PLUSE-TO-PULSE BEAM MODULATION FOR 4 STORAGE RINGSWITH 64 PULSED MAGNETS
Y. Enomoto∗ , K. Furukawa, T. Kamitani, F. Miyahara, T. Natsui,M. Satoh, K. Yokoyama, M. Yoshida, KEK, Tsukuba, Japan
S. Ushimoto, Mitsubishi Electric System & Service Co. Ltd. Tsukuba, Japan
H. Saotome, Kanto Information Service Tsukuba, Japan
Abstract
In 2017, sixty-four pulsed magnets (28 quadrupoles and36 steerings) were installed in the KEK electron positronlinac for simultaneous injection to four different rings. Since
each ring requires different injection energy, magnetic fieldin the injector linac has to be changed shot by shot (every20 ms) according to the destination of the beam. To realize
such operation, novel pulsed power supplies and an EVENT
timing system compatible PXI based control system weredeveloped. Installation and commissioning of the systemwere successful and it has been working for one year without
severe trouble.

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 forPF, 6.5 GeV for PF-AR, 4 GeV for SuperKEKB LER and7 GeV for SuperKEKB HER as shown in the Fig. 1. To
satisfy the requirement, 64 pulsed magnets were installed in2017 and 32 more are planned to be installed in 2018. Using
these magnets, magnetic field can be changed shot by shotin 20 ms and was optimized for each destination.

Figure 2: Beam energy along the beam line. Solid line showselectron beam dashed line shows positron beam respectively.

There are 8 (A-C, 1-5) sectors in the linac. Each sector
is about 80 m long and the total length of the linac is about
650 m. Figure 2 schematically shows beam energy along thebeam line. To minimize the installation of the pulsed magnets, acceleration scheme is carefully adjusted to minimize
the length of the beam line where the beam with different
energy pass through. The beam for the SuperKEKB HER,
it is accelerated all of the sectors. The beam for the PF, it isaccelerated in sector A to 2 and decelerated in sector 3 to5. The beam for the SuperKEKB LER, electrons are accelerated in sector A to 1 and generate positrons at the target
located in the middle of the sector 1. Positrons, shown indashed line, are accelerated rest of the sectors. Since thebeam energy is the same in the sector A to C and first halfof the sector 1 regardless of the destination, it is not necessary to use pulsed magnets. On the other hand, in sector
3 to 5 shaded by light blue in the Fig. 2, beam with very
different energy pass through, magnets in these sectors werecompletely replaced with pulsed magnets. In sector 2 and apart of sector 1, beam energy of the electron and positron isvery different. Magnetic field optimized for the low energy
positron beam affect the orbit of the high energy electron
beam very little. In these section, DC magnets with compatible setting for both electron and positron beam are used
except for several pulsed steering magnets at the moment.

MAGNET AND SUPPORTFigure 1: A schematic view of the electron and positron
accelerator complex in the KEK.

∗ yoshinori.enomoto@kek.jp

Several types of magnets were installed in the beam lines
as summarized in the Table 1. Appearance of these magnets
are shown in Fig. 3. In sector 3 to 5, a common unit shownin Fig. 4, which consists of two quad magnets (PM_32_4),
a horizontal steering magnet (PX_32_4), a vertical steering
magnet (PY_32_4) and a beam position monitor located on amotor controlled movable support, was installed at 13 points.

Table 1: Several Parameters of the Installed Pulsed Magnets
Type

L@1 kHzR

PX_16_5
PY_16_5
PX_17_2
PY_17_2
PX_32_4
PX_32_4
PM_32_4

2.4 mH
2.4 mH
2.6 mH
2.6 mH
2.9 mH
2.9 mH
1.0 mH71 mW
71 mW
127 mW
126 mW
115 mW
115 mW
8 mW

Max Magnetic
current
field
40 A
40 A
40 A
40 A
40 A
40 A
330 A

Gap

1040 AT 72 mm
1040 AT 72 mm
1440 AT 39 mm
1440 AT 39 mm
1440 AT 20 mm
1440 AT 20 mm
60 T/m φ 20 mmInstallednumber1
144131328

Other types of steering magnets were installed in sector 1and sector 2. Two quad magnets (PM_32_4) were installed
in sector 1 just before the positron production target to focus
the electron beam.

Figure 3: Appearance of installed pulsed magnets.

PULSED POWER SUPPLY
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,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 theEVENT timing system via optical fiber just after the previouspulse. 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, wedecide to develop new power supplies by ourselves following
the concepts bellows.
• 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 [3]Figure 4: The upper photo shows old DC magnets before
replacement. The lower photo shows newly installed unit.
Figure 5 shows a block diagram of the pulsed power supplysystem [4]. One standard unit which covers 4 quad and 4steering magnets, shown in Fig. 6, consist of a PXI express
unit for fast control, DC power supplies, pulse drivers andNI cRIO unit for interlock and slow data acquisition. Thereis one computer to control and monitor all of the 64 DC
power supplies (DC power supply control server). A CSS
archiver and A Network attached storage are used 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 so on. EPCIS channel access protocol ismainly used for the communication among computers. LXI
ver 1.3 protocol is used to control the DC power supplies andNI network shared variable is used to send fast waveform
data. As for the event timing system, dedicated optical fiber

is directly connected to the module. Most of the softwareis written by LabVIEW 2016 (32 bit) with NI DSC moduleand running on Windows 8.1.
CSS archiverNAS

DC power supply

PXI express(fast control)

pules driver

event signal
magnetEPICS CALXI ver. 1.3
NI network shared variable

ValuecRIO(interlock and data logging)

DC power supply
control server

Parameter

max current
330 A
max voltage
230 Vstability
0.1%
cooling
water cooled
power consumption
1500 W
repetition
50 Hz

operator´s machine

LANTable 2: Design Parameters of the Pulse Driver for Quad
Magnetstandard unit

Figure 5: Block diagram of the power supply control andmonitor system.
Figure 7: A photo of the pulse driver for quad magnet.

Figure 6: A photo of the standard unit for 4 quad and 4
steering magnets.

Pulse Driver for Quad Magnet
Design parameters of the pulse driver for the Q magnet
is summarized in Table 2. To achieve these values, a novelswitching power supply with energy recovery circuit wasdeveloped

Figures 7 and 8 show an appearance and a conceptual
circuit diagram of the pulse driver respectively. The circuit
consists of two IGBTs (IGBT 1 and IGBT 2), two capacitors(C_HV and C_LV), two DC power supply (VH and VL) andseveral diodes. After the trigger signal arrives, first, bothof the IGBTs turn on and current provided from both of thecapacitors pass the load through red lines shown in the upper
figure in Fig. 8. When the current reach the set value, IGBT
1 turn off and the gate voltage of the IGBT 2 is controlled tokeep constant output current. Finally, after the beam passthrough the magnet, IGBT 2 turn off. Stored energy in theload (magnet) is recovered to the capacitor (C_HV) throughthe red line shown in the bottom figure Fig. 8.
By combination of such energy recovery mechanism andwater cooling system, the outsize dimension of the pulse
driver is as small as EIA 3U in height. Output current ismonitored and fed back by two independent DCCTs withhall sensor (LEM LF 1005-S) which are calibrated by a more
precise external DCCT (Hioki 9709).

Pulse Driver for Steering Magnet
Design parameters of the pulse driver for steering magnet
is summarized in Table 3. Compared with the driver forquad magnet, output power is very small but bipolar output
is required. To meet with this condition, power operational
amplifier (Apex PA12 [5]) was used for the key device. Although such kind of amplifier is low efficiency compared㻻㻺㻵㻳㻮㼀㻌㻝

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Figure 9: A photo of the pulse driver for steering magnet.

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Figure 8: Conceptual circuit diagram of the pulse driver forquad magnet. Red allows shows the current path. Right sidefigures shows current profiles at corresponding states.

to switching power supply, the output power is very small
compared to the quad magnet above and the low efficiency
affect the total power consumption very little.
Table 3: Design Parameters of the Pulsed Driver for Steering
MagnetParameter

NAS Q nap T S- 431X U - 2G

operator´s machine

LANchassis NI PXIe- 1082

PCIe
G en2 x8

Value

max current± 10 A
max voltage± 40 Vstability
0.01%
cooling
air cooledpower consumption 750 W
repetition50 Hz
Figure 9 shows an appearance of the pulse driver for thesteering magnet. Air cooling was adopted for the simplicity
and cost. Usually steering magnets are used in a pair ofhorizontal and vertical magnets, there are two circuit in one
box of JIS 2U height (99 mm). Output current is monitored
and fed back by two independent precision resister of 1 ohm
which are calibrated by more precise external DCCT (Hioki6862).

PC W indows 8.1
LabV IEW 2016 (32 bi t)

EV R M RF PXI- EV R- 2 30

㻻㻲㻲

For the fast control, PXI express unit plays major role. Theunit shown in Fig. 10 consists of a PC and a PXI express
chassis (NI PXIe-1082) with four cards, a controller board(NI PXIe-8381) to connect to the PC, an event receiver board(EVR) (MRF PXI-EVR-230), a DAC board (NI PXI-6733),
and a ADC board (NI PXIe-6356), which can set and monitor
output current up to 8 pulsed power supply independently
in 16 bit resolution with 1 MSa/s sampling or update rate.
They are placed in the same rack and connected by a metalcable.

DAC NI PXI- 6 7 33

㼠

ADC NI PXIe- 6 35 6㻯㼋㻸㼂Control and Monitor SystemController NI PXIe- 8 38 1

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Figure 10: Components of the fast control system.
For the slow data acquisition and interlock system, NIcompactRIO (NI cRIO-9063) unit is used. One unit consistsof a 32 ch 250 kSa/s/ch ADC module (NI 9205), a 32 ch
TTL digital I/O modules (NI 9403) and two 4 ch relay outputmodules (NI 9482). It covers 4ch of the pulsed power supply,
namely for one PXI express unit (8 ch), two cRIO units areneeded. To realize robust interlock system, cRIO is working
not in a scan engine mode but in a FPGA mode. On the upperlayer, EPICS CA server is running on the NI RT Linux. Not
only the PVs for the ADC and DIO data, but the PVs forthe high and low threshold, average number to control dataacquisition are also prepared which can be set and read using
EPICS CA protocol.

Trigger System
An EVR board in PXI form factor is used to integrate
the timing system to the linac timing system. In our linac,
event timing system by Micro-Research Finland Oy (MRF)
is adopted. The EVR receive not only the timing information
but also the mode number and shot ID. The mode number
is used to determine the next output setting. The shot ID isused to tag the monitored information. The trigger timing isprecisely (8.77 ns step) adjusted 3 ms before the beam arrival.
Since the rising and falling time of the magnet current is in
the order of ms, pules shape of the power supply does notimportant as long as the reproducibility is assured.

Stability
Figure 12 shows a stability measurement result of pulsed
power supply of quad magnet for 24 hours. Horizontal axis
shows the measured output current and vertical axis shows
the number of entry. Bin width is 0.2 mA Output current was
set to alternate between 0 A and 166 A at 50 Hz. Measured
mean value and standard deviation of the output current were
165.946 A and 14.578 mA respectively which corresponds
to 88 ppm (0.0088%) relative stability at this current. Thisis much smaller than design value (see Table 2).

PERFORMANCE EVALUATION
Efficiency
Power consumption of the pulsed power supply for quadmagnet was calculated and measured by a power meter(Hioki, PW3335). Blue bars in Fig. 11 shows calculated
power consumption from measured resistance and inductance of the magnet and cables when one magnet was operated at 300 A and 50 Hz without energy recovery. About
15% of energy is lost by ohmic heating of the coil and cablebut 85% are stored in the inductance of the coil. It is inprinciple possible to recover the latter part of the energy tocapacitors. Green bar in Fig. 11 shows measured power
consumption in total including DC power supply. The red
allow corresponds to recovered energy. The energy recovery
efficiency compared with stored energy in inductance andtotal energy are as high as 80.1% and 68.5% respectively.

Figure 12: A histogram of the stability measurement ofpulsed power supply for quad magnet.

OPERATION
After four months installation work from May, comprehensive test was done for a month in September in 2017. In
November, simultaneous injection using the newly installed
pulsed magnets were demonstrated successfully. Since theSuperKEKB phase two operation start from March in 2018
and light source rings restart in May, real simultaneous injection operation started in the middle of May and ended
July in 2018 for summer shutdown. During entire period,
there was no sever problem and the beam was delivered toall of the four rings stably.

CONCLUSION
Large number of DC magnets was replaced with new
pulsed magnets in 2017 for the pulse-to-pulse beam modulation for 4 storage rings. Two kinds of pulsed power supplies
for quad and steering magnet respectively were developed.
Installation and commissioning of the system were successfull and they are now working in the KEK electron positron
injector linac without any severe trouble for about 1 year.

REFERENCES
Figure 11: Energy balance of pulsed power supply for Q
magnet.

[1] M. Akemoto et al., “The KEKB Injector Linac”, Prog. Theor.
Exp. Phys., vol. 2013, pp. 03A002, 2013. doi:10.1093/ptep/ptt011

[2] Y. Ohnishi et al., “Accelerator design at SuperKEKB”, Prog.
Theor. Exp. Phys., vol. 2013, pp. 03A011, 2013. doi:10.
1093/ptep/pts083[3] A. Akiyama et al., “Accelerator Control System at KEKB andthe Linac”, Prog. Theor. Exp. Phys., vol. 2013, pp. 03A008,
2013. doi:10.1093/ptep/pts081[4] Y. Enomoto et al., “A New Pulse Magnet Control System in
the KEK Electron Positron LINAC”, in Proc. IPAC2018, Vancouver, BC, Canada, pp. 2121-2123, 2018. doi:10.18429/
JACoW-IPAC2018-WEPAK014[5] https://www.apexanalog.com/products/pa12.html