JPS593040B2 - charged particle device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charged particle device, and more particularly to prevention of surge voltage generated between a core wire and an internal shield of a coaxial cable connecting a charged particle generator and a DC power source. It is.

An example of an electron beam device, which is a type of charged particle device, will be explained below.

FIG. 1 is a conceptual diagram showing a conventional electron beam device, where 1 is a power supply device including a bias power supply 10, a cathode heating power supply 11, an electron beam acceleration power supply 12, a current resistance 13, and a voltage division resistance 1.
4.15.

2 is a coaxial cable, core wire 2L 22, 23, core wire 2
1. It is composed of an inner shield layer 24 surrounding 22 and 23, and an outer shield layer 25 of the coaxial cable, 26 is the stray capacitance between the core wire 21 and the inner shield layer 24, and 27 is the stray capacitance between the inner shield layer 24 and the outer shield layer 25. capacity.

3 is an electron gun, which includes a cathode 31, a Wehnelt electrode 32, and an anode 3.
3, 34 is an electron beam, and 35 is a vacuum spark discharge.

The terminal of the cathode 31 is connected to the cathode heating power source 10 via the core wires 22 and 23 of the coaxial cable 2, and is also connected to the negative electrode of the electron beam accelerating power source 12 via dividing resistors 14 and 15.

The Wehnelt electrode 32 is connected to the bias power supply 1 via the core wire 21.
0 negative electrode.

The grounded anode 33 is connected to the outer shield layer 2 of the coaxial cable.
5 to the positive electrode of the electron beam accelerating power source 12.

Further, the inner shield layer 24 of the coaxial cable 2 is connected to the negative electrode of the bias power supply 10, as is the Wehnelt electrode 32.

In the conventional electron beam device configured as described above, the electron gun 2 is
When the inside is evacuated and a predetermined voltage is applied from the DC power supply 1 to each electrode of the electron gun 3 via the coaxial cable 2, thermionic electrons emitted from the cathode 31 heated by Joule heat are transferred to the cathode. The electron beam 34 is accelerated by a voltage applied 770 between the electron beam 31 and the anode 33, and an electron beam 34 is generated.

Since a high voltage is applied between the cathode part consisting of the cathode 31 and the Wehnelt electrode 32 and the anode 33, the Wehnelt electrode 32 and the anode 33, which are arranged on the outermost periphery of the cathode part and face the anode 33, A vacuum spark discharge 35 may occur between the two.

When the Wehnelt electrode 32 and the anode 33 are short-circuited due to spark discharge 35 in vacuum, the core wire 21 of the coaxial cable 2 is A surge voltage is generated between the inner shield layer 24 and the inner shield layer 24 .

Figure 2 shows an equivalent circuit in which the stray capacitance 26.27 of the coaxial cable and the inductance and resistance of the core wire 21 are lumped constants and R is replaced.

In the figure, L is the self-inductance of the core wire 21, R is the resistance of the core wire 21, C2fl is the stray capacitance between the core wire 21 and the inner shield layer 24, C2□ is the stray capacitance between the inner shield layer 24 and the outer shield layer 25, and S is spark discharge in vacuum 35
■ is the surge voltage generated between the core wire 21 and the inner shield layer 24 at the terminal of the coaxial cable 2 on the electron gun 3 side, and vo is the voltage applied between the inner shield layer 24 and the outer shield layer 25. This voltage is approximately equal to the electron beam acceleration voltage.

When S35 is closed, the charge accumulated in C27 is discharged through C26 and R, and a surge voltage V expressed by the following equation is induced across S35.

Since equation (1) represents damped oscillation, the surge voltage V reaches its maximum at t20 and is expressed by the following equation.

■=βVo... (2) The accelerating voltage of the electron beam is ■.

Taking as an example a 10 m long coaxial cable used in a -60 kV electron beam device, the surge voltage V has the following value since C'a has 2000 PF and C2 2 4000 PF.

y = 1yv.

=-vo= 40 (kv) -・-<3)) The insulation withstand voltage between the core wire 21 and the inner shield layer 24 is lower than the insulation voltage between the inner shield layer 24 and the outer shield layer 25 (generally 5 kW or less). ) 2/ of electron beam acceleration voltage
When three times the surge voltage is applied, dielectric breakdown occurs.

As described above, in the conventional device, when the spark discharge 35 in vacuum occurs between the Wehnelt electrode 32 and the anode 33 of the electron gun 3, the core wire 21 of the rotary couple 2 and the inner shield layer 2
However, this invention was made with the aim of solving the above-mentioned drawbacks of the conventional device, and it changes the connection method between the coaxial cable and the electron gun. This prevents surge voltage from being induced between the core wire of the coaxial cable and the internal shield layer when vacuum discharge occurs within the electron gun.

FIG. 3 is a conceptual diagram showing an embodiment of the present invention, in which the inner shield layer 24 of the coaxial cable 2 is connected to the Wehnelt electrode 32 inside the electron gun 3.

Figure 4 shows the equal circuit in this case, and when S35 closes, C
Since the charges accumulated in 2□ are discharged directly from the inner shield layer 24 through S35 without passing through R and L, no surge voltage is generated between the core wire 21 and the inner shield layer 24.

As shown in FIG. Even if a spark discharge 35 occurs in vacuum between the anodes 33, no surge voltage is induced between the core wire 21 of the coaxial cable 2 and the inner shield layer 24.

In the above embodiment, the inner shield layer 24 is connected to the Wehnelt electrode 32 inside the electron gun 3, but the inner shield layer 24 is connected to the core wire 24 connected to the Wehnelt electrode 32.
It is clear that the same effect can be obtained by connecting the electron gun side terminal or both terminals of the coaxial cable 2.

By the way, in the above invention, an electron beam device using an electron beam generator having a triode structure has been described as an example, but it is also possible to generate charged particles using an electron beam device or an ion beam device using an electron beam generator of other structure. It is obvious that it is applicable to a wide variety of devices without much explanation.

As is clear from the above description, the present invention includes a charged particle generator having a grounded electrode and a non-grounded electrode, a DC power supply that supplies driving power of a predetermined potential to each electrode of this generator, and this DC power supply. and a coaxial cable having a plurality of core wires connecting the charged particle generator and the inner shield surrounding the core wires, wherein a coaxial cable having a plurality of core wires and an inner shield surrounding the core wires, wherein a member of each electrode of the charged particle generator that is at ground potential is connected to the coaxial cable. The core wire connected to the nearest non-grounded electrode and the internal shield are connected on the side of the charged particle generator so that they have the same potential, and the member is at a ground potential with the non-grounded electrode. This prevents the generation of surge voltage between the inner shield and core wire of the coaxial cable when a spark discharge occurs between be able to.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of a conventional electron beam device, and Figure 2 is a conceptual diagram of a conventional electron beam device.
An equivalent circuit diagram when a spark discharge occurs in vacuum inside the electron beam source in the electron beam device shown in the figure,
FIG. 3 is a conceptual diagram showing one embodiment of the present invention, and FIG. 4 is an equivalent circuit diagram when spark discharge occurs in vacuum inside the electron beam generation source in the embodiment of FIG. 3. In the figure, 1 is a DC power supply, 2 is a coaxial cable, and 3
is an electron gun, 2L 22 and 23 are the core wires of the coaxial cable 2, and 24 are the core wires 21, 22, and 2 of the coaxial cable 2.
3, 25 is the outer shield layer of the coaxial cable 2, 26 is the stray capacitance between the core wire and the inner shield layer, 27 is the stray capacitance between the inner shield layer and the outer shield layer, 31 is the cathode, 32 is the Wehnelt electrode, 33 is an anode, 3
4 is an electron beam, and 35 is a spark discharge in vacuum. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A charged particle generator having a grounded Calorie speed electrode and an ungrounded control electrode, a DC power source that supplies driving power at a predetermined potential to each electrode of this generator, and each of the DC power source and the charged particle generator. In a coaxial cable having a plurality of core wires connected to the electrodes and an internal shield surrounding these core wires, a member at a ground potential among the non-grounded electrodes to which the accelerating voltage of the charged particle generator is applied. A charged particle device characterized in that a core wire connected to an electrode closest to the inner shield and the inner shield are connected on the charged particle generator side so that they have the same potential.