EPICS IOC OF WINDOWSXP-BASED OSCILLOSCOPE FOR FAST BPMDATA ACQUISITION SYSTEM
M. Satoh#, T. Suwada, K. Furukawa, Accelerator Laboratory, High Energy Accelerator Research
Organization (KEK), Ibaraki 305-0801, JapanY. Hu, Brookhaven National Laboratory, Upton, New York 11973, U.S.A.
T. Kudou, S. Kusano, Mitsubishi Electric System & Service Co., Ltd, Ibaraki 305-0045, Japan

Abstract
The KEK Linac is a 600-m-long injector that delivers
electron/positron beam to the four independent rings. The
non-destructive beam position monitor (BPM) is anindispensable diagnostic tool for a long-term stable beam
operation. In the KEK Linac, around one hundred BPMs
with the four strip-line type electrodes are used for thebeam orbit measurement. The beam orbit data is used forthe beam orbit and energy feedback loops. The previous
BPM data acquisition (DAQ) system consists of a VME
CPU and a digital oscilloscope, and it has been installed
more than decade ago. Although the maximum linac
beam repetition rate is 50 Hz, the maximum DAQ rate ofprevious system is about 1 Hz limited by an oscilloscope
performance.
Recently, we have started a fast beam-mode switch
operation aiming the simultaneous injection between
KEKB and PF rings, in which the fast beam position
measurement of 50 Hz is strongly required. For thispurpose, we developed a new BPM DAQ system using a
WindowsXP-based fast digital oscilloscope. In this paper,
we will present the system description of the new DAQ
system and the results of performance test in detail.

INTRODUCTION
The KEK Linac sequentially generates the beams in
different modes and delivers them to the following fourstorage rings: a KEKB low-energy ring (LER; 3.5
GeV/positron), a KEKB high-energy ring (HER; 8GeV/electron), a Photon Factory ring (PF ring; 2.5GeV/electron) and an Advanced Ring for pulse x-rays(PF-AR; 3 GeV/electron). So far, a beam injection to thePF ring and PF-AR has been carried out twice a day,whereas the KEKB rings are operated by a continuous
injection mode (CIM) so that the stored current is kept
constant. During the CIM operation, the linac beammodes are frequently switched so that the all settings ofmagnets, rf phases and timings are changed according tothe HER and LER beam injection. In the typical CIM
operation, the linac parameters are frequently changed inevery 30 s.
For increasing the stored current stability, the faster___________________________________________#masanori.satoh@kek.jp

lianc beam-mode switch between LER and HER isstrongly desired. In addition, the PF top-up injection is
also strongly required even during the KEKB CIM
operation. For these reasons, the injector upgrade project
has been started since 2004 so that the PF top-up neverinterrupts the CIM of KEKB [1, 2, 3]. This upgrade wasachieved in April 2009. Recently, the linac beam can bedelivered to the different rings in every 20 ms interval.
For the simultaneous top-up injection between PF and
the KEKB rings, a higher-performance new BPM DAQ
system is strongly required since the beam position
measurement should be carried out in pulse-by-pulse of50 Hz. For this purpose, we developed the new BPM
DAQ system and replaced all previous system by the newone.

BPM DAQ SYSTEM,System Overview
For a higher availability of beam operation, many kindsof feedback loops have been developed and utilized tostabilize the beam orbit, energy and energy spread [4, 5,6]. These feedback loops make use of the beam position
information acquired by the non-destructive BPMs [7].
About one hundred stripline-type BPMs have been
installed in the KEK Linac.
The twenty front-end systems have been installed in thelinac klystron gallery at a nearly equal interval along thebeam line. The each DAQ system deals with theanalogue signals of 3 to 12 BPMs. A schematic drawing
the former DAQ system are shown in Fig. 1. It consistsof a VME computer (OS-9 operating system with a 68060
microprocessor of 50 MHz), a digital oscilloscope(Tektronics TDS680B/C; 5 GSa/s, 2 channels, 8 bits) as a
waveform digitizer, and two signal combiners in a cablecombiner box.
The four signals coming from one BPM are fed to two
signal combiners (vertical and horizontal) together withthe signals from other BPMs.
The delay cables
corresponding to a 7 ns time delay are used to avoid
waveform overlaps at the signal combiners. The two
combined signals are digitized by an oscilloscope at asampling rate of 5 GSa/s. The digitized signals areMonitor Station

Linac Network

Digital Oscilloscope (5GS/s)
VME/ OS9yx

GPIB

Cable Combiner Box
8ch-Combiner

8ch-Combiner*Klystron Gallery
Linac Tunnel* Delay Cable (7-ns)

BPM

Figure 1: Schematic drawing of the previous BPM DAQsystem.
analyzed by a VME CPU in order to deduce the beam
parameters (beam charge, horizontal position, verticalposition), taking into account the calibration coefficients.
The trigger pulse signals, which are synchronized withthe linac beam, are provided to all DAQ systems at 0.7 Hz.
These signals are used to start the data taking cycle of theeach DAQ system. The trigger rate is limited by theGPIB communication throughput between the VME
computer and the oscilloscope.

New System
We adopted a WindowsXP-based fast digital
oscilloscope (Tektronix DPO7104; 10 GSa/s, 4 channels,
8 bits, CPU P4/3.4 GHz, Gigabit-Ethernet) as a new BPM
DAQ system. Its photograph is shown in Fig. 2. In thenew DAQ system, a VME computer and an oldoscilloscope was replaced by a fast digital oscilloscope asshown in Fig. 3. In the new system, CH1/CH2 andCH3/CH4 are used for the low charge modes and the highcharge mode, respectively since it is impossible to change
the vertical scale of oscilloscope in every 50 Hz
Because the Experimental Physics and Industrial
Control System (EPICS) has been utilized for the KEK

Figure 3: Schematic drawing of the new BPM DAQsystem.
Linac control system, we developed the EPICS
Input/Output Controller (IOC) for the new DAQ system
by using Microsoft Visual Studio 2005 C++ (MSVSC++),
TekVisa and EPICS R3.14.8.2 libraries. The new DAQ
software is running on the fast oscilloscope, and the eachoscilloscope can work as EPICS IOC.

PERFORMANCE TEST
Evaluation of DAQ Performance
We evaluated the speed performance of waveform
signal acquisition. The test software was also developedby MSVSC++, TekVisa and EPICS R3.14.8.2
environment. In this test, we changed the number of usedoscilloscope channels from one to four and the waveform
length from 1 k to 500 k data points independently. The
test software was carried out on the oscilloscope. During
all performance tests, the display update functionality ofthe oscilloscope was disabled for enhancing theperformance of DAQ speed, and the rectangle shaped
waveform of 15 MHz was used for an external trigger
350

Ch1Ch2Ch3Ch4DAQ speed (Hz)300
250200150100500050 100 150 200 250 300 350 400 450 500

Data length (k-points)
Figure 2: Photograph of the new BPM DAQSystem.

Figure 4: DAQ performance of the fast digital
oscilloscope.

signal.
Figure 4 shows the results of performance tests. The
dotted lines mean the DAQ speed averaged over 100
times measurements for the corresponding number ofused channels. The simultaneous acquisition of twochannel signals about 20 k data point length is needed forthe practical beam operation. From Fig. 4, it corresponds
to the DAQ speed of around 150 Hz. Even taking into
account the computation time, we confirmed that the new
DAQ system has enough high performance for the 50 Hz
beam position measurement.

Beam Test and Beam Orbit Display Panel
The beam test using the new DAQ system was carriedout for confirming the long term system stability. For thisbeam test, we used the BPM data of SP_R0_42 installedin the arc section and the beam mode patterncorresponding to the KEK electron (1 nC), KEKB
positron (10 nC) and PF electron (0.1 nC) mode
combination, in which the beam mode is switched inevery 20 ms interval. The test result of two hours beam
charge measurement is shown in Fig. 5. In this figure, thered, blue and black dots mean the measured beam chargeof KEKB electron, positron and PF modes. From thisresult, it was confirmed that the new system can work
properly up to 50 Hz beam measurement.
Figure 6 shows the example of beam orbit display panel
developed by using Python script language. During thedaily beam operation, the three different panels are

Figure 5: Test results of two hours beam charge
measurement.

Figure 6: Example of the beam orbit display panel.

launched, and each of them shows the beam position andcharge information corresponding to the specific beammode.

SUMMARY AND FUTURE PLAN
The KEK injector linac upgrade was carried out for thesimultaneous operation between the KEKB CIM and thePF top-up. For this purpose, a BPM DAQ system
upgrade is strongly required for the fast beam position
measurement up to 50 Hz since the previous DAQ system
has about 1 Hz data acquisition performance. We
developed the new BPM DAQ system by using aWindowsXP-based fast digital oscilloscope, and each ofthem can work as EPICS IOC.
All old DAQ systems have been already replaced bynew one. The new system is stably utilized for the daily
operation up to 50 Hz measurement. A similar system
was also developed and utilized for the BPM DAQ
system of KEKB beam transport [8]. In the near future,
we will study the correlation between the fast fluctuationof beam position and other parameters like rfphase/amplitude, and its results will be presentedelsewhere.

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