03aD17P
マグネトロン入射型電子銃におけるラミナー電子流の形成機構
Mechanism for Forming Laminar Electron Beam in a Magnetron Injection Gun
山口裕資，立松芳典，斉藤輝雄，Vladimir N. Manuilov 1)
Yuusuke Yamaguchi, Yoshinori Tatematsu, Teruo Saito and V. N. Manuilov 1)
福井大学 遠赤外領域開発研究センター, 1)ニジニノブゴロド州立大学
Research Center for Development of Far-Infrared Region, University of Fukui, Japan1)
Nizhny Novgorod State University, Russia

Outermost - Innermost

60.02

-12
VK = - 20 kV
Bcavity = 9.71 T

Cathode(b)0.0-0.02

αout. − αin.

-0.04

β//out. − β//in.

-0.06
50556065
Z [mm]

70-40.08
0.06
0.040.020.0

β out. − β in.

-0.08
45-8-0.028075Potential [kV]-20-15-10-5Innermost Trajectory(c)Outermost Trajectory

051015202530
Axial Distance from Emitting Point [mm]Fig. 1.
Beam parameters for a designed MIG. (a)Beam trajectories. (b) Difference in α−values,
β// = v// / c (c: speed of light in free space), β⊥ = v ⊥ / cand (c) potential on innermost and outermost
trajectories.

0.2

VK = -20 kV
IB = 0.50 A
IB = 0.55 AIB = 0.60 A

1010.2

10.6

11VKA

11.4

0.1

cavity102

Δα-16

14cavity-20(a)trajectories calculated with EGUN. Since electrons
on inner and outer trajectories are emitted fromdifferent axial positions, they have different rotatingphases in a plane perpendicular to the magnetic
field line. This makes the laminarity worse.
However, with an optimum potential profile,
α-values of electrons on the outer trajectory becomealways smaller than those of inner ones at eachaxial point in K-A region (Fig. 1(b)). Thus, electrons
on the outer trajectory travel a longer distance than
the inner ones during one cyclotron motion. As aresult, the phase differences between the rotating
trajectories become small (indicated by signs“→| |←” in Fig. 1(a)). After passing the K-A region,
the trajectories are distributed almost uniformly and awell laminated flow is formed.
Here, the differences in α-values are produced
by differences in the parallel velocities (β//) (Fig.
1(b)). According to different potential slopes shownin Fig. 1(c), electrons on the inner and outertrajectories are differently accelerated to haveappropriate values of β// in the K-A region.

α

1st AnodeEmitterR [mm]18Potential [kV]In gyrotrons, the magnetron injection gun(MIG) is a critical component, which must generatea high quality electron beam with a small velocityspread. As the current density increases, thespace-charge effect becomes large and increases thevelocity spread. To reduce the space-charge effect,
formation of a laminar flow is essential [1]. A
conventional design parameter has been a slant
angle θE of an emission surface to a magnetic field
line [2].
We have considered the mechanism of laminarflow formation to provide guidelines for MIG
designs. It is found that the laminarity depends not
only on θE, but also on a potential profile in aregion surrounded by a cathode, a first and a second
anodes (K-A region) [3]. By optimizing thepotential profile, a MIG is designed for a 265 GHz,
3 kW gyrotron. It produces a 20 kV, 0.5 A laminarbeam with a pitch factor (ratio of perpendicular toparallel velocities to magnetic field line) of α = 1.3
at the cavity.
Figure 1(a) shows electrodes shapes and beam

011.8[kV]Fig. 2. Pitch-factor α and its spread Δα as a functionof VKA for 20 kV, 0.5 A electron gun.

A high performance MIG with a wide operation
window is obtained. In Fig. 2, αcavity and the spreadΔαcavity (= [αmax. – αmin.] / αaverage) are plotted as afunction of the voltage between the cathode and 1stanode (VKA). The very small Δαcavity less than 5 %is achieved for a wide range of αcavity = 1.0~1.5.
[1] V. N. Manuilov and Sh. Ye. Tsimring, Radio Eng.
Electron. Phys. 23, 111 (1978).
[2] P. V. Krivosheev et al., Int. J. Infrared and Milli.
Waves 22, 1119 (2001)[3] Y. Yamaguchi et al., Phys. Plasmas 19, 113113(2012).