The ALICE Silicon Pixel Detector Control and Calibration Systems

The work presented in this thesis was carried out in the Silicon Pixel Detector (SPD) group of the ALICE experiment at the Large Hadron Collider (LHC). The SPD is the innermost part (two cylindrical layers of silicon pixel detec- tors) of the ALICE Inner Tracking System (ITS). During the last three years I have been strongly involved in the SPD hardware and software development, construction and commissioning. This thesis is focused on the design, development and commissioning of the SPD Control and Calibration Systems. I started this project from scratch. After a prototyping phase now a stable version of the control and calibration systems is operative. These systems allowed the detector sectors and half-barrels test, integration and commissioning as well as the SPD commissioning in the experiment. The integration of the systems with the ALICE Experiment Control System (ECS), DAQ and Trigger system has been accomplished and the SPD participated in the experimental December 2007 commissioning run. The complexity of the detectors, the high number of subcomponents and the harsh working environment make necessary the development of a control system parallel to the data acquisition. This online slow control, called Detector Control System (DCS), has the task of controlling and monitoring all hardware and software components of the detector and of the necessary infrastructures. The latter include the power distribution system, cool ing, interlock system, etc. In this scenario, the DCS assumes a key role. Its functionalities have extended well over the simple control and monitoring of the experiment. DCS, nowadays, are highly advanced and automated online data acquisition systems, with less stringent requirements compared to the DAQ. Moreover the SPD DCS has the unique feature of not only controlling but also operating the SPD front-end electronics. These requirements impose a high level of synchronization between the system components and a fast system response. The DCS, in this case, is a fundamental component for the detector calibration. The SPD DCS should be operated in the ALICE DCS framework hence a series of integration constraint should be applied to the system. Furthermore, in complex experiments such as ALICE, the detector operation is tightly bound to the connection and integration of the various systems such as DAQ, DCS, trigger system, Experiment Control System (ECS) and Offline framework. The operation of the SPD front-end electronics and services should be done at various levels of integration. At the first and bottom level it is required that each system runs safely and independently. At the second level the subsystem controls should be merged to form a unique entity. At this stage the components operation should be synchronized to reach the full detector operation. The third level requires the integration of the SPD control in the genera l ALICE DCS/ECS. These requirements have been fulfilled by designing the DCS with two main software layers. On the bottom a Supervisory Control And Data Acquisition (SCADA) layer controls and monitors the equipments. It is based on a commercial application, PVSS, and it also responsible of provide an user interface to the subsystem components. On top a Finite State Machine (FSM) Layer performs the logical connection between the SPD subsystems and it connects the SPD DCS with the ALICE DCS and ECS. PVSS is designed for slow control applications and it is not suitable for the direct control of the fast SPD front-end electronics. I designed a Front-End Device Server (FED Server) to interface the SCADA layer with the front-end electronics. The server receives macro-instructions from the SCADA and it operates autonomously the complex front-end electronics. The complexity of the detector calibration requires a high automation level and the integration of the calibration system with the ALICE calibration framework. In order to satisfy these requirements and provide the user with a simple and versatile interface, I decided to foresee two calibration scenarios. A calibration scenario, named DAQ ACTIVE, allows the fast detector calibration but it needs the control of the full detector and subsystems. A second calibration scenario, named DCS ONLY, slower than the DAQ ACTIVE scenario, allows the calibration of a detector partition without interference with the normal detector operation. The control and calibration systems have been used to characterize and test the SPD components before and after the integration in the detector, both in laboratory (DSF) and in the ALICE environment. Some calibration and control systems application examples as well as a brief overview of the detector performance evaluated during the commissioning phases are reported

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