Proceedings of IBIC2012, Tsukuba, JapanTUPB65TRANSVERSE-ACCEPTANCE MEASUREMENT SYSTEM FOR JAEA AVF
CYCLOTRON

Abstract
We are developing an acceptance measurement system
to evaluate the matching of the emittance of an injection
beam to the acceptance of the AVF cyclotron. The system
is composed of a phase-space collimator in the low
energy section and beam intensity monitors which areinstalled just after the phase space collimator and in thehigh energy section. The phase-space collimator, which
consists of two pairs of movable slits, is used to inject
beams with very small-emittance into the cyclotron bydefining position and divergence angle of the beam froman ion source. The acceptance is measured as the phasespace distribution of the ratio of the beam intensity at thehigh energy section to that at the phase space collimator.
In the preliminary test, only a part of distribution for theacceptance was measured because the injection-beamemittance from an ion source did not cover the wholeacceptance. A steering magnet has been added to expand
measurable area by scanning the injection beam insynchronization with the acceptance measurement. The
result of a test experiment showed the emittance of theinjection beam was able to be enlarged more than tentimes. It was confirmed that this technique was valid as
the method of increasing the injection emittance formeasuring the whole of the acceptance.

INTRODUCTION
The JAEA AVF cyclotron in TIARA (Takasaki Ion
accelerators for Advanced Radiation Application)
produces various kinds of ion beams from 10 MeV H+ to490 MeV 192Os30+ for research in biotechnology andmaterials sciences. The ion species and/or energy of thebeam are changed frequently (223 times a year in 2011[1]). Since the operating parameters of the cyclotron vary
according to the kind of beam, the parameters need to be
optimized for each beam to be accelerated and bedelivered to the target port with minimum beam loss.
Regarding the optimization of the beam injection to thecyclotron, it is required for the beam emittance to bematched to the acceptance of the cyclotron. A part of theinjected beam outside the acceptance is lost in thecyclotron. The condition of the injection in longitudinal
direction is determined mainly by the voltage and phaseof a buncher. The optimization procedure has been
established [2]. As for the condition of the injection in thetransverse direction, parameters of the magnets in the low
energy beam transport line are fine-tuned manually bymonitoring the accelerated beam current. However, it is
not easy to assess optimum condition because various
parameters are mutually related and the acceptance is notprecisely known.
We are developing a transverse acceptancemeasurement system to evaluate the state of the beam
injection. The system will help to optimize the injection
condition in the transverse direction.
This paper shows the outline of the measurement
system and a preliminary measurement test. In addition
the enlargement of the effective emittance of the injection
beam for expansion of the measurable area that iscurrently under developing is described.

SYSTEM FOR TRANSEVERSEACCEPTANCE MEASUREMENT
The system for transverse acceptance measurement isshown schematically in Fig. 1. The main components ofthe system are the phase-space collimator in the low
energy beam transport line and the intensity monitors in
the high energy section. One of the monitors is selected
depending on the position where the acceptance ismeasured. To measure the acceptance for accelerating andtransporting the beam to the deflector entrance in thecyclotron, for example, a current monitor inside thecyclotron is used, while in the case of acceptance to theoutside of the cyclotron a Faraday cup in the high energy
beam transport line is used.
Measurement of the acceptance is made by injecting
every portion in the whole phase-space, which should belarge enough to cover the acceptance. The acceptance canbe estimated from the sum of the portions of the beam
which passes through the system.

Beam intensity monitors

Ion source

Phase space collimator

Cyclotron

Figure 1: The system for transverse acceptance measurement.
_________________________________________#kashiwagi.hirotsugu@jaea.go.jp

ISBN 978-3-95450-119-9
Transverse & Longitudinal Emittance Measurements

1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Hirotsugu Kashiwagi#, Nobumasa Miyawaki, Satoshi Kurashima, Susumu Okumura ,Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency
1233 Watanuki-machi, Takasaki, Gunma, 370-1292, JapanTUPB65

Proceedings of IBIC2012, Tsukuba, JapanPhase Space Collimator
The phase space collimator, which limits the incident
beam to an arbitrary small area in the horizontal orvertical phase plane, is used to inject a small portion of
the beam into the cyclotron. It consists of two pairs of
position defining slits and angle defining slits. One pair isused to limit the beam in the horizontal (x-x’) plane andanother in the vertical (y-y’) plane. The slit is formed by apair of metal blades. The position and width of each slit
are variable by stepper motors which control the positionsof each blade. Figure 2 shows an example of definedphase-space area with one pair of slit. The main
specification of the phase space collimator is shown in thetable 1.

x'㻌Angle defining slit㻌

c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○x㻌

Position defining slit㻌Figure 2: Example of the region defined with the slits ofthe phase space collimator (shaded region).
Table 1: Main specification of the phase space collimatorcurrent, Faraday cups which measure absolute current
value, simple metal plates for relative current value
including emitted current of secondary electron or
scintillation counters which measure number of particles
are used.

Measurement Procedures
In acceptance measurement, small-emittance beams atvarious positions in a transverse phase-plane are injected
into the cyclotron by scanning the positions of the slits ofphase space collimator. As shown in Fig. 3, for example,
in the case of a measurement in the rectangle area (-p ≤ x≤ p , -q ≤ x’ ≤ q), the measurement procedures are as
follows : 1) the center of the position defining slit and theangle slit is moved to –p and –q respectively, 2) beam
intensity is measured continuously as moving the angle
defining slit from –q to q keeping the position defining
slit at p, 3) the position slit and angle slit is moved toposition of p + d, q by being shifted d in the positive x
direction 4) beam intensity is measured continuously as
moving the angle defining slit from q to -q keeping theposition defining slit at p+d, and these procedures arerepeated until the slit position reaches p. Thismeasurement is performed twice to determine thedistribution of the injected beam (Di(x,x’)) and thedistribution of the beam which reaches a location of thecurrent monitor at high energy section (Dh(x,x’)). TheDi(x,x’) and Dh(x,x’) are determined using a current
detecting devise just after the phase space collimator andinside or after the cyclotron respectively. The acceptanceis obtained by the ratio Dh(x,x’)/ Di(x,x’)

Position defining slit
Position range of the slit center(Measurement range of x and y)
Slit widthx'q±60 mm
0.1 mm 㹼 4 mm

Divergence defining slit-pPosition range of the slit center±77 mm(Measurement range of x’ and y’ ±25 mrad)

Slit width

0.1 mm 㹼 30mm

㸦Minimum resolution of x’ and y’ 0.15 mrad㸧

Beam Intensity Monitor
Acceptance is evaluated from the beam relativetransmission efficiency distribution, which is the ratio
distribution in a phase plane between beam distribution ata beam intensity monitor in high energy section andinjected beam distribution to the cyclotron from the phasespace collimator. Therefore the absolute beam current
value is not essential and relative value is adequate. Thecurrent value is expected to be the order of nano- or picoampares which depends on slit width. To detect the0px-qdSmall-emittance beamfrom the phase space collimator
Figure 3: The method of scanning the small emittancebeam in a phase plane by the phase space collimator.

PRELIMINARY MEASUREMENT TESTA preliminary measurement test was performed using
the 16O6+ beam extracted with the energy of 50.2 keVfrom a 14.5 GHz ECR ion source. The beam wasISBN 978-3-95450-119-92Transverse & Longitudinal Emittance MeasurementsProceedings of IBIC2012, Tsukuba, Japan

accelerated to 160 MeV and transported to one of theirradiation courses for heavy ion beam (HA course).

TUPB65

acceptance. A steering magnet just before the phase spacecollimator has been added to the system to manipulate theinjection beam in x’ and y’ direction. The expansion ofthe emittance is made by scanning the injection beamwith the steering magnet in synchronization with theacceptance measurement.
Figure 5 shows the beam emittance from the ion source
and the result of the effective emittance enlargement. The
effective emittance of the scanned beam was more thanten times larger than the original one despite several
unsynchronized region that are found as the white
quadrangles. It was confirmed that this technique wasvalid as the method of increasing the injection emittancefor measuring the whole acceptance

SUMMARY

The beam emittance at the phase space collimator wasmeasured by a metal plate just after the collimator. For
the acceptance measurement, a Faraday cup in the HA
course was used. Therefore the acceptance foraccelerating and transporting the beam from the phasespace collimator to the Faraday cup was obtained in theexperiment. The measured emittance and acceptance in xx’ phase planes are shown in Fig. 4. The whole
acceptance was not measured because the injection-beamemittance from the ion source did not cover the wholeacceptance.

EXPANSION OF EFFECTIVE
EMITTANCEThe system for measuring transverse-acceptance has
been developed. The acceptance is measured as the phasespace distribution of the ratio of the beam intensity at thehigh energy section to that at the phase space collimator.
The steering magnet which scans the injection beam has
been added to the system to increase the effective
emittance of the injection beam. The validity of thetechnique for expanding measurable area was confirmed
using the newly added steering magnet.

REFERENCES[1] S. Okumura et al., “Operation of the AVF Cyclotron”,
JAEA Takasaki Annual Report (2011), in press[2] S. Kurashima et al., “Useful technique for analysis andcontrol of the acceleration beam phase in the azimuthally
varying field cyclotron Rev. Sci. Instrum. 81, 033306(2010)To measure the whole acceptance, the emittance of theinjection beam needs to be so large as to cover the36 π mm mrad
(80% emittance)

413 π mm mrad(80% emittance)

Figure 5: Original beam emittance from the ion source (left) and the enlarged effective emittance by the steering
magnet (right).

ISBN 978-3-95450-119-9
Transverse & Longitudinal Emittance Measurements

3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Figure 4: Measured acceptance and emittance.