Proceedings of the 1st Annual Meeting of Particle Accelerator Society of Japanand the 29th Linear Accelerator Meeting in Japan (August 4 - 6, 2004, Funabashi Japan)

Present status of the beam test of the deflection element for dispersion control
Mikio Tanabe A), Masahiro Ikegami A), Toshiyuki Shirai A),
Hiromu Tongu A), Akira Noda A)Koji Noda B)
A)

Institute for Chemical Research, Kyoto University, Gokanosyo, Uji-City, 611-0011, Kyoto, Japan
National Institute of Radiological Science, 4-9-1, Inage-Ku, Chiba-City 263-8555, Chiba, JapanB)

Abstract
A deflection electrostatic deflector has been designedfor an ion storage ring. This electrostatic deflector,
together with a dipole magnet makes a condition where adispersion function of ion beams is controlled at abending section. For this purpose, the electrostatic
deflectors are designed, and the deviation of thecalculated field from the ideal value is less than 0.1%,
within 2.5mm from the beam axis. The effect of a hole
for laser injection is also considered. After modificationof the structure of the electrodes, the deviation near thehole is improved. We planned the experiment to verify
the effect of dispersion control by using the first
constructed deflection element. An ion beam will be
produced from an ion source and injected into thedeflection element directly. Adjustment of an ion source
and the setup of the experiment are also considered.

1 INTRODUCTION
An ion storage ring, S-LSR, is now under construction
at Institute for Chemical Research, Kyoto University [1].
S-LSR, whose circumference is 22.557m andsuperperiodicity is 6, is planned to use for the experimentof beam cooling. For this purpose, this ring is equippedwith an electron cooler and a laser cooling system. The
final goal of this experiment is realization of threedimensional crystalline beam. Three types of the beams,
proton, 12C6+, and 24Mg+ are prepared for storage in thisring.

includes an electrostatic deflector, as well as a dipole
magnet. These electrostatic deflectors make the electricfield perpendicular to both the beam path and themagnetic field. The beams passing through the bending
sections are bent by both Rorentz force and Coulombforce. A dispersion function of the beams is adjustable,
because of these two forces.[2] In particular, a dispersion
function is completely canceled, if the magnetic field andthe electric field satisfy the following equation,

G G 
1 G
B × v = 1 + 2  E
 γ0 
where γ 02 is gamma factor of a particle of the beam.
This effect is thought to be useful for stable storage of the
3-dimensional crystalline beam. [2]For this effect to be experimentally verified, we havedesigned the electrostatic deflectors installed in thevacuum vessels at the bending sections. The dipole
magnets used here have already constructed, and vacuum
vessels installed between the gaps of the dipole magnets
are under construction. The height of the vacuum vessels
is limited because of the limited gap of the dipole
magnets. The electrostatic deflectors must be equippedwith a mechanism to move them inside, when the ring isused for a normal storage ring. This mechanism is set atthe bottom of the electrostatic deflectors. So, theseelectrostatic deflectors are required to be installed intorather small gap of the vacuum vessels. The width
between the main electrodes is determined to be 30mm
because of two reasons; the aperture at the bending
sections must be kept wider, and the higher the ratio of
the height of the electrode to the width between theelectrodes is, the less the deviation of the electric field is.
For more precise electric field, we have changed thestructure of the electrodes, and added small intermediate
electrodes. We determined the structure of theelectrostatic deflectors with use of 3-dimensional
calculation code, in order for as precise electric fields aspossible.
.

2 DESIGN OF THE ELECTRODES
Figure 1: Ion storage ring, “S-LSR”.
This ring has its peculiarity in its bending sections .It2.1 Three-dimensional structure

The cross sectional view of the electrodes is shownin Fig 2.
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Proceedings of the 1st Annual Meeting of Particle Accelerator Society of Japanand the 29th Linear Accelerator Meeting in Japan (August 4 - 6, 2004, Funabashi Japan)

Figure 3: The deviation of the electric field near themedian plane.
Figure 2: Cross sectional view of the electrostaticdeflector.
The electrostatic deflector consists of two cylindricalmain electrodes and eight wires. The top and bottom partof the main electrodes are thicker than the others. Theseparts are called ‘shims’. The shims extend the effective
electric fields area above and below the median plane.
The eight wires, called ‘intermediate electrodes’, also
improve the quality of electric fields in the aperture ofelectrodes. The sizes and positions of them are optimized
with use of the 3-dimensional calculation code, TOSCA(TOSCA is known as a calculation code for magneticfields. It is also used for electrostatic fields.). The
voltages to be given on each electrode are also optimized
and determined as table 1.

2.2 Modification for laser injection
As is shown in Fig 1, a laser has to be injected thoroughthe bending section in order for the experiment of laser
cooling at the straight section of this ring. Therefore, wehave to make a hole on the main electrode. This hole will
naturally be thought to reduce the strength of the electricfield near the hole. In order to compensate field vacancy,
we changed the structure of the electrode as Fig. 4.

Voltages for
3-dimensional
calculation(V)
Inner main electrode1007
Intermediate electrode 1 and 5
562
Intermediate electrode 2 and 6
180Intermediate electrode 3 and 7-180
Intermediate electrode 4 and 8-558
Outer main electrode-993
Table 1: The optimized voltages to be given one theelectrode.
Name of the electrode

Then the error of the electric field on and 2.5mm above
the median plane are shown in Fig. 3. This shows that thedeviation of the electric field is less than 0.1%, in therange of surroundings 2.5mm of the reference orbit.
Figure 4: Three-dimensional view of the electrostatic
deflector is shown above. The cross section of themodified electrostatic deflector near the hole is shown
below.

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Proceedings of the 1st Annual Meeting of Particle Accelerator Society of Japanand the 29th Linear Accelerator Meeting in Japan (August 4 - 6, 2004, Funabashi Japan)

The thickness of the electrode near the hole is modified.
It is changed to be 1mm thicker than the other parts of theelectrode. This modified region is from 157mm to197mm measured from the end of the dipole magnet. By
the modification of the structure of the electrode near thelaser injection hole, the deviation of the electric field isimproved as shown in Fig. 5. This figure shows that thedeviation of the electric field is less than 0.2% within ±2.5mm from the beam axis.

The setup of this experiment is shown in Fig.6 .The ion
beam used here is 14N+. First, the beam is generated in an
ion source. Next, this beam passes through the watercooling aperture, whose bore radius is 16mm, and istransferred to the Einzel lens. This beam is made to be aparallel beam during passing through the lens. The
positions and the sizes of the beams are determined by thebeam defining slit placed after the Einzel lens. The
positions of the beams before and after passing throughthe bending section are measured with use of thefluorescent screens.
The kinetic energy of 14N+ is planned to be 35keV, andradius of the curvature of this ring is 1050mm. In order tosatisfy this condition, the strength of the magnetic field is0.192T. This strength of the magnetic field is able to bemade with the dipole magnets, the magnetic field strengthof which has already measured.

4 SUMMARY AND PROSPECT
Figure 5: The deviation of the electric field near thelaser injection hole.

3 SET UP OF THE EXPERIMENTThe electrostatic deflectors designed here are nowassembled. The deflectors installed in the vacuum
chamber first are estimated to be completely made by theend of July, in 2004. We are going to confirm theefficiency of the electrostatic deflectors for the dispersion
control experimentally, with use of the single set of thedeflection element, before construction of all electrostatic
deflectors is finished. And the closed orbit distortion
induced by the electric field error will be estimated bythis experiment.

The experiment to control a dispersion function ofbeams is planned. This effect is thought to be useful forstable storage of three-dimensionally crystalline beams,
which could be realized by the experiment of beamcooling also planned utilizing a storage ring, S-LSR. For
this experiment, an electrostatic deflection element isdesigned. The result of three-dimensional electrostatic
calculation shows that the deviation of the electric field isless than 0.1% within ±2.5mm from the beam axis.
The deflection element designed here is now underconstruction. The experiment to verify the effect of theelectrostatic electrode is also planned. An ion source forthis experiment is prepared. The experiment to make ion
beams directly pass through the bending section will
begin from September, in 2004.

REFERENCES[1] A. Noda et al., in this proceedings.
[2] M. Ikegami et al., submitted to Phys. Rev. ST-AB as a title“Heavy Ion storage ring without dispersion”

Beam defining slit
Figure 6: Setup of the experiment.

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