Pulsed Polarimeter for Non-Perturbative Plasma Magnetic Field Sensing
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Solution Overview
Problem
Current methods for non-perturbative, spatially resolved measurements of magnetic fields within high-temperature magnetically confined plasmas are challenging due to the hostile environment, with existing diagnostics being either perturbative, non-local, or providing poor accuracy and resolution, hindering the understanding and control of plasma stability and energy transport in fusion relevant plasmas.
Innovation Solution
A pulsed polarimeter system that uses a spatially narrow, powerful polarized light pulse to induce optical emission in the plasma, allowing for remote, non-perturbative measurement of magnetic fields by analyzing the polarization state and intensity of backscattered light, which is then used to determine the local magnetic field and electron density distribution without introducing foreign materials into the plasma.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional plasma diagnostic systems are used to measure magnetic fields in high-temperature plasmas, then measurement capability is provided, but the systems are perturbative or cannot withstand the harsh radiation environment
Solution Approach 1:
The patent replaces material probes and mechanical diagnostic systems with purely optical diagnostic systems. Light pulses are used to probe the plasma, and optical signals carry information about magnetic fields and electron densities. This substitution eliminates the need for physical components to be inserted into the harsh plasma environment, making the diagnostic system reliable and non-perturbative.
Solution Approach 2:
The patent introduces light pulses as an intermediary medium to transfer information from the plasma to external detectors. The light interacts with the plasma through well-understood physical effects (Faraday effect, scattering), allowing indirect measurement of magnetic fields and electron densities without direct contact between diagnostic components and the hostile plasma environment.
2Measurement precision
If external magnetic measurements and equilibrium codes are used to infer q-profile, then measurement capability is provided, but accuracy and localization are poor
Solution Approach 1:
The patent segments the plasma into discrete measurement locations along the light pulse path. By analyzing the temporal evolution of scattered light signals, the system determines local magnetic field and electron density at specific positions rather than providing only chord-averaged measurements. This segmentation enables precise localization of plasma parameters throughout the plasma volume.
Solution Approach 2:
The patent utilizes changes in the polarization state (analogous to color changes in optical properties) of light pulses as they traverse different regions of the plasma. The Faraday rotation and scattering effects modify the polarization characteristics in a location-dependent manner, allowing the system to extract spatially resolved information about magnetic fields and electron densities with high precision.
3Measurement precision
If material probes are inserted into plasma for direct measurement, then local magnetic field measurement is achieved, but the plasma is poisoned and perturbed
Solution Approach 1:
The patent replaces material probes with optical probes. Instead of inserting physical sensors that would contaminate and perturb the plasma, the system uses light pulses that interact with the plasma through electromagnetic fields. This substitution achieves local magnetic field measurements without introducing foreign materials that could poison or disturb the plasma.
Solution Approach 2:
The patent employs the plasma's own optical properties (scattering, Faraday effect) to perform self-diagnosis. The plasma responds to light pulses with scattered and polarized light that carries information about its own state, eliminating the need for external material probes that would interfere with plasma performance.
4Reliability
If continuous wave laser polarimetry is used for magnetic field measurement, then non-perturbative measurement is achieved, but spatial resolution is poor due to chord averaging
Solution Approach 1:
The patent uses pulsed light instead of continuous wave laser. The temporal structure of the pulses allows the system to distinguish signals from different spatial locations based on their arrival times. This periodic action maintains the non-perturbative advantage of optical probing while achieving high spatial resolution through time-gated detection of scattered light from different plasma regions.
Solution Approach 2:
The patent adds the time dimension to the measurement process by using pulsed light and time-resolved detection. This transforms the measurement from a spatially integrated (chord-averaged) approach to a spatially resolved approach, where the time of flight of scattered photons provides information about their origin location within the plasma.
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
Enables direct, spatially resolved, and accurate measurement of magnetic fields and electron densities within the plasma, providing real-time feedback for stabilizing plasma discharges and improving understanding of plasma dynamics, particularly in high-temperature and dynamic fusion plasmas.
Implementation Method 1
uses a spatially narrow, powerful polarized light pulse to induce optical emission in the plasma, allowing for remote, non-perturbative measurement of magnetic fields by analyzing the polarization state and intensity of backscattered light
Implementation Method 2
A non-perturbative, spatially resolved measurement of the magnetic field deep within a high temperature magnetically confined plasma
Data Source
AI summary
Embodiments of the present invention are directed to pulsed polarimeters for conducting remote, non-perturbative diagnostic measurements of inducing fields of a medium demonstrating induced optical activity. In one aspect, a pulse polarimeter 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 an emission from the medium into a collimated emission beam, while preserving the polarization state of the emission. The pulse polarimeter includes a directional coupler that makes coincident the propagation direction of the polarized light pulse with the optic axis and a polarization detection system for measuring the intensity and determining the polarization state of the collimated emission beam continuously in time as the polarized light pulse transits the medium.