JAERI-Conf 95-021

3a3-3
Development of Visual Beam Adjustment Method for Cyclotron
Takashi AGEMATSU, Kazuo ARAKAWA and Susumu OKUMURA,
Takasaki Radiation Chemistry Research Establishment
Japan Atomic Energy Research InstituteWatanuki-cho, Takasaki-shi, Gunma 370-12, Japan

Abstract
We have developed a computer-based visual assistancesystem for JAERI AVF cyclotron operation. This systemprovides a CRT display about the cyclotron beam
trajectories, feasible setting regions (FSRs), and searchtraces designed to improve beam parameter adjustment. As aresult of the test in actual operation, it was realized thatsimulated beam trajectories and FSRs ·nearly agree withactual beam conditions.

1. Introduction
A cyclotron design requires a large number of physicaltheories, calculation codes and analysis of the beam
trajectory. These codes and analyzed results have not beenused in actual operation. For a new cyclotron control
technique, we have developed a computer-based visual
assistance system 1,2) for the JAERI AVF c~clotron3) byusing the above codes. To examine the reliability of thissystem, the result of the simulation was compared with thatof the actual operation.

2. Human Interfaces

through a small gap of the inflector entrance. The FSRs arelimited mainly by the geometry of the inflector entrance.
We have compared the human interfaces with the resultsof actual operation in the accelerating conditions of H+ 45
MeV (harmonic mode 1: h=1), H+ 10 MeV (h=2) and 40~+
175 MeV (h=3). It was found that there was a discrepancy
between the simulated FSRs and the search traces obtained in
actual operation. The simulated beam trajectories deviate
from the search trace just after last GL. This deviation iscaused by the leakage of magnetic field from the main
magnet.
3.2 Central Region Block
The central region block is followed by the axial
injection block; The first turn of the beam trajectory after
the inflector is determined in this block. The adjustable·parameters in this region are dee voltages, trim coil currents
and the phase of beam buncher voltage. These parameters
are adjusted so that the beam passes through two sets of. phase slits. The beam trajectory and FSRs are calculated asfunctions of these parameters and magnetic and electric fielddata. The FSRs are limited mainly by the geometricalcondition of the phase slits.

The visual aSsistance system provides three functionsof human interfaces for beam parameter adjustment; (a) Beam
trajectory is rapidly calculated and graphically displayedwhenever the operators change the cyclotron parameters, (b)Feasible setting regions (FSRs) of the parameters which
satisfy beam acceptance criteria of the cyclotron's areindicated, (c) Search traces, which are historical visual mapsof beam current values represented by various colored dots,
are superimposed on the FSRs.
The system has been applied to three blocks of thecyclotron: the axial injection, the central region and theextraction. This system is constructed by the language of C
and works on workstation of VAX-3100 connected through
Ethernet with computers controlling4) the cyclotron.

3. Evaluation-of Simulation
3.1 Axial Injection Block
The axial injection block is a region between thebottom of the cyclotron yoke and the inflector. There are
four Glaser lenses (GLs) with adjustable focal lengths. The
beam is led into the cyclotron by adjusting these lenses-433-JAERI-Conf 95-021(;: Traiectorv

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I ESTIMATE -lO ;~. . l!llr----------?•~3~~------~-w~-3!l ;Fig. 2 Beam trajectory simulation at the extraction block.
The spiral beam trajectory is shown as a stretched line in this diagram.

At the first place, we have compared the position of
actual beam trajectory with the simulated beam one toevaluate the simulation model of beam trajectory. The actual
beam positions were measured by the following methods: (a)Searching a beam position of the maximum beam current
monitored at the main cyclotron beam probe by moving thephase slit, (b) Searching a beam position by measuring tum
patterns using the main probe. Figure 1 shows the top viewof a cross section of this block and a simulated trajectory ina solid line and actual slit positions. The trajectory passes
through the actual slit positions. The simulations are ingood agreement with the actual condition.
We have tested the· system for different values of themagnetic field of the central region and the phase of beam
buncher voltage. The intensities of magnetic bump field
produced by circular trimming coils little influence theposition of actual beam trajectory. The beam phasedependency on the beam po~:tion could not be measured
because the beam intensities were decreased drastically inchanging phase of the beam buncher.

executed simulations to obtain the beam trajectories,
passing through the exit of the cyclotron, for several beamenergies. The most suitable energy for the trajectory inactual operation condition is in a range from 18.98 to 19.06
MeV. On the other hand, the beam energy is evaluated at
19.10 MeV (-4.5%) from the magnetic field of the analyzing
magnet after the cyclotron. The simulated beam energy is inagreement with the beam energy measured by using
analyzing magnet.

Magneticchannel
probe

3.3 Extraction Block
The beam in the final tum is led into the deflector andthe magnetic channel, deflected from the circular orbit, andfinally extracted from the cyclotron. In this block, thesystem simulates the deflected beam trajectory. At the firststep, the beam trajectory entering the deflector is calculatedon the basis of the magnetic field data and two beam
positions detected by the main and the deflector probes. At
the second step, the beam trajectory in the deflector and themagnetic channel is simulated on the basis of the deflector
position, the deflecting field and the magnetic channel field.
The FSRs were calculated as functions of the above
parameters, and the clearance of the deflector and themagnetic channel.
An example of simulated beam trajectories fornominally 20 MeV 4He+2 ions is shown in Fig. 2. We have/Main probe
Fig. 3 Location of three beam probes.

To evaluate the trajectory model of the beam extraction
from the cyclotron, we have discussed how to estimate thebeam energy in the final tum. Inside the cyclotron, threeradial probes were installed to measure the beam intensity
distribution as shown in Fig. 3. A main radial probe covers
all the acceleration range of the radius from 40 mm to 1190

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min. A deflector probe provides the beam intensity before
the deflector. A magnetic channel probe provides the beamintensity" after the passing through the deflector. We have
tried to estimate the beam energy by following techniques.
1) Orbit. radius method; The beam position is measured
by the main radial probe. The energy (E) is evaluated fromthe simulated trajectories passing through the exit of thecyclotron. As shown in Fig; 4, the beam energies depend on
the beam positions of the final turn trajectory.
2) Three point method; The beam positions in the threepoints were measured by the main probe, the deflector probe
and the magnetic channel probe, respectively. The beamenergy (E') is estimated from simulated beam trajectory
passing through the above three points.
· Figure 5 shows the relation between the energy E andthe estimated energy E'. The solid line shows the energy
estimated experimentally and the dotted line shows the ideal
one. The result of estimations for beam energy, data has an
uncertainty within ±2% from linear approximation formula.

4. Upgrade of the System
Application of the system has been limited to several
accelerating conditions of ion beams. In the early stage ofdevelopment, it is not required to execute simulations for all
ihe available particles and energies. At present, this system
has been upgraded to simulate the beam trajectories and FSRs
in all accelerating beam conditions for the JAERI AVF
cyclotron. We can obtain the operating parameters for newion acceleration by using the new system.

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5. Future Activity
Precise comparison of the simulated beam trajectory
and the actual beam trajectory is planned for the extraction
block in new accelerating conditions. The extracted beamenergy will be measured accurately by other methods, such as-kinematics and TOF method. It is expected that the result
will be fed back to improve the system. We will expand thistechnique to the beam transport system.

6. References
1) T.Okamura and T.Murakami, "An Operator Assistance
System for Beam Adjustment of a Cyclotron", IEEETrans. on Nucl. Sci., Vo1.39, No.1, pp.13-20(1992).
2) T.Agematsu, K.Arakawa, S.Okumura, Y.Nakamura,W.Yokota, T.Nara, M.Fukuda, I.Ishibori, T.Okamura,and T.Tachikawa, "Development of Visual Beam
Adjustment Method for Cyclotron", Proc. 9th Symp.
Ace. Sci. Tech., Tsukuba, Japan, pp.65-67(1993).
3) K.Arakawa, Y.Nakamura, W.Yokota, M.Fukuda, T.Nara,T.Agematsu, S.Okumura, I.Ishibori, T.Karasawa andR.Tanaka "Construction and First Year's Operation ofthe JAERI AVF Cyclotron", Proc. 13th Int. Conf. onCyclotron and their Applications, Vancouver, Canada,
pp.119-122(1992).
4) S.Okumura, T.Agematsu, W.Yokota, T.Kamiya,
M.Fukuda, Y.Nakamura, T.Nara, llshibori, K.Arakawa,
M.Maruyama, K.lso, K.Hoshika and M.Tachibana,"Control System for JAERI AVF Cyclotron", Proc. 13thInt. Conf. on Cyclotron and their Applications,
Vancouver, Canada, pp.648-651(1992).

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Estimated energy difference E'-EO I EO x 100 [%]Fig. 4 Energy evaluation by orbit radius method.
E : energy evaluated from the simulated
trajectories passing through the exit of thecyclotron and the analyzing magnet.
EO: nominal energy.

Fig. 5 Energy estimation by three point method.
E': energy estimated from three point method.
EO: nominal energy.

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