Development and characterisation of silicon photomultipliers with bulk-integrated quench resistors for future applications in particle and astroparticle physics

Chinese Academy of Sciences, Grant/Award Number: XDA17010205 Abstract The compensation for non‐uniformity correction of multi‐channel time delay integration charge coupled device (TDI CCD) under variable gain is presented. The mathematical model of photoelectric conversion is established first, and, then, a two‐step non‐uniformity correction method for multi‐channel TDI CCD is proposed. Based on this method, a compensation algorithm for non‐uniformity correction under variable gain is elaborated in detail. The experimental results show that the proposed algorithm can always maintain the photo response non‐uniformity (PRNU) of the corrected images better than 1.14% when the programmable gain amplification (PGA) gain varies within the range of 1–3, compared to the conventional method of degrading to 2.91%. Meanwhile, a compression method for correction coefficients under multiple integral stages is proposed, which can reduce the storage space requirement by 50% at the cost of the PRNU being degraded by a maximum of 0.19% at all integral stages.

Compensation for the non-uniformity correction of multi-channel TDI CCD under variable gain

The multi-channel detectors are essential part of modern experiments. The number of readout channels for every future detector is usually much higher than before. Usually the number of channels of a detector constrains the minimal data acquisition system (DAQ) requirements and the total price of the readout system. For the future groundbased gamma-ray instruments like for example, the Cerenkov Telescope Array (CTA) the DAQ system should fulfill several stringent requirements: low power consumption, compactness, ability to record a rate of 1kHz for several thousand channels and affordable cost per channel. We present here an alternative to the conventional ADC system. The analog pulses from the light sensors are converted into optical signals and fed into the optical fibers, which are bundled as a fiber optic plate (FOP). The externally triggered high-speed CMOS camera coupled to a fast Gated Image Intensifier makes a photo of the FOP, when the optical signal flashes the FOP. The Gated Image Intensifier serves as an ultra-fast optical shutter and event delimiter.

Fast readout of multi-channel detectors by using a CCD/CMOS camera

We report on the characterization of candidate light sensors for use in the next-generation Imaging Atmospheric Cherenkov Telescope project called Cherenkov Telescope Array, a major astro-particle physics project of about 100 telescopes that is currently in the prototyping phase. Our goal is to develop with the manufacturers the best possible light sensors (highest photon detection efficiency, lowest crosstalk and afterpulsing). The cameras of those telescopes will be based on classical super-bi-alkali Photomultiplier tubes but also Silicon Photomultipliers are candidate light sensors. A full characterisation of selected sensors was done. We are working in close contact with several manufacturers, giving them feedback and suggesting improvements.

Light Sensor Candidates for the Cherenkov Telescope Array

For the first time, pulsed γ-rays above 25 GeV from the Crab pulsar have been detected with the MAGIC telescope [1]. All Crab pulsar emission models predict that the energy spectrum of the pulsed emission drops off sharply somewhere between a few GeV and a few tens of GeV. The lack of experimental data at the relevant energies prevente d so far the discrimination between the different theoretical scenarios of γ-ray emission in pulsars. The MAGIC measurements reveal that the drop-off in the emitted radiation occurs at relativ ely high energies, which indicates that the emission must occur far out in the Crab pulsar’s magnetos phere. All models in which the emitting region is located close to the Crab pulsar’s surfac e (e.g., the so-called polar cap model) are ruled out by the MAGIC results.

First detection of the Crab pulsar above 25 GeV with the MAGIC Telescope

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Fast readout of multi-channel detectors by using a CCD/CMOS camera

Light Sensor Candidates for the Cherenkov Telescope Array

First detection of the Crab pulsar above 25 GeV with the MAGIC Telescope