JP2017166886A - High-frequency power density distribution measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of easily measuring the distribution of high-frequency power density in a transmission channel.SOLUTION: In a system for propagating a high-frequency wave using a waveguide, a clearance into which a dielectric plate movable into or out of the waveguide is inserted, and the waveguide includes an observation window, and a temperature distribution measuring instrument for observing the temperature distribution in the dielectric plate disposed outside the waveguide via the observation window. When the high-frequency power distribution in the waveguide is measured, the dielectric plate is inserted into the waveguide through the clearance, the dielectric plate is moved to a prescribed position outside the waveguide after a lapse of a certain time, and the temperature distribution in the dielectric plate is measured by the temperature distribution measuring instrument via the observation window.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method used in a high-frequency heating apparatus using a waveguide, and more particularly to a high-frequency power density distribution measuring method for measuring a high-frequency power density distribution propagating in a waveguide. .

  The high-frequency power density distribution measuring method of the present invention is indispensable for improving the high-frequency propagation efficiency of the transmission path in a large-sized high-frequency heating apparatus. For example, the high-frequency power density distribution measuring method is not limited to the fusion apparatus described as an example in this document. It is also a useful method in general industrial fields such as quality ceramic sintering.

  In general, a large-sized high-frequency heating device includes a gyrotron that is an oscillation source that oscillates a high frequency (RF), and a waveguide that forms a transmission path that transmits the generated high-frequency power to a portion to be heated. In such a heating apparatus, conventionally, as a method for measuring high-frequency power propagating in a waveguide, (1) as shown in Patent Document 1, it is provided in a waveguide of a main transmission path. A method using a high-frequency power measuring device in which a dielectric is inserted into the gap and the temperature rise value of the dielectric is measured with a thermometer; (2) the high frequency of the main transmission path as shown in Non-Patent Document 1; A method using a high-frequency power measuring device is known in which the direction of the above is changed, the high frequency guided into the dummy load is changed to heat, and the temperature rise value of the cooling water is measured.

Japanese Unexamined Patent Publication No. 2006-132960

Lawrence Ives et al., Design and Operation of a 2-MW CW RF Load for Gyrotrons, IEEE Transactions on Electron Devices, Vol. 61, No. 6, June 2014.

  In a high-frequency heating device, how to efficiently transmit high-frequency power generated by a gyroton or the like to a heating target portion while minimizing power loss in the transmission path is a very important issue. For this purpose, it is important to optimize the power density distribution of the propagating high frequency. More preferably, the power density distribution that optimizes the transmission efficiency is provided near the required ends of the transmission path, for example, near both ends. This is very important.

  Therefore, the object of the present invention is to change the high-frequency power density in the transmission line in a relatively short time without changing the main transmission line of the high-frequency wave and maintaining the vacuum without disturbing the operation of the high-frequency heating device. It is to provide a method by which the distribution can be measured.

  According to one aspect of the present invention, a high frequency power density distribution measuring method includes a gap in which a movable dielectric plate can be inserted into and out of a waveguide in a system that propagates high frequency using a waveguide. And providing a temperature distribution measuring device for observing a temperature distribution of the dielectric plate outside the waveguide through the observation window and the observation window, the high-frequency power in the waveguide. When the distribution is measured, the dielectric plate is inserted into the waveguide through the gap, and after a predetermined time has passed, the dielectric plate is moved to a predetermined position outside the waveguide. The temperature distribution of the dielectric plate obtained by generating heat due to the dielectric loss due to is measured by the temperature distribution measuring instrument through the observation window.

  Preferably, in the above-described method, the movement of the dielectric plate from the inside of the waveguide to the predetermined position outside the waveguide is performed by gravity and stopped at the predetermined position suitable for observation.

  In the conventional method, although it is possible to measure the high frequency power transmitted by the waveguide, it is difficult to measure the high frequency power density distribution inside the waveguide. According to the measurement method of the present invention, the high-frequency power density distribution inside the waveguide can be changed at any position in the waveguide path by changing the high-frequency main transmission path. Moreover, the distribution of the high frequency power density in the transmission line can be measured in a relatively short time while maintaining the vacuum without interfering with the operation of the high frequency heating apparatus.

The longitudinal cross-sectional view which shows an example of the apparatus for enforcing the high frequency electric power density distribution measuring method which concerns on this invention. The longitudinal cross-sectional view which shows the other example of the apparatus for enforcing the high frequency electric power density distribution measuring method which concerns on this invention. The figure which showed the state which moved the dielectric plate out of the waveguide in the high frequency electric power density distribution measuring apparatus of FIG. FIG. 4 is a bird's-eye view of the high-frequency power density distribution measuring apparatus shown in FIG. 3. Figure showing a measurement example of high-frequency power density distribution inside the waveguide

  The embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 is a longitudinal sectional view showing an example of a high-frequency power distribution measuring apparatus to which the method of the present invention is applied. In FIG. 1, a dielectric plate 3 is inserted in the gap 2 in the waveguide 1. When a high frequency current flows, the dielectric plate 3 generates heat due to dielectric loss due to the high frequency power. The temperature distribution of the dielectric plate at that time is measured by a temperature distribution measuring device 5 such as an infrared camera through the observation window 4. Then, a high-frequency power density distribution propagating in the waveguide is calculated from the time change (temperature rise) of the temperature distribution.

  When an infrared camera, for example, an infrared thermography device is used, the time change of the temperature distribution on the surface of the dielectric disk can be measured. This apparatus has a function of outputting temperature on coordinates and time as data in addition to a measuring method for displaying temperature in color on a video screen. If this data is taken into a personal computer and graphed, the time distribution of temperature distribution (temperature rise) can be obtained.

  The initial temperature of the disk surface is uniform (uniform), but when a high frequency is transmitted, heat is generated in proportion to the power density distribution, resulting in a temperature distribution. Accordingly, distribution data obtained by subtracting the initial temperature from the temperature distribution immediately after high-frequency transmission (temperature increase) directly represents the power density distribution (relative value thereof).

  Here, the structure and function of each part of the high-frequency power density distribution measuring apparatus of FIG. 1 will be described. The dielectric plate 3 is a mirror-finished plate that transmits high-frequency power transmitted through the waveguide 1 and is used to detect heat generation due to dielectric loss due to high-frequency. The material is silicon nitride and the thickness is about 0.98 mm. .

  As the material of the dielectric plate 3, dielectric materials having different dielectric loss tangents were used according to the magnitude and frequency of the high frequency power. The device shown in FIG. 1 was designed on the assumption of high-frequency power density measurement at 110 GHz, 1 MW class, and short pulses. Since the dielectric loss is proportional to the frequency and the dielectric loss tangent of the material, a material having a lower dielectric loss tangent is suitable for high-frequency power transmission as the frequency becomes higher, such as 110 GHz. However, it is desired that the material required for this apparatus transmits high-frequency power with a low loss and the temperature change of the dielectric plate 3 that generates heat is as slow as possible. Therefore, in this example, silicon nitride having a dielectric loss tangent: 1.4 × 10 −4, thermal conductivity: 59 W / mK, and relative dielectric constant: d7.9 was used as the material of the dielectric plate 3.

The thickness of the dielectric plate 3 is
t = n · λL / 2 (t: thickness n: integer)
λL is the wavelength in the dielectric, and the wavelength in vacuum is λ0. λL = 1 / √ε · λ0 (ε: dielectric constant of the dielectric)
The dielectric constant of silicon nitride ε = 7.9, frequency f = 110GHz λL / 2 = 0.48 (mm)

  Therefore, the thickness t of the dielectric plate 3 is 0.97 mm when n = 2 and 1.45 mm when n = 3. Since the reflected wave is generated on the dielectric plate when the thickness is different, the manufacturing accuracy was set to ± 0.01 mm. In the example, n = 2 and 0.97 mm ± 0.01 mm.

  The dielectric plate support structure 8 has a structure in which the dielectric plate is supported at one point by a heat insulating material (PEEK material), and can be fixed at the same position even if the dielectric plate is replaced, thereby realizing accurate temperature measurement. it can. The observation window 4 is a germanium vacuum window in which the temperature distribution measurement window is optically coated in accordance with the transmission wavelength region of an infrared camera or the like. The gate valve 6 (FIG. 2) is for preventing high-frequency power from leaking to the measurement mechanism section during long-time operation during non-measurement. Moreover, the conversion flange 7 with a slit is provided with a conversion flange with a slit in order to further reduce high-frequency power to the seat surface of the gate valve, and the flange itself has a water cooling structure.

  Next, the operation of this apparatus will be described. The high-frequency power density measuring apparatus inserts a dielectric plate 3 of about 1 mm into a gap of about 2 mm between the waveguides 1 and transmits high-frequency power through the dielectric plate 3 for a short time (about 0.2 seconds). The dielectric plate that transmits the high-frequency power generates heat, but the portion with the higher power density has a higher temperature, so the temperature distribution reflects the power density distribution. After stopping the high frequency, the electrical signal (high frequency power stop signal) generated at the stop timing is used as a trigger to move the disk at high speed (less than 0.5 seconds) (including free fall) for temperature distribution observation (measurement) Stop at the window position. The temperature distribution (time change) of the dielectric plate is measured with an infrared thermography (infrared camera) through the observation window. After the temperature distribution measurement is completed, the metal closure plate (vacuum gate valve) is closed to prevent leakage high frequency in order to prevent damage to the measurement mechanism due to high frequency leakage when transmitting long-term high-frequency power. To do.

  On the other hand, FIG. 2 and FIG. 3 show the longitudinal cross-sectional view of the other example of the high frequency electric power distribution measuring apparatus for enforcing the measuring method of this invention. FIG. 2 is a longitudinal sectional view of the high-frequency power density distribution measuring apparatus in a state where the dielectric plate 3 is inserted into the gap 2 in the waveguide 1. In this state, when the high-frequency wave propagating through the waveguide passes through the dielectric plate 3, the temperature of each part in the dielectric plate 3 is caused by heat generated by the dielectric loss of the dielectric corresponding to the high-frequency power density distribution. To rise. FIG. 3 shows the same configuration example as FIG. 2, but shows a longitudinal sectional view of the high-frequency power density distribution measuring apparatus in which the dielectric plate 3 is moved out of the waveguide from the gap 2 in the waveguide 1. It is.

  The dielectric plate 3 whose temperature has risen due to the high frequency in the state of FIG. 2 is moved from the position of the gap of the waveguide in a very short time and stopped outside the waveguide as shown in FIG. . Note that a gap width of about 2 mm is considered appropriate for the gap between the waveguides, and the amount of leaking high frequency can be kept small. At this time, as shown in FIG. 3, by providing an observation window 4 in front of the position of the stopped dielectric plate 3 after the movement, the temperature distribution in the dielectric plate 3 can be facilitated. Can be measured. A temperature distribution measuring device 5 such as an infrared camera installed just outside the observation window 4 is used, and the temperature distribution of the dielectric plate is measured through the observation window 4.

  In this example, as already described, it is indispensable that the dielectric plate 3 is moved from the gap of the waveguide 1 and stopped in a short time. By doing so, the current density distribution can be accurately calculated from the temperature distribution. As a moving method, for example, the following method is used. The dielectric plate 3 and the dielectric plate support structure 8 (1 Kg) are inserted into the gap between the waveguides by a motor drive and fixed by a stopper driven by an air cylinder. After the high frequency power is transmitted through the dielectric plate, the stopper is removed using the high frequency power stop signal, the free fall is performed, and the dielectric plate is fixed to the temperature distribution measurement position by the catcher mechanism.

  In the example shown in FIG. 2 and FIG. 3, unlike the example of FIG. 1, it is not necessary to provide a direct observation window in the waveguide 1, and thus it is applied to high-frequency propagation. Since the influence can be suppressed to a small extent and the observation window is located in front of the dielectric plate 3, high-precision temperature measurement can be performed in the entire range of the dielectric plate 3. .

  In addition, since these measurements are performed while maintaining the vacuum, it is possible to efficiently perform the measurement without wasting time. In addition, in the state shown in FIG. 3, it is possible to operate the high-frequency heating device without changing the high-frequency main transmission path. Furthermore, by providing a conversion flange 7 with a slit between the observation window 4 and the waveguide 1, it is possible to minimize further spreading of the high frequency leaked from the gap between the waveguides and to cool the waveguide. Thus, problems such as overheating can be prevented.

  Further, in the state of FIG. 3, by closing the gate valve 6 provided between the waveguide 1 and the observation window 4, it is possible to block high frequency leaking from the gap between the waveguides. Here, the measurement by this apparatus can be performed in a short time (about 0.5 seconds or less).

  On the other hand, since the high-frequency pulse width (duration) that should be transmitted through the waveguide during non-measurement is long (eg, 100-1000 seconds), the amount of energy integrated over time even if the leakage power from the slit is small When the gate valve is not used, the dielectric and the support structure may be overheated. For this reason, it is important to close the gate valve 6 so as to block leakage high frequency from the gap 2 of the waveguide and prevent overheating of the dielectric and the support structure.

  As already described, in the configuration examples of FIGS. 2 and 3, the dielectric plate 3 is moved and stopped in a short time. As an example of the driving force, power such as compressed air is used. Can do. Moreover, gravity can also be used as a driving force. As an example, if the dielectric plate is dropped by 0.2-0.3m using gravity and stopped, it can move in about 0.2-0.3 seconds. At this time, the dielectric plate support structure 8 that is structurally integrated with the dielectric plate 3 falls together, and the lower portion of the dielectric support structure 8 is provided inside the vacuum chamber 9. It is possible to take a structure to stop using the body. Figure 4 shows a bird's-eye view of the actually manufactured structure as a reference diagram.

The method of the present invention can be implemented in a relatively small measuring apparatus, and can be installed in each waveguide even when the number of waveguides is installed close to each other in parallel.
The high frequency power density distribution in the waveguide can deviate significantly from the optimal distribution. FIGS. 5A and 5B show examples of high-frequency power density distribution inside the waveguide. In the situation where it deviates significantly from the optimum distribution as shown in FIG. 5A, efficient transmission of high frequency and high frequency heating are hindered. In order to prevent such a situation and improve the situation, it is first necessary to grasp whether or not the high-frequency power density distribution is in the optimum distribution, and if so, how much the deviation is. In order to realize such an object, the measuring apparatus of the present invention is effective and indispensable.

Claims (3)

  In a system for propagating high frequency using a waveguide, a gap is provided in which a movable dielectric plate can be inserted into and out of the waveguide, and an observation window and the observation window are provided in the waveguide. Provided with a temperature distribution measuring device for observing the temperature distribution of the dielectric plate outside the waveguide, and when measuring the high frequency power distribution in the waveguide, the dielectric plate is inserted into the waveguide through the gap. Temperature distribution of the dielectric plate obtained by moving the dielectric plate to a predetermined position outside the waveguide after a predetermined time has passed, and generating heat by dielectric loss due to high frequency power. Is measured by the temperature distribution measuring instrument through the observation window.   The high frequency power density distribution measuring method according to claim 1, wherein the dielectric plate is dropped after being dropped by gravity from the inside of the waveguide to a predetermined position outside the waveguide.   3. The measurement method according to claim 1, wherein the dielectric plate is inserted into the waveguide by driving a motor and fixed in the waveguide for a predetermined time.

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