Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “rf source”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Multi-beamlet investigation of the deflection compensation methods of SPIDER beamlets

SPIDER (Source for Production of Ions of Deuterium Extracted from a Rf plasma) is an ion source test bed designed to extract and accelerate a negative ion current up to 40 A and 100 kV whose first beam is expected by the end of 2016. Two main effects perturb beamlet optics during the acceleration stage: space charge repulsion and the deflection induced by the permanent magnets (called co-extracted electron suppression magnets) embedded in the EG. The purpose of this work is to evaluate and compare benefits, collateral effects, and limitations of electrical and magnetic compensation methods for beamlet deflection. The study of these methods has been carried out by means of numerical modeling tools: multi-beamlet simulations have been performed for the first time.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Plasma acceleration using a radio frequency self-bias effect

In this work plasma acceleration using a RF self-bias effect is experimentally studied. The experiments are conducted using a novel plasma accelerator system, called Neptune, consisting of an inductively coupled plasma source and a RF-biased set of grids. The plasma accelerator can operate in a steady state mode, producing a plasma flow with separately controlled plasma flux and velocity without any magnetic configuration. The operating pressure at the source output is as low as 0.2 mTorr and can further be decreased. The ion and electron flows are investigated by measuring the ion and electron energy distribution functions both space resolved and with different orientations with respect to the flow direction. It is found that the flow of electrons from the source is highly anisotropic and directed along the ion flow and this global flow of accelerated plasma is well localized in the plasma transport chamber. The maximum flux is about 7.5·10{sup 15} ions s{sup −1} m{sup −2} (at standard conditions) on the axis and decreasing to almost zero at a radial distances of more than 15 cm from the flow axis. Varying the RF acceleration voltage in the range 20–350 V, the plasma flow velocity can be changed between 10 and 35 km/s. The system is prospective for different technology such as space propulsion and surface modification and also interesting for fundamental studies for space-related plasma simulations and investigation of the dynamo effect using accelerated rotating plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2016

Global and Regional Radiative Forcing from 20 Reductions in BC, OC and SO4 an HTAP2 Multi-Model Study

In the Hemispheric Transport of Air Pollution Phase 2 (HTAP2) exercise, a range of global atmospheric general circulation and chemical transport models performed coordinated perturbation experiments with 20% reductions in emissions of anthropogenic aerosols, or aerosol precursors, in a number of source regions. Here, we compare the resulting changes in the atmospheric load and vertically resolved profiles of black carbon (BC), organic aerosols (OA) and sulfate (SO4/ from 10 models that include treatment of aerosols. We use a set of temporally, horizontally and vertically resolved profiles of aerosol forcing efficiency (AFE) to estimate the impact of emission changes in six major source regions on global radiative forcing (RF) pertaining to the direct aerosol effect, finding values between. 51.9 and 210.8mW/sq m/Tg for BC, between -2.4 and -17.9mW/sq m/Tg for OA and between -3.6 and -10.3W/sq m/Tg for SO4. In most cases, the local influence dominates, but results show that mitigations in south and east Asia have substantial impacts on the radiative budget in all investigated receptor regions, especially for BC. In Russia and the Middle East, more than 80 % of the forcing for BC and OA is due to extra-regional emission reductions. Similarly, for North America, BC emissions control in east Asia is found to be more important than domestic mitigations, which is consistent with previous findings. Comparing fully resolved RF calculations to RF estimates based on vertically averaged AFE profiles allows us to quantify the importance of vertical resolution to RF estimates. We find that locally in the source regions, a 20% emission reduction strengthens the radiative forcing associated with SO4 by 25% when including the vertical dimension, as the AFE for SO4 is strongest near the surface. Conversely, the local RF from BC weakens by 37% since BC AFE is low close to the ground. The fraction of BC direct effect forcing attributable to intercontinental transport, on the other hand, is enhanced by one-third when accounting for the vertical aspect, because long-range transport primarily leads to aerosol changes at high altitudes, where the BC AFE is strong. While the surface temperature response may vary with the altitude of aerosol change, the analysis in the present study is not extended to estimates of temperature or precipitation changes.

profiles of aerosol forcing efficiency (AFE)↗
DOE OSTI2025

Erosion of high-Z refractory coatings for helicon plasma source window

Proto-MPEX (Materials Plasma Exposure eXperiment), a linear plasma device (LPD), using a high power radio frequency (RF) (⩾100 kW, 13.56 MHz) helicon plasma source, has suffered RF sheath-induced window erosion. The sputtered impurities from the window surface transport toward the downstream target affecting plasma-material interaction studies. The rectified sheath voltage formed was high enough to cause window erosion by light ions due to its low-Z components (e.g. Si 3 N 4 and AlN). Hence, we are proposing impurity mitigation strategies, which involve the application of a Faraday screen to lower the rectified sheath voltage and the application of high-Z refractory coatings on the existing window plasma-facing surface. In this work, we report the erosion of two different coatings, i.e., tantalum oxide (Ta 2 O 5 ) and hafnium oxide (HfO 2 ) on a silicon nitride (Si 3 N 4 ) window material under conditions of low-energy deuterium (D) ion impact, well below the Ta 2 O 5 sputtering energy threshold (i.e. 250 eV). The test samples were RF-biased and exposed to a high D-ion fluence (∼10 26 m −2 ) in Plasma Interaction with Surface Component Experimental Station (PISCES-A) LPD. The experimentally measured sputtering yields of the high-Z refractory coatings below the sputtering energy threshold of Ta 2 O 5 indicate an increased erosion due to the plasma impurities, especially due to oxygen. Improving the vacuum level could reduce the oxygen impurities and increase the lifespan of the coated helicon window for plasma operation. Post-surface analysis indicates no preferential erosion of oxygen or enrichment of the high-Z surface component. This is likely due to an effective energy transfer from the impurity ion for sputtering of the high-Z component in the coating. With the reduced rectified sheath voltage at the window surface and improved vacuum conditions, the proposed high-Z refractory coatings offer a promising solution for reducing window erosion in future MPEX plasma operations at ORNL.

RF bias↗
DOE OSTI2021

Ion heating in the PISCES-RF liquid-cooled high-power, steady-state, helicon plasma device

Radio frequency (RF) driven helicon plasma sources are commonly used for their ability to produce high-density argon plasmas ( n > 10 19 m -3 ) at relatively moderate powers (typical RF power < 2 kW). Typical electron temperatures are <10 eV and typical ion temperatures are <0.6 eV. A newly designed helicon antenna assembly (with concentric, double-layered, fully liquid-cooled RF-transparent windows) operates in steady-state at RF powers up to 10 kW. We report on the dependence of argon plasma density, electron temperature and ion temperature on RF power. At 10 kW, ion temperatures >2 eV in argon plasmas are measured with laser induced fluorescence, which is consistent with a simple volume averaged 0D power balance model. 1D Monte Carlo simulations of the neutral density profile for these plasma conditions show strong neutral depletion near the core and predict neutral temperatures well above room temperatures. The plasmas created in this high-power helicon source (when light ions are employed) are ideally suited for fusion divertor plasma-material interaction studies and negative ion production for neutral beams.

Physics↗
DOE OSTI2012

Wave frequency dependence of H{sup -} ion production and extraction in a transformer coupled plasma H{sup -} ion source at SNU

The effect of rf wave frequencies on the production of H{sup -} ion is investigated in a transformer coupled plasma H{sup -} ion source at Seoul National University. A Langmuir probe is installed to measure the plasma density and temperature, and these plasma parameters are correlated to the extracted H{sup -} beam currents at various frequencies. The Langmuir probe is also used to measure the density of H{sup -} ions at the ion source by generating photodetachment with an Nd:YAG laser. The extracted H{sup -} currents decrease to a minimum value until 13 MHz and then, increase as the driving frequency increases from 13 MHz while the relative H{sup -} population measured by photodetachment monotonically decreases as the driving rf frequency increases from 11 MHz to 15 MHz. A potential well formed at the extraction region at high frequencies of more than 13 MHz is considered responsible for the increased H{sup -} beam extraction even with a lower photodetachment signal. The variation in the driving rf frequency not only affects the density and temperature of the plasma but also modifies the plasma potential with the existence of a filtering magnetic field and consequently, influences the extracted H{sup -} current through the extraction as well as formation of H{sup -} ions.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Operation and development status of the J-PARC ion source

A cesium-free H{sup −} ion source driven with a LaB{sub 6} filament is being operated at the Japan Proton Accelerator Research Complex (J-PARC) without any serious trouble since the restoration from the March 2011 earthquake. The H{sup −} ion current from the ion source is routinely restricted approximately 19 mA for the lifetime of the filament. In order to increase the beam power at the linac beam operation (January to February 2013), the beam current from the ion source was increased to 22 mA. At this operation, the lifetime of the filament was estimated by the reduction in the filament current. According to the steep reduction in the filament current, the break of the filament was predicted. Although the filament has broken after approximately 10 h from the steep current reduction, the beam operation was restarted approximately 8 h later by the preparation for the exchange of new filament. At the study time for the 3 GeV rapid cycling synchrotron (April 2013), the ion source was operated at approximately 30 mA for 8 days. As a part of the beam current upgrade plan for the J-PARC, the front end test stand consisting of the ion source and the radio frequency quadrupole is under preparation. The RF-driven H{sup −} ion source developed for the J-PARC 2nd stage requirements will be tested at this test stand.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Commissioning and Early Operation Experience of the NSLS-II Storage Ring RF System

The National Synchrotron Light Source II (NSLS-II) is a 3 GeV electron X-ray user facility commissioned in 2014. The storage ring RF system, essential for replenishing energy loss per turn of the electrons, consists of digital low level RF controllers, 310 kW CW klystron transmitters, CESR-B type superconducting cavities, as well as a supporting cryogenic system. Here we will report on RF commissioning and early operation experience of the system for beam current up to 200mA.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Developing field emission electron sources based on ultrananocrystalline diamond for accelerators

Radiofrequency (RF) electron guns work by establishing an RF electromagnetic field inside a cavity having conducting walls. Electrons from a cathode are generated in the injector and immediately become accelerated by the RF electric field, and exit the gun as a series of electron bunches. Finding simple solutions for electron injection is a long standing problem. While energies of 30-50 MeV are achievable in linear accelerators (linacs), finding an electron source able to survive under MW electric loads and provide an average current of 1-10 mA is important. Meeting these requirements would open various linac applications for industry. The natural way to simplify and integrate RF injector architectures with the electron source would be to place the source directly into the RF cavity with no need for additional heaters/lasers. Euclid TechLabs in collaboration with Argonne National Lab are prototyping a family of highly effective field emission electron sources based on a nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) platform. Determined metrics suggest that our emitters are emissive enough to meet requirements for magnetized cooling at electron-ion colliders, linac-based radioisotope production and X-ray sterilization, and others.

field emission↗
DOE OSTI2012

Recent progress on the superconducting ion source VENUS

The 28 GHz Ion Source VENUS (versatile ECR for nuclear science) is back in operation after the superconducting sextupole leads were repaired and a fourth cryocooler was added. VENUS serves as an R and D device to explore the limits of electron cyclotron resonance source performance at 28 GHz with its 10 kW gryotron and optimum magnetic fields and as an ion source to increase the capabilities of the 88-Inch Cyclotron both for nuclear physics research and applications. The development and testing of ovens and sputtering techniques cover a wide range of applications. Recent experiments on bismuth demonstrated stable operation at 300 e{mu}A of Bi{sup 31+}, which is in the intensity range of interest for high performance heavy-ion drivers such as FRIB (Facility for Rare Isotope Beams). In addition, the space radiation effects testing program at the cyclotron relies on the production of a cocktail beam with many species produced simultaneously in the ion source and this can be done with a combination of gases, sputter probes, and an oven. These capabilities are being developed with VENUS by adding a low temperature oven, sputter probes, as well as studying the RF coupling into the source.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

RF antenna helicity dependent particle heating in a helicon source

Experiments have demonstrated that ion phenomena, such as the lower hybrid resonance, play an important role in helicon source operation. Damping of the slow branch of the bounded whistler wave at the edge of a helicon source (i.e. the Trivelpiece-Gould mode) has been correlated with the creation of energetic electrons, heating of ions at the plasma edge, and anisotropic ion heating. Here we present ion velocity distribution function measurements, electron density and temperature measurements, and magnetic fluctuation measurements on both sides of an m = |1| helical antenna in a helicon source as a function of the driving frequency, magnetic field strength, and magnetic field orientation relative to the antenna helicity. Significant electron and ion heating (up to two times larger) occurs on the side of the antenna consistent with the launch of the m = +1 mode. The electron and ion heating occurs within one electron skin depth of the plasma edge, where slow wave damping is expected. The source parameters for enhanced particle heating are also consistent with lower hybrid resonance effects, which can only occur for Trivelpiece-Gould wave excitation.

wave modes↗
DOE OSTI2018

Heavy fossil hydrocarbon conversion and upgrading using radio-frequency or microwave energy

Conversion of heavy fossil hydrocarbons (HFH) to a variety of value-added chemicals and/or fuels can be enhanced using microwave (MW) and/or radio-frequency (RF) energy. Variations of reactants, process parameters, and reactor design can significantly influence the relative distribution of chemicals and fuels generated as the product. In one example, a system for flash microwave conversion of HFH includes a source concentrating microwave or RF energy in a reaction zone having a pressure greater than 0.9 atm, a continuous feed having HFH and a process gas passing through the reaction zone, a HFH-to-liquids catalyst contacting the HFH in at least the reaction zone, and dielectric discharges within the reaction zone. The HFH and the catalyst have a residence time in the reaction zone of less than 30 seconds. In some instances, a plasma can form in or near the reaction zone.

Strohm, James J.↗
NASA NTRSDate not supplied

3D Lightning Geolocation With the CubeSpark Constellation

The new CubeSpark mission concept is being developed as a constellation of up to six satellites for high-resolution 3D lightning mapping. Each satellite in low-Earth orbit (LEO) will use optical and radio frequency (RF) sensors to geolocate individual sources from lightning flashes. The purpose of this study is to evaluate the potential accuracies and feasibilities of RF-based geolocation methods. This is done using a robust simulation framework to accurately depict the ionosphere’s effect on propagating RF signals, using their arrival times at each station to reconstruct source locations. We identified the primary sources of error as geometric, ionospheric, and instrumental. These are each analyzed to determine their quantitative effect on geolocation uncertainty. CubeSpark’s science objectives include mapping thundercloud charge regions and even individual flash channel structure for applications across a wide range of fields from climatology to hydrology. These applications require geolocation accuracy better than 1-2 km in each dimension, thus special care must be taken to optimize constellation design, minimize the main sources of error, and maximize CubeSpark’s potential. The algorithms developed in this study show promising results, with large regions having both horizontal and vertical uncertainties less than 1 km. After the removal of the Lightning Imaging Sensor from the International Space Station, an observational gap has been left for lightning observers from LEO. It therefore becomes increasingly vital to evaluate and improve on the current state of lightning mapping to prepare for the next generation of 3D lightning geolocation.

lightning↗
NASA NTRSDate not supplied

3D Lightning Geolocation with the CubeSpark Constellation

The new CubeSpark mission concept is being developed as a constellation of up to six satellites for high-resolution 3D lightning mapping. Each satellite in low-Earth orbit (LEO) will use optical and radio frequency (RF) sensors to geolocate individual sources from lightning flashes. The purpose of this study is to evaluate the potential accuracies and feasibilities of RF-based geolocation methods. This is done using a robust simulation framework to accurately depict the ionosphere’s effect on propagating RF signals, using their arrival times at each station to reconstruct source locations. We identified the primary sources of error as geometric, ionospheric, and instrumental. These are each analyzed to determine their quantitative effect on geolocation uncertainty. CubeSpark’s science objectives include mapping thundercloud charge regions and even individual flash channel structure for applications across a wide range of fields from climatology to hydrology. These applications require geolocation accuracy better than 1-2 km in each dimension, thus special care must be taken to optimize constellation design, minimize the main sources of error, and maximize CubeSpark’s potential. The algorithms developed in this study show promising results, with large regions having both horizontal and vertical uncertainties less than 1 km. After the removal of the Lightning Imaging Sensor from the International Space Station, an observational gap has been left for lightning observers from LEO. It therefore becomes increasingly vital to evaluate and improve on the current state of lightning mapping to prepare for the next generation of 3D lightning geolocation.

lightning↗
DOE OSTI2022

Challenges of Future Accelerators for Particle Physics Research

For over half a century, high-energy particle accelerators have been a major enabling technology for particle and nuclear physics research as well as sources of X-rays for photon science research in material science, chemistry and biology. Particle accelerators for energy and intensity Frontier research in particle and nuclear physics continuously push the accelerator community to invent ways to increase the energy and improve the performance of accelerators, reduce their cost, and make them more power efficient. The accelerator community has demonstrated imagination and creativity in developing a plethora of future accelerator ideas and proposals. The technical maturity of the proposed facilities ranges from shovel-ready to those that are still largely conceptual. At this time, over 100 contributed papers have been submitted to the Accelerator Frontier of the US particle physics decadal community planning exercise known as Snowmass’2021. These papers cover a broad spectrum of topics: beam physics and accelerator education, accelerators for neutrinos, colliders for Electroweak/Higgs studies and multi-TeV energies, accelerators for Physics Beyond Colliders and rare processes, advanced accelerator concepts, and accelerator technology for Radio Frequency cavities (RF), magnets, targets and sources. This paper provides an overview of the present state of accelerators for particle physics and gives a brief description of some of the major facilities that have been proposed, their perceived advantages and some of the remaining challenges.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Radio-frequency sheath voltages and slow wave electric field spatial structure

We investigate theoretically how sheath radio-frequency (RF) oscillations relate to the spatial structure of the RF parallel electric field emitted by Ion Cyclotron (IC) wave launchers, using a simple model of Slow Wave (SW) evanescence coupled with Direct Current (DC) plasma biasing via sheath boundary conditions in a plasma-filled 2-dimensional (parallel, radial) rectangle. Within a “wide sheaths” asymptotic regime, valid for large-amplitude near RF fields, our model becomes partly linear: the sheath oscillating voltage at open field line boundaries is a linear combination of elementary contributions by every source point of the radiated RF field map. These individual contributions are all the more intense as the SW emission point is toroidally nearer to the sheath walls. A limit formula is given for a source infinitely close to the sheaths. The decay of sheath RF voltages with the sheath/source parallel distance is quantified as a function of two characteristic SW evanescence lengths. Decay lengths are smaller than antenna parallel extensions. The sheath RF voltages at an IC antenna side limiter are therefore mainly sensitive to SW emission near this limiter, as recent observations suggest. Toroidal proximity effects could also explain why sheath oscillations persist with antisymmetric strap toroidal phasing, despite the parallel anti-symmetry of the radiated field map. They could also justify current attempts at reducing the RF fields induced near antenna boxes to attenuate sheath oscillations in their vicinity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗