WO2008048019A1

WO2008048019A1 - An ionizer using soft x-ray and a method for removing electric charges of a charged body

Info

Publication number: WO2008048019A1
Application number: PCT/KR2007/004974
Authority: WO
Inventors: Dong-Hoon Lee; Sang-Hyo Kim; Yong-Chul Jung; Jae-Yeol Kim; Seung-Ook Shim; Won-Dae Lee; Mu-Ho Kim; Jong-Jin Ryu; Hyun-Soo Kim
Original assignee: Sunje Hitek Co., Ltd.
Priority date: 2006-10-16
Filing date: 2007-10-11
Publication date: 2008-04-24
Also published as: TWI339545B; CN101553882B; TW200820834A; CN101553882A; JP2008098129A; JP4087881B2; JP4435211B2; KR100676527B1; JP2008098144A

Abstract

This invention relates to an ionizer using soft X-ray comprising a head unit that generates soft X-ray in order to remove electric charges of a charged body by +/- ions or electrons generated from the gas in the air ionized by the soft X-ray, and a control unit to control at least one of the head unit, wherein said head unit comprises, a protective case consisting of a D-shaped side unit, and a D-shaped cover unit combined to said side unit and forming a housing space; an X-ray tube housed within said protective case and having an output window that emits soft X-ray generated when the electrons collide with the target; a flange unit thermally and electrically connected to said output window and forming a front end of said X-ray tube, supporting said output window, and radiating the heat generated from said target to outside of the X-ray tube by contacting with the front portion of said side unit of the protective case; a high voltage generation unit housed in said protective case and supplying high voltage to said X-ray tube; and a flange coupler fixing said X-ray tube to said front portion of said side unit of the protective case.

Description

AN IONIZER USING SOFT X-RAY AND A METHOD FOR REMOVING ELECTRIC CHARGES OF A CHARGED BODY

Technical Field

[1] This invention relates to an ionizer using soft X-ray and a method for removing electric charges of a charged body. More specifically, this invention improves structural defects of previous ionizers using soft X-ray, with easy external heat radiation which is necessary for decreasing size of the ionizer using soft X-ray, easy and simple construction, and stable support. Background Art

[2] As a prior art, there is a Japanese Patent Application No. H08-256780 (X-ray generator), whose structure is shown in figure 1. In this art, the flange portion (18) formed on the front end of the X-ray tube (8) is interposed between two supporting plates (5, 24) in order to fix the X-ray tube to the protective case. However, the ionizers adopting this art have not become practical, because they have problems like complex process of construction, electrically and thermally incomplete contact between the flange portion and the protective case.

[3] As another prior art, there is an ionizer whose structure is shown in figure 2.

However, it has similar problems as the prior art in figure 1. Disclosure of Invention Technical Problem

[4] To solve said problems of prior arts, this invention aims to provide an ionizer using soft X-ray which has high thermal conductivity, simple structure so that it can be easily constructed, have increased stability and improved function of shielding X-ray.

[5] Other purposes and merits of this invention will become clear upon reading the detailed explanation and referring to the attached drawings. Technical Solution

[6] A preferred embodiment of an ionizer using soft X-ray (hereafter called "ionizer") according to this invention comprises,

[7] a head unit that generates soft X-ray in order to remove electric charges of a charged body by +/- ions or electrons generated from the gas in the air ionized by the soft X-ray, and a control unit to control at least one of the head unit,

[8] wherein said head unit comprises,

[9] a protective case consisting of a D-shaped side unit, and a D-shaped cover unit combined to said side unit and forming a housing space;

[10] an X-ray tube housed within said protective case and having an output window that emits soft X-ray generated when the electrons collide with the target; [11] a flange unit thermally and electrically connected to said output window and forming a front end of said X-ray tube, supporting said output window, and radiating the heat generated from said target to outside of the X-ray tube by contacting with the front portion of said side unit of the protective case; [12] a high voltage generation unit housed in said protective case and supplying high voltage to said X-ray tube; and [13] a flange coupler fixing said X-ray tube to said front portion of said side unit of the protective case, [14] wherein said flange coupler has thermal and electrical conductivity, has a through hole as large as the flange unit so that the periphery of the flange unit can be fixed by the raised spot formed inside of said through hole, and wherein said flange coupler and said flange unit form one surface when they are coupled. [15] In this invention, it is preferable that each of said head unit further comprises a timer to display cumulative used time of said ionizer. [16] In this invention, it is preferable that the side unit, cover unit of the protective case, and the target are made of conductive materials, have ground potentials and thermal conductivities.

[17] In this invention, it is preferable that said control unit comprises

[18] a means of choice to choose the head unit; and

[19] a display window to display cumulative used time of chosen head unit by linking with the timer in the head unit. [20] In this invention, it is preferable that said control unit has functions of alarm, interlock, remote control, input and output of control signal of the power source of the controller. [21] In this invention, it is preferable that the head unit and the control unit are connected by a flexible tube when the head unit is installed outside of the protective case, wherein said flexible tube houses a high voltage cable that connects the head unit and the power control unit in order to protect the high voltage cable from external impact or vibration, and wherein said flexible tube allows the user to bend the head of said head unit at an arbitrary angle toward a charged body, and wherein the flange coupler is not used in this case. [22] In this invention, it is preferable that an RMS (Remote monitoring system) to monitor a number of ionizers remotely with one personal computer is adopted. [23] In this invention, it is preferable that the connector of said control unit adopts a single connector form. [24] This invention preferably further comprises a bracket for attaching said ionizer to the ceiling or the wall which consists of a D-shaped bracket unit to fix said head unit horizontally or vertically by screws; and [25] a reinforcing plate connected with one outer surface of said D-shaped bracket unit by screws and fixes said head unit by screws, wherein said D-shaped bracket unit is fixed to the ceiling or the wall by anchor bolts. [26] In this invention, it is preferable that the area which said flange coupler contacts with said side unit of the protective case can be set up from necessity. [27] In this invention, it is preferable that a space for the body of the X-ray tube is prepared beside said high voltage generation unit inside said side unit of the protective case. [28] In this invention, it is preferable that said X-ray tube is fixed and supported by the means that fixes said flange coupler to said side unit of the protective case. [29] In this invention, it is preferable that said control unit has a function of alarming to inform when the term of use of said head unit has expired or to be expired soon. [30] In this invention, it is preferable that an apparatus for shielding which has a hole for irradiation is placed on the side unit of the protective case on which the output window exists, so that various ionizing ranges and X-ray irradiation types including circle, square and ellipse can be obtained according to the shape of the hole and the distance to the output window. [31] A preferred embodiment of a method for removing electric charges of a charged body according to this invention is characterized in removing electric charges of a charged body by ionizing elements or materials near the charged body by irradiating soft X-ray having wavelengths in the range of 1-5 A generated from the soft X-ray tube that has a target with a predetermined target voltage and target current, and uses beryllium window evaporated with silver(Ag). [32] In this invention, it is preferable to remove electric charges by generating soft X-ray having main wavelengths in the range of 3.5-4.5A under the circumstance that the anode voltage is under 1OkV.

Advantageous Effects

[33] Various advantages can be expected according to work of this invention.

[34] First, more economical installation is possible because shielding is easier and stability is increased by using beryllium window evaporated with silver as the target material. [35] Second, faster heat transferring is possible because the area which the flange contacts with the protective case can be increased easily by using the flange coupler. [36] Third, constructing and manufacturing is easier because the interposing in the prior art is unnecessary.

Brief Description of the Drawings [37] Figure 1 is a structural diagram of an ionizer using soft X-ray according to a prior art. [38] Figure 2 is a structural diagram of an ionizer using soft X-ray according to another prior art. [39] Figure 3 is a structural diagram of an ionizer using soft X-ray according to a preferred embodiment of this invention. [40] Figure 4 presents characteristic curves showing the relation between the value of ion current multiplied by square of distance and the neutralization distance when tungsten or silver is used as the target material and the anode voltage is 9.5kV, 1OkV,

10.5kV. [41] Figure 5 presents curves showing generated soft X-ray radiation doses (Sv) per wavelength when tube current is 10OD, anode voltage is 6-13kV, and silver is used as the target material. [42] Figure 6 presents curves showing the relation between the neutralization distance and generated soft X-ray radiation doses when tungsten or silver is used as the target material, anode voltage is 9.48kV, and tube current is 0.24OmA. [43] Figure 7 presents curves showing the relation between the neutralization distance and the ion current when tungsten or silver is used as the target material, anode voltage is 10.5kV, and tube current is 0.24OmA. [44] Figure 8 presents curves showing the relation between the neutralization distance and generated soft X-ray radiation doses when tungsten or silver is used as the target material, anode voltage is 10.5kV, and tube current is 0.24OmA. [45] Figure 9 presents curves showing the relation between the neutralization distance and the ion current when tungsten or silver is used as the target material, anode voltage is 1OkV, and tube current is 0.2382mA. [46] Figure 10 presents curves showing the relation between the neutralization distance and generated soft X-ray radiation doses when tungsten or silver is used as the target material, anode voltage is 1OkV, and tube current is 0.2382mA. [47] Figure 11 presents curves showing the relation between the neutralization distance and the ion current when tungsten or silver is used as the target material, anode voltage is 9.48kV, and tube current is 0.24OmA. [48] Figure 12 is a diagram showing the state when the flange unit and the flange coupler of the ionizer using soft X-ray according to this invention are coupled. [49] < Explanation about important part of drawings >

[50] 310: X-ray tube

[51] 320: flange unit

[52] 330: flange coupler

[53] 340: front portion of the side unit of the protective case [54] 350: high voltage generation unit

[55] 360: side unit of the protective case

[56] 370: cover unit of the protective case

[57] 380: connector

[58] 390: bracket

Best Mode for Carrying Out the Invention

[59] Now referencing the attached drawings, we make an explanation about the structure and characteristics of this invention. The features of the ionizer using soft X-ray according to this invention are as follows.

[60] 1. The structure of supporting X-ray tube and transferring heat

[61] The head unit of the ionizer in this invention has a structure as shown in figure 3 to improve the structure of supporting X-ray tube and transferring heat.

[62] In this invention, a protective case consists of a D-shaped side unit (360) and a D- shaped cover unit (370) connected by screws, and forms a space in it. An X-ray tube (310) having output window emitting soft X-ray generated when the electrons collide with the target, and a high voltage generation unit (350) supplying high voltage to said X-ray tube are housed in the space. The protective case and the target are made of conductive materials, and have ground potentials and thermal conductivities. The ionizer is attached to the ceiling or the wall by a bracket (390) that consists of a D- shaped bracket unit and a reinforcing plate.

[63] A flange unit (320) is thermally and electrically connected to the output window, forms a front end of the X-ray tube (310), supports the output window, and radiates the heat generated from said target to outside of the X-ray tube by contacting with a front portion (340) of said side unit of the protective case. A flange coupler (330) has thermal and electrical conductivity, has a through hole as large as the flange unit (320) so that the periphery of the flange unit can be fixed by the raised spot formed inside of said through hole. The flange coupler (330) and the flange unit (320) form one surface when they are coupled. The area which said flange coupler (330) contacts with said front portion (340) of the side unit of the protective case can be set up from necessity. The X-ray tube (310) is fixed and supported by the screws that fix said flange coupler (330) to said side unit (360) of the protective case.

[64] Figure 12 is a diagram showing the state when the flange unit and the flange coupler in this invention are coupled. Like this, this invention produces a superior heat transferring effect compared with prior arts, because the area of the protective case which the flange unit of the X-ray tube contacts with becomes substantially larger by fixing and coupling the flange coupler to the flange unit. In addition, the ionizer in this invention has a simple structure, can be constructed easily, and can support the X-ray tube stably by fixing the flange coupler to the protective case by screws without adop ting the complex structure as interposing which is used when attaching the flange to the protective case in the prior art.

[65] 2. Evaporation of silver(Ag)

[66] General ionizer using soft X-ray in the prior art removed electric charges by generating soft X-ray having main wavelengths in the range of 1-2A under the circumstance that the anode voltage is under 9-1 IkV with beryllium window evaporated with tungsten. However, as a result of the experiment by the applicant with beryllium window evaporated with silver (Ag), it was discovered that the amount of ion current which is required for ionizing is almost the same as in the prior art, while the main wavelengths of the soft X-ray is in the range of 3.5-4.5A under the circumstance that the anode voltage is 9.5kV. Moreover, radiation doses were only half of the amount in the prior art. Now we make a detailed description of the result of the experiment. [67] Figure 4 shows decrease of ion current according to the distance when beryllium window evaporated with tungsten or silver is used as the target material and the anode voltage is 9.5kV, 1OkV, 10.5kV. When silver is evaporated, we expected ionizing effect at long distance would be inferior, because the main wavelengths (3.5-4.5A) are longer than the wavelength (1-2A) generated when tungsten is evaporated as in the prior art. However, we can see that the decrease of ion current according to the distance is almost the same in reality. We guess this is because of the long distance ionizing effect by the bremsstrahlung (1.5-2.5A) generated in addition to the main wavelengths when silver is evaporated. Because generated X-ray radiation doses are smaller than when tungsten is used, the target using beryllium window evaporated with silver has many merits like increased stability, easy shielding, and better economical efficiency, while the ionizing effect according to the distance is maintained as before. [68] Figure 5 presents curves showing the relation between the main wavelengths of soft

X-ray and generated soft X-ray radiation doses of corresponding wavelength when tube current is 10OD, anode voltage is 6-13kV, and beryllium window evaporated with silver is used as the target material. It is shown that as the anode voltage gets higher the soft X-ray of the same wavelength is generated more, the soft X-ray of 0.425nm (4.25A) is generated the most in this example, most of the soft X-rays have wavelengths of 1-5 A. In the figure, unit of the vertical axis is generated soft X-ray radiation doses (Sv) per wavelength. The tube current here means the current by the electrons moving to the inner target of the soft X-ray tube when the anode voltage is given.

[69] Figure 6 presents curves showing the relation between the neutralization distance and generated soft X-ray radiation doses when beryllium window evaporated with tungsten or silver is used as the target material, anode voltage is 9.48kV, and tube current is 0.24OmA. It is shown that generated soft X-ray radiation doses are smaller for the same distance when silver is evaporated. This means that using silver is safer and it can shield X-ray more easily.

[70] Figure 7 presents curves showing the relation between the neutralization distance and the ion current when beryllium window evaporated with tungsten or silver is used as the target material, anode voltage is 10.5kV, and tube current is 0.24OmA. The ion current when silver is used is a little smaller for the same distance. However, considering the time of ionization according to the ion current (ion current maintaining the time to drop +1000V to +100V within 0.5 seconds: 150~240nA), substantial efficiency of ionization is the same.

[71] Figure 8 presents curves showing the relation between the neutralization distance and generated soft X-ray radiation doses when beryllium window evaporated with tungsten or silver is used as the target material, anode voltage is 10.5kV, and tube current is 0.24OmA. When silver is used, generated soft X-ray radiation doses are smaller for the same distance, which shows that using silver is safer and it can shield X-ray more easily.

[72] Figure 9 presents curves showing the relation between the neutralization distance and the ion current when beryllium window evaporated with tungsten or silver is used as the target material, anode voltage is 1OkV, and tube current is 0.2382mA. The ion current when silver is used is a little smaller for the same distance. However, considering the time of ionization according to the ion current (ion current maintaining the time to drop +1000V to +100V within 0.5 seconds: 150~240nA), substantial efficiency of ionization is the same.

[73] Figure 10 presents curves showing the relation between the neutralization distance and generated soft X-ray radiation doses when beryllium window evaporated with tungsten or silver is used as the target material, anode voltage is 1OkV, and tube current is 0.2382mA. When silver is used, generated soft X-ray radiation doses are smaller for the same distance, which shows that using silver is safer and it can shield X-ray more easily.

[74] Figure 11 presents curves showing the relation between the neutralization distance and the ion current when beryllium window evaporated with tungsten or silver is used as the target material, anode voltage is 9.48kV, and tube current is 0.24OmA. The ion current when silver is used is a little smaller for the same distance. However, considering the time of ionization according to the ion current (ion current maintaining the time to drop +1000V to +100V within 0.5 seconds: 150-24OnA), substantial efficiency of ionization is the same. The difference in this case is smaller than other cases. From this fact, we can see that the generated amount of ion current is almost the same when the anode voltage is low. [75] The fact that we can see from the result of the above experiment is as follows.

[76] First, generated amount of ions is almost the same when the voltage is low.

[77] Second, dangerousness is much more reduced and shielding is easier compared to prior ionizers, while the efficiency of ionization is similar.

[78] Third, having 3.5-4.5A as the main wavelengths and 1.5-2.5A as the bremsstrahlung wavelengths in this invention, the ionizer of this invention is useful for ionization for both long distance and short distance. Main wavelengths in the range of 3.5-4.5A are useful for short distance ionization, and bremsstrahlung wavelengths in the range of 1.5-2.5A are useful for long distance ionization. Accordingly, this invention is very economical because one ionizer can be used both as long distance ionization and short distance ionization. In addition, the overall efficiency of ionization is expected to be improved.

[79] Meanwhile, a Japanese Patent No. 2951477 fixed the range of main wavelengths as

2-20A without defining the target material. However, this is not credible because it simply claims specific numerical value without considering a number of actual factors (for example, target material, anode voltage, tube current, etc.) and it is not based on any experimental foundation.

[80] 3. Improved functions of controller

[81] Compared to prior ionizers, a lot of functions of the ionizer using soft X-ray according to this invention were improved. They are arranged in Table 1 below. Table 1 illustrates a set up table of the functions of the ionizer using soft X-ray according to this invention. In this example, 10 functions can be set up. Improved functions of controller in the ionizer according to this invention are as follow.

[82] Table 1

[83] First, this invention added function of outputting signals of Alarm, Interlock,

Remote, Controller Power outside.

[84] Second, the flexible tube disclosed in the applicant's another Korean Patent Application No. 10-2005-32535 "A Flexible Soft X-ray Ionizer" can be applied to this invention. That is, another embodiment of an ionizer using soft X-ray according to this invention comprises a head unit generating soft X-ray, a soft X-ray protect unit shielding the leak of the soft X-ray from said head unit, and a power control unit supplying control signal and control voltage to the head unit, wherein the head unit is located outside of the soft X-ray protect unit, a high voltage cable that connects the head unit and the power control unit is protected from external impact or vibration, and it is possible to use the flexible tube which allows the user to bend the head of said head unit at an arbitrary angle toward a charged body.

[85] Third, an RMS (Real monitoring system) can be applied to this invention. The RMS is a system which can monitor a number of ionizers in the field conveniently with one PC prepared in the field. The RMS is explained in detail in the applicant's another Korean Patent Application No. 10-2005-32534 "A Bar Type Ionizer".

[86] The details of 10 functions above are as follows.

[87] The connector name (corresponds to the function) of Function 1 is OUTPUT 1-4, number of pins is 5, and this function is connecting the head. This function was also used in a prior art.

[88] The connector name of Function 2 is INTERLOCK, number of pins is 2, and this function is inputting external interlock signal. When a worker enters a shielding room in which ionizers are installed, operation of ionizers needs to be stopped for the safety of the worker. If the door of the shielding room is opened by the external interlock signal, operation of ionizers is stopped automatically. If the door is closed again, operation of ionizers is started only when the START button is pushed. Accordingly the worker can be safe. However, in some working environments, operation of ionizers should be started automatically when the door of the shielding room is closed, and this requirement can be satisfied by a circuit modification. This function was also used in a prior art.

[89] The connector name of Function 3 is REMOTE, number of pins is 2, and this function is inputting external remote signal. START/STOP function is applied when the external remote signal is inputted. This function was also used in a prior art.

[90] The connector name of Function 4 is INDICATOR, number of pins is 2. This function is confirming head ON/OFF status, which was also used in a prior art.

[91] The connector name of Function 5 is ALARM, number of pins is 2, and this function is outputting alarm status, which was not used in a prior art.

[92] The connector name of Function 6 is INTERLOCK OUT, number of pins is 2, and this function is outputting external interlock signal. This function is outputting while interlock is operating, which was not used in a prior art.

[93] The connector name of Function 7 is REMOTE OUT, number of pins is 2, and this function is outputting external remote signal. This function is outputting while operation is remote, which was not used in a prior art.

[94] The connector name of Function 8 is POWER ON/OFF, number of pins is 2. This function is power ON/OFF, and outputs signal according to the power input status, which was not used in a prior art.

[95] The connector name of Function 9 is POWER TYPE (AC). 100-240 volt is used as a prior art.

[96] The connector name of Function 10 is CONNECTOT TYPE. Single connector is used in this invention while individual connector was used in a prior art.

[97] This invention may be modified and embodied in various forms, and it has been described and illustrated herein with reference to a specific embodiment thereof. However, it should be understood that this invention is not limited to the particular form as described above, and that this invention includes all modifications, equivalents and substitutes within the spirits and scope of this invention as defined in the "claims" attached hereto. [98] [99]

Claims

[1] An ionizer using soft X-ray and having a head unit that generates soft X-ray in order to remove electric charges of a charged body by +/- ions or electrons generated from the gas in the air ionized by the soft X-ray, and a control unit to control at least one of the head unit, said head unit comprising, a protective case consisting of a D -shaped side unit, and a D -shaped cover unit combined to said side unit and forming a housing space; an X-ray tube housed within said protective case and having an output window that emits soft X-ray generated when the electrons collide with the target; a flange unit thermally and electrically connected to said output window and forming a front end of said X-ray tube, supporting said output window, and radiating the heat generated from said target to outside of the X-ray tube by contacting with the front portion of said side unit of the protective case; a high voltage generation unit housed in said protective case and supplying high voltage to said X-ray tube; and a flange coupler fixing said X-ray tube to said front portion of said side unit of the protective case, wherein said flange coupler has thermal and electrical conductivity, has a through hole as large as the flange unit so that the periphery of the flange unit can be fixed by the raised spot formed inside of said through hole, and wherein said flange coupler and said flange unit form one surface when they are coupled.

[2] The ionizer as set forth in claim 1, wherein each of said head unit further comprises a timer to display cumulative used time of said ionizer.

[3] The ionizer as set forth in claim 1, wherein the side unit, cover unit of the protective case, and the target are made of conductive materials, have ground potentials and thermal conductivities.

[4] The ionizer as set forth in claim 1, wherein said control unit comprises a means of choice to choose the head unit; and a display window to display cumulative used time of chosen head unit by linking with the timer in the head unit.

[5] The ionizer as set forth in claim 1, wherein said control unit has functions of alarm, interlock, remote control, input and output of control signal of the power source of the controller.

[6] The ionizer as set forth in claim 1, wherein the head unit and the control unit are connected by a flexible tube when the head unit is installed outside of the protective case, and wherein said flexible tube houses a high voltage cable that connects the head unit and the power control unit in order to protect the high voltage cable from external impact or vibration, and wherein said flexible tube allows the user to bend the head of said head unit at an arbitrary angle toward a charged body, and wherein the flange coupler is not used in this case.

[7] The ionizer as set forth in claim 1, wherein an RMS (Remote monitoring system) to monitor a number of ionizers remotely with one personal computer is adopted.

[8] The ionizer as set forth in claim 1, wherein the connector of said control unit adopts a single connector form.

[9] The ionizer as set forth in claim 1, wherein the ionizer further comprises a bracket for attaching said ionizer to the ceiling or the wall which consists of a D- shaped bracket unit to fix said head unit horizontally or vertically by screws; and a reinforcing plate connected with one outer surface of said D-shaped bracket unit by screws and fixes said head unit by screws, and wherein said D-shaped bracket unit is fixed to the ceiling or the wall by anchor bolts.

[10] The ionizer as set forth in claim 1, wherein the area which said flange coupler contacts with said side unit of the protective case can be set up from necessity.

[11] The ionizer as set forth in claim 1, wherein a space for the body of the X-ray tube is prepared beside said high voltage generation unit inside said side unit of the protective case.

[12] The ionizer as set forth in claim 1, wherein said X-ray tube is fixed and supported by the means that fixes said flange coupler to said side unit of the protective case.

[13] The ionizer as set forth in claim 1, wherein said control unit has a function of alarming to inform when the term of use of said head unit has expired or to be expired soon.

[14] The ionizer as set forth in claim 1, wherein an apparatus for shielding which has a hole for irradiation is placed on the side unit of the protective case on which the output window exists, so that various ionizing ranges and X-ray irradiation types including circle, square and ellipse can be obtained according to the shape of the hole and the distance to the output window.

[15] A method for removing electric charges of a charged body characterized in removing electric charges of a charged body by ionizing elements or materials near the charged body by irradiating soft X-ray having wavelengths in the range of 1-5 A generated from the soft X-ray tube that has a target with a predetermined target voltage and target current, and uses beryllium window evaporated with silver (Ag).

[16] The method for removing electric charges of a charged body as set forth in claim

15, characterized in removing electric charges by generating soft X-ray having main wavelengths in the range of 3.5-4.5A under the circumstance that the anode voltage is under 1OkV.