Development and commissioning of the ALICE pixel detector control system

Abstract

The Silicon Pixel Detector (SPD) is the innermost detector of the ALICE Inner Tracking System and the closest one to the interaction point. In order to operate the detector in a safe way, a control system was developed in the framework of PVSS which allows to monitor and control a large number of parameters such as temperatures, currents, voltages, etc. The control system of the SPD implements interlock features to protect the detector against overheating and prevents operating it in case of malfunctions. The nearly 50,000 parameters required to fully configure the detector are stored in a database which employs automatic configuration versions after a new calibration run has been carried out. Several user interface panels were developed to allow experts and non-expert shifters to operate the detector in an easy and safe way. This contribution provides an overview of the SPD control system. I. THE SILICON PIXEL DETECTOR SPD is based on a hybrid silicon pixels technology and contains around 9.8 M read-out channels. It is composed of 120 half-staves (HS) mounted on 10 carbon fibre supporting sectors (Fig. 1). Each half-stave is made of two ladders, a Multi Chip Module (MCM) and an aluminium-polyimide multilayer bus. Each ladder consists of 5 front-end chips flipchip bonded to a 200 microns thick silicon sensor [1]. Figure 1: The Silicon Pixel Detector The MCM constitutes the on-detector electronics and performs operations such as clock distributions, data multiplexing, etc. The multilayer bus provides the connection between the MCM and the front-end chips, while communication between the MCM and the off-detector electronics (Routers) is assured by three single-mode optical fiber links. The SPD low voltage power supply (PS) system is based on 20 CAEN A3009 dc-dc converter modules (1 for each half sector) housed in 4 CAEN Easy3000 crates located about 40m from the detector. The sensor bias voltage is provided by 10 CAEN A1519 modules (1 for each sector) housed in a CAEN SY1527 mainframe 100 m away from the detector. II. OVERVIEW OF THE DETECTOR CONTROL SYSTEM The DCS plays a leading role in operating the SPD and fulfils very stringent requirements. The ALICE Detector Control System (DCS), as well as all the LHC experiments, is supervised by a SCADA system (Supervisory Control and Data Acquisition) based on a software platform called PVSSII [2]. The aim of every control system is to supervise all the operations carried out in its structure and to react promptly in case of misbehaviors. The ALICE DCS group, in collaboration with every detector, foresaw a series of constrains to integrate the control system of each sub-detector into a unique control system. The DCS of the SPD was designed according to such requirements. Standard components were mainly used to reduce maintenance efforts and, in few cases, dedicated components were developed for specific and innovative tasks. The block diagram shows the connections between the hardware and software components (Fig. 2). Figure 2: Detector control system scheme There are 4 sub-control systems: PS control, Interlock control, Cooling Control and the Front-End driver (FED) control. The first three directly communicate with the hardware via Ethernet (TCP/IP, OPC protocol), while the last one uses the same protocol to connect to the FED, which is the driver that communicates with the off-detector electronics (20 routers) via a VME bus.