Control System for a High Average Power Free Electron Laser
K. Jordan, B. Cumbia, R. Evans, R. Hill, O. Garza, M. WiseThomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue,Newport News, VA 23606

A high-average-power infrared free-electron laser [1](IRFEL) capable of continuous kW-level operation at 3 - 6µm, is being commissioned at Jefferson Lab in Newport
News Virginia, USA. The IRFEL is located on the site ofthe CEBAF machine and is capable of being controlledfrom either the CEBAF Main Control Center (MCC) orfrom the local Laser Control Center (LCC). The plan is tocontrol all functions of the electron-beam transport from
the MCC except the final steering through the wiggler. Allhigh-power-optics control and photon-beam delivery will
be done from the LCC. The control system is based on
EPICS (Experimental Physics and Industrial ControlSystem) which is used at CEBAF. The IRFEL control
system is roughly 1/10 the size of the CEBAF system.
This paper will focus on new systems and describe thehardware implementation. Documentation for the systems
can found at http://www.jlab.org/FEL A paper devoted tothe FEL software is being presented at this conference byA. Hofler et. al.

Thus, 75% of its energy is put back into RF power for use
in accelerating other electrons, thereby reducing RF power
requirements. It also reduces waste heat and radiation,permitting use of a compact beam dump of uncomplicateddesign.
The injector comprises a 350 kV dc photocathode gun
driven by a commercial Nd:YLF laser. The gun is followed
by a copper buncher cavity and a CEBAF-type 1497 MHz
SRF cryounit raising the beam energy to 10 MeV. The
accelerator uses a full CEBAF-type 1497 MHz SRF
cryomodule to generate an average accelerating gradient of
8 MV/m, boosting the beam to 42 MeV energy. Twocommercial 50 kW klystrons power the injector's cryounit.
The control system for the FEL was designed andimplemented to take advantage of both the operational
experience of CEBAF and the decreases in cost ofcomputing power and increasing availability of VME
based interface boards. The philosophy for the design wasto move out of CAMAC and into VME where possible;
low risk for the short construction cycle, but to leave open
a clear path for future upgrades.

1 Introduction

2 Server computers

Jefferson Lab's FEL is pictured in Figure 1. It is a kWlevel FEL comprising a 10 MeV injector and a 32 MeVlinac to produce a 42 MeV, 5 mA CW electron beam foruse in lasing. The wiggler extracts about 0.5% of theelectron-beam energy, thereby producing kW-level light touser laboratories collocated with the FEL. After lasing, ahigh-acceptance lattice transports the electron beam backto the linac for deceleration down to 10 MeV to a dump.

The FEL Facility control system is implemented on aprivate IP subnet to provide isolation from other JLabcontrols and other networks. The system consists of dual,
HP D-250 servers, (figure 2) several console workstations,x-terminals, VME-based data acquisition nodes, printers,etc. These systems are interconnected using a combinationof 10Mbit and 100Mbit Ethernet, running over fiber andcategory-5 cabling.

Abstract

Fig. 1 Schematic of Jefferson Laborator's High-Power FEL.

The dual servers run a suite of HP products that provide
for auto-failover, disk mirroring, system monitoring, loadmanagement, etc. As with other Jefferson Lab controls, theservers are designed to host mission-critical applications
and services, while operator workstations are generic andcan be replaced quickly and easily in the event of failure.
The dual server configuration also provides a mechanism
whereby system maintenance can be performed without
incurring system downtime. The entire server system isfully redundant. Each system unit is provided withmultiple FWD SCSI interfaces for root and data disk
volumes and associated mirror volumes, multiple network
attachments are provided, and all components are provided
with uninterruptible power. A "heartbeat'' connection isprovided between the servers allowing each to monitor thehealth of the other (note: the LAN is used as fallback in theevent of failure of this heartbeat). In the event that a server
detects a failure of one of it's own components, alternate
interfaces are selected as needed to maintain service. In theevent of failure of an entire server system unit the alternate
server starts the necessary services locally. Additional
system level information can be found at the web site
http://devweb.cebaf.gov/acce/Network/FELDescription.ht
ml.

on two of the tables and a 20 inch color monitor on thethird table. Additionally there is an LCD projection display
which can project either of two VGA inputs or one RS-170
video signal. This 70 inch diagonal display has proved tobe very convenient to monitor the drive laser photo-diodeoutput (via Tectronics TDS 784 scope′s VGA output) or todisplay a beam viewer. The Viewsonic LCD projector alsoenables full remote control of a PC with the IR remotecontrol.
4 Operator consoles
FEL consoles are implemented using mid-range HP
desktop workstation systems. These systems are all
running HP UX 10.20. The installation, configuration andmanagement of software on these nodes is done using HP's
"software depot'' and "Ignite'' software. These nodes aregeneric, each having essentially identical root volumes. In
the event of failure of any of these nodes, the entire
functionality can be provided by readily available
alternates. Using the automated tools, new systems can beconstructed in the lab from scratch -- including applicationof security and operational patches within a couple ofhours, with little or no operator intervention. The longterm plan calls for the deployment of 2 operator consoles
within the FEL control room, with two additional installedin the primary Accelerator control room. In addition, twox-terminals are used to provide access to controls fromwithin the clean room and optical controls room.
In addition to the mid-range operator console workstations, a number of workstations are provided within theuser labs. These are entry-level workstations, configured
and managed similarly to the operator console workstations. During commissioning these workstations are usedas supplemental consoles throughout the facility to aid incommissioning.
5 IOCsFig. 2 Server Configuration.

Several Motorola VME-based CPUs are used as IOCs
within the system, all running VxWorks 5.2. These nodes
receive boot and file services from the FEL server cluster,and connect to the network using 10Mbps ethernet. Eachbeamline ″zone″ has a dedicated bridged segment for it's
associated IOCs.

3 Control room
The first electron beam in the new building was drawn
off the photo-cathode on September 29, 1997. The initialcommissioning will continue from the FEL control room.
The control room is modeled from the APS control room,
except a smaller version. There are three tables arranged ina broken circle, each table has two work areas. These work
areas support either HP workstations or, for the optics
table, a workstation and a PC to run the Spiricon Laserbeam analyzer.
Each table has a patch system that allows any of 128
analog signals to be connected to the eight 50 ohm BNC
ports or any one of the 64 video channels to the four 75
ohm video ports. There is a scope and two 9 inch monitors

6 Network
The FEL network implements a mix of 10/100BaseX. AFore Systems Powerhub 6000 acts as a "workgroupswitch'', providing multiple 10-base and 100-base segments. Routing for the FEL subnet is currently provided bythe controls hub in the MCC, but will eventually migrate tothe FEL hub. This migration will allow for implementation of a virtual LAN ``backbone'' carrying FELNET aswell as CTRLNET (Accelerator Controls) and CRYONET(Cryogenic Controls) to all three of these sites. Thus,
nodes can be placed into any of these three physicallocations while maintaining logical attachment of any ofthese subnets.

7 Drive laser pulse control
The Drive Laser Pulse Control (DLPC) was developedfor control of the photo-cathode drive laser. The pulsecontrol electronics enable full duty cycle control from
100% to less than 0.02% while holding the charge perbunch constant. A system level block diagram is shown in
Figure 3. The space charge dominated optics in hte injector require that the charge per micropulse be between 60pC
and 135pC for clean transmission and lasing.

boards and Oregon Micro Systems (OMS) VME-44. The
high power RF tuner control hardware was adopted
directly from the CEBAF application. All other applications utilize the OMS four channel VME motor controller.
The OMS system was chosen because it had been used
at Los Alamos by members of the EPICS collaboration.
The FEL I&C group has packaged four motor drives andmotor power supply in a chassis combined with anauxiliary power supply in a single chassis. A breakout
board has been produced to convert the P2 connections to
two "D" connectors; one for connections to the motor
driver chassis and one for connections to shaft encoders(not currently implemented).
The driver chassis can be configured with any of thethree motor drives available with current per phasevariable from 0.2 Amp to 14 Amps, the MD10A andMH10 drives can be operated at 1 or 10 microsteps perstep. The MD125 can be operated at 10, 25 50, and 125
microsteps per step for a maximum of 25,000 microsteps
per revolution.
11 Insertion device control

Fig. 3 Block Diagram of Pulse Control Electronic.
8 Video and analog distribution
The Analog Devices 16 X 16 cross-point switch
AD8116 was chosen to implement the 64:16 video
distribution system and the 128:16 Analog Monitoring
System (AMS). We have designed the system using thedevelopment board available from Analog Devices. Fourof these 16 X 16 boards are mounted in a single chassis,
one chassis provides for the video control and two chassis
are required for 128:16 AMS.
9 Pegasus TEC camera
The Pegasus CCD camera is going to be used to image
the synchrotron light emitted from the electron beam in thebend magnets. This camera uses a two stage thermoelectriccooler (TEC) to reduce the background noise resulting ion
an increased sensitivity. The CCD is cooled to -30°C.
This camera uses a 658H x 496V Frame Transfer type
CCD with a storage area equal in size to the image area orabout 0.5 Mbyte. An interface board is currently underdevelopment to interface to the EPICS control system.
10 Stepper motor control
There are two hardware implementations for stepper
motor control in the FEL; Highland Technology CAMAC

These insertion devices require 24 Volt DC power toactuate and provide 24 Volt DC status signals. Thesedevices include the beam viewers, optical shutters, flip-in
mirrors and lenses, and the ON/OFF control of the gun
power supply. A 12 channel interface chassis was designed
to work with the IP-Digital48. This chassis provides 48
optically coupled lines of I/O; two bits of drive and twobits for status for each of the 12 channels. The beam
viewers use drive bits for insertion solenoid and lamp
power, and the status bits for inserted/retracted status.
The Green Spring Computers IP-Digital48 is used as theinterface to the control system for 24 Volt DC devices.
Each Industry Pack uses one of the four available daughter
board slots on the Motorola MVME 162 VME module.
HiDEOS is required when using the MVME 162 for I/O
operations.
Acknowledgements
I would like to thank Frankie Manley and Jeff Brandt for
their help during installation and documentation.
References[1] L. Bohn, "Recirculating Accelerator Driver for aHigh-Power Free-Electron Laser: A Design Overview", in Proc. 1997 Particle Accelerator Conf.,
Vancouver, BC, 12-16 May 1997 (in press).
[2] A.S. Hofler, A.C. Grippo, M.S. Keesee, and J. Song,"Overview Of Control System For Jefferson Lab's
High Power Free Electron Laser'', This Conference.