[en] We have searched for baryon-containing radiative penguin decays in 9.7 x 10⁶ B anti B events collected at the Υ(4S) with the CLEO detector. We find no evidence for such decays, and set a 90% confidence level upper limit of B(B→X_sγX_s containing baryons)E_γ>2.0 GeV<3.8 x 10^-5. Corrections to CLEOs recent b→sγ measurement due to B→X_s(baryon)γ decays are well within the errors quoted. A search for semileptonic decays of B mesons to e anti p inclusive final states in the same data sample found no evidence for such decays and set an upper limit of B(B→anti pe^- anti ν_eX)<5.9 x 10^-4. These limits suggest that external W emission is not the dominant source of baryon production in B decay. (orig.)

[en] A Quadrupole Mass Spectrometer (QMS) based cw-RIMS (continuous wave-Resonance Ionisation Mass Spectroscopy) set up is being developed for trace level analysis of uranium (U) in environmental samples. For that a resistively heated effusive atomic vapor source has been developed indigenously in L and PTD, BARC. The design and working principle of the source were reported earlier. During the characterization of RIMS setup, it has been observed that a significant fraction of thermal ions generated in vapor source due to surface ionization in hot cavity, reach the laser-atom interaction region along with the neutral vapors and it increases the background noise in channeltron detector. So an effort has been made to suppress the thermal ions from the vapors. At interaction region, to form a collimated atomic beam, the vapors pass through a circular aperture of ion optics assembly in the QMS. The aperture is biased at -60 V to control and accelerate the electrons emitted from the filament for characterization of QMS setup by electron impact ionization. Three different assemblies were constructed where two circular apertures of ID- 8 mm and 4 mm and one tubular aperture (ID-4mm, OD-6mm, L-3mm) were used, respectively

[en] This study aims to determine how incorporating damages into energy costs would impact the US energy system. Damages from health impacting pollutants (NO_x, SO_2, particulate matter - PM, and volatile organic compounds - VOCs) as well as greenhouse gases (GHGs) are accounted for by applying emissions fees equal to estimated external damages associated with life-cycle emissions. We determine that in a least-cost framework, fees reduce emissions, including those not targeted by the fees. Emissions reductions are achieved through the use of control technologies, energy efficiency, and shifting of fuels and technologies used in energy conversion. The emissions targeted by fees decrease, and larger fees lead to larger reductions. Compared to the base case with no fees, in 2045, SO_2 emissions are reduced up to 70%, NO_x emissions up to 30%, PM_2_._5 up to 45%, and CO_2 by as much as 36%. Emissions of some pollutants, particularly VOCs and methane, sometimes increase when fees are applied. The co-benefit of reduction in non-targeted pollutants is not always larger for larger fees. The degree of co-reduced emissions depends on treatment of life-cycle emissions and the technology pathway used to achieve emissions reductions, including the mix of efficiency, fuel switching, and emissions control technologies. - Highlights: • Fees based on damages related to energy use are modeled on the US energy system. • Health impacting air pollutants and greenhouse gases are targeted by fees. • Both targeted and other pollutants are reduced compared to a system without fees. • Control technologies, energy efficiency, and shifts in fuels reduce emissions. • Co-benefits do not necessarily increase as fees increase.

[en] Photo-plasma is produced by laser-induced ionization of atoms by multi-step resonant absorption of one or more photons in general of different frequencies. Such plasmas have found technological applications in the production of radioactive ion beams and the production of isotopically pure elements. In the present work we report the investigation of photo-plasma in a high temperature electrostatic extractor. The extractor can operate at temperatures ∼900 K, at electric field ∼200 V/cm and in an environment where there is metal vapor and photon flux. It is used concurrently with another vapor generating furnace that is placed below it. It is observed that for operation over long duration (about 5 h) barium atoms from the vapor-producing furnace coat the electrodes. They are re-evaporated from the hot electrodes thereby forming a collision-less vapor cell between them. Multi-step, multi-wavelength resonant ionization process using lasers produce photo-plasma in the cell. Thermionic emission from barium coated hot electrodes provides the seed current flux for electron-impact ionization of the atoms in the cell. The ionized background plasma provides a steady state current between the electrodes. The transient photo-plasma motion is superimposed on it. The photo-ions decay as the ions are collected. The Bohm current and current due to sheath boundary motion determines their evolution

[en] Atomic beams can easily be produced by allowing atoms to effuse through a channel. In an earlier investigation [A. Majumder et al., Vacuum 83, 989 (2009)], we had designed, fabricated, and characterized an effusive metal-vapor source using collinear-array of multi-channel. In this note, we describe the theoretical basis of designing the source. Atom density in atomic beam has been estimated using a set of analytical expressions for long-channel operated in transparent mode. Parametric studies on aspect ratio of channel, inter-channel separation, beam width, and vertical distance from the source are carried out. They are useful in providing physical picture and optimizing design parameters

[en] Two-dimensional evolution of finite-size barium photoplasma, produced using multistep-resonant ionization is experimentally investigated in an externally applied electrostatic field. Several processes like bulk motion, ambipolar diffusion, Coulomb repulsion, Child-Langmuir flux, bounded diffusion, etc. that contribute to its expansion, have been identified. They are quantified with the help of signals recorded by Faraday cups, electrodes and plates and by two-dimensional particle-in-cell simulation. These processes are superimposed and their relative magnitudes decide the evolution of the photoions. When external field is dominant, a significant fraction of ions reach the cathode with negligible vertical spread and the plasma motion can be considered as one-dimensional. However, when plasma collective effects are dominant, then the different mechanisms become comparable and the photoplasma expands in two dimensions. The spread of photoions at different locations in parallel plate geometry is determined as a function of plasma density and compared with simulation.

[en] A photoplasma is produced by two-step resonant photoionization scheme by shining pulsed lasers on an atomic beam of barium (Ba). There is an interest in ion collection from photoplasma by electrostatic field when ion collection assembly is maintained at high temperature. A double furnace system consisting of two resistively heated furnaces has been developed. One furnace is placed on the top of the other in high vacuum chamber. The lower furnace is used to generate a wedge shaped barium atomic beam while the upper one heats the ion collection assembly. The photoplasma evolves in an external electric field produced by two parallel plate electrodes. The motion of electrons and ions in electric field generates currents that are recorded across series resistors connected to the electrodes. It is observed that a large dc current flows in the circuit when electrodes are kept at high temperature (∼800 K). The large current is probably due to thermionic emission from Ba coated electrodes, electron impact ionization of vapor between electrodes, thermal ionization of vapor and leakage through insulator that holds the electrodes etc. When electrodes are at room temperature, the photoplasma is embedded in the atomic beam, where as it is produced in a vapor cell when electrodes are at high temperature. The photo-ion pulse is superimposed on the dc background current and its amplitude as well as time duration increase compared to that when electrodes are at room temperature.

[en] Electron beam heating is a technique to generate vapor of refractory and high melting point metals. Vapor production finds application in thin film deposition and laser-based purification of materials. A strip electron-gun whose filament is heated by AC current is generally used because of larger molten pool formation and quiet evaporation. Electron-gun thus generates vapor. The incident beam of electrons is backscattered with large angular distribution. Both the electron groups, namely the primary and the backscattered electrons participate in production of plasma by electron-impact ionization. The plasma is weakly ionized (∼ 0.1% degree of ionization) with ion density ∼ 10⁸ cm⁻³ and has low electron temperature (∼ 0.3 eV). The vapor and the simultaneously produced plasma expand in the space above the target. Plasma expands by ambipolar diffusion in a transverse magnetic field while the vapor expands as a collision-less atomic beam. In this paper we study vapor and plasma formation of copper and zirconium. Details shall be discussed.

[en] The recently developed Lorentz Oscillator Model-inspired Oscillator Finite-Difference Time-Domain (O-FDTD) is one of the simplest FDTD models ever proposed, using a single field equation for electric field propagation. We demonstrate its versatility on various scales and benchmark its simulation performance against theory, conventional FDTD simulations, and experimental observations. The model’s broad applicability is demonstrated for (but not limited to) three contrasting realms: integrated photonics components on the nano- and micrometer scale, city-wide propagating radiofrequency signals reaching into the hundreds of meters scale, and for the first time, in support of 3D optical waveguide design that may play a key role in neuromorphic photonic computational devices.

[en] A finite-sized barium (Ba) photoplasma is generated through a two-step resonant photoionization method by shining laser pulses onto an atomic beam of Ba. The photoionization yield is estimated from the ratio of photoion density to neutral atom density measured in the laser–atom interaction region. The neutral atom density in the atomic beam is measured by an optical absorption technique where a Ba hollow cathode lamp (Ba-HCL) is used as an emission source. Since the photoplasma has a finite volume and it is pulsed in nature, the photoion density in the photoplasma is estimated through the collection of charge from the photoplasma. The measured ionization yield is compared with the calculated value that is obtained from an in-house developed code. It is observed that the values are in good agreement. (paper)