22P056-P
Characteristic of Relativistic Electron Beam Diode with Mesh Anodeメッシュ陽極を用いた相対論的電子ビームダイオードの特性
Daisuke Shimone, Tsubasa Ito, Hiroaki Ito and Katsumi Masugata
下根大侑, 伊藤 翼，伊藤弘昭，升方勝己
University of Toyama
3190, Gofuku, Toyama 930-8555, Japan
富山大学 〒930-8555 富山市五福3190番地
To realize the multi-shot operation of intense relativistic electron beam diode, mesh anode is utilized. The
diode was successfully operated at diode voltage 110 kA, diode current 35 kA, and beam current of 7 kA
and beam current density of 250 A/cm2 are obtained. The diode was stably operated for 10 continuous
shots without breaking the vacuum.

1. Introduction
Intense relativistic electron beam (IREB) has awide area of applications including intense
microwave generation, X-ray, γ-ray, and neutron
sources, and surface modifications of materials. In
those applications it is very important to know thecharacteristics of electron beam diode and the beam
propagation. Foil anode has been utilized togenerate very low impedance beam, however, in thediode the foil is broken in each shot due to theenergy deposition of electrons passing through thefoil. To realize the multi-shot operation, we havetested the metallic mesh as an anode.[1]2. Experiment
Pulsed power generator used in the experiment isshown in Fig.1. The generator consists of Marx
generator, pulse forming line (PFL), pulse
transmission line (PTL) and vacuum electron diode.
The Marx generator is 8 stage bipolar charging typeand produces high voltage pulse of 800 kV, 5 kJ at
maximum charging voltage of ±50 kV. The PFL
uses deionized water as dielectric and produceshigh power pulse of 400 kV, 3 Ω, 50 ns whencharged to 800 kV. The pulse is transported throughthe PTL and applied to the diode.
Figure 2 shows the cross-sectional view of theelectron diode. The diode consists of a aluminum
cathode of 60 mm diameter, mesh anode of 80 mm
diameter, and a drift tube of inner diameter 110 mm,length 245 mm. Stainless steel mesh of wire
diameter 0.25 mm, pitch 1.02 mm is used as theanode. Output voltage of the PTL (VPTL) is observedat the end of the PTL by a resistive voltage divider.
In the upstream and downstream of the anode, apair of Rogowski coil is installed to evaluate thegap current (Iup) and beam current injected to thedrift tube (Idown). Electron current density (Je) is
measured by a Faraday cup placed at 45 mm
downstream from the anode on the axis of the diode.
The diode voltage (Vd) is evaluated as Vd = VPFL –L(dIup/dt), where L is the inductance of the diode(110nH). The A-K gap was adjusted to 4.3 mm.

Fig.1. Overall view of laboratory equipment

Figure 4 shows the dependence of Je onthe shot number. From the figure we seethat electron beam is produced for 10
continuous shot. After 10 shot, the anodemesh has heavily damaged and has a holeof 30 mm diameter, where as no strong
damage was observed on the aluminum
cathode.

Fig.2. Cross section of electron beam diodeFigure 3 shows typical wave forms of VPTL, Vd, Iup,
Idown and Je. As seen in the figure, Vd and Iup have apeak at t ≈ 80 ns after the rise of VPTL. Peak valuesof Vd and Iup are 110 kV and 35 kA, respectively.
The beam current (Idown) raises at t = 30 ns andreaches 7 kA at t = 80 ns. The peak value of Je =250 A/cm2 is observed at t = 80 ns.

Fig.4. Electron current density to the number of shots

5. Summery
Characteristics of IREB diode with mesh
anode were evaluated. The diode wassuccessfully operated at diode voltage 110 kA,
diode current 35 kA, and beam current of 7kA and beam current density of 250 A/cm2
are obtained. The diode was stably operated
for 10 continuous shots without breaking thevacuum.
References[1] M. Onoi, M. Yamabuchi, and M. Yatsuzuka:Improvement of Microwave Power from a VirtualCathode Oscillator and Its Repetitive Operation
Using a Metal Mesh Anode Translated from Denki
Gakkai Ronbunshi, Vol. 123-A, No. 1, January 2003,
pp. 12-19

Fig.3. Vpfl, Vd, Iup, Idown, Je at the time