The Nuclear Science Laboratory at the University
of Notre Dame maintains and operates a SNICS II Sputter Ion Source,
manufactured by the National
Electrostatics Corp.(NEC). This ion source has been in operation
at Notre Dame since 1989, and is the primary source of ion beams for
injection into the FN Tandem Van de Graaff accelerator.
In addition to the original, manual mode of operations, we have installed
a computer based control system to allow for remote control operations
of the SNICS source. We chose Group3
with ControlNet, a fibre optically linked control system using distributed
I/O modules distributed by GMW
Associates, INC. The system consists of a fibre optic loop connecting
each of the I/O modules, known as Device Interfaces (DIs), to the computer
that houses the card containing the loop controller. Each DI can house
as many as three separate I/O cards, and each loop may contain as many
as 16 DIs.
Our system for controlling the SNICS II
ion source consists of two DIs on a single fibre optic loop controlled
by a loop controller card housed in a PC running Windows
XP. The use of a fibre optic loop has the advantage that a DI can
be mounted directly on the high voltage platform that operates the SNICS
source, which we typically operate at approximately 80 kV below ground.
In our case, we have one DI mounted on the high voltage platform and
one DI mounted at ground potential. The DI mounted on the high voltage
platform contains three I/O cards. Two of the cards are 8 channel analog
input cards, used to return current and voltage readings from the Ionizer,
Cathode, Extractor, and Focus power supplies. The third card is an 8
channel analog output card, used to provide an analog control voltage
for each of these power supplies.
The DI mounted at ground potential also contains three I/O cards. One card is an 8 channel analog input card, used to return current and voltage readings from the Bias (High Voltage Platform) and Analyzing Magnet power supplies. The second card is an 8 channel analog output card, used to provide an analog control voltage for each of these two supplies. The third card is a 24 channel digital I/O card, used for switching the inline Faraday cup.
The Cathode, Extractor, Focus, and Bias
power supplies are manufactured by Glassman,
and each of these supplies has the feature that an external analog voltage
in the range 0-10 V can be used to control the supply from zero to full
scale voltage. The Ionizer and Analyzing Magnet supplies are manufactured
by Electronics Measurements, Inc. and allow for an external voltage
in the range 0-100 mV to control each supply from zero to full scale
current. The 0-10 V analog voltage is easily produced with a standard
configuration of the Group3/ControlNet system, and we use a voltage
divider to produce the 0-100 mV signals.
The Faraday cup used to measure the beam intensity is controlled by a relay that is switched using a digital output from the Group3/ControlNet system. We designed some circuitry using a logarithmic amplifier to convert our beam currents (ranging from a few nano-Amps to tens of micro-Amps) into a 0-10 V analog voltage suitable for a standard input to our Group3/ControlNet system.
Our system operates under the LabVIEW
language, from National
Instruments, and is a collection of software built using the drivers
and subVIs contained in the ControlNet package, several routines and
ideas supplied by Group3, and many routines that we have written ourselves.
Our system is in full operation, and is capable of complete remote operation
of the SNICS source, including automated start-up and shut-down routines.
Below is an image of the front panel of the VI that we use to control
our SNICS II Ion Source.
Each of the power supplies is represented by both current and voltage meters (which also include digital readouts) as well as a colored slide bar indicator. As each supply is increased, its slider moves across the bar, with red coloring to the left of the slider. This gives the user a visual cue as to the status of each supply by simply glancing at the display. Each supply can be set using the digital control to the right of the slide bar indicator. The supplies can be increased or decreased by a preset increment by clicking on the arrows at the left edge of the digital control.
Near the bottom of the window is the Faraday cup current meter, which is designed to mimic the performance of a standard Keithley meter. The full scale range is selectable, from 3 nano-Amps full scale to 30 micro-Amps full scale, and the cup can be placed in the beam to measure the current or removed from the beam for running conditions using the virtual toggle switch.
Near the upper right of the window is a selectable virtual strip chart, which is used to monitor the Ionizer power level, the Cathode current, and the Extractor voltage. Other functions could be added with little difficulty. The Ionizer power level is also indicated by a vertical slide bar indicator, again with red and green coloring.
Near the bottom right of the window is the message box and the Standard Shutdown button. When the user no longer requires the SNICS source, they can simply click on the button and the source will automatically begin a slow, steady shutdown procedure which does not require any further input from the user. Please feel free to contact Ed Stech for more details regarding this system.
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