JP2889872B1 - electronic microscope - Google Patents

Abstract

Abstract: [PROBLEMS] When one insulating container of an ultra-high voltage electron microscope using a hollow high-voltage cable is opened to the atmosphere by maintenance or the like, the other insulating container connected by the cable is also opened to the atmosphere and mixed. Dust or moisture may cause discharge. In addition, the strength of the cable end portion cannot withstand the repetition of the decompression and pressurization, and there is a possibility that a crack may be formed. A high-voltage cable terminal is provided with a pair of check valves having conduction in opposite directions. [Effect] By appropriately selecting the cracking pressure of the check valve, the inside of the high-pressure cable is always filled with the insulating gas in a certain pressure range regardless of the insulating gas pressure in the insulating container, and the air can be prevented from flowing. . Also, the repetition of the pressure difference is kept small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrahigh-voltage electron microscope in which an electron microscope main body and a high-voltage power supply for supplying a high voltage thereto are separated, and both are connected by a high-voltage cable.

[0002]

2. Description of the Related Art In an electron microscope, there are roughly two parts which are housed in an insulating container and to which a high voltage is applied. One is an electron accelerating unit composed of an electron gun and an accelerating tube, which is a part of the electron microscope main body. The other is a high-voltage power supply that generates a high voltage. From the viewpoint of the shape, the electron microscope type includes the electron accelerating unit and the high-voltage power supply that are housed in one insulating container without being separated, the type that separates the two parts and connects them with a high-voltage cable, and the type that two parts are juxtaposed Are connected by a pipe and are connected in a pipe filled with an insulating gas.

Conventionally, a type connected with a high-voltage cable is a general type in an electron microscope having an acceleration voltage of about 300 kV. The reasons are as follows: 1) Since the required insulation distance in the electron acceleration section of the electron microscope can be as short as several tens of centimeters, this section can be made smaller than a high-voltage power supply. 2) The diameter of the high-voltage cable is as thin as 5 cm or less, and handling such as handling is easy. 3) Cable terminal receivers can be used, and cables can be easily removed. 4) By using a high-voltage cable, the electron microscope main body and the high-voltage power supply can be separated from each other so that noise such as magnetic induction generated by the high-voltage power supply does not affect the electron microscope main body. 5) It is possible to attenuate minute fluctuations (ripples) of high voltage generated by a high voltage power supply due to the electric capacity and resistance of the high voltage cable. 6) In this class of accelerating voltage, high voltage power supplies are often oil-insulated, whereas electron guns,
Accelerator tubes are often insulated by gas insulation or solid resin and cannot be placed in the same insulating container. For example, it was more advantageous to separate the electron microscope main body from the high voltage power supply and connect them with a high voltage cable.

However, in a so-called ultra-high voltage electron microscope having an acceleration voltage of 1 MV or more, the insulation distance is required to be 1 m or more, the electron acceleration section becomes large, and the diameter of the high-voltage cable becomes 10 mm.
cm or more, which is inconvenient to handle and the high voltage power supply is also gas-insulated due to voltage and maintenance reasons. In general, a type in which two members are juxtaposed, connected between them by a pipe, and connected in a pipe filled with insulating gas has been generally used.

[0005]

On the other hand, in the case of a so-called ultra-high voltage electron microscope having an acceleration voltage of 1 MV or more, the insulation distance of the high-voltage cable terminal must be increased, the cable terminal receiver becomes large, and the cable terminal becomes large. Because of the danger of discharge at the contact surface between the terminal and its receiver, it is advantageous to expose the cable terminal directly in the insulating container without making the cable terminal receiver. In the case of a high-voltage cable for an ultra-high voltage electron microscope, the reasons for manufacturing are that a small current of only about several A is required at maximum, and that the minimum bending radius of the cable is reduced to facilitate handling. A high pressure cable with a hollow section is used.

In this case, since the inside of the high-voltage cable is hollow, if one of the insulating containers is evacuated or opened to the atmosphere by maintenance or the like, the other insulating container connected by the cable is also opened to the atmosphere. is there. That is, there is a problem in that small dust, dust, and moisture flowing into the insulating container and the cable, which do not originally require maintenance, are mixed when the air is released to the atmosphere, which causes a discharge.

However, there is also a problem in that both ends of the cable are simply sealed and an insulating gas is sealed inside the cable. In other words, the insulating container changes the insulating gas from atmospheric pressure to atmospheric pressure +3.
It is sealed and used up to about atmospheric pressure, but the strength of the cable end portion cannot withstand the repeated decompression and pressurization, and there is a possibility of cracking. Therefore, it is necessary to reduce a pressure difference generated between the inside and outside of the cable terminal when the insulating gas is exchanged.

[0008]

In order to solve the above-mentioned problems, a set of check valves having conduction in opposite directions to each other is provided at a high voltage cable terminal.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention is shown in FIG.
FIG. FIG. 1 is a schematic diagram of the inside of the high-voltage cable 7 and the main body side insulating container 1, and shows the connection between the high-voltage cable 7 and the insulating container 1. In the insulating container 1, a high-voltage cable terminal portion 2, an electron gun 3, and an acceleration tube 4 connected thereto are provided. The electron gun 3 and the acceleration tube 4 are collectively referred to as an electron accelerator 5.

An electron source 10, a Wehnelt 11, and an anode 12 are provided inside the electron gun 3. In the case of a field emission electron gun, an electron source 10 and an extraction electrode (not shown) are provided. The accelerating tube 4 is a device for accelerating electrons, and is a vacuum vessel in which a cylindrical insulator and a perforated disk-shaped metal spacer are stacked and joined. An accelerating electrode 13 for electron acceleration is set inside, and a high voltage is applied to each stage by dividing the entire accelerating voltage by a bleeder resistor (not shown).

The cable end portion 2 comprises a hollow bushing 14 made of an insulating material, a metal fitting 15 molded at the tip of the hollow bushing 14, and a tip electrode 17 connected to the metal fitting 15 via a vacuum packing 16. The surface of the tip electrode 17 is polished so that there is no protrusion around the surface in order to prevent discharge.
The inside is filled with an insulating gas. An internal conductor 18 inserted into the cable hollow portion of the high-voltage cable 7 connects a high-voltage power supply (not shown) to the tip electrode 17. Here, it is assumed that the cable terminal (not shown) on the high voltage power supply side is sealed here.

Instead of the inner conductor 18, a wire or resistor having resistance may be inserted instead of the conductor, or a semiconductive layer may be formed on the inner wall of the cable hollow portion during the cable manufacturing process to be used as a resistance cable. . In the insulating container 1, in addition to a bleeder resistor for giving a predetermined potential distribution to the accelerating tube 4, a power supply for heating an electron source, an electron gun fine movement mechanism, and a local shape due to the uneven shape of each of the contents in the insulating container. Although an electric field alleviating cover or the like is installed to avoid the electric field concentration, it is not shown here for simplicity.

The tip electrode 17 and the electron source 10 are connected by a conducting wire 8 to apply an accelerating voltage to the electron accelerating section 5. The electrons that have exited the electron gun 3 are accelerated to a predetermined acceleration voltage by the acceleration tube 4, advance to the mirror 6, and finally form an enlarged image of the sample. Here, the electronic lens in the mirror body, the exhaust pump, their control power supply, and the like are not shown. The other end of the high voltage cable 7 is connected to an insulating container on the high voltage power supply side.

A check valve 19 is provided at the tip electrode 17 in a direction in which the insulating gas flows from the insulating container 1 into the cable 7, and a check valve 20 in a direction in which the insulating gas flows out from the cable 7 into the insulating container 1. Is attached. The operation of the check valve in which the conduction directions of the pair of insulating gases are reversed will be described with reference to FIG.

The pressure of the insulating gas (external pressure of the cable) in the insulating container 1 is set to A atmospheric pressure, and the pressure of the insulating gas in the hollow portion of the cable (internal pressure of the cable) is set to C atmospheric pressure. The atmospheric pressure is 0 atm, the vacuum is -1 atm, the cracking pressure of the check valve 19 installed in the direction in which the insulating gas flows into the cable is d, and the reverse valve is installed in the direction in which the insulating gas flows out of the cable. The cracking pressure of the stop valve 20 is set to e atmospheric pressure.

The procedure for installing the electron microscope and filling the insulating container 1 and the hollow cable 7 with the insulating gas prior to the operation is as follows. First, an insulating gas is introduced into the insulating container 1 through a pipe (not shown) while evacuating the insulating container 1 and the hollow cable 7. At this time, as described above, since the cable terminal (not shown) on the high-voltage power supply side is sealed, the insulating gas is also introduced into the hollow cable 7 through the check valve 19, and the point P _{1 in} FIG. The insulating container 1 is filled with an insulating gas at a predetermined pressure A ₀ , and the hollow cable 7 is filled with an insulating gas at a pressure A ₀ -d, corresponding to the positions shown in FIG.

Next, consider the case where the insulating container 1 is opened for maintenance or the like. Initial gas pressure within the dielectric casing 1 in is in A ₀ atm normal use, the insulating gas is recovered in the gas recovery device such that the gas pressure in the insulating container 1 -1 atm vacuum. During this time, the check valve 20 is open where it becomes cable external pressure (A ₀ -d-e) pressure shown at point P _2, beginning cable pressure C is lowered, the insulating gas in the cable 1 is also recovered. This condition, cable external pressure (e-1) shown in the point P ₃ in FIG. 3 until pressure. After that, air is put into the insulating container and released to the atmosphere to perform maintenance.

[0018] Once maintenance is completed, again, after evacuation, when we put an insulating gas, opens the check valve 19 in the cable external pressure (d + e-1) pressure shown at the point P ₄ in FIG. 3, the cable pressure C is Start to rise. This state continues to the cable external pressure (A ₀ -d) pressure shown at point P ₁ in FIG. This returns to the original state and returns to the normal use state. The cracking pressure d and e of the check valve 19 and 20, from the point P ₁ in FIG. 3 by choosing to draw a parallelogram path P _4, the cable pressure variation, in the absence of a check valve ( A ₀ +1) The pressure can be compressed from the atmospheric pressure, and the force applied to the cable terminal 2 can be reduced. Check valve 1
If the cracking pressure d of 9 is 0.5 atm and the cracking pressure e of the check valve 20 is 1.5 atm, the pressure difference between the inside and outside of the cable can be minimized both when vacuuming the insulating container and during normal use filled with insulating gas. ± 0.5 atm. This value is a small value that is sufficiently acceptable as the force applied to the cable terminal.

The above embodiment has described the case where the cable terminal is sealed on one side. The check valve set is preferably attached to the side of the insulating container where maintenance is frequently performed, but may be attached to both sides of the high-voltage cable. If one side of the cable is airtight, when recovering the insulating gas from the insulating container on the airtight side,
By simultaneously collecting the insulating gas in the other insulating container and slightly reducing the internal pressure of the cable, the pressure applied to the cable terminal can be reduced.

[0020] In the case of providing the set of check valves on both sides of the high-voltage cable but occurs insulating gas flowing from the other insulated vessel at the insulating gas recovery, in terms P ₁ in FIG. 3 P ₄ changes In no case does the air flow into the high-voltage cable or into the other insulating container.

In this embodiment, although the description is omitted, a multi-core wire is inserted into the hollow portion of the high-voltage cable 7 and various control voltages or signals required by the electron microscope are transmitted using the multi-core wire. It goes without saying that you can do it.

Another embodiment of the present invention will be described with reference to FIG. FIG. 2 is a schematic diagram of the entire electron microscope including a high-voltage power supply, and is a preferred embodiment particularly in the case of an ultra-high-voltage electron microscope using a field emission electron gun. This embodiment shows an example in which independent insulating containers 1, 45, and 30 are provided corresponding to the electron microscope main body, the high-voltage power supply, and the floating power supply, respectively.

2, a field emission electron gun 21, a field emission electron source 22, an accelerating tube 4 and a high-voltage multicore cable terminal 23 are provided in the insulating container 1 on the left side of FIG. Construct the microscope body. The high-voltage multi-core cable 33 is connected to the high-voltage multi-core cable terminal 23, and the high voltage introduced by the multi-core wire is applied to the field emission electron gun 2.
1, supplied to the acceleration tube 4 and the like.

The right side of FIG. 2 shows a high-voltage power supply 40 for generating a DC high voltage required for an electron microscope. A booster circuit (for example, Cockcroft-
C _o daltons circuit) 41 is provided, high DC voltage generated here via a protection resistor 43, is derived via a high-pressure single-core cable terminal portion 46. In addition, a discharge resistor (not shown) and the like for immediately discharging the electric charge stored in the capacitor used in the booster circuit 41 are provided in the insulating container 45. The high-voltage power supply 40 is connected to the step-up transformer 4.
2 and a drive power supply 44 for driving the step-up transformer. The high-frequency AC high voltage generated by the step-up transformer 42 is applied to the step-up circuit 41 to obtain a desired DC high voltage. Of course, in addition to this, a feedback circuit (not shown) for stabilizing the high voltage is provided.

In order to clean the surface of the field emission electron source 21, a flushing power supply for energizing and heating the field emission electron source 21 and a drawer for field emission of electrons are provided in the central insulating container 30 in FIG. A floating power supply 31 containing a power supply for supplying a voltage, a power supply for supplying a voltage for controlling an electrostatic lens action in the acceleration tube, and the like is stored. This floating power supply 31 is provided with a separation plate 35 on an insulating column 34.
Installed on top. The DC high voltage derived from the high-voltage power supply 40 via the high-voltage single-core cable end 46 is introduced into the insulating container 30 via the high-voltage single-core cable 32 and another high-voltage single-core cable end 46. The separation plate 35 is floating at the supplied potential. The floating power supply 31 is connected to a control device 36 placed on the low voltage side (earth potential) via an optical fiber 37 and can be controlled from the low voltage side (earth potential). Floating power supply 3
1 is supplied by a battery provided on the separation plate 35. This power may be transmitted at a high frequency from a low voltage side using a capacitor, or may be supplied by receiving a laser beam at a high voltage side and converting the power. Floating power supply 31 and control device 36
The communication between them may be by spatial light transmission using infrared light or the like instead of the optical fiber. In addition, a filter capacitor for reducing ripples, a reference resistor, and the like are arranged in the insulating container 30, but they are not shown here.

When the high-voltage single-core cable 32 is a resistance cable rather than a conductor cable, a high-voltage ripple attenuating effect and a highly stable DC high-voltage power supply can be obtained due to the capacitance and resistance components of the cable. However, the resistance may be connected in the insulating container using a conductor cable.

A wire for heating the electron source from the floating power supply 31 and a wire for applying an extraction voltage are led out through the high-voltage multi-core cable terminal section 23 and pass through the high-voltage multi-core cable 33 to another high-voltage multi-core cable. The field emission electron gun 21 is introduced into the insulating container 1 through the terminal section 23 and
Supplied to

In this embodiment, the high-voltage multi-core cable terminal section 23 and the high-voltage single-core cable terminal section 46 are provided with the check valve pair described in the first embodiment. , The pressure differential across the high-voltage cable is similarly reduced. Of course, the air does not flow into the insulating container or the high-voltage cable.

In this embodiment, the high-voltage multicore cable 3
Reference numeral 3 denotes a wire for controlling an electron gun inserted into a hollow portion of a high-voltage single-core cable as a core wire. As a result, the high-voltage multi-core cable 33 becomes a conductor cable, but the switching noise and the like of the booster circuit 41 are already sufficiently attenuated at the stage of the high-voltage single-core cable 32 and do not affect the electron microscope main body. The multi-core wire introduced by the high-voltage multi-core cable 33 is connected to the field emission electron source 22, the field emission electron gun 21, the acceleration tube 4, and the like.
1 controls the field emission electron gun 21 and controls the emission of the field emission electron beam.

[0030]

The main body of the electron microscope and the high voltage power supply are separated,
In an electron microscope of the type that connects between them with a high-voltage cable,
If a set of check valves having conduction in opposite directions is provided at the end of the high-voltage cable and the cracking pressure is properly selected, the pressure difference applied to the cable can be made sufficiently small, so that damage to the high-voltage cable can be prevented.

Furthermore, since gas conduction between the main body and the insulating container of each high-voltage power supply can be restricted, even if one of the insulating containers is opened to the atmosphere for maintenance or the like, a small flow that flows into the other insulating container when the air is opened to the atmosphere. There is no mixing of dust, dust and moisture, and the risk of discharge can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of connection between a high-voltage cable and an insulating container on the electron microscope main body side of the present invention.

FIG. 2 is a schematic view showing an embodiment of an ultra-high voltage field emission electron microscope using the high-voltage multicore cable of the present invention.

FIG. 3 is a graph showing a relationship between a cable external pressure and a cable internal pressure in a case where a pair of check valves having a pair of conducting directions reversed is provided.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Insulated container, 2 ... Cable terminal part, 3 ... Electron gun, 4 ...
Accelerator tube, 5: electron accelerator, 6: mirror, 7: high-voltage cable, 8: conducting wire, 10: electron source, 11: Wehnelt, 1
2 ... Anode, 13 ... Acceleration electrode, 14 ... Bushing, 15 ...
Metal fittings, 16: vacuum packing, 17: tip electrode, 18: internal conductor, 19: check valve (inflow direction), 20: check valve (outflow direction), 21: field emission electron gun, 22: field emission electron source , 23 ... High voltage multi-core cable end, 30 ... Insulated container (for floating power supply), 31 ... Floating power supply, 32 ... High voltage single core cable, 33 ... High voltage multi-core cable, 34 ... Insulation column, 35 ... Separation plate, 36 ... Control device, 3
7 optical fiber, 40 high-voltage power supply, 41 booster circuit
42 high-voltage transformer, 43 protection resistance, 44 drive power supply, 45 insulating container (for high-voltage power supply).

Continued on the front page (72) Inventor Shigeo Kubota 2520 Akanuma-cho, Hatoyama-cho, Hiki-gun, Saitama Pref., Ltd.Hitachi, Ltd. Within the Business Unit (72) Inventor Koichiro Hayashi 882 Ma, Hitachinaka-shi, Ibaraki Pref.Hitachi, Ltd.Measurement Equipment Division (72) Inventor Hideaki Takehara 5-1-1 Hidakacho, Hitachi City, Ibaraki Prefecture Hitachi Cable, Ltd. (56) References JP-A-4-332446 (JP, A) JP-A-9-190723 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01J 37 / 248

Claims (4)

(57) [Claims] 1. An electron microscope in which a high voltage required by an electron microscope is supplied by a hollow high-pressure cable filled with an insulating gas into an insulating container filled with an insulating gas, the electron microscope being provided in the insulating container. An electron microscope, wherein at least one end of a high-voltage cable is provided with a set of check valves having conduction in opposite directions and having a predetermined cracking pressure. 2. The check valve according to claim 1, wherein the check valve has a cracking pressure of less than 1 atm in a direction of flowing into the cable of the check valve, and a check valve having a cracking pressure of more than 1 atm in a direction of flowing out of the cable. 2. The electron microscope according to claim 1, which is a pair of: 3. An electron microscope main body, a high-voltage power supply for generating a high-voltage power supply required by the electron microscope, and a floating power supply for adding a control voltage and the like required by the electron microscope to the high-voltage power supply. Electron microscopes each connected by a hollow high-voltage cable filled with an insulating gas in an insulating container filled with an insulating gas, and connected to respective terminals of the high-voltage cable provided in the insulating container in directions opposite to each other. An electron microscope comprising a set of check valves having conduction. 4. The electron microscope according to claim 1, wherein a multi-core wire is inserted into a hollow portion of the high-voltage cable connecting the electron microscope body and the floating power supply.