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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Impedance measurement of vacuum chamber components for the Advance Photon Source(APS) Upgrade

The proposed Advance Photon Source Upgrade (APS-U) employs a multi-bend achromat (MBA) lattice to increase the photon brightness by two to three orders of magnitude. One of the main design challenges of the upgrade is to minimize rf heating and collective instabilities associated with the impedance of small-aperture vacuum components. As part of this effort, my research focuses on impedance measurement and simulation of various MBA vacuum components. Here, we present the summary of the impedance contributions for the APS-U and describe our planned impedance measurement technique, including some measurement results for the non-evaporative getter (NEG)-coated copper chamber and simulation results for other critical components using a novel Goubau line (G-line) set up.

Collective effects↗
NASA NTRS1982

The phototron: A light to RF energy conversion device

The phototron, a photoelectric device that converts light to radio frequency energy, is described. It is a vacuum tube, free electron, device that is mechanically similar to a reflex klystron with the hot filament cathode replaced by a large area photocathode. The device can operate either with an external voltage source used to accelerate the photoelectrons or with zero bias voltage; in which case the photokinetic energy of the electrons sustains the R.F. oscillations in the tuned R.F. circuit. One basic design of the phototron was tested. Frequencies as high as about 1 GHz and an overall efficiency of about 1% in the biased mode were obtained. In the unbiased mode, the frequencies of operation and efficiences are considerably lower. Success with test model suggests that considerable improvements are possible through design refinements. One such design refinement is the reduction of the length of the electron flight path.

Freeman, J. W.↗
DOE OSTI2016

High-field side scrape-off layer investigation: Plasma profiles and impurity screening behavior in near-double-null configurations

New experiments on Alcator C-Mod reveal that the favorable impurity screening characteristics of the high-field side (HFS) scrape-off layer (SOL), previously reported for single null geometries, is retained in double null configurations, despite the formation of an extremely thin SOL. In balanced double-null, nitrogen injected locally into the HFS SOL is better screened by a factor of 2.5 compared to the same injection into the low field side (LFS) SOL. This result is insensitive to plasma current and Greenwald fraction. Nitrogen injected into the HFS SOL is not as well screened (only a factor of 1.5 improvement over LFS) in unbalanced double-null discharges, when the primary divertor is in the direction of B×∇B. In this configuration, impurity ‘plume’ emission patterns indicate that an opposing E × B drift competes with the parallel impurity flow to the divertor. In balanced double-null plasmas, the dispersal pattern exhibits a dominant E × B motion. Unbalanced discharges with the primary divertor opposite the direction of B×∇B exhibit excellent HFS screening characteristics – a factor of 5 enhancement compared to LFS. These data support the idea that future tokamaks should locate all RF actuators and close-fitting wall structures on the HFS and employ near-double-null magnetic topologies, both to precisely control plasma conditions at the antenna/plasma interface and to maximally mitigate the impact of local impurity sources arising from plasma-material interactions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Ion Source Development For The Proposed FNAL 750 keV Injector Upgrade

Currently there is a Proposed FNAL 750 keV Injector Upgrade for the replacement of the 40 year old Fermi National Laboratory (FNAL) Cockcroft-Walton accelerators with a new ion source and 200 MHz Radio Frequency Quadruple (RFQ). The slit type magnetron being used now will be replaced with a round aperture magnetron similar to the one used at Brookhaven National Lab (BNL). Operational experience from BNL has shown that this type of source is more reliable with a longer lifetime due to better power efficiency. The current source development effort is to produce a reliable source with >60 mA of H{sup -} beam current, 15 Hz rep-rate, 100 {mu}s pulse width, and a duty factor of 0.15%. The source will be based on the BNL design along with development done at FNAL for the High Intensity Neutrino Source (HINS).

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Energy exchange in systems of particles with nonreciprocal interaction

A model is proposed to describe the sources of additional kinetic energy and its redistribution in systems of particles with a nonreciprocal interaction. The proposed model is shown to explain the qualitative specific features of the dust particle dynamics in the sheath region of an RF discharge. Prominence is given to the systems of particles with a quasi-dipole–dipole interaction, which is similar to the interaction induced by the ion focusing effects that occur in experiments on a laboratory dusty plasma, and with the shadow interaction caused by thermophoretic forces and Le Sage’s forces.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Detecing Surface Change Created by an Underground Chemical Explosion Using Fully Polarimetric VideoSAR

Sandia National Laboratories (SNL) flew its Facility for Advanced RF and Algorithm Development (FARAD) X-Band (9.6 GHz center frequency), fully-polarimetric synthetic aperture radar (PolSAR) in VideoSAR-mode to collect complex-valued SAR imagery before, during, and after the fifth and sixth Source Physics Experiment's (SPE-5 and SPE-6) underground explosion. The results from the fifth Source Physics Experiment (SPE-5) used single-polarimetric VideoSAR data while SPE-6 used single and fully-polarimetric VideoSAR data. We show that SAR can provide surface change products indicative of disturbances caused by the underground chemical explosions. These are surface coherence measures, Po1SAR change signatures, and differential interferometric SAR (InSAR) height change.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2019

High-field side scrape-off layer investigation: plasma profiles and impurity screening behavior in near-double-null configurations

New experiments on Alcator C-Mod reveal that the favorable impurity screening characteristics of the high-field side (HFS) scrape-off layer (SOL), previously reported for single null geometries, is retained in double null configurations, despite the formation of an extremely thin SOL. In balanced double-null, nitrogen injected locally into the HFS SOL is better screened by a factor of 2.5 compared to the same injection into the low field side (LFS) SOL. This result is insensitive to plasma current and Greenwald fraction. Nitrogen injected into the HFS SOL is not as well screened (only a factor of 1.5 improvement over LFS) in unbalanced double-null discharges, when the primary divertor is in the direction of B×?B. In this configuration, impurity ‘plume’ emission patterns indicate that an opposing E X B drift competes with the parallel impurity flow to the divertor. In balanced double-null plasmas, the dispersal pattern exhibits a dominant E X B motion. Unbalanced discharges with the primary divertor opposite the direction of B×?B exhibit excellent HFS screening characteristics – a factor of 5 enhancement compared to LFS. These data support the idea that future tokamaks should locate all RF actuators and close-fitting wall structures on the HFS and employ near-double-null magnetic topologies, both to precisely control plasma conditions at the antenna/plasma interface and to maximally mitigate the impact of local impurity sources arising from plasma-material interactions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Simulations of Ion Migration in the LCLS RF Gun and Injector

The motivation for this work was the observed surface contamination of the first LCLS RF gun copper cathode. We will present the results of simulations in regards to ion migration in the LCLS gun. Ions of residual gases will be created by interaction of molecular gas species with the UV drive laser beam and by the electron beam itself. The larger part of those ionized molecules remain in the vicinity of creation, are transported towards beam line walls or away from the cathode. However a small fraction gains enough kinetic energy, focused by RF and magnetic fields and propagates to the cathode, producing an undesirable increase of the cathode's surface work function. Although this fraction is small, during long term operation, this effect may become a significant factor limiting the source performance.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

The Baryon Mapping Experiment (BMX), a 21cm intensity mapping pathfinder

The Baryon Mapping eXperiment (BMX) is an interferometric array designed as a pathfinder for a future post- reionization 21 cm intensity mapping survey. It consists of four 4-meter parabolic reflectors each having offset pyramidal horn feed, quad-ridge orthomode transducer, temperature-stabilized RF amplification and filtering, and pulsed noise injection diode. An undersampling readout scheme uses 8-bit digitizers running at 1.1 Gsamples/sec to provide access to signals from 1.1 - 1.55 GHz (third Nyquist zone), corresponding to HI emission from sources at redshift 0 < z < 0.3. An FX correlator is implemented in GPU and generates 28 GB/day of time-ordered visibility data. About 7,000 hours of data were collected from Jan. 2019 - May 2020, and we will present results on system performance including sensitivity, beam mapping studies, observations of bright celestial targets, and system electronics upgrades. BMX is a pathfinder for the proposed PUMA intensity mapping survey in the 2030s.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

A discharge with a magnetic X-point as a negative hydrogen ion source

The study presents first results from investigations of a novel low-pressure plasma source, intended for a negative hydrogen ion production. The source utilizes a dc magnetic field, shaped to form a cusp with a magnetic null-point (X-point). Beside the common role of filtering out the high energy electrons, this magnetic field configuration ensures in the present case also an interesting mechanism of coupling the RF power to the plasma. Investigations performed using radio frequency modulation spectroscopy (RFMOS) reveal that the main power coupling to the electrons is confined in the region on one side of the X-point. The modulation of the light intensity indicates also the presence of a strong dc drift close to the plane of the X-point. Several hypothesises for its explanation are raised: an azimuthal diamagnetic drift due to strong axial gradients of the electron energy, the excitation of a standing helicon wave, which couples to the radial magnetic field in the plane of the X-point, or a Trivelpiece-Gould wave which is resonantly absorbed near the plane of the X-point.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

The proton injector for the accelerator facility of antiproton and ion research (FAIR)

The new international accelerator facility for antiproton and ion research (FAIR) at GSI in Darmstadt, Germany, is one of the largest research projects worldwide and will provide an antiproton production rate of 7 × 10{sup 10} cooled pbars per hour. This is equivalent to a primary proton beam current of 2 × 10{sup 16} protons per hour. For this request a high intensity proton linac (p-linac) will be built with an operating rf-frequency of 325 MHz to accelerate a 35 mA proton beam at 70 MeV, using conducting crossed-bar H-cavities. The repetition rate is 4 Hz with beam pulse length of 36 μs. The microwave ion source and low energy beam transport developed within a joint French-German collaboration GSI/CEA-SACLAY will serve as an injector of the compact proton linac. The 2.45 GHz ion source allows high brightness ion beams at an energy of 95 keV and will deliver a proton beam current of 100 mA at the entrance of the radio frequency quadrupole (RFQ) within an acceptance of 0.3π mm mrad (norm., rms)

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Structure and interface chemistry of MoO{sub 3} back contacts in Cu(In,Ga)Se{sub 2} thin film solar cells

Molybdenum oxide (MoO{sub 3}) is considered as a possible primary back contact for Cu(InGa)Se{sub 2} thin film solar cells for its potential as a transparent back contact for superstrate and bifacial devices. MoO{sub 3} films were deposited on Mo or ITO-coated soda lime glass substrates by reactive rf sputtering in an ambient of Ar + O{sub 2} with O{sub 2}/(O{sub 2} + Ar) = 35% on which Cu(In{sub 0.7}Ga{sub 0.3})Se{sub 2} alloy absorber layers were deposited using multi-source elemental evaporation. Scanning Electron Microscopy studies showed uniform coverage of the as-deposited MoO{sub 3} layer and good adhesion was obtained in all cases. X-ray Photoelectron Spectroscopy depth profile analysis showed that MoSe{sub 2} was not formed at the Cu(InGa)Se{sub 2} interface with either the Mo-MoO{sub 3} or ITO-MoO{sub 3} back contacts. Determination of the valence band offsets showed that the MoO{sub 3} layer at the interface changes the energy band alignment with Cu(InGa)Se{sub 2}, producing a primary contact with lower valence band offset than ITO. Cu(In,Ga)Se{sub 2} thin film solar cells prepared using an as-deposited Mo-MoO{sub 3} back contact yielded a best conversion efficiency of 14%, with V{sub OC} = 647 mV, J{sub SC} = 28.4 mA/cm{sup 2}, and FF = 78.1%. Cells with ITO-MoO{sub 3} back contact showed a best efficiency of 12%, with V{sub OC} = 642 mV, J{sub SC} = 26.8 mA/cm{sup 2}, and FF = 69.2%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

MARS15 Simulation of Radiation Environment at the ESS Linac

Comprehensive studies with the MARS15(2016) Monte-Carlo code are described on evaluation of prompt and residual radiation levels induced by nominal and accidental beam losses in the 5-MW, 2-GeV European Spallation Source (ESS) Linac. These are to provide a basis for radiation shielding design verification through the accelerator complex. The calculation model is based on the latest engineering design and includes a sophisticated algorithm for particle tracking in the machine RF cavities as well as a well-established model of the beam loss. Substantial efforts were put in solving the deep-penetration problem for the thick shielding around the tunnel with numerous complex penetrations. It allowed us to study in detail not only the prompt dose, but also component and air activation, radiation loads on the soil outside the tunnel, and skyshine studies for the complicated 3-D surface above the machine. Among the other things, the newest features in MARS15 (2016), such as a ROOT-based beamline builder and a TENDL-based event generator for nuclear interactions below 100 MeV, were very useful in this challenging application

Mokhov, N. V.↗
DOE OSTI2012

Production of low-Z ions in the Dresden superconducting electron ion beam source for medical particle therapy

We report on experiments with a new superconducting electron beam ion source (EBIS-SC), the Dresden EBIS-SC, with the objective to meet the main requirements for their application in particle-therapy facilities. Synchrotrons as well as innovative accelerator concepts, such as high-gradient linacs which are driven by a large-current cyclotron (CYCLINACS) and direct drive RF linear accelerators may benefit from the advantages of EBISs in regard to their functional principle. First experimental studies of the production of low-Z ions such as H{sup +}, H{sub 2}{sup +}, H{sub 3}{sup +}, C{sup 4+}, and C{sup 6+} are presented. Particular attention is paid to the ion output, i.e., the number of ions per pulse and per second, respectively. Important beam parameters in this context are, among others, ion pulse shaping, pulse repetition rates, beam emittance, and ion energy spread.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Improving efficiency of negative ion production in ion source with saddle antenna

Extraction of negative ions from a saddle antenna radio-frequency surface plasma source is considered. Several versions of new plasma generators with different antennas and magnetic field configurations were tested in the smal Oak Ridge National Laboratory Spallation Neutron Source Test Stand. The efficiency of positive ion generation in plasma has been improved to 200 mA/cm{sup 2} kW from 2.5 mA/cm{sup 2} kW. A small oven was developed for cesiation by cesium compounds and alloy decomposition. After cesiation, a current of negative ions to the collector was increased from 1 mA to 10 mA with 1.5 kW RF power in the plasma and longitudinal magnetic field B{sub l} ∼ 250 G. The specific efficiency of H{sup −} production was increased to 20 mA/cm{sup 2} kW from 2.5 mA/cm{sup 2} kW.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

First experimental results on the IShTAR testbed

IShTAR (Ion cyclotron Sheath Test ARrangement) is a linear magnetized plasma test facility dedicated to the investigation of RF wave/plasma interaction [1] in the Ion Cyclotron Range of Frequencies (ICRF). It provides a better accessibility for the instrumentation than tokamaks while being representative of the neighboring region of the wave emitter. It is equipped with a magnetized plasma source (1 m long, 0.4 m diameter) powered by a helical antenna up to 3 kW at 11 MHz. We present the results of the first analysis of the plasma characteristics (plasma density, electron temperature) in function of the operating parameters (injected power, neutral pressure and magnetic field) as measured with fixed and movable Langmuir probes, spectrometer and cameras. The plasma is presently produced only by the helical antenna (no ICRF). We show that the plasma exists in three regime depending on the power level: the first two ones are stable and separated by a jump in density; a first spatial profile of the plasma density has been established for these modes; The third mode is unstable, characterized by strong oscillations of the plasma tube position.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Beam dynamics study of a 30 MeV electron linear accelerator to drive a neutron source

An experimental neutron facility based on 32 MeV/18.47 kW electron linac has been studied by means of PARMELA simulation code. Beam dynamics study for a traveling wave constant gradient electron accelerator is carried out to reach the preferential operation parameters (E = 30 MeV, P = 18 kW, dE/E < 12.47% for 99% particles). The whole linac comprises mainly E-gun, pre-buncher, buncher, and 2 accelerating columns. A disk-loaded, on-axis-coupled, 2π/3-mode type accelerating rf cavity is considered for this linac. After numerous optimizations of linac parameters, 32 MeV beam energy is obtained at the end of the linac. As high electron energy is required to produce acceptable neutron flux. The final neutron flux is estimated to be 5 × 10{sup 11} n/cm{sup 2}/s/mA. Future development will be the real design of a 30 MeV electron linac based on S band traveling wave.

43 PARTICLE ACCELERATORS↗