JPH0772758B2 - Low energy charged particle beam chopping device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring apparatus using a charged particle beam, for example, 0 to several Ke which are continuous in time.
The present invention relates to a device for chopping a charged particle beam having a low energy of about V 2 at a high speed of several nanoseconds or less.

[0002]

2. Description of the Related Art Conventionally, as a high-speed chopping device of several nanoseconds or less, as shown in FIG. 3, a pair of deflection electrodes 8 are arranged between an entrance slit 6 and an exit slit 7 through which charged particles can pass. Chopping devices are known.

In this chopping device, a high-frequency electric field is applied between a pair of deflection electrodes 8 to deflect the continuous charged particle beam 1 that has passed through the entrance slit 6 and block the unnecessary beam at the exit slit 7, Only the required beam is passed through the exit slit 7 to intermittently pulse the beam.

[0004]

However, in this chopping device, when a magnetic field for beam transport is applied in the traveling direction of the beam, charged particles having low energy make cyclotron motion in the magnetic field, and the radius of this motion causes There is a problem that the beam diameter that can be chopped is limited by the chopping device.

Further, due to the cyclotron frequency of this motion, the chopping frequency is also limited, and it is difficult to change the frequency.

[0006]

In order to solve the above problems, according to the present invention, a large number of voids through which charged particles can pass are provided between an inlet electrode and an outlet electrode through which a large number of voids through which charged particles can pass. Alternatively, two or more intermediate electrodes are arranged, the size of the void is made smaller than the distance between the electrodes, and a chopping is performed by applying a time-varying potential to the intermediate electrode. A particle beam chopping device is proposed.

Here, the charged particles are particles having positive or negative charges such as electrons, ions, positrons, antiprotons, muons, molecules and clusters.

As the entrance electrode, the exit electrode, the intermediate electrode, etc. having a large number of voids, an electrode provided with a large number of holes through which a charged particle can pass in a conductive thin plate, a mesh-shaped or a blind formed by conductive thin wires. Shaped electrodes or the like can be used.

In these electrodes, the size d _{m of the} void formed in the electrodes is made sufficiently smaller than the gaps d _g , d _g '... Between the electrodes. Further, the smaller the gaps d _g , d _g ′ between the electrodes, the less the modulation of the beam energy .

In the above chopping device, an electrostatic potential lower than the energy (E ₀ ) of the charged particle beam (E ₀ > V ₂ , V when the charged particle has a positive charge) is applied to the entrance and exit electrodes.
₃ , when the charge of the charged particles is negative, E ₀ > −V ₂ , −V ₃ )
Then, a time-varying potential is applied to the intermediate electrode, and the beam is interrupted by the electric field between the electrodes to chop a continuous beam.

[0011]

When the energy of the charged particle beam is lower than the potential of the intermediate electrode, the beam is reflected by the electric field between the entrance electrode and the intermediate electrode, and the energy of the beam is lower than the potential of the intermediate electrode. When is also high, the beam passes through the exit electrode.

In this case, since the electrostatic potential is applied to the inlet electrode and the outlet electrode, the energy of the beam received by the chopping device outside the chopping device is very small.

In this chopping device, the beam can be interrupted at a high speed of about nanosecond or less by sufficiently narrowing the distance between the electrodes and the size of the air gap.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 shows an embodiment of the present invention,
1 is a schematic diagram of a chopping device that converts a positron beam 1 (mass of positrons: m) having a positive charge of energy E ₀ into a pulse beam of about _tw seconds.

Here, reference numerals 2, 3 and 4 are an intermediate electrode composed of mesh electrodes, an inlet electrode and an outlet electrode, and the distances d _g and d _g ′ between these electrodes are t when a beam of energy E ₀ is t. _It is made sufficiently smaller than the flight distance t _w (2m / E ₀ ) ^{1/2 at} the time of _w .

Further, the size d _m of the voids of the mesh of the electrodes 2, 3 and 4 is made sufficiently smaller than the intervals d _g and d _g ′ between the electrodes, and in this embodiment d _m is d _g and d _g ′. It is desirable to be 5 to 1/10 or less.

In the above structure, the positron beam 1 having the energy E ₀ is applied to the chopping device by applying a magnetic field for guiding in the traveling direction.

Here, electrostatic potentials V ₂ and V ₃ lower than the energy of the charged particle beam 1 are applied to the inlet electrode 3 and the outlet electrode 4, and the intermediate electrode 2 has a time-varying potential as shown in FIG. Apply V ₁ (t).

[0019] In this case, between the entrance electrode 3 and the intermediate electrode 2, when the potential V ₁ (t) is lower than the electrostatic potential V ₂ and V ₃ shown by a solid arrow direction, the potential V ₁ (t) Is higher than the electrostatic potentials V ₂ and V _3, a time-varying electric field 5 is generated as shown by the dotted arrow direction. Similarly, an electric field 5 ′ that changes with time is generated between the intermediate electrode 2 and the outlet electrode 4.

Therefore, the potential V ₁ (t) is equal to the positron beam 1
When the energy is higher than the energy E ₀ of the positron beam, the positron beam 1 is reflected by the electric field 5 generated between the entrance electrode 3 and the intermediate electrode 2 and shown by the dotted arrow direction.

On the other hand, when the potential V ₁ (t) is lower than the energy E ₀ of the positron beam 1, the positron beam 1 receives the entrance electrode 3
The intermediate electrode 2 and the intermediate electrode 2 are accelerated by an electric field 5 indicated by a solid arrow and pass between the intermediate electrode 2 and the outlet electrode 4. That is, in FIG. 2, the positron beam 1 passes through the chopping device for the time t _w .

Therefore, in this embodiment, what was a continuous beam before the chopping device is interrupted at high speed, and becomes a pulse beam of about t _w at the position immediately after the chopping device.

[0023]

In summary, according to the present invention, a low energy continuous beam can be chopped at high speed, and even when a magnetic field is applied in the beam traveling direction, the chopping frequency and the beam diameter that can be chopped. Is not affected by the magnetic field. If the beam diameter is large, chopping is possible by using an electrode with a large area.

[Brief description of drawings]

FIG. 1 is a schematic view of a charged particle beam chopping device showing an embodiment of the present invention.

FIG. 2 is a waveform diagram of a voltage input to an intermediate electrode in the above embodiment.

FIG. 3 is a schematic view of a conventional charged particle beam chopping device.

[Explanation of symbols]

 1 Direct-current positron beam 2 Intermediate electrode 3 Inlet electrode 4 Outlet electrode

Claims (1)

[Claims] 1. One or more intermediate electrodes having a large number of voids through which charged particles can pass are arranged between an inlet electrode and an outlet electrode having a large number of voids through which charged particles can pass, and the size of the voids. Of the charged particles on the inlet and outlet electrodes.
An electrostatic potential lower than the energy of the beam is applied to
A low-energy charged particle beam chopping device characterized by applying a time-varying potential to the poles for chopping.