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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Progress in the development of an H{sup −} ion source for cyclotrons

A multi-cusp DC H{sup −} ion source has been developed for cyclotrons in medical use. Beam optics of the H{sup −} ion beam is studied using a 2D beam trajectory code. The simulation results are compared with the experimental results obtained in the Mark I source, which has produced up to 16 mA H{sup −} ion beams. The optimum extraction voltages show good agreement between the calculation and the experimental results. A new ion source, Mark II source, is designed to achieve the next goal of producing an H{sup −} beam of 20 mA. The magnetic field configurations and the plasma electrode design are optimized for Cs-seeded operation. Primary electron trajectory simulation shows that primary electrons are confined well and the magnetic filter prevents the primary electrons from entering into the extraction region.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

The FNAL injector upgrade

The present FNAL H{sup -} injector has been operational since the 1970s and consists of two magnetron H{sup -} sources and two 750 keV Cockcroft-Walton Accelerators. In the upgrade, both slit-type magnetron sources will be replaced with circular aperture sources, and the Cockcroft-Waltons with a 200 MHz RFQ (radio frequency quadrupole). Operational experience at BNL (Brookhaven National Laboratory) has shown that the upgraded source and RFQ will be more reliable, improve beam quality and require less manpower than the present system. The present FNAL (Fermi National Accelerator Laboratory) injector has been operational since 1978 and has been a reliable source of H{sup -} beams for the Fermilab program. At present there are two Cockcroft-Walton injectors, each with a magnetron H{sup -} source with a slit aperture. With these two sources in operation, the injector has a reliability of better than 97%. However, issues with maintenance, equipment obsolescence, increased beam quality demands and retirement of critical personnel, have made it more difficult for the continued reliable running of the H{sup -} injector. The recent past has also seen an increase in both downtime and source output issues. With these problems coming to the forefront, a new 750 keV injector is being built to replace the present system. The new system will be similar to the one at BNL (Brookhaven National Laboratory) that has a similar magnetron source with a round aperture and a 200MHz RFQ. This combination has been shown to operate extremely reliably.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Power efficiency improvements with the radio frequency H{sup −} ion source

CW 13.56 MHz radio frequency-driven H{sup −} ion source is under development at the University of Jyväskylä for replacing an existing filament-driven ion source at the MCC30/15 cyclotron. Previously, production of 1 mA H{sup −} beam, which is the target intensity of the ion source, has been reported at 3 kW of RF power. The original ion source front plate with an adjustable electromagnet based filter field has been replaced with a new front plate with permanent magnet filter field. The new structure is more open and enables a higher flux of ro-vibrationally excited molecules towards the plasma electrode and provides a better control of the potential near the extraction due to a stronger separation of the main plasma from the plasma electrode. While the original system provided better control over the e{sup −}/H{sup −} ratio, the new configuration has led to a higher production efficiency of 1 mA H{sup −} at 1.75 kW RF power. The latest results and upgrade plans are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

A general solution-chemistry route to the synthesis LiMPO{sub 4} (M=Mn, Fe, and Co) nanocrystals with [010] orientation for lithium ion batteries

A general and efficient solvothermal strategy has been developed for the preparation of lithium transition metal phosphate microstructures (LiMnPO{sub 4}, LiFePO{sub 4}, and LiCoPO{sub 4}), employing ethanol as the solvent, LiI as the Li source, metal salts as the M sources, H{sub 3}PO{sub 4} as the phosphorus source, and poly(vinyl pyrrolidone) (PVP) as the carbon source and template. This route features low cost, environmental benign, and one-step process for the cathode material production of Li-ion batteries without any complicated experimental setups and sophisticated operations. The as-synthesized LiMPO{sub 4} microstructures exhibit unique, well-shaped and favorable structures, which are self-assembled from microplates or microrods. The b axis is the preferred crystal growth orientation of the products, resulting in a shorter lithium ion diffusion path. The LiFePO{sub 4} microstructures show an excellent cycling stability without capacity fading up to 50 cycles when they are used as a cathode material in lithium-ion batteries. - Graphical abstract: A general and efficient solvothermal strategy has been developed for the preparation of lithium transition metal phosphate microstructures under solvothermal conditions in the presence of PVP. Highlights: > A general and efficient solvothermal strategy has been developed for the preparation of LiMPO{sub 4} microstructures. > This route features low cost, environmental benign, and one-step process. > The LiMPO{sub 4} microstructures exhibit unique, well-shaped, and favorable structures. > The LiFePO{sub 4} microstructures show an excellent cycling stability up to 50 cycles as a cathode material of lithium-ion batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Research and development of H{sup -} ion source and low energy beam transport for a kaon-neutrino factory

A baseline H{sup -} ion source and low energy beam transport (LEBT) system have been identified for Project X. The filament-discharge H{sup -} ion source has been fabricated by D-Pace, Inc. and is now in operation at LBNL. The source is capable of delivering over 10 mA of H{sup -} beam in cw operation with normalized 4 rms emittances less than 0.7 {pi} mm mrad. A two-solenoid magnetic lens LEBT system has been design. The design has been validated with simulations of beam transport for 5 mA 30 keV H{sup -} beams using various simulation codes.

43 PARTICLE ACCELERATORS↗
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 OSTI2012

STAR FORMATION ACTIVITY IN THE GALACTIC H II REGION Sh2-297

We present a multiwavelength study of the Galactic H II region Sh2-297, located in the Canis Major OB1 complex. Optical spectroscopic observations are used to constrain the spectral type of ionizing star HD 53623 as B0V. The classical nature of this H II region is affirmed by the low values of electron density and emission measure, which are calculated to be 756 cm{sup -3} and 9.15 Multiplication-Sign 10{sup 5} cm{sup -6} pc using the radio continuum observations at 610 and 1280 MHz, and Very Large Array archival data at 1420 MHz. To understand local star formation, we identified the young stellar object (YSO) candidates in a region of area {approx}7.'5 Multiplication-Sign 7.'5 centered on Sh2-297 using grism slitless spectroscopy (to identify the H{alpha} emission line stars), and near infrared (NIR) observations. NIR YSO candidates are further classified into various evolutionary stages using color-color and color-magnitude (CM) diagrams, giving 50 red sources (H - K > 0.6) and 26 Class II-like sources. The mass and age range of the YSOs are estimated to be {approx}0.1-2 M {sub Sun} and 0.5-2 Myr using optical (V/V-I) and NIR (J/J-H) CM diagrams. The mean age of the YSOs is found to be {approx}1 Myr, which is of the order of dynamical age of 1.07 Myr of the H II region. Using the estimated range of visual extinction (1.1-25 mag) from literature and NIR data for the region, spectral energy distribution models have been implemented for selected YSOs which show masses and ages to be consistent with estimated values. The spatial distribution of YSOs shows an evolutionary sequence, suggesting triggered star formation in the region. The star formation seems to have propagated from the ionizing star toward the cold dark cloud LDN1657A located west of Sh2-297.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Plasma ignition and steady state simulations of the Linac4 H{sup −} ion source

The RF heating of the plasma in the Linac4 H{sup −} ion source has been simulated using a particle-in-cell Monte Carlo collision method. This model is applied to investigate the plasma formation starting from an initial low electron density of 10{sup 12} m{sup −3} and its stabilization at 10{sup 18} m{sup −3}. The plasma discharge at low electron density is driven by the capacitive coupling with the electric field generated by the antenna, and as the electron density increases the capacitive electric field is shielded by the plasma and induction drives the plasma heating process. Plasma properties such as e{sup −}/ion densities and energies, sheath formation, and shielding effect are presented and provide insight to the plasma properties of the hydrogen plasma.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Simulation of space charge compensation in a multibeamlet negative ion beam

Ion beam space charge compensation occurs by cumulating in the beam potential well charges having opposite polarity, usually generated by collisional processes. In this paper we investigate the case of a H{sup −} ion beam drift, in a bi-dimensional approximation of the NIO1 (Negative Ion Optimization phase 1) negative ion source. H{sup −} beam ion transport and plasma formation are studied via particle-in-cell simulations. Differential cross sections are sampled to determine the velocity distribution of secondary particles generated by ionization of the residual gas (electrons and slow H{sub 2}{sup +} ions) or by stripping of the beam ions (electrons, H, and H{sup +}). The simulations include three beamlets of a horizontal section, so that multibeamlet space charge and secondary particle diffusion between separate generation regions are considered, and include a repeller grid biased at various potentials. Results show that after the beam space charge is effectively screened by the secondary plasma in about 3 μs (in agreement with theoretical expectations), a plasma grows across the beamlets with a characteristic time three times longer, and a slight overcompensation of the electric potential is verified as expected in the case of negative ions.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Rod-filter-field optimization of the J-PARC RF-driven H{sup −} ion source

In order to satisfy the Japan Proton Accelerator Research Complex (J-PARC) second-stage requirements of an H{sup −} ion beam of 60mA within normalized emittances of 1.5πmm•mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500μs×25Hz) and a life-time of longer than 1month, the J-PARC cesiated RF-driven H{sup −} ion source was developed by using an internal-antenna developed at the Spallation Neutron Source (SNS). Although rod-filter-field (RFF) is indispensable and one of the most beam performance dominative parameters for the RF-driven H{sup −} ion source with the internal-antenna, the procedure to optimize it is not established. In order to optimize the RFF and establish the procedure, the beam performances of the J-PARC source with various types of rod-filter-magnets (RFMs) were measured. By changing RFM’s gap length and gap number inside of the region projecting the antenna inner-diameter along the beam axis, the dependence of the H{sup −} ion beam intensity on the net 2MHz-RF power was optimized. Furthermore, the fine-tuning of RFM’s cross-section (magnetmotive force) was indispensable for easy operation with the temperature (T{sub PE}) of the plasma electrode (PE) lower than 70°C, which minimizes the transverse emittances. The 5% reduction of RFM’s cross-section decreased the time-constant to recover the cesium effects after an slightly excessive cesiation on the PE from several 10 minutes to several minutes for T{sub PE} around 60°C.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

FORMALDEHYDE SILHOUETTES AGAINST THE COSMIC MICROWAVE BACKGROUND: A MASS-LIMITED, DISTANCE-INDEPENDENT, EXTINCTION-FREE TRACER OF STAR FORMATION ACROSS THE EPOCH OF GALAXY EVOLUTION

We examine the absorption of cosmic microwave background (CMB) photons by formaldehyde (H{sub 2}CO) over cosmic time. The K-doublet rotational transitions of H{sub 2}CO become 'refrigerated'-their excitation temperatures are driven below the CMB temperature-via collisional pumping by molecular hydrogen (H{sub 2}). 'Anti-inverted' H{sub 2}CO line ratios thus provide an accurate measurement of the H{sub 2} density in molecular clouds. Using a radiative transfer model, we demonstrate that H{sub 2}CO centimeter wavelength line excitation and detectability are nearly independent of redshift or gas kinetic temperature. Since the H{sub 2}CO K-doublet lines absorb CMB light, and since the CMB lies behind every galaxy and provides an exceptionally uniform extended illumination source, H{sub 2}CO is a distance-independent, extinction-free molecular gas mass-limited tracer of dense gas in galaxies. A Formaldehyde Deep Field could map the history of cosmic star formation in a uniquely unbiased fashion and may be possible with large bandwidth wide-field radio interferometers whereby the silhouettes of star-forming galaxies would be detected across the epoch of galaxy evolution. We also examine the possibility that H{sub 2}CO lines may provide a standardizable galaxy ruler for cosmology similar to the Sunyaev-Zel'dovich effect in galaxy clusters but applicable to much higher redshifts and larger samples. Finally, we explore how anti-inverted meter-wave H{sub 2}CO lines in galaxies during the peak of cosmic star formation may contaminate H I 21 cm tomography of the Epoch of Reionization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The mechanical design and simulation of a scaled H{sup −} Penning ion source

The existing ISIS Penning H{sup −} source is unable to produce the beam parameters required for the front end test stand and so a new, high duty factor, high brightness scaled source is being developed. This paper details first the development of an electrically biased aperture plate for the existing ISIS source and second, the design, simulation, and development of a prototype scaled source.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Size scaling of negative hydrogen ion sources for fusion

The RF-driven negative hydrogen ion source (H{sup −}, D{sup −}) for the international fusion experiment ITER has a width of 0.9 m and a height of 1.9 m and is based on a ⅛ scale prototype source being in operation at the IPP test facilities BATMAN and MANITU for many years. Among the challenges to meet the required parameters in a caesiated source at a source pressure of 0.3 Pa or less is the challenge in size scaling of a factor of eight. As an intermediate step a ½ scale ITER source went into operation at the IPP test facility ELISE with the first plasma in February 2013. The experience and results gained so far at ELISE allowed a size scaling study from the prototype source towards the ITER relevant size at ELISE, in which operational issues, physical aspects and the source performance is addressed, highlighting differences as well as similarities. The most ITER relevant results are: low pressure operation down to 0.2 Pa is possible without problems; the magnetic filter field created by a current in the plasma grid is sufficient to reduce the electron temperature below the target value of 1 eV and to reduce together with the bias applied between the differently shaped bias plate and the plasma grid the amount of co-extracted electrons. An asymmetry of the co-extracted electron currents in the two grid segments is measured, varying strongly with filter field and bias. Contrary to the prototype source, a dedicated plasma drift in vertical direction is not observed. As in the prototype source, the performance in deuterium is limited by the amount of co-extracted electrons in short as well as in long pulse operation. Caesium conditioning is much harder in deuterium than in hydrogen for which fast and reproducible conditioning is achieved. First estimates reveal a caesium consumption comparable to the one in the prototype source despite the large size.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Ring-opening and hydrodenitrogenation of indole under hydrothermal conditions over Ni, Pt, Ru, and Ni-Ru bimetallic catalysts

Here, the activity and selectivity of activated-carbon-supported Ni, Pt, Ru, and Ni-Ru bimetallic catalysts was examined for hydrothermal denitrogenation of indole. The molar yield of pyrrole ring-opening compounds, without an added hydrogen source, are in the order: Ni < Pt < Ni 90 Ru 10 < Ni 75 Ru 25 < Ni 50 Ru 50 ~ Ni 25 Ru 75 ~ Ru. Ru-containing catalysts facilitated production of hydrocarbons (hydrodenitrogenation (HDN) products) when used with added formic acid (hydrogen source). We elucidated catalytic hydrothermal HDN pathways for indole based on the product distributions and the variation of their yields with time. Hydrogenation of indole to indoline is the primary pathway and ring-opening of indoline to form alkyl anilines is faster than forming HDN products (alkyl benzenes). DFT calculations confirmed experimental activity trends, showing Ru is more active than Ni for indole ring opening and for o-toluidine deamination. If no hydrogen source is present, directly breaking the N-C bond in the pyrrole ring is more favorable than breaking the C-N bond with an aromatic carbon. If a H source is provided, the pyrrole ring hydrogenates first, forming indoline, followed by cleavage of the C-N bond.

42 ENGINEERING↗
DOE OSTI2017

Effect of the SiO 2 interlayer properties with solid-source hydrogenation on passivated contact performance and surface passivation

We investigate how SiO x oxide interlayers prepared by different techniques (chemical, thermal) in combination with hydrogen released from an ALD Al 2 O 3 source layer govern passivation in 1) passivated contacts based on doped poly-Si layers and tunneling SiO 2 , and 2) wafer surface passivation by Al 2 O 3 . Profiles of O and H in these structures with engineered, buried SiOx interlayers were measured by Time-of-Flight SIMS (TOF-SIMS) at nanometer resolution. Passivated contacts perform best with thermally oxidized SiOx, while chemical SiO x causes poly-Si film blistering and performance degradation. ALD Al 2 O 3 acts as passivating H source, significantly improving B-doped and intrinsic poly-Si contacts for IBC cells. Fast-diffusing hydrogen from the Al 2 O 3 source layer appears to penetrate Si wafer thickness, improving the passivation of structures at the opposite side. In contrast to the passivated contacts, chemical SiOx interlayer promotes wafer surface passivation by ALD Al 2 O 3 , while similarly thin thermal SiO 2 suppresses passivation and built-in charge.

14 SOLAR ENERGY↗
DOE OSTI2016

Balmer-α spectrum measurements of the LHD one-third ion source

Wavelength spectra of Balmer-α light from plasmas in the extraction region of the Large Helical Device-R&D negative ion source, or the LHD one-third ion source have exhibited a blue shift as a negative bias voltage was applied to the plasma grid. The blue shift increased as the negative bias voltage with respect to the local plasma potential was increased. The measured spectra were compared with the velocity distributions of surface reflected hydrogen atoms calculated by atomic collisions in amorphous target code. The arc power and the source H{sub 2} pressure also affected the shift and broadening in the observed Balmer-α spectra. The possibility of identifying the negative hydrogen ions produced at the low work function plasma grid surface by high resolution spectroscopy is discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Pre-conditioning procedure suitable for internal-RF-antenna of J-PARC RF-driven H{sup −} ion source

The Japan Proton Accelerator Research Complex (J-PARC) cesiated RF-driven H{sup −} ion source has been successfully operated for about 1 yr. By the world brightest level beam, the J-PARC design beam power of 1 MW was successfully demonstrated. Although no internal-RF-antenna failure, except for the once caused by an excess cesium due to a misoperation, occurred in the operation, many antennas failed in pre-conditionings for the first hundred days. The antenna failure rate was drastically decreased by using an antenna with coating thicker than a standard value and the pre-conditioning procedure repeating 15 min 25 kW RF-power operation and impurity-gas evacuation a few times, before the full power (50 kW) operation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Fine-tuning to minimize emittances of J-PARC RF-driven H{sup −} ion source

The Japan Proton Accelerator Research Complex (J-PARC) cesiated RF-driven H{sup −} ion source has been successfully operated for about one year. By the world’s brightest level beam, the J-PARC design beam power of 1 MW was successfully demonstrated. In order to minimize the transverse emittances, the rod-filter-field (RFF) was optimized by changing the triple-gap-lengths of each of pairing five piece rod-filter-magnets. The larger emittance degradation seems to be caused by impurity-gases than the RFF. The smaller beam-hole-diameter of the extraction electrode caused the more than expected improvements on not only the emittances but also the peak beam intensity.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗