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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

A Classification of Ice Crystal Habits Using Combined Lidar and Scanning Polarimeter Observations during the SEAC4RS Campaign

Using collocated NASA Cloud Physics Lidar (CPL) and Research Scanning Polarimeter (RSP) data from the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign, a new observational-based method was developed which uses a K-means clustering technique to classify ice crystal habit types into seven categories: column, plates, rosettes, spheroids, and three different type of irregulars. Intercompared with the collocated SPEC, Inc., Cloud Particle Imager (CPI) data, the frequency of the detected ice crystal habits from the proposed method presented in the study agrees within 5% with the CPI-reported values for columns, irregulars, rosettes, and spheroids, with more disagreement for plates. This study suggests that a detailed ice crystal habit retrieval could be applied to combined space-based lidar and polarimeter observations such as CALIPSO and POLDER in addition to future missions such as the Aerosols, Clouds, Convection, and Precipitation (A-CCP).

Natalie Midzak↗
DOE OSTI2013

Construction and Testing of Data Acquisition Components for the Hall A Compton Polarimeter

Nuclear physics experiments require accurate knowledge of the spin polarization of the electron beam delivered to the experimental halls. Hall A is upgrading its Compton polarimeter in support of the lab's 12 GeV beam energy upgrade. This project centered around the data acquisition (DAQ) system for the scattered-photon detection component of the polarimeter. The goal was to test whether the DAQ software and hardware are capable of capturing, recording, and processing electron helicity-dependent scattering rate asymmetry data at high rates, while maintaining appropriate accuracy. We created the necessary circuits, and are able to reliably extract asymmetries of between 0.5{\%} and 11.5{\%} to 0.2{\%}. We did this in a deadtime-free regime at rates between 100 KHz and 350 KHz. We currently are unable to measure the system deadtime after it becomes manifest at about 350 KHz. These tests support the use of a scaled version of this configuration.

Hill, Joshua↗
DOE OSTI2012

Upgraded photon calorimeter with integrating readout for Hall A Compton Polarimeter at Jefferson Lab

The photon arm of the Compton polarimeter in Hall A of Jefferson Lab has been upgraded to allow for electron beam polarization measurements with better than 1% accuracy. The data acquisition system (DAQ) now includes an integrating mode, which eliminates several systematic uncertainties inherent in the original counting-DAQ setup. The photon calorimeter has been replaced with a Ce-doped Gd 2 SiO 5 crystal, which has a bright output and fast response, and works well for measurements using the new integrating method at electron beam energies from 1 to 6 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Design of a millimeter-wave polarimeter for NSTX-Upgrade and initial test on DIII-D

Polarimetry is a powerful diagnostic technique to probe plasma equilibria and magnetic fluctuations in fusion plasmas. In a high beta plasma such as the National Spherical Torus eXperiment (NSTX), these measurements are important to understand plasma stability and anomalous transport. A 288 GHz polarimeter operating along a major radial chord in retroreflection geometry has been developed and is being tested on the DIII-D tokamak to prepare for future implementation on NSTX-Upgrade. The system launches a rotating linearly polarized beam and detects the phase shift directly related to the polarization change caused by the plasma. To accomplish this, a pair of orthogonal linearly polarized beams with a stable difference frequency is generated using a single sideband modulation technique, then combined and transformed to be counter-rotating circularly polarized. To improve phase resolution, quasi-optical isolation, using Faraday rotators and polarizers, is utilized to eliminate a multi-path feedback effect, which is found to be the primary source of phase error. The bench tests in the laboratory and DIII-D power supply test discharges indicate {<=}1 Degree-Sign phase resolution.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Conceptual design of the tangentially viewing combined interferometer-polarimeter for ITER density measurements

One of the systems planned for the measurement of electron density in ITER is a multi-channel tangentially viewing combined interferometer-polarimeter (TIP). This work discusses the current status of the design, including a preliminary optical table layout, calibration options, error sources, and performance projections based on a CO{sub 2}/CO laser system. In the current design, two-color interferometry is carried out at 10.59 {mu}m and 5.42 {mu}m and a separate polarimetry measurement of the plasma induced Faraday effect, utilizing the rotating wave technique, is made at 10.59 {mu}m. The inclusion of polarimetry provides an independent measure of the electron density and can also be used to correct the conventional two-color interferometer for fringe skips at all densities, up to and beyond the Greenwald limit. The system features five chords with independent first mirrors to reduce risks associated with deposition, erosion, etc., and a common first wall hole to minimize penetration sizes. Simulations of performance for a projected ITER baseline discharge show the diagnostic will function as well as, or better than, comparable existing systems for feedback density control. Calculations also show that finite temperature effects will be significant in ITER even for moderate temperature plasmas and can lead to a significant underestimate of electron density. A secondary role TIP will fulfill is that of a density fluctuation diagnostic; using a toroidal Alfven eigenmode as an example, simulations show TIP will be extremely robust in this capacity and potentially able to resolve coherent mode fluctuations with perturbed densities as low as {delta}n/n Almost-Equal-To 10{sup -5}.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

A high spatial resolution Stokes polarimeter for motional Stark effect imaging

We describe an enhanced temporally switched interfero-polarimeter that has been successfully deployed for high spatial resolution motional Stark effect imaging on the KSTAR superconducting tokamak. The system utilizes dual switching ferroelectric liquid crystal waveplates to image the full Stokes vector of elliptically polarized and Doppler-shifted Stark-Zeeman Balmer-alpha emission from high energy neutral beams injected into the magnetized plasma. We describe the optical system and compare its performance against a Mueller matrix model that takes account of non-ideal performance of the switching ferro-electric liquid crystal waveplates and other polarizing components.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

An electron beam polarimeter based on scattering from a windowless, polarized hydrogen gas target

Here we present the idea to develop a precision polarimeter for low energy, intense polarized electron beams using a windowless polarized hydrogen gas cell fed by an atomic beam source. This technique would use proven technology used successfully in both the electron scattering experiments: HERMES with 27 GeV electron and positron beams at DESY, and BLAST with 850 MeV electron beams at MIT-Bates. At 100 MeV beam energy, both spin-dependent Mo/ller and elastic electron-proton scattering processes have a high cross section and sizable spin asymmetries. The concept is described and estimates for realistic rates for elastic electron-proton scattering and Mo/ller scattering are presented. A number of important issues which affect the ultimate systematic uncertainty are identified.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Faraday-effect polarimeter-interferometer system for current density measurement on EAST

A multichannel far-infrared laser-based POlarimeter-INTerferometer (POINT) system utilizing the three-wave technique is under development for current density and electron density profile measurements in the EAST tokamak. Novel molybdenum retro-reflectors are mounted in the inside wall for the double-pass optical arrangement. A Digital Phase Detector with 250 kHz bandwidth, which will provide real-time Faraday rotation angle and density phase shift output, have been developed for use on the POINT system. Initial calibration indicates the electron line-integrated density resolution is less than 5 × 10{sup 16} m{sup −2} (∼2°), and the Faraday rotation angle rms phase noise is <0.1°.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Optical layout and mechanical structure of polarimeter-interferometer system for Experimental Advanced Superconducting Tokamak

A Far-InfaRed (FIR) three-wave POlarimeter-INTerferometer (POINT) system for measurement current density profile and electron density profile is under development for the EAST tokamak. The FIR beams are transmitted from the laser room to the optical tower adjacent to EAST via ∼20 m overmoded dielectric waveguide and then divided into 5 horizontal chords. The optical arrangement was designed using ZEMAX, which provides information on the beam spot size and energy distribution throughout the optical system. ZEMAX calculations used to optimize the optical layout design are combined with the mechanical design from CATIA, providing a 3D visualization of the entire POINT system.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

High resolution polarimeter-interferometer system for fast equilibrium dynamics and MHD instability studies on Joint-TEXT tokamak (invited)

A high-performance Faraday-effect polarimeter-interferometer system has been developed for the J-TEXT tokamak. This system has time response up to 1 μs, phase resolution < 0.1° and minimum spatial resolution ∼15 mm. High resolution permits investigation of fast equilibrium dynamics as well as magnetic and density perturbations associated with intrinsic Magneto-Hydro-Dynamic (MHD) instabilities and external coil-induced Resonant Magnetic Perturbations (RMP). The 3-wave technique, in which the line-integrated Faraday angle and electron density are measured simultaneously by three laser beams with specific polarizations and frequency offsets, is used. In order to achieve optimum resolution, three frequency-stabilized HCOOH lasers (694 GHz, >35 mW per cavity) and sensitive Planar Schottky Diode mixers are used, providing stable intermediate-frequency signals (0.5–3 MHz) with S/N > 50. The collinear R- and L-wave probe beams, which propagate through the plasma poloidal cross section (a = 0.25–0.27 m) vertically, are expanded using parabolic mirrors to cover the entire plasma column. Sources of systematic errors, e.g., stemming from mechanical vibration, beam non-collinearity, and beam polarization distortion are individually examined and minimized to ensure measurement accuracy. Simultaneous density and Faraday measurements have been successfully achieved for 14 chords. Based on measurements, temporal evolution of safety factor profile, current density profile, and electron density profile are resolved. Core magnetic and density perturbations associated with MHD tearing instabilities are clearly detected. Effects of non-axisymmetric 3D RMP in ohmically heated plasmas are directly observed by polarimetry for the first time.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Invited Article: A novel calibration method for the JET real-time far infrared polarimeter and integration of polarimetry-based line-integrated density measurements for machine protection of a fusion plant

In this paper, we present the work in the implementation of a new calibration for the JET real-time polarimeter based on the complex amplitude ratio technique and a new self-validation mechanism of data. This allowed easy integration of the polarimetry measurements into the JET plasma density control (gas feedback control) and as well as machine protection systems (neutral beam injection heating safety interlocks). The new addition was used successfully during 2014 JET Campaign and is envisaged that will operate routinely from 2015 campaign onwards in any plasma condition (including ITER relevant scenarios). This mode of operation elevated the importance of the polarimetry as a diagnostic tool in the view of future fusion experiments.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Compton polarimeter for 10–30 keV x rays

We present a simple and versatile polarimeter for x rays in the energy range of 10–30 keV. It uses Compton scattering in low-Z materials such as beryllium or boron carbide. The azimuthal distribution of the scattered x rays is sampled by an array of 12 silicon PIN diodes operated at room temperature. We evaluated the polarimetry performance using Monte-Carlo simulations and show experimental results.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Far-forward collective scattering measurements by FIR polarimeter-interferometer on J-TEXT tokamak

The multi-channel three-wave polarimeter-interferometer system on J-TEXT tokamak has been exploited to measure far-forward collective scattering from electron density fluctuations. The diagnostic utilizes far infrared lasers operated at 432 μm with 17-channel vertical chords (3 cm chord spacing), covering the entire cross section of plasma. Scattering laser power is measured using a high-sensitivity Schottky planar diode mixer which can also detect polarimetric and interferometric phase simultaneously. The system provides a line-integrated measurement of density fluctuations with maximum measurable wave number: k{sub ⊥max} ≤ 2 cm{sup −1} and time response up to 350 kHz. Feasibility of the diagnostic has been tested, showing higher sensitivity to detect fluctuation than interferometric measurement. Capability of providing spatial-resolved information of fluctuation has also been demonstrated in preliminary experimental applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

A Faraday-effect polarimeter for fast magnetic dynamics measurement on DIII-D

A Faraday-effect-based radial-interferometer-polarimeter diagnostic has been developed to explore fast magnetic dynamics in high-performance DIII-D plasmas. The instrument measures radial magnetic field perturbations using three chords positioned near the magnetic axis. Newly developed solid-state sources operating at 650 GHz provide phase noise down to 0.01°/$\sqrt{kHz}$ and tunable bandwidth up to 10 MHz. Various systematic errors which can contaminate the polarimetric measurement have been investigated in detail. Distortion of circular polarization due to non-ideal optical components is calibrated using a rotating quarter wave plate technique. The impact of perpendicular magnetic field, i.e., the Cotton-Mouton effect, is evaluated. The error due to non-collinearity of probe beams is minimized to less than 0.5° for electron density up to 7 × 10 19 m -3 by alignment optimization. Optical feedback, due to multiple reflections induced by the double-pass configuration, is identified and reduced. Lastly, coherent and broadband high-frequency magnetic fluctuations for DIII-D H-mode plasmas are observed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Design study of a combined interferometer and polarimeter for a high-field, compact tokamak

This article is the first design study of a combined interferometer and polarimeter on a compact, high-field, high-density, net-energy tokamak. Recent advances in superconducting technology have made possible designs for compact, high magnetic field fusion power plants, such as ARC [Sorbom et al., Fusion Eng. Des. 100, 378 (2015)], and experiments, such as SPARC [Greenwald et al., PSFC Report No. RR-18-2 (2018)]. These new designs create both challenges and opportunities for plasma diagnostics. The diagnostic proposed in this work, called InterPol, takes advantage of unique opportunities provided by high magnetic field and density to measure both line-averaged density and poloidal magnetic field with a single set of CO 2 and quantum cascade lasers. These measurements will be used for fast density feedback control, constraint of density and safety factor profiles, and density fluctuation measurements. Synthetic diagnostic testing using a model machine geometry, called MQ1 (Mission Q ≥ 1), and profiles simulated with Tokamak Simulation Code indicate that InterPol will be able to measure steady state density and poloidal magnetic field, as well as fluctuations caused by toroidal Alfven eigenmodes and other phenomena on a high-field compact tokamak.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Upgrade of DIII-D radial interferometer–polarimeter for large bandwidth, low noise, and toroidal mode number measurements

Near ion-cyclotron frequency (f ci ) fluctuations, such as those originating from Global and Compressional Alfvén Eigenmodes (GAEs/CAEs), are expected to be present in future fusion reactors but are not well understood due to the limited availability of core measurements in present-day tokamaks. The measurement bandwidth of the Radial Interferometer–Polarimeter (RIP) diagnostic has been upgraded from 1 to 5 MHz to detect these fluctuations in DIII-D. RIP adopts the three-wave technique for simultaneous polarimetric and interferometric measurements. Solid-state microwave sources operating at 650 GHz are used as probe beams and provide 5 MHz bandwidth for both polarimetric and interferometric measurements. Bandwidths of related hardware, including mixer amplifier, signal cable, and digital phase demodulator, are increased correspondingly. Measurement noise is minimized by reducing the time delay between reference and probe signals to nanosecond level and employing correlation-based techniques. Using the upgraded diagnostic, CAE/GAE-like bursting fluctuations are observed in neutral-beam heated plasmas with toroidal magnetic field B φ ≈ 1 T. Current upgrades being undertaken would enable the evaluation of toroidal mode number for these modes. Furthermore, this work opens the possibility of better understanding near ion-cyclotron frequency fluctuations in fusion relevant plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Design of radial interferometer–polarimeter for internal magnetic and density fluctuation measurements at multiple space–time scales in the National Spherical Torus Experiment-Upgrade (NSTX-U)

A Faraday-effect radial interferometer–polarimeter is designed for the National Spherical Torus Experiment-Upgrade (NSTX-U) to measure multiscale magnetic and density fluctuations critical to understanding fusion plasma confinement and stability, including those originating from magnetohydrodynamic instabilities, energetic particle-driven modes, and turbulence. The diagnostic will utilize the three-wave technique with 5 MHz bandwidth to simultaneously measure line-integrated magnetic and density fluctuations up to the ion-cyclotron frequency. Probe beams will be launched radially from the low-field side at the NSTX-U midplane, where the measured Faraday fluctuations mainly correspond to radial magnetic fluctuations that directly link to magnetic transport. A correlation technique will be employed to reduce the measurement noise to below 0.01° enabling detection of small amplitude fluctuations. Two toroidally displaced chords with 7° separation will be installed to measure toroidal mode numbers up to n = 25 for mode identification. Finally, solid-state microwave sources operating at 321 μm (935 GHz) will be used to minimize the impact of the Cotton–Mouton effect.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

THE IMAGING PROPERTIES OF THE GAS PIXEL DETECTOR AS A FOCAL PLANE POLARIMETER

X-rays are particularly suited to probing the physics of extreme objects. However, despite the enormous improvements of X-ray astronomy in imaging, spectroscopy, and timing, polarimetry remains largely unexplored. We propose the photoelectric polarimeter Gas Pixel Detector (GPD) as a candidate instrument to fill the gap created by more than 30 yr without measurements. The GPD, in the focus of a telescope, will increase the sensitivity of orders of magnitude. Moreover, since it can measure the energy, the position, the arrival time, and the polarization angle of every single photon, it allows us to perform polarimetry of subsets of data singled out from the spectrum, the light curve, or an image of the source. The GPD has an intrinsic, very fine imaging capability, and in this work we report on the calibration campaign carried out in 2012 at the PANTER X-ray testing facility of the Max-Planck-Institut für extraterrestrische Physik of Garching (Germany) in which, for the first time, we coupled it with a JET-X optics module with a focal length of 3.5 m and an angular resolution of 18 arcsec at 4.5 keV. This configuration was proposed in 2012 aboard the X-ray Imaging Polarimetry Explorer (XIPE) in response to the ESA call for a small mission. We derived the imaging and polarimetric performance for extended sources like pulsar wind nebulae and supernova remnants as case studies for the XIPE configuration and also discuss possible improvements by coupling the detector with advanced optics that have a finer angular resolution and larger effective areas to study extended objects with more detail.

79 ASTRONOMY AND ASTROPHYSICS↗