Charged Bi Research Articles

Development of a Bi+ high current source for heavy ion driven plasma generators

The development of a high current bismuth ion source is motivated by heavy ion driven fusion (HIF) and is part of the conceptual design of a HIF-relevant Bi+ test injector with four beamlets, which could serve as a HIF driver front end element. Envisaged is the development of a 300 mA Bi+ injector that can deliver four parallel beams from a 500 kV platform with 75 mA per beam. The first prototype source is driven by an arc discharge and provides singly charged Bi ions with a fraction more than 92% of the total extracted current. At its perveance limit this source delivers current of 70 mA, with the corresponding voltage being 27.5 kV. The emittance of a 21 mA/18.2 keV beam was measured and it amounted to 0.27 π mm mrad (80%, normalized, 4 root mean square) provided by a seven hole extraction system. Based on these investigations a new ion source will be designed and tested that will deliver current of 75 mA at ion energies up to 65 keV. In order to fulfill the requirements of HIF the emittance has to be in the vicinity of 0.4 π mm mrad (normalized). In this article we give a brief description of the design of an advanced ion source. Based on experimental experience using the previous prototype source one major modification made is the construction of an external oven. The use of more than one filament to increase the source lifetime is also planned.

Lessons to be learned from the HIDIF-study for a full driver

The scope of the European Bi + HIDIF study with its 3 MJ total driver energy was to demonstrate the feasibility of an RF linac and storage based scheme for ignition with an indirectly driven low gain target. More recent upgrade scenarios with at least 4.5 MJ total driver energy are focused on energy production and high gain targets. Keeping the linac beam current constant and increasing instead the number of storage rings from 12 to 18 will give the required 4.5 MJ total driver energy. Aiming for high total driver efficiency was not a topic for the ignition facility, however it is a very crucial item for a heavy ion fusion power plant. All RF linac components should be feasible for up to 50 Hz rep. rate in order to be cost effective for energy production. A total driver efficiency of 20% is only achievable at 50 Hz rep. rate. However, it is preferred to have the 20% driver efficiency at 10 Hz rep. rate, which is expected to be the maximal achievable rep. rate for a single target station. One elegant way to get the wanted 20% driver efficiency at 10 Hz rep. rate with 4.5 MJ total driver energy and 12 storage rings only, is to change the HIDIF layout from single charged Bi + to double charged Bi 2+ ions. The layout of a cost effective and less complex Bi 2+ separated section main linac from 10 MeV/n on is outlined. Reduced numbers of large apertures, high gradient external quadrupoles, feasible up to 50 Hz rep. rate are used for focusing the high intensity beam. Monte Carlo simulations for a Bi 2+ beam with 600 mA particle current are presented, demonstrating the feasibility of such a Bi 2+ linac as injector for the storage rings. By adding more target stations later on, the full potential of a 50 Hz rep. rate Bi 2+ fusion power plant can be realized.

Scanning force microscopy of ion-irradiated organic single crystals of benzoyl glycine

Single crystals of the amino acid benzoyl glycine (hippuric acid) are irradiated normal to the as-grown surface by highly charged Bi ions with a kinetic energy of 2.38 GeV and a fluence of 1×1010 ions/cm2. The projectiles create circular craters with a mean diameter of 40 (10) nm on the surface of the crystal as observed by scanning force microscopy (SFM). The mean depth amounts to 4 (1) nm, this value being considered as a lower limit due to the finite radius of curvature of the force cantilever tip. Thus, on the average, each single-ion projectile seems to eject about 104 molecules. On the surface of non-irradiated crystals, SFM reveals terraces of a few monolayers in height. In water, it was possible to visualize the lattice periodicity. Terraces were also observed on the irradiated crystal surface in the presence of the craters, indicating that the crystal is still intact at the given dose.

First Quaternary A−Pb−Bi−Q (A = K, Rb, Cs; Q = S, Se) Compounds: Synthesis, Structure, and Properties of α- and β-CsPbBi3Se6, APbBi3Se6, (A = K, Rb), and APbBi3S6 (A = Rb, Cs)

{alpha}-CsPbBi{sub 3}Se{sub 6} (I), {beta}-CsPbBi{sub 3}Se{sub 6} (II), RbPbBi{sub 3}Se{sub 6} (III), KPbBi{sub 3}Se{sub 6} (IV), CsPbBi{sub 3}S{sub 6} (V), and RbPbBi{sub 3}S{sub 6} (VI) were synthesized by the polychalcogenide flux method. {alpha}-CsPbBi{sub 3}Se{sub 6} was obtained at 720 C and crystallizes in the space group Pnma (No. 62) with a = 23.564(6) {angstrom}, b = 4.210(2) {angstrom}, c = 13.798(3) {angstrom} at room temperature. Final R/R{sub w} = 3.0/3.6%. In this compound, parallel NaCl-type Pb/Bi/Se columns with rectangularly shaped cross-sections are interconnected by edge sharing to build a 3-D tunnel framework with Cs atoms located inside the tunnels. The hexagonal plates of {beta}-CsPbBi{sub 3}Se{sub 6} were obtained at 400 C and crystallize in the space group P6{sub 3}/mmc (No. 194) with a = 4.213(2) {angstrom}, c = 25.22(1) {angstrom}, {gamma} = 120 at {minus}100 C. Final R/R{sub w} = 4.2/4.7%. APbBi{sub 3}Se{sub 6} (A = Rb, K) and APbBi{sub 3}S{sub 6} (A = Cs, Rb) are isostructural with {beta}-CsPbBi{sub 3}Se{sub 6} and their hexagonal cell parameters were obtained at room temperature. The structure is composed of negatively charged Bi{sub 2}Te{sub 3}-type bilayers separated by alkali metals, which are distributed over two different crystallographic sites. The alkali metal ions are more » loosely packed in the interlayer space making them mobile. Topotactic ion-exchange reactions of two compounds, {beta}-CsPbBi{sub 3}Se{sub 6} and RbPbBi{sub 3}Se{sub 6}, were examined with LiI and NaI in the solid state and in aqueous solution. Prolonged water contact of the hexagonal compounds leads to decomposition and leaching of alkali metal and Pb{sup 2+} ions. Electrical conductivity and thermopower measurements for single crystals of I, II, and III show n-type semiconductor behavior with 0.6, 0.3, and 0.3 S/cm and {minus}730, {minus}550, and {minus}560 {micro}V/K at room temperature, respectively. The optical band gaps of all compounds range from 0.27 to 0.89 eV. Thermal properties of the compounds are reported. « less

X-ray photoelectron spectroscopy studies of n-type bismuth-modified amorphous thin films of Ge20Se80 and As2Se3

The charged state of bismuth atoms in n-type bismuth-modified amorphous thin films of Ge20Se80 and As2Se3 has been studied by x-ray photoelectron spectroscopy. On the basis of the observed chemical shift, it is concluded that the Bi atoms in the modified films are positively charged. The charged Bi atoms perturb the equilibrium between positively and negatively charged defect centers, thereby causing a shift of the Fermi level towards the conduction band. The observed enhanced electrical conductivity and the conductivity conversion from p to n type in the modified films is the result of such a Fermi level shift.

Improvements on the HIBALL Heavy Ion Fusion Driver

Preliminary studies of accelerator scenarios suitable for the HIBALL Heavy Ion Fusion Reactor Study have shown that it is of interest to consider an RF linac beam current as high as possible in order to reduce the filling time of the storage rings to about 1 msec. It is shown here for singly charged Bi ions (10 GeV kinetic, 5 MJ total energy) that such a scenario helps to avoid growth of the resistive microwave mode and reduces the complexity of transverse stacking manipulations in the rings. This work indicates that it might be desirable for future studies to lower the linac current and thus the enormous instantaneous RF power consumption by finding ways to suppress microwave growth in order to stretch the storage ring filling time.

Electron capture by slow multiply charged Mg, Al, Cs, Pb and Bi ions from He, Ne, Kr and H2

Total charge transfer cross sections involving single and double electron capture processes by multiply charged Mg, Al, Pb and Bi ions in He and H2 and Cs ions in He, Ne, Kr and H2 have been measured in the energy range of 0.5-8 keV. Charge numbers q between 2 and 8 were available for the different projectile ions. Scaling of the cross sections with q and with the binding energy of the target particles has been studied. Non-monotonic structures in the q dependence of the cross sections are supposed to be due to the oscillatory structure theoretically described for low collision energies by Ryufuku et al. (1980). The scaling with the binding energy of the target particles does not prove a definite dependence at charge states of 5 or less. For charge states q>or approximately=7 the experimental cross sections approach the theoretical values.

Preparation and conduction mechanism of n-type semiconducting chalcogenide glasses chemically modified by bismuth

Two serieses of Bi containing glasses Ge 20Bi xSe 80−x (x≦13) and Ge 20Bi xSe 70−xTe 10 (x≦11) in at.% were prepared, and their resistivity, thermoelectric power, and optical absorption coefficient were measured. The resistivity at 25°C of Ge 20Bi xSe 80−x glasses decreased by about four orders of magnitude between x=9 and 10, and remained constant for x≧10 ; accompanied with this abrupt decrease, the conduction type changed from p to n in the thermoelectric power measurement. In Ge 20Bi xSe 70−xTe 10 glasses the conduction type changed from p to n at practically the same value of x as in Ge 20Bi xSe 80−x glasses; the resisitivity was nearly the same for both serieses of glasses with x≧10 , while for x<10 Te containing glasses showed lower resistivities by about four orders of magnitude. Optical absorption measurements revealed that the band gap decreased with the incorporation of a small amount of Bi, while remained nearly constant for the further increase in Bi content, indicating that the conduction type was controlled independently of the band gap. These results were discussed on the basis of chemical bonds present in the glasses, and the shift of the Fermi energy toward the conduction band was related to the formation of negatively charged Bi and positively charged dangling bonds.

Interimpurity Recombinations Involving the Isoelectronic Trap Bismuth in Gallium Phosphide

A new type of pair spectrum involving the radiative recombination of holes bound to Bi isoelectronic traps with electrons bound to remote shallow group-VI donors has been observed in GaP. The existence of these spectra proves that an isoelectronic impurity forms a stable trapping state for a single electronic particle. The binding energy of this state can be calculated from the positions of the pair spectra, and is 40\ifmmode\pm\else\textpm\fi{}1 meV for the Bi hole trap in GaP. The prominent phonon sidebands in the Bi-donor pair spectra and in the luminescence spectrum due to recombination from the $J=1$ Bi bound exciton state are similar, although the latter contains more detailed structure. The relatively large increase in the transition energy with decreasing pair separation $r$, characteristic of donor-acceptor pair spectra, is not observed in the Bi-donor pair spectra, where the first-order Coulomb interaction is zero because the Bi trap is neutral before the hole is captured. Instead, the Bi-donor pair transition energy decreases slightly with decreasing $r$ as a result of the electrostatic polarization interaction between the charged Bi trap and the neutral donor. The low-temperature time decay of both the Bi-donor and donor-acceptor pair spectra in GaP are slow and nonexponential, confirming that remote Bi-donor pairs of widely variable separation are involved. The decay time of the total luminescence is dramatically reduced, and the slow-decaying Bi-donor pair luminescence is quenched relative to the fast Bi-exciton luminescence, when the temperature is increased above \ensuremath{\sim}15\ifmmode^\circ\else\textdegree\fi{}K. These changes are attributed to the phonon-assisted tunneling of electrons from the donors to Bi traps already filled by holes.