JPH06150859A - Electron gun - Google Patents

Abstract

PURPOSE:To provide a highly efficient electron gun by which strong electron beam intensity can be obtained under low pulse voltage by forming microscopic recesses and projections in a large number on a surface of a cathode housed in a position opposed to an electrically conductive extracting grid. CONSTITUTION:Almost several micron microscopic recesses and projections 20 are formed in a large number on a surface of a cathode 5. When pulse voltage is impressed between an anode wire 1 arranged in an ionization chamber 2 and an ionization chamber wall 3, wire discharge is ignited easily between the anode wire and the ionization chamber wall, and plasma is generated. A cation in this plasma is accelerated toward the cathode 5 in a high voltage chamber 6, and passes through an electrically conductive extracting grid 4, and collides with the cathode 5. Since the almost several (mu) microscopic recesses and projections 20 are formed on the surface of the cathode, an electric field becomes strong in the surface vicinity of an electrode. As a result, since a large number of electrons are supplied even by field emission in addition to a secondary electron emitted by the cation, the number of electrons is increased significantly, and electron beam intensity is also increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high power electron gun,
In particular, the present invention relates to an electron gun improved so that the electron beam intensity can be easily increased.

[0002]

2. Description of the Related Art In recent years, an electron beam has been used in many fields of advanced materials such as chemical reaction, microscopy, analysis, welding, etc., and an electron gun is used as a source of this electron beam. FIG. 3 shows an example of an electron gun conventionally used. That is, the electron gun is composed of an ionization chamber 2 in which an anode wire 1 is arranged, and a high voltage chamber 6 which communicates with the ionization chamber 2 via a conductive extraction grid 4 described later. Further, the ionization chamber 2 is formed with an exit window 11 that is transparent to electrons on the side opposite to the high voltage chamber 6, and the exit window 11 is provided at the connecting portion with the high voltage chamber 6. A conductive extraction grid 4 of a voltage equal to the voltage of is formed.

On the other hand, in the high voltage chamber 6, a cathode 5 having a high negative bias voltage is accommodated by being supported by an insulator 8, and a high voltage introducing terminal 9 from the cathode 5 to the outside of the high voltage chamber 6. Has been pulled out. In addition, the high-voltage chamber 6 has an exhaust port 1
0 is provided and is connected to an exhaust device (not shown) so that the pressures in the ionization chamber 2 and the high voltage chamber 6 can be controlled.

Both the ionization chamber 2 and the high voltage chamber 6 contain a gas having an extremely low pressure capable of achieving positive ionization, and usually helium of 10 to 50 millitorr is used. The wall 3 of the ionization chamber 2 and the wall 7 of the high voltage chamber 6 are both at the ground potential. Furthermore, during ionization, a pulse voltage of -10 kilovolts is applied between the anode wire 1 and the wall 3 of the ionization chamber.

On the other hand, the cathode 5 is constantly maintained at a negative bias voltage (for example, -150 kilovolts) through a high voltage introduction terminal 9 connected to a high voltage supply source (not shown). . The exit window 11 is also composed of a somewhat thin sheet that is transparent to high energy.
This sheet can be made of a metal such as aluminum or titanium and has a thickness of tens of micrometers. Furthermore, this window width requires a window width of more than 1 cm in many applications, especially those relating to the treatment of materials by irradiation.

In the conventional electron gun constructed as described above, electrons serving as an electron beam source are emitted as described below. That is, when a pulse voltage is applied to the anode wire 1 arranged in the ionization chamber 2 under a low pressure, a wire discharge occurs between the anode wire 1 and the wall 3 of the ionization chamber at the ground potential, and the anode wire in the ionization chamber 2 Plasma is generated between the walls of the ionization chamber.

On the other hand, the cathode 5 arranged in the high voltage chamber 6
Extract positive ions from the plasma through the conductive extraction grid 4. The cations penetrate into the high voltage chamber 6 through the conductive extraction grid 4 arranged between the ionization chamber 2 and the high voltage chamber 6 and collide with the cathode 5. Then, on the surface of the cathode 5, electrons are emitted by the impact of the cations.

The electrons thus emitted travel in the opposite direction to the cations and are accelerated toward the conductive extraction grid 4, and further pass through the ionization chamber 2 to reach the exit window 11 and the electron beam. Supplied as a source.

Here, ignoring the initial energy of positive ions in the vicinity of the conductive extraction grid 4, and assuming that the negative bias voltage at the cathode 5 is VHT and the charge amount of positive ions is e, the positive ions are (single It can be considered that the cathode 5 reaches the cathode 5 with energy equal to e · VHT. Also,
Electrons secondary emitted on the surface of the cathode 5 by the impact of the cations extracted from the extraction grid are accelerated toward the conductive extraction grid 4, where the electrons are e · VHT.
Reach the energy of. Under these conditions, 1
The individual cations and the electrons emitted by the cations have substantially overlapping orbits corresponding to the same electric field line.

The electron gun as described above mainly generates X-rays by replacing the electron gun with a gas laser or magnet hydrodynamic generator by electronic excitation, and by replacing the exit window 11 with a target for X-ray generation. It is applicable to a device.

By the way, the intensity of the electron beam generated by the electron gun remarkably depends on the object of application (for example, a gas or laser by electron excitation). So, conventionally,
As a measure against the above-mentioned beam intensity, by changing the pulse voltage applied to the anode wire 1 shown in FIG. A method of controlling the electron beam intensity by changing the number of electrons emitted by cations has been used.

[0012]

However, the conventional electron gun as described above has the following problems to be solved. That is, in order to increase the electron beam intensity, it suffices to increase the number of positive ions as described above. Conventionally, as this means, an increase in the plasma density in the ionization chamber, that is, the anode wire is used. It was necessary to increase the pulse voltage applied to the. for that reason,
In order to increase the electron beam intensity, the pulse power source capacity must be increased, which is very inefficient.

The present invention has been proposed in order to solve the above-mentioned drawbacks of the prior art, and an object thereof is to provide a highly efficient electron beam capable of obtaining a strong electron beam intensity at a low pulse voltage. To provide a gun.

[0014]

According to a first aspect of the present invention, there is provided an exit window that is transparent to electrons and a conductive extraction grid provided on the opposite side of the exit window, and ionization is performed at a low pressure. Gas to be ionized, an ionization chamber equipped with an anode wire for ionizing the gas to generate cations, and the ionization chamber through the conductive extraction grid, and the cathode is placed at a position facing the conductive extraction grid. An electron gun comprising a high voltage chamber housed therein is characterized in that a large number of minute irregularities are formed on the surface of the cathode.

The invention described in claim 2 is characterized in that a carbon felt having a large number of minute irregularities formed on the surface is attached to the surface of the cathode.

[0016]

According to the electron gun of the present invention, by providing a large number of minute irregularities on the surface of the cathode housed in the high voltage chamber, the cations extracted from the ionization chamber collide with the cathode and are emitted. The number of electrons generated can be significantly increased by the field emission effect. As a result, the electron beam intensity can be easily increased.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be specifically described below with reference to FIGS. The same members as those of the conventional type shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted.

(1) First Embodiment In this embodiment, as shown in FIG. 1, a large number of minute irregularities 20 of about several microns are formed on the surface of the cathode 5. The other structure is the same as that of the conventional type shown in FIG.

In the electron gun of this embodiment having such a structure, the electron beam intensity can be easily increased as described below. That is, when a pulse voltage is applied between the anode wire 1 arranged in the ionization chamber 2 and the wall 3 of the ionization chamber, wire discharge easily ignites between the anode wire and the wall of the ionization chamber, Plasma is generated.

The positive ions in the plasma thus generated are accelerated toward the cathode 5 in the high voltage chamber 6, pass through the conductive extraction grid 4, and collide with the cathode 5. At this time, in the electron gun of this embodiment, since the minute irregularities 20 of about several microns are formed on the surface of the cathode 5, the electric field near the electrode surface becomes strong. As a result, in addition to the electrons secondary-emitted by the cations, a large number of electrons are also supplied by the field emission, so that the number of electrons is significantly increased and the electron beam intensity is also increased. Therefore, even when the pulse voltage applied between the anode wire 1 and the wall 3 of the ionization chamber is low, a high electron beam intensity can be obtained.

Furthermore, since the present embodiment does not involve the addition of additional electric circuits or structural modification to the conventional type, the apparatus is the same as the conventional example although a high electron beam intensity can be obtained. There is also an advantage that a very simple structure is sufficient.

As described above, according to this embodiment, the number of electrons emitted from the cathode can be easily increased, and the pulse voltage applied to the anode wire can be changed even when the same electron beam intensity as in the conventional case is obtained. It can be reduced. further,
Since the pulse voltage applied to the anode wire can be reduced, it is possible to easily realize a long life of the pulse power supply and a high repetition rate of the pulse.

(2) Second Embodiment In this embodiment, as shown in FIG. 2, a carbon felt 22 is attached to the metal cathode 21 over the entire surface facing the conductive extraction grid 4. Has been. The carbon felt 22 has a large number of microscopic irregularities on the surface thereof. In addition,
As a method of attaching the carbon felt 22 to the metal cathode 21, a predetermined portion of the cathode 21 is cut to a depth of about several millimeters, and the carbon felt 22 having a thickness and shape capable of filling the cut portion is cut. Is used. The other structure is the same as that of the conventional type shown in FIG.

In the electron gun of this embodiment having such a structure, the electron beam intensity can be easily increased as described below. That is, when a pulse voltage is applied between the anode wire 1 arranged in the ionization chamber 2 and the wall 3 of the ionization chamber, wire discharge easily ignites between the anode wire and the wall of the ionization chamber, Plasma is generated.

The cations in the plasma thus generated are accelerated toward the cathode 21 in the high voltage chamber 6, pass through the conductive extraction grid 4, and collide with the carbon felt 22 mounted on the cathode 21. . At this time, since minute irregularities of the order of several microns are formed on the surface of the carbon felt 22, the electric field near the electrode surface becomes strong. As a result, in addition to the electrons secondary-emitted by the cations, a large number of electrons are also supplied by the field emission, so that the number of electrons is significantly increased and the electron beam intensity is also increased. Therefore, even when the pulse voltage applied between the anode wire 1 and the wall 3 of the ionization chamber is low, a high electron beam intensity can be obtained.

Also, in this embodiment, since the addition of an additional electric circuit and the structural modification to the conventional type are not required, the apparatus is the same as the conventional example although a high electron beam intensity can be obtained. There is also an advantage that a very simple structure is sufficient.

Thus, also in this embodiment, as in the first embodiment, the number of electrons emitted from the cathode can be easily increased, and even when the same electron beam intensity as in the conventional case is obtained, the anode The pulse voltage applied to the wire can be reduced. Furthermore, since the pulse voltage applied to the anode wire can be reduced, it is possible to easily realize a long life of the pulse power supply and a high pulse repetition rate.

The present invention is not limited to the above-described embodiment, but a carbon felt in which microscopic irregularities are formed on a predetermined portion of the surface of a conventionally used cathode is formed. Even if the foil is attached, the same effect as in the above embodiment can be obtained.

[0029]

As described above, according to the present invention, a carbon felt having a large number of minute irregularities formed on the surface of the cathode or a carbon felt having a large number of minute irregularities formed on the surface is formed on the surface of the cathode. By attaching it, it is possible to provide an efficient electron gun capable of obtaining a strong electron beam intensity at a low pulse voltage.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of an electron gun of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the electron gun of the present invention.

FIG. 3 is a sectional view showing an example of a conventional electron gun.

[Explanation of symbols]

 1 ... Anode wire 2 ... Ionization chamber 3 ... Ionization chamber wall 4 ... Conductive extraction grid 5 ... Cathode 6 ... High voltage chamber 7 ... High voltage chamber wall 8 ... Insulator 9 ... High voltage introduction terminal 10 ... Exhaust port 11 … Exit window 20… Unevenness 21… Cathode 22… Carbon felt

Claims (2)

[Claims] 1. An exit window permeable to electrons, and a conductive extraction grid provided on the opposite side of the exit window, the gas to be ionized at a low pressure, and the cation by ionizing the gas. In an electron gun comprising an ionization chamber equipped with an anode wire for generating an ionization chamber, and a high-voltage chamber communicating with the ionization chamber via the conductive extraction grid, and containing a cathode at a position facing the conductive extraction grid, the cathode An electron gun having a large number of minute irregularities formed on its surface. 2. An exit window permeable to electrons, and a conductive extraction grid provided on the opposite side of the exit window, the gas to be ionized at a low pressure, and the cation by ionizing the gas. In an electron gun comprising an ionization chamber equipped with an anode wire for generating an ionization chamber and a high voltage chamber communicating with the ionization chamber through the conductive extraction grid and containing a cathode at a position facing the conductive extraction grid, An electron gun comprising a carbon felt having a large number of minute irregularities formed on the surface of the cathode.