Neutrino factory plans at CERN

The considerable interest raised by the discovery of neutrino oscillations and recent progress in studies of muon colliders has triggered interest in considering a neutrino factory at CERN. This paper explains the reference scenario, indicates the other possible choices and mentions the R&D that are foreseen

Dynamics in isochronous machine of FFAG type

Machines of FFAG type are considered for the different stages of a neutrino factory: ionization cooling, phase rotation and acceleration of the muons. Ionization cooling and phase rotation of the muons are performed at low energy. One could match the accelerating field frequency with the variation of the revolution frequency if the energy dispersion of the injected beam was small. But efficiency requires the acceptance of a large energy spread of the injected muons. Therefore a machine isochronous for all energies is an attractive solution. Isochronisms can be provided as the result of two effects: a magnetic field variation with the distance to the machine centre and a variation of the azimuthal separation between the magnets with the distance to the centre [1]. A suitable combination of these effects may give the best results in geometry and focusing properties. Because of the lifetime constraints, high accelerating gradients are required and one may accept crossing betatron resonances because their effects cannot build up much in a limited number of turns. The purpose is to follow the trajectories by direct intergration of the action of the fields

Tracking particles with wake fields and space charge effects

A simple and precise way to account for beam cavity interactions is the use of delta wake potentials known from RF calculations or measurements. When this procedure is introduced in a tracking program following super-particles such as in PARMELA, besides the effect of the space charge, the evolution of the charge distribution within the bunches of a train can be determined. The interesting application is for non-rigid bunches at intermediate or low energy, as for the study of Compact Linear Collider beams in the CLIC Test Facility at CERN

A code for multibunched beams with wakefields, group velocities and space charge

Tracking multiparticle bunches with PIC codes is possible, but limited to very short distances. Using the modal description these codes provide, PARMTRACK can calculate detailed intra bunch dynamics, and bunch to bunch dynamics for travelling in relatively long beam lines. Macro-particle simulation allows for permanent redistribution in longitudinal as well as in transverse space, without any limiting approximations. Care is taken of group velocities associated with each frequency of the wakefield description. Applications are shown for the part of the CLIC two-beam test facility producing the 30 GHz power

The Drive Beam Decelerator of CLIC

In the Compact Linear Collider (CLIC) a high-current, low-energy beam will be decelerated in a chain of power extraction structures to produce the RF-power necessary to accelerate a low-current, high-energy beam in the main linac. The transverse dynamics of the decelerated beam is discussed, based on results of the programs WAKE [1] and PLACET [2]. The very large energy spread and strong transverse wakefields as well as the high group velocity of these fields and the considerable length of the bunch train are important factors. Static and dynamic imperfections are considered including ground motion. The choice of parameters for the structures is investigated. A promising beam-based alignment technique is presented that makes use of a low emittance beam

Impacts of G x E x M on Nitrogen Use Efficiency in Wheat and Future Prospects

Globally it has been estimated that only one third of applied N is recovered in the harvested component of grain crops (Raun and Johnson 1999). This represents an incredible waste of resource and the overuse has detrimental environmental and economic consequences. There is substantial variation in nutrient use efficiency (NUE) from region to region, between crops and in different cropping systems. As a consequence, both local and crop specific solutions will be required for NUE improvement at local as well as at national and international levels. Strategies to improve NUE will involve improvements to germplasm and optimized agronomy adapted to climate and location. Essential to effective solutions will be an understanding of genetics (G), environment (E) and management (M) and their interactions (G x E x M). To implement appropriate solutions will require agronomic management, attention to environmental factors and improved varieties, optimized for current and future climate scenarios. As NUE is a complex trait with many contributing processes, identifying the correct trait for improvement is not trivial. Key processes include nitrogen capture (uptake efficiency), utilization efficiency (closely related to yield), partitioning (harvest index: biochemical and organ-specific) and trade-offs between yield and quality aspects (grain nitrogen content), as well as interactions with capture and utilization of other nutrients. A long-term experiment, the Broadbalk experiment at Rothamsted, highlights many factors influencing yield and nitrogen utilization in wheat over the last 175 years, particularly management and yearly variation. A more recent series of trials conducted over the past 16 years has focused on separating the key physiological sub-traits of NUE, highlighting both genetic and seasonal variation. This perspective describes these two contrasting studies which indicate G x E x M interactions involved in nitrogen utilization and summarizes prospects for the future including the utilization of high throughput phenotyping technology

Beam Stability in the Drive-Beam Decelerator of CLIC Using Structures of High-Order Symmetry

The RF power necessary to accelerate the main beam of the Compact Linear Collider (CLIC) is produced by decelerating a high-current drive beam in Power Extraction and Transfer Structures (PETS). The reference structure is not cylindrically symmetric but has longitudinal waveguides carved into the inner surface. This gives rise to a transverse component of the main longitudinal mode which can not be damped, in contrast to the transverse dipole wake- field. The field is non-linear and couples the motion of the particles in the two planes. Limits of the stability of the decelerated beam are investigated for different structures

User Guide for Wake

WAKE is a code simulating multi-bunch, multi-particle beams in linac with wakefields having high group velocity. The group velocity complicates the calculation because of the constant relocation of the particles creating the field and because the path length of a particle within the field of a preceding particle is not the length of the RF structure, but depends on the distance between the particles. It is the potential, i.e. the product of the field and the path length which is considered, rather than the field itself. In order to account for the varying positions of the particles, the structure is divided into intervals at the end of which the potentials are calculated. To save time, summing the potentials is not repeated, but the vector sum is transformed by the difference in phase when a particle replaces the preceding one at the same section end. A complementary update is necessary because the transverse positions have changed. The equations of the dynamics are then applied. In addition to this specific treatment for the wakefields, more conventional operators for travelling wave acceleration and focusing are provided. The focusing forces may be automatically adjusted for a decelerator or given at each focusing element. The input list is simple and one can select output graphics representing the results of the longitudinal and the transverse motions for the whole beam train, or for groups of particles. The code, written in FORTRAN 77, is the result of years of studies of the CLIC decelerator and of the CTF accelerator and decelerator. It has been tested against experimental measurements in CTF. Examples are given for these machines

A Multi-Drive Beam Scheme for Two-Beam Acceleration in a TeV Linear Collider

The Compact Linear Collider (CLIC) study of an e+/e- linear collider in the TeV energy range is based on Two-Beam Acceleration (TBA) in which the overall RF power needed to accelerate the beam is extracted from high intensity relativistic electron beams, the so-called drive beams. Due to the high beam power, acceleration and transport of the drive beams in an efficient and reliable way is specially challenging. An overview of a potentially effective scheme is presented. It is based on the generation of trains of short bunches, accelerated in low frequency c.w. superconducting cavities, stored in an isochronous ring and combined at high energy by funneling before injection by sectors into the drive linac. The various systems of the complex are discussed as well as the beam dynamics all along the process. An original method has been specially developed to stabilize such an intense beam during deceleration and RF power production in the drive lina