JPH07230895A - Electron density measuring device - Google Patents

Abstract

PURPOSE:To remarkably improve measuring accuracy by making a probe laser beam incident on an observational laser beam in plasma when electron density in the plasma is measured according to an interferential image by a reference beam and observational light passing through the plasma. CONSTITUTION:A laser beam 6 is divided into an observational laser beam 6a and a reference laser beam 6b by a half mirror 4a, and the beam 6a passes through plasma 1, and a phase is changed according to electron density of the plasma 1, and both beams are synthesized together by a half mirror 4b, and an interferential image is formed, and is observed by a camera 7. In this case, a probe laser beam 11 is made incident on the beam 6a passing through the plasma 1 through a variable wave length laser oscillator 10 on a movable stage 12, and an electron plasma wave can be generated only in a position where a conformity condition is satisfied by two different laser beams, and the occurrence of distortion in a secondary interferential image created through the beam 6b is restrained. Thereby, an electron density measuring device whose measuring accuracy is remarkably enhanced is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron density measuring device used for measuring plasma in a nuclear fusion reactor or the like.

[0002]

2. Description of the Related Art An electron density measuring device is used for measuring plasma in a nuclear fusion reactor or the like. The conventional electron density measuring device is
As shown in FIG. 2, a laser beam 6 emitted from a laser oscillator 2 is guided to a beam expander 3 to expand the diameter of the laser beam 6, and then to a half mirror 4a, and an observation laser beam 6a and a reference laser Divided into beam 6b,
The observation laser beam 6a is reflected by the total reflection mirror 5a and guided to the plasma 1.

Since the plasma 1 has a refractive index depending on the electron density, when the laser beam 6a passes through the plasma 1, the phase shifts according to the electron density. The laser beam 6a passing through the plasma 1 is guided to the half mirror 4b, and the reference laser beam 6b is guided to the half mirror 4b via the total reflection mirror 5b, mixed with each other, incident on the camera 7, and observed from the image. The electron density in the plasma 1 was measured by reading the phase shift amount of the laser beam 6a for use.

[0004]

In the conventional electron density measuring apparatus shown in FIG. 2, since the phase shift occurring on the optical path of the observation laser beam 6a is integrated on the optical path, the electron density is measured on the optical path. It appears only as the average value of. Further, if the shape of the plasma 1 is not accurately grasped, it becomes difficult to expand the two-dimensional phase shift information obtained by the camera 7 into the three-dimensional space, and the measurement accuracy of the electron density distribution in the plasma 1 is high. There was a problem that was worse.

The present invention is proposed in view of the above problems, and an object of the present invention is to provide an electron density measuring apparatus capable of greatly improving the accuracy of electron density measurement. .

[0006]

In order to achieve the above object, the electron density measuring apparatus of the present invention emits a laser beam divided into a reference laser beam and an observation laser beam passing through plasma by a half mirror. Laser oscillator, a half mirror for splitting / mixing the laser beam, a camera for photographing a two-dimensional interference image generated by mixing the reference laser beam and the observation laser beam, and plasma. A tunable wavelength laser oscillator for injecting a probe laser beam provided on the optical path of the observation laser beam.

[0007]

Since the electron density measuring device of the present invention is constructed as described above,

[0008]

[Equation 1] Is the following matching condition ((1) is the conservation law of energy, (2)
Is a conservation law of momentum), an electron plasma wave is generated in the region where the condition is satisfied.

[0009]

[Equation 2]

[0010]

[Equation 3] Since the electron plasma wave creates shades in the distribution of electron density,
The refractive index of the region satisfying the matching condition changes, and the phase of the observation laser beam shifts. When the observation laser beam in this state is mixed with the reference laser beam and caused to interfere with each other, the two-dimensional interference image of the portion corresponding to the region where the electron plasma wave is generated is distorted. Since electron plasma waves generated by two laser beams having different frequencies satisfying the matching condition are generated by a resonance phenomenon, it is possible to accurately determine the electron density at the position where the electron plasma waves are generated by knowing the frequencies of the two lasers. It becomes possible to measure.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the electron density measuring device of the present invention will be described with reference to FIG. The basic structure is the same as that of the above-mentioned conventional example (see FIG. 2), and will be omitted. Reference numeral 10 denotes a variable wavelength laser oscillator 10, and the variable wavelength laser oscillator 10 is installed so that the probe laser beam 11 emitted from the variable wavelength laser oscillator 10 is perpendicular to the observation laser beam 6a.

The variable wavelength laser oscillator 10 is placed on the movable stage 12 so that the incident position on the plasma 1 can be changed. Instead of fixing the variable wavelength laser oscillator 10, an optical system such as a mirror may be placed on the movable stage 12 to change the incident position of the probe laser beam 11. The frequency ω is applied to the plasma 1 on which the observation laser beam 6a having the frequency ω ₀ is incident.
_{When the} probe laser beam 11 having ₁ is incident, an electron plasma wave is generated at a position satisfying the matching condition.
The position where the electron plasma wave is generated is the position of the distortion of the two-dimensional interference image captured by the camera 7 and the probe laser beam 1
1 can be determined from the incident position.

Since the electron plasma wave is generated only when the two laser beams 6a and 11 satisfy the matching condition (1), the relation between the electron density n and the plasma frequency ω _p is

[0014]

[Equation 4] From this, the electron density can be determined as follows.

[0015]

[Equation 5] By changing the oscillation frequency of the variable wavelength laser oscillator 10, it is possible to know the position of any electron density. Further, since the electron density can be measured with high accuracy, the accuracy of three-dimensionalization of the two-dimensional interference image by Abel transform or the like is also improved.

[0016]

As described above, the electron density measuring apparatus of the present invention can generate electron plasma waves only at the position where the matching condition is satisfied by the two lasers having different frequencies. Therefore, the electron density measuring accuracy can be improved. Can be greatly improved.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of an electron density measuring device of the present invention.

FIG. 2 is a system diagram showing a conventional electron density measuring device.

[Explanation of symbols]

 1 Plasma 2 Laser Oscillator 3 Beam Expander 4a, 4b Half Mirror 5a, 5b Total Reflection Mirror 6 Laser Beam 6a Observation Laser Beam 6b Reference Laser Beam 7 Camera 10 Variable Wavelength Laser Oscillator 11 Probe Laser Beam 12 Movable Stage

Claims (1)

[Claims] 1. A laser oscillator that emits a laser beam that is divided into a reference laser beam and an observation laser beam that passes through plasma by a half mirror, a half mirror that divides and mixes the laser beam, and a reference laser beam. And a tunable laser oscillator for injecting a probe laser beam provided on the optical path of the observing laser beam passing through the plasma. An electron density measuring device characterized by being provided.