Jianu, A

Martin, D

Toma, M

Zoita, V

CERN Document Server

CONTROL AND PROTECTIVE SYSTEMFOR A PLASMA FOCUS INSTALLATIOND. Martin, V. Zoita, A. Jianu, M. TomaNational Institute for Lasers, Plasma and Radiation Physics, Electron Accelerator Laboratory,P.O.Box: MG-36, #111 Atomistilor St., 76900 Bucharest, RomaniaAbstractThe paper presents a control and protective system for theplasma focus installation IPF-4/5A of 1 MA plasmacurrent. All the fusion installation sequences are governedby strict hard and soft interlocking using in parallel twocontrol and protective systems: one based on PC-controlmethods and other based on classical control techniques.1   INTRODUCTIONA Control and Protective System, designated CPS-4/5A, was designed for the plasma focus installation IPF-4/5A, the fifth installation of this type designed and built inRomania. IPF-4/5A main parameters are: capacitor bankcharging voltage 14-20 kV, maximum stored energy 45 kJ,peak plasma current 1 MA, working gas (deuterium)pressure 1-5 torr.2   DESCRIPTION OF THE IPF-4/5APLASMA FOCUS INSTALLATIONAn overall view of the IPF-4/5A plasma focusinstallation is presented in Fig. 1, showing the maincomponents of the high power circuit (capacitor bank,switches, and high voltage pulse generators). IPF-4/5Amain sub-systems are described below.The discharge chamber consists of the coaxial plasmaaccelerator connected to the plasma focus driver (pulsedpower supply) by means of a disk shaped current collector.The coaxial accelerator uses stainless steel electrodes, withthe central electrode having a heavy alloy insert.The high voltage capacitor bank (modular structure)uses high current spark gap switches of the CIT-10/20 type[1]. Energy transfer from the HV capacitors to the dischargechamber collector is done by means of 150 low inductancecoaxial HV cables.The measurement and acquisition system consists of 12devices for the detection of the electromagnetic, optical andnuclear phenomena. Signals generated by varioustransducers are simultaneously transmitted over 30acquisition channels (bandwidth ~200 MHz).The control and protective system CPS-4/5A ensuresthe control and automatic operation of the wholeexperimental facility [2].IPF-4/5A has been used mainly for fusion studies(investigation of the plasma focus neutron generation):produces neutron yields up to 5x109 neutrons/pulse [3].Figure 1: Overall view of the IPF-4/5A plasma focusinstallation3   DESCRIPTION OF CPS-4/5ACPS-4/5A was designed to operate in a very harshenvironment due to high voltage (tens of kV, d.c. andpulsed), high currents (around 1 MA) with very highderivatives (1012A/s), intense nuclear radiation (neutronand hard X-rays) pulses. Due to IPF-4/5A complexity andthe specific conditions under which it operates, CPS-4/5Ahas been designed to allow simultaneous or alternate use ofboth classical automation techniques and modern on-linecomputer control. Main CPS-4/5A functions are:• Personnel and sensitive apparata protection againstdangerous events by centralized control of all protectiondevices (programmed interlocking and warning signalsduring experimental runs);• Prevention of IPF-4/5A malfunction and reduction ofdevice misfire, as well as control of fusion deviceoperation in a preselected time sequence;• Protection against electromagnetic interference.3.1 System configuration and workingprinciples of CPS-4/5ACPS-4/5A block diagram and IPF-4/5A main sub-assemblies are shown in Fig. 2. The control andprotective system allows main IPF-4/5A subassemblies(condenser bank charging and discharging system CDS,spark gap switch triggering system SGS-TS, vacuum andgas filling system VGFS) to be operated bothindividually, at the same control level, and centralized, ina hierarchy-like structure.International Conference on Accelerator and Large Experimental Physics Control Systems296International Conference  Accel rator and L rge Experim ntal Physics Control Systems, 1999, Trieste, ItalyFigure 2: CPS-4/5A block diagram and IPF-4/5A mainsubassembliesMoreover, main IPF-4/5A subassemblies may becontrolled from their local control panels as well as fromthe corresponding modules in the central control panel(CCP). Fig. 3 shows the IPF 4/5A central control panel,illustrating the location of the operating modules: SGS-TS, CDS, VGFS, discharge pulse counter (DPC), plasmadiagnostic devices (PDD) status signaling, classic centralcontrol system (CCCS) and CCCS to computer controlsystem (CCS) interface. In order to prevent anyelectromagnetic coupling between high powercomponents of the fusion installation and the controlsystem, the latter is separated by a galvanic separationbarrier consisting of optic fiber cable assemblies (foranalogue signals) and of low stray-capacitancetransformers (for logical commands and states).The slow time-varying signals (working gas pressurein the discharge chamber, switch triggering systemcharging voltage and condenser bank charging voltage)are transmitted to CPS-4/5A via the measurement chains(transducer, voltage to frequency converter, infraredemitter, optic fiber cable, optical pulse detector andfrequency to voltage converter). The measurement chainsdeliver voltages proportional to the input value (within aprecision of 2%). The evolution of the slow time-varyingsignals is surveyed by the operator both by means ofclassical instruments (on control panel) and by means ofthe computer control system. Digital commands andstatuses are transmitted via high voltage and low straycapacitance separation transformers (24 Vac/24 Vac).CPS-4/5A units and the HV components of IPF-4/5A arecoupled to the main a.c. supply via separationtransformers of various powers from 500 VA to 6 kVA.Figure 3: IPF-4/5A central control panelFig. 4 shows some parts of the galvanic barrier. Thehigh voltage on CB modules is detected by five HVdividers and transmitted to the operator via five opticalchains, each ending up with a LED on the central controlpanel(a) (b) (c)Figure 4:  Some parts of the galvanic separation barrier;(a) Optical system which transmits the analogue signalsthrough fiber optic cable assemblies; (b) high voltage–low stray capacitance separation transformers of 24 VAfor the logical commands and states (24 Va.c. /24 V a.c.and 0.022pF measured stray capacitance); (c) highvoltage –low stray capacitance separation transformers of500 VA for the feeding to the main a.c. supply (0.025 pFmeasured stray capacitance);The spark gap switches operation is detected by fiveRogowsky coils and transformed into five optical signalsof 30 seconds duration. The information provided bythese two systems is used to locate certain post-dischargefailure effects within the experimental installation. Thecurrent through the discharge chamber is detected by amagnetic probe, giving a fast rising, short signal that istransmitted via a high voltage-high frequency separationtransformer, processed in order to increase its duration toa few seconds and then supplied to the discharge pulsecounter (DPC). This delivers a delayed command toactuate both the high current switch gas purging deviceand the neutron activation counter.The computer-controlled system (CCS) is used bothas operator interface and as input-output controller. Thelatter function is based on a general-purpose control andacquisition interface (CAI) mounted in the IBM-297compatible PC, as shown in Fig. 2. CCCS is interfaced toCCS by a dedicated module, which transfers logicalcommands/states between the digital I/O bus of CAI andCCCS as well as analogic signals between CAI andCCCS.CCS provides mainly the following functions:• Applies 23 interlocked logical commands to the IPF-4/5A subassemblies;• Acquires and processes 28 logical states from the in-stallation subassemblies;• Acquires, processes and displays three slow time-varying signals (condenser bank high voltage, switchtriggering system high voltage and pressure in thedischarge chamber).Certain precautions have been taken in order toprotect the personnel working on the installation, takinginto account the presence of tens of kV (d.c. andimpulse), of intense nuclear radiation and of high voltageinterferences during the experiment. In this respect certaintechnical solutions were implemented, using bothclassical and computer (soft) interlocking:• Condenser bank charging system is interlocked withsafety devices that control the access of any person to theexperimental area;• Condenser bank charging is continuously announcedaround the experimental area by optical and acousticaldevices;• The actual condenser bank discharge pulse is delayedby a few seconds introduced after the operator "STARTPULSE" command• IPF –4/5A operation sequences are governed by stricthard and soft interlocking in order to reduce the risk of, orentirely prevent, any operation error.3. 2   Computer-controlled operating modeBefore the start of the experiment the operator has tointroduce by means of the keyboard, in a conversationalway, the experimental parameters and the operating mode(completely automated or sequential):In the completely automated operating mode, theoperator commands only the start of the experiment, thesystem operation being software and hardware-controlledafterwards. The evolution of the experiment iscontinuously presented on the PC display, everyexperimental phase providing the operator with a set ofcommands, which he could use in case of systemmalfunction. In the sequential mode, the operator from the systemkeyboard commands both the start of the experiment andalso the evolution from one phase to the other. Thesystem displays continuously each phase of theexperiment, the measured values of the main deviceparameters, as well as a set of commands for operatorintervention in case of malfunction.Both operating modes provide the operator with thepossibility of interrupting the experiment at a certainphase ("decision phase"), in order to change theexperimental parameters that have been previouslyintroduced. At the end of experiment, the operator has thepossibility of adding his observations regarding theevolution of the experiment. He also decides whether theexperiment data are to be stored on PC as experimentaldata files.Software development occurred under MS-WINDOWS. It is therefore in close proximity to theanalysis, modeling and office tools running on the PC.Application programs were developed with the BorlandC/C++. The software package has a modular structureallowing the implementation of new functionalities as thedemands for changes/additions appear.The operator interface software is simple, menudriven and has been optimized for minimum operatorinteraction (completely automated operating mode). Thesoftware guarantees:• The possibility of a dialogue between the operator andthe system:-The selection of the operating mode (completelyautomated or sequential) by the operator;-The interruption of the experiment by the operator usingdedicated commands;-The remote control of the whole experimental run(recommended start-up and shut-down sequences for IPF-4/5A are provided);-Delivery of alarm messages and guidance fortroubleshooting in case of operational problems;• Sequence interlocks to prevent unsafe (to system andpersonnel) conditions;• The software-controlled interruption of the experimentin case of different kinds of damages;The acquisition and pre-processing of relevantparameters;• Presentation of data as tables and charts;• The transfer of the experimental data to the PC,archiving.The software consists of a set of applications forexecution of control algorithms, data acquisition, initialpre-processing of data for protection of equipment andinterlocks, transfer of information to the PC.[1] V. Zoita, “New type drivers for the plasma focus”, 4thInt. Workshop on Plasma Focus and Z-Pinch Research,Warsaw, 9-11 Sept., 1985, p. 244[2] D. Martin, V. Zoita, D. Cotruta, A. Serban, G.Cojocaru, A. Radu, “Control and command system forpulsed, high power fusion experiment”, FusionEngineering and Design, 19, 281, 1992[3] I. Tiseanu, R. Presura, V. Zoita, P. Choi, M. G.Haines, R. Aliaga, H. Herold, “Two component ionpopulation from neutron anisotropy in plasma focusdevices”, Bul. Am. Phys. Soc. 36, 2396, 1991   4   REFERENCES298

Control and Protective System for a Plasma Focus Installation

Abstract

Similar works

Full text

Available Versions

CERN Document Server