Javier Resta-Lopez

Present status and first results of the final focus beam line at the KEK Accelerator Test Facility

ATF2 is a final-focus test beam line which aims to focus the low emittance beam from the ATF damping ring to a vertical size of about 37 nm and to demonstrate nanometer level beam stability. Several advanced beam diagnostics and feedback tools are used. In December 2008, construction and installation were completed and beam commissioning started, supported by an international team of Asian, European, and U. S. scientists. The present status and first results are described.

Simulation studies of the beam cooling process in presence of heating effects in the Extra Low ENergy Antiproton ring (ELENA)

The Extra Low ENergy Antiproton ring (ELENA) is a small synchrotron equipped with an electron cooler, which is currently being constructed at CERN to further decelerate antiprotons from the Antiproton Decelerator (AD) from 5.3 MeV to energies as low as 100 keV . At such low energies it is very important to carefully take contributions from electron cooling and beam heating mechanisms (e.g. on the residual gas and intrabeam scattering) into account. Detailed investigations into the ion kinetics under consideration of effects from electron cooling and heating sources have been carried out, and the equilibrium phase space dimensions of the beam have been computed, based on numerical simulations using the code BETACOOL. The goal is to provide a consistent explanation of the different physical effects acting on the beam in ELENA.

Beam Dynamics Studies and Design Optimisation of New Low Energy Antiproton Facilities

Antiprotons, stored and cooled at low energies in a storage ring or at rest in traps, are highly desirable for the investigation of a large number of basic questions on fundamental interactions. This includes the static structure of antiprotonic atomic systems and the time-dependent quantum dynamics of correlated systems. The Antiproton Decelerator (AD) at CERN is currently the worlds only low energy antiproton factory dedicated to antimatter experiments. New antiproton facilities, such as the Extra Low ENergy Antiproton ring (ELENA) at CERN and the Ultra-low energy Storage Ring (USR) at FLAIR, will open unique possibilities. They will provide cooled, high quality beams of extra-low energy antiprotons at intensities exceeding those achieved presently at the AD by factors of ten to one hundred. These facilities, operating in the energy regime between 100 keV down to 20 keV, face several design and beam dynamics challenges, for example nonlinearities, space charge and scattering effects limiting beam life time. Detailed investigations into the low energy and long term beam dynamics have been carried out to address many of those challenges towards the design optimisation. Results from these studies are presented in this contribution, showing some examples for ELENA.

Physical Society of Japan : Beam diagnostics for low energy antiprotons

This paper presents a comprehensive set of beam diagnostics that has been developed to characterize low energy antiproton and ion beams (during initial machine commissioning) and subsequent facility operation. It shows results from simulations and experiments using invasive and non-invasive monitors for absolute beam current measurements; capacitive pickups for position detection; scintillating screens, secondary emission monitors and micro channel plate detectors for transverse profile monitoring, as well as an ultra-cold gas jet for minimally-invasive profile measurements and in-ring experiments. The identified limits are discussed for each technique, and options for further improvements are indicated.

Energy efficiency studies for dual-grating dielectric laser-driven accelerators

Abstract Dielectric laser-driven accelerators (DLAs) can provide high accelerating gradients in the GV/m range due to their having higher breakdown thresholds than metals, which opens the way for the miniaturization of the next generation of particle accelerator facilities. Two kinds of scheme, the addition of a Bragg reflector and the use of pulse-front-tilted (PFT) laser illumination, have been studied separately to improve the energy efficiency for dual-grating DLAs. The Bragg reflector enhances the accelerating gradient of the structure, while the PFT increases the effective interaction length. In this paper, we investigate numerically the advantages of using the two schemes in conjunction. Our calculations show that, for a 100-period structure with a period of 2 μ m, such a design effectively increases the energy gain by more than 100 % when compared to employing the Bragg reflector with a normal laser, and by about 50 % when using standard structures with a PFT laser. A total energy gain of as much as 2.6 MeV can be obtained for a PFT laser beam when illuminating a 2000-period dual-grating structure with a Bragg reflector.

Emittance Measurements in Low Energy Storage Rings

The development of the next generation of ultra-low energy antiproton and ion facilities requires precise information about the beam emittance to guarantee optimum performance. In the Extra-Low ENergy Antiproton storage ring (ELENA) the transverse emittances will be measured by scraping. However, this diagnostic measurement faces several challenges: non-zero dispersion and systematic errors due to diffusion processes, such as intra-beam scattering, and the speed of the scraper with respect to the beam revolution frequency. In addition, the beam distribution will likely be non-Gaussian. Here, we present algorithms to efficiently address the emittance reconstruction in presence of the above effects, and present simulation results for the case of ELENA. We also discuss the feasibility of using alternative non-invasive techniques for profile and emittance measurements. INTRODUCTION ELENA is a low energy storage ring designed to increase the efficiency of the antimatter experiments at CERN [1]. Currently under construction, ELENA will accept antiprotons from the Antiproton Decelerator (AD) [2] and employ the use of an electron cooler to keep the beam under control while they are decelerated from a kinetic energy of 5.3 MeV to 100 keV. At these lower energies, fewer antiprotons will be lost to degrader foils at the end of the deceleration process and as a result the anti-hydrogen experiments will receive higher intensity beams. In order to monitor the quality of the beam between deceleration and cooling phases, emittance measurements will be taken using a scraper. A scraper is a destructive diagnostics device, comprising a set of blades individually moving orthogonal to the beam, into the path of the beam at a low velocity compared to that of the beam. The scraper removes particles from the beam and measurements of the beam intensity as a function of the position of the scraper are taken. A fit to the intensity data is used to reconstruct the transverse beam profile and obtain emittance measurements. A scraper was chosen due to its simple operation with low intensity antiproton beams with the additional feature of being able to collimate the beam (to a specific size or intensity) if desired. In the AD ring two pairs of horizontal and vertical tungsten scrapers are used to destructively measure the beam profile [3]. To simplify the algorithm the scrapers are located in a dispersive-free region. In ELENA there is no region with zero dispersion which complicates the data fitting and beam analysis process. The details of these challenges are discussed in the following section. THEORY Reconstruction for a Gaussian Beam The working idea for the scraper is to sweep through the beam in a specific direction e.g. from the positive x-direction, to obtain a density distribution for that plane. If the scraper blades are aligned correctly, the measurement will only act in one plane and any particles with larger betatron amplitudes than the scraper edge are removed from the beam. The scraper blade moves slowly in comparison to the beam velocity to allow time for higher amplitude particles to be eliminated. Here, for simplicity, to illustrate the process let us consider a single scraper blade moving the x-plane (Fig. 1). However in ELENA the scraper consists of four scraper blades coming from the ±x and ±y directions. Figure 1: Schematic representation of a scraper; acceptance for a beam with zero momentum offset (black ellipse), with positive momentum offset (red ellipse) and with negative momentum offset (blue ellipse). Considering only a 2D Gaussian beam, an integration over the density distribution can be performed to reconstruct the beam profile. Combining this with parameters describing the beam and the accelerator’s optics at the scraper position, the emittance can be calculated. In the primary method presented here, we expand upon this technique to consider a beam with a non-zero momentum distribution in a dispersive region. The momentum component is accounted for by including an additional energy term (dependent on the relative momentum offset and the rms relative momentum spread) in the integral and averaging over the momenta of the beam. The rms relative momentum spread of the beam can be taken as a free parameter or if known, used in the calculation. In order to account for the dispersion in the Gaussian calculation, the upper limit on the energy integral must be changed from infinity to the maximum relative momentum offset which is dependent on the dispersion at the position of the scraper. An additional term, which depends on the relative momentum offset and also the dispersion at the WEPOR052 Proceedings of IPAC2016, Busan, Korea ISBN 978-3-95450-147-2 2788 C op yr ig ht