[en] The vacuum chamber of a storage ring normally consists of periodically spaced pumping slots. The longitudinal impedance of slots are analyzed in this paper. It is found that although the broad-band impedance is tolerable, the narrow-band impedance, as a consequence of the periodicity of the slots, may exceed the stability limit given by natural damping with no feedback system on. Based on this analysis, the PEP-II distributed-ion-pump (DIP) screen uses long grooves with hidden holes cut halfway to reduce both the broad-band and narrow-band impedances. (author)

[en] An important factor that limits the PEP-II from operating at high currents is higher-order-mode (HOM) heating of the bellows. One source of HOM heating is the formation of trapped modes at the bellows as a result of geometry variation in the vacuum chamber, for example, the masking near the central vertex chamber. Another source comes from HOMs generated upstream that leak through the gaps between the bellows fingers. Modeling the fine details of the bellows and the surrounding geometry requires the resolution and accuracy only possible with a large number of mesh points on an unstructured grid. We use the parallel finite element eigensolver Omega3P for trapped mode calculations and the S-matrix solver S3P for transmission analysis. The damping of the HOMs by the use of absorbers inside the bellows will be investigated

[en] The TEM3P module of ACE3P, a parallel finite-element electromagnetic code suite from SLAC, focuses on the multiphysics simulation capabilities, including thermal and mechanical analysis for accelerator applications. In this pa- per, thermal analysis of coupler feedthroughs to supercon- ducting rf (SRF) cavities will be presented. For the realistic simulation, internal boundary condition is implemented to capture RF heating effects on the surface shared by a di- electric and a conductor. The multiphysics simulation with TEM3P matched the measurement within 0.4%.

[en] A single-cell superconducting deflecting cavity operating at 2.812 GHz has been proposed and designed for the Short Pulse X-ray (SPX) project for the Advanced Photon Source upgrade. A cryomodule of 4 such cavities will be needed to produce the required 2-MV deflecting voltage. Each deflecting cavity is equipped with one fundamental power coupler (FPC), one lower order mode (LOM) coupler, and two higher order mode (HOM) couplers to achieve the stringent damping requirements for the unwanted modes. The damping of the HOM/LOM modes below the beampipe cutoff has been analyzed in the single cavity geometry and shown to meet the design requirements. The HOMs above beam pipe cutoff in the 4-cavity cyromodule, however, may result in cross coupling which may affect the HOM damping and potentially trapped modes between the cavities which could produce RF heating to the beamline bellows and even be detrimental to the beam. We have evaluated the HOM damping and trapped modes in the 4-cavity cryomodule using the parallel finite element EM code ACE3P developed at SLAC. We will present the results of the cryomodule analysis in this paper.

[en] We use MAFIA to analyze the PEP-II button-type beam position monitor (BPM). Employing proper termination of the BPM into a coaxial cable, the output signal at the BPM is determined. Thus the issues of signal sensitivity and power output can be addressed quantitatively, including all transient effects and wakefields. Besides this first quantitative analysis of a true BPM 3D structure, we find that internal resonant modes are a major source of high value narrow-band impedances. The effects of these resonances on coupled-bunch instabilities are discussed. An estimate of the power dissipation in the ceramic vacuum seal under high current operation is given. (author)

[en] The PEP-II B-Factory is designed to operate at high currents with many bunches (1658) to achieve the luminosity required for physics studies. Interactions of a beam with its environment in a storage ring raise various issues of concern for accelerator physics, mechanical design and device performance. First, for accelerator physics, wakefields generated by interactions of a beam with beamline components, if not properly controlled, will drive single-bunch and coupled-bunch instabilities. The total broad-band impedance of the ring cannot exceed a budget limited by single-bunch effects. The growth rate of a coupled-bunch mode contributed from narrow-band impedance should be smaller than the damping rate due to synchrotron radiation; otherwise, suppression by feedback control will be necessary. Second, the energy loss by a beam at a beamline component in the form of higher-order-mode (HOM) power leads to additional heating on the component, and to TE mode radiation through openings on vacuum chamber walls. Last, calculations of transfer and beam impedances of pickup and kicker devices are essential for improving their performance and for identifying trapped modes. To address these issues quantitatively requires numerical simulations of each beamline component which include the realistic geometry and the relevant physics involved in the particular beam-environment interactions

[en] Using the emission of secondary electron (SE) from a thin carbon foil in transmission geometry guided by a strong radial electric field in the region between the foil and the sample under investigation, a new variable energy positron annihilation lifetime spectroscopy (PALS) system is being implemented. To this end, the SE emission from a carbon foil of 30nm thick has been investigated in transmission geometry. Considerable emission of SE from the foil with peak energy of about 5eV is observed. We have found that both the energy loss and dispersion of the positrons after transmission through the carbon foil are small enough for the proposed positron lifetime-depth profiling PALS system to be realised. These experimental results and the timing simulations of Cai et. al. indicate that the proposed variable PALS based on secondary electrons generated by carbon foil have a high time resolution.

[en] Nickel-based alloys and the associated welds are susceptible to Primary Water Stress Corrosion Cracking. In Pressurized Water Reactor nuclear power plants, the reactor vessel closure head upper penetration nozzles used for the Control Rod Drive Mechanisms and other instrumentation systems are made of such nickel-based alloys. Cracking and leakage have been observed in the upper head penetration nozzles in nuclear power plants worldwide. Such cracking and the resulting leakage is a degradation of the reactor vessel pressure boundary. Regulatory requirements have been issued by the Nuclear Regulatory Commission regarding periodic inspection of the susceptible areas to enable detection of indications and provide reasonable assurance of continued structural integrity for reactor vessel closure head. A flaw tolerance approach has been used in the disposition of detected indications to minimize outage delays, by performing up-front fracture mechanics evaluations for the common types of indications detected in the susceptible areas. Details of the flaw tolerance approach are presented in this paper. (authors)

[en] Recent Pressurized Water Reactor power plant field experiences and the potential for Primary Water Stress Corrosion Cracking require reassessment of the examination frequency and the overall examination strategy for nickel-based alloy components and weldments. Service induced cracking of these nickel-based alloy components and weldments have been occurring more and more frequently in recent years, resulting in the need to repair and/or replace these components. Inspection and evaluation guidelines for these nickel-based alloy components and weldments were developed by the nuclear power plant industry and the Nuclear Regulatory Commission. These inspection guidelines often require 100% examination volume for the affected components and weldments. However due to physical obstructions, component specific geometry and current Ultrasonic Examination detection capability, full examination of these nickel-based alloy components and weldments cannot be easily achieved as required in the inspection guidelines. This paper provides a discussion of some of the inspection issues encountered by the nuclear power plants and the use of flaw tolerance evaluation to support alternative examination volume and/or inspection interval resulting in reduced Operation and Maintenance costs and eliminating potential outage delays. (authors)

[en] The increasingly demanding design requirements of the next-generation particle accelerators have placed heavy emphasis on the accuracy and reliability of RF computer programs in order that accelerator components can be modeled and analyzed with greater confidence. Presently popular codes are inefficient in handling complex geometrical shapes, or are limited in their ability to solve large scale problems. The Numerical Modeling Group at SLAC has an ongoing effort to develop advanced numerical tools that specifically address these issues through the use of unstructured grids and multi-processing capability. This tool set consists of both time-domain (Tau) and frequency-domain (Omega) modules that calculate the standard circuit parameters of RF cavities and traveling wave structures. We will present some of the unique features (e.g. geometry from solid model, adaptive refinement, parallel processing) being included in these programs, and will show results from their use in cavity and component design for e⁺e^- colliders such as the NLC (Next Linear Collider). (author)