The Low-Energy Demonstration Accelerator (LEDA) injector is designed to inject 75-keV, 110-mA, proton beams into the LEDA RFQ. The injector operation has been automated to provide long term, high availability operation using the Experimental Physics and Industrial Control System (EPICS). Automated recovery from spark-downs demands reliable spark detection and sequence execution by the injector controller. Reliable computer control in the high-energy transient environment required transient suppression and isolation of hundreds of analog and binary data lines connecting the EPICS computer controller to the injector and it's power supplies and diagnostics. A transient suppression design based on measured and modeled spark transient parameters provides robust injector operation. This paper describes the control system hardware and software design, implementation and operational performance

Arvin, A

Bolt, S

Dalesio, L R

Harrington, M

Hodgkins, D J

Kerstiens, D M

Quintana, B

Richards, M

Sherman, J D

Stettler, M

Thuot, M

Warren, D

Zaugg, T J

Thuot, M.E.

Dalesio, L.R.

Harrington, M.

Hodgkins, D.

Kerstiens, D.M.

Stettler, M.W.

Warren, D.S.

Zaugg, T.

Arvin, A.

Bolt, S.

Richards, M.

UNT Digital Library

IRECEIVEDsEPof#$Jcw--*.Ftle: A TRANSIENT TOLERANT A OMATED CONTROLSYSTEM FOR THE LEDA 75kV INJECTORAuthor(s): M. E. Thuot, L. R. Dalesio, M. Barrington, D. Hodgkins, D. M.Kerstiens, M. W. Stettler, D. S. Warren, T. Zaugg, A. Arvin S.Bolt, M. Richards:. -%<.. LA-UR- 99-1391. .Approvedbrpubfic releasa;dktrrbution is unfimitedbSubmlted to: p~cle Accelerator conferenceNew York, NYMarch 29-April 2, 1999Los AlamosNATIONAL LABORATORYLos Alamos National Laboratory, an affirmative actiotiequal opportunity emplcyer, is operated by the University of California for the U.S.Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the U.S. Governmentretains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for U.S.Government purposes. Los Alamos National Laboratory requests that the publisher identify this article as work performed under theauspices of the U.S. Department of Energy. Los Alamoa National Laboratory strongly supports academic freedom and a researcher’s right topublish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness.Form 836 (10/96)DISCLAIMERThis report was prepared as an account of work sponsoredby an agency of the United States Government. Neitherthe United States Government nor any agency thereof, norany of their employees, make any warranty, express orimplied, or assumes any legal liability or responsibility forthe accuracy, completeness, or usefulness of anyinformation, apparatus, product, or process disclosed, orrepresents that its use would not infringe privately ownedrights. Reference herein to any specific commercialproduct, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constituteor imply its endorsement, recommendation, or favoring bythe United States Government or any agency thereof. Theviews and opinions of authors expressed herein do notnecessarily state or reflect those of the United StatesGovernment or any agency thereof.DISCLAIMERPortions of this document may be illegiblein electronic image products. Images areproduced from the best available originaldocument.*‘ ‘“A TRANSIENT TOLERANT AUTOMATED CONTROL SYSTEM FOR THE..LEDA 75kV INJECTOR*M. Thuot, L. R. Dalesio, M. Barrington, D. Hodgkins, D. Kerstiens, B. Quintanz J. D. Sherman,M. Stettler, D. Warren, and T. Zaugg, LANL, Los Akunos, NMA. Arvin, S. Bolt and M. Richards, SRS, Aiken, SCAbstractThe Low-Energy Demonstration Accelerator (LEDA)injector [1] is designed to inject 75-keV, 11O-mA, protonbeams into the LEDA RFQ [2]. The injector operation hasbeen automated to provide long term, high availabilityoperation using the Experimental Physics and IndustrialControl System (EPICS) [3]. Automated recovery fromspark-downs demands reliable spark detection andsequence execution by the injector controller. Reliablecomputer control in the high-energy transientenvironment required transient suppression and isolationof hundreds of analog and binary data lines connectingthe EPICS computer controller to the injector and it’spower supplies and diagnostics. A transient suppressiondesign based on measured and modeled spark transientparameters provides robust injector operation. This paperdescribes the control system hardware and soflwaredesign, implementation and operational performance.1 INTRODUCTIONAccelerator Production of Tritium (APT) applications ofhigh power accelerators requires high beam availability.To maximize beam-on time, rapid recovery from routineevents, like injector spark- down, is needed. Reliablerecovery from injector spark-down can be providedthrough computer based automated sequencing. Forreliable operation, the data in computers must beprotected fi-om being corrupted by the severe EMItransients produced during the spark-down. Couplingbetween the high voltage power supply (HVPS) and thecomputer control system is a primary cause of thedisruption or damage to computersAogic that occasionallyoccurs during injector high voltage spark-down. TheHVPS circuitry, the method of connecting to the injector,and the physical layout of the injector determinessignificant EMI coupling parameters such as storedenergy, peak current, discharge llequency, diidt anddvldt. Computer interface designs, based on circuitmodels that generate values for these parameters, caneffectively suppress the transients and provide reliableoperation in a harsh EMI environment.* Work supported by tbe U. S. Department of Energy under contract W-7405-ENG-36.f Email: mthuot@,hml.gov2 MODELING THE SPARK DISCHARGEAND HVPS CIRCUITTo estimate the peak current, dildt, dvldt and thefrequency content of the spark transient, a spark-downcircuit model of the LEDA injector and the HVPS wasconstructed. (See Figure 1). The values of the HVPScomponents in the modeI were set to the actual circuitvalues. The inductance of two of the major loopsinvolved in the discharge of the injector control thenatural Ilequency of the discharge current. These twoloops are a large loop formed by the RG218 coaxial HVcable connecting the HVPS to the injector, and a muchsmaller Ioop formed by the source and the wave-guideabove the grounded source table. The inductance of theseconductors was calculated using the formulz ti-om Ott[4], for the inductance of a conductor above a groundplane. These calculated inductance values were comparedto actual circuit values by comparing the naturalfrequency of the calculated spark transients withoscilloscope traces taken during actual spark-downtransients on the CW injector.The I-IV coaxial cable that connects the HVPS to theinjector was modeled as a transmission line. The model ofthe discharge circuit produced waveform records throughSPICE analysis petiormed by a commercial softwarepackage, Electronic Workbench@ running on a PC.Electronic Workbench represents the circuit as aschematic rather than a SPICE node list, which simplifiesthe modification of circuit values and connections...=s,..[f,x . .+,*:.-, .:... .,=... ,.—-—-..=’ ;.’ .,,—.:. ..=~:,..,<,.-,...,.. ,, ..,...... ... ......: ........L._,7. .. ..>r.. . . . .,-+,,::,,,..I-JFigure 1. LEDA injector and HVPS transient analysiscircuit model in Electronic Workbench@.. 3‘.‘ 2.1 Results of the spark-down transient analysis.The waveforms from the SPICE model of the injector andHVPS were analyzed to extract the peak current (300 to1200 A), the transient cument natural frequencies (2 to 6MHz) and the maximum di/dt (-1E+1O A/s) and dv/dt(-2E+12 V/s). These parameters quantify the level of thesource of the electromagnetic interference (EMI) thecontrol system interface must suppress. If these levels orcoupling from this source exceed me transientsuppression capability of the control system interface,then they represent a threat to the proper operation of thecontrol system.The coupling between sparks in the HVPS and thecontrol system follows several paths, each with somecoupling constant that primarily depends on the naturalfrequency of discharge circuit. Capacitive coupling fromthe HVPS’ high dv/dt through the high impedance electricfield is relatively easy to shield. Proper grounding of themetal enclosures surrounding the HVPS and of the shieldson signal cables will eliminate almost all of the dv/dtdriven interference. The only area of the injector systemwhere this EMI source may dominate is if unshieldedcables or transducers are exposed to the high voltagecircuits. The effect of this, sometimes unavoidable,coupling can be minimized by shielding the exposedcables and transducers andlor shunting their straycapacitance with an RC low pass filter.The most likely path of EMI into the control system isdtidt (I3) coupling through the transient low impedance(magnetic) fieId. This low impedance field is much moredifllcult to shield. Coupling paths will exist through anymutual inductance between the HVPS discharge circuitsand the control system. To control low impedancecoupling, the best defense is the reduction of theinductance of all source and signal loops. This source ofEMI may be suppressed on signal cables by installingisolators that break the low impedance loop formed by thesignal cable conductors and thus convert the @ inducedvoltage into a common mode voltage on the isolators.This defense is usually effective, but it can fail if thefrequency and/or amplitude of the source of the EMI isextreme, thus driving noise current through the isolators.If the isolators are preceded by a passive low pass filter,the effect of extreme dtidt is mitigated. Our designemploys this arrangement with the low pass filtersfollowed by isolators built into the wiring terminal barrierstrips.3 GROUNDINGProper grounding will reduce the coupling of the sparkinduced transients into the data acquisition system. Thereare three grounding systems of particular interest the ACpower system, the HVPS system and the signal cable/dataacquisition system. After analysis of the transientsestimated the transient frequencies, an eiegant solution tothe issue of AC power conducted interference wasindicated. The thickness of common constructionmaterials used in electrical power distribution systems ismuch greater than a skin depth at the transientfrequencies. This fact allows the use of conduits andjunction boxes for barrier shields and permits effectivesafety and transient current grounds to be easily made. Athree phase shielded isolation transformer is employed toisolate the three phase ac power to the HVPS therebylimiting the coupling of spark transients to the AC powerlines. The secondary wiring of this transformer isenclosed in rigid conduit to prevent coupling to the dataacquisition environment. Another shielded three-phasetransformer provides three isolated single phase 115Vpower sources for “clean” power for the computer andADCS, “semi-clean” power for the vacuum controls and“dirty” power for the injector auxiliary power supplies.The HVPS is grounded for safety and the injector isalso grounded by the beam line. To avoid a large groundloop with high transient currents, the HVPS cable must beshielded and the shield must be grounded at both ends.This arrangement insures the HVPS transient dischargecurrent (primarily) flows back along the cable shield sincethe coaxial cable/shield is in “cutoff [4]. Measurementsmade on the CW LEDA injector demonstrated a greaterthan four times reduction in ground displacement voltageat the irjector after grounding the high voltage cableshield at both ends. The concurrent advantage is that theinductance of the primary transient discharge loop, amajor source of@ coupling, is greatly minimized.The few hundred signal cables are wired ilom theinjector transducers with shielded twisted pair cable withthe cable shields connected to a system ground point atthe low pass filters. This arrangement helps convertnormal mode transients into common mode transients dueto the distributed capacitance of the cable shield. The lowpass filters effectively attenuate the high frequencycommon mode transients. The shielded twisted paircables transferring the signals tlom the low-pass filtercircuits to the signal isolators have the shields grounded atthe isolator end, again to help convert any remainingnormal mode transients to common mode since theisolators attenuate only common mode transients.4 TWO STAGE SIGNAL FILTERINGAND ISOLATIONThe analog isolation board and low-pass filter board weredesigned from the transient parameter analysis data toprotect the control computer and data acquisitionelectronics from spark-down transients. The passive low-pass (1 to 100 kHz, -3 db) filter board is an RC network,built into a terminal barrier strip, placed in the fieldwiring junction box close to the injector to shunt the bruntof the spark down energy. This filter is used for allanalog and binary input and output channels.—., -.... The analog and binary isolation boards are located near. the computer and ADCS to provide common modeattenuation and to isolate signal ground loops. The analogisolator also provides isolated power, 1, 2, 5, 10 signalgain and a 100 ma. current driver output if needed.Assembly and wiring costs are both reduced bypackaginglmounting the isolators on Phoenix Contactrails in the trunk wiring junction box. (see figure 2) Theisolators provide 1500 Vrms isoIation a with a -3 dbfrequency of 6 to 60 kHz, depending on componentselection.Figure 2: Junction Box Rail mounted Analog IsolatorsThis two stage transient suppression system has been inuse for about four months and has demonstrated itseffectiveness. The fourth spark the injector systemexperienced, shortly after the wiring, filters and isolatorshad been installe~ interrupted computer operation. Aninspection revealed that several ground wires on the filterboards were miscormected, bypassing the filters. Oncecorrected, there has not been any loss of data or computerinterrupts during more than 200 spark-downs.5 EPICS CONTROL ANDAUTOMATIONEPICS is a toolkit for building network distributedprocess control and data acquisition systems. EPICS(originated at Los Alarnos) is now developed jointly by acollaboration of> 100 institutions, including accelerators,light sources, telescopes, detector collaborations,universities, etc.[5]. EPICS provides control andmonitoring of the LEDA injector. Logic in the EPICSrun-time database enforces proper operation of theinjector to provide equipment protection, as outlined inthe LEDA injector standard operating procedure. Thislogic controls the order in which devices may be turnedon when starting up the injector. Logic is used to checkthe injector status to determine if a controlled device maybe safely operated. This status consists of both discretestatus, including the PSS (Personnel Safety System) andcooling water flow, and analog read-backhhresholdswhich determine whether or not the injector is in a statethat is proper for operations initiated by the injectoroperator or by an automatic sequence. Control thresholdsare available to the operator to modi@ as needed forrunning beam in varying conditions. For example, theHVPS thresholds are different when conditioning theinjector than when operating.To provide automatic shutdown and recovery frominjector sparks, sequence logic was implemented in anEPICS database. The spark detection is based upon thevoltage read-back of the FuG HVPS and is executed at arate of 10 Hz. When this voltage drops below a specifiedthreshold, the ion source microwave power is disabled.The operator may adjust the spark detection threshold asnecessary, depending on injector operating conditions. Inthe automatic spark recovery mode, the disabling ofmicrowave power is followed by a few seconds delaywhich allows the system to stabilize. Then the magnetronpower is reset to the set-point recorded befme the spark.The automated recovery ilom spark down will berepeated, if necessary, up to 3 times within a 30-secondtime ti-ame. If a fourth spark occurs within the 30-secondtime frame, the automatic recovery sequence is disabledby logic until an operator intervenes, preventing a seriesof continuing sparks from causing damage.The automatic shutdown and recovery has fimctionedwell for the past four months of operation under mostconditions. There are, however, conditions when theinjector insulators are degraded and the injectorexperiences a rapid series of external sparks. The 10 Hzsoftware detection in this case is not suftlcient, so wehave implemented fast hardware logic to provideadequate spark detection and shutdown under theseconditions.6 CONCLUSIONSReliable computer automation “ofprocesses operating in ahigh-energy transient environment can be assured byemploying proper grounding and transient suppressingcomputer interfaces. Modelling the transient sourcesleads to computer interface designs that are effective intransmitting control signals while attenuating transients.By employing a cost-effective two stage transientsuppression system, reliable EPICS based automation ofthe LEDA injector has been demonstrated.7 REFERENCES[1] Status Report on a dc 130-mA, 75-keV Proton Injector, J.D.Sherman et al., Rev. Sci. Instrum. 69 (1998) 1003-8.[2] ~, D. Schrage, Q,Proc. LINAC98 (Chicago, 24-28 Aug. 1998) (in press).[3] The Success and the Future of EPICS, M. Thuo~ Q,Proc. LINAC96 (Genev% 26-30 Aug. 1996).[4] H. W. OtL Noise Reduction Techniques in ElectronicSystems, Wiley -Interscience 1976.[5] http:lAvww.atdiv.lanl.govlaot8/epicsfepicshm.htm

Transient Tolerant Automated Control System for the LEDA 75kV Injector

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A Transient Tolerant Automated Control System for the LEDA 75kV Injector

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A Transient Tolerant Automated Control System for the LEDA 75kV Injector

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