Use of the nuclear reaction for diagnostics of energetic particles in burning plasmas

Application of reaction-produced γ-rays to diagnostics of energetic particles in burning plasmas is analyzed. Particularly, we focus on 0.981 MeV γ-rays emitted in the nuclear reaction solely governed in the plasmas by energetic tritons. It is shown that these γ quanta can serve as a promising tool to diagnose α knock-on tritons and α-particles confined in burning DT plasmas. Key parameters of the α knock-on triton population and the α-particle confinement property can be obtained by comparing the experimental γ-ray yield and spectrum with theoretical slowing-down calculations. Even if the γ-ray spectral shape cannot be acquired, one can monitor densities of these tritons and α-particles at energies of 0.6–1.8 MeV and 2.0–3.5 MeV, respectively, in a nearly steady-state plasma. The 0.981-MeV photons also would help to display time evolution of the α-particle population in experiments of deuterium plasmas with pulsed tritium beam shots.     

Conversion of Ca/K projectile fragments into thermalized ion beams

The results of tests for stopping and extraction of energetic, 92 MeV/u, short-lived ³⁸Ca and ³⁷K fragments of 0.5% and 0.1% full-width of momentum spread with the first version of the National Superconducting Cyclotron Laboratory (NSCL) gas cell are reported. The projectile fragments were thermalized in 51 cm of helium at 1 bar and were transported by electric fields and gas flow into an expansion chamber through a supersonic nozzle, guided by an radio frequency quadrupole (RFQ) guide and collected on a metallic wire. The extraction efficiency was measured for different implantation rates, different electrical field distributions inside the gas cell, and different values of beam degrader thicknesses. The extraction measurements were compared with the experimental stopping efficiency and measurement of ionization induced in the helium gas. Mechanisms responsible for ion losses were identified and possible improvements of the gas cell performance were discussed.     

Characterization of thick epitaxial silicon detectors from different producers after proton irradiation

Epitaxial (EPI) silicon has recently been investigated for the development of radiation tolerant detectors for future high-luminosity HEP experiments. A study of thick EPI silicon diodes irradiated with protons up to a fluence of has been performed by means of Charge Collection Efficiency (CCE) measurements, investigations with the Transient Current Technique (TCT) and standard CV/IV characterizations. The aim of the work was to investigate the impact of radiation damage as well as the influence of the wafer processing on the material performance by comparing diodes from different manufacturers. The changes of CCE, full depletion voltage and leakage current as a function of fluence are reported. While the generation of leakage current due to irradiation is similar in all investigated series of detectors, a difference in the effective doping concentration can be observed after irradiation. In the CCE measurements an anomalous drop in performance was found even for diodes exposed to very low fluences in all measured series. This result was confirmed for one series of diodes in TCT measurements with an infrared laser. TCT measurements with a red laser showed no type inversion up to fluences of for n-type devices whereas p-type diodes undergo type inversion from p- to n-type for fluences higher than .     

Structural evolution of clusters using genetic algorithm and density functional theory method

Structural evolution of clusters have been studied using an extensive, unbiased search based on genetic algorithm and density functional theory (DFT) methods. Cationic, neutral, and anionic silver clusters have planar shapes for their lowest-energy structures up to n = 7, 6, and 6, respectively. Most of the competitive candidates for are found to adopt close-flat configurations. The present results obtained by employing the Perdew–Wang 91 (PW91) exchange-correlation functional are significantly different from those predicted in earlier work using empirical and semi-empirical potentials, and partly in line with the previous first-principles calculations. The dependences of the lowest-energy structures of on second finite differences of total energy, binding energies per atom, highest occupied and lowest unoccupied molecular orbital energy gaps, ionization potentials, and electron affinities are studied in detail. The calculated ionization potentials and electron affinities of the optimal clusters display distinct even–odd oscillations. The neutral Ag clusters with 6-, 8-, and 14-atoms are suggested to be “magic” clusters by an analysis of their geometric and electronic properties.     

Proton polarizing system with Ar-ion laser for -RI scattering experiments

A proton polarizing system for use in scattering experiments with radioactive isotope beams is described. Protons in a naphthalene crystal doped with pentacene are polarized in a magnetic field of 0.3 T at 100 K by transferring a large population difference among the photo-excited triplet states of pentacene to the hydrogen nuclei. An Ar-ion laser, which demands minimal maintenance during scattering experiments, is employed to excite the pentacene molecules. A proton polarization of 37% is obtained.     

The Neptune photoinjector

The RF photoinjector in the Neptune advanced accelerator laboratory, along with associated beam diagnostics, transport and phase-space manipulation techniques are described. This versatile injector has been designed to produce short-pulse electron beams for a variety of uses: ultra-short bunches for injection into a next-generation plasma beatwave acceleration experiment, space-charge dominated beam physics studies, plasma wake-field acceleration driver, plasma lensing, and free-electron laser microbunching techniques. The component parts of the photoinjector, the RF gun, photocathode drive laser systems, booster linac, RF system, chicane compressor, beam diagnostic systems, and control system, are discussed. The present status of photoinjector commissioning at Neptune is reviewed, and proposed experiments are detailed.     

The electromagnetic calorimeter of the HERA-B experiment

The electromagnetic calorimeter of the HERA-B experiment built at the HERA proton accelerator at DESY (Hamburg) is described. The construction characteristics of the detector, of the related front-end, readout, trigger and service electronics are discussed together with the constraints and the motivations which inspired the design philosophy. The detector performance are presented as obtained from the analysis of the data acquired during the HERA-B running period, including calibration procedures and achievements and the electron identification capability exploiting a method, proposed here for the first time, based on the observation of the associated bremsstrahlung γ. Finally, some observed physical signals and a short overview of the main obtained physics results are presented.     

Generation of neutron multigroup constants in the energy range –10 MeV for light and heavy water at four different temperatures

On the basis of the cross section models of neutron scattering in liquid H₂O and D₂O, which have been developed in the previous papers, we have generated eight sets of multigroup constants (energy-averaged cross sections) for each liquid at 5, 27, 52 and . The multigroup constants cover a wide energy range –10 MeV with 140 energy groups at equal logarithmic intervals and represent an angular scattering distribution by the Legendre polynomial expansion up to order 3. Major characteristics of neutron scattering inherent to liquid water are fully included in terms of coherent and incoherent properties and temperature-dependent quasi-elastic and inelastic scattering. These characteristics are assured by comparison with relevant experimental results of scattering cross section and also by neutron slowing-down and thermalization analysis in liquid H₂O and D₂O. It is shown that the present multigroup constants serve for analysis of neutron moderation from fission/spallation to ultra-cold energies, in combination with the already-generated ones for liquid ⁴He, H₂, D₂ and CH₄ and solid CH₄.     

Injection and dynamics of accelerated beams

This paper is a summary of the discussions undertaken by the working group on injection and accelerated beam dynamics at the 1st ICFA Novel and Advanced Accelerator Workshop on Second Generation Plasma Accelerators. The second generation of work on plasma accelerators is aimed to bring the accelerated beams up to the quality needed for applications such as high-energy physics linear colliders. To begin, first generation, or proof-of-principle, experiments and concepts were reviewed. To map the work needed in the second generation of development, the demands of the applications were examined, and an improved framework for discussing the viability of plasma accelerators was constructed. In particular, the issues scaling applications to the short wavelengths characteristic of plasma accelerators was discussed, as was the appropriate characterization of the beam quality in these devices, and the connection between plasma accelerator and conventional accelerator design. Within this framework, the working group discussed electron sources and injectors, the effects of drive beam evolution on accelerated beam dynamics, this effects of nonlinear plasma wave fields on beam phase space, stochastic processes, spatial and temporal beam-plasma wave matching, and future second-generation experimental goals and techniques.     

Ultra-High Energy Cosmic Particles studies from space: , a possible next-generation experiment

After the Pierre Auger Observatory, it is likely that space-based experiments might be required for next-generation studies of Ultra-High Energy Cosmic Particles. An overview of this challenging task is presented, emphasizing the main design issues, the criticalities and the intermediate steps required to make this challenging task a reality.     

Synthesis and degradation properties of b\boldsymbol{\beta} -TCP/BG porous composite materials

b\boldsymbol{\beta}-TCP/BG porous composite materials were successfully fabricated by foaming technology. X-ray diffraction was used to determine the crystal structure of powders. The pore size and distribution of the resulting materials were characterized using scanning electron microscopy. The porosity and degradation performance of materials were also investigated. The results showed that the porous composite materials possessed the pore size ranging from 100 to 500 m\boldsymbol{\mu} m in diameter, whereas the interconnection among macrospores was poor. The porosity in materials increased from 58·7% to 63·47% with BG content ranging from 0 to 3 wt%, further increasing of BG content results in a decrease in porosity. The degradation rate of composite materials can be adjusted by varying the BG content.     

Critical discussion of the single-fibre pull-out test: does it measure adhesion?

With a comprehensive finite-element model the interface failure process of the single-fibre pull-out test, for the measurement of fibre/matrix adhesion, is investigated on the basis of a fracture-mechanics debonding criterion. Special emphasis is placed on the interface local mixed-mode load, which is shown to have an important influence on the debonding process and is taken into account by a fracture ellipsoid criterion. Additional features investigated are residual thermal stresses, specimen geometrical details (wetting meniscus, drop shape) and a simplistic model of fibre/matrix interfacial friction. For medium debonding lengths the energy release rate runs through a plateau range that can be approximated by a simple analytical approach and can be observed experimentally with a very stiff loading configuration. The mixed-mode state in the plateau range is uniform and dominated by mode 2, but its actual value is quite uncertain. From experimental experience the actual adhesion failure is closely connected with the interface local normal load, while local shear load induces submicroscopic friction and matrix inelasticity which strongly reduce the interface sensitivity, resulting in G_1c<G_2c. G_1c seems to be more significant for adhesion. The interpretation of the plateau range may provide the total critical energy release rate, G_c, for the debonding process, but from a region where mode II prevails. G_c will therefore be far from G_1c, reducing the significance of the tests results for characterization of adhesion.     

Towards a plasma wake-field acceleration-based linear collider

A proposal for a linear collider based on an advanced accelerator scheme, plasma wake-field acceleration in the extremely nonlinear regime, is discussed. In this regime, many of the drawbacks associated with preservation of beam quality during acceleration in plasma are mitigated. The scaling of all beam and wake parameters with respect to plasma wavelength is examined. Experimental progress towards high-gradient acceleration in this scheme is reviewed. We then examine a linear collider based on staging of many modules of plasma wake-field accelerator, all driven by a high average current, pulse compressed, RF photoinjector-fed linac. Issue of beam loading, efficiency, optimized stage length, and power efficiency are discussed. A proof-of-principle experimental test of the staging concept at the Fermilab test facility is discussed.     

Two-Band Eliashberg Theory in Doped MgB $_{2}$_{2}: Experimental Tc and Superconductive Gaps

The variation of the critical temperature and of the superconductive gaps as functions of doping (Al, C) in the diboride MgB has been studied in the framework of the two-band Eliashberg theory and traditional phonon coupling mechanism. We have solved the two-band Eliashberg equations using first-principle calculations or simple assumptions for the variation of the relevant physical quantities. We have found that the experimental curves can be exactly explained only if the Coulomb pseudopotential changes with x by tuning the Fermi level toward the σ band edge. We also found that a small amount of impurities changes the structural properties of the material, so we cannot treat the Mg and MgB systems as a contamination with Al or C of MgB, but as new materials. Finally, we compare the predictions of our theory with the available experimental data.     

Disordering of the Pb (110) surface

Molecular dynamics simulations incorporating a many-body glue model potential (GM) have been used to investigate the atomic structure and dynamics of the Pb (1 1 0) surface in the range from room temperature up to the bulk melting point. The main features of the surface disordering process include: generation of vacancies and the formation of an adlayer, the formation of so-called “local steps” and further their proliferation including wandering, creation and propagation of a quasiliquid surface film. These processes are illustrated by the use of a modern visualization technique.