Hasil untuk "physics.acc-ph"

M. I. Ayzatsky

A self-consistent semi-analytical theory of beam loading in inhomogeneous accelerating structures based on the generalized theory of coupled modes is proposed. A single-mode approximation was used when the fields are represented as a sum of two components, one of which is associated with the right travelling eigen wave, and the second with the left. However, this second component is not always a left travelling. When a field is excited by an electron beam it can have complex spatial distribution. The results of calculation of the distribution of electric fields excited by a relativistic electron beam are presented.

N. V. Okhotnikov, K. V. Lotov

In a plasma wakefield accelerator driven by a train of short particle bunches, it is possible to locally increase the acceleration rate by introducing a small negative gradient of the plasma density. A regime is possible in which the gradient affects only the relative phasing of the driver bunches and the wave, keeping the wave phase behind the driver stable. With this technique, it is possible to increase the energy gain of the accelerated witness bunch in a plasma section of limited length.

Vojtěch Horný, Konstantin Burdonov, Alice Fazzini et al.

Compact laser-plasma acceleration of fast ions has made great strides since its discovery over two decades ago, resulting in the current generation of high-energy ($\geq 100\,\rm MeV$) ultracold beams over ultrashort ($\leq 1\,\rm ps$) durations. To unlock broader applications of these beams, we need the ability to tailor the ion energy spectrum. Here, we present a scheme that achieves precisely this by accelerating protons in a "lighthouse" fashion, whereby the highest-energy component of the beam is emitted in a narrow cone, well separated from the lower-energy components. This is made possible by a two-stage interaction in which the rear surface of the target is first set into rapid motion before the main acceleration phase. This approach offers the additional advantages of leveraging a robust sheath acceleration process in standard micron-thick targets and being optically controllable.

Johannes J. van de Wetering, Simon M. Hooker, Roman Walczak

We explore the regime of operation of the modulator stage of a recently proposed laser-plasma accelerator scheme [Phys. Rev. Lett. 127, 184801 (2021)], dubbed the Plasma-Modulated Plasma Accelerator (P-MoPA). The P-MoPA scheme offers a potential route to high-repetition-rate, GeV-scale plasma accelerators driven by picosecond-duration laser pulses from, for example, kilohertz thin-disk lasers. The first stage of the P-MoPA scheme is a plasma modulator in which a long, high-energy 'drive' pulse is spectrally modulated by co-propagating in a plasma channel with the low-amplitude plasma wave driven by a short, low-energy 'seed' pulse. The spectrally modulated drive pulse is converted to a train of short pulses, by introducing dispersion, which can resonantly drive a large wakefield in a subsequent accelerator stage with the same on-axis plasma density as the modulator. In this paper we derive the 3D analytic theory for the evolution of the drive pulse in the plasma modulator and show that the spectral modulation is independent of transverse coordinate, which is ideal for compression into a pulse train. We then identify a transverse mode instability (TMI), similar to the TMI observed in optical fiber lasers, which sets limits on the energy of the drive pulse for a given set of laser-plasma parameters. We compare this analytic theory with particle-in-cell (PIC) simulations and find that even higher energy drive pulses can be modulated than those demonstrated in the original proposal.

Luca Cultrera

This paper summarizes the state of the art of photocathode based on III-V semiconductors for spin polarized electron beam production. The limitations preventing this class of material to provide the long term reliability at the highest average beam currents necessary for some of the new accelerator facilities or proposed upgrades of existing ones are illustrated. Promising alternative classes of materials are identified showing properties that can be leveraged to synthesize photocathode structures that can outperform III-V semiconductors in the production of spin polarized electron beams and support the operating conditions of advanced electron sources for new facilities.

Brigitte Cros

Relativistic electrons are easily generated by self-injection when an intense laser drives a wakefield in a plasma, giving rise to wide electron energy distributions. Several mechanisms involving additional laser beams or different gas composition or distribution can be used to improve the electron beam quality. These mechanisms are introduced and discussed in the perspective of using laser driven electron sources as injectors for plasma accelerators.

V. A. Skalyga, I. V. Izotov, A. G. Shalashov et al.

Fundamental studies of excitation and non-linear evolution of kinetic instabilities of strongly nonequlibrium hot plasmas confined in open magnetic traps suggest new opportunities for fine-tuning of conventional electron cyclotron resonance (ECR) ion sources. These devices are widely used for the production of particle beams of high charge state ions. Operating the ion source in controlled turbulence regime allows increasing the absorbed power density and therefore the volumetric plasma energy content in the dense part of the discharge surrounded by the ECR surface, which leads to enhanced beam currents of high charge state ions. We report experiments at the ECR ion source at the JYFL accelerator laboratory, in which adopting of a new approach allows to increase the multicharged ion beam current up to two times, e.g. to 95 $μ$A of O$^{7+}$ achieved with mere 280 W power at 11.56 GHz. A theoretical model supporting and explaining the experimental findings is presented. The study suggests that the controlled turbulence regime has the potential to enhance the beam currents of modern high-performance ion sources, including state-of-the-art superconducting devices.

R. Bailey

These proceedings collate lectures given at the course on Accelerators for Medical Applications, organised by the CERN Accelerator School (CAS). The course was held at the Eventhotel Pyramide, Vösendorf, Austria from 26 May to 5 June, in collaboration with MedAustron. Following introductory lectures on radiobiological and oncological issues, the basic requirements on accelera- tors and beam delivery are reviewed. The medical applications of linear accelerators, cyclotrons and synchrotrons are then be treated in some detail, followed by lectures on the production and use of radioisotopes and a look at some of the acceleration techniques for the future.

Eric Montesinos

This paper reviews the main types of radio-frequency powering systems which may be used for medical applications. It gives the essentials on vacuum tubes, including tetrodes, klystrons, and inductive output tubes, and the essentials on transistors. The basics of combining systems, splitting systems, and transmission lines are discussed. The paper concludes with a case study specific to medical applications, including overall efficiency and cost analysis regarding the various available technologies.

M. Liu, S. M. Weng, H. C. Wang et al.

We propose a hybrid laser-driven ion acceleration scheme using a combination target of a solid foil and a density-tailored background plasma. In the first stage, a sub-relativistic proton beam can be generated by the radiation pressure acceleration in the intense laser interaction with the solid foil. In the second stage, this sub-relativistic proton beam is further accelerated by the laser wakefield driven by the same laser pulse in a near-critical-density background plasma with a decreasing density profile. The propagating velocity of the laser front and the phase velocity of the excited wakefield wave are effectively lowered at the beginning of the second stage. By decreasing the background plasma density gradually from near critical density along the laser propagation direction, the wake travels faster and faster while it accelerates the protons. Consequently, the dephasing between the protons and the wake is postponed, and an efficient wakefield proton acceleration is achieved. This hybrid laser-driven proton acceleration scheme can be realized by using ultrashort laser pulses at the peak power of 10 PW for the generation of multi-GeV proton beams.

W. Moolenaar, L. Tertoolen, S. W. Laat

T. Hesketh, John P. Moore, Jonathan D. H. Morris et al.

J. Faure

Plasma injection schemes are crucial for producing high-quality electron beams in laser-plasma accelerators. This article introduces the general concepts of plasma injection. First, a Hamiltonian model for particle trapping and acceleration in plasma waves is introduced; ionization injection and colliding-pulse injection are described in the framework of this Hamiltonian model. We then proceed to consider injection in plasma density gradients.

V. Mironov, S. Bogomolov, A. Bondarchenko et al.

Charge-breeding processes in Electron Cyclotron Resonance Ion Sources are numerically simulated by using the target helium plasma parameters obtained with NAM-ECRIS code. Breeding efficiency is obtained as a function of 1+ ion injection energy for some alkali ion beams. Time dependencies of extracted ions are calculated; typical times for reaching saturation in currents are in the range of few tens of milliseconds. Role of charge-exchange processes in breeding of ions is discussed. Recycling of ions on the source walls is shown to be important.

Ph. Korneev, Y. Abe, K. -F. -F. Law et al.

Electron acceleration by relativistically intense laser beam propagating along a curved surface allows to split softly the accelerated electron bunch and the laser beam. The presence of a curved surface allows to switch an adiabatic invariant of electrons in the wave instantly leaving the gained energy to the particles. The efficient acceleration is provided by the presence of strong transient quasistationary fields in the interaction region and a long efficient acceleration length. The curvature of the surface allows to select the accelerated particles and provides their narrow angular distribution. The mechanism at work is explicitly demonstrated in theoretical models and experiments.

M. I. Ayzatsky, V. V. Mytrochenko

We present the short description of the methods for calculation of the coupling coefficients in the Coupling Cavity Model of arbitrary chain of resonators. In the first part the procedure that is based on the Mode Matching Method is given. Then we present the new method that used only one eigen vector.

Vladimir Baryshevsky, Alexandra Gurinovich, Evgeny Gurnevich et al.

Triode reflex geometry vircator operating within 3.0 - 4.2 GHz range with efficiency up to 6% is developed and experimentally investigated. Shiftable reflectors are shown to enable frequency tuning and output power control. Radiation frequency and power are analyzed for different cathode-anode gap values and varied reflector positions.

Stephen P. Flood, David A. Burton

We investigate the effects of a Stern-Gerlach-type addition to the Lorentz force on electrons in a laser wakefield accelerator. The Stern-Gerlach-type terms are found to generate a family of trajectories describing electrons that surf along the plasma density wave driven by a laser pulse. Such trajectories could lead to an increase in the size of an electron bunch, which may have implications for attempts to exploit such bunches in future free electron lasers.

G. Doglio, J. Pusajo, M. A. Egurrola et al.

H. Feil, Y. Bae, J. Feijen et al.