Advances in Laser Driven Accelerator R&D

Current activities (last few years) at different laboratories, towards the development of a laser wakefield accelerator (LWFA) are reviewed, followed by a more in depth discussion of results obtained at the L'OASIS laboratory of LBNL. Recent results on laser guiding of relativistically intense beams in preformed plasma channels are discussed. The observation of mono-energetic beams in the 100 MeV energy range, produced by a channel guided LWFA at LBNL, is described and compared to results obtained in the unguided case at LOA, RAL and LBNL. Analysis, aided by particle-in-cell simulations, as well as experiments with various plasma lengths and densities, indicate that tailoring the length of the accelerator has a very beneficial impact on the electron energy distribution. Progress on laser triggered injection is reviewed. Results are presented on measurements of bunch duration and emittance of the accelerated electron beams, that indicate the possibility of generating femtosecond duration electron bunches. Future challenges and plans towards the development of a 1 GeV LWFA module are discussed

Hepatitis B virus infection: Is patient tailored treatment feasible?

The hepatitis B virus (HBV) belongs to the family of hepadna viridae and has a diameter of 42-47 nm. The virus particle encloses a partially double-stranded DNA genome with a length of approximately 3200 base pairs. Within the viral DNA genome four open reading frames (ORFs) can be identified and are termed in analogy of their encoding protein S (surface), C (core), P (polymerase) and X (HBx protein). The ORF S contains 3 regions, the ore S1, pre S2 and S, which encode for the large, middle and small hepatitis B surface glycoproteins depending on the start of the transcription site, respectively. The ORF C is responsible for encoding the hepatitis B e-antigen (HBeAg) and the core antigen (HBcAg). After the binding of the virus particle to the hepatocyte, the HBV viral genome is converted into covalently closed circular DNA (cccDNA) in the hepatocyte nucleus. This cccDNA form the key template for pregenomic RNA in the HBV replication cycle and acts as a reservoir for the HBV. In the hepatocyte cytoplasm, along with the core and polymerase proteins the pregenomic RNA is assembled to virus particles. Sequentially, the RNA is reversed transcribed into a HBV-DNA minus strand, which is finally transcribed by a HBV DNA polymerase into the HBV DNA plus strand. The formed particle can either be excreted via the Golgi apparatus or recycled into the nucleus to form ccc-DNA. As a result of variety in expression of the viral genome, the HBV is divided into 8 different genotypes, A-H. The HBV genotypes are also characterized by different geographical and demographical distribution. Genotype A is predominantly found in North-West Europe and North America, whereas genotypes B and C are mostly seen in Asian countries. Genotype D is most common in the Mediterranean area. Consequently, Caucasians harbor predominantly genotype A and D, while Asians harbor almost exclusively the genotypes B and C. Hepatitis B virus infection is a serious global health problem with more than 350 million people suffering from chronic hepatitis B virus infection

Pulse evolution and plasma-wave phase velocity in channel-guided laser-plasma accelerators.

The self-consistent laser evolution of an intense, short-pulse laser exciting a plasma wave and propagating in a preformed plasma channel is investigated, including the effects of pulse steepening and energy depletion. In the weakly relativistic laser intensity regime, analytical expressions for the laser energy depletion, pulse self-steepening rate, laser intensity centroid velocity, and phase velocity of the plasma wave are derived and validated numerically

THE 13TH ADVANCED ACCELERATOR CONCEPTS WORKSHOP (AAC'8)

The Thirteenth Workshop on Advanced Accelerator Concepts (AAC) was held from July 27 to August 2, 2008 at the Chaminade Conference Center in Santa Cruz, California, USA, organized by the Lawrence Berkeley National Laboratory and the University of California at Berkeley. There were unprecedented levels of interest in the 2008 AAC Workshop, and participation was by invitation, with 215 workshop attendees, including 58 students. Reflecting the world-wide growth of the advanced accelerator community, there was significant international participation, with participants from twelve countries attending

Summary Report of Working Group 6: Laser-Plasma Acceleration

A summary is given of presentations and discussions in theLaser-Plasma Acceleration Working Group at the 2006 Advanced AcceleratorConcepts Workshop. Presentation highlights include: widespreadobservation of quasi-monoenergetic electrons; good agreement betweenmeasured and simulated beam properties; the first demonstration oflaser-plasma acceleration up to 1 GeV; single-shot visualization of laserwakefield structure; new methods for measuring<100 fs electronbunches; and new methods for "machining" laser-plasma acceleratorstructures. Discussion of future direction includes: developing a roadmapfor laser-plasma acceleration beyond 1 GeV; a debate over injection andguiding; benchmarking simulations with improved wake diagnostics;petawatt laser technology for future laser-plasmaaccelerators

Immersive Neural Graphics Primitives

Neural radiance field (NeRF), in particular its extension by instant neural graphics primitives, is a novel rendering method for view synthesis that uses real-world images to build photo-realistic immersive virtual scenes. Despite its potential, research on the combination of NeRF and virtual reality (VR) remains sparse. Currently, there is no integration into typical VR systems available, and the performance and suitability of NeRF implementations for VR have not been evaluated, for instance, for different scene complexities or screen resolutions. In this paper, we present and evaluate a NeRF-based framework that is capable of rendering scenes in immersive VR allowing users to freely move their heads to explore complex real-world scenes. We evaluate our framework by benchmarking three different NeRF scenes concerning their rendering performance at different scene complexities and resolutions. Utilizing super-resolution, our approach can yield a frame rate of 30 frames per second with a resolution of 1280x720 pixels per eye. We discuss potential applications of our framework and provide an open source implementation online.Comment: Submitted to IEEE VR, currently under revie

Low transverse emittance electron bunches from two-color laser-ionization injection

A method is proposed to generate low emittance electron bunches from two color laser pulses in a laser-plasma accelerator. A two-region gas structure is used, containing a short region of a high-Z gas (e.g., krypton) for ionization injection, followed by a longer region of a low-Z gas for post-acceleration. A long-laser-wavelength (e.g., 5 micron) pump pulse excites plasma wake without triggering the inner-shell electron ionization of the high-Z gas due to low electric fields. A short-laser-wavelength (e.g., 0.4 micron) injection pulse, located at a trapping phase of the wake, ionizes the inner-shell electrons of the high-Z gas, resulting in ionization-induced trapping. Compared with a single-pulse ionization injection, this scheme offers an order of magnitude smaller residual transverse momentum of the electron bunch, which is a result of the smaller vector potential amplitude of the injection pulse

Laser and electron deflection from transverse asymmetries in laser-plasma accelerators.

We report on the deflection of laser pulses and accelerated electrons in a laser-plasma accelerator (LPA) by the effects of laser pulse front tilt and transverse density gradients. Asymmetry in the plasma index of refraction leads to laser steering, which can be due to a density gradient or spatiotemporal coupling of the laser pulse. The transverse forces from the skewed plasma wave can also lead to electron deflection relative to the laser. Quantitative models are proposed for both the laser and electron steering, which are confirmed by particle-in-cell simulations. Experiments with the BELLA Petawatt Laser are presented which show controllable 0.1-1 mrad laser and electron beam deflection from laser pulse front tilt. This has potential applications for electron beam pointing control, which is of paramount importance for LPA applications