Proceedings of ICALEPCS2003, Gyeongju, Korea

FAST DATA-ACQUISITION SYSTEM FOR
THE BEAM-ENERGY-SPREAD-MONITOR
M. Satoh, T. Suwada, K. Furukawa
Accelerator Laboratory, KEK, Ibaraki 305-0801, JapanAbstract
A non-destructive beam-energy-spread monitor (ESM)
using multi-stripline electrodes has been developed inorder to measure and control the energy spread of asingle-bunch electron beam. In the KEK injector linac,
the non-destructive ESM has been installed at an 180degree arc section with a beam energy of 1.7-GeV. The
data-acquisition system of ESM was developed for pulseby-pulse measurement. This system works well and isused for a daily operation. In this paper, we will present
this DAQ system in detail.

Software
PC (Linux)

Python / Tkinter (GUI)(Oscilloscope,Data processing

C++/Linux / OS

Linac Control Network

INTRODUCTION

Oscilloscope

The KEK linac injects electrons and positrons into four
different rings (PF, PF-AR, KEKB-HER and KEKBLER). In a daily operation, a continuous beam tunning isvery important for keeping the beam injection rate high.
In the KEK linac, a screen monitor has been used as anESM. However, the beam injection cannot be carried out
during the beam measurement using a screen monitor
since it is a destructive beam monitor. To realize thecontinuous injection, we have developed and installed thenon-destructive ESM [1]. To acquire and process theanalogue signal from ESM, the high-performance DAQ
system is also needed. The most important requirement isa high-reliability for the long-term running.

DATA ACQUISITION SYSTEM
General Description
In the KEK linac, 90 strip-line-type beam-positionmonitors (BPMs) with 4-electrode have been alreadyinstalled and used stably for a daily operation [2]. Its
DAQ system consists of 19 oscilloscopes, 19 VME
computers and several server computers (hp Tru64 UNIX)[3]. The waveform digitized by an oscilloscope is sent toa VME computer via GPIB. After that, a VME computertranslates the voltage data to the beam position and beam
charge data. The calculated data is sent to a sharedmemory located in a server computer. Using this sharedmemory, many application programs can obtain the beam
position and charge data. The data taking speed of theoscilloscope used in this ordinary system is not very high,and it cannot get the data in 50-Hz. Since the ESM aimed
to be used for a fast beam-energy-spread feedback system,
its DAQ system was developed independently of ordinary
DAQ system. Schematic drawing of DAQ system isshown in Fig. 1.

527

DAQ System
Energy Spread Monitor (ESM)
Fig. 1: Schematic drawing of DAQ system.It consists of a
PC/Linux-based and a fast digital oscilloscope (LeCroywavepro-950).

Hardware
DAQ system developed here consists of a digital
oscilloscope and a PC/Linux-based. Any other analogue
and digital circuit is not used. Such simple system setup
can enhance the system reliability very much.
The eight signals from the ESM are divided by twosignal groups alternately (2x4 signals). The four signals ofeach signal group are sent directly to a signal combiner
through 35-m-long coaxial cables with suitable delaylines, which are required to avoid a superposition of theanalogue signals. The two combined signals out of thesignal combiners are directly connected to the digital
oscilloscope. The trigger pulses synchronized with thebeam are provided to the oscilloscopes at a maximum rateof 50-Hz cycle. This rate is applicable for communication
between the PC and the oscilloscope through an ethernet.
The PC receives the digitized waveform from theoscilloscope, extracts the eight-pickup voltages, andcalculates the beam positions, charge and the multipole
moments in 50-Hz via linac control network. It is evenpossible to observe two beam bunches separated 96-ns in
an rf pulse. In a practical operation, every average overlast 50 data is recorded into a log file. Using this log file,the analyzed data are displayed on any X terminals
through a trend display software.
To evaluate the system performance, the dataacquisition speed from an oscilloscope to a PC wasProceedings of ICALEPCS2003, Gyeongju, Korea

measured. Its result is shown in Fig. 2. In this test, twochannels of an oscilloscope were simultaneously
measured with 125-ps time resolution (8-GS/sec). For
single bunch operation, a signal width from ESM isapproximately 50-ns. Using a signal combiner, one
oscilloscope can operate about ten ESMs up to 50-Hz
operation. For two-bunch operation, one oscilloscope canoperate only two ESMs since a signal width is about 200ns with 100-ns bunch interval.
Max.
MinAverage

24
22module. Python-Mega-Widget (PMW) [5] and TkInterface-eXtension) [6] can also used for easy GUIconstruction. It can reduce the consumed time for theimplement of a complicated GUI. In addition, we can use
the numerical calculation packages for easy dataprocessing [7]. One example of software GUI is shown inFig. 3. In this case, upper and lower plot mean themeasured data of single bunch and two-bunch operationrespectively. In the lower plot, red and green dot show theenergy spread of 1st and 2nd bunch beam respectively.
Using this software, the energy spread can be always
watched. Before the extreme deterioration of energyspread, we can adjust the beam condition in order to avoid
a decrease of the beam transmission rate.

DAQ rate [ms]20181nC

1614

blue:energy spread

50Hz

121086010nC

100 200 300 400 500 600 700 800 900 1000

red: energy spread (1st bunch)green: energy spread(2nd bunch)

Signal length [ns]Fig. 2: Result of data acquisition speed. Square (red),triangle (black) and circle (blue) mean maximum,minimum and average data acquisition time.

TimeSoftware

Fig. 3: Software GUI

Software should work stably with high data taking
repetition. In addition to that, easy modification andextension of the software is strongly needed. For thesereasons, DAQ software was developed under PC/Linux.
The C++ was used for the main routine, which treats tocontrol an oscilloscope, transfer the data to PC, calculate
the energy spread and store data into a log file. The
reasons for using C++ are as follows:(1) High execution speed (compiler language)(2) High reusability (Object-Oriented language)(3) STL (standard template library) can be used.
In the practical operation, all signal pulses (up to 50-Hz)
are digitized, and the voltage amplitudes are calculated.
Using this amplitude, we can calculate the beam positions(horizontal and vertical) and the energy spreads of eachbunch. This software continues storing the data including
its standard deviation into a log file during beamoperation.
Python language is used for a graphical user interface(GUI) [4]. Python is an object oriented script language
and it can use a wealth Tk GUI component via Tkinter

528

BEAM TEST
Pulse-by-Pulse Measurement
Most advantage point of this DAQ system is able tomeasure every data up to 50-Hz beam repetition. We
measured the pulse-by-pulse variation of the beam-energy
spread for 1-nC single bunch and 10-nC two-bunch mode.
In this beam test, a series of 100-pulse beam wasmeasured. The measured data of 1-nC and 10-nC modeare shown in Fig. 4-(a) and (b) respectively. In this figure,solid (red), dotted (black) and broken (blue) lines mean
horizontal, vertical beam positions and energy spread,respectively. A standard deviation of this pulse-by-pulse
fluctuation is summarized in Table 1. Its result shows thatthe variation of energy spread increases as the beam
charge increases. It means that the beam-energy spread
due to the beam loading increases as the beam charge
increases.

Proceedings of ICALEPCS2003, Gyeongju, Korea

Horizontal position [mm]Vertical position [mm]
Energy spread [a.u.]

1 nC

2In this figure, filled circle (blue) and open circle (red)show the energy spread of 1st and 2nd bunch respectively.
It turns out that such long-term variation correlates withthe drift of the sub-booster klystron phase. Therefore,
controlling the sub-booster klystron phase can performthe energy-spread feedback.

12614
2
00-2
020

4060

80

1st bunch
2nd bunch

15

Energy spread [a.u.]

8

Energy spread [a.u.]

Beam position [mm]10-4100

Pulse No.

(a) 1-nC mode

1050-5

Horizontal position [mm]Vertical position [mm]
Energy spread [a.u.]

10 nC212-102003/02/2010
Beam position [mm]61420020406080

CONCLUSIONS-4100Pulse No.

(b) 10-nC mode
Fig. 4: Result of pulse-by-pulse measurement. (a) and (b)show the result of 1-nC (single bunch) and 10-nC (twobunch) operation modes respectively. Solid (red), dotted(black) and broken (blue) lines mean horizontal, verticalbeam positions and energy spread, respectively.
Table 1: Variation of energy spread
Standard diviationof beam charge

2003/03/10Fig. 5: Result of long-term mesasurement. Filled circle(blue) and open circle (red) show the energy spread of 1stand 2nd bunch respectively.

-20

2003/03/04

Date [yyyy/mm/dd]

Energy spread [a.u.]

82003/02/26

1nC

10nC

Magnification(10nC/1nC)

Horizontal position 0.247
[mm]

0.262

1.063

Vertical position
[mm]

0.077

0.101

1.32

Energy spread [a.u.]

1.800

2.603

1.446

Long Term Measurement
This DAQ system has been used for a daily operationof KEK linac since Feb. of 2003. It has works stably
without any trouble until now. Figure 5 shows the resultof the two-bunch energy-spread variation during 20-days.

529

The fast and stable DAQ system was developed for thenon-destructive ESM and used for a daily operation.
Simple system setup consisting of an oscilloscope and a
Linux/PC can realize a high reliability, which is strongly
needed for a practical beam operation. It can also realize
the two-bunch simultaneous measurement up to 50-Hz
beam repetition. The beam-energy-spread feedback using
this DAQ system is under development, and its result will
be presented in the elsewhere.

REFERENCES[1] T. Suwada, et al., “Nondestructive beam energyspread monitor using multi-strip-line electrodes”, Phys.
Rev. ST Accel. Beams 6, 032801 (2003).
[2] T. Suwada, et al., “Stripline-type beam-positionmonitor system for single-bunch electron/positronbeams”, Nucl. Instrum. & Methods. A 440 No.2
(2000) pp.307-319.
[3] N. Kamikubota, et al., “Data Acquisition of BeamPosition Monitors for the KEKB Injector-Linac”,
Proceedings of ICALEPCS’99, Trieste, Italy, October
4-8, pp.217-219 (1999).
[4] http://www.python.org/[5] http://pmw.sourceforge.net/[6] http://tix.sourceforge.net/[7] http://www.pfdubois.com/numpy/