JP2001194229A - Infrared imaging video bolometer, frame member used for same, and incident power distribution measuring method using infrared imaging bolometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved infrared imaging video bolometer and a frame memory used for it. SOLUTION: The whole metal thin film is exposed to plasma radiation light by an IRIB device by removing a mask corresponding to spatial resolution. Consequently, a video image of the plasma radiation light can be obtained by increasing the spatial resolution. A mask which thermally separate respective pixels is not necessary any more, because algorithm representing heating value on each pixel is developed by using an FTCS method which solves a heat diffusion equation for a thin film. Technology regarding a calibrating method for a thin film is also disclosed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an infrared imaging video bolometer, a frame member used therein, and a method for measuring incident power distribution using the infrared imaging video bolometer.

[0002]

2. Description of the Related Art IR imaging bolometer (IRI)
B) was developed as a detector that measures the amount of plasma radiation from the temperature change of the metal thin film [TFR Group (presented b
y AL Pecquet), Journal of Nuclear Materials, 93
-94, 377 (1980), JC Ingraham and G. Tonini, Re
v. Sci. Instrum. 61, 2976 (1990)]. A method using an IR camera to measure the temperature change of a thin film was first proposed in a paper describing the relationship between operating thin film temperature, wavelength, and SNR [G. Apruzzese and G. Tonini, Rev. Sc
i. Instrum. 61, 2976 (1990)]. The two-dimensional IRIB concept initially introduced the use of a two-dimensionally partitioned matrix to project the temperature rise of the absorber [GA Wurd
en, in Diagnostics for Experimental Thermonuclear
Fusion Reactors, edited by PE Stott et al. (Ple
num, New York, 1996), pp. 603-606]. It has evolved into a two-dimensional array composed of pixels in a metal thin film [GA Wurden, BJ Peterson and S. Sudo, Re
v. Sci. Instrum. 68, 766 (1997), GA Wuerden, U.
S. Patent 5,861,625]. This technology, known as the infrared imaging bolometer (IRIB), has been designed, assembled, and experimentally tested on CHS devices [GA Wurden and BJ Peterson, Rev. Sci. Instu.
rm. 70, 766 (1999)]. Details of IRIB are shown below.

As shown in U.S. Patent 5,861,625
In addition, two identically shaped mats with a two-dimensional hole pattern
Sandwich the metal thin film between the disks,
Fig. 1 shows a two-dimensional array with a thin film exposed on both sides
Shown in One side of the array passes through pinholes and slits
Facing the emitted plasma radiation. On the other hand, IR
As shown in Figure 2, the back of the blackened thin film array
And the thin-film array is
The emitted light causes a temperature increase in the pixel. Copper mask
Acts as a heat sink for the pixels and
The sensitivity K of each pixel depends on the size, thickness and thermal characteristics of the pixel.
The thermal diffusion time τ is determined. Thin film thickness t _fIs assumed
Should be decided to stop the highest energy photons
It is.

The diameter of the thin film should be determined so that the thermal diffusion time of each pixel matches the frame interval Δt of the camera. The relationship between the pixel diameter d _pix and its thermal diffusion time is given by equation (1):

[0005]

(Equation 1)

Κ is the thermal diffusion coefficient due to the metal properties of the thin film.

If this value is large, the measurement time interval is not sufficient, and there is a problem that the amount of heat absorbed before the next measurement does not decrease to the reference value. However, if this value is small, the thermal diffusion is rapid. Happen too much. Spatial resolution is determined by the pinhole and the field of view of the camera. Each pixel is signal calibrated by launching a choppered He-Ne laser beam of a known frequency of laser output power onto the blackened thin film surface and measuring the values of τ and κ. The radiation light power to each pixel is given by equation (2).

[0008]

(Equation 2)

Here, T is the temperature of the metal thin film in consideration of the mask temperature, as in the case of the resistance type metal film bolometer.

[0010]

By the way, in the above-mentioned conventional bolometer, various problems arise from a matrix-shaped mask divided into segments.

First, heat leaks across the mask to pixels where there is no signal, such as crosstalk, due to heat exchange between adjacent pixels which are recesses on the copper mask.

Second, a part of the edge of the pixel on the mask becomes a shadow on the edge of the mask. The third problem arises from the above-mentioned shadow. However, when the carbon spray used for blackening is sprayed on the metal thin film, the surface of the metal thin film and the copper mask thereon are not flush with each other. Is that the carbon film is not uniform.

In addition, since a large number of pixels are fixed by a mask divided into segments, and a part of a metal thin film covering the mask becomes a shadow of the mask and cannot be used, the spatial resolution is reduced. is there.

The present invention has been made to solve the above problems, and provides an improved infrared imaging video bolometer, a frame member used therein, and a method of measuring incident power distribution using the infrared imaging video bolometer. The purpose is to do.

[0015]

The infrared imaging bolometer according to the present invention comprises a vacuum container in which plasma is confined, and a black sprayed carbon inner surface attached to the vacuum container to prevent light reflection from the plasma. A light shield tube, provided on the end face of the tube, an infrared vacuum window attached to the vacuum vessel, and a plate provided on the end face of the tube opposite to the infrared vacuum window, the pin A plate having holes or slits for taking in light from the plasma, a frame member provided in parallel with the plate, attached to the tube at a distance from the plate, and having a thin film, and the infrared vacuum window. An infrared video camera for viewing the thin film of the frame member through the frame member, wherein the frame member is made of metal. A film and two frames made of a heat conductive material, each frame being provided with a window, the metal thin film being sandwiched by the frame so as to cover the window and held so as to be exposed on both sides. And a frame that is provided.

A frame member for an infrared imaging bolometer of the present invention comprises a metal thin film and a heat conductive material.
One frame, wherein each frame is provided with a window, and the metal thin film is held between the frame so as to cover the window and held so as to be exposed on both sides. Features.

Preferably, the frame member has a cavity capable of adjusting pressure on both sides of the metal thin film and blocking light.

The method for measuring the incident power distribution using the infrared imaging video bolometer according to the present invention comprises the steps of measuring the thin film temperature distribution of the frame member using the infrared imaging video bolometer, and measuring the metal distribution using the FTCS algorithm. Obtaining a distribution of incident power on the thin film.

IR imaging video bolometer (I
RVB) uses a copper frame member to hold the large metal film as shown in FIG. 3 by removing the mask separating the pixels from the IRIB. This IRVB
As a result, the detectable area is increased by about 60%, and the spatial resolution can be increased by about 25%.

The problem of the concave portion on the mask described above is as follows.
The problem is solved by fixing and firmly contacting the copper frame and the metal film with screws near the edge of the copper frame member, and further improvement is possible by using an indium gasket.

Further, it is possible to prevent a shadow on the metal thin film due to the copper mask. The IRVB also has experimental flexibility that the sensitivity and the signal intensity can be adjusted because the size and number of bolometer pixels can be changed according to the experimental situation.

Another feature is that an IRIB image can be obtained by splitting an IRIB image, whereas an IRVB image can be obtained as a whole video image of plasma radiation.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Configuration of the Present Invention The overall configuration of an infrared imaging bolometer of the present invention is the same as the configuration shown in FIG. That is, the vacuum vessel 1 confines the plasma. A light shield tube 3 is attached to the vacuum vessel 1, and its inner surface is blackened with a carbon spray to avoid light reflection from plasma. An infrared vacuum window 5 is provided on the end face of the tube 3 and is attached to the vacuum vessel 1.

A plate 7 is provided on the end face of the tube 3 on the side opposite to the infrared vacuum window 5, and a pinhole or a slit 9 is formed. Light from the plasma is introduced into the tube 3. A frame member (mask) 11 is provided in parallel with the plate 7, and is attached to the tube 3 at a distance from the plate 9. This frame member 11 has a thin film.

An infrared video camera 13 is provided near the infrared vacuum window 5 so that the thin film of the frame member 11 can be viewed through the infrared vacuum window 5.

The structure of the frame member 11 including the IRVB metal thin film 27 will be described with reference to FIGS.

A. The round copper frame 21 shown in FIG. 4 includes two frames, a front frame 21a and a back frame 21b, and is made of non-oxidized copper having the following holes. The frame 21 is provided with a rectangular window 29 having a size smaller than the metal thin film 27.

Four holes, that is, holes for assembling bolts 23, are arranged at equal intervals along the edge to mount the light shield frame 21.

Frame 21 for tightening bolts
4 holes on the top, bottom, left and right sides, holes for fixing bolts 25
Is open. This secures the metal thin film 27 and provides sufficient thermal contact between the metal thin film 27 and the frame 21.

A vent hole 31 as shown in FIGS. 5 and 6 is formed so as to allow air to pass therethrough so that the air pressure does not differ on both sides of the metal thin film 27. At this time, the structure is as shown in FIG. 6 when viewed from the cross section so that light does not pass directly from the vent hole (hole) 31 and the other cannot be seen through the vent hole 31 from either surface. It is a crank type.

A large rectangular window 29 is opened in the center of the frame 21, and its size is slightly smaller than the metal thin film 27.

B. The metal thin film 27 has a thickness of 1 to 4 μm, and can be made of aluminum, gold, or another metal.

C. Stainless steel bolts, washers, and nuts are used to sandwich and fix the metal thin film 27 between the two copper frames 21.

D. The metal thin film 27 and the frame 21 on the IR camera 13 side are painted black with a carbon spray in order to increase the emissivity of the metal thin film 27 to improve the measurement sensitivity.

E. An indium gasket used between the metal film 27 and the frame 21 is optionally used to improve the thermal contact between the metal film 27 and the frame 21.

(2) Function of the present invention a. Method of Determining Incident Power from Temperature Measured by IR Camera The incident power distribution on the thin metal film 27 as a function of time is represented by F
It is obtained by the temperature distribution on the metal thin film 27 in the time function measured by the IR camera using the TCS (Forward Time Center Space) algorithm and the following equation.

[0037]

(Equation 3)

Each parameter is as follows.

X-horizontal position on metal thin film 27 y-vertical position on metal thin film 27 t-time P _rad (x, y, t) -radiation power t incident on metal thin film 27 _f- thickness of the metal thin film 27 k-thermal conductivity of the metal thin film 27 l-width of bolometer pixel Δt-time interval of each frame of the IR camera 13 T (x, y, t)-temperature of the metal thin film 27 κ- The condition of the stable solution for the thermal diffusion coefficient FTCS algorithm is

[0040]

(Equation 4)

And used to determine the minimum value of l _bol . Temperature measurements of the images of the IR pixels that make up each pixel of the bolometer can be averaged to reduce noise and increase sensitivity.

If necessary, the pixel size l _bol can be increased beyond the minimum value to improve the signal-to-noise ratio by sacrificing the time resolution and the spatial resolution depending on the signal level. This method unique to IRVB can be used more flexibly as needed than IRIB in which the spatial resolution is fixed by a copper mask.

B. Since the calibration assembly stroke at t _f of the metal thin film 27 is κ and k by blackening the mask surface of the IR camera 13 side, there is a possibility that a non-uniform,
Signal calibration is required. Equation (3) can be rewritten in the form of equation (2).

[0044]

(Equation 5)

Thus, calibration is performed by determining two quantities for each bolometer pixel. This calibration is performed for each IR pixel by κ (x, y) and τ (x,
Determine y) and average the amounts on the IR pixels that make up the bolometer pixel for maximum effect. The heat time τ is measured by rapidly heating the metal thin film 27 and measuring the temperature lag time of each pixel after the heat source moves. The sensitivity K of each IR pixel is determined by heating the metal thin film 27 with a light source of constant intensity and

[0046]

(Equation 6)

The relative measurement can be made by measuring the temperature distribution in the above. Metal thin film 27 related to flame temperature
The above temperature distribution is compared with the completely uniform temperature distribution of the metal thin film 27 given by equation (6).

[0048]

(Equation 7)

Each of the ends of the metal thin film 27 has x = ± a /
2, y = ± b / 2, and S _heat is the power density from a constant heat source on the metal thin film 27. Since S _heat is not known, the ratio of the measured temperature to this temperature distribution is generalized to the center pixel of the IR camera 13 on the thin film performing the relative calibration of each pixel.

[0050]

(Equation 8)

The output power Pla from the He-Ne laser
If ser is known, the Gaussian distribution of the laser light is given by equation (9).

[0052]

(Equation 9)

Here, α and β indicate the radius of the laser beam in the x and y directions, respectively, which are values when the center of the thin film is heated by the laser. The initial time of the thin film 27 is t =
When 0, the temperature change T _laser obtained at a position distant from the center of the thin film 27 is

[0054]

(Equation 10)

Where α, β≪a, b. By taking the thermal limit value of the thin film 27 that has reached the thermal equilibrium state (t = ∞), integrating it on the IR pixel, and dividing by the area, the center temperature T _center of the IR pixel is obtained.

[0056]

[Equation 11]

By solving equation (11) for K _center , the absolutely calibrated heat quantity K (x,
y) is determined as follows:

[0058]

(Equation 12)

(3) Results According to the Present Invention Using the above equation, a test was conducted to check the accuracy of the FTCS algorithm for giving the incident power on the metal thin film 27.

First, the laser incident power on the metal thin film 27 is modeled by a Gaussian distribution given by the equation (9). The result when P _laser = 20 mW and α = β = 4 mm is shown by the solid line in FIG. The incident power density of this model is the value expected from a typical LHD plasma (10 mW / cm ² ). Next, the resulting change in the temperature distribution of the metal thin film 27 is calculated using the equation (10) when the terms (m, l) of the Fourier series are set to 70 for each element.

In this study, the calculation is performed assuming a uniform gold thin film 27 (a = b = 9 cm, t _f = 1 μm, k
= 3.16 W / cm ° C, κ = 1.27 cm ² / s). FIG. 8 shows an example of a change in the temperature distribution of the metal thin film 27 for the first 40 ms when the time resolution Δt = 4 ms. The vertical axis indicates a temperature change from room temperature. The temperature level in this case is the current I
Much higher than the accuracy of the R camera 13 (0.025-0.1 ° C).

[0062] Finally, using the temperature distribution changes, the incident power distribution is calculated by FTCS algorithm used to (3) using l _{bo l} = 1 mm given by Equation (4).
The result is shown by the broken line in FIG. The difference in the peak between the distribution obtained by this calculation and the original Gaussian distribution is 6% or less. This indicates that the thermal radiation power distribution can be accurately reproduced by the FTCS algorithm.

[0063]

As compared with IRIB, IRVB has the following advantages.

1) For a mask in which the end portion of the pixel hole on the mask becomes a shadow with respect to the thin film, or the contact between the thin film and the mask is incomplete because the mask is curved. There are no accompanying problems.

2) The spatial resolution is improved by about 25%.

3) A video image of the emitted light power is obtained using the FTCS algorithm.

4) A qualitative real-time video image of the plasma radiation is obtained.

5) A flexible pixel size can be selected in response to a request for data according to various parameters of a plasma experiment.

6) The SN ratio is improved 2 to 5 times.

[Brief description of the drawings]

FIG. 1 shows a conventional infrared imaging bolometer (IR)
FIG. IB) is a view showing the arrangement of a mask and a thin film.

FIG. 2 is a diagram showing an entire configuration of a conventional IRIB and an infrared imaging video bolometer (IRVB) of the present invention.

FIG. 3 is a plan view showing an arrangement of a mask and a thin film of the infrared imaging video bolometer (IRVB) of the present invention, showing an FTCS algorithm geometric arrangement.

FIG. 4 is a perspective view showing an arrangement of a mask and a thin film of the infrared imaging video bolometer (IRVB) of the present invention.

FIG. 5 is an exploded view showing through holes of air of the infrared imaging video bolometer (IRVB) of the present invention.

FIG. 6 is a cross-sectional view showing a through hole of air of the infrared imaging video bolometer (IRVB) of the present invention.

FIG. 7: Incident power density profile (solid line) and FTC
The graph of the Gauss model of the S algorithm calculation result (broken line).

FIG. 8 is a graph showing the change in thin film temperature distribution with time as a parameter, the data being used for the FTCS algorithm calculation whose results are shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Vacuum container 3 ... Optical shield tube 5 ... Infrared vacuum window 7 ... Plate 9 ... Pinhole or slit 11 ... Frame member 13 ... Infrared video camera 21 ... Copper frame 21a ... Front frame 21b ... Back frame 23 ... Hole for assembly bolt 25… Hole for fixing bolt 27… Metal thin film 29… Window 31… Vent hole

Claims (5)

[Claims] 1. A vacuum vessel in which plasma is confined, a light shield tube attached to the vacuum vessel, and an inner surface of which is blackened with a carbon spray to avoid light reflection from the plasma, and provided on an end face of the tube. An infrared vacuum window attached to the vacuum vessel; and a plate provided on the end face of the tube opposite to the infrared vacuum window, the plate having a pinhole or slit, and light from plasma. A frame member provided in parallel with the plate, attached to the tube at a distance from the plate, and having a thin film, and an infrared video camera for viewing the thin film of the frame member through the infrared vacuum window. The frame member is a metal thin film and two frames made of a heat conductive material, A frame provided with a window, wherein the metal thin film is sandwiched between the frame so as to cover the window and held so as to be exposed on both sides. Meter. 2. The infrared imaging bolometer according to claim 1, wherein the frame member further has a cavity capable of adjusting pressure on both sides of the metal thin film and blocking light. 3. A frame comprising a metal thin film and a heat conductive material, wherein each frame has a window, and the metal thin film is sandwiched between the frames so as to cover the window. A frame member for an infrared imaging bolometer, comprising: a frame held so as to be exposed. 4. The frame member according to claim 3, wherein the frame member further has a cavity capable of adjusting pressure on both sides of the metal thin film and blocking light. 5. A step of measuring a thin film temperature distribution of the frame member using the infrared imaging video bolometer of claim 1, and a step of obtaining an incident power distribution on the metal thin film using an FTCS algorithm. Power distribution measurement method using infrared imaging video bolometer.