Electron tube

An electron tube includes a photoelectric conversion unit, an electron detection unit configured to receive a photoelectrons from the photoelectric conversion unit, a gate electrode disposed between the photoelectric conversion unit and the electron detection unit, and a housing configured to accommodate the photoelectric conversion unit, the electron detection unit, and the gate electrode. The housing has a lid portion to which the photoelectric conversion unit is fixed and which constitutes one end side of the housing. The gate electrode includes a main body portion that control passage of the photoelectrons by applying a voltage, and a power supply part that supports the main body portion so as to be spaced apart from the photoelectric conversion unit and applies a voltage to the main body portion. The power supply part is held by the lid portion.

TECHNICAL FIELD

The present disclosure relates to an electron tube.

BACKGROUND

An electron tube which includes a photoelectric conversion unit that emits photoelectrons corresponding to incident light, an electron detection unit that receives the photoelectrons from the photoelectric conversion unit, and a housing that accommodates the photoelectric conversion unit and the electron detection unit is known (refer to, for example, U.S. Pat. No. 5,374,826).

SUMMARY

In the above-described electron tube, a gate electrode that controls passage of the photoelectrons by applying a voltage may be disposed between the photoelectric conversion unit and the electron detection unit inside the housing. In such an electron tube, it is not easy to speed up switching of the voltage applied to the gate electrode due to an influence of electrostatic capacitance between the photoelectric conversion unit and the gate electrode, and it is difficult to speed up an operation of the gate electrode.

An object of the present disclosure is to provide an electron tube capable of speeding up the operation of the gate electrode.(1) An electron tube according to one aspect of the present disclosure includes a photoelectric conversion unit configured to emit photoelectrons corresponding to incident light, an electron detection unit configured to receive the photoelectrons from the photoelectric conversion unit, a gate electrode disposed between the photoelectric conversion unit and the electron detection unit, and a housing configured to accommodate the photoelectric conversion unit, the electron detection unit, and the gate electrode, wherein the housing has a lid portion to which the photoelectric conversion unit is fixed and which constitutes one end side of the housing, the gate electrode includes a main body portion that controls passage of the photoelectrons by applying a voltage, and a power supply part that supports the main body portion so as to be spaced apart from the photoelectric conversion unit and applies a voltage to the main body portion, and the power supply part is held by the lid portion.

In the electron tube, the power supply part of the gate electrode is held by the lid portion, so that it is not necessary to arrange and hold the power supply part so as to extend parallel to the photoelectric conversion unit, for example. Therefore, it is possible to reduce an electrostatic capacitance between the photoelectric conversion unit and the gate electrode. As a result, it is possible to speed up switching of the voltage applied to the gate electrode and to realize a high speed operation of the gate electrode.(2) The electron tube described in (1) may further include a focusing electrode provided between the photoelectric conversion unit and the electron detection unit so as to face the photoelectric conversion unit and configured to focus the photoelectrons from the photoelectric conversion unit, and the gate electrode may be electrically connected to the focusing electrode. In this case, it is possible to reliably perform a gate operation and a focus control for photoelectrons.(3) In the electron tube described in (2), the gate electrode may be provided integrally with the focusing electrode. In this case, the gate electrode and the focusing electrode can be disposed efficiently.(4) In the electron tube described in any one of (1) to (3), the power supply part may include a plurality of rods each fixed to the lid portion and having one end portion located in the housing, and a connection portion that connects one end portion of each of the plurality of rods to the main body portion. In this case, it is possible to efficiently reduce the electrostatic capacitance between the photoelectric conversion unit and the gate electrode by supporting the main body portion of the gate electrode inside the housing so as to be suspended from the lid portion by the plurality of rods.(5) In the electron tube described in (4), the plurality of rods may include a first rod that passes through the lid portion and a second rod having the other end portion embedded in the lid portion. In this case, since the second rod can be made shorter than the first rod by embedding the other end portion of the second rod in the lid portion, it is possible to further efficiently reduce the electrostatic capacitance between the photoelectric conversion unit and the gate electrode.(6) The electron tube described in any one of (1) to (5) may further include a first electric field concentration relaxation electrode electrically connected to the lid portion so as to have the same potential as that of the photoelectric conversion unit, and configured to relax concentration of an electric field formed inside the housing, and a part of the first electric field concentration relaxation electrode may be located closer to the electron detection unit than the main body portion in a facing direction in which the photoelectric conversion unit and the electron detection unit face each other. In this case, the first electric field concentration relaxation electrode relaxes the concentration of the electric field inside the housing, and a withstand voltage of the electron tube can be increased.(7) The electron tube described in (4) or (5) may further include a second electric field concentration relaxation electrode electrically connected to the lid portion so as to have the same potential as that of the photoelectric conversion unit and configured to relax concentration of an electric field formed inside the housing, and an end portion of the second electric field concentration relaxation electrode on an inner side of the housing may be located closer to the electron detection unit than the main body portion in a facing direction in which the photoelectric conversion unit and the electron detection unit face each other, and may extend to a position close to the power supply part in an intersecting direction that intersects the facing direction. In this case, the second electric field concentration relaxation electrode relaxes the concentration of the electric field inside the housing, and the withstand voltage of the electron tube can be increased.(8) In the electron tube described in (7), the rod may be fixed to the lid portion by a hermetic seal portion, and the end portion of the second electric field concentration relaxation electrode on the inner side of the housing may extend until it reaches the hermetic seal portion in the intersecting direction. In this case, the second electric field concentration relaxation electrode further relaxes the concentration of the electric field inside the housing, and the withstand voltage of the electron tube can be further increased.(9) The electron tube described in (4) or (5) may further include a third electric field concentration relaxation electrode electrically connected to the lid portion so as to have the same potential as that of the photoelectric conversion unit and configured to relax concentration of an electric field formed inside the housing, and an end portion of the third electric field concentration relaxation electrode on an inner side of the housing may be located closer to the electron detection unit than a connection point between the rod and the connection portion in the facing direction in which the photoelectric conversion unit and the electron detection unit face each other. In this case, the third electric field concentration relaxation electrode relaxes the concentration of the electric field inside the housing, and the withstand voltage of the electron tube can be increased.(10) In the electron tube described in (9), one end portion of the third electric field concentration relaxation electrode may extend until it reaches the connection portion in an intersecting direction that intersects the facing direction. In this case, the third electric field concentration relaxation electrode further relaxes the concentration of the electric field inside the housing, and the withstand voltage of the electron tube can be further increased.(11) The electron tube described in (4) or (5) may further include a fourth electric field concentration relaxation electrode configured to extend along an intersecting direction that intersects the facing direction in which the photoelectric conversion unit and the electron detection unit face each other, having one end portion located inside the housing and the other end portion located outside the housing, and configured to relax concentration of an electric field formed inside the housing, and one end portion of the fourth electric field concentration relaxation electrode is located closer to the electron detection unit than a connection point between the rod and the connection portion in the facing direction, and extends to a position close to the power supply part in the intersecting direction. In this case, the fourth electric field concentration relaxation electrode relaxes the concentration of the electric field inside the housing, and the withstand voltage of the electron tube can be increased.(12) In the electron tube described in (11), one end portion of the fourth electric field concentration relaxation electrode may extend until it reaches the connection portion in the intersecting direction. In this case, the fourth electric field concentration relaxation electrode further relaxes the concentration of the electric field inside the housing, and the withstand voltage of the electron tube can be further increased.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following description, the same reference numerals are used for the same or corresponding elements, and overlapping descriptions will be omitted. The dimensions in the following description do not necessarily correspond to the drawings.

First Embodiment

As shown inFIG.1, an electron tube1is a so-called hybrid photo-detector (HPD). The electron tube1is used, for example, in an electron microscope. The electron tube1includes a housing2, a photocathode3and an electron detection unit4.

The housing2forms an internal space of which the inside is maintained in a vacuum. The housing2has a substantially cylindrical shape. As an example, the housing2has an outer diameter of about 30 mm and a height of about 25 mm. The housing2accommodates at least the photocathode3and the electron detection unit4therein. The housing2includes a tubular side portion21having an axis G as a central axis, a lid portion22that constitutes one end side (one end portion) of the housing2, and a stem23that forms the other end side (the other end portion) of the housing2.

One end side of the side portion21is airtightly connected and sealed with the lid portion22. The other end side of the side portion21is airtightly connected and sealed with the stem23. The lid portion22is a disk-shaped member made of a conductive member having a light-shielding property (for example, a metal material such as Kovar). The lid portion22has a lid upper surface22aand a lid lower surface22b. The lid upper surface22ais exposed outside the housing2. The lid lower surface22bis a surface on the side opposite to the lid upper surface22aand is exposed inside the housing2. An axis of the lid portion22overlaps the axis G of the housing2. The lid lower surface22bof the lid portion22faces the stem23.

The stem23has a base17, a power supply pin18, a signal pin19, a tubular portion46and a window portion28. The disk-shaped base17has a base main surface17aand a base back surface17b. The base main surface17ais exposed inside the housing2. The base back surface17bis a surface opposite to the base main surface17aand is exposed outside the housing2. The electron detection unit4is mounted via a substrate24on a central portion of the base main surface17a. Examples of a material of the base17include copper which is a metal material with high heat dissipation, but other metal materials such as Kovar, conductive materials, and insulating materials such as ceramics can also be used. The base17effectively dissipates heat generated during the operation of the electron detection unit4.

The power supply pin18applies a voltage to the substrate24on which the electron detection unit4is mounted. The power supply pin18is a rod-shaped conductive member that extends parallel to the axis G. One end of the power supply pin18is exposed inside the housing2. The other end of the power supply pin18is exposed outside the housing2. One end of the power supply pin18is electrically connected to the substrate24via a wire (not shown). The power supply pin18is insulated from the stem23.

The signal pin19picks up a signal from the electron detection unit4. The signal pin19is a rod-shaped conductive member that extends parallel to the axis G. One end of the signal pin19is electrically connected to the electron detection unit4via the substrate24. The other end of the signal pin19is exposed outside the housing2. The signal pin19is insulated from the stem23.

The tubular portion46is a cylindrical member that constitutes a light incidence hole26for receiving light inside the housing2. The tubular portion46protrudes from the base17toward the outside of the housing2in a direction that is inclined with respect to the axis G. The window portion28is airtightly joined to a flange47on the tip end side of the tubular portion46via an aluminum ring48. The window portion28allows light from the outside to pass through the housing2. The window portion28is made of a glass material (for example, quartz or sapphire glass) that is transparent to light. The window portion28made of quartz can effectively transmit light having a short wavelength such as ultraviolet light. The material of the window portion28may be selected according to the wavelength of light to be detected.

The photocathode3emits photoelectrons corresponding to incident light. The photocathode3is a film-like portion disposed on the lid portion22. The photocathode3is formed on a recessed curved surface22cthat is recessed in the lid lower surface22bof the lid portion22. The curved surface22cis a curved surface formed on the inner space side of the housing2in the lid portion22. The curved surface22cis a paraboloid of revolution with the axis G as an axis of rotation. The photocathode3is an alkali photocathode made of, for example, Sb-K-Cs. A crystalline photocathode material such as GaAsP can also be used as the photocathode material. Electric potential supply to the photocathode3is performed via the lid portion22. In the present embodiment, as described above, since the lid portion22is made of a conductive material having the light shielding property, the photocathode3functions as a reflective photocathode, and incidence of noise light to the photocathode3from the lid portion22side is suppressed.

The electron detection unit4is an electron detection unit that receives photoelectrons from the photocathode3. An example of the electron detection unit4is a semiconductor element, and particularly preferably one having an electron multiplying function. Such semiconductor elements include, for example, avalanche photodiodes. An avalanche photodiode is a semiconductor element in which heavily doped P and N regions are joined to form an electric field high enough for avalanche amplification there. The electron detection unit4is disposed on the base main surface17aof the stem23with the substrate24interposed therebetween. The electron detection unit4is disposed on the axis G. When photoelectrons are incident on an incident surface of the electron detection unit4, the photoelectrons are multiplied and an electric signal is output. Therefore, the electron detection unit4can also be said to be an electron multiplier.

In the present embodiment, the side portion21of the housing2has a first focusing electrode5, an insulating tubular portion12, an intermediate electrode part6, an insulating tubular portion14and an electric field concentration relaxation electrode7. The first focusing electrode5, the insulating tubular portion12, the intermediate electrode part6, the insulating tubular portion14, and the electric field concentration relaxation electrode7are disposed so as to be stacked in this order from the stem23side to the lid portion22side. The first focusing electrode5is an electrode part disposed between the photocathode3and the electron detection unit4. The first focusing electrode5is an electrode part closest to the electron detection unit4. The first focusing electrode5is disposed so as to directly face the electron detection unit4. The first focusing electrode5focuses photoelectrons on the electron detection unit4. The first focusing electrode5is a conductive member having a substantially cap shape. The first focusing electrode5has a flat plate portion5xhaving a circular flat plate shape of which a thickness direction is a direction of the axis G, and a peripheral wall portion5gthat stands upright on an outer peripheral edge of the flat plate portion5x. The first focusing electrode5is airtightly connected to the insulating tubular portion12and the stem23between the insulating tubular portion12and the stem23. The first focusing electrode5is provided at the same potential as that of the stem23. The first focusing electrode5is supplied with a voltage of 6 kV, for example, from an electrically connected power supply (not shown).

A light passage hole5aand a passage hole5bare formed in the flat plate portion5xof the first focusing electrode5. The light passage hole5ais a through hole that guides the light that has passed through the window portion28and the light incidence hole26to the photocathode3. The passage hole5bis a through hole through which at least photoelectrons from the photocathode3pass. The passage hole5bis provided in a central portion of the flat plate portion5xof the first focusing electrode5. The passage hole5bis formed adjacent to but separated from the light passage hole5ain the flat plate portion5x.

The insulating tubular portions12and14are insulating members having a cylindrical shape with the axis G as a central axis. The insulating tubular portions12and14are made of, for example, a ceramic material. The insulating tubular portion12is airtightly connected to the first focusing electrode5and the intermediate electrode part6between the first focusing electrode5and the intermediate electrode part6. The insulating tubular portion14is airtightly connected to the intermediate electrode part6and the electric field concentration relaxation electrode7between the intermediate electrode part6and the electric field concentration relaxation electrode7.

The intermediate electrode part6is an electrode part disposed between the photocathode3and the first focusing electrode5. The intermediate electrode part6is a plate-like conductive member having an annular shape with the axis G as a central axis thereof and having a thickness direction along the direction of the axis G. The intermediate electrode part6has a function of stabilizing an electric field formed inside the housing2. The intermediate electrode part6is airtightly connected to the insulating tubular portions12and14between the insulating tubular portions12and14. The intermediate electrode part6is supplied with a voltage of 3 kV, for example, from an electrically connected power supply (not shown). The intermediate electrode part6has a passage hole6aprovided in a central portion thereof. The passage hole6ais a through hole through which at least light to the photocathode3and photoelectrons from the photocathode3pass. An inner diameter of the passage hole6ais larger than the inner diameter of the passage hole5b.

The electric field concentration relaxation electrode7is electrically connected to the lid portion22so as to have the same potential as that of the photocathode3. In the present embodiment, the electric field concentration relaxation electrode7is an electrode part that directly contacts the lid portion22. The electric field concentration relaxation electrode7relaxes concentration of the electric field formed inside the housing2. The electric field concentration relaxation electrode7has a passage hole7aprovided in a central portion thereof. An inner diameter of the passage hole7ais larger than the inner diameter of the passage hole6a. Details of the electric field concentration relaxation electrode7will be described below.

As shown inFIGS.1,2and3, the electron tube1of the present embodiment includes a second focusing electrode8. The second focusing electrode8is accommodated inside the housing2. The second focusing electrode8is an electrode part disposed between the photocathode3and the intermediate electrode part6. The second focusing electrode8is a substantially annular plate-shaped conductive member with the axis G as a central axis thereof. The second focusing electrode8is provided so as to face the photocathode3and focuses photoelectrons from the photocathode3.

The second focusing electrode8includes a flat plate-like annular plate portion8xhaving the axis G as a central axis thereof and having a thickness direction along the direction of the axis G, and a tapered portion8ythat is continuous with an inner peripheral edge of the annular plate portion8x. The annular plate portion8xhas a substantially polygonal (substantially triangular in the present embodiment) external shape when seen in the direction along the axis G. Polygonal corner portions of the annular plate portion8xhave a rounded R shape. Thus, disturbance of the electric field due to the corner portions can be suppressed, and electric discharge can be suppressed. The tapered portion8yis inclined so as to be bent to the curved surface22cside of the lid portion22(the photocathode3side), and protrudes from the inner peripheral edge of the annular plate portion8xin a direction of decreasing a diameter toward the axis G. The tapered portion8yhas an outer surface of a truncated cone having the axis G as a central axis thereof of which a diameter decreases toward the curved surface22cside of the lid portion22(the photocathode3side). The second focusing electrode8has a passage hole8aprovided in a central portion thereof. The passage hole8ais a through hole through which at least light to the photocathode3and photoelectrons from the photocathode3pass. An inner diameter of the passage hole8ais formed so as to decrease toward the curved surface22c(the photocathode3) of the lid portion22.

One end portion of a rod80made of a conductive material that extends in the direction of the axis G is fixed and connected by laser welding, for example, to a plurality of positions of an edge portion of the annular plate portion8xof the second focusing electrode8, more specifically, at positions corresponding to the corner portions of a substantially polygonal shape (a substantially triangular shape). Each of a plurality of rods80is airtightly fixed to the lid portion22at the other end portion with one end portion located inside the housing2. Thus, the second focusing electrode8is suspended from the lid portion22by the plurality of rods80and held at a position between the photocathode3and the intermediate electrode part6inside the housing2. Along with this, the second focusing electrode8is supplied with a voltage from a power supply (not shown) through the rods80.

The first focusing electrode5, the intermediate electrode part6, and the second focusing electrode8as described above generate an electric field of a group of equipotential lines (equipotential surfaces) forming an electron lens that focuses photoelectrons from the photocathode3toward the electron detection unit4inside the housing2.

The electron tube1of the present embodiment includes a gate electrode9. At least part of the gate electrode9is accommodated inside the housing2. The gate electrode9includes a main body portion91that controls passage of the photoelectrons by applying a voltage, and a power supply part92that supports the main body portion91so as to be spaced apart from the photocathode3and applies a voltage to the main body portion91. The gate electrode9is electrically connected to the second focusing electrode8. In the present embodiment, the gate electrode9is provided integrally with the second focusing electrode8. That is, part of the gate electrode9is configured of the second focusing electrode8.

The main body portion91is an electrode part closest to the photocathode3. The main body portion91is a conductive member having a shape that curves and extends along (follows) the photocathode3provided on the curved surface22cthat is a paraboloid of revolution with the axis G as the axis of rotation. In other words, the main body portion91is formed of a paraboloid of revolution with the axis G as the axis of rotation, and has a dome-like shape that protrudes toward the photocathode3. The main body portion91is disposed apart from the photocathode3at a certain distance. The main body portion91and the photocathode3are spaced apart from each other with a substantially constant gap therebetween. Thus, a uniform gate operation can be performed over the entire surface of the photocathode3. The main body portion91is made of a fine wire-shaped metal member, and has a diameter (a width) smaller than a diameter of the rod80, for example. When seen in the direction of the axis G, the main body portion91has a web structure such as a spider's web having a circular opening in the center. Specifically, the main body portion91includes, for example, a plurality of concentric ring members having different diameters, and a plurality of radial members that intersect the plurality of ring members and extend radially. Further, the main body portion91is disposed so as to be smoothly continuous with the outer surface of the tapered portion8yof the second focusing electrode8in a cross section seen in a direction along the axis G. Thus, the disturbance of the electric field during a gate operation can be suppressed, and the electric discharge can be suppressed.

The power supply part92is configured of the plurality of rods80and the second focusing electrode8described above, and is held by the lid portion22. The plurality of rods80are conductive members each having a bar shape with a circular cross section. The plurality of rods80include one first rod81that passes through the lid portion22and extends to the outside, and two second rods82of which the other end portions are embedded in the lid portion22.

The first rod81is longer than the second rod82. The first rod81passes through the lid portion22. The other end portion of the first rod81is located outside the housing2. For example, a central portion of the first rod81is airtightly fixed to the lid portion22by a hermetic seal (a hermetic seal portion)22hcontaining an insulating material such as glass. The hermetic seal22his provided in a through hole formed in lid portion22. The second rod82is shorter than the first rod. The second rod82does not pass through the lid portion22. The other end portion of the second rod82is airtightly fixed to the lid portion22by a hermetic seal (a hermetic seal portion)22scontaining an insulating material such as glass. The hermetic seal22sis provided in the recess in the lid portion22that opens to the lid lower surface22bside. The hermetic seal22sis not exposed to the outside.

The second focusing electrode8constitutes a connection portion that connects one end portion of each of the plurality of rods80to the main body portion91. The edge portion of the main body portion91is fixed to a top portion (an edge of the passage hole8a) of the tapered portion8yof the second focusing electrode8on the lid portion22side. Thus, a voltage is applied from a power supply (not shown) to the main body portion91via the first rod81.

The electron tube1of the present embodiment includes the electric field concentration relaxation electrode7as described above. The electric field concentration relaxation electrode7is electrically connected to the lid portion22so as to have the same potential as that of the photocathode3. In the present embodiment, the electric field concentration relaxation electrode7is an electrode part that is in direct contact with the lid portion22. The electric field concentration relaxation electrode7is a conductive member including an annular plate portion7xhaving an annular shape with the axis G as a central axis and having a thickness direction in the direction of the axis G, a peripheral wall portion7gthat stands upright on an outer peripheral edge of the annular plate portion7x. The electric field concentration relaxation electrode7is airtightly connected between the insulating tubular portion14and the lid portion22of the housing2.

The annular plate portion7xwhich is a part of the electric field concentration relaxation electrode7is located closer to the electron detection unit4than the main body portion91of the gate electrode9in the direction of the axis G (a facing direction). Specifically, the annular plate portion7xis located at substantially the same position as the annular plate portion8xof the second focusing electrode8in the direction of the axis G. In the electric field concentration relaxation electrode7, the second focusing electrode8is disposed in the passage hole7athereof. Such an electric field concentration relaxation electrode7shifts an equipotential line related to the potential of the photocathode3(the cathode potential) to the electron detection unit4side, and relaxes concentration of the electric field formed inside the housing2. The electric field concentration relaxation electrode7constitutes a first electric field concentration relaxation electrode.

As described above, in the electron tube1, since the power supply part92of the gate electrode9is held by the lid portion22, it is not necessary to arrange and hold the power supply part92so as to expand parallel to the photocathode3, for example. Therefore, it is possible to reduce a volume of a member constituting the power supply part92, and to reduce an electrostatic capacitance between the photocathode3and the gate electrode9. As a result, it is possible to speed up switching of the voltage applied to the gate electrode9and to realize a high speed operation of the gate electrode9.

The electron tube1has the second focusing electrode8between the photocathode3and the electron detection unit4, and the gate electrode9is electrically connected to the second focusing electrode8. Therefore, it is possible to reliably perform a gate operation for photoelectrons (control of passage of photoelectrons) and a focus control. Furthermore, the gate electrode9is provided integrally with the second focusing electrode8. In this case, the gate electrode9and the second focusing electrode8can be disposed efficiently.

In the electron tube1, the power supply part92has the plurality of rods80and the second focusing electrode8. In this case, when the main body portion91of the gate electrode9inside the housing2is supported to be suspended from the lid portion22by the plurality of rods80, for example, as compared with a structure in which the power supply part92is disposed and held so as to expand parallel to the photocathode3, the volume of the member constituting the power supply part92can be further reduced, and it is possible to efficiently reduce the electrostatic capacitance between the photocathode3and the gate electrode9.

In the electron tube1, the plurality of rods80includes the first rod81that passes through the lid portion22and the second rod82of which the other end portion is embedded in the lid portion22. It is possible to reduce the volume of the member constituting the power supply part92and to efficiently reduce the electrostatic capacitance between the photocathode3and the gate electrode9by making the second rod82shorter than the first rod81. Further, since the other end portion of the second rod82is embedded in the lid portion22, it is possible to suppress unintentional fluctuation of the potential of the gate electrode9due to potential disturbance caused by an external factor or the like being transmitted to the gate electrode9via the second rod82. In addition, the configuration in which the main body portion91of the gate electrode9is supported to be suspended from the lid portion22can be realized using the first rod81and the second rod82.

In the gate electrode9suspended from the lid portion22, due to the structure thereof, electric field concentration (rapid bending of equipotential line) tends to occur around the gate electrode9, and a withstand voltage tends to be insufficient. In this regard, the electron tube1is provided with the electric field concentration relaxation electrode7, and the electric field concentration relaxation electrode7has a shape that measures the withstand voltage, that is, a shape in which the annular plate portion7xis located closer to the electron detection unit4than the main body portion91in the direction of the axis G. In such a configuration, the concentration of the electric field inside the housing2can be relaxed by the electric field concentration relaxation electrode7, and the withstand voltage of the electron tube1can be increased.

FIG.4is a cross-sectional view showing an enlarged part of the inside of the housing2ofFIG.1.FIG.4shows a group of equipotential lines inside the housing2(the same applies toFIGS.5and6described below). As shown inFIG.4, it can be understood that the electric field concentration relaxation electrode7shifts the equipotential line (the cathode potential) closest to the photocathode3to the electron detection unit4side, and thus the electric field concentration (rapid bending of the equipotential line) can be suppressed. It can be understood that the electric field concentration relaxation electrode7guides the equipotential lines so as to extend along a direction perpendicular to the axis G, and intrusion (penetration) of the equipotential lines into the photocathode3side can be suppressed.

The electric field concentration relaxation electrode7relaxes the electric field concentration inside the housing2, making it possible to increase the withstand voltage of the electron tube1.

Second Embodiment

Next, a second embodiment will be described. In the description of the present embodiment, points different from the first embodiment will be described.

As shown inFIG.5, an electron tube101according to a second embodiment is different from the first embodiment in that an electric field concentration relaxation electrode27is provided instead of the electric field concentration relaxation electrode7(refer toFIG.1). The electric field concentration relaxation electrode27is electrically connected to a lid portion22so as to have the same potential as that of the photocathode3. In the present embodiment, the electric field concentration relaxation electrode27is an electrode part that is in direct contact with the lid portion22. The electric field concentration relaxation electrode27has a passage hole27aprovided in a central portion thereof. In the electric field concentration relaxation electrode27, the second focusing electrode8is disposed in the passage hole27a.

The electric field concentration relaxation electrode27is a conductive member including an annular plate portion27xhaving an annular shape with the axis G as a central axis thereof and having a thickness direction along the direction of the axis G, and a peripheral wall portion27gthat stands upright on an outer peripheral edge of the annular plate portion27x. The electric field concentration relaxation electrode27is airtightly connected between the insulating tubular portion14and the lid portion22of the housing2.

An end portion27x1on the inner peripheral side of the annular plate portion27xof the electric field concentration relaxation electrode27is located closer to the electron detection unit4than the main body portion91of the gate electrode9in the direction of the axis G. Specifically, the end portion27x1of the annular plate portion27xon the inner peripheral side is located at substantially the same position as the annular plate portion8xof the second focusing electrode8in the direction of the axis G. The end portion27x1on the inner peripheral side of the annular plate portion27xof the electric field concentration relaxation electrode27extends until it reaches a position close to the power supply part92, particularly the annular plate portion8xof the second focusing electrode8in the present embodiment, in an orthogonal direction (an intersecting direction) perpendicular to the direction of the axis G. In other words, in the orthogonal direction (the intersecting direction) perpendicular to the direction of the axis G, a distance H1between the end portion27x1on the inner peripheral side of the annular plate portion27xof the electric field concentration relaxation electrode27and the outer peripheral edge of the annular plate portion8xfacing thereto is shorter than a distance H2between the end portion27x1on the inner peripheral side of the annular plate portion27xof the electric field concentration relaxation electrode27and an end portion27x2of the annular plate portion27xon the outer peripheral side. In the present embodiment, the end portion27x1on the inner peripheral side of the annular plate portion27xof the electric field concentration relaxation electrode27extends until it reaches the hermetic seal22sin the orthogonal direction (the intersecting direction) perpendicular to the direction of the axis G. Specifically, the end portion27x1of the annular plate portion27xon the inner peripheral side extends until it reaches the outer peripheral edge of the annular plate portion8xof the second focusing electrode8. The end portion27x1of the annular plate portion27xon the inner peripheral side extends inward in the orthogonal direction with respect to the intermediate electrode part6. The electric field concentration relaxation electrode27constitutes a second electric field concentration relaxation electrode.

As described above, in the electron tube101as well, it is possible to realize a high speed operation of the gate electrode9. Further, the electric field concentration relaxation electrode27shifts the equipotential line (the cathode potential) closest to the photocathode3to the electron detection unit4side, and thus the electric field concentration (the rapid bending of the equipotential line) can be suppressed. The electric field concentration relaxation electrode27further guides the equipotential lines to extend in the direction perpendicular to the axis G, and thus the intrusion (penetration) of the equipotential lines into the photocathode3side can be further suppressed. The electric field concentration relaxation electrode27relaxes the electric field concentration inside the housing2and makes it possible to increase the withstand voltage of the electron tube201.

Third Embodiment

Next, a third embodiment will be described. In the description of the present embodiment, points different from the second embodiment will be described.

As shown inFIG.6, an electron tube201according to the third embodiment is different from the second embodiment in that it includes a second focusing electrode38in which a connection point P with one end portion of the rod80is located on the side of the photocathode3in the direction of the axis G, instead of the second focusing electrode8(refer toFIG.1).

The second focusing electrode38has a substantially cylindrical portion38xwith the axis G as a central axis thereof, and a flange portion38yprovided at the end portion on the photocathode3side of an outer peripheral surface of the cylindrical portion38x. A passage hole38acorresponding to an inner hole of the cylindrical portion38xis inclined so that a diameter thereof increases as a distance increases from the photocathode3except for the end portion on the photocathode3side. In other words, the cylindrical portion38xhas a shape such that a width (a thickness) in the orthogonal direction (the intersecting direction) perpendicular to the direction of the axis G decreases as a distance from the photocathode3increases. In a cross section seen in a direction along the axis G, an inner wall surface of the cylindrical portion38xforming the passage hole38ais a tapered surface of which a diameter increases so that a distance from the axis G increases as a distance from the photocathode3increases. On the other hand, an outer wall surface of the cylindrical portion38xis a circumferential surface that extends along the axis G. Further, a surface (an upper surface) of the cylindrical portion38xon the photocathode3side is an annular planar portion that extends along the orthogonal direction (the intersecting direction) orthogonal to the direction of the axis G. A connection region between the upper surface and the inner wall surface of the cylindrical portion38xand a connection region between the outer wall surface and the inner wall surface of the cylindrical portion38xboth have an R shape with rounded corner portions. Thus, the disturbance of the electric field due to the corner portions can be suppressed, and the electric discharge can be suppressed.

The flange portion38yhas an annular plate shape of which a thickness direction is along the direction of the axis G. The flange portion38yis provided so as to protrude radially outward from the outer peripheral surface of the cylindrical portion38xon the upper surface side. The upper surface of the flange portion38yis flush with the upper surface of the cylindrical portion38x. In addition, an end portion of the flange portion38ythat protrudes radially outward has an R shape with rounded corner portions. Thus, the disturbance of the electric field due to the corner portions can be suppressed, and the electric discharge can be suppressed. One end portions of the rods80that extend along the direction of the axis G are fixed and connected at connection points P by laser welding, for example, to a plurality of positions of the flange portion38y.

An end portion27x1on the inner peripheral side of the annular plate portion27xof the electric field concentration relaxation electrode27is located closer to the electron detection unit4than the connection point P between the rod80and the second focusing electrode38in the direction of the axis G. Further, the end portion27x1on the inner peripheral side of the annular plate portion27xof the electric field concentration relaxation electrode27extends until it reaches a position close to the power supply part92, particularly, the cylindrical portion38xof the second focusing electrode38in the orthogonal direction (the intersecting direction) perpendicular to the direction of the axis G in the present embodiment. In other words, in the orthogonal direction (the intersecting direction) perpendicular to the direction of the axis G, a distance H3between the end portion27x1on the inner peripheral side of the annular plate portion27xof the electric field concentration relaxation electrode27and the outer wall surface of the cylindrical portion38xfacing it is shorter than a distance H4between the end portion27x1on the inner peripheral side of the annular plate portion27xof the electric field concentration relaxation electrode27and the end portion27x2on the outer peripheral side of the annular plate portion27x. In the present embodiment, the end portion27x1on the inner peripheral side of the annular plate portion27xof the electric field concentration relaxation electrode27extends until it reaches the hermetic seal22sin the orthogonal direction (the intersecting direction) perpendicular to the direction of the axis G, and extends until it reaches the flange portion38yhere. The end portion27x1on the inner peripheral side of the annular plate portion27xextends inward in the orthogonal direction with respect to the intermediate electrode part6. The electric field concentration relaxation electrode27constitutes a third electric field concentration relaxation electrode.

As described above, in the electron tube201as well, it is possible to realize a high speed operation of the gate electrode9. Further, in the electron tube201, the connection point P between the second focusing electrode38and one end portion of the rod80can be located on the photocathode3side in the direction of the axis G which is less susceptible to the influence of the electric field. In the electron tube201, the electric field concentration relaxation electrode27relaxes the concentration of the electric field inside the housing2, so that the withstand voltage of the electron tube201can be increased.

In the present embodiment, instead of the electric field concentration relaxation electrode27, an electrode part57, a conductive tubular portion16and an electric field concentration relaxation electrode37may be provided as shown inFIG.7. The electrode part57is electrically connected to the lid portion22, is an electrode part in direct contact with the lid portion22in the present embodiment, and has a passage hole57aprovided in a central portion. The electrode part57is a conductive member including an annular plate portion57xhaving an annular shape with the axis G as a central axis thereof and having a thickness direction along the direction of the axis G, and a peripheral wall portion57gthat stands upright on an outer peripheral edge of the annular plate portion57x. The conductive tubular portion16is a conductive member having a cylindrical shape with the axis G as a central axis thereof.

The electric field concentration relaxation electrode37is a plate-like conductive member having an annular shape with the axis G as a central axis thereof and having a thickness direction in the direction of the axis G. The electric field concentration relaxation electrode37has an annular plate portion37athat extends into the housing2. The annular plate portion37ais a portion of the electric field concentration relaxation electrode37that extends into the housing2. An end portion37a1on the inner peripheral side of the annular plate portion37aof the electric field concentration relaxation electrode37is located closer to the electron detection unit4than the connection point P between the rod80and the second focusing electrode38in the direction of the axis G. The end portion37a1on the inner peripheral side of the annular plate portion37aof the electric field concentration relaxation electrode37extends in the orthogonal direction (the intersecting direction) perpendicular to the direction of the axis G until it reaches a position close to the power supply part92, particularly, the cylindrical portion38xof the second focusing electrode38in the present embodiment. In other words, in the orthogonal direction (the intersecting direction) perpendicular to the direction of the axis G, a distance H5between the end portion37a1on the inner peripheral side of the annular plate portion37aof the electric field concentration relaxation electrode37and the outer wall surface of the cylindrical portion38xfacing it is shorter than a distance H6between the end portion37a1on the inner peripheral side of the annular plate portion37aof the electric field concentration relaxation electrode37and an end portion37a2on the outer peripheral side of the annular plate portion37aof the electric field concentration relaxation electrode37. In the present embodiment, the end portion37a1on the inner peripheral side of the annular plate portion37aof the electric field concentration relaxation electrode37extends until it reaches the hermetic seal22sin the orthogonal direction (intersecting direction) perpendicular to the direction of the axis G, and extends until reaches the flange portion38yhere. The end portion37a1on the inner peripheral side of the annular plate portion37aof the electric field concentration relaxation electrode37extends inward in the orthogonal direction with respect to the intermediate electrode part6. The electric field concentration relaxation electrode37constitutes a fourth electric field concentration relaxation electrode.

The electrode part57, the conductive tubular portion16, and the electric field concentration relaxation electrode37are disposed to be stacked in this order and are electrically connected to each other. The electrode part57, the conductive tubular portion16, and the electric field concentration relaxation electrode37are airtightly connected between the lid portion22and the insulating tubular portion14of the housing2. In such a configuration, the electric field concentration relaxation electrode37relaxes the concentration of the electric field inside the housing2, and the withstand voltage of the electron tube201can be increased.

Although the embodiments have been described above, one aspect of the present disclosure is not limited to the above embodiments. In the above embodiment, although the gate electrode9is

provided integrally with the second focusing electrode8, the gate electrode9may be provided separately from the second focusing electrode8. In this case, the gate electrode9may be electrically connected to the second focusing electrode8via a conductive member, or may have a power supply part separately. Although the above embodiment includes the first rod81and the second rod82, only the first rod81may be included.

In the above embodiment, although the main body portion91of the gate electrode9is electrically connected to the rod80via the second focusing electrode8, instead thereof or in addition thereto, the main body portion91may be electrically connected to the rod80via a separate conductive member.

In the above embodiment, the photocathode3has a curved surface, but the shape of the photocathode3is not limited to the curved surface, and may have various shapes. For example, the photocathode3may be planar. In the above embodiment, the photocathode3is a reflective photoelectric conversion unit, but may be a transmissive photoelectric conversion unit.

In the above embodiment, an avalanche photodiode is used as the electron detection unit4, but the present disclosure is not limited thereto. The electron detection unit may use other semiconductor electron detection element, may have a simple anode, or may have a dynode and an anode.

Various materials and shapes can be applied to each of the configurations in the above embodiments and modified example without being limited to the materials and shapes described above. Each of the configurations in the above embodiment or modified example can be arbitrarily applied to each of the configurations in other embodiments and modified examples. A part of each of the configurations in the above embodiments and modified example can be omitted as appropriate without departing from the gist of one aspect of the present disclosure.

According to the present disclosure, it is possible to provide an electron tube capable of speeding up the operation of the gate electrode.