Halo Formation in Spheroidal Bunches with Self-Consistent Stationary Distributions

A new class of self-consistent 6-D phase space stationary distributions is constructed both analytically and numerically. The beam is then mismatched longitudinally and/or transversely, and we explore the beam stability and halo formation for the case of 3-D axisymmetric beam bunches using particle-in-cell simulations. We concentrate on beams with bunch length-to-width ratios varying from 1 to 5, which covers the typical range of the APT linac parameters. We find that the longitudinal halo forms first for comparable longitudinal and transverse mismatches. An interesting coupling phenomenon - a longitudinal or transverse halo is observed even for very small mismatches if the mismatch in the other plane is large - is discovered.Comment: 3 pages, 3 figures; presented at European Particle Accelerator Conference, Stockholm, Sweden (June 22-26, 1998

Beam Loss Studies for Rare Isotope Driver Linacs Final Report

The Fortran 90 RIAPMTQ/IMPACT code package is a pair of linked beam-dynamics simulation codes that have been developed for end-to-end computer simulations of multiple-charge-state heavy-ion linacs for future exotic-beam facilities. These codes have multiple charge-state capability, and include space-charge forces. The simulations can extend from the low-energy beam-transport line after an ECR ion source to the end of the linac. The work has been performed by a collaboration including LANL, LBNL, ANL, and MSU. The code RIAPMTQ simulates the linac front-end beam dynamics including the LEBT, RFQ, and MEBT. The code IMPACT simulates the beam dynamics of the main superconducting linac. The codes have been benchmarked for rms beam properties against previously existing codes at ANL and MSU. The codes allow high-statistics runs on parallel supercomputing platforms, particularly at NERSC at LBNL, for studies of beam losses. The codes also run on desktop PC computers for low-statistics work. The code package is described in more detail in a recent publication [1] in the Proceedings of PAC07 (2007 US Particle Accelerator Conference). In this report we describe the main activities for the FY07 beam-loss studies project using this code package

Basis for low beam loss in the high-current APT linac

The present evidence that the APT proton linac design will meet its goal of low beam loss operation. The conclusion has three main bases: (1) extrapolation from the understanding of the performance of the 800-MeV LANSCE proton linac at Los Alamos, (2) the theoretical understanding of the dominant halo-forming mechanism in the APT accelerator from physics models and multiparticle simulations, and (3) the conservative approach and key principles underlying the design of the APT linac, which are aimed at minimizing beam halo and providing large apertures to reduce beam loss to a very low value

The use of the system dynamics model to determine the probability of company default

Abstract This research demonstrates the approach of using the system dynamics model to assess the probability of company default that is a relevant problem in credit risk analysis. System dynamics offers models in which the reality is simulated structurally. According to the principles of system dynamics, the company is represented in the form of continuously interacting elements and external factors. Enterprise dynamics and the enterprise’s resistance to various macroeconomic environments are determined by functional dependencies and differential equations that describe the links between the elements of the model. The behavior of random macroeconomic variables is described with a multivariate ARIMA-GARCH model, which is used in econometrics to predict non-stationary time series. The probability of company default is determined as a result of experiments with the obtained system dynamics model using the Monte Carlo simulation. The estimation of a default probability is the overall share of macroeconomic scenarios leading to the ruin of the enterprise. A comparative analysis of the obtained results and data from Moody’s and Fitch demonstrates the closeness of the probability of company defaults obtained by simulation and corresponding estimates of rating agencies, which makes it possible to conclude that the considered approach is acceptable for estimating the probability of default of a borrower.</jats:p

Variability in the properties of wakes generated by high-speed ferries

The largest impact on the coast of waves generated by high-speed ferries is usually caused by the highest and longest components of transcritical wakes. Building reliable statistics of these parts of vessel-generated waves is usually nontrivial because of the high variability in the properties of wakes and their infrequent occurrence. Tallinn Bay is one of the few places where high-speed ferries frequently operate at transcritical speeds close to the shoreline. We report the results of measurements performed in 2008 at the entrance of Tallinn Bay. The time series of water surface elevations were collected in 2.5-3 in water depth, similar to 100 m offshore from an almost non-reflecting beach, similar to 2700 m from the sailing line. The data from 418 wakes on 15 days allows the construction of distribution functions of different wake properties (maximum height, wake energy,and energy flux) with an acceptable accuracy. The periods of the highest waves vary insignificantly and are closely related to the cruise speed of the vessels. An appropriate measure of the properties and variability of wakes is the maximum wave height. Wakes from `classic' high-speed ships are very variable. Wakes from large, basically conventional, but strongly powered ferries show quite limited variability, thus, both the average and extreme wake properties of such ships can be more easily adjusted by changing their sailing regime

Fast-ferry generated waves in South-West Tallinn Bay

Waves generated by high-speed ferries sailing at near-critical speeds (depth Froude number ~1) may\ud substantially affect the coastal zone. As typical for large-amplitude waves in shallow water, waves from fast ferries frequently have a substantially nonlinear nature and are often able to seriously damage the coastal environment. We report wake characteristics of fast-ferries sailing in Tallinn Bay in June 2009. Waves were measured using an echosounder in the nearshore at Pikakari Beach at a depth of 2.7 m, 2.4 km from the sailing line. The record contains ~150 wake events for which primary wake parameters as the maximum wave height, wake energy and its flux were estimated. The shape of the highest vessel waves was analyzed in terms of cresttrough asymmetry. Maximum wave heights (up to 0.7 m) occurred exclusively for the longest waves with periods ~10 s. These waves are substantially nonlinear with wave crests exceeding wave troughs typically by a factor of 1.3. Incoming ferries generally excited smaller waves compared to a previous study of outgoing ferry\ud wakes in north-west Tallinn Bay. This apparently reflects the high spatial variability of wake waves along the\ud impacted coastal sections and is not an evidence of an overall decrease in the ship wave intensity

Reducing Beam Coupling Impedances in SNS Ring Extraction Kickers

The Spallation Neutron Source (SNS) Accumulator ring extraction kickers [1] consists of 14 modules of windowframe ferrite pulsing magnets with the rise time of about 200 ns. Their contribution to the beam coupling impedances is a serious concern. The kicker impedances, as well as its deflecting magnetic field versus time, are studied using detailed 3-D MAFIA modeling. Various design options, external circuit resistances, and a range of ferrite permeabilities are explored. A kicker module with wide conductor windings around the ferrite behind the kicker current sheet suggests a significant reduction of the kicker transverse and longitudinal coupling impedances. This design provides a good extraction field performance, as demonstrated by electromagnetic simulations. Results of measurements for a small model are also presented