JAERI-Conf 95-021

PA45
RADIAL AND VERTICAL BETATRON OSCILLATION FREQUENCIESOBSERVED BY A SCINTILLATION PLATE AND A THREE WIRETOMOGRAPHY MONITOR
T.ltahashi, K.Hosono, K.Hatanaka, !.Miura, T.Saito, A.Shimizu, K.Tamura,
K.Takahisa, T.Yamazaki, S.Ano, M.Kibayashi, H.Tamura and M.Uraki

Research Center for Nuclear Physics, Osaka University
Abstract
We report here diagnostic measurements ofaccelerated protons of 400MeV in RCNP Ring
Cyclotron.
!.Introduction
To clear the problems on the extracted beam
qualities concerned with accelerated beam
dynamics in RCNP Ring Cyclotron[!] , wedeveloped a beam viewing system with TV
camera and a phosphor covered scintillation
plate. It enable us to take a continuous picture ofbeam position and size in full radius ofacceleration. The scintillation plate is mounted in
front of the copper beam stopper of the mainprobe head. From these measurements, we candeduce the vertical and radial oscillation
frequencies in each radial positions.
2. T.V. camera and scintillation plate
The phosphor plate which has scintillating
surface obtained by sprayingZnson an aluminum
plate(lmm thickness) is mounted in front of thecopper beam stopper( on the main probe head for
an integral current monitor). The viewing ports
for this is set at the valley region beyond the one
sector magnet from the main probe location. TheT.V. monitor camera outside the vacuum chamber
views the inside mirror inclined 45-degree to themedian plane of the accelerator. In order to lookover the whole view for the radial range of themain probe, the setting of the mirror and T.V.
camera should be changed several times. One
measurement for that radial range is about
600mm. The scintillation plate on the main probemoves at the speed of 20mm/sec by taking apicture for the monitor TV with POLAROID
camera at B-mode. The observed verticaloscillation is shown in Fig. 1.
3. Main probe
A main probe measures the current and thetransverse shape of the beam in the Ring
Cyclotron. It consists of a tomography head ofthree thin platinum wires and an indirectly cooledbeam stop. The probe can be adjusted for theprobe head to face the tangential direction of thebeam orbit at any radius. The driving speeds canbe chosen between 20mrnlsec and 200mm/sec.
At the beam tuning, the current measured withthis probe is about 1OnA. Thus the efforts to getgood signal to noise ratio for weak beam current
down to lnA are being made. A 30 Hz 5thorder(30dB/Oct.) low pass filter is used.
Moreover, the attenuation of 30dB for 60Hz was

Fig.l. Observed vertical oscillation- 153-

JAERI-Confachieved by using an integrated circuit ofswitched capacitor filter LTC1062.
4.Results and discussion(1) Both from the observed pattern for thevertical beam oscillation and from the recorded
turn numbers obtained with the three wire
tomography monitor, we can deduce the tum
numbers in each oscillation cycle. Thus, there are
two results when the cycle is estimated from thesuccessive top peak positions or from the bottom
peak positions in the observed figures. Specified
radial length in Fig.2. shows this oscillationintervals and specified ones are described at themiddle of the cycle in the radial axis. The
betatron oscillation frequency can be estimatedfrom the reciprocal number of turns in this cycle
plus one. Less than about 1500mm in radial, thepattern of tomography monitor can bedistinguished in tum by turn, although some ofthem are a little overlapped each other which
introduced more errors.
With these· procedures, we can obtain
vertical betatron oscillation frequency at eachradial intervals as shown in Fig.2.

95-021

turn of the radial spectra observed with verticalwire of the tomography monitor from injection to
the distinguished turn about 1600mm where wecan put the turn number 260-revolutions. Thus,
we plotted dr separation to this revolution
numbers. It shows oscillatory pattern with aincrease of the radial position as shown in Fig.

3.

dr....
drdr......
1.1-100

110

120

uo110

TURN NUMBER

Fig.3. Measured dr separation in eachacceleration tum

1.05

to o':--------'-----1-'-o'o_ _ __.__ _ _zo.. .jo
R(cm)Fig. 2. Deduced vertical oscillation frequency(2) We assume that the betatron oscillation ofthe beam is enhanced with miss matching in theinjection to the Ring Cyclotron and purely
introduces the unequal separation in successive
turns. Thus, we measured dr separation in each

Between the successive dr maxima or dr
minima in this figure we can measure the tum
numbers in the one cycle from which weestimated radial betatron frequencies. Over the1OOOmm in radius the figure shows an irregularpattern mixed with two or three cycles ofoscillation intervals. Even taking into account theregular increase of the radial betatron oscillation
frequency, the observed structure was somewhat
disturbed with several processes such as unequal- 154-

JAERI-Conf 95-021

acceleration process in beam phase, imperfectisochronous field and considerable amount ofbeam dispersion in energy.
As a result, we can deduce radial betatronfrequencies from injection to almost fullacceleration radius as shown in Fig.4.
Compared with the betatron frequencies
calculated from the data of magnetic sector field,
these observed values are roughly consistent
with their radial response for both betatronoscillation frequencies[!]. However, verticaloscillation frequency rapidly increases at around
1500mm over vr=l.O which may suggest the-2.0 f-Yr
1.5

1.0 ' - - - - - - - - l i . - - - - 1 . - - - - ' - - - - - - - - J
2001000

unstable behavior of accelerated beam induced
from magnetic field structure and trim coilparameter optimization.
This phenomen a is coincided with themeasurement of induced radio activities remainedin acceleration gaps of three cavities. Although
this oscillation have not brought about a fatalsituation for obtaining the full transmission fromthe injection to the extraction, it needs precise
tuning the isochronous field shape and the beam
injection phase.
Acknowledgments
The authors wish to express their thanks toRCNP cyclotron operation crews for the various
tuning of machine for the accelerator
development.
References[1] I. Miura, T. Yamazaki, A. Shimizu, K.
Hosono, T. Itahashi, A. Ando, K. Tamura, K.
Hatanaka, M. Kibayashi, M. Uraki, H. Ogata,
M. Kondo and H. Ikegami, Proc. of the 13thConf. on Cyclotrons and their Applications,
Vancouver, Canada July 6-10, 1992 pp3-10- 155-R(cm)Fig.4. Observed radial betatron frequency