15 research outputs found
NUMERICAL CALCULATIONS OF THE ELECTRON COOLING DRAG FORCE IN A MAGNETIC FIELD
Abstract The longitudinal drag force that the electrons in an electron cooler exert on a circulating ion beam has been measured at many electron-cooling installations and also at CRYRING. Although different theoretical models have been used for calculation of this drag force, the discrepancy between theory and experiment have sometimes been quite big due to the theoretical difficulty in treating the interaction between charged particles in a magnetic field. We here present the beginning of an attempt to numerically calculate the energy loss suffered by ions in binary collisions with electrons in the presence of a finite magnetic field. Results for the longitudinal drag force are presented for relative velocities between ions and electrons and magnetic fields that are relevant for electron cooling at CRYRING and similar storage rings. THE PROBLEM The magnitude of the drag force that an ion experiences when it moves through the electron beam of an electron cooler has been calculated, with or without the inclusion of a magnetic field, using a number of different approaches such as binary collisions [1], dielectric theory [2] or molecular-dynamics simulations In our case, the electron is more or less strongly bound to a field line and it can approach the ion several times during successive cyclotron orbits. For large impact parameters this is conventionally regarded as the ions colliding with an electron "disk", whose charge is smeared out over the cyclotron orbits and which has a very small transverse motion, leading to an increased drag force. Indeed, a drag force larger than what has been calculated from theories that do not take the magnetic field into account has been observed at several cooler installations. Another feature of magnetized collisions, in contrast to classical Rutherford scattering, is that negative and positive ions have different drag forces. This effect that also has been observed experimentally Here we present the beginning of an attempt to get accurate numerical values for the electron-cooling drag force in the presence of a finite magnetic field using a binarycollision approach. The aim is to calculate the energy loss for heavy ions passing through an electron gas that has the anisotropic temperature and the magnetization that are characteristic of an electron cooler. Outside the scope of this investigation, however, is the inclusion of plasma effects or electron-electron interactions. THE METHOD The method we use to calculate the energy loss of an ion colliding with an electron is simply to numerically integrate the classical equations of motion of the two particles. We define the magnetic field to be in the positive z direction, and the terms 'longitudinal' and 'transverse' refer to the direction of the field. The initial condition is that the electron is performing gyro motion on a circle around the origin in the plane z = 0 with velocity v e,0 . The ion starts far below that plane and moves toward it with a velocity v i,0 directed along the z axis. It scatters against the electron and continues until it no longer is influenced by the force of the electron, whereupon the energy loss suffered by the ion is computed. The energy loss thus gives the longitudinal drag force for an ion that has an initial velocity that is purely longitudinal. This energy loss or drag force is then integrated over all impact parameters of the ion and over all phases of the electron gyro motion (or, equivalently, over an impact-parameter plane assuming that the electron always starts in the same (x, y) coordinate). The drag force is finally normalized to an electron density of 1 × 10 14 m −3 . The force acting between the ion and the electron is a screened Coulomb force, and the Debye length is used as the screening length. Since the Debye length depends on the electron density n e and the electron temperature T , there are two additional choices to be made here. We have used an electron density of 1 × 10 13 m −3 , which is typical for CRYRING, and as the electron temperature we have taken kT e = m e v 2 e,0 /2. However, for a few different combinations of v e,0 and v i,0 other values of λ D were also used in order to test how sensitive the results are to the choice of λ D , see below. The calculations were performed for a magnetic field of 0.1 T, but the results can easily be transformed to other fields. It is readily seen that the equations of motion ar
European Spallation Source Lattice Design Status
The accelerator of the European Spallation Source (ESS) will deliver 62.5 mA proton beam of 2.0 GeV onto the target, offering an unprecedented beam power of 5 MW. Since the technical design report (TDR) was published in 2013, work has continued to further optimise the accelerator design. We report on the advancements in lattice design optimisations after the TDR to improve performance and flexibility, and reduce cost of the ESS accelerato
Induced activation in accelerator components
The residual activity induced in particle accelerators is a serious issue from the point of view of radiation safety as the long-lived radionuclides produced by fast or moderated neutrons and impact protons cause problems of radiation exposure for staff involved in the maintenance work and when decommissioning the facility. This paper presents activation studies of the magnets and collimators in the High Energy Beam Transport line of the European Spallation Source due to the backscattered neutrons from the target and also due to the direct proton interactions and their secondaries. An estimate of the radionuclide inventory and induced activation are predicted using the GEANT4 code
The RF power source for the high beta elliptical cavities of the ESS linac,
The European Spallation Source (ESS) is an intergovernmental project building amultidisciplinary research laboratory based upon the worlds most powerful neutron source. The main facility will be built in Lund, Sweden. Construction is expected to start around 2013 and the first neutrons will be produced in 2019. The ESS linac will deliver 5 MW of power to the target at 2.5 GeV, with a nominal current of 50 mA. The 120 high beta elliptical cavities, which operate at a frequency of 704 MHz and accelerate protons from 600 MeV to 2.5 GeV, account for more than half of the total number of RF cavities in the ESS linac and three quarters of the total beam power needed. Because of the large number of RF power sources and the high power level needed, all the design and development efforts for the RF power source have so far been focused on this part of the accelerator. The design and development status of the RF power source is reported in this paper with emphasis on reliability, maintainability, safety, power efficiency, investment cost and production capacity
ESS Linac Beam Physics Design Update
The European Spallation Source, ESS, uses a linear accelerator to bombard the tungsten target with the high intensity protons beam for producing intense beams of neutrons. The nominal average beam power of the linac is 5~MW with a peak beam power at target of 125~MW. This paper focuses on the beam dynamics design of the ESS linac and the diagnostics elements used for the tuning of the lattice and matching between sections
A Planning and Scheduling System for the ESS Accelerator Project
Constructing a large, international research infrastructure is a complex task, especially when a large fraction of the equipment is delivered as in-kind contributions. A mature project management approach is essential to lead the planning and construction to deliver scientifically and technically. The purpose of this paper is to present how the ESS accelerator project is managed in terms of planning and scheduling from the design phase until commissioning, keeping time, budgets and resources constraints, as well as creating and maintaining a strong and trust-based partnership with the external contributors
The European Spallation Source
In 2003 the joint European effort to design a European Spallation Source (ESS) resulted in a set of reports, and in May 2009 Lund was agreed to be the ESS site. The ESS Scandinavia office has since then worked on setting all the necessary legal and organizational matters in place so that the Design Update and construction can be started in January 2011, in collaboration with European partners. The Design Update phase is expected to end in 2012, to be followed by a construction phase, with first neutrons expected in 2018-2019. (C) 2011 Elsevier By. All rights reserved