Proton Bursts Research Articles

Intermittent proton bursts of single lactic acid bacteria.

Lactic acid bacteria are a kind of probiotic microorganisms that efficiently convert carbohydrates to lactic acids, thus playing essential roles in fermentation and food industry. While conventional wisdom often suggests continuous release of protons from bacteria during acidification, here we developed a methodology to measure the dynamics of proton release at the single bacteria level, and report on the discovery of a proton burst phenomenon, i.e., the intermittent efflux of protons, of single Lactobacillus plantarum bacteria. When placing an individual bacterium in an oil-sealed microwell, efflux and accumulation of protons consequently reduced the pH in the confined extracellular medium, which was monitored with fluorescent pH indicators in a high-throughput and real-time manner. In addition to the slow and continuous proton release behavior (as expected), stochastic and intermittent proton burst events were surprisingly observed with a typical timescale of several seconds. It was attributed to the regulatory response of bacteria by activating H+-ATPase to compensate the stochastic and transient depolarizations of membrane potential. These findings not only revealed an unprecedented proton burst phenomenon in lactic acid bacteria, but also shed new lights on the intrinsic roles of H+-ATPase in membrane potential homeostasis, with implications for both fermentation industry and bacterial electrophysiology.

Experimental demonstration of accurate Bragg peak localization with ionoacoustic tandem phase detection (iTPD)

Accurate knowledge of the exact stopping location of ions inside the patient would allow full exploitation of their ballistic properties for patient treatment. The localized energy deposition of a pulsed particle beam induces a rapid temperature increase of the irradiated volume and leads to the emission of ionoacoustic (IA) waves. Detecting the time-of-flight (ToF) of the IA wave allows inferring information on the Bragg peak location and can henceforth be used for in-vivo range verification. A challenge for IA is the poor signal-to-noise ratio at clinically relevant doses and viable machines. We present a frequency-based measurement technique, labeled as ionoacoustic tandem phase detection (iTPD) utilizing lock-in amplifiers. The phase shift of the IA signal to a reference signal is measured to derive the ToF. Experimental IA measurements with a 3.5 MHz lead zirconate titanate (PZT) transducer and lock-in amplifiers were performed in water using 22 MeV proton bursts. A digital iTPD was performed in-silico at clinical dose levels on experimental data obtained from a clinical facility and secondly, on simulations emulating a heterogeneous geometry. For the experimental setup using 22 MeV protons, a localization accuracy and precision obtained through iTPD deviates from a time-based reference analysis by less than 15 μm. Several methodological aspects were investigated experimentally in systematic manner. Lastly, iTPD was evaluated in-silico for clinical beam energies indicating that iTPD is in reach of sub-mm accuracy for fractionated doses < 5 Gy. iTPD can be used to accurately measure the ToF of IA signals online via its phase shift in frequency domain. An application of iTPD to the clinical scenario using a single pulsed beam is feasible but requires further development to reach <1 Gy detection capabilities.

Real-Time Electron Solvation Induced by Bursts of Laser-Accelerated Protons in Liquid Water.

Understanding the mechanisms of proton energy deposition in matter and subsequent damage formation is fundamental to radiation science. Here we exploit the picosecond (10^{-12} s) resolution of laser-driven accelerators to track ultrafast solvation dynamics for electrons due to proton radiolysis in liquid water (H_{2}O). Comparing these results with modeling that assumes initial conditions similar to those found in photolysis reveals that solvation time due to protons is extended by >20 ps. Supported by magnetohydrodynamic theory this indicates a highly dynamic phase in the immediate aftermath of the proton interaction that is not accounted for in current models.

Suprathermal Proton Spectra at Interplanetary Shocks in 3D Hybrid Simulations

Abstract Interplanetary shocks are one of the proposed sources of suprathermal ion populations (i.e., ions with energies of a few times the solar-wind energy). Here we present results from a series of 3D hybrid simulations of collisionless shocks in the solar wind. We focus on the influence of the shock-normal angle, θ Bn , and the shock speed, V s , on producing protons with energies a few to hundreds of times the thermal energy of the upstream plasma. The combined effects of θ Bn and V s result in shocks with Alfvén Mach numbers in the range 3.0–6.0 and fast magnetosonic Mach numbers in the range 2.5–5.0, representing moderate to strong interplanetary shocks. We find that θ Bn largely organizes the shape of proton energy spectra, while shock speed controls acceleration efficiency. All shocks accelerate protons at the shock front, but the spectral evolution depends on θ Bn . Shocks with θ Bn ≥ 60° produce isolated bursts of suprathermal protons at the shock front, while shocks with θ Bn ≤ 45° create suprathermal beams upstream of the shock. Downstream proton energy spectra have exponential or smoothed broken power-law forms when θ Bn ≥ 45° and a single power-law form when θ Bn ≤ 30°. Protons downstream of the strongest shocks have energies at least 100 times the upstream thermal energy, with θ Bn ≤ 30° shocks producing the highest-energy protons and θ Bn ≥ 60° shocks producing the largest number of protons with energies at least a few times the thermal energy.

A multihertz, kiloelectronvolt pulsed proton source from a laser irradiated continuous hydrogen cluster target

A high-repetition rate laser-driven proton source from a continuously operating cryogenic hydrogen cluster target is presented. We demonstrate a debris-free, Coulomb-explosion based acceleration in the 10s of kilo-electron-volt range with a stability of about 10% in a 5 Hz operation. This acceleration mechanism, delivering short pulse proton bursts, represents an ideal acceleration scheme for various applications, for example, in materials science or as an injector source in conventional accelerators. Furthermore, the proton energy can be tuned by varying the laser and/or cluster parameters. 3D numerical particle-in-cell simulations and an analytical model support the experimental results and reveal great potential for further studies, scaling up the proton energies, which can be realized with a simple modification of the target.

Probing ultrafast proton induced dynamics in transparent dielectrics

A scheme has been developed permitting the spatial and temporal characterisation of ultrafast dynamics induced by laser driven proton bursts in transparent dielectrics. Advantage is taken of the high degree of synchronicity between the proton bursts generated during laser-foil target interactions and the probing laser to provide the basis for streaking of the dynamics. Relaxation times of electrons (<10−12 s) are measured following swift excitation across the optical band gap for various glass samples. A temporal resolution of <500 fs is achieved demonstrating that these ultrafast dynamics can be characterized on a single-shot basis.

Relativistic electron precipitation as seen by NOAA POES

AbstractWe performed a survey of relativistic electron precipitation (REP) events revealed by the Medium Energy Proton and Electron Detector instrument on board NOAA Polar‐orbiting Operational Environmental Satellites during a 38 day interval. We have divided the observed REP events into three groups with respect to the simultaneous observations of energetic (&gt;30 keV) electron and proton precipitation. The first group consists of REP enhancements forming the isotropy zone at the poleward edge of trapped relativistic electron fluxes. These REP events are observed on the nightside, and they are, apparently, produced by isotropization process related to nonadiabatic motion of particles in the stretched magnetic field. The second group are the REP events related to simultaneous enhancements of energetic &gt;30–300 keV electrons. These events have a wider magnetic local time range of occurrence with a maximum in the premidnight sector. They can be related to the interaction of electrons with waves whose possible nature is briefly discussed on the basis of comparison with the cold plasma density in the conjugated region of the equatorial plane. The third group consists of the REP events correlated with the burst‐like precipitation of &gt;30–keV protons within an anisotropy zone, where the trapped flux dominates. These events are found in the dusk sector in association with enhanced cold plasma density in the conjugate equatorial magnetosphere. As is known, proton bursts within the anisotropy zone indicate the location of the electromagnetic ion cyclotron (EMIC) wave source. Such REP events can be due to scattering of the relativistic electrons by EMIC waves. However, we noted that some of these REP events are associated with precipitation of energetic electrons with low‐energy cutoff below 100 keV. We suggest that in such cases the electrons within a wide energy range are precipitated by other waves (probably, by plasmaspheric hiss).

Picosecond metrology of laser-driven proton bursts.

Tracking primary radiation-induced processes in matter requires ultrafast sources and high precision timing. While compact laser-driven ion accelerators are seeding the development of novel high instantaneous flux applications, combining the ultrashort ion and laser pulse durations with their inherent synchronicity to trace the real-time evolution of initial damage events has yet to be realized. Here we report on the absolute measurement of proton bursts as short as 3.5±0.7 ps from laser solid target interactions for this purpose. Our results verify that laser-driven ion acceleration can deliver interaction times over a factor of hundred shorter than those of state-of-the-art accelerators optimized for high instantaneous flux. Furthermore, these observations draw ion interaction physics into the field of ultrafast science, opening the opportunity for quantitative comparison with both numerical modelling and the adjacent fields of ultrafast electron and photon interactions in matter.

Analysis of lower atmosphere pressure field response for short-time cosmic ray variations by Multifield Comparison Measure method

Pressure variation in lower atmosphere which take place after intensive solar proton events and Forbush-decreases of galactic cosmic rays (GCRs) are analyzed for the period 1980-2006. There were plotted groups of charts (multifields) for 48 solar proton events with energies of particles Ep > 90 MeV and for 48 Forbush-decreases of GCRs with amplitudes dN/N > 2.5%. These multifields revealed a growth of matrix norm over North Atlantic region and North of European part of Russia during days following the bursts of solar protons and Forbush-decreases of GCRs, respectively. These results confirm hypothesis about relation of regional cyclogenesis processes with short-term variations of solar and galactic cosmic rays.

Correlation of very low and low frequency signal variations at mid-latitudes with magnetic activity and outer-zone particles

Abstract. The disturbances of very low and low frequency signals in the lower mid-latitude ionosphere caused by magnetic storms, proton bursts and relativistic electron fluxes are investigated on the basis of VLF–LF measurements obtained in the Far East and European networks. We have found that magnetic storm (−150 &lt; Dst &lt; −100 nT) influence is not strong on variations of VLF–LF signals. The anomalies with negative amplitude were registered during the main and recovery phases for several magnetic storms (mainly for three northernmost paths). The correlation between VLF–LF signals and geomagnetic activity is rather weak even for these paths (≈ 12–18%). Also, the correlation between magnetic activity and VLF signal variations recorded onboard the DEMETER satellite is not found. The significant influence of outer-zone particles (energetic particle sensor on board/Geostationary Operational Environmental Satellite (GOES) measurements) on the VLF–LF signal variations is found for almost half of the sub-ionospheric paths.

Generation of a quasi-monoergetic proton beam from laser-irradiated sub-micron droplets

Proton bursts with a narrow spectrum at an energy of (2.8 ± 0.3 MeV) are accelerated from sub-micron water spray droplets irradiated by high-intensity (∼5 × 1019 W/cm2), high-contrast (∼1010), ultra-short (40 fs) laser pulses. The acceleration is preferentially in the laser propagation direction. The explosion dynamics is governed by a residual ps-scale laser pulse pedestal which “mildly” preheats the droplet and changes its density profile before the arrival of the high intensity laser pulse peak. As a result, the energetic electrons extracted from the modified target by the high-intensity part of the laser pulse establish an anisotropic electrostatic field which results in anisotropic Coulomb explosion and proton acceleration predominantly in the forward direction. Hydrodynamic simulations of the target pre-expansion and 3D particle-in-cell simulations of the measured energy and anisotropy of the proton emission have confirmed the proposed acceleration scenario.

Laser-driven quasimonoenergetic proton burst from water spray target

A narrow band proton bursts at energies of 1.6±0.08 MeV were observed when a water spray consisting of ∅(150 nm)-diameter droplets was irradiated by an ultrashort laser pulse of about 45 fs duration and at an intensity of 5×1019 W/cm2. The results are explained by a Coulomb explosion of sub-laser-wavelength droplets composed of two ion species. The laser prepulse plays an important role. By pre-evaporation of the droplets, its diameter is reduced so that the main pulse can interact with a smaller droplet, and this remaining bulk can be ionized to high states. In the case of water, the mixture of quite differently charged ions establishes an “iso-Coulomb-potential” during the droplet explosion such that protons are accelerated to a peak energy with a narrow energy spread. The model explains this crucial point, which differs critically from usual Coulomb explosion or ion sheath acceleration mechanisms.

Ultrafast laser-driven proton sources and dynamic proton imaging

Ion bursts, accelerated by an ultrafast (40 fs) laser-assisted target normal sheath acceleration mechanism, can be adjusted so as to deliver a nearly pure proton beam. Such laser-driven proton bursts have predominantly a low transverse emittance and a broad kinetic spectrum suitable for continuous probing of the temporal evolution of spatially extended electric fields that arise after laser irradiation of thin foils. Fields with a strength of up to 1010 V/m were measured with a new streaklike proton deflectometry setup. The data show the temporal and spatial evolution of electric fields that are due to target charge-up and ion-front expansion following intense laser-target interaction at intensities of 1017-1018 W/cm2. Measurement of the field evolution is important to gain further insight into lateral electron-transport processes and the influence of field dynamics on ion beam properties.

HIGH BRIGHTNESS LASER INDUCED MULTI-MEV ELECTRON/PROTON SOURCES

The chirped pulse amplification (CPA) technique has opened new perspectives in the radiation-matter interaction studies using ultra-short laser pulses at ultra-relativistic intensities. In particular the original idea, proposed by Tajima and Dawson, of accelerating electrons by the huge electric fields of plasma waves which develop in the wake of a laser pulse propagating in a plasma, become feasible. Some laboratories all over the world have produced by such a technique collimated electron busts of hundreds of MeV along acceleration lengths of a few hundreds of microns. In other experiments, using thin solid targets, intense bursts of energetic protons have been at the same time detected. The proton acceleration mechanism is essentially based on the Coulomb force appearing at the thin solid target surface as a consequence of the previous escape of the energetic electrons from the target. In the paper some experimental results will be presented as well as the opportunities the INFN PLASMONX project will offer in this research field at LNF.

Suprathermal proton andα-particle bursts (E/q = 6.5–225 keV/e) observed by the WIND-, ACE- and IMP8–S/C during depressions of the interplanetary magnetic field

The present study deals with suprathermal proton (E/q = 6.5-225 keV/e) and α-particle bursts measured by the WIND-SMS experiment in the interplanetary space. They reach up to ∼5-20 times the solar wind speed and last froma few minutes up to ∼30 min. Measurements obtained simultaneously by the Solar Wind Ion Composition Sensor SWICS (E/q = 0.5-31.5 keV/e) were also available for this study, as well as magnetic field and particle data recorded by ACE near the Libration point L1 and the IMP8-S/C near the Earth. In order to exclude particles escaping from the magnetosphere or accelerated by the Earth's bow shock, interplanetary shocks, coronal mass ejections and corotating interaction regions, we selected ion bursts which were associated with a distinct decrease in the interplanetary magnetic field magnitude and with changes in the azimuthal and tangential field direction. Such changes have been known for a long time as magnetic holes or field depressions. We interpret these signatures as a manifestation of a reconnection process in the interplanetary space near the heliospheric current sheet at about 1 AU distance from the Sun and show for the first time that thermal particles can be accelerated up to 100 keV/e. The suprathermal particles are most likely accelerated in the electric field of the X-line. Inductive electric fields caused by changes in the field magnitude could also be responsible for the particle acceleration.

Linear electronics for Si-detectors and its energy calibration for use in heavy ion experiments

Abstract The design and implementation of linear electronics based on small-size, low-power charge preamplifiers and shaping amplifiers, used in connection with Si-detector telescopes employed in heavy ion experiments, are presented. Bench tests and “under beam” performances are discussed. In particular, the energy calibration and the linearity test of the overall system (Si-detector and linear and digital conversion electronics) has been performed with a procedure which avoids the pulse height defect problems connected with the detection of heavy ions. The procedure, basically, consists of using bursts of MeV protons, releasing up to GeV energies inside the detector, with low ionization density.

Evidence for acceleration of ions to ∼ 1 Mev by adiabatic‐like reflection at the quasi‐perpendicular Earth's bow shock

On December 6, 1994, during a CIR (Corotating Interaction Region) event, the WIND 3D‐Plasma and energetic particle experiment observed a burst (≤24 s) of 238–676 keV protons close to the electron foreshock boundary, followed by a 156–236 keV, 101–156 keV and 33–101 keV proton bursts about ∼40 s, 65 s and 85 s later, respectively. Similar dispersed bursts of helium with energies between ∼50 keV and ∼1 MeV followed the proton bursts. During this time, the IMF direction varied slowly with an almost monotonic decrease in θBn. The proton energy spectrum is initially peaked at ∼350 keV, and progresses to lower energies with time. The proton 3D angular distributions are peaked at ∼30° pitch‐angle, propagating away from the shock, but they are nongyrotropic. Finally, we show that the proton energy‐spectra as well as the pitch angle distribution agree quantitatively with a model of a single adiabatic reflection of the incident energetic interplanetary ions by the quasi‐perpendicular shock.

An 800-MeV proton radiography facility for dynamic experiments

The capability has successfully been developed at the Los Alamos Nuclear Science Center (LANSCE) to utilize a spatially and temporally prepared 800 MeV proton beam to produce proton radiographs. A series of proton bursts are transmitted through a dynamic object and transported, via a unique magnetic lens system, to an image plane. The magnetic lens system permits correcting for the effects of multiple coulomb scattering which would otherwise completely blur the spatially transmitted information at the image plane. The proton radiographs are recorded either on a time integrating film plate or with a recently developed multi-frame electronic imaging camera system. The latter technique permits obtaining a time dependent series of proton radiographs with time intervals (modulo 358 ns) up to many microseconds and variable time intervals between images. One electronically shuttered, intensified, CCD camera is required per image. These cameras can detect single protons interacting with a scintillating fiber optic array in the image plane but also have a dynamic range which permits recording radiographs with better than 5% statistics for observation of detailed density variations in the object. A number of tests have been carried out to characterize the quality of the proton radiography system for absolute mass determination, resolution, and dynamic range. Initial dynamic experiments characterized the temporal and spatial behavior of shock propagation in a high explosive sample with up to six images per experiment. Based on experience with the prototype system, a number of upgrades are being implemented including the anticipated capability for enhanced mass discrimination through differential multiple coulomb scattering radiographs and more images with improved imaging techniques.

Impulsive bursts of energetic particles in the high‐latitude duskside magnetosphere of Jupiter

Recent studies using the entire set of proton and electron measurements of the cosmic and solar particle investigations (COSPIN) on Ulysses revealed that the impulsive, sometimes quasi‐periodic bursts discovered during the Ulysses' pass through Jupiter's duskside magnetosphere consisted not only of relativistic electrons and radio wave emissions but also protons and helium nuclei of energies from ∼0.7 to ∼10 MeV/nucleon. In this paper we present a detailed analysis of observations of the proton and helium bursts and of their correlation with relativistic electron bursts. Using an automated computer algorithm, we found 37 nucleonic bursts, all of which occurred in the duskside magnetosphere. Typically, the nucleonic bursts lasted only ∼20 s to ∼2 min and had a very rapid onset and shutoff, showing a spike‐like profile. The flux during the bursts often increased by a factor &gt;10 above the background and had a very strong unidirectional anisotropy directed along the magnetic fields outward from the southern polar region of the planet. The half width of the pitch angle distributions for protons in the bursts was usually less than a few degrees. In the bursts, particles with highest energies were detected first, followed by lower‐energy particles, consistent with the velocity dispersion expected for particles arriving from a source at a significant distance. From this velocity dispersion relation and the O4CS magnetic field model we found that the source of the bursts was located a few Jovian radii above the surface over the southern high‐latitude polar region. Of the 37 nucleonic bursts, about half were associated with an electron burst originating at the same source and at the same time. Energy spectra for protons in the bursts often showed a peak at ∼1 MeV, and above this energy there was spectral hardening relative to preburst and postburst background spectra. These observations suggest that particle acceleration occurs in the high‐latitude polar inner magnetosphere of Jupiter and may be similar to those phenomena observed in the auroral region of Earth's magnetosphere. If the same acceleration process operates on both Earth and Jupiter, these observations imply that Jovian aurorae are probably associated with the high‐latitude boundaries of the polar cap rather than with the Io torus.

Temporal dispersion structures of proton and electron bursts in the Earth's magnetotail

We present an analytical approximation of the behavior of the velocity dispersion structure of the energetic particle bursts generated during magnetic field topology reconstruction within the Earth's magnetotail. We show that some critical distance S exists, such that if the distance S between the source and the spacecraft S > S c , the burst exhibits only normal velocity dispersion (more energetic particles appear before low energy particles). For S < S c , both inverse (for higher energies) and normal (for lower energies) parts coexist in the structure. These calculations are compared with the observational data.