JPH09304539A - Electron detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron detector which is suitable for measuring the direction and the energy of escaping electrons from a plasma in a nuclear fusion apparatus. SOLUTION: A coil 8 for magnetic-field generation is installed between a vertical drift chamber 10 and a vertical drift chamber 11, and an electron beam detector 18 which contains a plastic scintillator 15, a light guide 16 and a photomultiplier tube 17 is installed at the rear of the vertical drift chamber 11. On the basis of the time difference between signals from respective wires at the vertical drift chambers 10, 11 and a signal from the electron beam detector 18, the track of electrons at the vertical drift chambers 10, 11 can be found. On the basis of the found track of the electrons and on the basis of a magnetic field generated by the coil, for magnetic-field generation, installed between the vertical drift chambers 10, 11, the direction and the energy of escaping electrons are measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron detector suitable for measuring the direction and energy of escape electrons from plasma in a fusion device.

[0002]

2. Description of the Related Art In a fusion device, electrons are accelerated by an electric field and decelerated by a Coulomb collision with electrons and ions. However, since the degree of collision decreases with speed,
Electrons having a certain energy or more increase in speed and become escape electrons. For example, when the electron density is 10 ¹⁹ m ³ and the electric field strength is 1 V / m, electrons of 5 KeV or more become runaway electrons, and the energy is 200 in the international thermonuclear reactor 1TER.
It is considered to be about MeV. Such high-energy electrons cause great damage to the fusion device. However, there is no detailed measurement of how much energy and how many escape electrons escape from which direction. It is considered that these measurements will become necessary in the future.

The vertical type drift chamber is a detector for measuring the trajectory of electrons, and was developed by MIT in 1977.
It is mainly used as a measuring instrument for scattered electrons in nuclear experiments using electron beams.

Known example: W. Bertozzi, et al., Nucl Instr
141 (1977) 457.

[0005]

With the above-mentioned conventional technique, it is possible to measure the trajectory of escape electrons. However, there is a problem that energy cannot be measured. Also,
Since it is necessary to measure the escape electrons in a vacuum container,
It is not preferable for the fusion device to use the gas pressure inside the chamber at atmospheric pressure as in the conventional vertical drift chamber. However, when the pressure of the gas inside the chamber is lowered, there is a problem that the vertical drift chamber does not function.

It is an object of the present invention to provide an electron detector suitable for measuring the direction and energy of escape electrons from plasma in a fusion device.

[0007]

In order to achieve the above object, the present invention provides a magnetic field generating coil between two vertical drift chambers. The orbit is bent by the magnetic field generated by the magnetic field generating coil with a curvature according to its energy. This curvature can be obtained by measuring the orbits of the electrons by the two vertical drift chambers installed before and after the magnetic field generating coil. The energy of the electron can be obtained from the value of the magnetic field created by the magnetic field generating coil and this curvature. Further, in order to achieve the above object, the present invention changes the gas mixture ratio inside the vertical drift chamber so that the vertical drift chamber operates normally even at atmospheric pressure or lower.

The principle of the vertical drift chamber is shown in FIG. FIG. 2 is a cross-sectional view of the vertical drift chamber.
The vertical drift chamber has an electron entrance window 1, a cathode plate 2,
It is composed of a wire 3 and a gas 4. A negative voltage is applied to the cathode plate 2 so that an electric field of about 1 kV / mm is created between the cathode plate 2 and the wire 3. The electrons 5 obliquely incident through the electron incident window 1 ionize the gas 4 inside the chamber.
The electron group 6 generated by the ionization is the cathode plate 2 and the wire 3.
Drift towards the wire 3 along the direction 7 of the electric field created by. The drifted electron group 6 causes an electron avalanche in a region 8 near the wire 3 where the electric field is high. A signal is generated on the wire due to the electronic avalanche. If the drift velocity is constant, the position where the electron group 6 is generated can be identified by measuring the time from the time when the electron 5 passes to the time when the signal is generated. When a mixed gas of argon and isobutane is used as the gas 4, the drift velocity becomes constant at about 40 mm / μsec regardless of the electric field strength. From the generation position of the electron group 6 obtained from the signals from the three or more wires 3,
The trajectory of the incident electron 5 can be identified. The outline of the present invention is shown in FIG. By installing the coil 9 for generating a magnetic field between the two vertical drift chambers, the electrons passing through the first chamber 10 receive Lorentz force corresponding to energy from the magnetic field and bend their trajectories. It enters the third chamber 11. The incident direction of the electrons can be identified by the first chamber 10, and the energy of the electrons can be identified from the magnitude of the magnetic field generated by the magnetic field generating coil 9 and the difference in the orbits of the electrons in the first and second chambers. it can. When using gas 4 at atmospheric pressure, isobutane and argon are used in a volume ratio of about 1: 1. Isobutane has a function of suppressing electron avalanche, and argon has a function of increasing electron avalanche. When gas 4 is used at a pressure lower than atmospheric pressure, electron group 6 generated by incident electrons 5
The number of electrons contained in is small. Therefore, no measurable signal is generated on the wire 3. Therefore, in order to generate a sufficiently large signal even at a low pressure, the proportion of argon should be increased to increase the electron avalanche.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIG. In FIG. 3, vertical drift chambers 10 and 11 are installed on both sides of the magnetic field generating coil 9. When the electrons 5 pass through the vertical drift chambers 10 and 11, a signal is generated on each wire 3. After this signal is amplified by the preamplifier 13, it is converted into a rectangular wave using the discriminator 14 or the like. Behind the second vertical drift chamber 11, the plastic scintillator 1
5. An electron detector 18 including a light guide 16 and a photomultiplier tube 17 is installed. The signal from the electron detector 18 is converted into a rectangular wave using the discriminator 14 or the like, and used as a reference rectangular wave of time for measuring the drift time. The time difference between the reference rectangular wave of this time and the signal from each wire 3 converted into the rectangular wave is measured using the time digital converter 19 or the like to obtain the drift time. From the drift velocity measured in advance and the measured drift time, the distance from the position where the gas 4 is ionized by the incident electrons 5 to each wire can be obtained. From the information on the drift time from three or more wires 3, gas 4 is generated by the incident electrons.
Information of three or more points is obtained for the position where the ionization is performed, and the orbit of the electron is obtained. The electrons that have passed through the vertical drift chamber 10 receive the Lorentz force due to the magnetic field generated by the magnetic field generation coil 9, and bend the trajectory according to the electron energy.
By changing the magnetic field value created by the magnetic field generating coil, the width of the escape electron energy to be measured can be changed. For example, when the electron energy is 200 MeV,
The magnetic field generated by the magnetic field generating coil 9 is 0.1T, and the magnetic field is 0.1T.
If the electron 5 passes through the area of 1 m, it is about 9 °
Orbits. When the energy of the electron 5 is 100 MeV, the orbit of the electron 5 is bent by about 13 °. The electrons 5 whose orbit is bent by the magnetic field generated by the magnetic field generating coil 8 enter the vertical drift chamber 11. Chamber 10
In the same manner as in the case of, the orbit of the electron in the chamber 11 can be obtained. These two chambers 10
The energy of the electron can be measured from the difference in the angles of the orbits of the electron measured by the methods 11 and 11. Since the measurement accuracy of the electron angle of the vertical drift chamber is about 1 °, an electron with an energy of about 200 MeV is about 0.
Approximately 25M when passing a magnetic field of 1T for a distance of approximately 0.1m
The electron energy can be measured with an accuracy of about eV.

FIG. 4 shows another embodiment of the present invention. Instead of the second vertical drift chamber 11 shown in FIG. 3, a plurality of electron detectors 18 are installed. The electron passing through the first vertical drift chamber 10 receives the Lorentz force by the magnetic field generated by the magnetic field generating coil 9, bends the trajectory, and then enters one of the plurality of electron detectors 18.
The angle bent by the magnetic field can be identified from the information on the position where the electron has entered the electron detector 18 and the measured value of the orbit of the electron from the vertical drift chamber 10. The energy of the incident electrons 5 can be measured from this information and the magnitude of the magnetic field generated by the magnetic field generating coil 8.

[0011]

According to the present invention, the direction and energy of the escape electrons from the plasma can be measured, and the degree of damage to the fusion device due to the escape electrons can be identified in detail.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention.

FIG. 2 is a sectional view of a vertical drift chamber.

FIG. 3 is an explanatory diagram of one embodiment of the present invention.

FIG. 4 is an explanatory diagram of another embodiment of the present invention.

[Explanation of symbols]

3 ... Wire, 5 ... Incident electron, 8 ... High electric field region, 1
0, 11 ... Vertical drift chamber, 13 ... Preamplifier, 14 ... Discriminator, 15 ... Plastic scintillator, 16 ... Optical guide, 17 ... Photomultiplier tube, 1
8 ... Electron detector, 19 ... Time digital converter.

Claims (3)

[Claims] 1. An electron detector comprising two vertical drift chambers, a data processing system, and a magnetic field generating coil installed between the two vertical drift chambers, before and after passing through the magnetic field generating coil. The electron trajectory and the electron movement in the vertical drift chamber are measured by the two vertical drift chambers, and the energy and the moving direction of the electron are measured by using the measurement result and the strength of the magnetic field generated by the magnetic field generating coil. Detector. 2. The electron detector according to claim 1, wherein the electron detector after passing through the magnetic field generating coil uses an electron detector composed of two or more plastic scintillators and a data processing system. 3. The electron detector according to claim 1, wherein the gas pressure in the vertical drift chamber is equal to or higher than atmospheric pressure.