Proceedings of IBIC2012, Tsukuba, Japan

MOPA28

TURN-BY-TURN BPM SYSTEM USING COAXIAL SWITCHES AND ARM
MICROCONTROLLER AT UVSOR
Tomonori Toyoda, Kenji Hayashi, and Masahiro Katoh, IMS, Okazaki, Japan
Abstract

Table 1: Main Parameters of UVSOR-III

A major upgrade of the electron storage ring at
UVSOR facility (Institute for Molecular Science, Japan)
started from April 2012. To assist the commissioning
procedure, we have developed a turn-by-turn Beam
Position Monitor (BPM) system which consists of asignal switching circuit, a digital oscilloscope andsoftware. Using this system, we have been able todetermine not only the orbit but also the betatron tune.
The system was very powerful to achieve the beamstorage at the commissioning.

Electron Beam energy

750MeV

Circumference

53.2m

Straight Sections

4m x 4, 1.5m x 4Emittance

17nm-radEnergy Spread

5.4m x 10-4

Betatron Tunes(3.70, 3.20)

Momentum Compaction Factor

0.033

OUTLINE OF UVSORXY Coupling(presumed)

3%

A 750 MeV synchrotron light source, UVSOR (Fig. 1),
has been operational since 1983. In 2003, the ring had amajor upgrade to reduce the emittance and increase thestraight sections available for insertion devices. Since
then, the ring has been called UVSOR-II. Since 2010, thestorage ring had been operated for users fully in the topup injection mode, in which the beam current is kept
constant at 300 mA.

RF Accelerating Voltage

100kV

RF Frequency

90.1MHz

Figure 1: UVSOR-III electron storage ring.
In 2012, a new upgrade program is in progress. The
bending magnets were replaced with combined-function
ones to reduce the emittance by about a factor of two. A
new in-vacuum undulator was installed in the last straightsection reserved for insertion devices. A pulse sextupole
magnet for injection without a bump orbit wasconstructed and is ready for commissioning. After thisupgrade, the ring is called UVSOR-III. Parameters ofUVSOR-III are shown in Table 1.

Figure 2: Layout of the BPM heads along the ring.
Position of the electron beam is calculated using theequations:

X = KX

VA − VB − VC + VD
VA + VB + VC + VD

(1)ISBN 978-3-95450-119-9
Beam Position Monitor System

1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○BPM AT UVSOR
UVSOR-III storage ring has 24 BPMs (Fig. 2), each ofwhich consists of 4 button electrodes (Fig. 3 and 4). We
use a commercial signal processing system (Bergoz Co.
[1]) for regular operation.

MOPA28

Proceedings of IBIC2012, Tsukuba, JapanY = KY

VA + VB − VC − VD
VA + VB + VC + VD

(2)

Here Kx,y is the sensitivity parameter, VA,B,C,D is theelectric voltage induced by the electron beam at eachelectrode. The Kx, Ky, are listed in Table 2.

c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Figure 3: Electrodes of BPM.

DESIGN AND CONSTRUCTION OF
TURN-BY-TURN BPM SYSTEMAt the commissioning, especially before success ofbeam storage, we have to find out how many turns thebeam has circulated, where the beam has lost. It is also
important to measure the orbit parameters before thestorage, such as closed orbit or betatron tunes. Most ofthese can be realized by a turn-by-turn BPM system. On
the other hand, such a system is not necessary in the daily
operation. Considering these, we have decided toconstruct a turn-by-turn BPM system as follows.
• We construct it as low-cost and simple as possible.
• We use an existing digital oscilloscope for waveform
observation and recording.
• We use existing RF cables that are normally used forconnecting the BPM heads and Bergoz signal
processing system.
• We set the oscilloscope in the ring and we control it
through LAN.
• We develop a signal switching box that can becontrolled through LAN.
The block diagram of the system is shown in Fig. 5.

Figure 4: Layout of electrodes.
Table 2: Position Sensitivity (Kx, Ky) of Electrodes
Bending section

Straight section

Kx (mm)

12.89

13.61

Ky (mm)

41.84

26.6

The characteristics of the cable (FHPX-5D (1/4”),
Hitachi Cable) used between the electrode and theelectronics are shown in Table 3, 4. This cable ismanufactured with deep helical corrugations in the outerconductor for flexibility, and has a foam-polyethylene
dielectric that offers good electrical performance. This
coaxial cable is used in normal BPM system.
Table 3: Characteristics of Coaxial Cable [2]Frequency

Attenuation (dB/100m)

100MHz6.04

1000MHz

19.8

Figure 5: Block diagram of BPM system.

OVERVIEW OF SIGNAL SWITCHINGBOX
The signal switch box is shown in Fig. 6 and 7. The
total number of the BPM electrodes in UVSOR is 96, but,as the first step, we have constructed a system in which
only signals from 8 BPM heads can be treated.
Since the BPM signal is a weak (tens of mV to submV) high-speed pulse (hundred ps bunch length
corresponds to several GHz in frequency region) byelectron beam circulating about 90 MHz, we have usedcoaxial switches (CCR-33-506 and CCR-38, TELEDYNE
COAX SWITCHES) to switch signals at low attenuation.
We had also considered using semiconductor switches.
However, as shown in Table 5, since generally losses ofcoaxial switches were less and wider frequency bands
than those of semiconductor switches, we decided to use
coaxial switches.

ISBN 978-3-95450-119-9
2Beam Position Monitor System

Proceedings of IBIC2012, Tsukuba, Japan

MOPA28Figure 6: Signal switching box (front view).

We decided to control the coaxial switches by amicrocontroller, which can be controlled remotelythrough LAN.
There are a variety of microcontroller products, withsome differences in CPU, clock frequency, the numberand type of peripherals, and the number of pins. This time,
we have adopted ‘mbed’.
The ‘mbed’ is the ARM microcontroller development
kit by NXP semiconductors. ARM microcontroller is ageneric term of a microcontroller core design information(IP: Intellectual Property) of the ARM company in UK.
Semiconductor companies sign licensing agreements with
ARM company, product and sell ARM microcontrollers
by adding original peripherals [4]. The ‘mbed’ has avariety of functions shown in Table 5 with Cortex-M3
core, which is one of the 32 bit ARM microcontroller. We
connect the ‘mbed’ to a PC with USB, transfer theprogram that we have developed.
We program the ‘mbed’ with C language. The
Integrated Development Environment (IDE) of the ‘mbed’is on the Web server and run on a Web browser. In thisenvironment which is generally called to ‘Cloud
Computing’, we can develop regardless of Operating
System of PC if we have an internet connection [5].
Table 5: Key Features of the ‘mbed’ [6]Figure 7: Signal switching box (inside).
Table 4: RF Parameters of Coaxial Switches [3] andCertain Semiconductor SwitchProductsFrequency

Insertion Loss(max)CCR-33-506

DC-6GHz

0.2dB

CCR-38

DC-6GHz

0.2dB

Semiconductor

DC-2.5GHz

3.8dB

First, we select 4 X 4 = 16 from 8 X 4 = 32 BPM
signals by SPDT (Single-Pole Double-Throw) type
coaxial switch. Next, we select 1 X 4 = 4 by SP4T(Single-Pole 4-Throw) type coaxial switch. We record 4signals from one BPM head by 4-channel digital
oscilloscope (5GHz sampling frequency, 1GHz / 2GHz
analog signal band) while selecting the BPM heads one
by one. The data was analysed off-line.

CPUARM Cortex-M3

Processing speed

100MHz, 120MIPS(max)Memory512kB Flash ROM, 64kB SRAM

Ethernet

10/100BASE-T

USB

USB2.0 OTG

A/D converter

12bit X 8

D/A converter

10bit

The ‘mbed’ can be connected to LAN by simply
connecting to the LAN connector. The device control
through LAN often requires expertise, such as TCP/IP, but
the control application for the BPM system wasconstructed in HTML (and CSS) which implements
JavaScript library that can handle multiple I/O ports. Inother words, we can construct it like a general web page.
First, we store necessary files for the ‘mbed’. When weaccess the ‘mbed’ from the web browser, the ‘mbed’
responds as HTTP server, a control application isdisplayed in web browser. By using the application, wecan control the coaxial switches by controlling I/O portsof the ‘mbed’ via JavaScript library.

PERFORMANCES
An example of the observed BPM signal waveform isshown in Fig. 8 . An example of injection beam trajectoryis shown in Fig. 9. The data are simply processed by Eqs.
ISBN 978-3-95450-119-9
Beam Position Monitor System

3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○REMOTE CONTROL OF SWITCHINGBOXMOPA28

Proceedings of IBIC2012, Tsukuba, Japan(1) and (2), using the peak voltage obtained from thewaveform as shown in Fig. 8, and no compensation for thenon-linear responses is applied.

position data also should depend on the mismatch of thelengths of each cable for 4 electrodes.

c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Figure 8: An example of BPM signal waveforms froma BPM head.

Figure 10: Measured beam position for first three turns
after injection.

Figure 9: An example of measured injection beam
trajectory.
The betatron tune could be also determined byobserving multi-turn orbit. At present, Ȟx is 3.7 and Ȟy is3.2 (Fig. 10). This was very useful during thecommissioning.
An example of accuracy check is shown in Fig. 11 using
a stored beam. The fluctuation is typically around submillimeter, whereas periodic fluctuation is clearly seen.
The period is 5 turns, and this is simply due to the factthat beam revolution period is not integer multiple of thesampling period of oscilloscope. Divergence in theFigure 11: Turn-by-turn BPM data of the stored beam.

ISBN 978-3-95450-119-9
4Beam Position Monitor System

MOPA28

CONCLUSION AND FUTURE PLAN

REFERENCES

We have developed a turn-by-turn BPM system asswitching the BPM signals through LAN with coaxial
switches and the ‘mbed’. It was demonstrated that thesystem was very powerful to achieve the beam storage atthe commissioning.
We have some following future plans to improve theBPM system.
First: Improvement of accuracy by adopting advanced
data processing to extract more exact peak of waveform
and improve the accuracy of beam position.
Second: Expansion of the switching system to deal with
24 BPMs. Another switching system to switch signals toordinary BPM or turn-by-turn BPM.
Third: Full automatic and fast data acquisition and fully
automated data processing.

[1] http://www.bergoz.com.
[2] “HITACHI HIGHLY FOAMED POLYETHYLENE
DIELECTRIC HIGH FREQUENCY COAXIAL CABLE”,p.5,
7,
HitachiCable;
http://www.hitachicable.co.jp/catalog/T302.pdf.
[3] CCR-33 Series and CCR-38 Datasheets, TELEDYNE
COAX SWITCHES; http://www.teledynecoax.com.
[4] Shuu Nagahara, “Why 32bit?”, Transistor Gijutsu Vol.48
No.558, p.73, CQ Publishing (2011) (in Japanese).
[5] Yoshikazu Okada, “Fundamentals and application
productions of ‘mbed’ programming”, “Thorough researchof latest ARM / Cortex microcontrollers”, p.5, CQ
Publishing (in Japanese).
[6] “AppendixAHigh-performancemicrocontroller!
specification of ‘mbed’”, “Introduction of ultra-handy
microcontroller ‘mbed’”, p.116, CQ Publishing (inJapanese).

ISBN 978-3-95450-119-9
Beam Position Monitor System

5c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Proceedings of IBIC2012, Tsukuba, Japan