JPH05346471A - Neutron measuring device - Google Patents

Abstract

PURPOSE:To make the precise measurement of a neutron yield possible even in the case where disruption occurs by calculating an integration value of the number of the neutrons generated from the start of discharge up to the time of starting occurrence of a disruption. CONSTITUTION:A signal transmitted from a plasma current detector 6 for detecting voltage of a coil generated in response to a time change of a magnetic field which is formed with plasma current is time-integrated with a time integrator. And its integrated value is transmitted to a data processing calculator 8 used as a data processing means and the presence of disruption occurrence of plasma 1 and a disruption occurrence start time are found. On the other hand, a neutron detector 10 serves to detect neutrons generated in the plasma and its detected value is processed with an electronic device composed of a preamplifier 11, a counter 14 and the like. A data processing calculator 15 used as a second data processing means serves to calculate the integration value of the number of the neutron generation up to a disruption occurrence start time from discharge start even in the case where disruption occurs on the basis of a calculation result of th counter 14 and the calculator 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a neutron measuring device in a tokamak fusion device.

[0002]

2. Description of the Related Art FIG. 3 shows a schematic structure of a tokamak type fusion apparatus, in which a plasma 1 which is an ionized gas of fuel such as deuterium D is confined in a vacuum vessel 2 in a torus shape, and a plasma heating apparatus is provided. Is used to inject energy from the outside to heat the plasma 1 to a high temperature of about 100 million degrees. As a result, nuclear reaction between deuterium D and deuterium D in plasma 1

[Equation 1] Resulting in high energy neutrons of about 2.5 MeV and helium ³ He of 0.8 MeV.

Further, a shield 3 is installed around the vacuum container 2 in a torus shape, and the shield 3 shields neutrons generated in the plasma 1. Further, around the shield 3, a toroidal magnetic field coil group 4 for installing a magnetic field in the toroidal direction (outer peripheral direction of the torus) inside the vacuum container 2 is installed.

In order to confine the plasma 1, the toroidal magnetic field coil group 4 alone is not sufficient, and it is necessary to generate a magnetic field in the poloidal direction (inner circumferential direction of the torus) by the poloidal magnetic field coil group 5. The poloidal magnetic field coil group 5 itself has the primary side and the plasma 1 as the secondary side, and changes the coil current with time, that is, a current in the toroidal direction flows in the plasma 1 by the principle of a transformer ( Hereinafter, this is referred to as plasma current). This plasma current creates a poloidal magnetic field necessary for confining the plasma 1.

The superposed magnetic field generated by these toroidal magnetic field and poloidal magnetic field forms a toroidal magnetic surface inside the vacuum chamber 2. As a result, the high temperature plasma 1 does not directly contact the wall surface of the vacuum container 2,
It is confined in the vacuum container 2 while maintaining the torus shape.

FIGS. 4A, 4B and 4C show one cycle of so-called operation of the tokamak fusion device from the start of discharge by the rise of plasma current by the poloidal magnetic field coil group 5 to the end of discharge by the fall. It is the figure which showed notionally (1 shot). As shown in FIG. 4A, after the plasma current becomes almost constant, FIG.
The heating power shown in FIG. Along with this, the temperature of the plasma 1 rises, and as described above, high-energy neutrons are generated by the reaction of the equation (1) (shown in FIG. 4C). Here, since the number of neutrons generated in the plasma 1 is proportional to the output of the fusion reaction, it is important to monitor the number of generated neutrons in real time from the viewpoint of measuring and controlling the fusion power.

In addition to the measurement of the number of neutrons generated at each time in the nuclear fusion device, the sum of the number of neutrons generated from each shot from the start of the experiment to the present is an important measurement amount for the following reasons. That is, the high-energy neutrons generated in the plasma 1 according to the equation (1) and the constituent materials such as the vacuum container 2 and the shield 3 surrounding the plasma 1 are, for example,

[Equation 2] ⁵⁸ Ni (n, 2n) ⁵⁷ Ni (2) and other nuclear reactions may occur, and these peripheral structures may be replaced with radioactive materials.

The activation amount of these peripheral structures is plasma 1
Is proportional to the total time integral of the neutrons generated from. Therefore, in order to suppress the activation amount of the peripheral structures such as the vacuum container 2 and the shield 3 to a certain level or less, the total time integral amount of neutrons generated from the plasma 1 should be measured with sufficient accuracy. Will be required.

Next, a conventional neutron measuring device will be specifically described with reference to FIGS. 3 and 5. A neutron detector 10 for detecting neutrons is installed near the plasma 1 as shown in FIG. FIG. 5 shows the overall configuration of a neutron measuring device equipped with such a neutron detector 10. This neutron measuring device uses a pulse counting mode, and the detection signal pulse from the neutron detector 10 is sufficiently amplified by the preamplifier 11 and then sent to the proportional amplifier 12. The sent detection signal pulse is pulse-shaped by the proportional amplifier 12, and when the shaped pulse exceeds the wave height discrimination level preset by the wave height analyzer 13, the exceeded signal is output as a neutron detection signal.

Based on this output signal, the counter 14 records the number of output pulses within a preset fixed time and sends the count value at each sampling time to the data processing computer 15. The data processing computer 15 calculates the count rate based on the count value at each time point and the sampling time interval, and

[Equation 3] Based on the above, the total time integrated amount Ni of neutrons in each shot is calculated. However, in equation (3), t1, t2
Are the discharge start time and discharge end time shown in FIG. 4, respectively, and f (t) is the neutron count value at each time.

Further, from the time integrated value of the equation (3), the time integrated amount of neutron counting from the start of the experiment to the present is

[Equation 4] Calculated by. Here, nT is the total number of shots from the start of the experiment to the present.

[0012]

However, in the above-described tokamak type fusion device, when the plasma 1 becomes unstable for some reason, the magnetic surface for confining the plasma 1 is destroyed and the plasma current flowing in the plasma 1 is reduced. A phenomenon of abrupt decrease (hereinafter, referred to as disruption) may occur. When this disruption occurs, heat and electromagnetic energy accumulated in the plasma 1 are rapidly released, and the electromagnetic field around the plasma 1 is also rapidly changed accordingly.

At this time, as shown by the solid line in FIG. 6 (C), the neutron generation amount becomes instantaneously zero, but due to the sudden change in the electromagnetic field, the neutron detector 10
Therefore, it is expected that a detection signal (indicated by a broken line) is generated through the signal cable 20 as if the number of generated neutrons increased.

Therefore, in the neutron measuring device in the above-described tokamak-type nuclear fusion device, when the disruption frequently occurs, the total time integral amount of neutrons generated from the plasma 1 is measured with sufficient accuracy. Can not. This makes it difficult to accurately predict the activation amount of the surrounding structure, and the experimental plan related to the neutron production amount such as the incident power and the incident time from the heating device in each shot,
As a result, it will cause serious obstacles to the experimental design and operation management of the entire fusion device.

The present invention has been made in consideration of the above-mentioned circumstances, and even if an error occurs in the count value of the neutron measuring device due to the disruption of plasma, the total neutron generation amount of It is an object of the present invention to provide a neutron measuring device that enables measurement with sufficient accuracy.

[0016]

Means for Solving the Problems In order to solve the above-mentioned problems, a neutron measuring apparatus according to the present invention comprises a detecting means for detecting the presence or absence of plasma disruption and a disruption start time, First data processing means for determining the presence or absence of disruption of the plasma based on the detection signal and determining the disruption generation start time, neutron detection means for detecting neutrons generated in the plasma, Based on the neutron count value data from this neutron detection means and the calculation result of the first data processing means, if no disruption occurs, the integral value of the neutron generation number from the discharge start to the discharge end, When a disruption occurs, calculate the integrated value of the number of neutrons generated from the start of discharge to the time when disruption starts. Are those in which a second data processing means for calculating.

[0017]

In the present invention having the above structure, since the integrated value of the number of neutrons generated from the discharge start to the disruption generation start time is calculated, even when the disruption occurs, The time integrated value of the amount of neutrons generated from the plasma can be accurately obtained.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show an embodiment of the neutron measuring apparatus according to the present invention. Note that the same or corresponding portions as those of the conventional configuration will be described using the same reference numerals.

The neutron measuring apparatus of this embodiment has a plasma current detector (Rogowski coil) 6 as a detecting means. The plasma current detector 6 is installed around the vacuum container 2 to generate a plasma current. The voltage of the coil generated by the temporal change of the magnetic field is detected, and the presence or absence of the disruption of the plasma 1 and the disruption start time are detected. The signal from the plasma current detector 6 is sent to the integrator 7 and time-integrated by the integrator 7. The signal from the integrator 7 is sent to a data processing computer 8 as a first data processing means, and the data processing computer 8 determines whether or not the disruption of the plasma 1 is generated based on the signal from the integrator 7. Find the start time of rupture.

On the other hand, the neutron detector 10 detects neutrons generated in the plasma 1, and the detection signal from this neutron detector 10 is composed of a preamplifier 11, a proportional amplifier 12, a pulse height analyzer 13 and a counter 14. It is processed by an electronic device. That is, the detection signal pulse from the neutron detector 10 is amplified by the preamplifier 11, and the preamplifier 1
The signal from 1 is further amplified or pulse-shaped by the proportional amplifier 12, and then sent to the pulse height analyzer 13. In this wave height analyzer 13, a signal that exceeds the wave height discrimination level set in advance based on the output signal of the proportional amplifier 12 is output to the counter 14 as a neutron detection signal, and based on this output signal, a constant value set in advance in the counter 14 is set. The number of output pulses in time is recorded as a count value.

Second data processing based on the count value from each counter 14 at each sampling time and the calculation result of the data processing computer 8 for determining the presence or absence of the above-mentioned disruption and the start time of the disruption occurrence. The data processing computer 15 as a means calculates the integrated value from the discharge start to the discharge end when the disruption does not occur, and the discharge occurrence start time from the discharge start when the disruption occurs. The integral value of the number of neutrons generated up to the present is calculated, and the integral value of the number of neutrons generated in all discharges from the start of the experiment to the present is calculated. The signal cable 2 is provided between the above-mentioned components
Connected by 0.

Next, the operation of this embodiment will be described.

In this embodiment, the plasma current detector 6 detects the voltage of the coil generated by the time change of the magnetic field generated by the plasma current, and the output voltage is detected by the integrator 7
The time change of the plasma current is measured by performing time integration by. The time change of the measured plasma current is sent to the data processing computer 8. In the data processing computer 8, the time derivative (dIp / dt) cal of the plasma current at each time from the measured value of the plasma current.
To calculate.

When a disruption occurs, the plasma current sharply decreases as compared with the normal operation as shown in FIGS. Therefore, based on the following conditions, it is determined whether or not a disruption has occurred, and the disruption occurrence start time is obtained.

That is, the time change of the plasma current assumed in the disruption is (dIp / d) in advance before the operation.
t) ref, and the actual calculated value (dIp / dt) cal is (dIp / d) in comparison with this set value.
t) cal <0,

[Equation 5] If so, it is considered that a disruption has occurred, and (5)
The time when the inequality of the equation is satisfied is defined as the disruption occurrence start time td, while the discharge end time t2 is defined when the disruption does not occur. The value of td is sent to the data processing computer 15 for processing the signal from the neutron detector 10. This data processing computer 15
Then, based on the signal from the neutron detector 10 and the value of td, the following equation,

[Equation 6] Then, the number of neutrons generated in one discharge is calculated. Furthermore, the number of neutrons generated in all discharges from the start of the experiment to the present is calculated by the formula (4).

Therefore, the upper limit of the time integration of the equation (3A) is the discharge end time when the disruption does not occur, and becomes the disruption start time when the disruption occurs. This makes it possible to eliminate the error in the integrated value of the number of neutrons that is considered to occur when the disruption occurs.

As described above, according to the present embodiment, when the disruption occurs, the integration value of the number of neutrons generated from the start of the discharge to the start time of the disruption is calculated, so that the disruption is frequent. Even if it happens to
It is possible to accurately measure the total time integration amount of neutrons generated from the plasma 1.

In the above embodiment, the plasma current detector is used as the detection means for detecting the presence or absence of the disruption and the start time of the disruption, but other than this, for example, the hard X-ray loss from the plasma is used. Means for measuring quantity may be used.

Further, in the above embodiment, the neutron detector and the electronic device use the pulse signal as the detection signal, but a continuous electric signal may be used. In this case, the configuration of the electronic device is slightly changed, but the basic configuration is not changed.

Furthermore, in the above embodiment, two data processing computers were used, one for calculating the presence / absence of disruption and for calculating the time at which the disruption occurred, and one for calculating the integral value of the neutron production amount. If you have it, you only need one. That is, the first data processing means and the second
The data processing means may be incorporated in one data processing computer.

[0032]

As described above, according to the neutron measuring apparatus of the present invention, the integrated value of the number of neutrons generated from the discharge start to the disruption start time is calculated. Frequently generated, even if the count value has an error, the total time integrated amount of neutrons generated from the plasma can be measured with sufficient accuracy,
Therefore, the total amount of neutrons generated can be measured with sufficient accuracy throughout the operation period of the fusion device.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a neutron measuring device according to the present invention.

FIG. 2 is a cross-sectional view showing an arrangement state of plasma current detectors in FIG.

FIG. 3 is a sectional view showing a general tokamak nuclear fusion device.

4 (A), (B), and (C) are diagrams showing one cycle from the start of discharge due to rise of plasma current to the end of discharge due to fall when no disruption occurs.

FIG. 5 is a block diagram showing a neutron measuring device of a conventional tokamak nuclear fusion device.

6 (A), (B), and (C) are diagrams showing one cycle from the discharge start due to the rise of the plasma current to the discharge end due to the fall when the disruption occurs.

[Explanation of symbols]

 1 plasma 2 vacuum container 3 shield 4 toroidal magnetic field coil 5 poloidal magnetic field coil 6 plasma current detector (detection means) 7 integrator 8 data processing computer (first data processing means) 10 neutron detector 11 preamplifier 12 proportional Amplifier 13 Wave height analyzer 14 Counter 15 Data processing computer (second data processing means)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeo Nishitani 2-2-2, Saiwaicho, Chiyoda-ku, Tokyo Nihon Atomic Energy Research Institute

Claims (1)

[Claims] 1. A detection means for detecting the presence / absence of plasma disruption and the time at which disruption starts, and determining the presence / absence of plasma disruption based on this detection signal and generating the disruption. First data processing means for obtaining a start time, neutron detection means for detecting neutrons generated in the plasma, neutron count value data from the neutron detection means, and calculation results of the first data processing means Based on the above, if the disruption does not occur, the integrated value of the number of neutrons generated from the discharge start to the discharge end, if the disruption occurs, the neutron from the discharge start to the disruption start time A neutron measuring device comprising: second data processing means for calculating the respective integrated values of the number of occurrences. Place