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PubMed2005

Observation of vertical betatron sideband due to electron clouds in the KEKB low energy ring.

The effects of electron clouds on positively charged beams have been an active area of research in recent years at particle accelerators around the world. Transverse beam-size blowup due to electron clouds has been observed in some machines and is considered to be a major limiting factor in the development of higher-current, higher-luminosity electron-positron colliders. The leading proposed mechanism for beam blowup is the excitation of a fast head-tail instability due to short-range wakes within the electron cloud. We present here observations of betatron oscillation sidebands in bunch-by-bunch spectra that may provide direct evidence of such head-tail motion in a positron beam.

Journal Article↗
PubMed2005

Emission of electromagnetic pulses from laser wakefields through linear mode conversion.

Powerful coherent emission around the plasma oscillation frequency can be produced from a laser wakefield through linear mode conversion. This occurs when the laser pulse is incident obliquely to the density gradient of inhomogeneous plasmas. The emission spectrum and conversion efficiency are obtained analytically, which are in agreement with particle-in-cell simulations. The emission can be tuned to be a radiation source in the terahertz region and with field strengths as large as a few GV/m, suitable for high-field applications. The emission also provides a simple way to measure the wakefield produced for particle acceleration.

Journal Article↗
PubMed2005

Cross-scale nonlinear coupling and plasma energization by Alfvén waves.

We present a new channel for the nonlocal transport of wave energy from the large (MHD) scales to the small (kinetic) scales generated by the resonant decay of MHD Alfvén waves into kinetic Alfvén waves. This process does not impose any restriction on the wave numbers or frequencies of initial MHD waves, which makes it superior compared to the mechanisms of spectral transport studied before. Because of dissipative properties of the nonlinearly driven kinetic Alfvén waves, the decay leads to plasma heating and particle acceleration, which is observed in a variety of space and astrophysical plasmas. Two examples in the solar corona and the terrestrial magnetosphere are briefly discussed.

Journal Article↗
PubMed2005

Self-consistent generation of superthermal electrons by beam-plasma interaction.

It has been known since the early days of plasma physics research that superthermal electrons are generated during beam-plasma laboratory experiments. Superthermal electrons (the kappa distribution) are also ubiquitously observed in space. To explain such a feature, various particle acceleration mechanisms have been proposed. However, self-consistent acceleration of electrons in the context of plasma kinetic theory has not been demonstrated to date. This Letter reports such a demonstration. It is shown that the collisionality, defined via the "plasma parameter" g=1/n(lambda(D)(3), plays a pivotal role. It is found that a small but moderately finite value of is necessary for the superthermal tail to be generated, implying that purely collisionless (g=0) Vlasov theory cannot produce a superthermal population.

Journal Article↗
PubMed2006

Observation of the second harmonic in Thomson scattering from relativistic electrons.

A free relativistic electron in an electromagnetic field is a pure case of a light-matter interaction. In the laboratory environment, this interaction can be realized by colliding laser pulses with electron beams produced from particle accelerators. The process of single photon absorption and reemission by the electron, so-called linear Thomson scattering, results in radiation that is Doppler shifted into the x-ray and gamma-ray regions. At elevated laser intensity, nonlinear effects should come into play when the transverse motion of the electrons induced by the laser beam is relativistic. In the present experiment, we achieved this condition and characterized the second harmonic of Thomson x-ray scattering using the counterpropagation of a 60 MeV electron beam and a subterawatt CO2 laser beam.

Journal Article↗
PubMed2006

Displacement current and the generation of parallel electric fields.

We show for the first time the dynamical relationship between the generation of magnetic field-aligned electric field (E||) and the temporal changes and spatial gradients of magnetic and velocity shears, and the plasma density in Earth's magnetosphere. We predict that the signatures of reconnection and auroral particle acceleration should have a correlation with low plasma density, and a localized voltage drop (V||) should often be associated with a localized magnetic stress concentration. Previous interpretations of the E|| generation are mostly based on the generalized Ohm's law, causing serious confusion in understanding the nature of reconnection and auroral acceleration.

Journal Article↗
PubMed2006

Absolute measurement of electron-cloud density in a positively charged particle beam.

Clouds of stray electrons are ubiquitous in particle accelerators and frequently limit the performance of storage rings. Earlier measurements of electron energy distribution and flux to the walls provided only a relative electron-cloud density. We have measured electron accumulation using ions expelled by the beam. The ion energy distribution maps the depressed beam potential and gives the dynamic cloud density. Clearing electrode current reveals the static background cloud density, allowing the first absolute measurement of the time-dependent electron-cloud density during the beam pulse.

Journal Article↗
PubMed2003

DELSY project: status and development.

The DELSY (Dubna Electron Synchrotron) project is under development at the Joint Institute for Nuclear Research [Arkhipov et al. (2001). Nucl. Instrum. Methods, A467, 57-62; Arkhipov et al. (2001). Nucl. Instrum. Methods, A470, 1-6; Titkova et al. (2000). Proceedings of the Seventh European Particle Accelerator Conference, pp. 702-704]. It is based on an acceleration facility donated to the Joint Institute for Nuclear Research by the Institute for Nuclear and High Energy Physics (NIKHEF, Amsterdam). The NIKHEF accelerator facility consists of the linear electron accelerator MEA, which has an electron energy of 700 MeV, and the electron storage ring AmPS, with a maximum energy of 900 MeV and a beam current of 200 mA. There are three phases to the construction of the DELSY facility. Phase I will be accomplished with the construction of a complex of free-electron lasers covering continuously the spectrum from the far infrared down to the ultraviolet ( approximately 150 nm). Phase II will be accomplished with the commissioning of the storage ring DELSY. Complete commissioning of the DELSY project will take place after finishing Phase III, the construction of an X-ray free-electron laser. This phase is considered as the ultimate goal of the project; it is currently under development and is not described in this paper.

Journal Article↗
PubMed2000

Solar Particle Events from a risk management perspective.

Solar Particle Events pose a health risk to astronauts in space. Today, SPE forecasts are inadequate to provide advance warning with sufficient credibility to lead operators to initiate protective measures. However, research on SPEs and Coronal Mass Ejections suggests that the space weather community is on the verge of substantial improvements in understanding solar energetic particle acceleration and propagation. This paper describes the impact of SPEs, reviews the physics of SPEs, discusses current SPE forecast tools, and describes an approach to provide the comprehensive space weather data necessary to implement physics-based SPE risk management.

Algorithms↗
PubMed2001

Acoustic waves generated by pulsed microwaves in viscoelastic rods: modeling and experimental verification.

The acoustic wave generation in a specimen irradiated by a pulsed microwave is predicted theoretically. The specimen is a viscoelastic rod inserted into a wave guide. The model is based on Maxwell's equations, heat equation and thermoviscoelasticity theory. Computations show the presence of temperature oscillations due to the electromagnetic interferences in the irradiated rod if its electromagnetic absorption is low. An experimental method to infer indirectly the detailed behavior of microwave-generated acoustic waves in polymer rods, including the influence of electromagnetic wave reflection at the rod ends, is presented. The method consists of measuring the oscillations in the particle acceleration detected at the end of the rod that are induced by variations in the polymer rod length. The oscillations are caused by changing electromagnetic standing-wave conditions within the rod. It is found that these oscillations are in agreement in period, amplitude, and phase, with independent values of the complex dielectric constant and complex acoustic slowness of the polyvinyl chloride samples used in the study.

Journal Article↗
PubMed2003

The anomalous Hall effect and magnetic monopoles in momentum space.

Efforts to find the magnetic monopole in real space have been made in cosmic rays and in particle accelerators, but there has not yet been any firm evidence for its existence because of its very heavy mass, approximately 10(16) giga-electron volts. We show that the magnetic monopole can appear in the crystal momentum space of solids in the accessible low-energy region (approximately 0.1 to 1 electron volts) in the context of the anomalous Hall effect. We report experimental results together with first-principles calculations on the ferromagnetic crystal SrRuO3 that provide evidence for the magnetic monopole in the crystal momentum space.

Journal Article↗
PubMed2004

Phase-resolved spectroscopy of Geminga shows rotating hot spot(s).

Isolated neutron stars are seen in x-rays through their nonthermal and/or surface thermal emissions. X-ray Multimirror Mission-Newton observations of the Geminga pulsar show a 43-electron volt spectrum from the whole neutron star surface, as well as a power-law component above 2 kiloelectron volts. In addition, we have detected a hot (170 electron volts) thermal emission from an approximately 60-meter-radius spot on the pulsar's surface. Such a thermal emission, only visible at selected phase intervals, may be coming from polar hot spot(s), long thought to exist as a result of heating from magnetospheric accelerated particles. It may provide the missing link between the x-ray and gamma-ray emission of the pulsar.

Journal Article↗
PubMed1971

Spatial distribution of biological effect n a 3.9-Gev nitrogen ion beam.

A beam of nitrogen ions obtained with the Princeton Particle Accelerator was used for the irradiation of Chinese hamster (M3-1) cells in monolayer culture. The 3.9-billion-electron-volt (Gev) beam passed along the monolayer, so that ions were stopped in the culture. A sharply defined zone of extensive cell destruction occurred in the last centimeter of the beam path.

Animals↗
PubMed2004

Characterization of the epitopes specific for the monoclonal antibody 9F5-3a and quantification of oxidized HDL in human plasma.

BACKGROUND: We previously isolated a monoclonal antibody, 9F5-3a, that is specific for HDL oxidized by CuSO(4). METHODS: We examined the characteristics of the 9F5-3a epitope by Western blot and measured the concentration of oxidized HDL in human plasma by enzyme-linked immunosorbent assay using this antibody. RESULTS: The monoclonal antibody specifically reacted with oxidized HDL in a mixture of HDL, LDL and modified lipoproteins. Oxidation of the HDL particles accelerated cross-linkage of apolipoproteins caused by lipid peroxidation, and the cross-linked apolipoprotein AI selectively reacted with the 9F5-3a antibody. Mean (standard deviation) plasma concentrations of oxidized HDL were 127 (50) microg/L in 23 healthy controls, 191 (65) microg/L in 30 patients with non-insulin-dependent diabetes mellitus (P < 0.01 versus healthy controls) and 200 (87) microg/L in 25 patients with coronary artery disease (P < 0.01 versus healthy controls). The concentrations of oxidized HDL did not correlate with the concentrations of thiobarbituric acid-reactive substances. CONCLUSIONS: The results indicate that determination of oxidized HDL concentration may be useful for identifying patients with atherosclerotic disease.

Adult↗
PubMed2005

Influence of radiation protocols on graft-vs-host disease incidence after bone-marrow transplantation in experimental models.

Bone-marrow transplantation is an approved curative treatment for many hemato- and oncologic diseases. Nevertheless, the severe acute clinical course of graft-vs-host disease (GVHD) after allogeneic bone-marrow transplantation is frequently fatal, and is to date not curable. Acute GVHD must, therefore, be prevented from the start of the bone-marrow transplantation by immunosuppressive medication, causing sometimes serious side effects. Therefore, new preventive strategies are tested, starting with animal experiments. Often mice are chosen for this kind of trial, and the clinical protocol of bone-marrow transplantation is transferred into the experimental settings. The first step to induce an acute GVHD is whole-body irradiation of the recipients. Several methods are available for this purpose: the most common is a 60cobalt source (gamma-irradiation); less common are a 137cesium source (gamma-irradiation) and a linear (particle) accelerator (photons). Differences between these radiation techniques can occur and can unexpectedly interfere with the results of the experiments. In this chapter, the materials and methods for bone-marrow transplantation in mice, with particular emphasis on the different radiation techniques, are explained; furthermore, the advantages and disadvantages in regard to the underlying physical principles will be discussed.

Animals↗
PubMed2006

Microneedles and other physical methods for overcoming the stratum corneum barrier for cutaneous gene therapy.

The outermost layer of skin, the epidermis, has developed formidable physical and immunological barrier properties that prevent infiltration of deleterious chemicals and pathogens. Consequently, transdermal delivery of medicaments is currently restricted to a limited number of low molecular weight drugs. As a corollary, there has been significant recent interest in providing strategies that disrupt or circumvent the principal physical barrier, the stratum corneum, for the efficient cutaneous delivery of macromolecular and nucleic acid based therapeutics. These strategies include: electrical methods, intradermal injection, follicular delivery, particle acceleration, laser ablation, radiofrequency ablation, microscission, and microneedles. The application of microfabricated microneedle arrays to skin creates transient pathways to enable transcutaneous delivery of drugs and macromolecules. Microneedle use is simple, pain-free, and causes no bleeding, with further advantages of convenient manufacture, distribution, and disposal. To date, microneedles have been shown to deliver drug, peptide, antigen, and DNA efficiently through skin. Robust and efficient microneedle designs and compositions can be inserted into the skin without fracture. Further progress in microneedle array design, microneedle application apparatus, and integrated formulation will confirm this methodology as a realistic clinical strategy for delivering a range of medicaments, including DNA, to and through skin.

Animals↗
PubMed2001

Shielded Heavy-Ion Environment Linear Detector (SHIELD): an experiment for the Radiation and Technology Demonstration (RTD) Mission.

Radiological assessment of the many cosmic ion species of widely distributed energies requires the use of theoretical transport models to accurately describe diverse physical processes related to nuclear reactions in spacecraft structures, planetary atmospheres and surfaces, and tissues. Heavy-ion transport models that were designed to characterize shielded radiation fields have been validated through comparison with data from thick-target irradiation experiments at particle accelerators. With the RTD Mission comes a unique opportunity to validate existing radiation transport models and guide the development of tools for shield design. For the first time, transport properties will be measured in free-space to characterize the shielding effectiveness of materials that are likely to be aboard interplanetary space missions. Target materials composed of aluminum, advanced composite spacecraft structure and other shielding materials, helium (a propellant) and tissue equivalent matrices will be evaluated. Large solid state detectors will provide kinetic energy and charge identification for incident heavy-ions and for secondary ions created in the target material. Transport calculations using the HZETRN model suggest that 8 g cm -2 thick targets would be adequate to evaluate the shielding effectiveness during solar minimum activity conditions for a period of 30 days or more.

Computer Simulation↗
PubMed2002

Space life sciences: biological research and space radiation. Proceedings of the F1.2, F1.3, F2.2 and F2.6 Symposia of COSPAR Scientific Commission F which were held during the Thirty-third COSPAR Scientific Assembly, Warsaw, Poland, July, 2000.

This issue of Advances in Space Research contains a large number of manuscripts in the discipline of Space Life Sciences including papers from the following sessions of the Warsaw COSPAR Assembly: Gravity-related research with animals--past, present, future; The nervous system: space flight environmental factors effects--present results and new perspectives; Investigating space radiation effects at particle accelerators--biology and physics experiments; Perspectives on radiation risks on long space missions: deterministic and stochastic effects.

Adaptation, Physiological↗