There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Controlling chaos

http://ab-initio.mit.edu/~oskooi/papers/Oskooi10.pdf

Meep: A flexible free-software package for electromagnetic simulations by the FDTD method

Laser-driven accelerators, in which particles are accelerated by the electric field of a plasma wave (the wakefield) driven by an intense laser, have demonstrated accelerating electric fields of hundreds of GV m-1 (refs 1–3) These fields are thousands of times greater than those achievable in conventional radio-frequency accelerators, spurring interest in laser accelerators4,5 as compact next-generation sources of energetic electrons and radiation To date, however, acceleration distances have been severely limited by the lack of a controllable method for extending the propagation distance of the focused laser pulse The ensuing short acceleration distance results in low-energy beams with 100 per cent electron energy spread1,2,3, which limits potential applications Here we demonstrate a laser accelerator that produces electron beams with an energy spread of a few per cent, low emittance and increased energy (more than 109 electrons above 80 MeV) Our technique involves the use of a preformed plasma density channel to guide a relativistically intense laser, resulting in a longer propagation distance The results open the way for compact and tunable high-brightness sources of electrons and radiation

https://escholarship.org/content/qt9c55r46s/qt9c55r46s.pdf?t=lnras5

High-quality electron beams from a laser wakefield accelerator using plasma-channel guiding

Summary form only given. Fundamental processes in atoms, molecules, as well as condensed matter are triggered or mediated by the motion of electrons inside or between atoms. Electronic dynamics on atomic length scales tends to unfold within tens to thousands of attoseconds (1 attosecond [as] = 10-18 s). Recent breakthroughs in laser science are now opening the door to watching and controlling these hitherto inaccessible microscopic dynamics. The key to accessing the attosecond time domain is the control of the electric field of (visible) light, which varies its strength and direction within less than a femtosecond (1 femtosecond = 1000 attoseconds). Atoms exposed to a few oscillations cycles of intense laser light are able to emit a single extreme ultraviolet (XUV) burst lasting less than one femtosecond. Full control of the evolution of the electromagnetic field in laser pulses comprising a few wave cycles have recently allowed the reproducible generation and measurement of isolated sub-femtosecond XUV pulses, demonstrating the control of microscopic processes (electron motion and photon emission) on an attosecond time scale. These tools have enabled us to visualize the oscillating electric field of visible light with an attosecond "oscilloscope", to control single-electron and probe multi-electron dynamics in atoms, molecules and solids. Recent experiments hold promise for the development of an attosecond X-ray source, which may pave the way towards 4D electron imaging with sub-atomic resolution in space and time.

Attosecond Physics

For a particle moving in the electric field of many, randomly phase waves, numerical measurements show that the Lyapunov exponent (1) asymptotes to a value of 0.4 times the resonance broadening frequency, in contrast with previous calculations, and (2) has a peak at intermediate values of the overlap parameter. This latter result indicates that the previously observed enhancement of the diffusion coefficient is not due to coherence effects near stable regions of phase space. These results provide further evidence that the standard model is an inadequate description of the turbulent electric field.

Enhancement of Lyapunov exponents in one‐dimensional, randomly phased waves

Many high power electronic devices operate in a regime where the current they draw is limited by the self-fields of the particles. This space-charge-limited current poses particular challenges for numerical modeling where common techniques like over-emission or Gauss Law are computationally inefficient or produce nonphysical effects. In this paper we show an algorithm using the value of the electric field in front of the surface instead of attempting to zero the field at the surface, making the algorithm particularly well suited to both electromagnetic and parallel implementations of the PIC algorithm. We show how the algorithm is self-consistent within the framework of finite difference (for both electrostatics and electromagnetics). We show several 1D and 2D benchmarks against both theory and previous computational results. Finally we show application in 3D to high power microwave generation in a 13 GHz magnetically insulated line oscillator.

A new simple algorithm for space charge limited emission

Submitted for the DPP05 Meeting of The American Physical Society Modeling of complex geometries with the plasma simulation code VORPAL CHET NIETER, JOHN R. CARY1, PETER MESSMER, DAVID BRUHWILER, DAVID SMITHE, Tech-X Corporation, GREGORY R. WERNER, University of Colorado — Modeling complex structures and boundaries on a Cartesian grid is a challenge for many Finite Difference Time Domain (FDTD) electromagnetic PIC codes. The simulation of a variety of devices such as accelerating cavities, plasma processing chambers, and antennas at the edge of tokamaks require conformal (curve fitting) boundaries. Since these devices are fundamentally three dimensional, the capability to run in parallel on large numbers of processors is needed. We have recently added conformal boundaries using the method of Zagorodnov to the plasma simulation code VORPAL. Our boundary approximation can be viewed with a 3D VRML viewer. Also these complex devices often include open boundaries. VORPAL includes Perfectly Matched Layer (PML) boundaries which efficiently absorb out-going waves of any frequency and angle of incidence. VORPAL’s FDTD algorithms scale to thousands of processors allowing for large 3D simulations. Simulations of complex structures using VORPAL will be presented. 1also at University of Colorado

http://absimage.aps.org/image/DPP05/MWS_DPP05-2005-000499.pdf

Modeling of complex geometries with the plasma simulation code VORPAL

Three-dimensional laser wakefield acceleration (LWFA) simulations have recently been performed to benchmark the commonly used particle-in-cell (PIC) codes VORPAL, OSIRIS, and QuickPIC. The simulations were run in parallel on over 100 processors, using parameters relevant to LWFA with ultra-short Ti-Sapphire laser pulses propagating in hydrogen gas. Both first-order and second-order particle shapes were employed. We present the results of this benchmarking exercise, and show that accelerating gradients from full PIC agree for all values of a0 and that full and reduced PIC agree well for values of a0 approaching 4.

/pdf/benchmarking-the-codes-vorpal-osiris-and-quickpic-with-laser-19kflikw8o.pdf

Benchmarking the codes VORPAL, OSIRIS, and QuickPIC with Laser Wakefield Acceleration Simulations

A laser driven wakefield accelerator has been tuned to produce high energy electron bunches with low emittance and energy spread by extending the interaction length using a plasma channel. Wakefield accelerators support gradients thousands of times those achievable in RF accelerators, but short acceleration distance, limited by diffraction, has resulted in low energy beams with 100% electron energy spread. In the present experiments on the L’OASIS laser, the relativistically intense drive pulse was guided over 10 diffraction ranges by a plasma channel. At a drive pulse power of 9 TW, electrons were trapped from the plasma and beams of percent energy spread containing > 200 pC charge above 80 MeV and with normalized emittance estimated at < 2 π-mm-mrad were produced. Data and simulations (VORPAL code) show the high quality bunch was formed when beam loading turned off injection after initial trapping, and when the particles were extracted as they dephased from the wake. Up to 4 TW was guided without trapping, potentially providing a platform for controlled injection. The plasma channel technique forms the basis of a new class of accelerators, with high gradients and high beam quality.

/pdf/mono-energetic-beams-from-laser-plasma-interactions-v0zll2qdi0.pdf

John R. Cary

Papers

Enhancement of Lyapunov exponents in one‐dimensional, randomly phased waves

A new simple algorithm for space charge limited emission

Modeling of complex geometries with the plasma simulation code VORPAL

Benchmarking the codes VORPAL, OSIRIS, and QuickPIC with Laser Wakefield Acceleration Simulations

Mono-Energetic Beams from Laser Plasma Interactions