Contributions to phase two of AGATA electronics

Resumen

In the field of Nuclear Physics, high-resolution gamma ray spectroscopy is an accurate method to perform nuclear structure studies, retrieving the energy and angular distributions from gamma photons emitted in the transition between nuclear states. In order to obtain the nucleus in an excited state, such that will emit gamma-rays, we are forced to collide matter, doing nuclear reactions (in the in-beam spectroscopy) or resort to the radioactive decay (decay spectroscopy). The High Purity Germanium (HPGe) semiconductor detectors have shown to provide good response as gamma-ray detector. As other semiconductor detectors, HPGe produce, with high sensitiveness, a current proportional to gamma ray energies while there are subject to high voltage inverse polarization, in cryogenic conditions. The AGATA (Advanced GAmma Tracking Array) HPGe detector array is a state-ofthe-art detector array for the gamma ray spectroscopy technique in nuclear physics. In order to improve the sensitivity, AGATA HPGe detectors have the outer contact divided in 36 segments in order to determine photon position and energy deposited in each segment. With the interaction energy and position information is possible to reconstruct (Track) the gamma-ray interaction sequence using tracking algorithms. With such technique is possible to maximize the sensitivity of the detector array (energy resolution and P/T) without using part of the detection solid angle for the anti-Compton active shields. In addition to the segmented detectors, the positions sensitive HPGe arrays require sampling electronics with spectroscopic signal-to-noise ratios, which provides the traces to be processed by the Pulse Shape Analysis algorithms. To provide maximum efficiency and sensitivity, the AGATA project aims to construct a 4π solid angle detector array. This geometry optimizes as well the information obtained, something that is especially important in experiments using expensive radioactive ion beams. Another goal in the construction of AGATA is the mobility of the array. AGATA is installed in different laboratoriesto take advantage of the variety of beams and complementary instrumentation existing in different European centres. -IVThe AGATA project is currently in its Phase 1, using a second generation electronics, which aims at building a 1 π solid angle coverage. This requires 45 detectors, that today are partly instrumented with the previous Phase 0 electronics, mostly design and produced in the period from 2005 to 2007. Presently, the main goal for the AGATA collaboration, regarding electronics, is the development of the Phase 2 version, with the objective of instrumenting 180 detectors, which is partly done by the work described in this thesis. The main improvements for this Phase 2 electronics are: the integration of all the electronics from digitizers to readout, including Pre-processing, in one standalone system and the use of Ethernet as the readout protocol. The Ethernet technology will enable a multipoint connection and the possibility to distribute the data anywhere within the AGATA processing farm. One of the main problems found in the integration of all the system is the optimization of the FPGA resources used in the Pre-processing. Despite of the increase in the high-speed transceiver data rates of the last FPGA developed in the industry, the number of transceivers on the devices is limited. Furthermore, the FPGA cost increases largely with the amount of transceivers, which is an issue for the AGATA detectors, with a need for a large number of transceivers but not at an especially high data rate. To reduce system complexity, cost and power, the number of high speed digital lines is optimized through data aggregation, increasing the speed data rate of each line but with a reduction of 4 to 1 in the total number of transceiver lines. The solution is carried out through the Input Data Mezzanine board, conceived and developed completely under this thesis work. From a technological point of view, the main objective of the thesis is to prove the possibility of reading up to 40 optical or copper low rate inputs, using JESD204 or equivalent protocol, in the FPGA using only 10 transceivers through a time division multiplexing technique. The work is done with state-of-the-art in hardware-software FPGA design, highspeed digital design and digital communications, as well as with the knowhow of the AGATA current electronics. Although this device is designed for AGATA, we consider that this technology will be of interest for other instruments and applications.