High efficiency hollow cathode and cathode system applying same

Abstract

The present invention relates to a high efficiency hollow cathode and a cathode system applying the same, and comprises: a tube comprising at least two refractory metal parts; a gas providing unit and a gas outlet which are respectively formed at the distal ends of the tube; and an insert mounted inside the tube. According to the present invention, since the present invention constitutes a hollow cathode using more than two substances, the present invention can not only enhance thermal stability, lifespan and efficiency, but also can reduce costs accordingly.

Claims

1. A hollow cathode comprising: a tube comprising at least two refractory metal parts; a gas providing unit and a gas outlet which are respectively formed at the distal ends of the tube; and an insert mounted inside the tube; wherein the tube includes a plurality of tube parts formed of refractory metal materials different from each other and integrally connected to each other in a longitudinal direction; and wherein a part adjacent to the gas providing unit is formed of a refractory metal material with low thermal conductivity; and a part adjacent to an electron discharge hole is formed of a refractory metal material with a high melting point.

2. The hollow cathode of claim 1, wherein a first part and a second part of the tube are formed of the same refractory metal material and a third part is formed of a different refractory metal material, and the thickness and diameter of each of the tube part are made to be the same or different.

3. The hollow cathode of claim 1, wherein a thermal radiation insulation layer is formed at an interval in the outer side of the tube where the insert is located.

4. The hollow cathode of claim 1, wherein the tube is formed of a tube part made of titanium, titanium alloy, tantalum material or a combination thereof.

5. The hollow cathode of claim 1, wherein part of or the entire insert is formed of refractory metal wire.

6. The hollow cathode of claim 5, wherein the insert comprises a wire type insert and a foil type insert.

7. The hollow cathode of claim 6, wherein the innermost layer or inner layers are formed of the wire type insert and the outer part thereof is formed of the foil type insert.

8. A cathode system using a high efficiency hollow cathode comprises: a body; a keeper electrically connected to one end of the body; a hollow cathode according to claim 1 mounted in the body; an injection hole injecting gas to the hollow cathode; a ceramic structure coinciding the hollow cathode with the center of the keeper; and a wire connected to the body, the wire providing a large potential difference between the keeper and the hollow cathode.

9. The cathode system of claim 8, wherein the hollow cathode is mounted inside the body, and the cathode is insulated from the gas injection hole so that cathode potential is not exposed outside the body.

10. The cathode system of claim 8, comprising a power unit using an electric condenser for initial discharge.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a cross sectional view illustrating the industrial hollow cathode according to an embodiment of prior art;

(2) FIG. 2 is a result calculating the temperature of the industrial hollow cathode according to an embodiment of prior art;

(3) FIG. 3 is a result calculating the temperature distribution of the hollow cathode using a tube made of molybdenum in the industrial hollow cathode structure according to an embodiment of prior art;

(4) FIG. 4 is a result calculating the electron discharge probability distribution in the industrial hollow cathode according to an embodiment of prior art;

(5) FIG. 5 is a cross sectional view illustrating a cross section of the insert of the industrial hollow cathode according to an embodiment of prior art;

(6) FIG. 6 is a cross sectional view illustrating the hollow cathode structure according to the present invention;

(7) FIG. 7 is a cross sectional view illustrating another embodiment of the hollow cathode structure according to the present invention;

(8) FIG. 8 is a cross sectional view illustrating another embodiment of the hollow cathode structure according to the present invention;

(9) FIGS. 9 and 10 are cross sectional views illustrating the insert constituting the hollow cathode structure according to the present invention;

(10) FIG. 11 is a view illustrating the cathode system applying the high efficiency hollow cathode according to the present invention;

(11) FIG. 12 is a view illustrating another embodiment of the cathode system applying the high efficiency hollow cathode according to the present invention;

(12) FIG. 13 is an electric circuit diagram briefly illustrating the power unit of the hollow cathode system according to an embodiment of the present invention;

(13) FIGS. 14a and 14b are graphs illustrating the change of voltage and current according to time measured at initial discharge using the conventional industrial hollow cathode in order to determine the capacity of the electric condenser of the power unit of the hollow cathode system according to an embodiment of the present invention; and

(14) FIGS. 15a and 15b are graphs illustrating the energy distribution function of discharge image and ion beam obtained by applying the hollow cathode according to an embodiment of the present invention to an ion beam source.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

(15) Hereinafter, embodiments of the present invention will be explained in detail with reference to the accompanying drawings. However, the present invention is not limited or restricted by the following embodiments, and all combinations explained in the following embodiments are not necessarily essential to the technical solution of the present invention.

(16) Hereinafter, the constitution of the present invention is explained with reference to the accompanying drawings. FIG. 6 is a cross sectional view illustrating the hollow cathode structure according to the present invention. FIG. 7 is a cross sectional view illustrating another embodiment of the hollow cathode structure according to the present invention. FIG. 8 is a cross sectional view illustrating another embodiment of the hollow cathode structure according to the present invention. FIGS. 9 and 10 are cross sectional views illustrating the insert constituting the hollow cathode structure according to the present invention. FIG. 11 is a view illustrating the cathode system applying the high efficiency hollow cathode according to the present invention. FIG. 12 is a view illustrating another embodiment of the cathode system applying the high efficiency hollow cathode according to the present invention. FIG. 13 is an electric circuit diagram briefly illustrating the power unit of the hollow cathode system according to an embodiment of the present invention.

(17) The hollow cathode 10 according to an embodiment of the present invention comprises a tube 11 comprising two parts 11a and 11b, a gas providing unit 13 and a gas outlet 14 which are respectively formed at the distal ends of the tube 11, and an insert 12 mounted inside the tube 11.

(18) Also, parts 11a and 11b constituting the tube 11 may be made of materials different from each other. A first part 11a adjacent to the gas providing unit 13 uses a refractory metal material with low thermal conductivity to reduce heat loss by thermal conduction, and a second part 11b adjacent to the election discharge hole uses a refractory metal with a high melting point to prevent damage by heat. As illustrated in FIG. 6, the tube parts 11a, 11b are integrally connected to each other in a longitudinal direction.

(19) Here, the first part 11a selectively uses titanium, etc. with low thermal conductivity, and the second part 11b selectively uses tantalum, etc. with a high melting point.

(20) Next, an insert 12 mounted inside the tube 11, which performs the role of a thermal radiation shielding layer with respect to the surface discharging internal thermal electron may be formed of at least one layer (for example, 15 layers) of a thin (for example, a thickness of 0.013 mm) tantalum foil.

(21) Also, the insert 12 may be formed as illustrated in FIGS. 9 and 10.

(22) First, an insert 12 illustrated in FIG. 9 may comprise an inner insert 12a comprising a thin wire (for example, a diameter of 0.025 mm) layer winding the insert in the form of solenoid, and a shielding layer 12b mounted outside the inner insert 12a.

(23) That is, the inner insert 12a is made of a thin wire to reduce damage by ion bombardment while increasing the effective surface area discharging thermal electrons, so as to increase the amount of current discharging thermal electrons at the same temperature. Also, the shielding layer 12b may reduce thermal radiation loss of the inner insert 12a.

(24) Also, an insert 12 illustrated in FIG. 10 comprises the innermost two layers 12c and 12d in a thin wire layer to reduce damage by ion bombardment and increase the amount of current discharging thermal electrons by the increase of effective surface area, so as to enhance the performance of the cathode.

(25) The hollow cathode structure 20 according to another embodiment of the present invention comprises a tube 21 comprising at least two refractory metal parts 21a, 21b and 21c, a gas providing unit 23 and a gas outlet 24 which are respectively formed at the distal ends of the tube 21, and an insert 22 mounted inside the tube 21.

(26) Also, an example where a first part 21a and a second part 21b constituting the tube 21 of the present invention are formed of the same material, and a third part 21c is formed of a different material will be explained.

(27) In this case, the first part 21a and the second part 21b not only may be formed of the same thickness and diameter, but may also be formed of different thicknesses as illustrated in the drawing.

(28) That is, the first and second parts 21a and 21b constituting the tube 21 use a refractory metal material with low thermal conductivity to reduce heat loss by thermal conduction, and the third part 21c adjacent to the electron discharge hole uses a refractory metal material with a high melting point to prevent damage by heat.

(29) Here, the first and second parts 21a and 21b selectively use titanium, etc. with low thermal conductivity, and the third part 21c selectively uses tantalum, etc. with a high melting point.

(30) Next, an insert 22 mounted inside the tube 21, which performs the role of a thermal radiation shielding layer with respect to the surface discharging internal thermal electron may be formed of at least one layer (for example, 15 layers) of a thin (for example, a thickness of 0.013 mm) tantalum foil.

(31) Also, the insert 22 may be formed as illustrated in FIGS. 9 and 10.

(32) First, an insert 22 illustrated in FIG. 9 may comprise an inner insert 22a comprising a thin wire (for example, a diameter of 0.025 mm) layer winding the insert in the form of solenoid, and a shielding layer 22b mounted outside the inner insert 22a.

(33) That is, the inner insert 22a is made of a thin wire to reduce damage by ion bombardment while increasing the effective surface area discharging thermal electrons, so as to increase the amount of current discharging thermal electrons at the same temperature. Also, the shielding layer 22b may reduce thermal radiation loss of the inner insert 22a.

(34) Also, an insert 22 illustrated in FIG. 10 comprises the innermost two layers 22c and 22d in a thin wire layer to reduce damage by ion bombardment and increase the amount of current discharging thermal electrons by the increase of effective surface area, so as to enhance the performance of the cathode.

(35) Next, the hollow cathode structure 30 according to another embodiment of the present invention comprises a tube 31 comprising two parts 31a and 31b, a gas providing unit 33 and a gas outlet 34 which are respectively formed at the distal ends of the tube 31, and an insert 32 mounted inside the tube 31.

(36) Also, parts 31a and 31b constituting the tube 31 may be made of materials different from each other. A first part 31a adjacent to the gas providing unit 33 uses a refractory metal material with low thermal conductivity to reduce heat loss by thermal conduction, and a second part 31b adjacent to the electron discharge hole uses a refractory metal material with a high melting point to prevent damage by heat.

(37) Here, the first part 31a selectively uses titanium, etc. with low thermal conductivity, and the second part 31b selectively uses tantalum, etc. with a high melting point.

(38) Also, a thermal radiation shielding layer 35 is formed at certain intervals in the outer surface of the second part 31b.

(39) To explain this in more detail, the thermal radiation shielding layer 35 is formed at certain intervals in the outer surface of the second part 31b where the insert 32 is located so as to reduce heat loss by thermal radiation of the high temperature region.

(40) Next, an insert 32 mounted inside the tube 31, which performs the role of a thermal radiation shielding layer with respect to the surface discharging internal thermal electron may be formed of at least one layer (for example, 15 layers) of a thin (for example, a thickness of 0.013 mm) tantalum foil.

(41) Also, the insert 32 may be formed as illustrated in FIGS. 9 and 10.

(42) First, an insert 32 illustrated in FIG. 9 may comprise an inner insert 32a comprising a thin wire (for example, a diameter of 0.025 mm) layer winding the insert in the form of solenoid, and a shielding layer 32b mounted outside the inner insert 32a.

(43) That is, the inner insert 32a is made of a thin wire to reduce damage by ion bombardment while increasing the effective surface area discharging thermal electrons, so as to increase the amount of current discharging thermal electrons at the same temperature. Also, the shielding layer 32b may reduce thermal radiation loss of the inner insert 32a.

(44) Also, an insert 32 illustrated in FIG. 10 comprises the innermost two layers 32c and 32d in a thin wire layer to reduce damage by ion bombardment and increase the amount of current discharging thermal electrons by the increase of effective surface area, so as to enhance the performance of the cathode.

(45) The cathode system 100 according to an embodiment of the present invention (hereinafter, cathode system) comprises a body 120; a keeper 110 electrically connected to one end of the body 120; a hollow cathode 10, 20 and 30 mounted in the body 120; an injection hole 170 injecting gas to the hollow cathode 10, 20 and 30; a ceramic structure 130 coinciding the hollow cathode 10, 20 and 30 with the center of the keeper 110; and a wire 150 and 160 connected to the body 120, the wire 150 and 160 providing a large potential difference between the keeper 110 and the hollow cathode 10, 20 and 30.

(46) Also, the keeper 110 and body 120 are electrically connected to be equipotential, and the hollow cathode 10, 20 and 30 applied with a relatively negative potential is electrically separated.

(47) Also, the body 120 is electrically insulated from the hollow cathode 10, 20 and 30, and in order to fix the hollow cathode 10, 20, 30 to coincide with the center axis of the keeper 110, a ceramic structure 130 stable at high temperature and an insulation tube 140 such as cryogenic break may be used.

(48) Next, for initial discharge, according to the cathode system 100, gas of high flow is injected through the injection hole 170, and a potential with a great potential difference (for example, 700 V) is applied to the keeper 110 and cathode 10, 20 and 30, respectively through two wires 150 and 160.

(49) In this case, according to the conventional structure, an insulation tube 140 is located outside the body so that the potential applied to the cathode 10, 20 and 30 during initial discharge is exposed to the outside, and thus there is a problem in electric stability (the potential is discharged at the gas providing tube and damaged, etc.). In comparison, the present invention can solve this problem through an insulation tube 140 installed inside the body 120.

(50) FIG. 12 illustrated next illustrates another embodiment of the cathode system. The cathode system 100 comprises a body 120; a keeper 110 electrically connected to one end of the body 120; a hollow cathode 10, 20 and 30 mounted in the body 120; and an injection hole 170 injecting gas to the hollow cathode 10, 20 and 30, etc.

(51) That is, the cathode system illustrated in FIG. 12 is a miniature of the cathode system illustrated in FIG. 11 which has a structure similar thereto.

(52) To explain this in more detail, the cathode system 100 minimizes its structure to reduce weight, so that it can be applied to satellites easily while reducing material. Also, it is formed so that Ti has different diameters to have thermal stability and structural stability at the same time.

(53) Also, the keeper 110 and body 120 are electrically connected to be equipotential, and the hollow cathode 10, 20 and 30 applied with a relatively negative potential is electrically separated.

(54) Also, the body 120 is electrically insulated from hollow cathode 10, 20 and 30, and in order to fix the hollow cathode 10, 20 and 30 to coincide with the center axis of the keeper 110, a ceramic structure 130 stable at high temperature and an insulation tube 140 such as cryogenic break may be used.

(55) Next, for initial discharge, according to the cathode system 100, gas of high flow is injected through the injection hole 170.

(56) FIG. 13 illustrated next is an electric circuit diagram briefly illustrating the power unit 200 of the hollow cathode system according to an embodiment of the present invention.

(57) That is, according to prior art, for initial discharge, power of large capacity (starter power supply) is used, whereas according to the present embodiment, without using power of large capacity, power 201 of small capacity and an electric condenser 202 are used instead of the conventional power of large capacity.

(58) This may be a form economically using the fact that the power for initial discharge is used only for a very short period of time, and after initial discharge, power 203 may be used to maintain the plasma as in prior art.

(59) Here, the cathode 204 and anode 205 may be connected to the connecting line 160 of the hollow cathode 10, 20 and 30 of the hollow cathode system 100, and the connecting line 150 of the keeper 110.

(60) FIGS. 14a and 14b are graphs illustrating the change of voltage and current according to time measured at initial discharge using the conventional industrial hollow cathode in order to determine the capacity of the electric condenser 202 of the power unit of the hollow cathode system 200 according to an embodiment of the present invention. Through them, the change in power and effective resistance according to time may be obtained.

(61) In this case, the voltage applied first increases and then plasma is discharged at a certain voltage (about 700 V) so that a low current (about 4 mA) flows and the cathode is heated. Referring to the change of resistance according to time, it may be seen that the resistance is maintained at a certain level during initial discharge. This shows that the plasma is discharged. The total amount of current flowing during initial discharge and the total energy delivered may be calculated. The capacity of the electric condenser may be selected using these values.

(62) FIG. 15 illustrated next is a graph illustrating the energy distribution function of discharge image and ion beam obtained by applying the hollow cathode 10, 20 and 30 according to an embodiment of the present invention to an ion beam source 300.

(63) To explain this in more detail, in order to examine the effect of the hollow cathode 10, 20 and 30, the case of operating the cathode and not operating the cathode are compared under the same discharge condition of ion beam source 300.

(64) The electron beam created and discharged from the hollow cathode 10, 20 and 30 is distributed along the magnetic field line of the ion beam.

(65) The energy distribution function of the ion beam may be measured by locating a retarding potential analyzer at a location apart in a certain distance (for example, 150 mm) from the ion beam source 300. It can be confirmed that the ion amount of a specific energy (about 0.5 keV) region increased by the electron supplied from the hollow cathode 10, 20 and 30. According to another embodiment of the present invention, by varying the installment method of the hollow cathode 10, 20 and 30 and process conditions, the hollow cathode may be applied in order to control the properties of the energy distribution function of the ion beam source 300 and ion current density.

(66) The hollow cathode may be applied to the process of using ion beams according to another embodiment of the present invention to prevent charging and arcing.

(67) While the present invention has been described with reference to the embodiments of the present invention, it is to be appreciated that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention, as defined by the appended claims.