Dieter Walz

Bio: Dieter Walz is an academic researcher from Stanford University. The author has contributed to research in topics: Plasma acceleration & Particle accelerator. The author has an hindex of 10, co-authored 30 publications receiving 1175 citations.

Energy doubling of 42 GeV electrons in a metre-scale plasma wakefield accelerator

Abstract: The energy frontier of particle physics is several trillion electron volts, but colliders capable of reaching this regime (such as the Large Hadron Collider and the International Linear Collider) are costly and time-consuming to build; it is therefore important to explore new methods of accelerating particles to high energies. Plasma-based accelerators are particularly attractive because they are capable of producing accelerating fields that are orders of magnitude larger than those used in conventional colliders. In these accelerators, a drive beam (either laser or particle) produces a plasma wave (wakefield) that accelerates charged particles. The ultimate utility of plasma accelerators will depend on sustaining ultrahigh accelerating fields over a substantial length to achieve a significant energy gain. Here we show that an energy gain of more than 42 GeV is achieved in a plasma wakefield accelerator of 85 cm length, driven by a 42 GeV electron beam at the Stanford Linear Accelerator Center (SLAC). The results are in excellent agreement with the predictions of three-dimensional particle-in-cell simulations. Most of the beam electrons lose energy to the plasma wave, but some electrons in the back of the same beam pulse are accelerated with a field of approximately 52 GV m(-1). This effectively doubles their energy, producing the energy gain of the 3-km-long SLAC accelerator in less than a metre for a small fraction of the electrons in the injected bunch. This is an important step towards demonstrating the viability of plasma accelerators for high-energy physics applications.

Observation of the Askaryan effect: coherent microwave Cherenkov emission from charge asymmetry in high-energy particle cascades.

Abstract: We present the first direct experimental evidence for the charge excess in high-energy particle showers and corresponding radio emission predicted nearly 40 years ago by Askaryan. We directed picosecond pulses of GeV bremsstrahlung photons at the SLAC Final Focus Test Beam into a 3.5 ton silica sand target, producing electromagnetic showers several meters long. A series of antennas spanning 0.3 to 6 GHz detected strong, subnanosecond radio-frequency pulses produced by the showers. Measurements of the polarization, coherence, timing, field strength vs shower depth, and field strength vs frequency are completely consistent with predictions. These measurements thus provide strong support for experiments designed to detect high-energy cosmic rays such as neutrinos via coherent radio emission from their cascades.

Production and characterization of attosecond electron bunch trains

Abstract: We report the production of optically spaced attosecond electron microbunches produced by the inverse free-electron-laser (IFEL) process. The IFEL is driven by a Ti:sapphire laser synchronized with the electron beam. The IFEL is followed by a magnetic chicane that converts the energy modulation into the longitudinal microbunch structure. The microbunch train is characterized by observing coherent optical transition radiation (COTR) at multiple harmonics of the bunching. Experimental results are compared with 1D analytic theory showing good agreement. Estimates of the bunching factors are given and correspond to a microbunch length of 410 attosec FWHM. The formation of stable attosecond electron pulse trains marks an important step towards direct laser acceleration.

About these proceedings

Abstract: Mes premiers remtrciements trout aux auteurs des 206 communications th6matiquts et notes de projet, sans qui ces actes n'auraient 6videmment pas vu le jour. / Is oat contribu6 h la qualit6 scientifique et ,5 I'hmuog6t~6it6 pr6sentationntlle de leurs articles en refondant les versions iuitiales soumises an comit6 de programme, ea acceptant de suivre les r~gles de pr6sentation indiqu6es, et en nous envoyant parrots plusieurs versions am61ior6es surun point ou sur l'autrc.

Physics of plasmas

Abstract: 1 The Equations of Gas Dynamics 2 Magnetoplasma Dynamics 3 Waves in Magnetoplasmas 4 Magnetoplasma Stability 5 Transport in Magnetoplasmas 6 Extensions of Theory Bibliography Index

OSIRIS: A Three-Dimensional, Fully Relativistic Particle in Cell Code for Modeling Plasma Based Accelerators

Abstract: We describe OSIRIS, a three-dimensional, relativistic, massively parallel, object oriented particle-in-cell code for modeling plasma based accelerators. Developed in Fortran 90, the code runs on multiple platforms (Cray T3E, IBM SP, Mac clusters) and can be easily ported to new ones. Details on the code's capabilities are given. We discuss the object-oriented design of the code, the encapsulation of system dependent code and the parallelization of the algorithms involved. We also discuss the implementation of communications as a boundary condition problem and other key characteristics of the code, such as the moving window, open-space and thermal bath boundaries, arbitrary domain decomposition, 2D (cartesian and cylindric) and 3D simulation modes, electron sub-cycling, energy conservation and particle and field diagnostics. Finally results from three-dimensional simulations of particle and laser wakefield accelerators are presented, in connection with the data analysis and visualization infrastructure developed to post-process the scalar and vector results from PIC simulations.

Principles and applications of compact laser–plasma accelerators

Abstract: Rapid progress in the development of high-intensity laser systems has extended our ability to study light–matter interactions far into the relativistic domain, in which electrons are driven to velocities close to the speed of light. As well as being of fundamental interest in their own right, these interactions enable the generation of high-energy particle beams that are short, bright and have good spatial quality. Along with steady improvements in the size, cost and repetition rate of high-intensity lasers, the unique characteristics of laser-driven particle beams are expected to be useful for a wide range of contexts, including proton therapy for the treatment of cancers, materials characterization, radiation-driven chemistry, border security through the detection of explosives, narcotics and other dangerous substances, and of course high-energy particle physics. Here, we review progress that has been made towards realizing such possibilities and the principles that underlie them.

High-efficiency acceleration of an electron beam in a plasma wakefield accelerator

Abstract: To develop plasma wakefield acceleration into a compact and affordable replacement for conventional accelerators, beams of charged particles must be accelerated at high efficiency in a high electric field; here this is demonstrated for a bunch of charged electrons ‘surfing’ on a previously excited plasma wave. Particle colliders that operate at the high-energy frontier using electric fields generated by radio waves are approaching the limits of feasibility in terms of size and cost, but there are other acceleration techniques that could make less expensive and more compact devices. The plasma wakefield accelerator, in which an electron bunch is accelerated by making it 'surf' on a plasma wave excited by another electron bunch, promises an energy gain in the gigaelectron-volt regime over just a few centimetres — an energy gain that requires hundreds of metres using traditional accelerators. Previously, this technique had only been used to accelerate a very small number of electrons at a time. Now, researchers working at FACET, the Facility for Advanced Accelerator Experimental Tests at SLAC National Accelerator Laboratory, USA, have achieved acceleration of about half a billion electrons at once with an unprecedented efficiency for a plasma accelerator. This achievement could be a milestone in the development of affordable and compact accelerators for applications ranging from high energy physics to medical and industrial applications. High-efficiency acceleration of charged particle beams at high gradients of energy gain per unit length is necessary to achieve an affordable and compact high-energy collider. The plasma wakefield accelerator is one concept1,2,3 being developed for this purpose. In plasma wakefield acceleration, a charge-density wake with high accelerating fields is driven by the passage of an ultra-relativistic bunch of charged particles (the drive bunch) through a plasma4,5,6. If a second bunch of relativistic electrons (the trailing bunch) with sufficient charge follows in the wake of the drive bunch at an appropriate distance, it can be efficiently accelerated to high energy. Previous experiments using just a single 42-gigaelectronvolt drive bunch have accelerated electrons with a continuous energy spectrum and a maximum energy of up to 85 gigaelectronvolts from the tail of the same bunch in less than a metre of plasma7. However, the total charge of these accelerated electrons was insufficient to extract a substantial amount of energy from the wake. Here we report high-efficiency acceleration of a discrete trailing bunch of electrons that contains sufficient charge to extract a substantial amount of energy from the high-gradient, nonlinear plasma wakefield accelerator. Specifically, we show the acceleration of about 74 picocoulombs of charge contained in the core of the trailing bunch in an accelerating gradient of about 4.4 gigavolts per metre. These core particles gain about 1.6 gigaelectronvolts of energy per particle, with a final energy spread as low as 0.7 per cent (2.0 per cent on average), and an energy-transfer efficiency from the wake to the bunch that can exceed 30 per cent (17.7 per cent on average). This acceleration of a distinct bunch of electrons containing a substantial charge and having a small energy spread with both a high accelerating gradient and a high energy-transfer efficiency represents a milestone in the development of plasma wakefield acceleration into a compact and affordable accelerator technology.