Vacuum Pulse Research Articles

Sensitiveness of axial magnetic field on electron acceleration by a radially polarized laser pulse in vacuum

We examine the electron acceleration by a radially polarized (RP) laser pulse in vacuum under influence of an intense axial magnetic field. The electron while interaction with a RP laser pulse gets accelerated with high energy gain. The attained energy gain further enhanced up-to the order of GeV with an intense RP laser pulse. We observe a significant enhancement in energy gain in the presence of an intense axial magnetic field in the direction of propagation of laser pulse. The presence of axial magnetic field improves the strength of v→×B→ force which supports the retaining of betatron resonance for longer durations. This improves the electron acceleration with an enhanced energy gain up to 5.2GeV. It is noticed that the axial magnetic field is sensitive to electron acceleration, small change in magnetic field leads to enhance electron energy gain significantly. Our results also show relatively smaller scattering of the electrons in the presence of axial magnetic field.

Electron acceleration by a chirped laser pulse in vacuum under the influence of magnetic field

A linearly polarized (LP) chirped laser pulse is employed for electron acceleration to GeV energy under the influence of azimuthal magnetic field in vacuum. LP laser pulse supports the trapping of pre-accelerated electron during laser–electron interaction in vacuum. The electron gains energy from LP laser pulse and gets accelerated in the direction of propagation of laser pulse. Additionally, the chirping increases the electron laser interaction for longer duration while the azimuthal magnetic field having pinching effect keeps the motion of electron parallel to the direction of propagation of laser pulse leads to enhance the electron acceleration. The combined effect of chirping of laser pulse and pinching of azimuthal magnetic field not only enhances the electron energy gain but also supports in retaining of gained energy by the electron for longer distances. The accelerating distance is observed to be of three times the Rayleigh length where the Rayleigh length is about 6.78 μm. We observe electron energy gain of about 1.47 GeV in the presence of azimuthal magnetic field of about 438 kG with an intense LP laser pulse of peak intensity of about 3.4 × 1021 W/cm2. Higher electron energy gain may be obtained with highly intense laser pulse.

Intensificación de la crioconcentración en bloque por medio de pulsos de microondas y vacío

La crioconcentración en bloque ha ganado interés como una tecnología de separación, ya que es más sencilla queel proceso de suspensión. Sin embargo, no ha sido implementada en una escala industrial ya que su eficiencia deseparación es menor que la del proceso de crioconcentración tradicional. Por lo tanto, numerosas técnicas de apoyoestán siendo estudiadas en todo el mundo para superar esta deficiencia. En este trabajo, se estudia la combinaciónde calentamiento por microondas y la separación con vacío y se compara con el calentamiento por convección yla separación con gravedad. La eficiencia de separación se midió utilizando el factor de concentración acumulativa(CumCI ) y el área bajo la curva definida por el rendimiento (Y) como una función de la fracción descongelada (f ).Se ha observado que todos los tratamientos que utilizan vacío como método de separación mostraron una eficienciasuperior a los de condiciones de procesamiento similares que utilizan a la gravedad como el método de separación. Encuanto al efecto de los pulsos de microondas, se ha observado que aquellos que están por debajo de 2,4 kJ aumentaronla eficiencia de separación cuando se combinaron con el efecto hidrodinámico generado por los pulsos de vacío.

Breaking DNA strands by extreme-ultraviolet laser pulses in vacuum.

Ionizing radiation induces a variety of DNA damages including single-strand breaks (SSBs), double-strand breaks (DSBs), abasic sites, modified sugars, and bases. Most theoretical and experimental studies have been focused on DNA strand scissions, in particular production of DNA double-strand breaks. DSBs have been proven to be a key damage at a molecular level responsible for the formation of chromosomal aberrations, leading often to cell death. We have studied the nature of DNA damage induced directly by the pulsed 46.9-nm (26.5eV) radiation provided by an extreme ultraviolet (XUV) capillary-discharge Ne-like Ar laser (CDL). Doses up to 45 kGy were delivered with a repetition rate of 3 Hz. We studied the dependence of the yield of SSBs and DSBs of a simple model of DNA molecule (pBR322) on the CDL pulse fluence. Agarose gel electrophoresis method was used for determination of both SSB and DSB yields. The action cross sections of the single- and double-strand breaks of pBR322 plasmid DNA in solid state were determined. We observed an increase in the efficiency of strand-break induction in the supercoiled DNA as a function of laser pulse fluence. Results are compared to those acquired at synchrotron radiation facilities and other sources of extreme-ultraviolet and soft x-ray radiation.

Electron acceleration to GeV energy by a chirped laser pulse in vacuum in the presence of azimuthal magnetic field

Electron acceleration by a frequency-chirped circularly polarized (CP) laser pulse in vacuum in the presence of azimuthal magnetic field has been studied. A laser pulse propagating along +z-axis interacts with a pre-accelerated electron injected at a small angle in the direction of propagation of laser pulse in vacuum. The electron is accelerated with high energy in the presence of azimuthal magnetic field till the saturation of betatron resonance. A linear frequency chirp increases the duration of interaction of laser pulse with electron and hence enforces the resonance for longer duration. The presence of azimuthal magnetic field further improves the electron acceleration by keeping the electron motion parallel to the direction of propagation for longer distances. Thus, resonant enhancement appears due to the combined effect of chirped CP laser pulse and azimuthal magnetic field. An electron with few MeV of initial energy gains high energy of the order of GeV. Higher energy gain is obtained with intense chirped laser pulse in the presence of azimuthal magnetic field.

Analysis on quantum bit error rate in measurement-device-independent quantum key distribution using weak coherent states

A measurement-device-independent quantum key distribution (MDI-QKD) protocol is immune to all detection side-channel attacks and guarantees the information-theoretical security even with uncharacterized single photon detectors. A weak coherent source is used in the current MDI-QKD experiments, it inevitably contains a certain percentage of vacuum and multi-photon pulses. The security issues introduced by these source imperfections can be avoided by applying the decoy state method. Here, through modeling experimental devices, and taking into account the weak coherent source and the threshold detectors, we have evaluated the gain, the probability to get successful Bell measurement and incorrect Bell measurement, and the quantum bit error rate (QBER), given a practical setup. In our simulation, we show how QBER varies with different transmission distances in the cases when the average photon numbers per pulse from Alice and Bob are symmetric and asymmetric. Result shows that the multi-photon pulses do not cause error in the Z basis of polarization encoding scheme, but produce a large QBER in phase encoding scheme and in the X basis of polarization encoding scheme. QBER is affected by the dark count rate and the system optical error associated with the multi-photon pulses. For different encoding schemes, QBER caused by each kind of average photon numbers from Alice and Bob increases to different degrees with the transmission distance, and finally is close to 50%. With the increase of the transmission distance, the average photon number per pulse decreases and the fraction of the dark count rate causing QBER gradually increases. Under the same effect of the dark count rate, the smaller the average photon number per pulse, the bigger the QBER. After a certain transmission and at the same transmission distance, the QBER is largest when average photon numbers used by Alice and Bob are both smallest. For the short distance transmission of phase encoding scheme and the X basis, we find that QBER is larger when average photon numbers from the two arms are asymmetric, as compared to the symmetric case. For the Z basis, the QBER caused by the system optical error and the dark count rate is very small.

Synthesis of Ti-based metallic glass thin film in high vacuum pressure on 316 L stainless steel

Surface modification of ordinary alloys by advanced coating provides a means to maintain the bulk properties of the alloy and thereby its utility in sensitive applications. In this paper, we describe the deposition of a Ti-based metallic glass thin film on 316L stainless steel using a high vacuum pulse laser deposition (HVPLD) process without a bulk metallic glass (MG) source as target. A predominant amorphous single phase film was obtained in the proper chemical composition (Ti57Cu28{Zr0.95–Hf0.05}5Si10) by controlling several process parameters, including the target rotation speed and vacuum pressure. Our HPLD configuration entailed high vacuum pressure (less than 13.3×10−6Pa), a target rotation speed in the range of 1500–2000rotation per minute (rpm) and a substrate temperature between 450 and 600°C. These parameters provide excellent control over the amorphicity of the film matrix. Our work opens up interesting opportunities to improve the poor surface properties of metallic alloys specially biometallic alloys by depositing a thin film of Ti-based MG on their surface, which can also overcome the problem of MG bulk form production as we just deposited a thin film of MG.

Simulation of Water Removal in Paper Based on a 2D Level-Set Model Coupled with Volume Forces Representing Fluid Resistance in 3D Fiber Distribution

A numerical model of a vacuum dewatering process was established with a level-set method to simulate two-phase flow in a two-dimensional paper sheet model with constructed volume forces representing flow resistance in a three-dimensional environment. Nine cases of various volume force representations were investigated by comparing numerical and experimental data. Based on the dry content and dwell time relation, the best model is obtained when accounting for in-plane flow resistance at the paper–wire interface. Compared to the other numerical cases, considering the blockage of the pore space, the top layer of the wire plays an essential role in determining the flow resistance during the vacuum process. To validate the maximum dewatering rate obtained in the model, new experimental data with a higher frequency of sampling are needed.The computational time for the two-phase flow models in this study is extensively reduced due to the removal of the internal structure. This distinction enables time-efficient simulations of the vacuum dewatering process in which several dewatering parameters such as the level of the vacuum, the influence of a moving vacuum pulse, and higher basis weights could be investigated.

Online Measurement of Pulsed Electric Field of Insulator Surface in Vacuum Based on Kerr Effect

An online measurement system based on Kerr electro-optical effect is developed to investigate the surface electric field of insulator stressed by high-voltage (HV) pulse in vacuum. A basic principle of Kerr effect is narrated. According to this principle, a circular optical polarization configuration is arranged to detect the phase difference caused by Kerr effect. An 180-kV Marx generator and an HV cable serving as pulse-forming line are utilized to output an HV pulse stressing on insulator specimen in Kerr cell. In addition, a synchronous controlling apparatus is developed to make sure that an online measurement on surface electric field is performed during the HV pulse being stressed on the insulator. As a result, distortion of surface electric field of insulator is observed in experiments preliminarily.

Modeling of vacuum pulse carburizing of steel

A review on carburization process modeling is presented and a new model for carbon diffusion in steel subjected to heat treatment by vacuum pulse carburizing is proposed. Such a process is carried out by repeating consecutively a carburizing stage (the boost), when the carburizing gas is supplied into a carburizing chamber, and the diffusion stage at vacuum conditions, when the carburizing gas is exhausted and only the diffusion in steel takes place. The model is based on Darken bi-velocity method which comprises two velocities: the diffusion velocity, various for various components, which depends on the diffusion potential gradient and is independent of the choice of the reference frame, and the drift velocity which is equivalent to the lattice velocity, and is common for all components. The model allows predicting the kinetics of carbon transfer at various processing conditions and has been applied in computer simulations. The numerical calculations were performed for varying carburizing and diffusion intervals and the results were compared to the experimental data On the basis of the series of computer experiments some findings, which are important for the carburizing process design, have been formulated.

Generation of nanosecond neutron pulses in vacuum accelerating tubes

The generation of neutron pulses with a duration of 1–100 ns using small vacuum accelerating tubes is considered. Two physical models of acceleration of short deuteron bunches in pulse neutron generators are described. The dependences of an instantaneous neutron flux in accelerating tubes on the parameters of pulse neutron generators are obtained using computer simulation. The results of experimental investigation of short-pulse neutron generators based on the accelerating tube with a vacuum-arc deuteron source, connected in the circuit with a discharge peaker, and an accelerating tube with a laser deuteron source, connected according to the Arkad’ev-Marx circuit, are given. In the experiments, the neutron yield per pulse reached 107 for a pulse duration of 10–100 ns. The resultant experimental data are in satisfactory agreement with the results of computer simulation.

Laser acceleration in novel media

With newly available compact laser technology [1] we are capable of producing 100 PW-class laser pulses with a single-cycle duration on the femtosecond timescale. With this fs intense laser we can produce a coherent X-ray pulse that is also compressed, well into the hard X-ray regime (∼10 keV) and with a power up to as much as 10 Exawatts. We suggest utilizing these coherent X-rays to drive the acceleration of particles. Such X-rays are focusable far beyond the diffraction limit of the original laser wavelength and when injected into a crystal it forms a metallic-density electron plasma ideally suited for laser wakefield acceleration. If the X-ray field is limited by the Schwinger field at the focal size of ∼100 nm, the achievable energy is 1 PeV over 50 m. (If the X-rays are focused further, much higher energies beyond this are possible). These processes are not limited to only electron acceleration, and if ions are pre-accelerated to beyond GeV they are capable of being further accelerated using a LWFA scheme [2] to similar energies as electrons over the same distance-scales. Such high energy proton (and ion) beams can induce copious neutrons, which can also give rise to intense compact muon beams and neutrino beams that may be portable. High-energy gamma rays can also be efficiently emitted with a bril- liance many orders of magnitude above the brightest X-ray sources by this accelerating process, from both the betatron radiation as well as the dominant radiative-damping dynamics. With the exceptional conditions enabled by this technology we envision a whole scope of new physical phenomena, including: the possibility of laser self-focus in the vacuum, neutron manipulation by the beat of such lasers, zeptosecond spectroscopy of nuclei, etc. Further, we now introduce along with the idea of vacuum as a nonlinear medium, the Schwinger Fiber Accelerator. This is a self-organized vacuum fiber acceleration concept, in which the repeated process of self-focusing and defocusing for the X-ray pulse in vacuum forms a modulated fiber that guides the intense X-rays.

Creation of electron-positron plasma with superstrong laser field

We present a short review of recent progress in studying QED effects within the interaction of ultra-relativistic laser pulses with vacuum and e − e + plasma. Current development in laser technologies promises very rapid growth of laser intensities in the near future. Two exawatt class facilities (ELI and XCELS, Russia) in Europe are already in the planning stage. Realization of these projects will make available a laser intensity of ∼ 1026 W/cm2 or even higher. Therefore, discussion of nonlinear optical effects in vacuum are becoming compelling for experimentalists and are currently gaining much attention. We show that, in spite of the fact that the expected field strength is still essentially less than E S = m 2 c 3/eℏ = 1.32 · 1016 V/cm, the nonlinear vacuum effects will be accessible for observation at the ELI and XCELS facilities. The most promissory effect for observation is pair creation by a laser pulse in vacuum. It is shown, that at intensities ∼ 5 · 1025 W/cm2, creation even of a single pair is accompanied by the development of an avalanche QED cascade. There exists a distinctive feature of the laser-induced cascades, as compared with the air showers arising due primarily to cosmic rays entering the atmosphere. In our case the laser field plays not only the role of a target (similar to a nucleus in the case of air showers) but is also responsible for the acceleration of slow particles. It is shown that the effect of pair creation imposes a natural limit for the attainable laser intensity and, apparently, the field strength E ∼ E S is not accessible for a pair-creating electromagnetic field at all.

Study of correlation of deuterium content in a-C:D dust induced by laser irradiation from the co-deposited surface with the grain size and velocity

In the study described here, the laser ablation method was applied to clean thick (40–60 μm) a-C:D co-deposits on the ALT-II limiter blade from the TEXTOR tokamak, and at the same time to characterize the ejected particles formed during ablation and measure the amount of fuel carried by them. Ablation was accomplished by ∼ 3.5 ns, 0.5 J Nd:YAG laser pulses in either vacuum or an O2 atmosphere at different pressures. Fast camera tracking of the process provided an estimate of the population and velocity of up to 100 m s−1 for larger dust particles. In the same experiment, the dust particles were caught using ultra-light Si aerogel collectors placed in front of the ablation target. SEM analysis of aerogel surfaces verified the speed estimate, providing the trapped particles’ size distribution and particle yield during ablation. The D/C atomic concentration ratio was measured with the 3HE ion beam nuclear reaction analysis method in deposited layers before ablation and with a micro-ion beam in individual particles on aerogel collectors. This indicated that most of the D was thermally released during ablation, leaving no more than 5% of its original amount in the particles. The effect of ablation conditions on the acceleration of ejected particles, their population, composition and D content is the main subject of this paper.

Passive Modified Atmosphere Packaging Extends Shelf Life of Enzymatically and Vacuum‐Peeled Ready‐to‐Eat Valencia Orange Segments

AbstractApplication of passive modified atmosphere packaging (MAP) for shelf life extension of enzymatically and nonenzymatically peeled orange segments was evaluated. Oranges (Citrus sinensis cv. Valencia) were washed, sanitized and peeled by applying vacuum pulses only (vacuum peeling) and vacuum pulses followed by incubation in enzymatic solution (enzymatic peeling). Segments were packaged in polypropylene film and stored at 7C for 16 days. Package atmosphere composition, weight loss, respiration rate, color, instrumental texture, pH, soluble solids, sensory attributes, and bacterial and fungal growth were evaluated during storage. Microbiological limits (cfu/g > 106) were reached by enzymatically and vacuum‐peeled segments on days 12 and 8, respectively. Integrity and characteristic odor had significantly changed by this day. Vacuum‐peeled segments presented better texture attributes and integrity (50% higher scores in sensory evaluation). Both types of segments benefited from MAP and are an attractive alternative for commercialization of ready‐to‐eat oranges.Practical ApplicationsThe information presented in this paper can assist fresh‐cut producers in developing ready‐to‐eat oranges. Quality of segments obtained with two peeling methods was evaluated, and potentials and limitations of the segments obtained by each process were pointed out. Passive MAP in polypropylene at a reasonable storage temperature (7C) resulted to be an inexpensive technology that can extend segment shelf life in eventual cold storage of orange segments.

Optimisation of vacuum pulse osmotic dehydration of blanched pumpkin

SummaryPulsed vacuum osmotic dehydration (PVOD) is an efficient process for obtaining semi‐dehydrated food. The effects of temperature (30–50°C), solute concentration (NaCl 0–15 kg per 100 kg solution, sucrose, 15–35 kg per 100 kg solution) and vacuum pulse application (50–150 mbar and 5–15 min) on water loss (WL), solid gain (SG), water activity (aw) and total colour difference (∆E) of previously blanched pumpkin slices were assessed through Plackett–Burman experimental design. Temperature was not statistically significant in the process. Later, with the aid of a central composite design (CCD), it was found that concentration of sucrose and NaCl was influent on the WL, SG, aw and ∆E, and the pressure and time of application of vacuum were influent on WL and SG. The optimal conditions of process were stabilised with the desirable function, and the simulated data were similar from the experimental ones.

Efficient generation of vacuum and extreme ultraviolet pulses

We demonstrated efficient vacuum and extreme ultraviolet third harmonic generation driven by intense ultrashort fundamental-wave pulses. As the driving pulses were tightly focused upon an argon gas jet to reach relatively high peak intensities, we achieved vacuum ultraviolet pulse energy of 6.4 μJ at 133 nm and extreme ultraviolet (XUV) pulse energy of 199 nJ at 89 nm, with the corresponding conversion efficiency up to 0.26‰ and 0.008‰, respectively. In addition, the intense 400-nm ultrashort driving pulse was up-converted to a 79-nm XUV pulse with pulse energy of 251 nJ and the harmonic generation efficiency was 0.01‰.

On-line measurement on surface electric field of insulator in vacuum based on Kerr effect

Kerr effect is defined as an electro-optical physical phenomenon, in which the testing laser can change its polarization state as passing through a Kerr medium stressed by applied field. In this work, an on-line measurement system based on Kerr effect is established to investigate the surface electric field of insulator stressed by nanosecond HV pulse in vacuum which include a HV pulse source, YAG laser, synchronous controlling apparatus, Kerr cell & insulator sample, optical phase shift detecting subsystem. According to comparison experiments, the distortion of insulator surface electric field caused by surface charging is observed. And a time-resolution measurement on this field distortion is also performed.

Laser-Induced Point Defects in Fused Silica Irradiated by UV Laser in Vacuum

High-purity fused silica irradiated by third harmonic of the Nd:YAG laser in vacuum with different laser pulse parameters was studied experimentally. Laser-induced defects are investigated by UV spectroscopy, and fluorescence spectra and correlated to the structural modifications in the glass matrix through Raman spectroscopy. Results show that, for laser fluence below laser-induced damage threshold (LIDT), the absorbance and intensity of fluorescence bands increase with laser energies and/or number of laser pulses, which indicates that laser-induced defects are enhanced by laser energies and/or number of laser pulses in vacuum. The optical properties of these point defects were discussed in detail.

ANALYSIS OF EXCITATION PULSED SIGNAL PROPAGATION FOR ATOM PROBE TOMOGRAPHY SYSTEM

The purpose of this paper is on the behavioral modelling of surge voltage pulses used in Atom Probe Tomography. After brief description of the atom probe functioning principle, we examine the excitation electrical pulse signal integrity along the electric pulser (E-pulser) feeding line modelling with respect to the IEC1733/04 standard. This feeding electric line is ended by cylindrical via ground to control the ion emission. By using the transmission line (TL) ultra-broadband RLCG model, the propagating pulsed signals degradation is predicted. The signal propagation was analysed in both frequency and time domains by taking into account the substrate dispersion. The wideband frequency behaviours of the surge signal along the feeding line were examined from DC-to-2GHz. In addition, by considering pulse surge signals with pulse-width and rise-/fall-time parameters (T1 = 9ns, tr1 = tf1 = 1:6ns) and (T2 = 30ns, tr2 = 4ns/tf2 = 18ns), the transient responses from 5cm-to- 20cm length TL are characterized. It was shown that the excitation pulse was signiflcantly distorted. It was emphasized that the operated signal delay varies from 0.3ns-to-1.5ns in function of the via capacitor value. The time-dependent radiated E-fleld on the performance of the atom probe system which enables to characterize the nature of tested materials (ions or atoms) is discussed. The presented analysis approach is particularly useful for E-pulser integrated in measurement scientiflc instruments as Atom Probe Tomography time of ∞ight optimisation, a nano-analysing technique that uses ultra-sharp high vacuum pulse to induce controlled erosion of samples. In this application, the excitation voltage pulse integrity during the propagation is required in order to improve the measurement instrument performances.