Modifying Halide Perovskites Using Charged Particle Beams

One approach to controlled thermonuclear fusion for power production requires the irradiation of centimetre-size targets containing heavy hydrogen (D–T) fuel by intense charged particle beams (CPB). Beam energy and pulse length requirements are ∼1 MJ and 10ns. In certain studies1 the CPBs are beams of light ions, such as helium, with kinetic energies per nucleon in the range 1–5 MeV. These beams can be transported by preformed, current-carrying, plasma discharge channels. The fields from the channel currents (supplied by capacitor banks) confine the CPBs. These channels can be laser-initiated in a background gas that has a pressure between 10 and 100 torr. This gas blanket enables first wall loading, by X rays, shocks and thermal radiation to be mitigated. Although intense relativistic electron beams (REBs), which were developed before intense light ion beams, have achieved higher intensities2, ion beams have more favourable deposition characteristics in targets3. Proton beams have driven exploding pusher targets4 to implosion velocities of 20 cm µs−1 and have attained power of ∼1 TW cm−2, which is a factor of 40 below that estimated (G. Allshouse, personal communication) to be necessary for target ignition and for net system energy gain. To close the gap between present capabilities and future requirements, beam bunching and beam overlap are being studied. The current density gain G is important to the CPB overlap process and is the ratio of beam current density at the target surface to that of the individual beams in the transport channels; it depends on particle species, transverse energy, geometry of the channel-target interface, and so on. Detailed calculations5–7 indicate that for electron beams, G<3, while for practical cases of light ions, G can exceed 10. This is due to the difference in masses and effective temperatures of the two types of beams. Sources providing multiple ion beams are not available to test this overlap theory experimentally, hence it has been tested using a multiple electron beam system. Here we outline the experiment and describe the apparatus, and then summarize the theoretical treatment of beam overlap, describe diagnostic procedures, and compare the experimental results with calculations.

Copyright © 2016 CC-BY-3.0 and by the respective authors. The measurement of beam bunch length with high resolution is very important for the latest generation light sources and also a key parameter for the optimization of the final beam quality in high gradient plasma accelerators. In this contribution we present progress in the development of novel single shot, RMS bunch length diagnostic techniques based on imaging the near and far fields of coherent THz diffraction radiation (CDR) that is produced as a charged particle beam interacts with a solid foil or an aperture. Recent simulation results show that the profile of a THz image of the point spread function (PSF) of a beam whose radius is less than the image produced by a single electron, is sensitive to bunch length and can thus be used as a diagnostic. The advantages of near (source) field imaging over far field imaging are examined and the results of recent high energy (20 GeV) CDR THz experiments at SLAC/FACET are presented. Plans for experiments to further validate and compare these imaging methods for both moderate and high energy charged particle beams are discussed.

Study of the response of the novel LAr LEM-TPC detector exposed to cosmic rays and a charged particle beam

A fast cooling technique is described that simultaneously reduces all six phase-space dimensions of a charged particle beam. In this process, cooling is accomplished by reducing the beam momentum through ionization energy loss in absorbers and replenishing the momentum loss only in the longitudinal direction rf cavities. In this work we review its main features and describe the main results.

Hadrontherapy is an emerging technique in cancer therapy that uses beams of charged particles. To meet the improved capability of hadrontherapy in matching the dose release with the cancer position, new dose-monitoring techniques need to be developed and introduced into clinical use. The measurement of the fluxes of the secondary particles produced by the hadron beam is of fundamental importance in the design of any dose-monitoring device and is eagerly needed to tune Monte Carlo simulations. We report the measurements carried out with charged secondary particles produced from the interaction of a 80 MeV/u fully stripped carbon ion beam at the INFN Laboratori Nazionali del Sud, Catania, with a poly-methyl methacrylate target. Charged secondary particles, produced at 90° with respect to the beam axis, have been tracked with a drift chamber, while their energy and time of flight have been measured by means of a LYSO scintillator. Secondary protons have been identified exploiting the energy and time-of-flight information, and their emission region has been reconstructed backtracking from the drift chamber to the target. Moreover, a position scan of the target indicates that the reconstructed emission region follows the movement of the expected Bragg peak position. Exploiting the reconstruction of the emission region, an accuracy on the Bragg peak determination in the submillimeter range has been obtained. The measured differential production rate for protons produced with EProdkin > 83 MeV and emitted at 90° with respect to the beam line is dNP/(dNCdΩ) (EProdkin > 83 MeV, θ = 90°) = (2.69 ± 0.08stat ± 0.12sys) × 10−4 sr−1.

Passage of fast charged particles through bent crystals and nanotubes

A system is presented that is capable of confining an ion beam or plasma within a region that is essentially free of applied fields. An Artificially Structured Boundary (ASB) produces a spatially periodic set of magnetic field cusps that provides charged particle confinement. Electrostatic plugging of the magnetic field cusps enhances confinement. An ASB that has a small spatial period, compared to the dimensions of a confined plasma, generates electro- magneto-static fields with a short range. An ASB-lined volume thus constructed creates an effectively field free region near its center. It is assumed that a non-neutral plasma confined within such a volume relaxes to a Maxwell-Boltzmann distribution. Space charge based confinement of a second species of charged particles is envisioned, where the second species is confined by the space charge of the first non-neutral plasma species. An electron plasma confined within an ASB-lined volume can potentially provide confinement of a positive ion beam or positive ion plasma. Experimental as well as computational results are presented in which a plasma or charged particle beam interact with the electro- magneto-static fields generated by an ASB. A theoretical model is analyzed and solved via self-consistent computational methods to determine the behavior and equilibrium conditions of a relaxed plasma. The equilibrium conditions of a relaxed two species plasma are also computed. In such a scenario, space charge based electrostatic confinement is predicted to occur where a second plasma species is confined by the space charge of the first plasma species. An experimental apparatus with cylindrical symmetry that has its interior surface lined with an ASB is presented. This system was developed by using a simulation of the electro- magneto-static fields present within the trap to guide mechanical design. The construction of the full experimental apparatus is discussed. Experimental results that show the characteristics of electron beam transmission through the experimental apparatus are presented. A description of the experimental hardware and software used for trapping a charged particle beam or plasma is also presented.

Scanning electron microscope is not only a versatile visualization and characterization tool for nanomaterials, but it is also widely used for visual feedback during assembly and manipulation of micro- and nanoparticles, novel devices based on 2D and 1D materials, and microrobots. Due to increase in the surface-to-volume ratio, adhesion forces play a significant role in micro- and nanorobotic applications. We investigate the quantitative effect of electron beam irradiation on nanoscale adhesive interactions between different end effector types and plain substrates. For this purpose, we use an interferometry-based force measurement setup integrated into the chamber of a scanning electron microscope capable of a subnano Newton force resolution. We provide quantitative results for the influence of the electron beam on the adhesion forces depending on the exposure dose, geometrical configuration in which it is applied, as well as on the material of the end effector. Simulation results, atomic force microscope adhesion measurements, and measurements with piezoresistive cantilevers serve as references. Our findings indicate that the electron beam influences the adhesive interaction not only in the case of insulating probes but also for well-grounded conducting and semiconducting probes. Its influence can range from several 10% to several 100% in comparison to the adhesion values measured with an atomic force microscope in an ambient atmosphere and no charged particle beam is applied. Moreover, it is shown that the influence of a charged particle beam is a multidimensional phenomenon that depends on several factors such as end effector and substrate material, geometry and aspect ratio of the end effector, geometrical configuration between particle beam and probe–sample arrangement, as well as exposure dose and field of view. We provide recommendations for handling and characterization of micro- and nano-objects using end effectors under the influence of charged particle beams: not to rely on adhesion values acquired in different environmental and exposure conditions, not to expect the application of conductive materials and grounding to completely avoid the effect of charged particle beams, and to be aware that charged particle beams can lower or increase the adhesion force in vacuum depending on material properties, among others.

A statistical theory of the momentum and energy exchange between beams of particles interacting by Yukawa-type potentials is presented. A theoretical description is given for the slowing down of the beams, the thermalization and heating of the beams, and the establishment of the isothermal state in the beams. The associated collision integrals are evaluated, with consideration of the velocity dependence of various Coulomb logarithms. The kinetic processes are shown to depend crucially on whether the relative velocity of the beams is supersonic or subsonic. The theory is applicable to (i) beams of charged and neutral particles interacting by a Coulomb potential screened by bound electrons, and (ii) beams of charged particles interacting by a Coulomb potential screened by free charges. In the region of low energies, the results are applicable to the components of collision-dominated ionized gases and plasmas, and represent an essential contribution to the transport theory of collision-dominated media with nondivergent Coulomb interactions.

We calculate exact two-dimensional analytic expressions for the electric and magnetic fields and their potentials generated by a linear beam of relativistic charged particles between infinite ideally conducting planes and ferromagnetic poles. We use the method of summing an infinite sequence of fields of linear image charges and image currents to obtain solutions and also calculate the density distribution of the electric charge on the conductor surface induced by the charged particle beam. We obtain new formulas for the linear approximation of the fields near the beam and discuss the mathematical features of the exact solutions and the applicability constraints for the linear approximations.

The most obvious components of particle accelerators and beam transport systems are those that provide the beam guidance system. Whatever the application may be, a beam of charged particles is designed to follow closely a predescribed path along a desired beam transport line or along a closed orbit in case of circular accelerators. The forces required to bend and direct the charged particle beam or to hold particles close to the ideal path are known as the Lorentz forces and are derived from electric and magnetic fields through the Lorentz equation.

The most obvious components of particle accelerators and beam transport systems are those that provide the beam guidance and focusing system. Whatever the application may be, a beam of charged particles is expected by design to follow closely a prescribed path along a desired beam transport line or along a closed orbit in case of circular accelerators. The forces required to bend and direct the charged particle beam or provide focusing to hold particles close to the ideal path are known as the Lorentz forces and are derived from electric and magnetic fields through the Lorentz equation.

Quantum mechanics of bending of a nonrelativistic charged particle beam by a dipole magnet

This paper discusses three new issues that necessarily arise in realistic attempts to apply nonlinear dynamics to galaxy evolution, namely: (i) the meaning of chaos in many-body systems, (ii) the time-dependence of the bulk potential, which can trigger intervals of {\em transient chaos}, and (iii) the self-consistent nature of any bulk chaos, which is generated by the bodies themselves, rather than imposed externally. Simulations and theory both suggest strongly that the physical processes associated with galactic evolution should also act in nonneutral plasmas and charged particle beams. This in turn suggests the possibility of testing this physics in real laboratory experiments, an undertaking currently underway.

In plasmas with strongly anisotropic distribution functions, collective instabilities may develop if there is sufficient coupling between the transverse and longitudinal degrees of freedom. Our previous numerical and theoretical studies of intense charged particle beams with large temperature anisotropy [E. A. Startsev, R. C. Davidson and H. Qin, PRSTAB, 6, 084401 (2003); Phys. Plasmas 9, 3138 (2002)] demonstrated that a fast, electrostatic, Harris-like instability develops, and saturates nonlinearly, for sufficiently large temperature anisotropy (T{sub {perpendicular}b}/T{sub {parallel}b} &gt;&gt; 1). The total distribution function after saturation, however, is still far from equipartitioned. In this paper the linearized Vlasov-Maxwell equations are used to investigate detailed properties of the transverse electromagnetic Weibel-type instability for a long charge bunch propagating through a cylindrical pipe of radius r{sub w}. The kinetic stability analysis is carried out for azimuthally symmetric perturbations about a two-temperature thermal equilibrium distribution in the smooth-focusing approximation. The most unstable modes are identified, and their eigenfrequencies, radial mode structure and instability thresholds are determined. The stability analysis shows that, although there is free energy available to drive the electromagnetic Weibel instability, the finite transverse geometry of the charged particle beam introduces a large threshold value for the temperature anisotropy ((T{sub {perpendicular}b}/T{sub {parallel}b}){sup Weibel} &gt;&gt; (T{sub {perpendicular}b}/T{sub {parallel}b}){sup Harris}) below which the instability is absent. Hence, unlike the case of an electrically neutral plasma, the Weibel instability is not expected to play as significant a role in the process of energy isotropization of intense unneutralized charged particle beams as the electrostatic Harris-type instability.