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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Direct observations of L-I-H and H-I-L transitions with the X-point reciprocating probe in ASDEX Upgrade

A reciprocating Langmuir probe was used to directly measure the behavior of turbulence and flows in the X-point region during transitions between low-(L) and high-confinement (H) mode in ASDEX Upgrade. The probe traverses the divertor horizontally in 140 ms, typically 2–5 cm below the X-point. Toroidal Mach number, density, floating potential (ϕ{sub f}), and electron temperature (T{sub e}) are measured. In the regime accessible to the probe (P{sub inj}<1.5 MW, line-integrated core density <4×10{sup 19} m{sup −2}), the L-H transition features an intermediate phase (I-phase), characterized by limit-cycle oscillations at 0.5–3 kHz [Conway et al., Phys. Rev. Lett. 106, 065001 (2011)]. The probe measurements reveal that this pulsing affects both the density and the toroidal Mach number. It is present in both the low-(LFS) and high-field sides (HFS) of the scrape-off layer, while high-amplitude broadband turbulence usually dominates the private-flux region. Profile comparisons between L-mode and I-phase show lower density in pulsing regions and small shifts in T{sub e}, directed oppositely on LFS and HFS, which are compensated by shifts in ϕ{sub f} to yield a surprisingly unchanged plasma potential profile. Directly observed L-I-phase transitions reveal that the onset of the pulsing is preceded by a fast 50% density drop in the HFS X-point region. Back transitions to L-mode occur essentially symmetrically, with the pulsing stopping first, followed by a fast recovery to L-mode density levels in the divertor.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Pump-probe surface photovoltage spectroscopy measurements on semiconductor epitaxial layers

Pump-probe Surface Photovoltage Spectroscopy (SPS) measurements are performed on semiconductor epitaxial layers. Here, an additional sub-bandgap cw pump laser beam is used in a conventional chopped light geometry SPS setup under the pump-probe configuration. The main role of pump laser beam is to saturate the sub-bandgap localized states whose contribution otherwise swamp the information related to the bandgap of material. It also affects the magnitude of Dember voltage in case of semi-insulating (SI) semiconductor substrates. Pump-probe SPS technique enables an accurate determination of the bandgap of semiconductor epitaxial layers even under the strong influence of localized sub-bandgap states. The pump beam is found to be very effective in suppressing the effect of surface/interface and bulk trap states. The overall magnitude of SPV signal is decided by the dependence of charge separation mechanisms on the intensity of the pump beam. On the contrary, an above bandgap cw pump laser can be used to distinguish the signatures of sub-bandgap states by suppressing the band edge related feature. Usefulness of the pump-probe SPS technique is established by unambiguously determining the bandgap of p-GaAs epitaxial layers grown on SI-GaAs substrates, SI-InP wafers, and p-GaN epilayers grown on Sapphire substrates.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Simultaneous use of camera and probe diagnostics to unambiguously identify and study the dynamics of multiple underlying instabilities during the route to plasma turbulence

We use multiple-tip Langmuir probes and fast imaging to unambiguously identify and study the dynamics of underlying instabilities during the controlled route to fully-developed plasma turbulence in a linear magnetized helicon plasma device. Langmuir probes measure radial profiles of electron temperature, plasma density and potential; from which we compute linear growth rates of instabilities, cross-phase between density and potential fluctuations, Reynold's stress, particle flux, vorticity, time-delay estimated velocity, etc. Fast imaging complements the 1D probe measurements by providing temporally and spatially resolved 2D details of plasma structures associated with the instabilities. We find that three radially separated plasma instabilities exist simultaneously. Density gradient driven resistive drift waves propagating in the electron diamagnetic drift direction separate the plasma into an edge region dominated by strong, velocity shear driven Kelvin-Helmholtz instabilities and a central core region which shows coherent Rayleigh-Taylor modes propagating in the ion diamagnetic drift direction. The simultaneous, complementary use of both probes and camera was crucial to identify the instabilities and understand the details of the very rich plasma dynamics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Tracing ultrafast dynamics of strong fields at plasma-vacuum interfaces with longitudinal proton probing

If regions of localized strong fields at plasma-vacuum interfaces are probed longitudinally with laser accelerated proton beams their velocity distribution changes sensitively and very fast. Its measured variations provide indirectly a higher temporal resolution as deduced from deflection geometries which rely on the explicit temporal resolution of the proton beam at the position of the object to probe. With help of reasonable models and comparative measurements changes of proton velocity can trace the field dynamics even at femtosecond time scale. In longitudinal probing, the very low longitudinal emittance together with a broad band kinetic energy distribution of laser accelerated protons is the essential prerequisite of the method. With a combination of energy and one-dimensional spatial resolution, we resolve fast field changes down to 100 fs. The used pump probe setup extends previous schemes and allows discriminating simultaneously between electric and magnetic fields in their temporal evolution.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Numerical matching of the sheath and presheath solutions for a spherical probe in radial-motion theory

The theory of positive-ion collection by a probe immersed in a low-pressure plasma was reviewed and extended by Allen, Boyd, and Reynolds [Proc. Phys. Soc. 70, 297 (1957)]. For a given value of the ion current, the boundary values of the matched “nonneutral” or “sheath” solution V{sup ~}{sub nn}{sup (m)}(r; r{sub m}) were obtained from the “quasineutral” or “presheath” solution V{sup ~}{sub qn}(r) by choosing the small potential and electric-field values corresponding to some large “matching radius” r{sub m}. Here, a straightforward but efficient numerical method is presented for systematically determining an optimal value of the matching radius at which the presheath and sheath solutions are joined to yield the “matched” potential profile. Some suitable initial matching radius r{sub m1} is chosen and the related potential and electric-field values of the quasineutral solution are calculated. Using these as boundary conditions, Poisson's equation is integrated to yield the matched nonneutral solution including the corresponding potential at the probe surface. This procedure is repeated for increasing values r{sub m2}, r{sub m3},…. until the resulting potential at the probe surface becomes practically constant. The corresponding value of r{sub m} is taken as the “optimal” matching radius r{sub mo} at which the presheath and sheath solutions are ultimately joined to yield the “optimal” matched potential profile in the entire plasma-probe transition region. It is also shown that the Bohm criterion is inapplicable in the present problem.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

High-bandwidth, high-sampling-rate, low-noise, two-probe transient photovoltage measuring system

In this article, we present a two-probe configuration for measuring transient photovoltage (TPV) signals from photo-electronic semiconductor devices. Unlike in a conventional one-probe system, the two electrodes of the devices under test in this study are both monitored in our new measuring system, giving rise to a significantly enhanced signal-to-noise ratio. Tentative experimental data ob tained from N, N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine-based organic semiconductor devices show that the bandwidth and the sampling rate of the system reach 1.5 GHz and 50 GS/s, respectively, without degradation of the noise level. In addition, the study of TPV signals on each individual electrode is allowed. The TPV values measured by the two individual probes are not identically equal to half of the differential TPV and will not cancel each other out as expected. This abnormal phenomenon is due to the photoelectric response of the photo-electronic material. This novel two-probe TPV measuring technique and abnormal TPV behavior might be useful for studying more dynamic processes in photo-electronic semiconductors.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Sensitivity enhancement of surface thermal lens technique with a short-wavelength probe beam: Experiment

Surface thermal lens is a highly sensitive photothermal technique to measure low absorption losses of various solid materials. In such applications, the sensitivity of surface thermal lens is a key parameter for measuring extremely low absorption. In this paper, we experimentally investigated the influence of probe beam wavelength on the sensitivity of surface thermal lens for measuring the low absorptance of optical laser components. Three probe lasers with wavelength 375 nm, 633 nm, and 1570 nm were used, respectively, to detect the surface thermal lens amplitude of a highly reflective coating sample excited by a cw modulated Gaussian beam at 1064 nm. The experimental results showed that the maximum amplitude of surface thermal lens signal obtained at corresponding optimized detection distance was inversely proportional to the wavelength of the probe beam, as predicted by previous theoretical model. The sensitivity of surface thermal lens could, therefore, be improved by detecting surface thermal lens signal with a short-wavelength probe beam.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Experimental validation of an 8 element EMAT phased array probe for longitudinal wave generation

Sodium cooled Fast Reactors (SFR) use liquid sodium as a coolant. Liquid sodium being opaque, optical techniques cannot be applied to reactor vessel inspection. This makes it necessary to develop alternative ways of assessing the state of the structures immersed in the medium. Ultrasonic pressure waves are well suited for inspection tasks in this environment, especially using pulsed electromagnetic acoustic transducers (EMAT) that generate the ultrasound directly in the liquid sodium. The work carried out at CEA LIST is aimed at developing phased array EMAT probes conditioned for reactor use. The present work focuses on the experimental validation of a newly manufactured 8 element probe which was designed for beam forming imaging in a liquid sodium environment. A parametric study is carried out to determine the optimal setup of the magnetic assembly used in this probe. First laboratory tests on an aluminium block show that the probe has the required beam steering capabilities.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

The time resolved measurement of ultrashort terahertz-band electric fields without an ultrashort probe

The time-resolved detection of ultrashort pulsed THz-band electric field temporal profiles without an ultrashort laser probe is demonstrated. A non-linear interaction between a narrow-bandwidth optical probe and the THz pulse transposes the THz spectral intensity and phase information to the optical region, thereby generating an optical pulse whose temporal electric field envelope replicates the temporal profile of the real THz electric field. This optical envelope is characterised via an autocorrelation based FROG (frequency resolved optical gating) measurement, hence revealing the THz temporal profile. The combination of a narrow-bandwidth, long duration, optical probe, and self-referenced FROG makes the technique inherently immune to timing jitter between the optical probe and THz pulse and may find particular application where the THz field is not initially generated via ultrashort laser methods, such as the measurement of longitudinal electron bunch profiles in particle accelerators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

A model of plasma current through a hole of Rogowski probe including sheath effects

In TST-2 Ohmic discharges, local current is measured using a Rogowski probe by changing the angle between the local magnetic field and the direction of the hole of the Rogowski probe. The angular dependence shows a peak when the direction of the hole is almost parallel to the local magnetic field. The obtained width of the peak was broader than that of the theoretical curve expected from the probe geometry. In order to explain this disagreement, we consider the effect of sheath in the vicinity of the Rogowski probe. A sheath model was constructed and electron orbits were numerically calculated. From the calculation, it was found that the electron orbit is affected by E × B drift due to the sheath electric field. Such orbit causes the broadening of the peak in the angular dependence and the dependence agrees with the experimental results. The dependence of the broadening on various plasma parameters was studied numerically and explained qualitatively by a simplified analytical model.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Upgrade of Langmuir probe diagnostic in ITER-like tungsten mono-block divertor on experimental advanced superconducting tokamak

In order to withstand rapid increase in particle and power impact onto the divertor and demonstrate the feasibility of the ITER design under long pulse operation, the upper divertor of the EAST tokamak has been upgraded to actively water-cooled, ITER-like tungsten mono-block structure since the 2014 campaign, which is the first attempt for ITER on the tokamak devices. Therefore, a new divertor Langmuir probe diagnostic system (DivLP) was designed and successfully upgraded on the tungsten divertor to obtain the plasma parameters in the divertor region such as electron temperature, electron density, particle and heat fluxes. More specifically, two identical triple probe arrays have been installed at two ports of different toroidal positions (112.5-deg separated toroidally), which can provide fundamental data to study the toroidal asymmetry of divertor power deposition and related 3-dimension (3D) physics, as induced by resonant magnetic perturbations, lower hybrid wave, and so on. The shape of graphite tip and fixed structure of the probe are designed according to the structure of the upper tungsten divertor. The ceramic support, small graphite tip, and proper connector installed make it possible to be successfully installed in the very narrow interval between the cassette body and tungsten mono-block, i.e., 13.5 mm. It was demonstrated during the 2014 and 2015 commissioning campaigns that the newly upgraded divertor Langmuir probe diagnostic system is successful. Representative experimental data are given and discussed for the DivLP measurements, then proving its availability and reliability.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Integration of conductivity probe with optical and x-ray imaging systems for local air–water two-phase flow measurement

Various techniques have been developed in the past to measure different parameters in two-phase flow. Among them, the multi-sensor conductivity probe is one of the most commonly used techniques because of its good overall performance. Recently, more advanced techniques such as high speed optical imaging and fast X-ray densitometry become mature and easily accessible. The main objective of this work is to compare and integrate these different techniques, to achieve a more accurate and complete measurement of two-phase flow. In this study, a double-sensor conductivity probe is used to measure the local time-averaged parameters along the radial direction of a 2.54 cm ID round pipe. An X-ray densitometry system is used to measure the chordal averaged void fraction and gas velocity. A high speed camera system is employed to provide the visualization of the two-phase flow structure and obtain the line-averaged gas velocity. The unique advantages and main uncertainties of these three techniques are analyzed by considering their measuring principles and possible issues in practical measurements. From this, a method is developed to integrate the data obtained by the optical and X-ray systems into the probe signal processing. Finally, a better accuracy could be achieved using this method for various local two-phase flow parameters including void fraction, bubble velocity and superficial gas velocity, compared to the original probe measurements.

42 ENGINEERING↗
DOE OSTI2016

Measurement of atmospheric pressure microplasma jet with Langmuir probes

A radio frequency argon microplasma jet at atmospheric-pressure is characterized using Langmuir probes. While optical methods are the typical diagnostic for these small scale plasmas, the simplicity and low cost of Langmuir probes makes them an attractive option. The plasma density and electron temperature are measured using existing high-pressure Langmuir probe theories developed for flames and arcs. The density and temperature vary from 1 × 10{sup 16} to 1 × 10{sup 19} m{sup −3} and 2.3 to 4.4 eV, respectively, depending on the operating condition. The density decreases while the electron temperature increases with axial distance from the jet exit. The applicability of the probe theories as well as the effect of collisionality and jet mixing is discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

PICO - the probe of inflation and cosmic origins

Downloading of the abstract is permitted for personal use only. The Probe of Inflation and Cosmic Origins (PICO) is a NASA-funded study of a Probe-class mission concept. The toplevel science objectives are to probe the physics of the Big Bang by measuring or constraining the energy scale of inflation, probe fundamental physics by measuring the number of light particles in the Universe and the sum of neutrino masses, to measure the reionization history of the Universe, and to understand the mechanisms driving the cosmic star formation history, and the physics of the galactic magnetic field. PICO would have multiple frequency bands between 21 and 799 GHz, and would survey the entire sky, producing maps of the polarization of the cosmic microwave background radiation, of galactic dust, of synchrotron radiation, and of various populations of point sources. Several instrument configurations, optical systems, cooling architectures, and detector and readout technologies have been and continue to be considered in the development of the mission concept. We will present a snapshot of the baseline mission concept currently under development.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

The Probe Length Effect on the Cantilever of an Atomic Force Microscope in Measuring the Mechanical Properties of Living Neurons

Living sensory neurons were studied by atomic force microscopy in the PeakForce QNM mode under near-physiological conditions. The dependence of the measured apparent Young modulus of cells on the ratio of the probe height to the beam length on a used cantilever was revealed. A qualitative explanation based on the analysis of beam strains in two limit cases, in which the probe slides over a studied object and the probe sticks to the latter, was given to the obtained result. It was proposed to classify native cells by the character of their interaction with the probe (sliding or sticking).

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Assessment of the Revised 3410 Building Filtered Exhaust Stack Sampling Probe Location

In order to support the air emissions permit for the 3410 Building, Pacific Northwest National Laboratory performed a series of tests in the exhaust air discharge from the reconfigured 3410 Building Filtered Exhaust Stack. The objective was to determine whether the location of the air sampling probe for emissions monitoring meets the applicable regulatory criteria governing such effluent monitoring systems. In particular, the capability of the air sampling probe location to meet the acceptance criteria of ANSI/HPS N13.1-2011 , Sampling and Monitoring Releases of Airborne Radioactive Substances from the Stack and Ducts of Nuclear Facilities was determined. The qualification criteria for these types of stacks address 1) uniformity of air velocity, 2) sufficiently small flow angle with respect to the axis of the duct, 3) uniformity of tracer gas concentration, and 4) uniformity of tracer particle concentration. Testing was performed to conform to the quality requirements of NQA-1-2000. Fan configurations tested included all fan combinations of any two fans at a time. Most of the tests were conducted at the normal flow rate, while a small subset of tests was performed at a slightly higher flow rate achieved with the laboratory hood sashes fully open. The qualification criteria for an air monitoring probe location are taken from ANSI/HPS N13.1-2011 and are paraphrased as follows with key results summarized: 1. Angular Flow—The average air velocity angle must not deviate from the axis of the stack or duct by more than 20°. Our test results show that the mean angular flow angles at the center two-thirds of the ducts are smaller than 4.5% for all testing conditions. 2. Uniform Air Velocity—The acceptance criterion is that the COV of the air velocity must be ≤ 20% across the center two thirds of the area of the stack. Our results show that the COVs of the air velocity across the center two-thirds of the stack are smaller than 2.9% for all testing conditions. 3. Uniform Concentration of Tracer Gases—The uniformity of the concentration of potential contaminants is first tested using a tracer gas to represent gaseous effluents. The tracer is injected downstream of the fan outlets and at the junction downstream fan discharges meet. The acceptance criteria are that 1) the COV of the measured tracer gas concentration is ≤20% across the center two-thirds of the sampling plane and 2) at no point in the sampling plane does the concentration vary from the mean by >30%. Our test results show that 1) the COV of the measured tracer gas concentration is < 2.9% for all test conditions and 2) at no point in the sampling plane does the concentration vary from the mean by >6.5%. 4. Uniform Concentration of Tracer Particles—Tracer particles of 10-μm aerodynamic diameter are used for the second demonstration of concentration uniformity. The acceptance criterion is that the COV of particle concentration is ≤ 20% across the center two thirds of the sampling plane. Our test results indicate that the COV of particle concentration is <9.9% across the center two-thirds of the sampling plane among all testing conditions. Thus, the reconfigured 3410 Building Filtered Exhaust Stack was determined to meet the qualification criteria given in the ANSI/HPS N13.1-2011 standard. Changes to the system configuration or operations outside the bounds described in this report (e.g., exhaust stack velocity changes, relocation of sampling probe, and addition of fans) may require re-testing or re-evaluation to determine compliance.

3410 building↗
DOE OSTI2015

Assessment of the LV-C2 Stack Sampling Probe Location for Compliance with ANSI/HPS N13.1-1999

This document reports on a series of tests conducted to assess the proposed air sampling location for the Hanford Tank Waste Treatment and Immobilization Plant (WTP) Low-Activity Waste (LAW) C2V (LV-C2) exhaust stack with respect to the applicable criteria regarding the placement of an air sampling probe. Federal regulations require that a sampling probe be located in the exhaust stack according to the criteria established by the American National Standards Institute/Health Physics Society (ANSI/HPS) N13.1-1999, Sampling and Monitoring Releases of Airborne Radioactive Substances from the Stack and Ducts of Nuclear Facilities. These criteria address the capability of the sampling probe to extract a sample that represents the effluent stream. The tests were conducted on the LV-C2 scale model system. Based on the scale model tests, the location proposed for the air sampling probe in the scale model stack meets the requirements of the ANSI/HPS N13.1-1999 standard for velocity uniformity, flow angle, gas tracer and particle tracer uniformity. Additional velocity uniformity and flow angle tests on the actual stack will be necessary during cold startup to confirm the validity of the scale model results in representing the actual stack.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS2012

The Fixed-bias Langmuir Probe on the Communication-navigation Outage Forecast System Satellite: Calibration and Validation

A fixed-bias spherical Langmuir probe is included as part of the Vector Electric Field Instrument (VEFI) suite on the Communication Navigation Outage Forecast System (CNOFS) satellite.CNOFS gathers data in the equatorial ionosphere between 400 and 860 km, where the primary constituent ions are H+ and O+. The ion current collected by the probe surface per unit plasmadensity is found to be a strong function of ion composition. The calibration of the collected current to an absolute density is discussed, and the performance of the spherical probe is compared to other in situ instruments on board the CNOFS satellite. The application of the calibration is discussed with respect to future xed-bias probes; in particular, it is demonstrated that some density fluctuations will be suppressed in the collected current if the plasma composition rapidly changes along with density. This is illustrated in the observation of plasma density enhancements on CNOFS.

VEFI↗