Designing Superconducting Magnet Controls for the
Super High Momentum Spectrometer
Brian Mastracci
Office of Science, Science Undergraduate Laboratory Internship Program
Virginia Polytechnic Institute and State University
Blacksburg, Virginia
Thomas Jefferson National Accelerator Facility
Newport News, Virginia
July 30, 2010
Prepared in partial fulfillment of the requirement for the Office of Science, Department of
Energy’s Science Undergraduate Laboratory Internship under the direction of Paul Brindza and
Steven Lassiter in the Experimental Nuclear Physics division at Thomas Jefferson National
Accelerator Facility.
Participant:
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Research Advisor:
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TABLE OF CONTENTS
ABSTRACT
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INTRODUCTION
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MATERIALS AND METHODS
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RESULTS
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DISCUSSION AND CONCLUSIONS
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ACKNOWLEDGEMENTS
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REFERENCES
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FIGURES AND TABLES
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ABSTRACT
Designing Superconducting Magnet Controls for the Super High Momentum Spectrometer.
BRIAN MASTRACCI (Virginia Polytechnic Institute and State University, Blacksburg, VA,
24061) PAUL BRINDZA, STEVEN LASSITER (Thomas Jefferson National Accelerator
Facility, Newport News, VA, 23606).
Hall C of Jefferson Lab is building the Super High Momentum Spectrometer (SHMS),
which will be capable of analyzing charged particles scattered by its upgraded 11 GeV electron
beam. Particles will be focused into detectors using five superconducting magnets. Each magnet
will be monitored and controlled using integrated hardware and software systems to ensure
particles are delivered precisely and accurately to the detectors. Electronic data flows from
instruments built into the magnet through various hardware devices that transform the data into a
signal usable by a Programmable Logic Controller (PLC), where user-designed software
continually monitors the status of the magnet. The focus of this project was to design and
document the hardware that will be used to control the SHMS superconducting magnets. This
was accomplished by revising wiring diagrams for the existing High Momentum Spectrometer
(HMS) controls using AutoCAD drafting software. Technical drawings of new magnet designs
and hardware manufacturers’ documentation were also used to ensure the proper signal will be
delivered to each PLC. The end result was a map of the signals used to control liquid cryogen
flow valves and to monitor temperature, strain, and potential difference within the magnets’
superconducting coils. A complete and accurate signal diagram is essential for ease of
construction and maintenance of control systems, since poorly designed or incomplete hardware
configurations could supply improper PLC input, leading to malfunction of and damage to
SHMS components. A complete and well-designed control system optimizes performance of the
machine, increasing its value to the study of particle physics.
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INTRODUCTION
Jefferson Lab is in the process of increasing the energy of its electron beam accelerator
from 6 GeV to 12 GeV. The equipment in each experimental end station is also being upgraded
to handle the increased beam energy. Hall C is building the Super High Momentum
Spectrometer (SHMS), which will be capable of analyzing charged particles at momenta created
by a beam energy of up to 11 GeV [1]. Five superconducting magnets focus scattered particles
into detectors. Each magnet is precisely monitored and controlled using integrated hardware and
software systems.
A complete control and monitoring system must be designed for safety and functionality
of the SHMS. A programmable logic controller (PLC) will process data from sensors built into
each magnet using software that must be designed and programmed into the PLC. Electronic
data from sensors monitoring temperature, pressure, strain, liquid levels, potential taps,
cryogenic flow valve position, vacuum pressure, and helium mass flow need to be amplified,
conditioned, and converted to usable PLC input signals [2].
In order to create a complete control system all hardware, including cabling, must be
acquired and assembled; technical drawings must be created to document signal paths and show
how the components are to be connected; and software must be written that tells the PLC how to
process input signals and what signals to output.
The High Momentum Spectrometer (HMS) that already exists in Hall C uses the same
style of integrated control system that will be designed for the SHMS. Designing controls for the
SHMS will be largely a modification of the HMS controls [2]. Changes will be made to
incorporate different types of magnets and different hardware components and configurations. It
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was determined that modifying the existing technical drawings and software would be more
efficient than creating completely new documents.
MATERIALS AND METHODS
HMS wiring diagrams were created using AutoCAD 2D drafting software [3]. AutoCAD
was used to edit existing drawings and create the wiring diagrams for the SHMS. RSLogix 5000
software [4] was used to write the programs that allowed the PLCs to control and monitor the
HMS magnets. Inputs and outputs, or program tags, were modified for the purpose of testing
some components of the SHMS control system.
Creating Wiring Diagrams
The main procedure for creating wiring diagrams was to update labels on HMS wiring
diagrams. In some cases lines representing wires needed to be removed and redrawn and
hardware representations needed editing to reflect the use of new hardware components. In the
case of strain gauge measurement, this was accomplished by erasing the representation for
Oxford’s strain gauge measurement devices [5] and instead connecting strain gauges to Dataforth
signal conditioners [6] so that the signal could be analyzed by the PLC. Low-voltage
conditioners (LVCs) were also updated by removing representation for the old unit and
reconnecting wires to a diagram of the new unit. Proper methods for wiring the new components
were identified by consulting the manufacturer’s documentation provided with the product.
Assembling Hardware
Installing hardware onto the local control rack was a simple matter of snapping it into
place. Wiring together the devices was a majority of the work required to assemble the rack.
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Wires needed to be cut to the proper length and stripped using wire cutters. Ferrules were applied
to the end of each length of wire using a crimper to facilitate connection and removal of cables.
Finished cables were connected to the terminals specified in the updated wiring diagrams.
Low-Voltage Conditioner Calibration
LVC signal conditioners required calibrating once they were properly connected. Each
LVC will measure the position of a Joule-Thomson (JT) cryogenic flow valve by converting the
signal output by a linear voltage differential transducer (LVDT) to a current within the input
range of the PLC. An electric linear actuator drive motor, which moves the JT valve, and LVDT
were connected to the control rack for sensor calibration. By changing program tag values in
RSLogix, the valve was moved to its fully open and fully closed positions. The current and
voltage outputs from the LVC were recorded at each position. At the maximum closed position,
the signal conditioner offset was adjusted until the dual output read 2 V and 4 mA. At the
maximum open position, the signal conditioner gain was adjusted until the output was 10 V and
20 mA. Adjusting the offset or gain affected the both the high and low signal output. The process
of opening and closing the valve was repeated until the open and closed output signal was within
±0.1 V of the desired value. Once the first LVC was calibrated the valve was connected to the
next LVC unit so that all six signal conditioners could be calibrated using the same valve
assembly.
RESULTS
A set of wiring diagrams for monitoring temperature, strain, potential difference, and JT
valve position was produced. Drawing labels were revised to reflect new SHMS temperature
sensor names. Potential difference will be measured across different coils of each
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superconducting magnet. Drawings of potential taps were revised to show which coils will be
measured on each of the new magnets (see example in Figure 1). Strain gauge representation was
changed to show the use of a full-bridge instead of half-bridge strain gauge. The drawing of the
Oxford strain gauge measurement unit was replaced by a series of signal conditioners that will
send a signal to the PLC for measurement. Drawings for the JT valve system, including LVDT
sensors, LVCs, and electric linear actuator drive motors, were revised to show that the SHMS
will use only six JT valves on each magnet. Representation for a different LVC replaced the
drawing for an old LVC that was prone to failure (see Figure 2). Calibration data for the new
sensors was compiled for use in the software program (see Table 1). All hardware components
featured in the upgraded signal diagrams were assembled on a prototype local control panel (see
Figure 3).
DISCUSSION/CONCLUSION
The local control rack constructed and documented is a prototype rack for the integrated
control system that will be used to operate the SHMS. After the liquid level and pressure, helium
mass flow, and vacuum pressure measurement devices have been completed, the rack will be
shipped to Michigan State University to be tested with the SHMS Horizontal Bender (HB)
magnet. Once the first control rack has been tested and completed, additional racks for each of
the four remaining magnets will be constructed, tested, and installed.
ACKNOWLEDGMENTS
This project was completed at Thomas Jefferson National Accelerator Facility between
the dates of June 24 and July 30, 2010. Thanks to the United States Department of Energy and
Thomas Jefferson National Accelerator Facility for creating, funding, and organizing the Science
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Undergraduate Laboratory Internship program. Thanks to Lisa Surles-Law and the Jefferson Lab
education department for organizing the SULI program at Jefferson Lab. Thanks to Paul Brindza
for sponsoring me as a SULI intern. Special thanks to Steven Lassiter for guiding me through
completion of this project.
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REFERENCES
[1]
“Design Solutions Document – Upgrade Hall C,” May 23, 2007 (Updated may 9, 2008).
[2]
S. Lassiter and M. Fowler, “SHMS Magnet Controls,” June 27, 2010.
[3]
Autodesk, Inc., 111 McInnis Parkway, San Rafael, CA 94903, USA
[4]
Rockwell Automation, 1201 South Second Street, Milwaukee, WI 53204, USA
[5]
Oxford Instruments plc, Abingdon, Oxfordshire OX13 5QX, UK
[6]
Dataforth Corp., 3331 E Hemisphere Loop, Tucson, Arizona (AZ) 85706, USA
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FIGURES AND TABLES
Figure 1
Figure 2
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Figure 3
Table 1
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