JPH0437529B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cathode structure for a high intensity pulsed electron beam source used in a free electron laser oscillation device, an electron beam excited excimer laser oscillation device, etc.

In the case of an electron beam source that generates an electron beam of several milliamperes under an accelerating voltage of several tens of kilovolts to 100 kilovolts, a negative voltage with respect to the central cathode is applied from an external voltage source to the focusing cathode surrounding the central cathode. This creates an electric field between the focusing cathode and the central cathode that repels the electrons emitted from the central cathode toward the anode, ultimately preventing the electron flow from diverging and causing it to follow parallel trajectories. Obtaining electron flow.

However, in the case of an electron beam source that generates a pulsed electron beam of 30 kiloamperes under an accelerating voltage of 1 megavolt, the accelerating voltage is extremely high, so the focusing cathode is The external voltage source becomes prohibitively large to apply a negative convergence voltage. For this reason, convergence by a magnetic field rather than an electric field has been proposed and implemented as a means of converging the electron flow, but the coil for generating the convergence magnetic field placed around the cathode structure is large and often poses a problem when using the device. Moreover, the operating power is also large. In addition to these disadvantages, the electron beam diverges in the absence of a magnetic field, so only an electron beam that is always accompanied by a magnetic field can be used, and this converging magnetic field causes undesirable interactions with the experimental magnetic field.

An object of the present invention is to provide a cathode structure for a high-intensity pulsed electron beam source that generates a convergent electric field and suppresses electron beam divergence without using an external voltage source.

The purpose of this is to apply a high negative accelerating potential (e.g. 1 megavolt) directly to the focusing cathode according to the invention, and at the same time, to the central cathode via the plasma, an absolute value equal to the voltage drop of the plasma is lower than the high negative accelerating potential. This is achieved by applying a reduced negative potential (for example 0.9 megavolts).

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the structural principle of a cathode for a high-intensity pulsed electron beam source according to the present invention.

A focusing cathode 2 is placed around the center cathode 1 with an insulator 6 in between. Grounded anode 5 and focusing cathode 2
is connected to an accelerating high-voltage power source 7 (for example, 1 MV) to maintain the focusing cathode 2 at a large negative potential. The adjustment cathode 3 is placed with a gap 4 from the center cathode 1.
This adjusting cathode 3 is also connected to the accelerating power source 7, and has the same potential as the focusing cathode. During operation, plasma is generated in the gap 4, and due to the potential drop of the plasma, the potential of the central cathode 1 moves toward the positive, and becomes, for example, a potential of -0.9 MV with respect to the focusing cathode 2 of -1 MV. The distribution of equipotential lines at this time and the potential distribution with respect to the central axis x of the central cathode 1 are shown in Fig. 2b, and the distribution of equipotential lines of the cathode structure without the adjustment cathode 3 is shown in Fig. 2a for comparison. Shown below. In FIG. 2b, the equipotential lines are curved toward the front of the central cathode 1 and act to narrow down the emitted electrons.

FIG. 3 shows details of the structure of an embodiment of the present invention.
The same reference numbers as in FIG. 1 are used to indicate the same parts. In order to be able to adjust the gap 4 between the tuning cathode 3 and the central cathode 1 to control the focusing effect, the tuning cathode 3 can be moved axially when rotated.

FIG. 4 shows a modification of the central cathode 1 and the focusing cathode 2 suitable for carrying out the present invention.

In FIG. 4a, the central cathode 1 is a cylinder and the focusing cathode 2 is a cylinder. In FIG. 4b, the center cathode 1 and the focusing cathode 2 are flat plates. In both cases, the focusing cathode 2 is movable with respect to the central cathode 1.
It may be possible to adjust the position of the focusing cathode 2 relative to the object.

As is clear from the above description, the present invention applies a negative potential to the focusing cathode 2 with respect to the center cathode 1 without using an external voltage source, thereby suppressing the divergence of electrons from the front surface of the center cathode. In order to obtain the required convergent electric field using a method that can be called self-bias,
No external voltage source is required and the device is lightweight.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structural principle of the present invention. Figure 2a shows the distribution of equipotential lines between the central cathode and the anode without the use of a regulating cathode, and Figure 2b shows the distribution of the equipotential lines between the central cathode and the anode when a regulating cathode is used according to the invention. The distribution of equipotential lines between is shown. FIG. 3 is a longitudinal sectional view of an embodiment of the invention. Figures 4a and 4b illustrate a center cathode and focusing cathode structure suitable for practicing the invention. In the figure: 1...center cathode, 2...focusing cathode, 3
...Adjustment cathode, 4...Gap, 5...Anode, 6...
...Insulator, 7...Acceleration power source.

Claims (1)

[Scope of Claims] 1. A central cathode, a converging cathode placed outside the central cathode and capable of applying a negative accelerating voltage to the anode, a converging cathode placed at a distance from the central cathode, an adjustment cathode that is electrically connected to the cathode for adjustment and applies a negative potential that is smaller in absolute value than the negative accelerating potential by the voltage drop of the plasma to the center electrode via the plasma generated between the electrodes; A cathode for a high-intensity pulsed electron beam source, comprising: 2. The cathode for a high-intensity pulsed electron beam source according to claim 1, wherein the adjusting cathode is movable so as to change the interval. 3. The cathode for a high-intensity pulsed electron beam source according to claim 1, wherein the central cathode is cylindrical, and the focusing cathode is cylindrical. 4. The cathode for a high-intensity pulsed electron beam source according to claim 1, wherein the center cathode and the focusing cathode are plate-shaped.