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Network Based Control System and Automated Operation of Low Energy Accelerator Facility at
BARC, Mumbai
Arindam Basu, Sudheer Singh, Subrahmanyam B.V. Nagraju, Arun Agarwal , Sapna Padmakumar,
Jignesh Bhatt , Shailaja Ware , Shrikrishna Gupta, Pitamber Singh
Ion Accelerator Development Division, Bhabha Atomic Research Centre, Mumbai - 400085, India.
[email protected]
Abstract
A Low Energy Accelerator Facility (LEAF) has been set
up at BARC which is in operation with several beams
available to the users. The facility can deliver singly
charged negative ion beams of energy upto 50 keV.
Already H- , Li- , C- , O- , Al-, Fe-, F- , Si-, S-,P-, Sb-,
Ag- and Au- beams have been extracted and delivered on
to the target.
Experiments have been done with H-, Li-, C- , Si-,S-,Pand Sb- beams. Typical particle currents available are up
to few micro amperes.
Network based control system of this accelerator is used,
apart from normal control operation, to auto start up and
shutdown the accelerator and it is successfully working
since two years. This paper will present the details of the
LEAF control system and its automated start up and
shutdown.
INTRODUCTION
Low Energy Accelerating Facility (LEAF) is a 50 keV
DC electrostatic accelerator (Figure 1) operational at
Van de Graaff building at Bhabha Atomic Research
Centre, Trombay, Mumbai.[1] LEAF can accelerate
various beams across periodic table. Current delivered at
target is micro amperes of particle current for prolific
beams such as C- or H- and for difficult beams such as Li, delivered current at target is few hundred nano amperes.
This accelerator has already delivered negative ion beams
of Hydrogen, Lithium, Carbon, Sulphur, Tellurium, Gold,
Silver etc. This accelerator is used various experiments in
material science and atomic physics studies using ion
clusters.
Negative ion beam is generated in a SNICS ion source
and accelerated in an accelerating tube. Accelerated
beams are bended 90 degree by an electromagnet to
transport the beam to the experimental chamber. This
electromagnet also works as a mass selector. To focus the
beam on the target an electrostatic quadrupole triplet is
used after the bending magnet. There are two sets of
steerers for the beam path correction. First set is just after
the accelerating tube, second is after bending magnet.
Three Faraday cups are used to measure the beam
currents at different locations and three beam profile
monitor are used to monitor beam profile.
Throughout the length of beam line vacuum of order
10-7 Torr is maintained. Two turbo pumps and one ion
pump are used to maintain the vacuum during operation
of facility. SNICS ion source is kept under vacuum
continuously by a small ion pump (pumping speed 35
l/sec) when facility is not running.
Though LEAF is a small accelerator but smooth and
efficient running of this accelerator requires robust
control system. As ion source is on a high voltage deck,
so ion source parameters must be controlled remotely.
Also, other controlling equipments like steerers, bending
magnet current supply, high voltage power supply of the
ion source deck, Faraday cups and entire vacuum system
must be controlled independently to tune the beam and
deliver it to conduct the experiments. To deliver the
various energies and masses of the ion beams at the target
it is required to control the accelerator and tune the beam
Figure 1: Low Energy Accelerator Facility at BARC, Mumbai
considering the actual field data. Thus a control system
consists of a data acquisition window, and Graphic User
Interface (GUI) based analog and digital control operator
interface. The control system is a network based system
which gives the ability to control this accelerator from
any computer connected to the network. This network
based control system is modelled as client server system
and server system runs a routine to accomplish the task of
automatic start up, shut down and auto experiment.
TCP/IP protocol. Next server reads the client command, if
any, and decoding the command apply analog or digital
signal in the USB-6008 microcontroller. In LEAF control
system each server’s scan cycle period is 250 milli
second.
DESCRIPTION
Analog and digital data is acquired from the field via
National Instrument’s micro-controller based (NI 6008)
system. It is a low cost, USB powered multifunction DAQ
which gives 12 bit resolution for analog channels and up
to 10kS/s sampling rate which is sufficient for the control
purpose of LEAF.
Precision, high performance isolation amplifier, AD210
is used for control signals of the ion source devices.
AD210 is a full-featured isolator providing numerous
benefits like, high common-mode performance, high
accuracy, isolated power etc.
LEAF control and instrumentation is physically divided
into two parts because Ion source of LEAF is floating at
negative 50 kV. Hence all the power supplies required for
the ion source operation are on high voltage deck floating
Figure 3: Server Scan Cycle
Client cum operator interface receives the field data from
both the servers, decode them and display the field
parameters on GUI. Operator can change different analog
and digital values as per operational requirements and that
is communicated to the server as the client command.
Client side also has an interlock module. In the client
cycle various interlock conditions are evaluated and either
alarm is raised for operator or appropriate action
according to defined rule is executed automatically.
.
at negative 50 kV Other parameters are at ground
potential.
LEAF control software has the client server
architecture (Figure 2). Since ion source side is floating at
50 kV so a dedicated server is written for the ion source
side. The computer on which the ion source server is
running is also floating at negative 50 kV. Fiber to
Ethernet converter is used to bring the data from the
server to router, which is lying at the ground potential.
For other part of the accelerator, which is at ground
potential, there is another server.
Router
Figure 2: Control System architecture.
Each server is having its own scan cycle. In a typical
scan cycle server first acquire analog and digital field
data, code them and send it to client via LAN using
Figure 4: Client Scan Cycle
Software Description
Entire software is written in Qt 4.0 [2]. Server side is a
console program and no GUI is there. Qt’s network
module is used to communicate over TCP/IP. National
Instrument’s USB-6008 interaction library is imported to
interact with it. Effort has been made to use only those
calls which can also be used in LINUX operating system.
Presently server side program runs in windows 7 Home
versions in the ion Source server and under windows XP
professional in beam line server. Server side is operating
satisfactorily under both operating systems.
Client cum operator interface used extensively Qt’s
excellent graphical capabilities.
All relevant details of the analog and digital channels
and description of all field devices are kept in the
configuration files. Servers and client read relevant
configuration files and sets up control program by taking
data from configuration files. After initial configuration,
repetitive server and client cycles described in the figure 3
& 4, keep on running till the programs are alive.
In every scan cycle collected data is logged in the file,
which helps to understand the dynamics of machine and
to troubleshoot. Each server keeps a log file of the
commands it received from the client console to analyze
and understand the problem in case of a failure.
AUTOMATION
Since LEAF is a very small accelerator dealing with a
small number of parameters, it is felt that entire operation
of the LEAF can be automated. An automated operation
follows a predetermined set of actions to establish
vacuum in the system and setting up all the power supply
values. In most cases that establish a reasonably good
quality of the beam just before the target.
Three sets of automatic tasks are implemented in
LEAF. They are auto startup, auto shutdown and auto
experiment.
During auto start-up, upon receiving the operator
command, each server starts a predefined set of action.
Upon completion of every step of the task, routine checks
the integrity of the set values and field values. If this
check is passed then next step of the task is started
automatically. In case of failure, program halts and an
alarm is raised for the operator to inspect the reason of
failure and to take necessary appropriate action. Upon
successful completion of automatic task, a success
message is displayed in the GUI for operator.
During auto shut down, upon receiving command from
the operator a similar loop described in auto start up is
executed. Responsibility of this loop is to bring down the
power supplies to the required state (in most cases
switched off state) in a safe and gradual manner. Once
that is achieved vacuum system is isolated, turbo pumps
are switched off along with its backing pump and ion
pump is switched on to maintain vacuum during period of
non operation.
A large number of experiments carried out at LEAF are
of irradiation type experiment, where user needs to
irradiate their sample for a pre determined amount of
time, ranging from few seconds to several hours. In auto
experiment upon a command from the operator control
system remove the final Faraday cup, thereby starting the
irradiation. It is the responsibility of the auto experiment
loop to keep track of the time , which user feed in graphic
user interface , and when time is over final Faraday cup is
re-inserted and irradiation stop.
This feature is highly useful for the sensitive
experiments like irradiation of nano dots where
sometimes irradiation time is only few seconds and
operator response can introduce significant error in the
irradiation dose.
PERFORMANCE
The control system along with the automation feature is
working very satisfactorily as per specification and design
for more than one and half years. Some minor bugs
surfaced during the first few days of run which has been
immediately taken care. After that no new bug has been
reported by operators.
FUTURE SCOPE
The LEAF control system is designed to scale up as and
when required. After successful implementation of the
automation feature next step of improvement involves
auto tuning. For that, digitization of BPM profile is
required and work is being carried out in that direction.
Along with that operator and user feedbacks are being
collected and most of them will be incorporated in the
future to make the machine more operator and user
friendly.
ACKNOWLEDGEMENT
We acknowledge all the users of LEAF for their
encouragement, support and constructive feedback.
REFERENCES
[1] A Basu et al. “Operation and Updradation of Low
energy Accelerator Facility”, InPAC 2011
[2] http://doc.qt.nokia.com/4.7-snapshot/
[3] http://www.ni.com/pdf/manuals/373552a.pdf