Pulsed Spectropolarimeter for Plasma Magnetic Field Measurement
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Solution Overview
Problem
Existing plasma diagnostic techniques face challenges in accurately measuring magnetic field distributions in high-density and high-temperature plasmas relevant to fusion energy, due to the entanglement of Faraday and Cotton-Mouton effects and temperature-dependent corrections.
Innovation Solution
The development of a pulsed spectropolarimeter that incorporates a wavelength-sensitive detection system, allowing for the measurement of intensity distribution in wavelength along the pulse trajectory, which enables the determination of electron temperature and separate measurement of parallel and perpendicular magnetic field components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pulsed polarimeter is used to measure magnetic field distributions in high-density and high-temperature plasmas, then remote and non-perturbative measurements are enabled, but the Faraday and Cotton-Mouton effects become entangled making accurate measurement difficult
Solution Approach 1:
The patent segments the measurement of magnetic field components by separating the detection of parallel and perpendicular components through polarimetry measurements. By measuring the state of polarization at multiple wavelengths and applying mathematical decomposition, the entangled Faraday and Cotton-Mouton effects are separated into distinct magnetic field components, enabling accurate measurement despite the entanglement.
Solution Approach 2:
The patent adds the wavelength dimension to the measurement system by implementing multi-wavelength or spectropolarimetry capabilities. This additional dimension allows the separation of the wavelength-dependent Faraday effect from the Cotton-Mouton effect, enabling the determination of both parallel and perpendicular magnetic field components that would be entangled in single-wavelength measurements.
2Measurement precision
If conventional plasma diagnostic techniques are used, then simpler measurement systems are employed, but accurate measurement of magnetic field distributions in high-density and high-temperature plasmas is not achieved
Solution Approach 1:
The patent uses polarimetry as an intermediary measurement technique that indirectly probes the magnetic field through its effect on the state of polarization of light. By measuring polarization changes caused by the entangled Faraday and Cotton-Mouton effects and applying mathematical reconstruction, the magnetic field distribution is determined without direct contact with the plasma, maintaining both accuracy and remote sensing capabilities.
Solution Approach 2:
The patent changes the measurement parameters by utilizing multiple wavelengths or spectral information to differentiate between the Faraday and Cotton-Mouton effects. By varying the wavelength parameter and observing the different wavelength dependencies of the two effects, the system can separate their contributions and accurately determine the magnetic field components.
3Adaptability or versatility
If single-wavelength polarimetry is used, then the system is simpler, but electron temperature determination and separate magnetic field component measurement are not possible
Solution Approach 1:
The patent implements a multi-wavelength or spectropolarimetry system that provides multiple measurement functions using a unified detection framework. The same polarimetry measurements at multiple wavelengths enable simultaneous determination of electron temperature, parallel magnetic field component, and perpendicular magnetic field component, making the system versatile for multiple diagnostic purposes without requiring separate measurement systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate, remote, and non-perturbative measurements of magnetic field, plasma density, and temperature distributions within magnetized plasma media, overcoming previous limitations and enhancing the diagnostic capabilities for fusion relevant plasmas.
Implementation Method 1
a pulsed laser source, which generates an ultrashort pulsed laser beam that lases at a wavelength in the far-infrared region
Implementation Method 2
The scattering process is known as Thomson scattering. A measurement of the state of polarization and intensity of the backscattered emission from the light pulse can be used to determine the local magnetic field and density distributions
Implementation Method 3
The Faraday effect is by far the dominate effect, producing a circular birefringence, or a rotation of the pulse's polarization azimuth, α
Implementation Method 4
The second magneto-optical activity is the Cotton Mouton (CM) effect, producing a linear birefringence, more commonly known as a retardance, the state of polarization of the light pulse becomes elliptically polarized
Data Source
AI summary
This disclosure is directed to pulsed spectropolarimeters for conducting remote, non-perturbative measurements of the local magnetic field, density and temperature fields of a magnetized plasma medium. In one aspect, a pulsed spectropolarimeter includes a light source emitting a polarized light pulse having sufficiently narrow spatial extent at a prescribed wavelength and a light gathering optical system including a light gathering optic having an optic axis directed toward the medium and positioned to collect and collimate a predetermined solid angle of the scattered emission by the pulse in the backward direction, toward the source, while preserving the polarization state of the emission. A proportion of the emission is redirected to a spectrometer detector to determine the spectral distribution of the emission. A second optical collection and spectrometer system collects emission other than backscatter localized to the intersection of the pulse trajectory and the focus of this collection system.