The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

HIGH CURRENT CIRCULAR MICROTRON WITH THE RECTANGULAR
RF CAVITY FOR THE TABLETOP SYNCHROTRON “MIRRORCLE-20”
Y. Sugihara, A. I. Kleev, D. Hasegawa#, H. Yamada and I. Tohyama#
Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu-City, Shiga 525, Japan#Photon Production Laboratory, Lt’d, 4-2-1 Takagaichominami, Omihachiman, Shiga 523, Japan
Abstract
The 20 MeV microtron with the rectangular cavity isused as an injector of the world smallest synchrotron“MIRRORCLE-20”. The careful investigations of theelectron beam dynamics in the present 20MeV microtron
has been carried out to increase the capture efficiency.
We have find out, that the microtron cavity design should
be based on the beam trajectory numerical modeling. Itwas shown, that this requirement is determined by the socall “first orbit tracing problem”, which is typical for themicrotron with high current and high energy gain.
We have experimentally demonstrated, that for themicrotron with the second type acceleration mode andrectangular cavity it is possible to obtain the 4% capture
coefficient and get 30mA beam current.

accelerating current directly. The method, used in [9],need the integration procedure over the captured are,which, in general, not obvious. Indeed, as it was shownin [3] and [5], in some cases the structure of the capture
region is very complicated. We do not dwell on thisquestion and said only that the correct analysis need somespecial approach.

THE BEAM DYNAMIC AND THE CAVITYDESIGNIn the MIRROCLE-20 Project, the rectangular
waveguide type cavity is used for the microtron [1], [2],[3]. This is well known, that the rectangular cavity hassome advantages in comparison with the conventional
cylindrical one. As it was shown in [4] and [5], using therectangular cavity we can use the larger values of energy
gain Ω as well as to decrease the gap between the magnetpoles. The further microtron cavity improving is basedon the ideas, suggested in the paper [6]. The authors findout, that the acceleration modes with an increased cavity
thickness are of practical interest. There are at least two
reasons for such conclusion. The first one is that theincreasing the cavity thickness lead to the increasing theefficiency of using microwave power. The next one is theQ -value increasing. All of this must result in an increasein current of the acceleration beam without an increase in
the microwave power.
At the same time, using the thick rectangular cavity
result in some difficulties, caused by the passing the beamon the first external orbit. As it was shown in [5] and [6],in the case under consideration, the beam passes in theimmediate vicinity of the cavity corner. This phenomena
apparently is the reason why the advantages of using
rectangular thick cavities practically does not realized yet.
In the papers [2] and [3] the new method of particles
dynamic simulation was suggested. The method is basedon the macroparticles approach. It is necessary tounderline, that our approach allow us to calculate theFig. 1. The microtron cavity structure and the first andauxiliary beam orbit.
In the Fig. 1 the results of microtron cavity design,
based on the orbit tracing is shown. During oursimulations, we took into account all orbits, but in thisfigure, we show (for simplicity) only the beam envelope,corresponding the auxiliary and first orbits. This result
demonstrate, that the orbits pass very close to the cavity
corner and so the careful design, based on the beam
tracing is quite desirable for the successful realization theadvantages of the thick rectangular microtron cavity.

EXPERIMENTAL RESULTS: EMITTANCEAND CURRENT MEASUREMENTS.
In this section we present the last experimental resultsof the MIRRORCLE-20 microtron investigation. Thecavity, shown in Fig.1 was used for the particle
acceleration. The system of the electron beam transport
in “MIRRORCLE-20” is shown in Fig. 2 (see also thedetails in [1]).

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

Fig. 3 (c). . The typical electron beam images on thescreen 3.
Fig. 2. The “MIRRORCLE-20” beam transport system.
The electron beam was detected with the fluorescentscreens 1 - 3. The fluorescence from the screens wascaptured by CCD camera. The typical electron beam
images is shown in Fig. 3. We have measured theemittance of microtron beam by scanning the quadrupole
magnet (QM) force [1].

The measurements show, that the horizontal emittance is
1.17π mm ⋅ mrad while the vertical emittance is
1.36π mm ⋅ mrad . We have measured the beam current
with current transformer. The maximum current recorded
32mA and so we enlarge the previous value (see [1])more than 20 times. In this case, the emission current of
the electron source was 1100mA, and the capture
coefficient was 2.9%. The maximum capture coefficientwas 3.5% (the beam current is 28mA, the emission
current is 800mA).
These results demonstrate, that using the thick rectangularcavity is possible in the classical circular microtron.
However, high efficiency and high current can beobtained after very careful design: the accurate beam
tracing should be performed.

REFERENCES
Fig. 3 (a) . The typical electron beam images on thescreen 1

Fig. 3 (b) . The typical electron beam images on thescreen 2[1] Y.Ohguma, A.I.Kleev, G.D.Bogomolov, H.Yamada,
D.Hasegawa, Y.Kitazawa, I. Tohyama, “Presentstatus of 20 MeV classical Microtron for the tabletop
synchrotron "MIRRORCLE-20"”, Proceedings of the
13th Symposium on Accelerator
Science andTechnology, October 29--31, Japan, 2001, 178-180.
[2] A.I.Kleev. “The Particles Dynamics in Microtron”,Report. Photon Production Laboratory, Lt’d:
December 2000 – April 2001
[3] A.I.Kleev. “On the Microtron cavity improving”,Report. Photon Production Laboratory, Lt’d: May
2003[4] S.P.Kapitza and V.N.Melekhin, “The Microtron”.
London: Harwood, 1978.
[5] Yu.M.Tsipenyuk, “The Microtron. Development andApplications”, Taylor&Francis, 2001.
[6] V.M.Aleshin and A.V.Doronin, ”Efficient microtronacceleration mode”, Instr. Exp. Techn., 34 (1991) 26.
[7] A.Takafuji, K.Sugiyama, K.Kuroda, K.Koyanagi,
M.Nishimura, “Numerical Analysis of Electron
Orbits in a Compact High-Current Circular
Microtron”, IEEE Trans. on Nuclear Science, 1997.
Vol. 44. No 4, pp. 1677-1683