The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

Present status of 20 MeV classical Microtron for the tabletop synchrotron"MIRRORCLE-20"
Y. Ohkuma, A. I. Kleev\ G. D. Bogomolov\ H. Yamada,
D. Hasegawa2 , Y. Kitazawa2 , and I. Tohyama2
Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu-City, Shiga 525, Japan
1Kapitza Institute for Physical Problems, Moscow, Russian
2Photon Production Laboratory Ltd., 4-2-1 Takagaichominami, Omihachiman, Shiga 523, JapanAbstract

1.2 The Results Ofsimulations

Study on the beam dynamics and the emittance measurements of the classical microtron are shown. Thismicrotron is featured by the electron emitter positioned
inside of the cavity. It is found that the observed
emittance is satisfactory small for the injector of thesmallest synchrotron.

The cathode position ~c is the major concern. The
curves in the Fig.l demonstrate the captUre coefficientversus the equilibrium phase 'Ps for the different cathodepositions.
0.10

c1. INTRODUCTION
We have introduced the 20 MeV classical microtron as
an injector of the world smallest synchrotron,"MIRRORCLE-20". The requirement on the beam
quality for the beam injection is of 30xl0-6 mrademittance, and less than 1% energy spread. Also thesame timing and the accelerating frequency between theinjector and the synchrotron are recommended. This
microtron was originally equipped with a magnetron
microwave source, but we have replaced this to theklystron source because of the above requirements. The
synchrotron is driven by the 2.45 GHz CW klystron.
We have studied the beam dynamics prior to thismodification incorporating with the internal electron
emitter and the rectangular shaped cavity.
Thecommissioning of the microtron with the klystron andnew cavity was successfully made. In this paper theemittance measurement is also reported.

0.05

Fig.l The capture coefficient vs the equilibrium phasrps • The curves are formed to the centre positio1~c·0.10

2. PARTICLES DYNAMIC
SIMULATION IN MICROTRON
Associated with the change in the microwave powersource of the microtron from magnetron (2.8GHz) toklystron (2.4446GHz), we have changed the size of RFcavity. To do so the study on the microtron operating
under the second type-accelerating mode was performed.
The terminology and notations used here are typical forthis type of accelerators [1]. The computer simulations
were carried out in order to obtain an optimal emitter andslits positions. The simulation technique is based on theMacro Particles Approach.

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ec

0.00 ~__...._......_..;...J...C___.__;_J_...__:...._....J.-.__._---So.oo
0.50

Fig. 2 The dependence of CMAX vs. the cathode position~c is shown. This curve is obtained from theresults shown in Fig. I.

The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October2001

Using the results shown in Fig. 1, we have obtained thedependence of the capture cmax versus the cathodeThe maximum
as shown in the Fig. 2.
position=0.32.
aroundcapture is obtained at the distance
We have also studied the optimal cavity parameters.
The question was the ratio between the horizontal size"a" and the vertical size "b" of the cavity. In the Fig. 3
the dependencies of capture C versus parameter (/Js areshown. The curves are constructed for different values of;cof (h, corresponding to these results is shown in the Fig.
6.

;c0.10(h= 0.7386

cb~a2 +b2 'X==---;===

where a is the half length of the cavity (along x axes),
and b is the half width of the cavity (along y axes).
The dependence of Cmax versus the value of X isshown in the Fig. 4.

0.00 W-J.,_._.,-W~~............._._.J::!II.,............................j.J t.p,j'lf
0.25
0.20
0.00

Fig. 5. The dependencies of capture C vs. parameter(/J s • The curves are constructed for different
values of ( h •

0.10

00.10
0.05

0.05

o.oo

0.00

0.05

Fig. 3. The capture coefficient C vs. parameter(/Js •

o.oo ._,___,___.__...._-'~----'----1--~-'---' (h0.70

0.10

0.75

0.80

Fig. 6. The dependencies of C MAX vs the values of(h, corresponding to the results, shown in thefig.S.
0.05

3. EMITTANCE MEASURMENTS
3.1 Beam size and Emittance
0.00
0.45

X
0.50

0.55

0.60

Fig. 4. The dependence of C MAX vs. the value of X ,according to the results, shown in the fig. 3.
In the Fig. 5 the dependencies of capture C versus
parameter (/Js are shown. The curves are constructed fordifferent values of (h , where (h is the dimensionlesscavity height. The dependence of Cmax versus the value

We have measured the emittance ofmicrotron beam byscanning the quadrupole magnet (QM) force. The beamtransport system is shown in fig. 7. We have used theQM after the bending magnet.
The emittance is calculated by investigating the changeof the electron beam size caused by alternating the QM
force. The square of beam size is given by the followingrelation.

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where a is the beam size, K is the resistive force by
QM, A, 8, and C are the parameters related to theemittance by the following formulas:

E=~JAC.
LIn this relation L is the distance to the screen from QM.
So the emittance can be calculated after finding theconstant A and C, using the dependence of the beam size
vsQM force.

expected value 8 1r mm mrad. On the other hand thepresent beam current (2 rnA) is not yet reached to thedesigned value 1OmA peak current. · This could be causedby the low Q-value of the cavity. The training of thecavity is under progress.

IITable. 1. The latest emittance ofmicrotron.
Horizontal
Vertical
0.82 ( 1r mm mrad)1.50 ( 1r mm mrad)

BM
2000
1800
1600
1400
1200
1000
800

Microtron

600
400

Fig. 7. The beam transport system of MIRRORCLE20. The screen for electron detection is set atthe injection point after passing the QM.
Electron beam was detected with the fluorescentscreen monitor. The fluorescence from the screen wascaptured by CCD camera, and digitised. The size ofelectron beam was measured by analysing the projectionsof beam profile. The profile of electron beam is shownin fig. 8. According to this beam size measurement, thebeam emittance was obtained. Table. 1 shows the latest
results. The obtained value is much better than the2000~~~~~--~~~-r~~~~~

Fig. 8 The observed beam profile

4.

REFERENCES[1] S.P.Kapitza and V.N.Melekhin. The Microtron, ed.
by E.M.Rowe, Harwood Acad. Pubs, London, 1978-180-