JAERI-Conf 95-021

PA51
Stability study of ATF 80MeV injector linac
T. Naito, H. Hayano, H. Matsumoto, J.Urakawa,
M. Ross*, K.Jobe*, D. McComick*
KEK, National Laboratory for High Energy Physics,
1-1 Oho, Tsukuba-shi, Ibaraki-ken, 305 Japan*Stanford Linear Accelerator Center(SLAC),
Stanford, California 94309, USA
length using a streak camera and a photomultiplier(PMT ) with a scintillator which measure abearri loss.
In order to produce a stable beam at the injector
is a key issue for a stable operation of ATF. 4% of thefluctuation of beam intensity at the injector ismeasured which should be reduce to less than 1%. In
order to investigate a source of the fluctuation, the test
was performed by acquiring the pulse to pulse datafrom each monitors in each position. The dataacquisition system consist of a PC and a GPIB
network which connect between the PC and the dataacquisition devices. The acquired data are treatedstatistically and analyzed by 'Correlation plot'. The
correlation coefficient which is evaluated in thecorrelation plot exhibits a strength of connection ·between the two measured quantities. This technique
is used at SLC beam tuning.2)

Abstract
A beam stability test was carried out at ATF
SOMeV injector linac. The test was performed bytaking data of each monitor in pulse to pulse base. A
data acquisition system which consists of a PC and aGPIB network was used for the test. In order toanalyze the data, 'Correlation plot' method is usedwhich is effective to find out some source of theobserved the beam fluctuation. This paper describes
the result of the stability measurement and thecomparison between ATF injector and SLC injector.
1. Introduction
The Accelerator Test Facility(ATF) consists of a
1.5 GeV linac and a damping ring which is underconstruction in KEK.1) .The purpose of the ATF isdevelopment of accelerator components to realize
future Linear Collider. The injector part of the linac
consists of a thermionic gun, two SHBs(357MHz ),seven cells of buncher following to a 3m long Sband(2856MH z) accelerating structure(AS). Theenergy of beam is 80MeV at the exit of the AS when
60MW of RF power is fed into the AS. The diagnosticsof the injector are an amorphous core currenttransformer(CT ), an integrated current transformer(ICT), wall current monitors(WCM s), beam position
monitors(BPM s), florescent screen profilemonitors(PRMs ) which measure the beam size andthe relative position, optical transition radiation
monitors(OTRM s) which measure a bunch by bunch
beam profile using a fast gate camera and a bunch

2. Data acquisition system
System configuration
The configuration ofthe data acquisition system isshown in Fig. 1. Two scopes for electrical pick up
signals, a streak camera for bunch length
measurement and a pulse generator for generating asystem trigger signal, are connected to a PC througha GPIB network. A video analyzer for the energy andthe energy spread measurement at PRM4 not yet
have the interface software. The beam trigger signal
starts the beam emission of the electron gun which is
distributed to each acquisition device as theacquisition trigger signal in order to acquire at same

PMTAce. Structure
PRMS{OTR)

PRM3i Beam trigger"""[[]/////t~~)J

I

Transformer(CT)D CUrrent
Integrated Current Transformer(ICT)
Wall Current Monitor(WCM)~Beam Position Monitor(BPM)
Profile Monitor(PRM)---,···-

Fig 1 ATF injector linac and acquisition system

171-JAERI-Conf 95-021.

cil • •l--+----1f---t--o•••••.•

1

7.1

Acc.phase(dog.)timing. The acquisition sequence is following, thepulse generator generates a single pulse for _thesystem trigger by the software, the other devices
acquire each points of monitors at same timing, theacquired data are recorded to the PC and then thepulse generator generates a next single pulse for next
data acquisition. For each test, 100 data are recordedand used for the analysis. The acquisition speed was
5-10 sec. per data. The size of data was 10k-20kbytes
per data. The software used in this system are VEE
for the GPIB control and MATLAB for the dataprocessing and analysis.

e) RF phase: The RF phases of two SHBs and a AS aremeasured by a mixer at the output level of <!>crossing.
f) Beam energy and energy spread: The PRM4(0TR)
is located after a 90 degree bending magnet. The
horizontal position and width of the profile show
the beam energy and the energy spread. The video
analyzer acquires the video signal and calculates
the projection of the profile. 3)g) Bunch length: The light from the PRM5(0TR) is
fed to feed to a streak camera. 4) The bunch lengthis measured by the projection of the sweeped imageof the light.

Monitoring beam signals.
Following signals were used for the test.
a) Gun high voltage: The gun use a pulsed highvoltage of 3 J.Lsec which is made by a PFN and athyratron circuit. The fluctuation of this voltage
will affect to the beam intensity and the beam optics
directly.
b) Beam intensity : The CT and the WCMs measure
the micro-pulse of beam intensity. The ICT
measure the total beam intensity of multi-bunch.
c) Beam loss: The PMT detects the beam loss at thedown stream of the accelerating structure.
d) Beam position: The signals from BPMs arestretched by the head amplifiers and recorded its
wave forms. The beam position are calculated byusing the peak amplitudes which are estimated bypolynomial fittings for the sample hold points of thescope. The sum of the opposing electrode signals is
proportional to the beam intensity approximately. ······ -The beam parameter for the test werefollowing, beam mode: single bunch, charge number-1.5 x 1Q10 electrons, beam energy: 80 MeV. None ofmachine parameters were changed during each test.
Signal distribution
The examples of the signal distribution are
shown in Fig.2. Fig.2a), b), c) show the distribution ofRF phase of SHB1(SHB1<!>), R)f phase of AS(AS<!>) andbeam intensity by ICT, respectively. The sigma valuesof the fitted gaussian distribution were SHB1<!>:0.16deg., AS$: 0.78deg., ICT: 4%. Some data points
which were deviated from the main distribution wereobserved in the phase distribution of SHB 1. It's
assumed to the possibility of discharge at inside of the9406

o.ooc 51SS. R· 0.1 151

f--y •16616 + 0.00828CJ-··•..

x R.. 0.4 244·····1--+=--+-+--+---1... :

0.041

.....
O.UI

I,UI

3.Result

0,41

• 0.

O.U4...!.!

Fig. 2c) Beam intensity distribution

Fig. 2b) AS<!> distribution

Fig. 2a) SHB1<!> distribution

55.5....._·_. . ..
•·••• l----;;-f-':......,-J;-!7--+--+---1.

-:'--~,.

·.

6.5
7accph(deg)

::;

~ o.u

····l---f--!..,...!-j7.....~',.;:.'--t---j... : ..

-~ ... ~~

O.UI

7.5

.....,.. ·p.ms • 1.686x R- 0.90135

8.5

Fig. 3a) AS<!> -ICT correlation

·..

..

·.··.·~
1--+---f-"7--t---'--t--"'"-10'131 15... 7I

15.1

15.2

15.3

15."

15.5

SHB phase

Fig. 3b) SHB<!> -ICT correlation- 172-d....
.
v'·'
a.a.ua.o"0.04

y0.041

1.0440,141

ICTFig. 3c) ICT-BPMsingle correlation

JAERI-Conf 95-021

cavity.
Correlation plot
The examples of the correlation plot are shownin Fig.3. Fig.3a), b), c) show the correlation plot of
AScp-ICT, SHB1cp-ICT and ICT-BPMsingle signal.
The correlation coefficients were 0.12, 0.40 and 0.90,respectively. A correlation of 0.2 or lower is hard tofind out the causality. Correlation of 0.3 or more areassumed to be the causality between two observed
quantities. In the case of Fig.3c), the beam intensity
monitored two different monitors exhibits a strong
correlation.
Same measurement were repeated for eachsignals. The result are summarized in table 1 and 2.
The tables are presented in the form of correlation
coefficients matrix with one-sigma of the distribution
in the diagonal. In the table 1, correlation can be seen
between SHB2cp-BPMposition and SHB2cp-BPMsum. No
other correlation except for between the same physicalvalue. It's assumed that the change of the RF phase ofSHB2 affect to the beam position and the intensity.
4.SummaryThe stability of ATF injector is compared to thestability of SLC injector in table 3. The ATF data is
two times to several times lager than the SLC data.
The one of reason come from the noise from klystron
modulator. The small correlation coefficient wasobserved even between two current monitors that is aevidence of the noise· effect. The noise cure issignificant problem to realize the stable beam at ATF.
The unexpected distribution of RF phase ofSHBs were observed in the result. The fluctuations
were assumed to be correlated to the beam current
and the position. The after the test, we could find theevidence of the discharge at the vacuum shieldceramics of the couplers when open the cavities.
5. Acknowledgment
This study was executed in a framework of an
exchange program of SLAC and KEK collaboration.
We would like to express our thanks to Professors
Y.Kimura and K.Takata for their encouragement. We
also thank other members of ATF group and Mr.
S.Morita of ATC Corporation for their support.
6. References
1) F.Hinode et al, "ATF Design and Study Report",
KEK Internal 95-4, June1995
2) L.Hendricson et al, "Correlationplot Facility in the.SLC Control System", SLAC-PUB-5464 May 1991
3) T.Naito et al, "Bunch by bunch beam monitor for
ATF injector linac", Proc. of the 17thInternational Linac conference, Aug. 1994, KEK94-102(1994)
4) H.Hayano et al, "An 80MeV Injector for ATF
Linac", Proc. of the 17th International Linac
conference, Aug. 1994, KEK 94-110(1994)

Tablel. example of correlation coefficients and one-sigma distribution.
(SHB2 0 BPMs streak camera)
'SHB2
BPM8
BPM8
BPM9'Streak sig Streakphasepossumsingleinteg.
port.06deg
SHB20.34
BPM8 position
94j.l.m
-.67
0.8%
-.21
BPM8 sum-.33-.86.86
1.7%
BPM9' single.06.17-.09-.12
Streak sigma
14%
width.10.02
-.05
-.01
15%
-.62
Streakintegration.
Tablel. example of correlation coefficients and one-sigma distribution.
(AS0 SHB10 WCM BPM E dE/E)' WCM4'' ' BPM6AS 'SHB1
Energyphase
phase
singleport.47deg
AS00.06
O.lldeg.
SHB10
0.079
0.068
2.3%
WCM4
0.25
0.11
•BPM6 single port 0.094
2.9%
O.Q15
0.095
0.077
0.044
0.086%
Energy
0.017
0.057
0.21
0.092
0.1
dElE

dElE

13%

1 1ty of each components of ATF an dS LCTa bl e 3 companson of t h e stabT
ATF
SLC

AS phase
0.5-2 deg.07deg

SHB1 phase SHB2 phase Gun HV
0.16-0.4deg 0.11 deg
0.07%
0.02 deg
0.03 deg
O.Ol%DC- 173-BPMx
20-100j.i.m
15j.i.m

BPM sum
1%
0.5%