Borland, M

Christensen, S

Pasky, S

Soliday, R

Stein, J

CERN Document Server

 208 EFFICIENT AND EFFECTIVE OPERATION OF THE APS LINAC  S. Pasky, M. Borland, J. Stein, R. Soliday, S. Christensen Argonne National Laboratory, IL 60439, USA Abstract The Advanced Photon Source (APS) linear accelerator (linac) utilizes twothermionic cathode rf guns and one photocathode rf gun. The thermionic gunsare primarily for APS operations while the photocathode gun is used as afree-electron laser (FEL) driver. With each gun requiring a different latticeand timing configuration, the need to change quickly between guns andmaintain the required equipment protection puts great demands on the MainControl Room (MCR) operators. This paper discusses how the APS staff haslearned to deal with the frequent changes required by a newly upgradedequipment safety interlock system and how they have become familiar withthe automated control system called [1, 2] Procedure Execution Manager(PEM). Our linac is controlled via the Experimental Physics and IndustrialControl System (EPICS), but the lessons are applicable to any control system. 1. EQUIPMENT SAFETY SYSTEM1.1 Interlock Support Equipment protection interlocks are mandatory for all the linac subsystems. The original interlockchassis design consisted of a metal box enclosure containing 24 VDC relays, indicator lights, andterminal blocks that served as a hard-wired junction point between field sensors and the interlockchassis. This was a very robust and reliable interlock system until changes or additional interlocks wereneeded.In the past two years components have been added to the linac that required upgrades not only tothe interlock systems but also to the Motif Editor and Display Manager (MEDM), which consists ofcontrol screens used by the MCR operators. The hard-wired nature of the existing interlock systemmade it difficult to keep pace with these changes.It was apparent that in order to support these changes and future project upgrades in an efficientand effective way, a new linac interlock system was needed. This was done using a programmable logiccontroller (PLC) (see Figure 1) with the following requirements in mind.• The control logic should be flexible to accommodate frequent changes.• The system must be highly reliable.• The system must be physically compact due to space limitations.• The system must have increased capability for complex interlock conditions.• The system must provide enhanced information to MCR operators. 209 Fig. 1:  New Interlock Control Chassis Cabinet 1.2 PLC Selection A PLC-based system is particularly suitable for applications in which the requirements listed above areimportant. If system requirements call for flexibility for future growth, the programmable controllerbrings returns that outweigh any initial cost disadvantage relative to a relay-based system. Even ifneither flexibility nor future expansion is required, the PLC-based system can provide tremendousbenefits as a troubleshooting and maintenance aid, as well as providing detailed information to theMCR operators via MEDM screens.The 205 Direct Logic Controller using a DL250 CPU was found to meet or exceed all ourrequirements. The DL250 CPU had the best system capacity, performance, programming, anddiagnostic ability, which will save many hours of programming and debugging time. The DL250 alsointerfaces well with EPICS. 1.3 Interlock Function and MEDM Displays In EPICS, equipment is controlled from workstations that communicate over a network with localcomputers called input/output controllers (IOCs). All systems in the linac that require or use aninterlock for equipment or personnel safety protection require a latching function independent of theIOCs. Once a latch has been made, operator intervention is required to reset the interlock.A typical interlock example, shown in Figure 2, is provided by the linac rf systems. Eachklystron requires a 400-watt power amplifier to provide rf input at sufficient levels to drive the klystron.Each amplifier is potentially inhibited by two signals. The first originates in the personnel safetysystem, known as the Access Control Interlock System (ACIS). The second signal, independent of theACIS, is provided by the PLC Direct Logic system, which monitors the status of equipment, that mustfunction in order to enable the klystron drive without the possibility of damaging the klystron or theequipment it powers. Examples of monitored equipment include waveguide, arc detectors, VSWRmeasurements, vacuum measurements, SF6 pressure, and water flow and temperature.Using the PLC’s ability to monitor each interlocked signal separately, the MEDM screendeveloper was able to design a thorough and robust display for operations and diagnostics. Figure 3shows a typical MEDM screen that displays the status of interlocks for the sulfur hexafluoride (SF6)system and parts of the beam transport line. In the event of a trip, a quick glance at this screen shows thegeneral source of the problem in an easily understood graphical fashion. Detail screens, like thoseshown in Figure 4, can then be consulted to determine the exact cause of the problem. 210 Fig. 2:  Typical rf Interlock Logic Fig. 3:  Typical SF6 Interlock Logic MEDM ScreenVSWR Detector 1-2-3, OKARC Detector, OKSector One Vacuum,  OKWater Station L1 Temp.& Flow, OKZone C,  SF6 Pressure,  OK   Pin Switch One  OK400 WattAmpEnableACIS PermissiveLTP-B1Double StopsKlystronDrive OneEnableTrig.&InterlinkModule 211 Fig. 4:   Typical Interlock Detail MEDM Screens 2. LINAC AUTOMATED OPERATIONS  The APS linac comprises five modulators and klystrons; three electron guns; three dipole powersupplies; 35 quadrupole power supplies; 48 steering magnet power supplies; 18 beam positionmonitors; 7 current monitors; and complex timing, water, and vacuum systems. There are literallythousands of controls and thousands of read-backs incorporated in a multitude of screens that controlevery aspect of operations. Originally, operators had to switch back and forth among many MEDMscreens, performing procedures from memory or with the aid of a written document. In order toperform rapid changes in operating conditions, some Unix scripts were written to perform tasksautomatically. Though the scripts worked well under ideal conditions, they could not always be countedon because equipment and operational procedure changes were often made without warning.Furthermore, these scripts were not regulated or source controlled and did not have much of an errorchecking ability, making them unreliable. Finally, the Unix scripts were slow and did not have agraphical user interface.The Procedure Execution Manager (PEM) has been used at the APS for several years to controllong and complex tasks. PEM procedures, when configured properly, follow the same steps an operatorwould take during equipment start-ups and reconfiguration between injector lattices for user operationsand experimental projects. The only difference is the PEM has the ability to repeat steps faster and withless possibility of error. When using PEM procedures, the operator no longer has to open numerous MEDM screens andwork on one task at a time. Rather, the PEM is able to efficiently use multitasking to alleviate theburden on the operators in what can often be a stressful situation. The operators can read correspondingdescriptions and view the steps of a PEM procedure to become familiar with it. This is not intended toreduce operator training, but it does serve as an additional source of information that may be valuable tooperators.Complex PEM procedures are constructed by combining simpler PEM procedures in a seriesand/or parallel fashion. The PEM interface is expandable, simple, and consistent, so operators often donot need to learn anything new in order to correctly use a new procedure.   Using PEM’s ability toexecute steps in parallel can decrease the execution time and further enhance productivity.The dialog screen shown in Figure 5 for power supply start-up allows the operator to select asnapshot file to be restored at the end of a magnet conditioning. A snapshot file (see Figure 6) is a 212 database file including all the settings necessary to reproduce the conditions existing when the snapshotwas recorded. Once executed, the PEM procedure opens another display window, shown in Figure 7,that shows each step as it occurs and reports procedure status.  Fig. 5:  Procedure Execution Manager Prior to the use of PEM procedures for linac operation, reproducibility was difficult. Establishingand enforcing a uniform method for machine operation has resulted in a dramatic reduction in the timespent by the control room operator for accelerator tune-ups. Start-up and switch-over activities betweenexperimental projects and daily injections have also benefited from the PEM program.There are two principal difficulties with the PEM process. First, changes in the controls systemor hardware can cause procedures to fail. This problem has been managed by the use of administrativecontrols and a device layer between the PEM procedures and EPICS. Second, thorough testing of theseprocedures requires machine time, which is in very high demand for experimental programs. This isperhaps the major factor slowing the development of these procedures. Fig. 6:  Initial Dialog Screen Fig. 7:  Status Monitor 213 3. CONCLUSION The new linac interlock upgrade and the use of the PEM procedures have proven to be very reliable forswitching between multiple operating modes. Without these tools, it would be difficult if not impossibleto ensure equipment safety, improve reliability, and efficiently provide consistent beam. Switchingbetween the operation modes safely with the assistance of the PEM has made the job of the controlroom operator much easier and has contributed to the success of experimental programs. 4. ACKNOWLEDGMENTS The following individuals are recognized:  Interlock Review Committee : Ned Arnold, Don Dohan, andArt Grelick;  Hardware Installation : S. Benes and M. Douell. This work is supported by U.S.Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38. References [1] M. Borland, ‘The Procedure Execution Manager and its Application to Advanced Photon SourceOperation,’ Proc. Of the 1997 Particle Accelerator Conference, May 12-16, 1997, Vancouver,Canada, pp. 2410-2412 (1999).[2] R. Soliday et al., ‘Automated Operation of the APS Linac using the Procedure ExecutionManager,’ XX International Linac Conference (LINAC2000), August 21–25, 2000, Monterey,California (to be published).

Efficient and Effective Operation of the APS Linac

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