Particle Acceleration

Due to the interaction of physics and astrophysics we are witnessing in these years a splendid synthesis of theoretical, experimental and observational results originating from three fundamental physical processes. They were originally proposed by Dirac, by Breit and Wheeler and by Sauter, Heisenberg, Euler and Schwinger. For almost seventy years they have all three been followed by a continued effort of experimental verification on Earth-based experiments. The Dirac process, e + e − → 2γ, has been by far the most successful. It has obtained extremely accurate experimental verification and has led as well to an enormous number of new physics in possibly one of the most fruitful experimental avenues by introduction of storage rings in Frascati and followed by the largest accelerators worldwide: DESY, SLAC etc. The Breit-Wheeler process, 2γ → e + e − , although conceptually simple, being the inverse process of the Dirac one, has been by far one of the most difficult to be verified experimentally. Only recently, through the technology based on free electron X-ray laser and its numerous applications in Earth-based experiments, some first indications of its possible verification have been reached. The vacuum polarization process in strong electromagnetic field, pioneered by Sauter, Heisenberg, Euler and Schwinger, introduced the concept of critical electric field E c = m 2 e c 3 /(e ). It has been searched without success for more than forty years by heavy-ion collisions in many of the leading particle accelerators worldwide.

Recently many ideas have been proposed for the use of a longitudinal field for particle acceleration, fluorescent imaging, secondharmonic generation and Raman spectroscopy. A few methods to enhance the longitudinal field component have been suggested, but all have insufficient optical efficiency and non-uniform axial field strength. Here we report a new method that permits the combination of very unusual properties of light in the focal region, permitting the creation of a 'pure' longitudinal light beam with subdiffraction beam size (0.43l). This beam is non-diffracting; that is, it propagates without divergence over a long distance (of about 4l) in free space. This is achieved by focusing a radially polarized Bessel -Gaussian beam with a combination of a binary-phase optical element and a high-numerical-aperture lens. This binary optics works as a special polarization filter enhancing the longitudinal component.

The compact linear collider (CLIC) is the particles accelerator project proposed by the european organization for nuclear research (CERN) for high energy physics after the large hadron collider (LHC). Because of the nanometric scale of the CLIC leptons beams, the emittance growth budget is very tight. It induces alignment tolerances on the positions of the CLIC components that have never been achieved. The last step of the CLIC alignment will be done according to the beam itself. It falls within the competence of the physicists. However, in order to implement the beam-based feedback, a challenging pre-alignment is required : 10 μm at 3σ along a 200 m sliding window. For such a precision, the proposed solution must be compatible with a feedback between the measurement and repositioning systems. The CLIC pre-alignment will have to be active. This thesis does not demonstrate the feasibility of the CLIC active prealignment but shows the way to the last developments that have to be done ...

excellent at most wavelengths. The plateau between 1,700 Å and 3,000 Å is due to a local minimum between two broad absorption features caused by amorphous carbon grains, with the added flat contribution from Fe 3 O 4 grains. Silicate grains contribute to the rise at shorter wavelengths.

The description of the motion of immersed bodies in fluids is present in several manufacturing processes. In the current study, the unsteady motion of a spherical particle rolling down an inclined plane submerged in a Newtonian environment has been studied using a drag of the form given by Chhabra and Ferreira, for wide range of Reynolds numbers. An analytical solution for velocity, acceleration and position of the particle is derived, using homotopy perturbation method. Equation of motion was solved generally and for some practical conditions. The present investigation shows the effectiveness of HPM and exhibits a new application of this method for nonlinear problems.

1] This paper addresses the question of particular characteristics and causes of intense space storms. We focus on several unresolved issues, which are critical to storm research and often nourish open disputes: the extent of interplanetary driving, the role of substorms in storm dynamics through the acceleration of particles to ring current energies, the identity of the lead agent of fast ring current decay right after storm maximum and the cause of the two-phase recovery of intense storms, the global morphology of the stormtime ring current, and the predictability of intense storms. Space storm physics has been driven by several more or less successful paradigms during the four decades following the dawn of the space flight era. However, recent suggestions and conclusions resulting from a number of observational and modeling studies have brought significant constraints to several of these paradigms. Thus for example, interplanetary driving through southward oriented magnetic fields is not always by itself sufficient to drive intense space storms because it is conditioned by internal magnetospheric conditions, the MLT distribution of storm-time magnetic disturbances is often asymmetric during the storm main phase, and charge exchange is not the lead agent of ring current decay at all times. Intense space storms: Critical issues and open disputes,

Hard X-ray emission from the solar corona the date of receipt and acceptance should be inserted later Abstract This review surveys hard X-ray emissions of non-thermal electrons in the solar corona. These electrons originate in flares and flare-related processes. Hard X-ray emission is the most direct diagnostic of electron presence in the corona, and such observations provide quantitative determinations of the total energy in the non-thermal electrons. The most intense flare emissions are generally observed from the chromosphere at footpoints of magnetic loops. Over the years, however, many observations of hard X-ray and even γray emission directly from the corona have also been reported. These coronal sources are of particular interest as they occur closest to where the electron acceleration is thought to occur. Prior to the actual direct imaging observations, disk occultation was usually required to study coronal sources, resulting in limited physical information. Now RHESSI 1 has given us a systematic view of coronal sources that combines high spatial and spectral resolution with broad energy coverage and high sensitivity. Despite the low density and hence low bremsstrahlung efficiency of the corona, we now detect coronal hard X-ray emissions from sources in all phases of solar flares. Because the physical conditions in such sources may differ substantially from those of the usual "footpoint" emission regions, we take the opportunity to revisit the physics of hard X-radiation and relevant theories of particle acceleration.

The terrestrial ring current consists of energetic charged particles owing toroidally around the Earth, and creating a ring of westward electric current, centered at the equatorial plane and extending from geocentric distances of about 3-8RE. Changes in this current are responsible for global decreases in the Earth's surface magnetic ÿeld, which is the deÿning feature of geomagnetic storms. The ring current is a critical element in understanding the onset and development of space weather disturbances in geospace. This review paper discusses recent developments in ring current research, and outlines the presently hottest issues, most of which were addressed at the Ring Current

In laser-plasma-based accelerators 1 , an intense laser pulse drives a large electric field (the wakefield) which accelerates particles to high energies in distances much shorter than in conventional accelerators. These high acceleration gradients, of a few hundreds of gigavolts per metre, hold the promise of compact high-energy particle accelerators. Recently, several experiments have shown that laser-plasma accelerators can produce high-quality electron beams, with quasi-monoenergetic energy distributions at the 100 MeV level 2-4 . However, these beams do not have the stability and reproducibility that are required for applications. This is because the mechanism responsible for injecting electrons into the wakefield is based on highly nonlinear phenomena 5 , and is therefore hard to control. Here we demonstrate that the injection and subsequent acceleration of electrons can be controlled by using a second laser pulse 6 . The collision of the two laser pulses provides a pre-acceleration stage which provokes the injection of electrons into the wakefield. The experimental results show that the electron beams obtained in this manner are collimated (5 mrad divergence), monoenergetic (with energy spread ,10 per cent), tuneable (between 15 and 250 MeV) and, most importantly, stable. In addition, the experimental observations are compatible with electron bunch durations shorter than 10 fs. We anticipate that this stable and compact electron source will have a strong impact on applications requiring short bunches, such as the femtolysis of water 7 , or high stability, such as radiotherapy with high-energy electrons 8,9 or radiography 10 for materials science.

■ Abstract Moving highly-charged ions carry strong electromagnetic fields that act as a beam of photons. In collisions at large impact parameters, hadronic interactions are not possible, and the ions interact through photon-ion and photon-photon collisions known as ultra-peripheral collisions (UPCs). Hadron colliders like the Relativistic Heavy Ion Collider (RHIC), the Tevatron, and the Large Hadron Collider (LHC) produce photonuclear and two-photon interactions at luminosities and energies beyond that accessible elsewhere; the LHC will reach a γ p energy ten times that of the Hadron-Electron Ring Accelerator (HERA). Reactions as diverse as the production of anti-hydrogen, photoproduction of the ρ 0 , transmutation of lead into bismuth, and excitation of collective nuclear resonances have already been studied. At the LHC, UPCs can study many types of new physics processes.

A desired trend within high energy physics is to increase particle accelerator luminosities, leading to production of more collision data and higher probabilities of finding interesting physics results. A central data analysis technique used to determine whether results are interesting or not is the maximum likelihood method, and the corresponding evaluation of the negative log-likelihood, which can be computationally expensive. As the amount of data grows, it is important to take benefit from the parallelism in modern computers. This, in essence, means to exploit vector registers and all available cores on CPUs, as well as utilizing co-processors as GPUs.

in natural, non-metamict zircon was characterized under both dry and water-present conditions at temperatures ranging from 765°C to 1500°C. Dry experiments were performed at atmospheric pressure by encapsulating polished zircon samples with a fine powder of "O-enriched quartz and annealing the sealed capsules in air. Hydrothermal runs were conducted in cold-seal pressure vessels (7-70 MPa) or a piston cylinder apparatus (400-1000 MPa) on zircon samples encapsulated with both "O-enriched quartz and "0 water. Diffusive-uptake profiles of 'so were measured in all samples with a particle accelerator, using the "O( p, (Y )15N reaction. For dry experimental conditions at 11 OO-1500°C the resulting oxygen diffusivities (24 in all) are well described by:

The physics of collisionless shocks is a very broad topic, which has been well studied for many decades. However, there are a number of important issues which remain unresolved. Moreover, there have been new findings, which cast doubt on well-established ideas. The purpose of this review is to address a subset of unresolved problems in collisionless shock physics from a theoretical and/or numerical modeling point of view. The topics which are addressed are: the nonstationarity of the shock front, the heating and dynamics of electrons through the shock layer, particle diffusion in turbulent electric and magnetic fields, particle acceleration, and the interaction of pickup ions with collisionless shocks.

An in-situ large-scale underground blast test program was conducted to investigate stress wave characteristics inside the medium, at the soil-rock interface and on the soil ground surface. The stress wave measurements were made through a vertical borehole and a horizontal borehole inside the rock mass, and along several horizontal lines arranged at the rock-soil interface and on the soil surface. Three different charge weights of 0.5, 2.5 and 10 t with loading densities of 0.5, 2.5 and 10 kg/m 3 , respectively, were used in the detonation. The measured stress wave time histories and their characteristic parameters, such as peak particle velocity (PPV) and peak particle acceleration (PPA), as well as the principal frequency (PF) at different locations are presented and analyzed in this paper. The results are also compared with those recorded from small-scale tests in a previous study and those from some other researchers, and the pertinent scale effects are discussed by observing differences of the stress wave intensities between the small-scale and the large-scale tests.

This chapter reviews the current understanding of ring current dynamics. The terrestrial ring current is an electric current flowing toroidally around the Earth, centered at the equatorial plane and at altitudes of ∼10,000 to 60,000 km. Enhancements in this current are responsible for global decreases in the Earth's surface magnetic field, which have been used to define geomagnetic storms. Intense geospace magnetic storms have severe effects on technological systems, such as disturbances or even permanent damage of telecommunication and navigation satellites, telecommunication cables, and power grids. The main carriers of the ring current are positive ions, with energies from ∼1 keV to a few hundred keV, which are trapped by the geomagnetic field and undergo an azimuthal drift. The ring current is formed by the injection of ions originating in the solar wind and the terrestrial ionosphere into the inner magnetosphere. The injection process involves electric fields, associated with enhanced magnetospheric convection and/or magnetospheric substorms. The quiescent ring current is carried mainly by protons of predominantly solar wind origin, while active processes in geospace tend to increase the abundance (both absolute and relative) of O + ions, which are of ionospheric origin. During intense geospace magnetic storms, the O + abundance increases dramatically. This increase has been observed to occur concurrently with the rapid intensification of the ring current in the storm main phase and to result in O + dominance around storm maximum. This compositional change can affect several dynamic processes, such as species-and energy-dependent charge-exchange and wave-particle scattering loss.

The plasma particle velocity distributions observed in the solar wind generally show enhanced (non-Maxwellian) suprathermal tails, decreasing as a power law of the velocity and well described by the family of Kappa distribution functions. The presence of non-thermal populations at different altitudes in space plasmas suggests a universal mechanism for their creation and important consequences concerning plasma fluctuations, the resonant and nonresonant wave -particle acceleration and plasma heating. These effects are well described by the kinetic approaches where no closure requires the distributions to be nearly Maxwellian. This paper summarizes and analyzes the various theories proposed for the Kappa distributions and their valuable applications in coronal and space plasmas.

We review basic theoretical concepts in particle acceleration, with particular emphasis on processes likely to occur in regions of magnetic reconnection. Several new developments are discussed, including detailed studies of reconnection in three-dimensional magnetic field configurations (e.g., current sheets, collapsing traps, separatrix regions) and stochastic acceleration in a turbulent environment. Fluid, test-particle, and particle-in-cell approaches are used and results compared. While these studies show considerable promise in accounting for the various observational manifestations of solar flares, they are limited by a number of factors, mostly relating to available computational power. Not the least of these issues is the need to explicitly incorporate the electrodynamic feedback of the accelerated particles themselves on the environment in which they are accelerated. A brief prognosis for future advancement is offered.

The energy released in solar flares derives from a reconfiguration of magnetic fields to a lower energy state, and is manifested in several forms, including bulk kinetic energy of the coronal mass ejection, acceleration of electrons and ions, and enhanced thermal energy that is ultimately radiated away across the electromagnetic spectrum from optical to x rays. Using an unprecedented set of coordinated observations, from a suite of instruments, we here report on a hitherto largely overlooked energy component-the kinetic energy associated with small-scale turbulent mass motions. We show that the spatial location of, and timing of the peak in, turbulent kinetic energy together provide persuasive evidence that turbulent energy may play a key role in the transfer of energy in solar flares. Although the kinetic energy of turbulent motions accounts, at any given time, for only ∼ð0.5-1Þ% of the energy released, its relatively rapid (∼1-10 s) energization and dissipation causes the associated throughput of energy (i.e., power) to rival that of major components of the released energy in solar flares, and thus presumably in other astrophysical acceleration sites.

excellent at most wavelengths. The plateau between 1,700 Å and 3,000 Å is due to a local minimum between two broad absorption features caused by amorphous carbon grains, with the added flat contribution from Fe 3 O 4 grains. Silicate grains contribute to the rise at shorter wavelengths.

"The Internet economy has been conceptualized as a contradiction or symbiosis between commodity and gift exchange. Richard Barbrook (2005) argues that the Internet, with its reliance on non-rivalrous digital data and low cost of copying, enables the existence of a high-tech version of the gift economies that Marcell Mauss (1954) and other economic anthropologists have theorized. Similarly, Christian Fuchs argues that "information gifts form a part of the Internet economy in which goods are distributed for free and openly accessible." Lawrence Lessig (2008) conceptualizes the gift economy as part of read-write culture, which is inherently about sharing. Lessig counterposes “read-write” culture with a commercial “read-only” culture. Read-only objects are subject to copyright and before they can be used permission must be given, usually granted through purchase. Barbrook also recognizes that the same piece of digital code may exist as both a gift and a commodity. Similarly, Fuchs argues that the circulation of digital commodities form part of a sub-system of the Internet economy that is controlled by intellectual property rights.

This paper, while agreeing with Barbrook, Fuchs and Lessig that the Internet economy is a contradiction between gifts and commodities, will argue that these theorists have focused only on appearances and have not recognized the fundamental contradiction of the Internet. Basing this argument on another iteration of Marx's argument that exchange “produces a differentiation of the commodity into two elements, commodity and money, an external opposition which expresses the opposition between use-value and value which is inherent in it” (1976:199), I will argue that gifts and commodities are the forms of appearance, or expression, of the fundamental and internal contradiction of the Internet economy. Conceiving the Internet as a real-time environment, the paper will argue that the internal contradiction is temporal: between simultaneity and immediacy"

Radio frequency and Microwave (RFM) infrastructure test facility is under development at RRCAT for evaluating and powering, subsystems of particle accelerator. As a part of this facility, design of 20-30 kW UHF Solid State Power Amplifiers is in progress. For this work, design procedure has been formulated for the development of solid state amplifier modules, radial combiner, divider and directional coupler; with specifications suited to RFM power system for particle accelerator. Methodology has been demonstrated by developing two different amplifiers with power output of 2 kW each, operating at 352 MHz and 505.8 MHz respectively. This paper describes underlying design principles and indigenous development of these amplifiers, consisting of 270-300 W amplifier modules, 8-way 2 kW radial combiner/divider and directional couplers. Design methodology for power combiner has been extended by physically realising higher power (4 kW) 16-way power combiner and 2-way combiner (8 kW) for higher power (8 kW) amplifier configuration planned. Simple design, indigenous technology, high efficiency and ease of fabrication, are the main features of this design.

NASA's two spacecraft ARTEMIS mission will address both heliospheric and planetary research questions, first while in orbit about the Earth with the Moon and subsequently while in orbit about the Moon. Heliospheric topics include the structure of the Earth's magnetotail; reconnection, particle acceleration, and turbulence in the Earth's magnetosphere, at the bow shock, and in the solar wind; and the formation and structure of the D.G. Sibeck ( ) Code 674, GSFC/NASA, J. Raeder UNH, Durham, NH, USA position of the lunar surface, the effects of electric fields on dust in the exosphere, internal structure of the Moon, and the lunar crustal magnetic field. This paper describes the expected contributions of ARTEMIS to these baseline scientific objectives.

Astrophysical fluids have very large Reynolds numbers and there- fore turbulence is their natural state. Magnetic reconnection is an important process in many astrophysical plasmas, which allows restructuring of magnetic fields and conversion of stored magnetic energy into heat and kinetic energy. Turbulence is known to dramatically change different transport processes and therefore it is not unexpected that turbulence can alter the dynamics of mag- netic field lines within the reconnection process. We shall review the interaction between turbulence and reconnection at different scales, showing how a state of turbulent reconnection is natural in astrophysical plasmas, with implica- tions for a range of phenomena across astrophysics. We consider the process of magnetic reconnection that is fast in magnetohydrodynamic (MHD) limit and discuss how turbulence - both externally driven and generated in the re- connecting system - can make reconnection independent on the microphysical properties of plasmas. We will also show how relaxation theory can be used to calculate the energy dissipated in turbulent reconnecting fields. As well as heating the plasma, the energy dissipated by turbulent reconnection may cause acceleration of non-thermal particles, which is briefly discussed here.

With the advent of the LHC and the continuing influx of cosmological data, phenomenological aspects of string theory have received renewed attention in recent years and many problems have been properly incorporated in this framework. For instance, recent theoretical considerations in string theory have applied a statistical approach to the enormous landscape of metastable vacua. The large number of vacua may shed some light on the cosmological constant problem. In addition, in string theory, attempts have been made to address the hierarchy problem within the context of the existence of large or warped internal dimensions transverse to a braneworld where we are confined, which lowers the effective scale of gravity to the TeV region. If this were the case, unseen dimensions of the space-time can be at the border of the energy domain within reach of the next generation of particle accelerators.

The Large Hadron Collider (LHC), a particle accelerator aimed at exploring deeper into matter than ever before, is currently being constructed at CERN. Beam optics of the LHC, requires stringent control of the field quality of about 8400 superconducting magnets, including 1232 main dipoles and 360 main quadrupoles to assure the correct machine operation. The measurement challenges are various: accuracy on the field strength measurement up to 50 ppm, harmonics in the ppm range, measurement equipment robustness, low measurement times to characterize fast field phenomena.

The Proton Synchrotron * accelerator (PS), installed at CERN † , although commissioned in 1959, still plays a central role in the production of beams for the Antiproton Decelerator, Super Proton Synchrotron, various experimental areas and for the Large Hadron Collider (LHC) ‡ .

This report documents the activities of the Snowmass 2001 T4 Particle Sources Working Group. T4 was charged with examining the most challenging aspects of positron sources for linear colliders and antiproton sources for proton-antiproton colliders, and the secondary beams of interest to the physics community that will be available from the next generation of high-energy particle accelerators. The leading issues, limiting technologies, and most important R&D efforts of positron production, antiproton production, and secondary beams are discussed in this paper. A listing of T4 Presentations is included.

Saturn is the result of a major metamorphosis of the Particle Beam Fusion Accelerator-I (PBFA-I) from an ICF research facility to the large-area x-ray source of the Simulation Technology Laboratory (STL) project. Renamed Saturn, for its unique

Boron-neutron capture therapy (BNCT) is an experimental radiation treatment modality used for highly malignant tumor treatments. Prior to irradiation with low energetic neutrons, a 10B compound is located selectively in the tumor cells. The effect of the treatment is based on the high LET radiation released in the ¹°B(n,α)⁷Li reaction with thermal neutrons. BNCT has been used experimentally for brain

Fast reconnection of magnetic field in turbulent fluids allows the field to change its topology and connec- tions. As a result, the traditional concept of magnetic fields being frozen into the plasma is no longer applicable. Plasma associated with a given magnetic field line at one instant is distributed along a different set of magnetic field lines at the next instant. This diffusion of plasmas and magnetic field is enabled by reconnection and therefore is termed ”reconnec- tion diffusion”. The astrophysical implications of this con- cept include heat transfer in plasmas, advection of heavy el- ements in interstellar medium, magnetic field generation etc. However, the most dramatic implications of the concept are related to the star formation process. The reason is that mag- netic fields are dynamically important for most of the stages of star formation. The existing theory of star formation has been developed ignoring the possibility of reconnection dif- fusion. Instead, it appeals to the decoupling of mass and magnetic field arising from neutrals drifting in respect to ions entrained on magnetic field lines, i.e. through the pro- cess that is termed ”ambipolar diffusion”. The predictions of ambipolar diffusion and reconnection diffusion are very different. For instance, if the ionization of media is high, am- bipolar diffusion predicts that the coupling of mass and mag- netic field is nearly perfect. At the same time, reconnection diffusion is independent of the ionization but depends on the scale of the turbulent eddies and on the turbulent velocities. In the paper we explain the physics of reconnection diffusion both from macroscopic and microscopic points of view, i.e. appealing to the reconnection of flux tubes and to the dif-
the dynamics of many key processes, including magnetic re- connection. Fast reconnection of magnetic field in turbulent fluids allows the field to change its topology and connec- tions. As a result, the traditional concept of magnetic fields being frozen into the plasma is no longer applicable. Plasma associated with a given magnetic field line at one instant is distributed along a different set of magnetic field lines at the next instant. This diffusion of plasmas and magnetic field is enabled by reconnection and therefore is termed ”reconnec- tion diffusion”. The astrophysical implications of this con- cept include heat transfer in plasmas, advection of heavy el- ements in interstellar medium, magnetic field generation etc. However, the most dramatic implications of the concept are related to the star formation process. The reason is that mag- netic fields are dynamically important for most of the stages of star formation. The existing theory of star formation has been developed ignoring the possibility of reconnection dif- fusion. Instead, it appeals to the decoupling of mass and magnetic field arising from neutrals drifting in respect to ions entrained on magnetic field lines, i.e. through the pro- cess that is termed ”ambipolar diffusion”. The predictions of ambipolar diffusion and reconnection diffusion are very different. For instance, if the ionization of media is high, am- bipolar diffusion predicts that the coupling of mass and mag- netic field is nearly perfect. At the same time, reconnection diffusion is independent of the ionization but depends on the scale of the turbulent eddies and on the turbulent velocities. In the paper we explain the physics of reconnection diffusion both from macroscopic and microscopic points of view. We make use of the Lazarian & Vishniac 1999 theory of magnetic reconnection and show that this theory is applicable to the partially ionized gas. We quantify the reconnection diffusion rate both for weak and strong MHD turbulence and address the problem of recon- nection diffusion acting together with ambipolar diffusion. In addition, we provide a criterion for correctly representing the magnetic diffusivity in simulations of star formation. We discuss the intimate relation between the processes of recon- nection diffusion, field wandering and turbulent mixing of a magnetized media and show that the role of the plasma ef- fects is limited to ”breaking up lines” on small scales and does not affect the rate of reconnection diffusion. We ad- dress the existing observational results and demonstrate how reconnection diffusion can explain the puzzles presented by observations, in particular, the observed higher magnetiza- tion of cloud cores in comparison with the magnetization of envelopes. We also outline a possible set of observational tests of the reconnection diffusion concept and discuss how the application of the new concept changes our understand- ing of star formation and its numerical modeling. Finally, we outline the differences of the process of reconnection diffusion and the process of accumulation of matter along magnetic field lines that is frequently invoked to explain the results of numerical simulations

A solid state pulsed power generator rated at 100 kV, 2 MW peak, 0.8 ms/2 Hz suited for klystrons cathode power supply (klystron modulator) is proposed as an alternative to traditional topologies, requiring thyratrons and PFN's, for long pulse width applications (ms range). Some technological issues and design criteria of the proposed circuit main sub-systems (solid state switch, pulse transformer,

Non-luminous relativistic electron beams above thunderclouds are detected by radio remote sensing with low frequency radio signals from ∼40-400 kHz. The electron beams occur ∼2-9 ms after positive cloud-to-ground lightning discharges at heights between ∼22-72 km above thunderclouds. The positive lightning discharges also cause 5 sprites which occur either above or before the electron beam. One electron beam was detected without any luminous sprite occurrence which suggests that electron beams may also occur independently. Numerical simulations show that the beamed electrons partially discharge the lightning electric field above thunderclouds and thereby gain a mean energy of ∼7 MeV to transport a total charge of ∼10 mC upwards. The impul-10 sive current associated with relativistic electron beams above thunderclouds is directed downwards and needs to be considered as a novel element of the global atmospheric electric circuit. ulation of energetic seed particles to initiate an electromagnetically radiating non-linear 15553 ACPD Abstract Relativistic electron beams M. Füllekrug et al. Title Page Abstract Relativistic electron beams M. Füllekrug et al. Title Page Abstract Relativistic electron beams M. Füllekrug et al. Title Page Abstract Relativistic electron beams M. Füllekrug et al.

Collisions of high Mach number flows occur frequently in astrophysics, and the resulting shock waves are responsible for the properties of many astrophysical phenomena, such as supernova remnants, Gamma Ray Bursts and jets from Active Galactic Nuclei. Because of the low density of astrophysical plasmas, the mean free path due to Coulomb collisions is typically very large. Therefore, most shock waves in astrophysics are "collisionless", since they form due to plasma instabilities and self-generated magnetic fields. Laboratory experiments at the laser facilities can achieve the conditions necessary for the formation of collisionless shocks, and will provide a unique avenue for studying the nonlinear physics of collisionless shock waves. We are performing a series of experiments at the Omega and Omega-EP lasers, in Rochester, NY, with the goal of generating collisionless shock conditions by the collision of two highspeed plasma flows resulting from laser ablation of solid targets using w10 16 W/cm 2 laser irradiation. The experiments will aim to answer several questions of relevance to collisionless shock physics: the importance of the electromagnetic filamentation (Weibel) instabilities in shock formation, the selfgeneration of magnetic fields in shocks, the influence of external magnetic fields on shock formation, and the signatures of particle acceleration in shocks. Our first experiments using Thomson scattering diagnostics studied the plasma state from a single foil and from double foils whose flows collide "headon". Our data showed that the flow velocity and electron density were 10 8 cm/s and 10 19 cm À3 , respectively, where the Coulomb mean free path is much larger than the size of the interaction region. Simulations of our experimental conditions show that weak Weibel mediated current filamentation and magnetic field generation were likely starting to occur. This paper presents the results from these first Omega experiments.

Three different target tissues (protoplast-derived ceils, nodules, and stems) and two unrelated hybrid genotypes of Populus (P. alba x P. grandidentata 'Crandon' and P. nigra 'Betulifolia' x P. trichocarpa) have been stably transformed by electric discharge particle acceleration using a 18.7 kb plasmid containing NOS-NPT, CaMV 35S-GUS, and CaMV 35S-BT. Four transformed plants of one hybrid genotype, NC5339, containing all 3 genes were recovered and analyzed. Two expressed GUS and one was highly resistant to feeding by 2 lepidopteran pests (the forest tent caterpillar, Malacosoma disstria, and the gypsy moth, Lymantria dispar). Pretreatment of the target tissues, fine-tuning of the bombardment parameters, and the use of a selection technique employing flooding of the target tissues were important for reliable recovery of transformed plants.

Current efforts in structural biology aim to integrate structural information within the context of cellular organization and function. X-rays and infrared radiation stand at opposite ends of the electromagnetic spectrum and act as complementary probes for achieving this goal. Intense and bright beams are produced by synchrotron radiation, and are efficiently used in the wavelength domain extending from hard X-rays to the farinfrared (or THz) regime. While X-ray crystallography provides exquisite details on atomic structure, Fourier transform infrared microspectroscopy (FTIRM) is emerging as a spectroscopic probe and imaging tool for correlating molecular structure to biochemical dynamics and function. In this manuscript, the role of synchrotron FTIRM in bridging the gap towards 'functional biology' is discussed based upon recent achievements, with a critical assessment of the contributions to biological and biomedical research.

High-energy particle accelerator UHV systems subjected to energetic charged particle or photon bombardment are particularly sensitive to surface contamination. Well-established cleaning procedures employing solvents such as Freon and perchloroethylene to prepare vacuum system components have been used at CERN for many years. The recently adopted legislation which prescribes or strongly limits the use of some chemicals has led CERN to undertake a qualification programme using electron stimulated desorption, Auger spectroscopy and radioactive tracers to compare the cleaning efficiency of a wide range of alternative cleaning agents.

This paper summarizes the results obtained with the HELEOS railgun which uses a two-stage light-gas gun (2SLGG) as an injector [ 11. The high velocity 2SLGG injector pre-accelerates projectiles up to -7 km/s. The high injection velocity reduces the exposure duration of the railgun barrel to the passing high temperature plasma armature, thereby reducing the ablation and subsequent armature growth. The 2SLGG also provides a column of cool, high pressure hydrogen gas to insulate the rails behind the projectile, thereby eliminating restrike. A means to form an armature behind the injected projectile has been developed. In preliminary tests, the third stage railgun has successfully increased the projectile velocity by 1.35 km/s. Extensive diagnostics have been used to determine the behavior of the armature and rrack the launcher's performance. In some cases, velocity increases in the railgun section have been achieved, which are in close agreement with theoretical predictions, whereas in other experiments deviations from theoretical have been observed. The reasons for and implications of these results are addressed. Recent tests are reported.

We present examples of the application of synchrotron-based spectroscopies and microscopies to environmentally relevant samples. The experiments were performed at the molecular environmental science beamline (11.0.2) at the Advanced Light Source, Lawrence Berkeley National Laboratory. Examples range from the study of water monolayers on Pt(1 1 1) single crystal surfaces using X-ray emission spectroscopy and the examination of alkali halide solution/water vapor interfaces using ambient pressure photoemission spectroscopy, to the investigation of actinides, river water biofilms, Al-containing colloids and mineral-bacteria suspensions using scanning transmission X-ray spectromicroscopy. The results of our experiments show that spectroscopy and microscopy in the soft X-ray energy range are excellent tools for the investigation of environmentally relevant samples under realistic conditions, i.e., with water or water vapor present at ambient temperature.

A rigorous detailed review of the concepts and calculations behind the acceleration of particles by the electromagnetic zero-point field is presented. The acceleration is enhanced in regions of great size and low particle density. Astrophysical scenarios are suggested and discussed and cosmological possibilities are briefly outlined. It is shown that the acceleration follows both from a semiclassical approach in the manner of Stochastic Electrodynamics and from quantum theory with a zero-point field that most naturally (but not necessarily) may be interpreted as time-symmetric in the manner of the Wheeler-Feynman form of Quantum Electrodynamics. It is shown that both approaches yield essentially identical results.

Episodes of southward (Bz<0) interplanetary magnetic field (IMF) which lead to disturbed geomagnetic conditions are associated either with coronal mass ejections (CMEs) and possess long and continuous negative IMF Bz excursions, or with high speed solar wind streams (HSS) whose geoeffectiveness is due to IMF Bz profiles fluctuating about zero with various amplitudes and duration. We simulate ring current evolution during a HSS-driven storm that occurred during 24-26 October 2002 and compare its dynamics with a CME-driven storm of similar strength during 22-23 April 2001. We use our kinetic ring current-atmosphere interactions model (RAM), and investigate the mechanisms responsible for trapping particles and for causing their loss. Ring current evolution depends on the interplay of time-dependent inflow of plasma from the magnetotail, particle acceleration and loss (mainly due to charge exchange) along adiabatic drift paths, and outflow of plasma from the dayside magnetopause; all of these processes are incorporated in our model. We compare results from simulations using a newly developed, Cluster data based, University of New Hampshire inner magnetospheric electric field (UNH-IMEF) convection model with simulations using a Volland-Stern (V-S) type convection model. We find that, first, periods of increased magnetospheric convection coinciding with enhancements of plasma sheet density are needed for strong ring current buildup. Second, during the HSS-driven storm the convection potential from UNH-IMEF model is highly variable and causes sporadic shallow injections resulting in a weak ring current. The long period of enhanced convection during the CME-driven storm causes a continuous ion injection penetrating to lower L shells and stronger ring current buildup. V-S model predicts larger ring current injection during both storms. Third, the RAM driven by either convection model underestimates the total ring current energy during the recovery phase of the HSS storm, thus indicating that additional injections from substorm-induced electric fields and/or radial diffusion are needed to better reproduce its several-day long geomagnetic activity.

The design, performance, and on-orbit operation of the three-axis electric field instrument (EFI) for the NASA THEMIS mission is described. The 20 radial wire boom and 10 axial stacer boom antenna systems making up the EFI sensors on the five THEMIS spacecraft, along with their supporting electronics have been deployed and are operating successfully on-orbit without any mechanical or electrical failures since early 2007. The EFI provides for waveform and spectral three-axis measurements of the ambient electric field from DC up to 8 kHz, with a single, integral broadband channel extending up to 400 kHz. Individual sensor potentials are also measured, providing for on-board and ground-based estimation of spacecraft floating potential and high-resolution plasma density measurements. Individual antenna baselines are 50-and 40-m in the spin plane, and 6.9-m along the spin axis.