Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Network Based Control System and Automated Operation of Low Energy Accelerator Facility at BARC, Mumbai Arindam Basu, Sudheer Singh, Subrahmanyam B.V. Nagraju, Arun Agarwal , Sapna Padmakumar, Jignesh Bhatt , Shailaja Ware , Shrikrishna Gupta, Pitamber Singh Ion Accelerator Development Division, Bhabha Atomic Research Centre, Mumbai - 400085, India. [email protected] Abstract A Low Energy Accelerator Facility (LEAF) has been set up at BARC which is in operation with several beams available to the users. The facility can deliver singly charged negative ion beams of energy upto 50 keV. Already H- , Li- , C- , O- , Al-, Fe-, F- , Si-, S-,P-, Sb-, Ag- and Au- beams have been extracted and delivered on to the target. Experiments have been done with H-, Li-, C- , Si-,S-,Pand Sb- beams. Typical particle currents available are up to few micro amperes. Network based control system of this accelerator is used, apart from normal control operation, to auto start up and shutdown the accelerator and it is successfully working since two years. This paper will present the details of the LEAF control system and its automated start up and shutdown. INTRODUCTION Low Energy Accelerating Facility (LEAF) is a 50 keV DC electrostatic accelerator (Figure 1) operational at Van de Graaff building at Bhabha Atomic Research Centre, Trombay, Mumbai.[1] LEAF can accelerate various beams across periodic table. Current delivered at target is micro amperes of particle current for prolific beams such as C- or H- and for difficult beams such as Li, delivered current at target is few hundred nano amperes. This accelerator has already delivered negative ion beams of Hydrogen, Lithium, Carbon, Sulphur, Tellurium, Gold, Silver etc. This accelerator is used various experiments in material science and atomic physics studies using ion clusters. Negative ion beam is generated in a SNICS ion source and accelerated in an accelerating tube. Accelerated beams are bended 90 degree by an electromagnet to transport the beam to the experimental chamber. This electromagnet also works as a mass selector. To focus the beam on the target an electrostatic quadrupole triplet is used after the bending magnet. There are two sets of steerers for the beam path correction. First set is just after the accelerating tube, second is after bending magnet. Three Faraday cups are used to measure the beam currents at different locations and three beam profile monitor are used to monitor beam profile. Throughout the length of beam line vacuum of order 10-7 Torr is maintained. Two turbo pumps and one ion pump are used to maintain the vacuum during operation of facility. SNICS ion source is kept under vacuum continuously by a small ion pump (pumping speed 35 l/sec) when facility is not running. Though LEAF is a small accelerator but smooth and efficient running of this accelerator requires robust control system. As ion source is on a high voltage deck, so ion source parameters must be controlled remotely. Also, other controlling equipments like steerers, bending magnet current supply, high voltage power supply of the ion source deck, Faraday cups and entire vacuum system must be controlled independently to tune the beam and deliver it to conduct the experiments. To deliver the various energies and masses of the ion beams at the target it is required to control the accelerator and tune the beam Figure 1: Low Energy Accelerator Facility at BARC, Mumbai considering the actual field data. Thus a control system consists of a data acquisition window, and Graphic User Interface (GUI) based analog and digital control operator interface. The control system is a network based system which gives the ability to control this accelerator from any computer connected to the network. This network based control system is modelled as client server system and server system runs a routine to accomplish the task of automatic start up, shut down and auto experiment. TCP/IP protocol. Next server reads the client command, if any, and decoding the command apply analog or digital signal in the USB-6008 microcontroller. In LEAF control system each server’s scan cycle period is 250 milli second. DESCRIPTION Analog and digital data is acquired from the field via National Instrument’s micro-controller based (NI 6008) system. It is a low cost, USB powered multifunction DAQ which gives 12 bit resolution for analog channels and up to 10kS/s sampling rate which is sufficient for the control purpose of LEAF. Precision, high performance isolation amplifier, AD210 is used for control signals of the ion source devices. AD210 is a full-featured isolator providing numerous benefits like, high common-mode performance, high accuracy, isolated power etc. LEAF control and instrumentation is physically divided into two parts because Ion source of LEAF is floating at negative 50 kV. Hence all the power supplies required for the ion source operation are on high voltage deck floating Figure 3: Server Scan Cycle Client cum operator interface receives the field data from both the servers, decode them and display the field parameters on GUI. Operator can change different analog and digital values as per operational requirements and that is communicated to the server as the client command. Client side also has an interlock module. In the client cycle various interlock conditions are evaluated and either alarm is raised for operator or appropriate action according to defined rule is executed automatically. . at negative 50 kV Other parameters are at ground potential. LEAF control software has the client server architecture (Figure 2). Since ion source side is floating at 50 kV so a dedicated server is written for the ion source side. The computer on which the ion source server is running is also floating at negative 50 kV. Fiber to Ethernet converter is used to bring the data from the server to router, which is lying at the ground potential. For other part of the accelerator, which is at ground potential, there is another server. Router Figure 2: Control System architecture. Each server is having its own scan cycle. In a typical scan cycle server first acquire analog and digital field data, code them and send it to client via LAN using Figure 4: Client Scan Cycle Software Description Entire software is written in Qt 4.0 [2]. Server side is a console program and no GUI is there. Qt’s network module is used to communicate over TCP/IP. National Instrument’s USB-6008 interaction library is imported to interact with it. Effort has been made to use only those calls which can also be used in LINUX operating system. Presently server side program runs in windows 7 Home versions in the ion Source server and under windows XP professional in beam line server. Server side is operating satisfactorily under both operating systems. Client cum operator interface used extensively Qt’s excellent graphical capabilities. All relevant details of the analog and digital channels and description of all field devices are kept in the configuration files. Servers and client read relevant configuration files and sets up control program by taking data from configuration files. After initial configuration, repetitive server and client cycles described in the figure 3 & 4, keep on running till the programs are alive. In every scan cycle collected data is logged in the file, which helps to understand the dynamics of machine and to troubleshoot. Each server keeps a log file of the commands it received from the client console to analyze and understand the problem in case of a failure. AUTOMATION Since LEAF is a very small accelerator dealing with a small number of parameters, it is felt that entire operation of the LEAF can be automated. An automated operation follows a predetermined set of actions to establish vacuum in the system and setting up all the power supply values. In most cases that establish a reasonably good quality of the beam just before the target. Three sets of automatic tasks are implemented in LEAF. They are auto startup, auto shutdown and auto experiment. During auto start-up, upon receiving the operator command, each server starts a predefined set of action. Upon completion of every step of the task, routine checks the integrity of the set values and field values. If this check is passed then next step of the task is started automatically. In case of failure, program halts and an alarm is raised for the operator to inspect the reason of failure and to take necessary appropriate action. Upon successful completion of automatic task, a success message is displayed in the GUI for operator. During auto shut down, upon receiving command from the operator a similar loop described in auto start up is executed. Responsibility of this loop is to bring down the power supplies to the required state (in most cases switched off state) in a safe and gradual manner. Once that is achieved vacuum system is isolated, turbo pumps are switched off along with its backing pump and ion pump is switched on to maintain vacuum during period of non operation. A large number of experiments carried out at LEAF are of irradiation type experiment, where user needs to irradiate their sample for a pre determined amount of time, ranging from few seconds to several hours. In auto experiment upon a command from the operator control system remove the final Faraday cup, thereby starting the irradiation. It is the responsibility of the auto experiment loop to keep track of the time , which user feed in graphic user interface , and when time is over final Faraday cup is re-inserted and irradiation stop. This feature is highly useful for the sensitive experiments like irradiation of nano dots where sometimes irradiation time is only few seconds and operator response can introduce significant error in the irradiation dose. PERFORMANCE The control system along with the automation feature is working very satisfactorily as per specification and design for more than one and half years. Some minor bugs surfaced during the first few days of run which has been immediately taken care. After that no new bug has been reported by operators. FUTURE SCOPE The LEAF control system is designed to scale up as and when required. After successful implementation of the automation feature next step of improvement involves auto tuning. For that, digitization of BPM profile is required and work is being carried out in that direction. Along with that operator and user feedbacks are being collected and most of them will be incorporated in the future to make the machine more operator and user friendly. ACKNOWLEDGEMENT We acknowledge all the users of LEAF for their encouragement, support and constructive feedback. REFERENCES [1] A Basu et al. “Operation and Updradation of Low energy Accelerator Facility”, InPAC 2011 [2] http://doc.qt.nokia.com/4.7-snapshot/ [3] http://www.ni.com/pdf/manuals/373552a.pdf