Top PDF Spectral modification of laser-accelerated proton beams by self-generated magnetic fields

Spectral modification of laser-accelerated proton beams by self-generated magnetic fields

Spectral modification of laser-accelerated proton beams by self-generated magnetic fields

40 fs laser pulse were found to have energy spectra that contained a broad peak near to 1 MeV. By carrying out 2D PIC simulations of the experiment, it has been concluded that quasi-static magnetic fields at the rear of the target are responsible for producing these spectral peaks. As the spectrometer only measures those protons that are emitted into a narrow cone, the quasi-static magnetic field will strongly shape the spectrum by deflections in the field that are dependent on the dwell time of the proton in the field. This produces broad spectral peaks. This may provide a new or complementary route to optically controlling the energy spectrum of laser-accelerated proton beams, in contrast to the ‘target engineering’ approach, which has previously been advocated [14]. This work also highlights a more generic issue—that of properly accounting for the limited angular sampling of magnetic spectrometers when interpreting ion acceleration experiments.
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Angle-dependent modulated spectral peaks of proton beams generated in ultrashort intense laser-solid interactions

Angle-dependent modulated spectral peaks of proton beams generated in ultrashort intense laser-solid interactions

Ultrafast laser-driven proton radiography shows that a large amplitude (thousands of Tesla) magnetic field is generated at the rear of foil targets irradiated by high-intensity laser pulse 18 . Robinson et al. has found that the self-generated magnetic field plays important role on the presence of the quasi-monoenergetic proton peaks for ultrathin foils 15 . To understand our observation for thick targets, we have carried out numerical simulations by the 2D3V PIC code KLAPS 19, 20 . The simulation parameters are similar to the experimental. The temporal and spatial resolutions in the simulations are dt=0.025τ 0 , and
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Guiding of relativistic electron beams in dense matter by laser-driven magnetostatic fields

Guiding of relativistic electron beams in dense matter by laser-driven magnetostatic fields

magnetization of the CH 60-μm-thick transport targets. According to benchmarked simulations accurately reproducing the experimental data in our best setup configuration, we found that the energy density transported by the fast electrons to the targets’ rear surface and the peak background electron tempera- ture increase, respectively, by factors of ≈ 5.3 and ≈ 5.9 compared to the case without imposed B-field. This enhancement in energy- density transport through dense matter is notable when com- pared to experiments based on the REB guiding by self-generated resistive B-fields 29–33 . Our experimental all-optical platform for strong B-field production and guided transport of laser- accelerated high-energy particles sets the ground for laboratory studies in regimes of matter opacities and equations of state at extreme temperatures. In the particular context of laser-fusion research, relevant experiments with target compression in mag- netized conditions and magnetically guided REB should poten- tially optimize energy coupling to high-density cores of nuclear fuel 9,28,53–55 .
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Effect of self-generated magnetic fields on fast-electron beam divergence in solid targets

Effect of self-generated magnetic fields on fast-electron beam divergence in solid targets

The laser pulse parameters were fixed throughout the experiment. The targets were 3 mm × 7 mm aluminium foils, with thickness, L , varied in the range of 25 µ m to 1.4 mm. Passive stacks of 5 cm × 5 cm dosimetry film (RCF: Gafchromic © film, HD-810 and MD-V2-55) were positioned 6 cm from the rear of the target (centred on the normal axis to the target) to measure the spatial intensity distribution of the beam of accelerated protons at energies given by the Bragg peak deposition in each piece of film. A 3-mm-wide slot machined in the RCF facilitated a line-of-sight for a Thomson parabola ion spectrometer positioned behind the stack along the target normal axis. Measurements of efficient acceleration of carbon and oxygen ions, sourced from contaminants on the rear surface of the targets, confirm that for the laser and target parameters of this experiment the rear-surface target normal sheath acceleration (TNSA) mechanism [3] dominates.
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Manipulation of the spatial distribution of laser-accelerated proton beams by varying the laser intensity distribution

Manipulation of the spatial distribution of laser-accelerated proton beams by varying the laser intensity distribution

A numerical model was developed to investigate how the size of the laser focus and the separation of the laser foci in the case of two beams may be expected to influence the resulting proton beam distribution. The model (an earlier version of which is described in Ref. 23) calculates how the evolving fast electron density distribution on a grid corre- sponding to the target rear surface maps into the beam of protons accelerated by TNSA. Fast electrons produced at the target front side in a given laser focus are assumed to be bal- listically transported through the target in a beam with a fixed divergence angle. Transport phenomena such as colli- sions and self-generated fields are not accounted for, but are expected to have a limited effect in relatively thin targets. 24 Recirculation or refluxing of fast electrons within the foil is also neglected. It was validated in simulations that refluxing for a 35 fs-duration laser pulse will occur essentially only for target thicknesses of more than 3 lm. The rear-surface fast electron sheath dynamics, field-ionization of hydrogen, and the direction of projection of the resulting protons are calcu- lated. Unlike more computationally intensive 3D Particle-in- Cell (PIC) modelling, this simpler approach enables a range of parametric scans to be performed relatively quickly, to explore the expected changes to the proton beam profile.
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Plasma Mirrors for Cleaning Laser Pulses from the Infrared to the Ultraviolet

Plasma Mirrors for Cleaning Laser Pulses from the Infrared to the Ultraviolet

We could demonstrate the high, ~70% efficiency even for the KrF laser system, although its 248 nm wavelength in the ultraviolet causes a deep penetration to the plasma, and therefore generally lower absorption than in the infrared. The method for obtaining it is that we could shorten the interaction length by choosing appropriate initial conditions with shorter scalelength plasmas. Basically there are 2 possible method to integrate it into the laser system In our previous paper [9] we suggested an arrangement in which the plasma mirror is applied in front of the final amplifier. It became possible because although the reflected beam suffers a spectral Doppler shift, the spectrum remains within the gain bandwidth of the final amplifier. In this case the final energy of the laser system will not decrease significantly because the amplifier operates in a saturation regime.
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Corrosion behaviour of post deposition polished droplets embedded arc evaporated and droplets free HIPIMS/DCMS coatings

Corrosion behaviour of post deposition polished droplets embedded arc evaporated and droplets free HIPIMS/DCMS coatings

During arc evaporation, the emission of the macro particles can be minimized by introduction of magnetic fields in the region near to the cathode. The plasma is steered away from the cathode to the substrate which is not in line of sight, by the combination of magnetic and electric fields generated by the magnetic filters. 14 Various designs of filter have been proposed by several researchers. 15-16 However, it has been reported that the up-scalability of many filters is not easy due to geometry of such filters. 17

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Direct observation of plasma waves and dynamics induced by laser-accelerated electron beams

Direct observation of plasma waves and dynamics induced by laser-accelerated electron beams

Plasma wakefield acceleration (PWFA) is a novel acceleration technique with promising prospects for both particle colliders and light sources. However, PWFA research has so far been limited to a few large- scale accelerator facilities worldwide. Here, we present first results on plasma wakefield generation using electron beams accelerated with a 100-TW-class Ti:sapphire laser. Because of their ultrashort duration and high charge density, the laser-accelerated electron bunches are suitable to drive plasma waves at electron densities in the order of 10 19 cm −3 . We capture the beam-induced plasma dynamics with femtosecond resolution using few-cycle optical probing and, in addition to the plasma wave itself, we observe a distinctive transverse ion motion in its trail. This previously unobserved phenomenon can be explained by the ponderomotive force of the plasma wave acting on the ions, resulting in a modulation of the plasma density over many picoseconds. Because of the scaling laws of plasma wakefield generation, results obtained at high plasma density using high-current laser-accelerated electron beams can be readily scaled to low-density systems. Laser-driven PWFA experiments can thus act as miniature models for their larger, conventional counterparts. Furthermore, our results pave the way towards a novel generation of laser-driven PWFA, which can potentially provide ultralow emittance beams within a compact setup.
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Experiments with a Metastable Helium Atomic Trap

Experiments with a Metastable Helium Atomic Trap

respectively. The saturated absorption peaks are 2.3 GHz apart and each has a width of 50 MHz due to a combination of pressure broad- ening, laser spectral width and natural width. Peak 3 occurs at the cross-over frequency, midway between the two transitions. Figure from [32]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.4 Schematic representation of the diode laser mount . . . . . . . . . . 29 3.5 Discharge cell used for the saturation spectroscopy. High voltage (1.6-

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Dynamics of an orbital polarization of twisted electron beams in electric and magnetic fields

Dynamics of an orbital polarization of twisted electron beams in electric and magnetic fields

We predict the new e ff ect of a radiative orbital polarization of twisted electron / positron beams in a magnetic field – orbital Sokolov-Ternov e ff ect [12]. The well-known e ff ect is the radiative spin polarization of electron / positron beams in storage rings caused by the synchrotron radia- tion (Sokolov-Ternov e ff ect [24]). The spin polarization is acquired by unpolarized electrons and is opposite to the direction of the main magnetic field. The reason of the e ff ect is a depen- dence of spin-flip transitions from the initial particle polarization. We can notice the evident similarity between interactions of the spin and the intrinsic OAM with the magnetic field [see Eq. (3)]. In particular, energies of stationary states depend on projections of the spin and the intrinsic OAM on the field direction. This similarity validates the existence of the effect of the radiative orbital polarization. As well as the radiative spin polarization, the correspond- ing orbital polarization acquired by unpolarized twisted electrons should be opposite to the direction of the main magnetic field (see Fig. 1). The e ff ect is conditioned by transitions with a change of a projection of the intrinsic OAM. The probability of such transitions is large enough if the electron energy is not too small. Similarly to the spin polarization, the orbital one is observable when electrons are accelerated up to the energy of the order of 1 GeV. The acceleration can depolarize twisted electrons but cannot vanish L. During the process of the radiative polarization, the average energy of the electrons should be kept unchanged.
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Free-ion hyperfine fields and magnetic-moment measurements on radioactive beams

Free-ion hyperfine fields and magnetic-moment measurements on radioactive beams

an aspect that is discussed further in [17]. Atomic calcu- lations have commenced with the goal to develop a quan- titative microscopic model of the free-ion hyperfine fields. The aim of the present work is to underpin magnetic mo- ment measurements on radioactive beams at international facilities. In future work, the experience with the atomic structure calculations for free ions will be adapted and ap- plied to calculations of Auger spectra for medical isotopes, as described elsewhere [18, 19].

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Terahertz generation from laser-driven ultrafast current propagation along a wire target

Terahertz generation from laser-driven ultrafast current propagation along a wire target

The distinctive pattern of the radiation emitted from laser driven wire target was shown in Fig. 2. Two spher- ical waves front, one centered at the middle of the wire and other centered at right end of the wire, were clearly distinguished. The first spherical wave was formed when the laser pulse reach at the center of the target and en- ergetic electrons was accelerated by the laser force. The second spherical wave is generated when hot electrons propagating stably long the wire reach the termination on the right. After that two spherical wave was escaping from the individual source and traveling outward at the speed of light. According to the direction and magni- tude of the field components, the Poynting vectors can be inferred to be predominantly normally over a spherical wavefront. The intensity of radiation is not distributed uniformly over the spherical wavefront, but obviously de- pendent on the emission angle. All this characteristic are much similar to typical radiation from a linear antenna driven by transient current pulse [24].
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New Theory of Superconductivity  Does the London Equation Have the Proper Solution? No, It Does Not  Self Generated and External Magnetic Fields in Superconductors

New Theory of Superconductivity Does the London Equation Have the Proper Solution? No, It Does Not Self Generated and External Magnetic Fields in Superconductors

pend on the critical field at all. In addition to, the superconductivity is taken for the equilibrium state of a substance– i.e. all values are not to depend on time t . But all these dependences are derived in the London brothers’ equation. The supercurrent can flow over the entire surface of the superconductor. This current can create self-magnetic field ( ) c

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Ultrafast laser parallel microdrilling using multiple annular beams generated by a spatial light modulator

Ultrafast laser parallel microdrilling using multiple annular beams generated by a spatial light modulator

Ultrafast laser parallel micro drilling using diffractive multiple annular beam patterns is demonstrated in this paper. The annular beam was generated by diffractive axicon computer generate holograms (CGHs) using a spatial light modulator (SLM). The diameter of the annular beam can be easily adjusted by varying the radius of the smallest ring in the axicon. Multiple annular beams with arbitrary arrangement and multiple annular beam arrays were generated by superimposing an axicon CGH onto a Grating and Lenses (GL) algorithm calculated multi-beam CGH and a binary Dammann grating CGH, respectively. Micro holes were drilled through a 0.03mm thick stainless steel foil using the multiple annular beams. By avoiding huge laser output attenuation and mechanical annular scanning, the processing is ~ 200 times faster than the normal single beam processing.
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Influence of strong magnetic fields on laser pulse propagation in underdense plasma

Influence of strong magnetic fields on laser pulse propagation in underdense plasma

Even in the linear wave regime, the magnetic fields result in unique effects of wave propagation. Observa- tions of anomalous radio waves were documented as early as 1894, termed whistlers due to the descending tone heard as the waves were picked up on receivers. Explanations of the physical processes underlying them developed in the 1950s as general understanding of plasma physics advanced [13]. The comparatively high frequency of laser light compared to radio waves has, until relatively recently, precluded the investigation of whistler mode lasers. However, advances in laser tech- nology and the creation of high strength magnetic fields now allow access to this parameter regime, and has spurred interest in the combination of magnetic and relativistic plasma effects.
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A Device for Ligand-Free Single Cell Loading Using Magnetic Fields and Paramagnetic Microspheres

A Device for Ligand-Free Single Cell Loading Using Magnetic Fields and Paramagnetic Microspheres

In this experiment cells experienced mechanical compression due to the attraction of the paramagnetic microsphere (residing upon the cellular surface) by the magnetic field generated by the solenoid. We recorded strain values of 1.3% for the Minor axis of the cell nucleus while we found a strain level of 5.6% in the direction of the Major axis. Sen et.al., applied daily regimens of mechanical strain to mesenchymal stem cells (MSCs) and recorded an inhibited expression of peroxisome proliferator-activated receptor γ and adiponectin mRNA suggesting that mechanical strain alone can affect cell differentiation. Regimens consisted of daily applications of 2% strain [6]. The operation of this device is certainly capable of applying such levels of mechanical stimulation as we can adjust strain levels through variations in solenoid current and number of solenoid wire turns.
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Schaudel, Daniel
  

(2003):


	X-ray Properties of Galactic Supernova Remnants.


Dissertation, LMU München: Fakultät für Physik

Schaudel, Daniel (2003): X-ray Properties of Galactic Supernova Remnants. Dissertation, LMU München: Fakultät für Physik

into the ISM, compressing the magnetic field and accelerating in their shock waves efficiently energetic cosmic rays as observed in the whole Galaxy. They are expected to leave behind compact, as well as diffuse, remnants. Depending on the mass of the progenitor star the compact remnants take usually the stage of neutron stars (NS) or black holes (BH). The expansion of the supernova remnant (SNR) illuminates the pre-existing structures in the ISM and forms new ones, transferring kinetic energy and material from the original supernova to the ISM and trigger star formation in nearby dense clouds. Supernovae therefore do not stand only for the end of stellar evolution but also act as a recycling machine, returning material to the ISM to form new stars. The recycled material is processed by the supernova explosion into iron and heavier elements which effect the energetics and chemical composition of the ISM and the next generation of stars which form out of it. The study of supernovae or supernova remnants of exploded stars is also essential for our understanding of the origin of life on Earth. The cloud of gas and dust which collapsed to form the Sun, Earth and other planets was composed mainly of hydrogen and helium with a small amount of heavier elements such as carbon, nitrogen, oxygen and iron which is required by complex life. The only place where these elements are produced by nucleosynthesis is deep in the interior of massive stars. They can only spread out in the ISM due to an explosion.
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Scintillator-based ion beam profiler for diagnosing laser-accelerated ion beams

Scintillator-based ion beam profiler for diagnosing laser-accelerated ion beams

Thomson parabola spectrometer consists of parallel electric and magnetic fields which disperse a narrow sample of the incoming beam as a function of particle energy and charge to mass ratio. Analysis of the parabolas formed at the detection plane reveals the beam’s species and spectral content. Columbia Resin 39 (CR-39) nuclear track detector 6 is typically used as a detector, yielding absolute ion numbers but requires labor intensive developing and scanning. Each individual ion detected forms a ‘pit’ (when etched in NaOH) on the CR-39, hence the dose dynamic range is limited by individual ion pits overlapping at high fluxes.
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Rapid measurement of biodiesel conversion rate by near infrared spectroscopy

Rapid measurement of biodiesel conversion rate by near infrared spectroscopy

This paper introduces a method based on the near-infrared spectroscopy for rapid measurement of the biodiesel conversion rate during the transesterification of triolein with methanol. To build the regression model between the conversion rate and the spectral date, the real conversion rate of glycerides to methyl esters was analyzed by Proton Nuclear Magnetic Resonance ( 1 HNMR) spectroscopy, and several steps were taken to the obtained spectra. Firstly, the raw spectra of all samples obtained were preprocessed by Savitzky-Golay smoothing method. Moreover, eighteen effective wavelength points were selected by successive projections algorithm (SPA). Finally, the partial least squares (PLS) model was constructed with the selected 18 wavelength points. The eventual regression model was validated and the Root Mean Square Error of Prediction (RMSEP) was 0.0115, coefficient of determination (R 2 ) was 0.9877. The total average absolute deviation of the measurements is 1.09%.
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Numerical simulations of the focal spot generated by a set of laser beams : LMJ⋆,⋆⋆

Numerical simulations of the focal spot generated by a set of laser beams : LMJ⋆,⋆⋆

R´ esum´ e. Afin d’obtenir la fusion de petites cibles contenant du deuterium-tritium, le laser M´ egaJoule doit focaliser un grand nombre de faisceaux laser ` a l’int´ erieur d’un cylindre (Hohlraum) contenant une de ces cibles. La maˆıtrise de ce processus n´ ecessite une bonne connaissance du champ ´ electromagn´ etique induit par les faisceaux laser sur chacune des ouvertures du Hohlraum. Cet article d´ ecrit l’outil num´ erique mis au point pour le calcul de ce champ ` a partir de la description des faisceaux laser avant la focalisation. La simplicit´ e du calcul n’est qu’apparente, puisque celui-ci a besoin d’une d´ ecomposition en ondes planes en deux ´ etapes et que la taille des donn´ ees n´ ecessite l’utilisation d’un grand nombre de processeurs.
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