A5046564349- Particle accelerators and beam dynamics
- Muon and positron interactions and applications
- Plasma Diagnostics and Applications
- Atomic and Molecular Physics
- Magnetic confinement fusion research
- Particle Accelerators and Free-Electron Lasers
- Nuclear Physics and Applications
- Particle Detector Development and Performance
- Nuclear physics research studies
- Gyrotron and Vacuum Electronics Research
- Superconducting Materials and Applications
- Neutrino Physics Research
- X-ray Spectroscopy and Fluorescence Analysis
- Astronomical and nuclear sciences
- Advanced biosensing and bioanalysis techniques
- Nuclear reactor physics and engineering
- Radiation Detection and Scintillator Technologies
- Radioactive Decay and Measurement Techniques
- Chemical Reactions and Isotopes
- Ion-surface interactions and analysis
- Radiation Effects in Electronics
- Physics of Superconductivity and Magnetism
- Particle physics theoretical and experimental studies
- Inorganic Fluorides and Related Compounds
- Cold Fusion and Nuclear Reactions
Spallation Neutron Source
2012-2024
Oak Ridge National Laboratory
2015-2024
Thomas Jefferson National Accelerator Facility
2002
University of Fribourg
1987-1999
Nantes Université
1992
Centre National de la Recherche Scientifique
1989-1990
Laboratoire de Physique Théorique
1989
The present work extends the systematics of nuclear charge radii obtained by method muonic atoms to nuclei with 8\ensuremath{\le}Z,N\ensuremath{\le}20. accuracy measured Lyman transition energies generally \ensuremath{\le}10 eV leads a precision in model-independent differences 2--3 am for isotope shifts and 4--9 isotone shifts. Both within s-d shell behave ``anomalously'' respect heavier nuclei. However, such behavior is predicted on theoretical grounds, if mixing shells strong deformation...
The transfer of negative muons from the ground state muonic hydrogen to argon and helium has been measured in gaseous mixtures at pressures between 10 15 bars different relative concentrations. rate argon, reduced liquid-hydrogen density [${\ensuremath{\Lambda}}_{p\mathrm{Ar}}$ =1.42(4)\ifmmode\times\else\texttimes\fi{}${10}^{11}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$], agrees well with those obtained ten times higher pressures....
The muonic atom 2${\mathit{p}}_{1/2}$-1${\mathit{s}}_{1/2}$ and 2${\mathit{p}}_{3/2}$-1${\mathit{s}}_{1/2}$ transition energies were measured with an experimental accuracy of better than 20 ppm for the isotope chain $^{112,114,116,117,118,119,120,122,124}\mathrm{Sn}$. Precise values Barrett equivalent nuclear radii ${\mathit{R}}_{\mathit{k}\mathrm{\ensuremath{\alpha}}}$ their differences as well root-mean-square deduced. \ensuremath{\Delta}N=2 shifts between even Sn isotopes show a subshell...
We report on muonic Lyman-series x-ray intensities measured in gaseous argon and ${\mathrm{K}}^{+}$, ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{Na}}^{+}$, ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ the compounds KF NaCl. The analysis of their structures, including neon, shows that both spatial symmetry binding energy electrons outer shells determine angular momentum distribution captured muons. conclusions are agreement with modified model ``large mesic molecules.''
Since 2009, the Spallation Neutron Source (SNS) has been producing neutrons with ion beam powers near 1 MW, which requires extraction of ∼50 mA H− ions from source a ∼5% duty factor. The 50 are achieved after an initial dose ∼3 mg Cs and heating collar to ∼170 °C. normally persist for entire 4-week service cycles. Fundamental processes reviewed elucidate persistence SNS beams without steady feed why temperature may have be kept 170
Recent measurements of the H− beam current show that SNS is injecting about 55 mA into RFQ compared to ∼45 in 2010. Since 2010, exiting dropped from ∼40 ∼34 mA, which sufficient for 1 MW power. To minimize impact degradation, service cycle best performing source was extended 6 weeks. The only degradation fluctuations electron dump voltage towards end some cycles, a problem being investigated. Very recently, retuned, partly restored its transmission. In addition, electrostatic low-energy...
Spallation Neutron Source ramps to higher power levels that can be sustained with high availability. The goal is 1.4 MW despite a compromised radio frequency quadrupole (RFQ), which requires than design approach the nominal beam transmission. Unfortunately at RFQ often loses its thermal stability, problem apparently enhanced by losses and influxes of hydrogen. Delivering as much H(-) possible least amount hydrogen led plasma outages. root cause dense 1-ms long ∼55-kW 2-MHz pulses reflecting...
The Oak Ridge National Laboratory operates the Spallation Neutron Source, consisting of a H− ion source, 1 GeV linac and an accumulator ring. accumulated <1 μs-long, ∼35 A beam pulses are extracted from ring at 60 Hz directed onto liquid Hg target. Spalled neutrons to ∼20 world class instruments. Currently, facility routinely with ∼1.2 MW average power, which soon will be raised 1.4 MW. future upgrade second target station calls for raising power 2.8 This paper describes status two...
Fundamentally, the electron and muon transfer mechanisms are same. We report on from ground state of muonic hydrogen to neon, measured in gas mixtures ${\mathrm{H}}_{2}$+Ne ${\mathrm{H}}_{2}$+Ne+Ar. Unexpectedly, x-ray time spectra binary mixture show two components. From extracted rates, higher one agrees with an older experiment, whereas lower one, which is reproduced triple mixture, was not observed before.
The LANSCE accelerator is currently powered by a filament-driven, biased converter-type H- ion source that operates at 10%, the highest plasma duty factor for this type of source, using only ∼2.2 SCCM H2. needs to be replaced every 4 weeks, which takes up days. measured negative beam current 12-16 mA falls below desired 24 acceptance LANCSE accelerator. SNS (Spallation Neutron Source) RF-driven, injects ∼50 into 60 Hz with 6% and an availability >99.5% but requires ∼30 Up 7 A h have been...
The U.S. Spallation Neutron Source (SNS) is a state-of-the-art neutron scattering facility delivering the world's most intense pulsed beams to wide array of instruments which are used conduct investigations in many fields science and engineering. Neutrons produced by spallation liquid Hg due bombardment short (∼1µs), (∼35 A) pulses protons delivered at 60 Hz from storage ring fed high-intensity, 1 GeV H− LINAC. This has operated almost continuously since 2006, with ion source performance...
Abstract Experimental campaigns were undertaken to understand and improve the coupling efficiency of Radio frequency (RF) power into plasma in three accelerator-based ion sources. Different matching circuit mechanical engineering setups used network resistance calculated. The was then measured for a range RF frequencies input gas flows. Coupling efficiencies around 60% using RF-coils mounted external chamber. is improved 80% when coil immersed plasma, allowing closer coupling. As well as...
Recent experimental results on the muon exchange from muonic hydrogen to argon show that reaction rate is energy dependent near 0.1 eV. A atom, formed by capture in ${\mathrm{H}}_{2}$ gas at 15 bars, thermalized a few hundreds of nanoseconds. If transfer occurs before time, shown be slightly lower compared atoms [${\ensuremath{\lambda}}_{\mathrm{pAr}}$=(1.63\ifmmode\pm\else\textpm\fi{}0.09)\ifmmode\times\else\texttimes\fi{}${10}^{11}$${\mathrm{fs}}^{\mathrm{\ensuremath{-}}1}$]. As an...
Ellipsoidal deformations have been introduced in the entrance channel of asymmetric heavy-ion reactions within liquid-drop model and including nuclear proximity energy. The corresponding maximal lowering fusion barrier heights is about 10 MeV takes place for Z1Z2 approximately=750. When Z1Z2<or=650-750 with regard to two-sphere configuration, more external its width reduced. At top, a transition prolate shapes occurs due increase force effects. For Z1Z2>or=650-750, at smaller inter-nuclear...
This paper reports the development of 350 MHz superconducting cavities a spoke-loaded geometry, intended for velocity range 0.2<v/c<0.6. Two prototype single-cell have been designed, one optimised v/c=0.4, and other v/c=0.29. Construction niobium is nearly complete. Details design construction are discussed, along with results cold tests.
After acquiring several reliable spare targets, SNS ramped the beam power from 850 kW to 1.4 MW, which required an increase in H− pulse length 0.88 1.0 ms at 60 Hz. This initially produced slow 2-MHz ramp-ups and, after weeks of uninterrupted operation, it plasma outages every time was raised above ∼0.95 ms. Similar were previously observed towards end long service cycles, believed indicate that breakdown voltage high purity hydrogen started exceed induced electric fields. In 2011 RF...
The 4 GeV CEBAF accelerator at Thomas Jefferson National Accelerator Facility (Jefferson Lab) is arranged in a five-pass racetrack configuration, with two superconducting radio-frequency (SRF) linacs joined by independent magnetic transport arcs. 1497 MHz continuous electron beam composed of three interlaced variable-intensity 499 beams that can be independently directed from any the five passes to experimental halls. Beam extraction made possible system nine warm sub-harmonic separator...
The Spallation Neutron Source H− ion source is operated with a pulsed 2-MHz RF (50-60 kW) to produce the 1-ms long, ∼50 mA beams at 60 Hz. A continuous low power (∼300 W) 13.56-MHz plasma, which initially ignited H2 pressure bump, serves as starter plasma for high discharges. To reduce risk of outages lower flow rates desired improved performance following radio frequency quadrupole, matching network was characterized over broad range its two tuning capacitors. H-α line intensity and...
The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory reached 1‐MW of beam power in September 2009, and now routinely operates near for the production neutrons. This paper reviews performance, operational issues, implemented planned mitigations SNS H− ion source to support such high power‐level beams with availability. Some results from R&D activities are also briefly described.