# US 2019/0378625 A1 · Plasma diagnosis system using multiple-reciprocating-pass thompson scattering

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- Number: US 2019/0378625 A1
- Document ID: US20190378625A1
- Status: Published application
- Kind: A1
- Application number: 16/519,588
- Filed: 2019-07-23
- Published: 2019-12-12
- Earliest claimed: 2016-01-08
- Assignees: Industry-University Cooperation Foundation Sogang University
- Applicants: Industry-University Cooperation Foundation Sogang University
- Inventors: Kyu Man CHO; June Gyu PARK; Seung Hyun YOON; Wha-Keun AHN
- Web page: https://patentgrep.com/patent/US20190378625A1

## CPC

- G21B 1/23: Optical systems, e.g. for irradiating targets, for heating plasma or for plasma diagnostics
- G01J 3/02: Details
- G02B 27/10: Beam splitting or combining systems (polarising systems G02B27/28; mixing and splitting light signals using optical waveguides G02B6/28; {beam shaping, e.g. changing the cross-sectional area, by dividing or superposing multiple light beams G02B27/0905})
- G02B 27/283: {used for beam splitting or combining}
- G21K 1/10: Scattering devices; Absorbing devices; Ionising radiation filters
- G21B 1/057: {Tokamaks}
- Y02E 30/10: Nuclear fusion reactors
- G21B: FUSION REACTORS (uncontrolled reactors G21J)
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G21K: HANDLING OF PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

Provided is a plasma diagnosis system using multiple-reciprocating-pass Thompson scattering. The plasma diagnosis system includes: a laser which supplies laser pulses; an optical system configured to make the laser pulse multiple roundtrips, focus the laser pulse to a predetermined position, rotate the plane of polarization by 90 degrees in every completion of the roundtrip; a collection optics which collects lights scattered from the focused region in plasma, which the collected light by the vertical polarization of the laser pulse is referred to as ‘first collected scattering’ and the collected light by the horizontal polarization of the laser pulse is referred to as ‘second collected scattering’; and a polychromator which measures spectral characteristics of the first and second collected scatterings and outputs Thomson scattering signal with the background noise and the background noise without Thomson scattering signal.

## Claims

### Claim 1

A plasma diagnosis system using multiple-pass Thomson scattering, comprising:
a laser which supplies a laser pulse having predetermined polarization state and wavelength;
an optical system configured to make the laser pulse multiple roundtrips along a predetermined optical path and focus the laser pulse to a predetermined location in plasma, and rotate a plane of polarization by 90 degrees after each complete roundtrip;
a collection optics which is configured with a lens or a combination of lenses, collects lights scattered from a focal point in plasma, whereas the collected light by the vertical polarization of the laser pulse is referred to as ‘first collected scattering’ and the collected light by the horizontal polarization of the laser pulse is referred to as ‘second collected scattering’; and
a polychromator which measures spectral characteristics of the first and second collected scatterings and outputs a Thomson scattering signal contaminated with a background noise and the background noise, respectively,
wherein the background noise is generated by scattering in plasma due to stray lights and is obtained from the second collected scattering, and the Thomson scattering signal contaminated with the background noise is obtained from the first collected scattering.

### Claim 2 (depends on 1)

The plasma diagnosis system according to claim 1, wherein the optical system includes:
a polarizing beam splitter (PBS) which is inserted in the predetermined optical path and reflects or transmits an incident laser pulse according to a polarization state of the incident laser pulse;
a first reflecting mirror which is inserted in the optical path and reflects the laser pulse exited from the PBS back into the optical path;
a Faraday rotator which rotates a plane of polarization of the laser pulse passing through the PBS by 45 degrees;
a focusing lens which focuses the laser pulse outputted from the Faraday rotator on the predetermined location in plasma; and
a second reflecting mirror which reflects the laser pulse outputted from the focusing lens back along the incident laser pulse path and refocuses the laser pulse to the predetermined location in plasma, and
wherein the vertical polarization of the laser pulse in a first roundtrip rotates the plane of polarization by 90 degrees and converts to a horizontal polarization in a second round trip.

### Claim 3 (depends on 1)

The plasma diagnosis system according to claim 1, further comprising an optical isolator between the laser and the optical system, and
wherein the optical isolator prevents any back reflected lights from feeding back into the laser.

### Claim 4 (depends on 1)

The plasma diagnosis system according to claim 1, further comprising a trigger module which is configured with a photo detector and outputs a trigger signal when the photo detector detects a part of the laser pulse on a predetermined position,
wherein a signal processing of the polychromator is synchronized by using the trigger signal.

### Claim 5 (depends on 4)

The plasma diagnosis system according to claim 4, wherein the photo detector is placed between the laser and the optical system or at an arbitrary position where stray light reflected from or transmitted through an optical component is accessible and outputs the trigger signal when detecting that the laser pulse is supplied from the laser to the optical system, detecting that the laser pulse is supplied from the optical system to the plasma, or detecting that the laser pulse is supplied at an arbitrary position of the optical system.

### Claim 6 (depends on 1)

Plasma diagnosis system according to claim 1, further comprising a computer which measure a pure Thomson scattering signal without the background noise by subtracting the background noise from the Thomson scattering signal contaminated with the background noise.

### Claim 7 (depends on 1)

Plasma diagnosis system according to claim 1, further comprising a computer which measures temperature and density of electrons in plasma by analyzing the spectral characteristics obtained in the polychromator.