Rota, Lorenzo

PhD thesis, Faculty of Electrical Engineering and Information Technology, Karlsruhe Institute of Technology, 2017.

Abstract

In modern particle accelerators, a precise control of the particle beam is essential for the correct operation of the facility. The experimental observation of the beam behavior relies on dedicated techniques, which are often described by the term “beam diagnostics”. Cutting-edge beam diagnostics systems, in particular several experimental setups currently installed at KIT’s synchrotron light source ANKA, employ line scan detectors to characterize and monitor the beam parameters precisely. Up to now, the experimental resolution of these setups has been limited by the line rate of existing detectors, which is limited to a few hundreds of kHz.

This thesis addresses this limitation with the development a novel line scan detector system named KALYPSO – KArlsruhe Linear arraY detector for MHz rePetition-rate SpectrOscopy. The goal is to provide scientists at ANKA with a complete detector system which will enable real-time measurements at MHz repetition rates. The design of both front-end and back-end electronics suitable for beam diagnostic experiments is a challenging task, because the detector must achieve low-noise performance at high repetition rates and with a large number of channels. Moreover, the detector system must sustain continuous data taking and introduce low-latency. To meet these stringent requirements, several novel components have been developed by the author of this thesis, such as a novel readout ASIC and a high-performance DAQ system.

The front-end ASIC has been designed to readout different types of microstrip sensors for the detection of visible and near-infrared light. The ASIC is composed of 128 analog channels which are operated in parallel, plus additional mixed-signal stages which interface external devices. Each channel consists of a Charge Sensitive Amplifier (CSA), a Correlated Double Sampling (CDS) stage and a channel buffer. Moreover, a high-speed output driver has been implemented to interface directly an off-chip ADC. The first version of the ASIC with a reduced number of channels has been produced in a 110 nm CMOS technology. The chip is fully functional and achieves a line rate of 12 MHz with an equivalent noise charge of 417 electrons when connected to a detector capacitance of 1.3 pF.

Moreover, a dedicated DAQ system has been developed to connect directly FPGA readout cards and GPU computing nodes. The data transfer is handled by a novel DMA engine implemented on FPGA. The performance of the DMA engine compares favorably with the current state-of-the-art, achieving a throughput of more than 7 GB/s and latencies as low as 2 us. The high-throughput and low-latency performance of the DAQ system enables real-time data processing on GPUs, as it has been demonstrated with extensive measurements. The DAQ system is currently integrated with KALYPSO and with other detector systems developed at the Institute for Data Processing and Electronics (IPE).

In parallel with the development of the ASIC, a first version of the KALYPSO detector system has been produced. This version is based on a Si or InGaAs microstrip sensor with 256 channels and on the GOTTHARD chip. A line rate of 2.7 MHz has been achieved, and experimental measurements have established KALYPSO as a powerful line scan detector operating at high line rates. The final version of the KALYPSO detector system, which will achieve a line rate of 10 MHz, is anticipated for early 2018.

Finally, KALYPSO has been installed at two different experimental setups at ANKA during several commissioning campaigns. The KALYPSO detector system allowed scientists to observe the beam behavior with unprecedented experimental resolution. First exciting and widely recognized scientific results were obtained at ANKA and at the European XFEL, demonstrating the benefits brought by the KALYPSO detector system in modern beam diagnostics.

 

First assessor: Prof. Dr. M. Weber
Second assessor: Prof. Dr.-Ing. Dr. h.c. J. Becker

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