The ISIS Proton Synchrotron – Beam Data Acquisition
and Analysis using PXI and LabVIEW
Bryan Jones and Sarah Whitehead, ISIS - Science and Technology Facilities Council, UK
Products Used:
LabVIEW 8.6, Internet Toolkit 6.0, PXI-1044/1000B/1042Q/1045, PXI-8196/8186/8105, PXI-6133,
PXI-6651, PXI-6533, PXI-5414/5124/5412.
The Challenge:
ISIS is the world-leading pulsed neutron and
muon source based at the Rutherford
Appleton Laboratory in the UK. The facility’s
50 Hz synchrotron accelerates proton beams
up to 800 MeV, delivering a mean beam
power of 0.24 MW. A recent major expansion
of ISIS requires higher beam currents from
the synchrotron and has led to a programme
of detailed studies and upgrades. A key part
of this is improving the beam diagnostic
systems to better monitor, control and
ultimately improve the accelerator’s
performance
The Solution:
Several new PXI based data acquisition
systems have been installed to increase the
quantity, accuracy and speed of diagnostic
data obtained. We report here on the
systems used to monitor beam loss, beam
position and transverse beam profiles. We
chose PXI systems for their compactness and
high-performance data acquisition and
synchronisation capabilities. With guidance
from NI engineers we rapidly created easyto-use well-designed LabVIEW user
interfaces to control the systems and process
and display data. These PXI based systems
have contributed towards a 20% increase in
accelerator performance.
Introduction
The ISIS synchrotron accelerates a beam of
2.8x1013 protons to 85% of light speed, fifty
times a second. Each acceleration cycle lasts
10 milliseconds during which the beam
makes 12000 revolutions of the 163m
circumference, with the proton energy
gradually rising from 70 to 800MeV.
DataSocket software. A LabVIEW application
has been produced to receive and display this
data. This system allows many users to
simultaneously access the data and analyse it
in different ways.
The main feature of the VI is an ActiveX 3D
graph control displaying the loss, Figure 1,
this is similar to the existing histogram
display with four times the spatial resolution
and a time axis to show loss at 50µs
intervals. At a glance beam loss can be
identified on individual monitors at any time
within the acceleration cycle. The GUI also
allows the user to print graphs, save
reference data and view individual monitors
or the sum of all monitors. It also recreates
the existing histogram display for
comparison.
Beam Loss Monitoring
The amount of beam the synchrotron can
accelerate is limited by the proportion of the
beam that is lost during acceleration i.e.
beam that escapes the accelerating fields and
hits the edge of the vacuum pipe. This lost
beam can cause activation of the synchrotron
components which makes hands-on
maintenance problematic. Monitoring loss
levels is therefore crucial to successful
operation of the facility.
There are 39 beam loss monitors distributed
around the circumference of the synchrotron.
These monitors are 3m long argon-filled gas
ionisation tubes which indirectly detect
protons striking the edge of the beampipe.
Previously, the loss levels have been
displayed in the ISIS control room in a
histogram showing total loss in each of the
10 sections of the synchrotron summed over
an acceleration cycle.
A new PXI based data acquisition system has
allowed us to improve this display; the
system consists of a PXI-1045 chassis
housing a PXI-8105 controller, a PXI-6651
synchronisation card and 5 PXI-6133
digitisers. Data is acquired at 20kS/s and
streamed over the lab network using NI
Figure 1: 3D display of beam loss levels
Multi-Channel Profile Monitoring
The two new multi-channel profile monitors
(MCPMs, Figure 2) each use an array of 40
electron multipliers (channeltrons) to
measure real-time transverse beam profiles
within the ISIS synchrotron. The circulating
proton beam interacts with the residual gas
in the beam pipe to produce positive ions. A
high voltage drift field is applied across the
beam which directs the ions towards the
monitor.
Figure 2: A Multi-Channel Profile
Monitor.
The data acquisition system consists of a PXI
controller and chassis and five 8-channel
PXI-6133 cards which are sampled
simultaneously using a PXI-6651 timing and
synchronisation card. On every 50Hz pulse of
ISIS each of the 40 channels are read at a
sample rate selected by the user for the
acceleration cycle. From the front panel of
the VI, Figure 3, the user can view the profile
of the beam at a selected time, view graphs
that display the 90% beam widths and
centres over the acceleration cycle and view
a 3D plot of all the profiles. The user can also
choose to subtract background data and save
data. The saved data can be loaded and
superimposed over the currently selected
profile.
driven by a D.C. motor across the beam. The
SCPM moves across the beam using a step
size that aligns it to the transverse positions
of the 40 channeltrons in the MCPM. The data
is saved to a database and using the HTTP
server, which is part of the Internet Toolkit,
the MCPM VI can access the data and use it
to create a calibration file which is then
applied to the raw data from the MCPM. The
PXI system has made the process of
simultaneously collecting and analysing large
amounts of data from each of the 40
channels relatively simple.
A profile simulator has been developed so
that all the electronics and computer
hardware and software can be tested in the
absence of a proton beam. The simulator is a
microcontroller which can be switched into
the circuit using the digital lines of one of the
PXI-6133 cards. Different profiles are
preloaded to the microcontroller and selected
using a PXI-6533 digital I/O card. A PXI-5412
signal generator card provides a waveform
equivalent to the intensity fall off that occurs
during the acceleration cycle. This waveform
is applied to potentiometers which adjust the
output level of each channel, Figure 4.
Figure 4: 3D plot of data produced by
the simulator
Figure 3: Front panel of the MCPM VI
As the gain of each of the 40 channeltrons
varies greatly the MCPM needs to be
calibrated. To do this we use a motorised
single-channel profile monitor (SCPM) which
is housed in the same assembly as the
MCPM. The SCPM is the predecessor to the
MCPM and has one channeltron which is
Beam Position Monitoring
Accurate determination and correction of the
transverse position of the proton beam is a
major factor in reducing beam loss and
thereby increasing acceleration efficiency.
There are 10 horizontal and 10 vertical beam
position monitors installed in the
synchrotron, each monitor has two
electrodes on which the beam induces a
charge as it passes, Figure 5.
Figure 5: An ISIS Beam Position Monitor
In the past, data from these monitors has
been acquired via five four-channel digital
oscilloscopes at 100MS/s with 8-bit resolution
and a 250kb record length. The data was
then read out by a PC and processed with a
library of FORTRAN routines. An IDL GUI
provided measurement control and data
visualisation.
The new PXI-based system consists of a PXI1045 chassis housing a PXI-8105 controller,
a PXI-6651 synchronisation card and 10 PXI5124 digitisers. These provide 200MS/s
sampling at 12-bit resolution and a 512Mb
record length. Data can now be acquired over
a whole acceleration cycle at double the
previous sample rate and sixteen times the
previous resolution. The data is processed via
a LabVIEW VI which synchronises and
configures the digitisers and acquires 10ms
of data from each monitor electrode. The
data is processed and for each monitor a file
is written containing the beam position on
each revolution of the synchrotron. This file
is then picked up by the IDL software for
further analysis and display.
LabVIEW modules are used to subtract the
signal baseline, find peaks and troughs of the
signal and calculate the beam position. The
data can also be converted and sent to our
existing FORTRAN dlls to benchmark the
system. Data acquisition is triggered from
any PC in the ISIS network using networkpublish shared-variables. The new system
has been well tested and the beam positions
can be closely monitored and corrected down
to ±1-2mm.