[en] Even though pressure tubes are major components of a CANDU reactor, only small proportions of pressure tubes are sampled for in-service inspections due to execution cost, outage duration, and site cumulative radiation exposure limits. In general, a realistic core assessment was not carried out based on all known information related to in-service degradation mechanisms. Recently, a hybrid deterministic and probabilistic core assessment (HDPCA) has been introduced to address the uncertainties associated with uninspected pressure tubes and diverse degradation mechanisms. In the present paper, the HDPCA was carried out for a CANDU unit based on cumulative operating experience and history in order to satisfy the requirements of Clause 7 of CSA Standard N285.8 by considering the uncertainties associated with the estimated distribution parameters, the limited inspected data, and pressure tube properties. The HDPCA is composed of two parts: a simulation part and a deterministic evaluation part. The outcome of the core assessment is the expected pressure tube failure frequency due to pressure tube flaws. In the simulations, pressure tube material properties were sampled from distributions derived from material surveillance and testing programs. The flaw dimensions and intensities were sampled from distributions fitted to in-service inspection data. The pressure tubes were then populated with flaws. Each simulated flaw was evaluated for DHC initiation under constant loading conditions. When Delayed Hydride Cracking initiation from a flaw was predicted, the pressure tube was evaluated for rupture in the Leak-Before-Break evaluation. Based on all the predicted pressure tube ruptures from simulations, the failure frequency was calculated on an annual basis. The largest expected mean and the 95% upper bound of the mean failure frequencies for any evaluation subinterval to the end of pressure tube design life of 210,000 EFPH are significantly below the allowable failure frequency limits in Table C.1 of CSA Standard N285.8. (author)

[en] This paper reports on fast ion-beam laser spectroscopy which constitutes a highly specialized tool in atomic physics and in fundamental studies of e.g. QED and Special Relativity. One limiting factor in many applications is the final velocity distribution of the accelerated particles. Thus methods to reduce phase-space is of utmost importance also in this field of physics as it certainly is in low energy atomic physics, where laser cooling and trapping has been highly developed. The light induced forces may be split into the scattering force and the dipole force, the former associated with a traveling plane wave and the latter with a standing plane wave. In general, laser cooling of gases and atomic beams exhibit rich structures, both experimentally and theoretically in one, two or three dimensions and in two and three level atoms. Dealing laser cooling of fast beams, a topic still in its infancy simpler considerations suffice at the present stage of its development

[en] The betatron and synchrotron tunes are measured frequently during the period of the machine operation and machine studies. The tune measurement system of the BEPC storage ring includes a spectrum analyzer, two sets of striplines, power amplifiers and a beam oscillation detector. As the upgrade scheme, Lab VIEW is ready to be used in the tune measurement system. This paper gives the tune measurements in the BEPC storage ring as well as the detailed description of the system hardware and software. (author)

[en] A new technique for measuring the transverse profile of ion beams, using laser induced fluorescence, is presented. The technique employs the resonant interaction of laser light with a beam of circulating ions in a storage ring. The light from the spontaneous decay of the excited ions is imaged by an optical system onto a high resolution CCD, making it possible to extract the beam's transverse spatial distribution. The first results from this technique, including studies of the transverse to longitudinal coupling in a circulating, laser-cooled ion beam, are presented

[en] To satisfy increasing demands on high-quality measurement of interior magnetic field in tokamak plasma, a far-infrared laser-based polarimeter-interferometer system has been developed on J-TEXT. With this system, high density disruption experiments have been performed on the J-TEXT tokamak to investigate the mechanism behind the density limit. Some interesting features of disruptions in high-density discharges are identified by carefully interpreting the measured polarimeter-interferometer data. During the density ramp-up phase of a high density discharge, asymmetry would occur on both electron density and at the High-Field-Side (HFS) edge (r < -0.8a) and extend gradually toward the center. Besides, a low-frequency (< 1 kHz) density perturbation suddenly occurs at the HFS edge and also gradually propagates towards the core region. The disruption takes place when the asymmetry on electron density reaches the q=2/1 resonant surface. Asymmetrical behaviors presented on reconstructed electron density and current density profiles provide a possible explanation for the high density disruption. (author)

[en] We report the results of laser cooling experiments on 100 keV Li⁺ beams in the storge ring ASTRID. The metastable fraction of the lithium beam has been laser cooled to a momentum spread δp/p ∼ 10^-6, corresponding to a rest frame temperture T = 1 mK. Laser diagnostic methods have been employed to study the dynamics of intrabeam relaxation. A theoretical model of laser cooling has been used to interpret the experimental results. We also discuss Molecular Dynamics simulations of intrabeam interactions and the connection with crystalline beams. (au)

[en] Secondary ion emissions from carbon nanotubes under bombardments of MeV Si and Si₂ clusters are measured by using a time of flight (TOF spectrometer). The measurements show that the emission yields of the secondary ions increase with increasing energy of Si and the secondary ion emissions are attributed to the electronic stopping processes. The emission yields of the secondary ions decrease with increasing energy of Si₂ clusters and the vicinage effect of cluster constituents plays more significant role in the enhanced secondary ion emissions at the low energies

[en] The interaction of laser-induced and intrabeam forces has been studied in a dense stored beam of 100-keV ⁷Li⁺ ions. A fraction of the ions (∼10^-4) exist in the metastable 1s2s ³S state. Using this state as a laser spectroscopic probe, we observe fast longitudinal heating in the injected, nonequilibrium distribution due to Coulomb scattering. Laser cooling of the metastable ions is ineffective during this heating period. The metastable fraction of the equilibrated beam is subsequently laser cooled to a longitudinal temperature of ∼1 mK, the lowest temperature ever reported in a stored ion beam

[en] Multifaceted asymmetric radiation as well as strong poloidal asymmetry of the electron density from the edge, dubbed as 'MARFE', has been observed in high electron density Ohmically heated plasmas on J-TEXT tokamak. Equilibrium reconstruction based on the measured data from the 17-channel FIR polarimeter-interferometer indicates that an asymmetric plasma current density distribution forms at the edge region and the plasma current shrinkage locates at the MARFE affected region. Furthermore, associated with the localized plasma current shrinkage, a locked mode MHD activity is excited, which then terminate the discharge with a major disruption. Localized plasma current shrinkage at the MARFE region is considered to be the direct cause for the density limit disruptions, and the proposed interpretation is consistent with the experimental observations. (author)

[en] Knowledge of the density distribution of a bunched beam is important for controlling and damping instabilities which often depend on the distribution function (A.W. Chao, in Physics of Collective Beam Instabilities in High Energy Accelerators, Wiley, New York, 1993). In this paper, experimental studies of the longitudinal bunch shapes and temperatures of laser-cooled bunched beams are presented. These studies are combined with measurements of the transverse density distribution of the beam using a novel technique (Madsen et al., Proceedings of the Sixth European Particle Accelerator Conference, EPAC'98, Stockholm, IOP Publishing, Bristol 1998, p. 1046). The bunch shapes for various temperatures comply with a model where the transverse temperature is assumed to be high. However, in the longitudinally space-charge limited case, it is observed that the maximum attainable density is much lower than it would be in a completely space-charge limited beam. Furthermore, it is observed that this maximum density decreases with increasing current. These observations might be important for the beam quality obtainable with laser-cooling