Simulation of the passage of ion flows through nanotracks

A computer model of a cylindrical nanopore created using the classical method of molecular dynamics is described. The essential element of the model is the potential wells of the adsorption centers on the internal surface of nanopore, the depth of which is determined by the coefficient in Hooke's law. The model describes well experimental features of the passage of ion flows in real nanotracks in modern biosensors

Small business innovation research. Abstracts of completed 1987 phase 1 projects

Non-proprietary summaries of Phase 1 Small Business Innovation Research (SBIR) projects supported by NASA in the 1987 program year are given. Work in the areas of aeronautical propulsion, aerodynamics, acoustics, aircraft systems, materials and structures, teleoperators and robotics, computer sciences, information systems, spacecraft systems, spacecraft power supplies, spacecraft propulsion, bioastronautics, satellite communication, and space processing are covered

Advanced Approaches to High Intensity Laser-Driven Ion Acceleration

Since the pioneering work that was carried out 10 years ago, the generation of highly energetic ion beams from laser-plasma interactions has been investigated in much detail in the regime of target normal sheath acceleration (TNSA). Creation of ion beams with small longitudinal and transverse emittance and energies extending up to tens of MeV fueled visions of compact, laser-driven ion sources for applications such as ion beam therapy of tumors or fast ignition inertial confinement fusion. However, new pathways are of crucial importance to push the current limits of laser-generated ion beams further towards parameters necessary for those applications. The presented PhD work was intended to develop and explore advanced approaches to high intensity laser-driven ion acceleration that reach beyond TNSA. In this spirit, ion acceleration from two novel target systems was investigated, namely mass-limited microspheres and nm-thin, free-standing diamond-like carbon (DLC) foils. Using such ultrathin foils, a new regime of ion acceleration was found where the laser transfers energy to all electrons located within the focal volume. While for TNSA the accelerating electric field is stationary and ion acceleration is spatially separated from laser absorption into electrons, now a localized longitudinal field enhancement is present that co-propagates with the ions as the accompanying laser pulse pushes the electrons forward. Unprecedented maximum ion energies were obtained, reaching beyond 0.5 GeV for carbon C$^{6+}$ and thus exceeding previous TNSA results by about one order of magnitude. When changing the laser polarization to circular, electron heating and expansion were shown to be efficiently suppressed, resulting for the first time in a phase-stable acceleration that is dominated by the laser radiation pressure which led to the observation of a peaked C$^{6+}$ spectrum. Compared to quasi-monoenergetic ion beam generation within the TNSA regime, a more than 40 times increase in conversion efficiency was achieved. The possibility to manipulate the shape of the ion acceleration front was successfully demonstrated by use of a spherically curved target surface. Finally, the last part of the presented work is devoted to accomplishments in laser development

Acoustic Waves

The concept of acoustic wave is a pervasive one, which emerges in any type of medium, from solids to plasmas, at length and time scales ranging from sub-micrometric layers in microdevices to seismic waves in the Sun's interior. This book presents several aspects of the active research ongoing in this field. Theoretical efforts are leading to a deeper understanding of phenomena, also in complicated environments like the solar surface boundary. Acoustic waves are a flexible probe to investigate the properties of very different systems, from thin inorganic layers to ripening cheese to biological systems. Acoustic waves are also a tool to manipulate matter, from the delicate evaporation of biomolecules to be analysed, to the phase transitions induced by intense shock waves. And a whole class of widespread microdevices, including filters and sensors, is based on the behaviour of acoustic waves propagating in thin layers. The search for better performances is driving to new materials for these devices, and to more refined tools for their analysis

High Energy Astrophysics Research and Programmatic Support

This report reviews activities performed by members of the USRA contract team during the six months of the reporting period and projected activities during the coming six months. Activities take place at the Goddard Space Flight Center, within the Laboratory for High Energy Astrophysics. Developments concern instrumentation, observation, data analysis, and theoretical work in Astrophysics. Missions supported include: Advanced Satellite for Cosmology and Astrophysics (ASCA), X-ray Timing Experiment (XTE), X-ray Spectrometer (XRS), Astro-E, High Energy Astrophysics Science Archive Research Center (HEASARC), and others

Binary gamma-ray pulsars

The first pulsar has been detected in 1967 as a seemingly pulsating radio source. Since then, more than 2800 pulsars have been discovered. Most of them also in radio. With the launch of the Fermi Gamma-ray Space Telescope in 2008, more than 250 gamma-ray pulsars have been detected. This thesis concerns the development of methods to directly search the gamma-ray data for pulsars in binary systems, and presents the discovery and analysis of four such pulsars.1967 wurde der erste Pulsar als scheinbar pulsierende Radioquelle entdeckt. Seitdem wurden mehr als 2800 weitere Pulsare gefunden, die meisten davon ebenfalls im Radiobereich. Mit dem Start des Fermi Gamma-ray Space Telescope im Jahr 2008 wurden mittlerweile mehr als 250 Gamma-Pulsare entdeckt. Diese Arbeit behandelt die Entwicklung von Suchmethoden, um Gamma-Daten direkt nach Pulsaren in Binärsystemen zu durchsuchen, und präsentiert die Entdeckung und Vermessung von vier solchen Pulsaren

Physics of intense light ion beams, production of high energy density in matter, and pulsed power applications. Annual report 1995

Physik intensiver Strahlen leichter Ionen, Erzeugung hoher Energiedichten in Materie und Anwendungen der Pulsed Power Technik Jahresbericht 1995 In dem Bericht werden die in 1995 erzielten Ergebnisse zum Arbeitsthema "Physik intensiver Ionenstrahlen und gepulster dichter Plasmen" dargestellt. Zus"tzlich wurden die neu hinzugekommenen Arbeiten zu industriellen Anwendungen der Pulsed Power Technik aufgenommen

High Field Plasmonics

Il manoscritto riguarda lo studio di effetti di plasmonica ad alti campi, ossia nel contesto dell'interazione laser-plasma ad altissima intensità (I > 10^18 W/cm^2). Si intende per "plasmonica" lo studio di plasmoni di superficie, che consistono in modi elettromagnetici all'interfaccia fra un metallo e un mezzo dielettrico. I plasmoni di superficie vengono normalmente eccitati con impulsi laser a bassa intensità.Questo regime è ben conosciuto dal punto di vista teorico e lo studio di schemi che coinvolgono effetti di plasmonica è un campo di ricerca molto vitale, motivato dalle possibili interessanti applicazioni (ad esempio per biosensori o microchip). Al contrario, non è, ad oggi, disponibile un modello teorico completo per plasmoni di superficie in regimi di altissima intensità, dove forti effetti non lineari e relativistici possono giocare un ruolo rilevante. Anche dal punto di vista sperimentale e numerico effetti di plasmonica in questo regime di interazione sono stati solo marginalmente esplorati. I risultati contenuti nella tesi sono principalmente frutto di investigazioni numeriche con codici Particle-In-Cell e risultati sperimentali relativi a effetti di plasmonica in regime di alti campi. Sono stati studiati diversi scenari, elencati di seguito. Si è studiata l'interazione di intensi impulsi laser (I~5x10^19 W/cm^2) con bersagli la cui superficie consisteva in un reticolo microstrutturato (attività sperimentale svolta presso il centro di ricerca CEA-Saclay, Gif-sur-Yvette, Francia). Si è osservata l'accelerazione di pacchetti collimati di elettroni lungo la superficie dei reticoli se irraggiati ad angoli vicini a quello atteso per l'eccitazione di un plasmone di superficie. E' stato misurato lo spettro energetico degli elettroni emessi, osservando una distribuzione piccata a 5-8 MeV e con una coda estesa fino a oltre 20 MeV. Sono state misurate cariche totali fino a oltre 100 pC. Tali caratteristiche rendono la sorgente potenzialmente di interesse per alcune applicazioni (diffrazione di elettroni ultra-veloce, produzione di fotoneutroni). Simulazioni numeriche Particle-In-Cell hanno mostrato ottimo accordo con i risultati sperimentali. Si fornisce anche un semplice modello teorico per chiarire il ruolo dei plasmoni di superficie nell'accelerazione degli elettroni Si è studiata l'interazione di impulsi laser con intensità superiori a 10^20 W/cm^2 con bersagli solidi sottili accoppiati ad una schiuma di carbonio con densità media tale da ottenere un plasma alla densità critica se completamente ionizzata (attività sperimentale svolta presso il centro di ricerca GIST, Gwangju, Corea del Sud). L'interazione laser-plasma in tali regimi consente un efficiente accoppiamento dell'impulso laser con plasmoni di volume, incrementando l'efficienza dell'assorbimento di energia da parte del bersaglio. L'attività si inquadra nel contesto dell'accelerazione di ioni con plasmi prodotti da laser (con potenziali future applicazioni in adroterapia o trattamento e diagnostica di materiali con fasci di ioni). Durante due campagne sperimentali si è osservato che la presenza di un sottile strato di schiuma consente di incrementare le energie massime degli ioni accelerati rispetto a bersagli semplici. Simulazioni numeriche con codici Particle-In-Cell hanno permesso di chiarire il ruolo giocato dalle microstrutture della schiuma. Si è studiato il ruolo di effetti plasmonici nell'instabilità di Rayleigh-Taylor “laser-driven”, che può svilupparsi in scenari di “Radiation Pressure Acceleration”, dove sottili bersagli solidi vengono accelerati direttamente dalla pressione di radiazione di un impulso laser ultraintenso. Utilizzando un semplice modello teorico si mostra che le modulazioni autoconsistenti della presione di radiazione dovute alla deformazione sinusoidale della superficie influenzano significativamente lo spettro dell'instabilità, dipendentemente dalla polarizzazione dell'impulso. L'evoluzione nonlineare è studiata con simulazioni Particle-In-Cell, che mostrano la formazione di strutture a rete. Si è studiato con simulazioni numeriche il ruolo dell'eccitazione di plasmoni di superficie nell'emissione di armoniche di ordine elevato da reticoli solidi irraggiati con impulsi laser ultra-intensi. All'eccitazione di un plasmone di superficie corrisponde un aumento dei campi elettromagnetici alla superficie del bersaglio, che incrementa l'efficienza di generazione di armoniche. Nelle simulazioni una migliore efficienza di emissione di armoiniche è stata osservata per bersagli irraggiati ad angoli vicini a quello atteso per l'eccitazione di un plasmone di superficie. I risultati presentati in quest'ultima sezione sono preliminari e saranno oggetto di studi ulteriori. The manuscript concerns the study of plasmonic effects at high fields, that is in the framework of laser-plasma interaction at ultra-high intensities (I > 10^18 W/cm^2). “Plasmonics” is the study of surface plasmons, which are electromagnetic modes at the interface between a metal and a dielectric medium. Surface plasmons are normally excited with low intensity laser pulses. This regime is well known from the theoretical point of view and the study of plasmonic schemes is a vibrant research field, motivated by the interesting possible applications (e.g. biosensors or plasmonic chips). On the other hand, a complete theoretical model is still lacking for surface plasmons in the high intensity regime, where strong non-linear and relativistic effects might play a relevant role. Also the numerical and experimental investigation of plasmonics in this regime has been limited up to now. This thesis presents mainly numerical (Particle-In-Cell simulations) and experimental results related to the study of plasmonic effects at high fields. A few scenarios were studied. They are listed hereunder. The interaction of intense laser pulses (I~5x10^19 W/cm^2) with microstructured grating targets was studied experimentally (this activity was carried out at the research center CEA-Saclay, Gif-sur-Yvette, France). We observed thee acceleration of collimated electron bunches along the surface of grating target when irradiated at angles close to that expected for the excitation of a surface plasmon. We measured the energy spectrum of the emitted electrons, observing a distribution peaked at 5-8 MeV with a tail extending up to more than 20 MeV. Total charges up to more than 100 pC were measured. These characteristics make the source interesting for some applications (like ultra-fast electron diffraction or photo-neutron generation). Particle-In-Cell numerical simulations proved to be in very good agreement with the experimental results. A theoretical model is provided to clarify the role played by surface plasmons in the electron acceleration process. The interaction of intense laser pulses (I> 10^20 W/cm^2) with solid targets coupled with a carbon foam was studied. The average density of the carbon foam was selected in order to obtain a plasma at the critical density if fully ionized (the experimental activity was carried out at the GIST research center, Gwangju, South Korea). Laser-plasma interaction in this regime allows for an efficient coupling of the laser pulse with bulk plasmons, enhanced the efficiency of the energy absorption by the target. The activity was carried out in the framework of ion acceleration with laser-produced plasmas (with potential future applications in hadron-therapy or diagnostic and treatment of materials with ion beams). During the two experimental campaigns we observed that targets coated with a thin foam allowed to obtained higher ion energies with respect to simple targets. Numerical simulations with Particle-In-Cell codes helped to clarify the role of the micro-structuring of the foam. We studied the role of plasmonic effects in laser-driven Rayleigh-Taylor instability, which may develop in Radiation Pressure Acceleration scenarios, where thin solid foils are directly accelerated by the radiation pressure of an ultra-intense laser pulse. Using a simple model it is shown that the self-consistent modulation of the radiation pressure caused by a sinusoidal rippling affects substantially the wavevector spectrum of the instability depending on the laser polarization. The nonlinear evolution is investigated by three dimensional simulations which show the formation of net-like structures. The role of surface plasmons in high order harmonic emission from solid grating targets irradiated with ultra-intense laser pulses was studied with numerical simulations. The excitation of a surface plasmon is associated with an enhancement of the electromagnetic field close to the target surface, which should increase the efficiency of harmonic generation. In the simulations, a higher emission efficiency for high-order harmonics was observed for targets irradiated at angles close to that expected for surface plasmon excitation. The results presented in this part are still preliminary. The topic will be addressed in future works