PULSED MAGNET CONTROL SYSTEM USING COTS PXIE DEVICES
AND LABVIEW
Y. Enomoto∗ , K. Furukawa, T. Natsui, M. Satoh, KEK, Tsukuba, Japan
H. Saotome1 , Kanto Information Service, Tsukuba, Japan
Abstract
About one hundred channel of pulsed magnet power supply control system was installed in 2017 in KEK electron
positron LINAC to realize pulse-to-pulse control of output
current every 20 ms. The control system totally consist ofcommercially available devices, namely a computer (Windows 8.1), a PXIe crate and several PXIe boards such as
ADC, DAC communication and timing. The software is
written by LabVIEW. EPICS channel access protocol isused to communicate with OPI over standard Ethernet network. Depending on the destination of the beam, there areten beam mode. The software is able to keep parameters foreach mode independently, which makes it possible for us tooperate one LINAC as if it were ten virtual LINACs. During
two years of operation, there were no significant problem.
Although the Windows is not a real-time OS, dropping rateof the trigger coming every 20 ms is less than ppm. Rebooting the computer or software is only a few times in ayear.

INTRODUCTION
The KEK injector linac [1] has delivered electrons andpositrons for particle physics and photon science experiments for more than 30 years. Figure 1 shows electron
and positron accelerator complex in the KEK Tsukuba site.
There are four storage rings, i.e. two rings for light source,
PF and PF-AR, and two rings for electron positron collider,SuperKEKB [2] HER and LER. In addition to them, positron
damping ring have been in operation since February 2018.
All of the rings require full energy injection, 2.5 GeV for PF,
6.5 GeV for PF-AR, 4 GeV for SuperKEKB LER and 7 GeV
for SuperKEKB HER as shown in the Fig. 1.
In 2009, simultaneous injection to three rings but PFAR were realized [3] with common DC magnet settings.
However, in the SuperKEKB era from 2016, the previous
scheme has no longer valid due to strict requirement for
injection beam to the SuperKEKB rings. Table 1 compares
several required injection parameter for the KEKB rings
and SuperKEKB rings. One of the big difference is that thebeam life time in the SuperKEKB rings expected to be as
short as 6 minutes that was 150 or 200 minutes in the KEKB
rings. Usually, it takes at least a few minutes to load theparameters for PF-AR ring, injection into the ring and reload
the parameters for SuperKEKB rings. It is not acceptable for
the SuperKEKB rings to stop injection for such a long time,otherwise most of the particles in the SuperKEKB rings havebeen lost. Another difference is the emittance requirement
to the SuperKEKB rings. To avoid emittance growth in the∗ yoshinori.enomoto@kek.jp

LINAC, optics and orbit setting should be optimized for bothof the rings which require different injection energy.
To satisfy these requirements, about one hundred pulsed
magnets were installed in 2017 and 2018 Using these magnets, magnetic field can be changed shot by shot in 20 ms
and was optimized for each destination.

Figure 1: A schematic view of the electron and positron
accelerator complex in the KEK.
Table 1: Required Injection Parameters
Stage

KEKB

Beam
Energy(GeV)Life time(min.)
Emittance
(𝜇 m)
Bunch
charge(nC)
Energyspread (%)

SuperKEKB

electron
8.0

positron
3.5

electron
7.0

positron
4.0

200

150

6

6

310

1400

1

1

40/20
(H/V)
4

100/15
(H/V)
4

0.13

0.13

0.07

0.16

In this paper, the control system and software are mainly
described. Details of the hardware such as magnet, power
supply circuit are found in the reference [6].

OVERVIEW OF THE SYSTEM
Concept and overview
There are many requirements for the power supply to truly
realize the required flexible operation. In addition, since therequired number of the power supply is not a few, unit cost,

CSS archiverNAS

operator´s machineLAN

DC power supply
control server

DC power supply

PXI express(fast control)

pules driver

event signal
magnetEPICS CALXI ver. 1.3
NI network shared variablecRIO(interlock and data logging)

installation space, energy efficiency are crucially important.
Trigger rate of our LINAC is 50 Hz, but injection pattern is
not fixed. The destination of the beam is delivered by the
EVENT timing system via optical fiber just after the previous
pulse. To interpret the information and change setting within
20 ms, fast and intelligent control system is necessary. To
realize these requirements with minimum risks and cost, we
decide to develop new power supplies by ourselves following
the concepts bellow .
• realize high efficiency with energy recovery• separate power circuit and control system• use commercially available components as much as
possible• compatible with existent EVENT timing system• compatible with existent EPICS control system [4]Figure 2 shows a block diagram of the pulsed power supply
system [5]. One standard unit which covers 4 quadrupole and4 steering magnets, shown in Fig. 3, consist of a PXI express
unit for fast control, DC power supplies, pulse drivers andNI cRIO unit for interlock and slow data acquisition.
In addition, there is one computer to control and monitor
all of the DC power supplies (DC power supply control
server). A CSS archiver and A Network attached storage areused to log various data not only output current of the power
supplies but temperature of the IGBT in the pulse driver,status of the DC power supplies and others. EPCIS channel
access protocol is mainly used for the communication among
computers over the standard network. LXI ver 1.3 protocol
is used to control the DC power supplies and NI network
shared variable is used to send fast waveform data. As forthe event timing system, dedicated optical fiber is directly
connected to the module. Most of the software is written by
LabVIEW 2016 (32 bit) with NI DSC module and runningon Windows 8.1.

standard unit

Figure 2: Block diagram of the power supply control andmonitor system.

pulse driver
Pulse driver in fig.2 is one of the core components of thepulsed power supply. For the steering magnets, the pulse
driver mainly consists of a power operational amplifier. The
driver linearly amplifies control signal from the DAC. For thequadrupole magnets, the pules driver consists of IGBTs andcapacitors. Unlike usual switching power supplies, output
current is controlled by the voltage between gate and emitter.
From the view point of the control system, both pules drivers
for steering and quadrupole magnets work as power amplifier
and output current is controlled by the voltage of the DAC.
In addition, the pulse drivers have output current monitor
which is independent from the one used for the feedback
control of the circuit in the driver. The output voltage of themonitor is proportional to the output current To monitor thesignal is important for the debugging the system in the caseof trouble.
Thus the requirement for the controlling system of thepulsed driver is simply equivalent to how to control the DAC
and ADC synchronised with beam.

Figure 3: A photo of the standard unit for 4 quadrupole and4 steering magnets.

SELECTION OF THE CONTROL BUS
AND DEVICES
As is often the case with many facilities, VME bus is
widely used for the communication bus of the many devices
especially ones which require timing control. Event timing
system of MRF is used in our LINAC for the timing control.
Thus the Event receiver with VME bus is common in ourenvironment. However, this time, PXI / PXI express bus waschosen for the pulsed magnet power supply control system.
The reasons are• availability of the EVR module• availability and cost of ADC and DAC boards• promising standards• fast bus speed
Not only the timing and trigger control but also many information such as destination of the next beam, shot ID andothers are delivered by the Event Timing System. It is necessary for the new system to be compatible with the present
Event Timing System. Fortunately, EVR module with PXI
bus was available.
Although many ADC and DAC boards are commerciallyavailable, sometimes it is not so easy to obtain the one suitable for the purpose. Developing the board from the IC willusually time-consuming and not cost effective for a small
scale system.
Looking back the progress of the PXI / PXI express bus
standards last 20 years, it is revised as new PCI / PCI express
standards appear in the market. As long as the PCI / PCI
express is adopted for the computer bus, PXI / PXI expressis expected to be maintained.
As for the performance, bus speed of the crate used in
the system (NI PXIe-1082) is up to 8 GB/s which is much
faster than that of the latest VME standard. It is suitable forthetransfer of the large amount of data from the ADC and
DAC.
Figure 4 shows the details of the PXI control system. One
unit consists of the• a remote controller card (NI PXIe-8381)• an 8 ch 16 bit 1MHz simultaneous sampling ADC (NIPXIe-6356)• an 8 ch 16 bit 1MHz simultaneous updating DAC (NIPXI-6733)• an EVR (MRF PXI-EVR-230)• a chassis (NI PXIe-1082)• a computer with Windows 8.1 and LabVIEW
Embedded controller with PXI express bus was not
adopted intentionally. The controller is a general PC. The
life cycle of the CPU is generally shorter than that of ADC
and DAC boards. Separation of the CPU makes it possible
for us to upgrade the system more flexibly with less cost in
the future.

Figure 4: Details of the PXI unit (top) and its outlook (bottom).

SOFTWARE
In our LINAC, EPICS is used for the infrastructure of thedevice control. The new system must be compatible withEPICS. In addition, since control boards made by National
instruments were adopted, it is straightforward to choose
LabVIEW for the programming language. Fortunately there
are software modules in LabVIEW to connect EPICS.
Figure 5 shows data flow in the software. Twelve DAC
data array according to the beam mode (ten beam mode
plus no injection mode and no trigger mode) are preparedin
advance in the computer’s memory. Each DAC data is recalculated by putting a new value using EPICS channel accessFigure 5: Data flow in software
protocol. Data buffer information from the EVR is delivered
to the main software a few millisecond after the last trigger.

Then, one of the DAC data array is selected according to
the next beam mode and updated to the DAC’s memory. By
the trigger signal from the EVR, the DAC and the ADC
start ouputting and digitizing data for 6 ms. Aquired ADC
data array is concatinated with shot ID and mode number,then issued to the network using NI network shared variable
protocol every 20 ms. At the same time, one point, at thetiming of the beam passing through, in the ADC data arrayis chosen and issued to the network with mode number using EPICS channel access protocol. Every one point datawith timestamp, shot ID and mode number is buffered in
the memory of the control computer for 10 s then they are
dumped to the text file in the local storage of the computer.
The file is copied to the NAS every 60 s by another process.
By this way, output current of the power supply for all of
the shot (every 20 ms) is stored in the disk. The amount of
the data is about 3 TB/year. In addition to real-time monitoring, logging by CSS archiver every 10 s is also available
for all the channel. Suplemental softwares such as, remotemonitoring ADC data array, detecting hung-up of the main
programs etc. are also prepared by LabVIEW and runnig on
the windows machine in the control room.

EVALUATION AND OPERATION
trigger dropping rate

Figure 6 shows trigger dropping rate for one day at one
unit. Shot ID is stored in the log file for every output pules.
If the trigger was not dropped, difference between adjacentshot IDs should be one. The upper graph shows this value
as a function of time and the lower one shows the histogramof them. In this example one trigger is dropped among 4.32
million pulses. (50 Hz repetition means 4.32 million pulses
per day.) Data from other unit and other day shows similar
results, namely trigger dropping rate is less than 1 ppm. Even
though this is a kind of Brute-force solution and the dropping
rate depend on the conditions, the value is acceptable for ourpresent operation.

experiences during two years operation
Long term stability of the Windows and LabVIEW is also
one of the concern. Presently, 16 units are in operation.
Most of the unit except for a few specific unit are very stable.
It is not necessary to restart the software and reboot the PC
during the operation term more than 6 months. Unstable
units require reboot once in a few months. Although thereasons is not clear, difference of the noise environment is
one of the candidate.

SUMMARY

The combination of Windows 8.1 and LabVIEW makeit possible for us to develop software in short time. However, asis well known, Windows is not a real-time operating
system. Whether the software is able to do all the tasks in
20 ms or not depend on the performance of the computer.
The specifications of the computer used in operation aresummarized in table 2.

Since the major installation of the pulsed magnet systemin the summer shut-down 2017, there has been no severe
trouble during two years operation. Although the systemusing Windows and LabVIEW is not a real-time system, trigger dropping rate is less than one ppm, which is practicallysufficient for the present operation. The control system inthis paper which fully utilize the COTS devices might be apossible candidate for the medium-scaled control system.

Table 2: Required Injection Parameters

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CT525MX300SSD1
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Figure 6: Difference of the adjacent shot ID for one day at
one unit.

[6] Y. Enomoto et al., “PULSE-TO-PULSE BEAM MODULATION FOR 4 STORAGE RINGS WITH 64 PULSEDMAGNETS”, in Proceedings of LINAC2018, Beijing, China,
pp.609-614 (2018)