Effect Of Electron Beam Energy Research Articles

Theoretical and numerical studies of the phase velocity of wakefields in plasma driven by self-modulated proton beams with electron beam seeding

Significant progress has been made in the studies of wakefield excitation in plasma by a self-modulated high energy proton beam in the past decade. The electron beams accelerated up to 2 GeV by using such a wakefield were demonstrated in the AWAKE experiment at CERN in 2018. Aiming at the application of high energy particle accelerators, new ideas have been investigated in recent years, such as seeding the proton beam self-modulation with an electron beam in order to enhance the strength and stability of the wakefield or adding a density transition in the plasma distribution to enhance the phase velocity and the strength of the wakefield. Here in this work, we investigate the effects of electron beam seeding on the phase velocity of the wakefield generated by the modulated proton beam in plasma. The physical mechanisms responsible for the phase velocity change and the roles played by the electron beam seeding are discussed. The theoretical analysis and two-dimensional particle-in-cell simulations show that both the growth rate and the phase velocity of the wakefield generated by the modulated proton beam can be enhanced by the electron beam seeding. The higher the charge density of the electron beam, the more significant the enhancement effects. The effects of electron beam energy and proton beam longitudinal profiles on the increase of phase velocity are also studied. It is shown that the evolution of the electron beam distribution has a significant effect on the seeding self-modulation process, and thus affecting the phase velocity. A self-focusing electron seeding beam can increase the phase velocity of the wakefield even to superluminal while an expanding seeding beam can reduce the phase velocity and destroy the stability of the whole process. This work may benefit the proton beam seeding self-modulation acceleration and its applications.

WE-E-AUD-05: Dosimetric Characteristics of GAFCHROMIC® EBT Film for Therapeutic Electron Beams

Purpose: To evaluate the dosimetric characteristics of GAFCHROMIC® EBT film when exposed by high‐energy electron beams.Method and Materials: Studies of the effects of the electron beam treatment parameters on dose calibration curves were performed with GAFCHROMIC® EBT radiochromic films. All films used in this study were from the same batch in order to remove any variability between batches. The films were irradiated in a multilayered 30 × 30 × 25 cm3 solid water phantom with source‐to‐surface (SSD) distance of 100 cm. The effects of electron beam energy, cone size, dose rate, depth, and MU end effect were studied. Results: The dose response curve was found to be independent of the electron energy (−2.2% to 3.6% difference of the averaged scan value). The dose calibration curves of EBT films were independent of MU end effect (from −1.0% to 2.2%) as well as electron beam dose rate (within 1.7%). For the field size dependence due to different electron cones, it is possible to calibrate GAFCHROMIC® EBT films using 10 × 10 cm2, cone size and then evaluate dose distributions resulting from various electron cone sizes. The EBT film did not show any impact of the depth on the dose response curve for electron beams. Conclusions: There was no much influence on dose response curves of GAFCHROMIC® EBT films due to electron beam energy, cone size, dose rate, depth, and MU end effect. The independence of the GAFCHROMIC® EBT on these electron beam dosimetric parameters studied for this kind of newly developed radiochromic film makes it an accurate and versatile dosimetric detector for two‐dimensional dose distribution measurements for therapeuticelectron beams.

Evaluation of damage induced by electron-beam irradiation to metal-oxide semicondoctor gate pattern and method for damage-free inspection

We analyze the electron-irradiation damage induced in wafers by scanning electron microscope (SEM) inspection, which uses SEM images of voltage contrast formed by the charges on the pattern. The effects of electron-beam energy and charging on a metal-oxide semiconductor (MOS) capacitor are studied. We find that the higher energy electron beam, whose electron range is larger than the thickness of the gate electrode, creates traps at the interface between the silicon substrate and the gate dielectric. The flat-band voltage is shifted by the created traps. Although these traps are created by the transmission of the electron beam into the dielectric, they are not created only by charging on the gate electrode; neither is an oxide fixed charge created in the MOS capacitor. Accordingly, for damage-free inspection of MOS devices, the electron-beam energy should be low enough that the electron range is smaller than the thickness of the gate electrode. On the other hand, the flat-band voltage does not shift, owing to charging on the pattern surface during the electron irradiation. However, the gate dielectric is broken down by charging on the gate electrode at high voltage. Accordingly, for damage-free inspection, the charging voltage should be controlled so as not to break down the gate dielectric.

A novel scanning electron microscope method for the investigation of charge trapping in insulators

A new technique using a copper detector in a scanning electron microscope is introduced for the investigation of charging in insulators, and pure single-crystalline α-quartz samples are studied. The curve of charging rate varying with time is obtained, and the total charge trapped in the sample is accurately determined. Furthermore, the effects of electron-beam energy and current on charging are also examined. Our results suggest that electron-radiation-induced defects in the sample play major roles in the charge trapping. Details of the experimental setup are given.

Electron dosimetry at junctions of electron fields

The positioning of adjacent electron fields on the skin surface is made more complex by the shape of the electron beam isodose distributions. With the constriction of the high dose levels and the bulging out of the low dose levels, it is difficult to achieve a junction region which does not show either a significant region of low dose, a region of high dose, or both without the use of beam edge modifiers. We have studied the abutment regions of adjacent electron fields using our three-dimensional radiation treatment planning system (3-D RTP). This study includes the effects of electron beam energy, field size, surface gap, and air gaps on the abutment regions of parallel beams directed normal to a flat surface. The input dose information was measured with film dosimetry for single fields. Films including two fields were also used to verify the method of beam superposition for the simulation of beam abutments in our 3D RTP system. The experiments were evaluated using dose-volume histograms to document the magnitude of the overdose/underdose region as well as the volumes involved. The junction regions were further reviewed using the dose surface display available on our 3-D RTP system as well as planar isodoses of the junction regions. The results of these experiments will be presented using the dose-volume histograms, dose surface displays and planar isodose displays. Analysis of optimal abutment techniques without using beam modifiers, as derived from this work, will also be presented.

Effect of electron beam energy on secondary negative ion—molecule reactions in NO 2 under high-pressure mass spectrometry conditions

The abundances of negative ions resulting from 1 keV electron beam irradiation of gaseous NO 2 and its mixtures with H 2 were measured in a high-pressure mass spectrometer. The influence of incident electron energy on the relative clustering efficiency of NO - 3 with HNO 3 and C 2H 5ONO 2 as well as of NO - 2 with HNO 2 and C 2H 5ONO 2 were investigated in NO 2, NO 2- M, HNO 3- M and C 2H 5ONO 2- M ( M = Ar, H 2, N 2, CH 4, C 2,H 6 gas systems. Significant changes in the ratios: R(NO - 3) = ∑ n [NO - 3 ·(HNO 3) n ]/[NO - 3] and R(NO - 2) = (NO - 2 ·HNO 2]/[NO - 2] with change of electron beam energy were found in the case, where the ions originated from NO 2 and its mixtures. The experimental data were correlated with the energy distribution of secondary electrons computed by Monte Carlo simulation of electron degradation in argon. The observed effect of electron beam energy on R(NO - 3) and R(NO - 2) for the systems containing NO 2 was interpreted in terms of a contribution of the excitation energy deposited in NO - 2 by impacting electrons to the internal energy of the (NO - 3 ·HNO 3) and (NO - 2 ·HNO 2) complexes.

Imaging of thermal and elastic surface properties by scanning electron acoustic microscopy

AbstractScanning electron acoustic microscopy is a new technique for imaging the thermal and elastic properties of surfaces and detecting subsurface flaws. It can be carried out in a modified scanning electron microscope. The effects of electron beam energy and phase angle on scanning electron acoustic images of the thermal and elastic properties of surfaces were studied with an alumina fiber/aluminum matrix composite for fiber directions both transverse and coaxial to the surface. Images produced with 10‐ and 30‐keV electrons at beam modulation frequencies of 80–1200 kHz appeared to be identical, with the exception of a lower signal‐to‐noise ratio for the lower electron energy. This observation suggests that the energy input from the beam can be considered to occur at the surface for electron energies below 30 keV and frequencies below 1200 kHz. Images recorded at 0° phase angle mapped regions of different thermal and elastic properties. Images recorded at 90° phase angle highlighted the boundaries between such regions. Scanning electron acoustic microscopy can image features of different thermal and elastic properties at greater depth than traditional imaging with backscattered electrons. The practical application of the technique to the study of surfaces is illustrated by the imaging of grain structure and subsurface particles for an extruder barrel.