Thin Solid Targets Research Articles

Antiproton annihilation at rest in thin solid targets and comparison with Monte Carlo simulations

AbstractThe mechanism of antiproton–nucleus annihilation at rest is not fully understood, despite substantial previous experimental and theoretical work. In this study we used slow extracted antiprotons from the ASACUSA apparatus at CERN to measure the charged particle multiplicities and their energy deposits from antiproton annihilations at rest on three different nuclei: carbon, molybdenum and gold. The results are compared with predictions from different models in the simulation tools Geant4 and FLUKA. A model that accounts for all the observed features is still missing, as well as measurements at low energies, to validate such models.

Exploring a tristhione scorpionate ligand as a suitable chelator for the theranostic pair antimony-119 and antimony-117

BackgroundThe highly potent Auger electron emitter antimony-119 (119Sb) and the SPECT-isotope antimony-117 (117Sb) comprise a true theranostic pair particularly suitable for cancer theranostics. Harnessing this potential requires development of a chelator that can rapidly form a stable complex with radioactive antimony ions at the low concentrations typical of radiopharmaceutical preparations. Stable Sb(III) complexes of hydrotris(methimazolyl)borate (TMe) are known, prompting our investigation of this chelator. Additionally, the production of radioantimony was optimized and the SPECT imaging properties of 117Sb was investigated, in an attempt to move towards biomedical implementation of the theranostic isotope pair of antimony.ResultsA method for rapid and effective labelling of TMe using 117Sb was developed, yielding high radiochemical purities of 98.5 ± 2.7% and high radionuclidic purities exceeding 99%. Radiolabelling yielded an Sb(III) complex directly from the acidic Sb(V) solution. [1XXSb]Sb-TMe in aqueous acidic solution showed high stability in the presence of cysteine, however, the stability of the radiocomplex at increased pH was significantly decreased. The production method of 117Sb was optimized, enabling a production yield of up to 19.6 MBq/µAh and the production of up to 564 MBq at end of bombardment, following irradiation of a thin 117Sn-enriched solid target. Preclinical SPECT/CT scanning of a mouse phantom containing purified 117Sb demonstrated excellent SPECT imaging properties of 117Sb with high spatial resolution comparable to that of technetium-99m.ConclusionWe have explored the TMe chelator for complexation of radioantimony and devised a rapid chelation protocol suitable for the short half-life of 117Sb (T1/2 = 2.8 h). [1XXSb]Sb-TMe (1XXSb = 117Sb, 118mSb, 120mSb and 122Sb) demonstrated a high stability in presence of cysteine, although low stability was observed at pH > 4. We have achieved a production yield of 117Sb high enough for clinical applications and demonstrated the excellent SPECT-imaging properties of 117Sb. The results contribute valuable information for the development of suitable chelators for radioantimony and is a step further towards implementation of the antimony theranostic pair in biomedical applications.

Enhanced terahertz radiation generated by intense laser interaction with a two-layer thin solid target

A terahertz radiation enhancing scheme, in which a linearly polarized weakly relativistic laser pulse irradiates a target consisting of two parallel thin-solid layers with a certain gap, is proposed and studied by using two-dimensional particle-in-cell simulations. The radiation is known to be produced by laser-produced hot electrons via mechanisms such as coherent transition radiation at the target surfaces. Under optimized conditions, the energy conversion efficiency of terahertz radiation can be as high as 3.3%, which is nearly 1.5 times higher than that obtained with a single-layer target with the same drive laser. This is mainly due to the enhanced hot electron generation with moderate energy via multiple reflections of the laser pulse between the two target layers. The radiation has two peaks close to 30° from the target surface, which are more collimated than that with the single-layer target. The dependence of the terahertz radiation on a variety of target parameters is given, which can control the terahertz spectrum and radiation efficiency and thus provide guidance for experimental investigations. Moreover, both the coherent transition radiation and antenna radiation models are applied to explain the angular distributions of the terahertz emission found in the simulations. Published by the American Physical Society 2024

Numerical studies of collinear laser-assisted injection from a foil for plasma wakefield accelerators

We present a laser-assisted electron injection scheme for beam-driven plasma wakefield acceleration. The laser is collinear with the driver and triggers the injection of hot electrons into the plasma wake by interaction with a thin solid target. We present a baseline case using the AWAKE Run 2 parameters and then perform variations on key parameters to explore the scheme. It is found that the trapped witness electron charge may be tuned by altering laser parameters, with a strong dependence on the phase of the wake upon injection. Normalized emittance settles at the order of micrometres and varies with witness charge. The scheme is robust to misalignment, with a 1/10th plasma skin-depth offset (20 μm for the AWAKE case) having a negligible effect on the final beam. The final beam quality is better than similar existing schemes, and several avenues for further optimization are indicated. The constraints on the AWAKE experiment are very specific, but the general principles of this mechanism can be applied to future beam-driven plasma wakefield accelerator experiments. Published by the American Physical Society 2024

Generating High Efficiency Terahertz Radiation From Relativistic Nano-Bunches in the Interaction of Ultrarelativistic Lasers With Thin Solid Targets

The interaction of femtosecond laser pulses with thin solid targets is one of the most efficient methods to obtain terahertz (THz) radiation. In the specific conditions, the electron of plasma surface distribution became so localized and nano-bunches are formed which causes coherent synchrotron emission (CSE). In this mechanism which occurs when the relativistic laser is obliquely incident on plasma, the plasma electrons gather in a very dense and thin layer of nanometer width. The electrons of nano-bunch can emit intense coherent emissions in different ranges of electromagnetic radiation. In this study, producing high-efficiency THz radiating from relativistic nano-bunches is discussed. The effect of plasma and nano-bunch parameters, the mobility of ions, the initial thermal velocity of electrons, and the speed of electrons are investigated. According to the results, the direct relation between the width of the nano-bunch and the efficiency is seen. The nonlinear relation between the initial thermal velocity of electrons and the THz yield is seen. In the desirable conditions, a high THz yield of up to 37% is obtained from nano-bunches with the initial thermal velocities as 0.3 of light speed.

Synthesis of solid mercury targets for nuclear astrophysics experiments

This paper describes several simple and cost-effective ways of making homogeneously thin solid mercury targets useful for nuclear astrophysics experiments at standard ambient temperature and pressure and in vacuum. The methods described here make use of mercury compounds such as mercury(II) acetate, mercury(II) oxide (yellow), mercury(II) chloride, mercury (II) nitrate monohydrate, and mercury(II) sulfide (red). Various methods like drop-casting, wet chemistry, electro-chemical deposition, amalgamation, and pelletization are described. Advantages and disadvantages of each method are described.

Radiation pressure acceleration of high-quality ion beams using ultrashort laser pulses

The generation of compact, high-energy ion beams is one of the most promising applications of intense laser-matter interactions, but the control of the beam spectral quality remains an outstanding challenge. We show that in radiation pressure acceleration of a thin solid target the onset of electron heating is determined by the growth of the Rayleigh-Taylor-like instability at the front surface and must be controlled to produce ion beams with high spectral quality in the light sail regime. The growth rate of the instability imposes an upper limit on the laser pulse duration and intensity to achieve high spectral beam quality and we demonstrate that under this optimal regime, the maximum peak ion beam energy per nucleon is independent of target density, composition, and laser energy (transverse spot size). Our predictions are validated by two- and three-dimensional particle-in-cell simulations, which indicate that for recent and upcoming experimental facilities using ultrashort ($\lesssim 25$ fs) laser pulses it is possible to produce $100 - 300$ MeV proton beams with $\sim 30\%$ energy spread and high laser-to-proton energy conversion efficiency.

Enhanced Broadband Terahertz Radiation from Two-Colour Laser Pulse Interaction with Thin Dielectric Solid Target in Air

We report enhanced broadband Terahertz (THz) generation and detailed characterization from the interaction of femtosecond two colour laser pulses with thin transparent dielectric tape target in ambient air. The proposed source is easy to implement, exhibits excellent scalability with laser energy. Spectral characterization using Fourier transform spectrometer reveals yield enhancement of more than 150 % in the THz region of 0.1 - 10 THz with respect to conventional two-colour laser plasma source in ambient air. Further, the source spectrum extends up to 40 THz with an enhancement of flux > 30 %. Experimental results, well supported with two-dimensional particle-in-cell simulations establishes that the transient photo-current produced by the asymmetric laser pulse interaction with air plasma as well as near solid density plasma formed on the tape surface is responsible for the enhanced terahertz generation. The source will be useful for the multidisciplinary activities and ongoing applications of the laboratory-based terahertz sources.

Amplification of separated electric charge field due to the capture of laser-produced fast electrons oscillating near thin target

The effect of increasing strength of the electric field of separated charge due to the capture of laser-accelerated fast electrons in a thin solid target is theoretically substantiated. The target considered is so thin that a fast electron passes through the target during the time less than at least half of the applied laser pulse with the additional requirement that energy loss of a fast electron in the balk target is negligible compared to the energy transfer to ions accelerated in a sheath field. An analytical model is proposed of sheath field formation when fast electrons oscillate due to their reflections in the double layers at both boundaries of a thin target. It is shown that the increasing density of fast electrons inside the double layer and shortening of this layer are the reasons of sheath field strength amplification in a thin target in comparison with a thick target. The increase in the number and the energy of fast ions due to field amplification in a thin target is discussed.

Differential cross-section for the T(12C,T)12C elastic recoil reaction

The differential cross-section for the T(12C,T)12C elastic recoil reaction was measured at a laboratory angle of 30° and over an incident energy range from 5.2 to 12.2 MeV. A thin solid target Ni/TiTx/Al2O3 was prepared by the conventional hydrogenation method. The relative determination method for cross-section measurement was employed to avoid uncertainty in solid angle and number of incident ions, so that the uncertainty in the cross-section is less than 5.8%.

Time-resolved characterization of ultrafast electrons in intense laser and metallic-dielectric target interaction.

High-intensity ultrashort laser pulses interacting with thin solid targets are able to produce energetic ion beams by means of extremely large accelerating fields set by the energetic ejected electrons. The characterization of such electrons is thus important in view of a complete understanding of the acceleration process. Here, we present a complete temporal-resolved characterization of the fastest escaping hot electron component for different target materials and thicknesses, using temporal diagnostics based on electro-optical sampling with 100 fs temporal resolution. Experimental evidence of scaling laws for ultrafast electron beam parameters have been retrieved with respect to the impinging laser energy (0.4-4 J range) and to the target material, and an empirical law determining the beam parameters as a function of the target thickness is presented.

Evidence of radial Weibel instability in relativistic intensity laser-plasma interactions inside a sub-micron thick liquid target

Super-intense laser plasma interaction has shown great promise as a platform for next generation particle accelerators and sources for electron, x-rays, ions and neutrons. In particular, when a relativistic intense laser focus interacts with a thin solid density target, ionized electrons are accelerated to near the speed of light (c) within an optical cycle and are pushed in the forward and transverse directions away from focus, carrying a significant portion of the laser energy. These relativistic electrons are effectively collisionless, and their interactions with the ions and surrounding cold electrons are predominantly mediated by collective electromagnetic effects of the resulting currents and charge separation. Thus, a deeper understanding of subsequent high energy ions generated from various mechanisms and their optimization requires knowledge of the relativistic electron dynamics and the fields they produce. In addition to producing MV/m quasi-static fields, accelerating the ions and confining the majority of the electrons near the bulk of the laser target, these relativistic electron currents are subject to plasma instabilities like the Weibel instability as they propagate through the thermal population in the bulk target. In this work, we present high temporal (100 fs) and spatial (1 μm) resolution shadowgraphy video capturing relativistic radial ionization front expansion and the appearance of filamentation radiating from the laser spot within a sub-micron thick liquid sheet target. Filamentation within the region persists for several picoseconds and seeds the eventual recombination and heating dynamics on the nanosecond timescale. A large scale three-dimensional particle-in-cell (PIC) simulation of the interaction revealed the presence of strong magnetic fields characteristic of Weibel Instability, and corroborated the relativistic radial expansion of the ionization front, whose speed was determined to be 0.77c. Both the experimental and simulation results strongly point towards the target field ionization and the outward expanding hot electron current as the cause of the radial expansion.

Uniform warm dense matter formed by direct laser heating in the presence of external magnetic fields.

With the recent realization of kilotesla quasistatic magnetic fields, the interaction of a laser with magnetized solids enters an unexplored new regime. In particular, a circularly polarized (CP) laser pulse may propagate in a highly magnetized plasma of any high density without encountering cutoff reflection in the whistler mode. With this, we propose a scheme for producing uniform warm dense matter (WDM) by direct laser heating with a CP laser irradiating onto the target along the magnetic field. It is shown by particle-in-cell simulations, which include advanced ionization dynamics and collision dynamics, moderately intense right-hand CP laser light at 10^{15}W/cm^{2} can propagate in solid aluminum and heat it efficiently to the 100eV level within picoseconds. By using two laser pulses irradiating from two sides of a thin solid target, uniform heating to WDM can be achieved. This provides a controllable way to create WDM at different temperatures.

Low-divergence relativistic proton jet from a thin solid target driven by an ultra-intense circularly polarized Laguerre–Gaussian laser pulse

We propose a new ion acceleration scheme of irradiating a thin solid target with an ultraintense circularly polarized Laguerre–Gaussian (LG) laser pulse. Three-dimensional particle-in-cell simulations are performed to demonstrate that this scheme can generate a low-divergence high-density relativistic proton jet. By this scheme, the number of protons emitted with a small angle (<1°) from the laser axis can be more than tens of times as high as that of the protons accelerated by a circularly polarized Gaussian pulse. The inward ponderomotive force of the LG pulse drives such a proton beam along the laser axis.

Direct observation of ultrafast electrons generated by high-intensity laser-matter interaction

High intensity ultrashort laser pulses interacting with thin solid targets are able to produce energetic protons and ions by means of extremely large accelerating fields, generated by escaping electrons. The characterization of such electrons is thus a key factor for the understanding of the accelerating potential temporal evolution. Here, we present temporally resolved measurements of the ultrafast escaping electron component. The charge, electric field, and temporal duration of the emitted ultrafast electron beams are determined using temporal diagnostics with a 100 fs temporal resolution. Experimental evidence of scaling laws for the ultrafast electron beam parameters with respect to the incident laser pulse energy is retrieved and compared with theoretical models, showing an excellent agreement.

Charge-state distributions of 20Ne ions emerging from thin foils

Abstract New experimental measurements of charge state distributions produced by a 20Ne10+ beam at 15 MeV/u colliding on various thin solid targets are presented. The use of the MAGNEX magnetic spectrometer enabled measurements of the 8+ charge state down to fractions of a few 10−5. The use of different post-stripper foils located downstream of the main target is explored, showing that low Z materials are particularly effective to shift the charge state distributions towards fully stripped conditions. The dependence on the foil thickness is also studied and discussed.

All-optical structuring of laser-driven proton beam profiles

Extreme field gradients intrinsic to relativistic laser-interactions with thin solid targets enable compact MeV proton accelerators with unique bunch characteristics. Yet, direct control of the proton beam profile is usually not possible. Here we present a readily applicable all-optical approach to imprint detailed spatial information from the driving laser pulse onto the proton bunch. In a series of experiments, counter-intuitively, the spatial profile of the energetic proton bunch was found to exhibit identical structures as the fraction of the laser pulse passing around a target of limited size. Such information transfer between the laser pulse and the naturally delayed proton bunch is attributed to the formation of quasi-static electric fields in the beam path by ionization of residual gas. Essentially acting as a programmable memory, these fields provide access to a higher level of proton beam manipulation.

Получение и применение тонких твердотельных мишеней для ядерно-физических экспериментов

Получение и применение тонких твердотельных мишеней для ядерно-физических экспериментов

Ionization and reflux dependence of magnetic instability generation and probing inside laser-irradiated solid thin foils

When an intense laser accelerated electron beam, with large current density on the order of 1012 A/cm2, enters a solid density plasma, it is well-known to be subject to a number of different types of instabilities that cause it to filament. In this work, we investigate the transport instability of a fast electron beam that is imprinted on the self-generated magnetic filaments inside the solid density plasmas using particle-in-cell simulations. By varying collisional ionization models, our simulations show that the atomic ionization process is crucial to determine the structure of the magnetic filaments. We further attribute the generation of bulk magnetic filaments to Weibel-like instability mechanism caused by counter-propagating hot forward-bulk return current streams and counter-propagating hot forward-reflux current streams. It is found that the magnetic fields in the filament channels near the rear surface are around one order of magnitude higher than those near the front surface of the thin solid target. This asymmetry is likely induced by the very different properties of bulk electron stream and hot reflux electron stream in terms of density and velocity distribution. Finally, we propose to probe the magnetic fields inside the solid density plasmas by X-Ray polarimetry via Faraday rotation using X-Ray free electron lasers (XFELs). The synthetic simulations show that XFELs are capable to detect the magnetic fields from relativistic laser-solid interactions.

Positron generation via two sequent laser pulses irradiating a solid aluminum target

A scheme of two sequent laser pulses irradiating a thin solid aluminum target to generate electron-positron pairs via the multi-photon Breit-Wheeler (BW) process is proposed, in order to ease the usual requirement of the laser intensity. 2D and 3D particle-in-cell simulations show that the peak intensity of the laser pulses used in our scheme is only half of that in the case of one laser pulse with a peak intensity of 2 × 1023 W/cm2, but the positron yield is one order higher than that of the latter, which is around 3.7894 × 107 and has a maximal density of 3.134 × 1022 cm−3 when the time interval between the two pulses is set to Δt ≈ 2T0. Therefore, our scheme provides a helpful suggestion for the observation of the BW process in laboratories.