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At least 631 records · Page 35

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NASA NTRS1980

POLAR 5 - An electron accelerator experiment within an aurora. III - Evidence for significant spacecraft charging by an electron accelerator at ionospheric altitudes

The POLAR 5 rocket experiment carried an electron accelerator on a 'daughter' payload which injected a 0.1 A beam of 10 keV electrons in a pulsed mode every 410 ms. With spin and precession, injections were made over a wide range of pitch angles. Measurements from a double probe electric field instrument and from particle detectors on the 'mother' payload and from a crude RPA on the 'daughter' payload are interpreted to indicate that the 'daughter' charges to a potential between several hundred volts and 1 kV. The neutralizing return current to the 'daughter' is shown to be asymmetrically distributed with the majority being collected from the direction of the beam. The additional electrons necessary to neutralize the daughter are thought to be produced and heated through beam-plasma interactions postulated by Maehlum et al. (1980) and Grandal et al. (1980) to explain the particle and optical measurements. Significant electric fields emanating from the charged 'daughter' and the beam are seen at distances exceeding 100 m at the 'mother' payload.

Jacobsen, T. A.↗

NASA NTRS1980

Plasma double-layers produced by ponderomotive force

Non-linear rectification of the RF electric fields excited in a convectively amplifying electron beam-plasma interaction results in a dc electric field, and a corresponding ponderomotive force acting on the charged particles to produce a space-charge separation, i.e. a type of plasma double-layer. This paper analyses the effect, taking into account plasma electron temperature and electron-neutral collisions. To measure such double-layers, an electron beam probe constitutes a convenient non-perturbing diagnostic technique, but great care is required in its calibration. An analysis is presented taking into account significant non-linear effects which had been neglected in previous work. The paper concludes with some preliminary experimental results illustrating the use of the technique in a beam-plasma interaction for which a weak double-layer electric field is predicted.

Levine, J. S.↗

DOE OSTI2022

Ionization-Based Optical Structures for the Control of Short-Pulse Lasers (Abbreviated LDRD Report)

The intensity of light from the highest-power lasers is limited by the size of the optics required to amplify, compress, transport, and focus a laser beam. Indeed, optics damage puts strict constraints on the laser energy density that solid optics can sustain; this leads to enormous optics sizes and limits the maximum intensity that these lasers can achieve. In this project we investigated new types of diffractive optics based on mixtures of neutral gas and plasmas. The basic idea is to interfere laser beams in a gas near the ionization threshold, so that plasma is created in the constructive interference regions (i.e., the “bright” fringes of the interference pattern) while the destructive interference regions remain a neutral gas. The resulting refractive index modulation, due to the different indices in gas vs. plasma, effectively turns such structures into diffractive optics elements. We proposed several new types of optics based on this general concept: i) reflection gratings, which can act as mirrors of “pulse cleaners” to eliminate laser pre-pulse; ii) transmission gratings, as part of a new type of pulse compression scheme with the potential to achieve laser intensities orders of magnitude above what is currently feasible using solid-state optics; and iii) holographic lenses, to focus high-power lasers. We conducted laboratory experiments which demonstrated high efficiency reflection gratings, paving the way for practical applications of our new concepts.

47 OTHER INSTRUMENTATION↗

NASA NTRS2006

Finite Gyro-Radius Ion Pickup Current at Titan: Application to T9 and T5

We propose a possible explanation for the second wake event observed by Cassini during the T9 encounter with Titan. As shown in Hartle and Sittler [2007a], ions will emanate from Titan's upper atmosphere as ion beams when the ion gyroradii are large compared to the neutral scale height. Furthermore, Sittler and Hartle [2007] and Hartle and Sittler [2007b] showed that when this condition is satisfied and the electric field of the external flow is not reduced significantly due to draping field lines, the heavier pickup ions will be highly localized in space and velocity, or beam-like, in Titan's wake. This can cause these ion bunches to jump across the spacecraft trajectory and not be observed except for the lighter ions such as H+ and H2+, which have smaller gyroradii. These heavy ions will form a large pickup current which can deflect the tail position away from Saturn. We will discuss this model for the T9 encounter, which was a wake pass, and also explore its possible application for T5.

Sittler, Edward C.↗

NASA NTRS1978

The collisional interaction of a beam of charged particles with a hydrogen target of arbitrary ionization level

The classical theory of scattering under the Coulomb potential of both charged and neutral particles is used to derive formulae for the energy deposition rate and mean scattering of a beam of charged particles interacting with a cold hydrogen target of arbitrary ionization level as a function of the column density traversed by the beam. These general results hold for any form of stable injection energy spectrum, and their relevance to the existing literature on chromospheric heating during solar flares is discussed.

Emslie, A. G.↗

DOE OSTI2021

Analysis of the Ion Conversion Mechanisms in the Effluent of Atmospheric Pressure Plasma Jets in Ar with Admixtures of O 2 , H 2 O and Air

Ionic species in atmospheric pressure plasma jets (APPJs) play an important role in plasmasurface and plasma-liquid interactions, nonetheless, they have not received the same attention as their neutral reactive species counterparts. In this work, a molecular beam mass spectrometer (MBMS) was used to characterize the ion compositions in the effluent of an APPJ operating in ambient air for different feed gases including Ar + O 2 , Ar + air and Ar + H 2 O mixtures inspired by gas compositions used for biomedical applications. Changes in compositions of positive and negative ions as a function of nozzle-to-substrate distance along the plasma plume were analyzed and compared with a pseudo-1D plug flow model. Positive and negative ions were detected up to distances of 12 mm from the visible plasma plume tip. The measurements enable to follow the ion conversion pathways in the effluent of the APPJs as a function of distance from the nozzle. The trends in ion yield obtained from a pseudo-1D plug flow model showed generally a good agreement with the experimentally observed trends after addition of ionic reactions to the previously reported reaction set but also some distinctive differences were observed. The dominant positive ions in the far effluent are water ion clusters, the most stable ion for all gas mixtures investigated, while a large variety of negative ions was found for different gas mixtures.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1975

15 cm cusped magnetic field mercury ion thruster research

The importance of achieving a uniform current density in the exhaust beam of an electrostatic ion thruster is discussed in terms of thrust level and accelerator grid lifetime. A neutral residence time approach is used to propose a magnetic field geometry which should produce a highly uniform beam current density. The discharge chamber length to diameter ratio is shown to be an important optimization parameter and experimental evaluation of the cusped field thruster over a wide range of this parameter is presented. Beam profile measurements 5 cm downstream of the accelerator grid indicate a beam profile flatness parameter which is 25% greater than the SERT II value. Flatness parameters extrapolated to the plane of the accelerator grid are demonstrated to be as high as 0.9.

Beattie, J. R.↗

NASA NTRS1981

Space assembly methodology

Large space structure assembly analysis techniques are defined and simulation activities are described. The simulations included are: an extravehicular activity assembly simulation; a fabricated beam assembly series using a beam generating machine end caps, and cross beam brackets; deployment of a deployable truss, using the neutral buoyancy remote manipulator system with crewman assistance; and a series aboard the KC-135 zero g aircraft.

Stokes, J. W.↗

NASA NTRS1985

ACCESS (Assembly Concept for Construction of Erectable Space Structure) - A Shuttle flight experiment

ACCESS is a planned Shuttle flight experiment to assess the potential of an on-orbit construction concept designed for efficient manual assembly of a space truss. The experiment, which is scheduled for launch November 27, 1985, on the Space Transportation System (STS) flight 61-B, uses two astronauts secured in fixed foot restraints located in the Shuttle cargo bay to assemble a 45-foot long aluminum truss beam from 93 tubular struts and 33 nodal joints. Neutral buoyancy simulations of the flight experiment indicate the truss can be assembled in less than thirty minutes. Structural assembly, structural repair, flexible cable attachment and manual manipulation of the truss is also planned for the experiment using an astronaut secured in the Manipulator Foot Restraint attached to the Remote Manipulator System arm. Flight assembly data will be generated for correlation of the neutral buoyancy ground test data. This paper describes the ACCESS flight experiment and presents results of the neutral buoyancy development and training tests.

Heard, W. L., Jr.↗

DOE OSTI2022

Hydroxyl radical yields in the heavy ion radiolysis of water

Scavenging experiments coupled with Monte Carlo track structure and kinetics simulations have been used to determining and understand the yields of hydroxyl radicals in the radiolysis of water with protons and carbon ions. Carbon dioxide production from aerated formic acid solutions with concentrations ranging from 10-3 to 1 mol./dm3 was used as a probe of the time dependence of the hydroxyl radical yield from about 5 ns to 1 ?s. Numerical extrapolation of the results at slightly different ion energies in combination with data from gamma radiolysis experiments allows a systematic analysis of both track average and track segment yields, with considerable track chemistry found to occur on the nanosecond to microsecond time scale. Track chemistry calculations utilizing Monte Carlo track structure simulations and nonhomogeneous independent reaction times diffusion-reaction modeling of product yields reproduce experimental observations. Subsequently, the track simulation methods were used to predict hydroxyl radical kinetics in deaerated and aerated water at neutral pH. Taken with literature data for helium ion beam studies, the results offer insight into the potential for indirect radiation induced damage to biological systems for light ions with very different track structures.

38 - RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCL↗

NASA NTRS1973

High intensity copper atom beam - Preliminary results

The development of a nozzle which gas-dynamically accelerates neutral copper atoms at controlled energy levels and flux rates suitable for the investigation of inelastic copper atom collision processes is reported. Preliminary test data demonstrate that vapor-deposited rhenium nozzles do not degrade in the presence of copper vapor at high temperatures. Operation with high purity helium gas at nozzle stagnation temperatures in the range 2650-2700 K and total stagnation pressures from 1/4 to 2 atm with continuous copper atom flux rates of approximately 10 to the 18th power per second has been maintained, for a total time of 8-1/2 h to date.

Kelly, A. J.↗

DOE OSTI2024

Infrared bands of neutral gas-phase carbon clusters in a broad spectral range

The identification of species in the interstellar medium requires precise and molecule-specific spectroscopic information in the laboratory framework, in broad spectral ranges and under conditions relevant to interstellar environments. In this work, we measure the gas-phase infrared spectra of neutral carbon clusters, C N (N = 6–11), in a molecular beam. The C N distribution is formed by photofragmentation of C 60 molecules, concurrently showing a top-down formation mechanism. A broad spectral range in the infrared between 500–3200 cm -1 (20–3.125 μm) is investigated. We observe strong bands between 5 and 6 μm, in conjunction with novel features in the 3 μm region. Density functional theory calculations reveal that these short wavelength modes correspond to combination bands with significant infrared intensity. Moreover, we identify the N ≤ 10 clusters as linear, while C 11 adopts a ring configuration, placing the linear-to-ring transition at N = 11 under our molecular beam conditions. The linearity of C 10 is discussed based on the formation pathway from larger clusters in energetic conditions. Given the vast and very precise infrared information already been released from the James Webb Space Telescope mission, this infrared spectroscopic data set in conjunction with information on formation mechanisms is of major relevance for identifying neutral carbon clusters in astronomical environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1980

TEBPP: Theoretical and Experimental study of Beam-Plasma-Physics

The interaction of an electron beam (0 to 10 keV, 0 to 1.5 Amp) with the plasma and neutral atmospheres at 200 to 400 km altitude is studied with emphasis on applications to near Earth and cosmical plasmas. The interaction occurs in four space time regions: (1) near electron gun, beam coming into equilibrium with medium; (2) equilibrium propagation in ionosphere; (3) ahead of beam pulse, temporal and spatial precursors; (4) behind a beam pulse. While region 2 is of the greatest interest, it is essential to study Region 1 because it determines the characteristics of the beam as it enters 2 through 4.

Anderson, H. R.↗

DOE OSTI2024

Measurement of γ -ray production via the neutron- O 16 reaction using a 77 MeV quasimonoenergetic neutron beam

Understanding of γ-ray production via neutron interactions on oxygen is essential for the study of neutrino neutral-current quasielastic interactions in water Cherenkov detectors. A measurement of γ-ray production from such reactions was performed using a 77 MeV quasi-monoenergetic neutron beam. Several γ-ray peaks, which are expected to come from neutron- 16 O reactions, are observed and production cross sections are measured for nine γ-ray components of energies between 2 and 8~MeV. Finally, these are the first measurements at this neutron energy using a nearly monoenergetic beam.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Deeply Virtual Compton Scattering Using a Positron Beam in Hall-C at Jefferson Lab

In this study we propose to use the High Momentum Spectrometer of Hall C combined with the Neutral Particle Spectrometer (NPS) to perform high precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section using a beam of positrons. The combination of measurements with oppositely charged incident beams is the only unambiguous way to disentangle the contribution of the DVCS 2 term in the photon electroproduction cross section from its interference with the Bethe-Heitler amplitude. This provides a stronger way to constrain the Generalized Parton Distributions of the nucleon. A wide range of kinematics accessible with an 11 GeV beam off an unpolarized proton target will be covered. The $\mathcal{Q}^2$-dependence of each contribution will be measured independently.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2026

Multiple interaction points in ghost collisions

The Ghost Collider makes use of unique “ghost” bunches, which are electrically neutral combinations of electrons and positrons within the same RF bucket, eliminates the beam-beam effects typically present at the interaction point (IP) in conventional colliders. This allows for the novel possibility of placing multiple interaction regions in series, achieving additive luminosity without introducing significant disruption. However, to get higher luminosity, the beta functions at the IP reaches millimeter scale, which in turn adds significant chromatic contribution to the collider. Correcting these chromatic effects is essential to maintain beam stability and ensure high luminosity during collider operation. By carefully adjusting the phase advance between two IRs that are placed in series, it becomes possible to cancel chromaticity globally, enabling stable collider operation while preserving high luminosity. In this paper we discuss the design of such IR/IRs to be used in a ghost collider.

Accelerator Physics↗

NASA NTRS1995

Sputtering erosion in ion and plasma thrusters

An experimental set-up to measure low-energy (below 1 keV) sputtering of materials is described. The materials to be bombarded represent ion thruster components as well as insulators used in the stationary plasma thruster. The sputtering takes place in a 9 inch diameter spherical vacuum chamber. Ions of argon, krypton and xenon are used to bombard the target materials. The sputtered neutral atoms are detected by a secondary neutral mass spectrometer (SNMS). Samples of copper, nickel, aluminum, silver and molybdenum are being sputtered initially to calibrate the spectrometer. The base pressure of the chamber is approximately 2 x 10(exp -9) Torr. the primary ion beam is generated by an ion gun which is capable of delivering ion currents in the range of 20 to 500 nA. The ion beam can be focused to a size approximately 1 mm in diameter. The mass spectrometer is positioned 10 mm from the target and at 90 deg angle to the primary ion beam direction. The ion beam impinges on the target at 45 deg. For sputtering of insulators, charge neutralization is performed by flooding the sample with electrons generated from an electron gun. Preliminary sputtering results, methods of calculating the instrument response function of the spectrometer and the relative sensitivity factors of the sputtered elements will be discussed.

Ray, Pradosh K.↗

NASA NTRS2007

Sensitivity Testing of the NSTAR Ion Thruster

During the Extended Life Test of the DS1 flight spare ion thruster, the engine was subjected to sensitvity testing in order to characterize the macroscopic dependence of discharge chamber sensitivity to a +\-3% vatiation in main flow, cathode flow and beam current, and to +\5% variation in beam and accelerator voltage, was determined for the minimum- (THO), half- (TH8) and full power (TH15) throttle levels. For each power level investigared, 16 high/low operating conditions were chosen to vary the flows, beam current, and grid voltages in in a matrix that mapped out the entire parameter space. The matrix of data generated was used to determine the partial derivative or senitivity of the dependent parameters--discharge voltage, discharge current, discharge loss, double-to-single-ion current ratio, and neutralizer-keeper voltage--to the variation in the independent parameters--main flow, cathode flow, beam current, and beam voltage. The sensititivities of each dependent parameter with respect to each independent parameter were determined using a least-square fit routine. Variation in these sensitivities with thruster runtime was recorded over the duration of the ELT, to detemine if discharge performance changed with thruster wear. Several key findings have been ascertained from the sensitivity testing. Discharge operation is most sensitve to changes in cathode flow and to a lesser degree main flow. The data also confirms that for the NSTAR configuration plasma production is limited by primary electron input due to the fixed neutral population. Key sensitivities along with their change with thruster wear (operating time) will be presented. In addition double ion content measurements with an ExB probe will also be presented to illustrate beam ion production and content sensitivity to the discharge chamber operating parameteres.

electric propulsion↗