Electron Beam Loss Research Articles

Impact study of beam losses in TRIUMF’s BL4N proton cave and ARIEL tunnel

As part of the ARIEL project, currently under construction at TRIUMF, a new proton beam line will be installed to transport up to 100 µA of nominal beam energy 480 MeV protons from the main cyclotron extraction port to an isotope separator on-line (ISOL) proton target station. This new beam line, approximately 80 m long, designated beam line 4-North (BL4N), will connect the cyclotron to the ARIEL facility via a tunnel. The proton beam line is designed for beam losses lower than 1 nAm−1 and will feature a collimator to remove the beam halo produced by large-angle scattering in the cyclotron extraction foil.The tunnel will be shared with an electron beam line with its own specific requirements for beam loss mitigation and machine protection, leading to another ISOL electron target station. The electron beam is generated by an e-linac with capacity for 500 kW beam power operation, but is ultimately expected to operate at 100 kW with losses not exceeding 20 nAm−1. After an initial stage of operation at 25 MeV the beam energy will be upgraded to 50 MeV.In this work, the effect of the beam losses, both chronic and catastrophic, in the tunnel and adjacent areas were studied. The FLUKA particle transport and interaction code was employed to estimate the impact of the combined proton and electron beam losses to the shielding, including as well the reflection of radiation from the target stations into the tunnel during ARIEL operation. This analysis resulted into a better assessment of the damage to equipment in the tunnel and the impact on maintenance due to activation of elements of the beam line. Maximum credible accidental scenarios were also detailed to validate the shielding configuration and the safety systems location.

The Characteristics of the Second and Third Virtual Cathodes in an Axial Vircator for the Generation of High-Power Microwaves

A virtual cathode oscillator or vircator is a vacuum tube for producing high-power microwaves (HPM). The efficiency of the vircator has been a difficult task for decades. The main reasons for low efficiency are intense relativistic electron beam (IREB) loss and few or no interactions between IREB and HPM. In this case, forming multiple virtual cathodes may be beneficial in overcoming these constraints. By reusing the axially propagating leaked electrons (LE), we could confine them and form multiple virtual cathodes (VCs). This article discussed the characteristics of newly formed VCs based on simulation results. The formation time of new VCs was discovered to be highly dependent on the reflector position and the density of LE approaching their surfaces. Furthermore, multiple VC formation in the waveguide region does not affect conventional VCs’ position or forming time. The emission mode of the generated HPM was TM01 with single and multiple VCs and remained unaffected. The formation of multiple VCs positively influenced the axial and radial electric fields. When compared to a single VC, the axial and radial electric field increased 25.5 and 18 times with multiple VCs. The findings suggested that forming multiple VCs could be a future hope for achieving high vircator efficiency.

Evaluation of Skyshine from an Accelerator Facility: Dependence on Distance and Angle.

Neutron skyshine from Linac Coherent Light Source II 4 GeV electron beam operation at SLAC National Accelerator Laboratory can contribute to prompt radiation exposure to the public at distances far beyond the accelerator tunnel housing. One of the shielding design requirements at SLAC is that the annual dose to a member of the public is no more than 0.05 mSv y. This study uses Monte Carlo code FLUKA to simulate the generation of neutrons from 4 GeV electron beam losses on a thick copper target inside a generalized geometry of the Linac Coherent Light Source II Beam Transport Hall accelerator tunnel section. The effective dose from neutron skyshine was characterized as a function of both distance from the tunnel wall (up to 1 km away) and angle relative to the beam direction (between 0° and 180°). This new methodology for evaluating neutron skyshine dose is applicable to high-energy GeV-range electron accelerator facilities both at SLAC and elsewhere.

Flame-retardant cotton fabrics modified with phosphoramidate derivative via electron beam irradiation process

In this study, a novel flame-retardant diethyl methacryloylphosphoramidate containing phosphorus and nitrogen was synthesized and characterized by Fourier transform infrared and nuclear magnetic resonance. The synthesized compound was grafted onto cotton fabrics using electron beam irradiation and pad dry cure processes. Scanning electron microscope and X-ray photoelectron spectroscopy were used to characterize the surfaces of the modified cotton fabrics to confirm that diethyl methacryloylphosphoramidate was grafted on cotton fabrics successfully. Both electron beam–cotton and pad dry cure–cotton exhibited efficient flame retardancy which was proved by limiting oxygen index and vertical flammability test. Thermogravimetric analysis results showed that both electron beam-cotton and pad dry cure–cotton degraded at lower temperature and produced higher yields at 600℃. The tensile loss of electron beam–cotton was lower than that of pad dry cure–cotton, and within the acceptable range in flame retardant finishing.

Design and dynamic studies for a compact storage ring to generate gamma-ray light source based on Compton backscattering technique

As the development of nuclear physics and atomic sciences progresses, monochromatic and high-flux gamma-ray light sources are highly demanded by many experiments in these fields. We have designed a compact storage ring for gamma-ray source generation based on the Compton backscattering technique. The energy range of the electron beam stored in the ring will be from 500 to 800 MeV, with the capability of generating a gamma ray with an energy range from about 4 to 10 MeV. The maximum energy loss for an electron could be more than 1% for one scattering event, which could have a significant impact on electron beam dynamics. To study this impact, a 6D macroparticle tracking code has been developed by including the Compton scattering, damping, quantum excitation, and synchrotron radiation in the storage ring. The equilibrium states have been studied with this code, and the results show good agreement with theoretical predictions. The electron beam loss rate induced by Compton scattering has also been investigated by varying the input laser beam parameters. This study allows us to optimize the storage ring operation for a stable, high-flux, and narrow-bandwidth gamma-ray beam generation.

Estimation of Beam and Plasma Parameters for Electron Beam Transport in Ion-Focused Regime

This paper presents the analysis of cylindrical electron beam and beam-impact-generated plasma using particle-in-cell simulation code VSim 6.2 at different operating conditions. The transient plasma parameters, such as, beam density, charge neutralization factor, space charge potential, ionization time, beam compression, and plasma electron temperature, have been estimated and analyzed for a 40-keV, 10–100-A electron beam propagating in argon gas-filled drift space at different operating pressures. These parameters are difficult to be measured experimentally. The evaluated charge-neutralizing factor has been found dynamic in space and time, which is maximum at the beam envelope. The voltage profile of space charge potential required for effective electron beam propagation approaches zero due to formation of the plasma in the order of ionization time. The estimated average plasma electron temperature has been found to be less than ~1 eV, which is less damaging for interaction structure of the plasma-assisted microwave sources. It has been observed that an optimum pressure limit needs to be maintained inside the drift space to prevent the loss of electron beam due to instabilities resulting in excessive collisions with the drift space walls.

Diagnostics of Local Electron Beam Losses in Microtron-recuperator on Novosibirsk Free Electron Laser Beamline via Detection of Induced X-rays

The Novosibirsk Free Electron Laser (NovoFEL) is based on a four-turn microtron-recuperator. To ensure its stable operation and radiation generation, it is necessary to provide a stable mode of electron beam recirculation and minimize beam losses on the vacuum chamber wall on all the beam way in the accelerator beamline. To this end it is necessary to know the longitudinal distribution of these losses along the beamline.A system for registration of beam losses was created. The system applies optical fibers placed along the vacuum chamber and nearby it. If local electron beam losses occur somewhere in the vacuum chamber, electrons falling to the vacuum chamber wall cause generation of X- and gamma rays. This radiation in turn originates optical emission in an optical fiber nearby the region of electron “precipitation” on the chamber wall. Then, executing some transformation and processing of the time dependencies of signals from these optical fibers, one can obtain the longitudinal distribution of electron beam losses along the accelerator line in all its four turns.

유한요소법과 몬테카를로법을 이용한 X선 튜브에서 전자빔 충격에 의한 열 발생 해석

We analyze heat generation as well as temperature distribution induced by accelerated electron impact on a target in a closed x-ray tube. For the sake of accuracy, we use Monte carlo analysis. This method gives accurate energy deposit in a medium with additional information such as secondary and backscattered electron as well as their paths. A Tungsten coated layer is divided by small rectangular cell which accumulate energy loss of primary electron beam. The cells and their accumulated energy datum are used for the input of finite element analysis. The Maximum temperature rising and temperature distribution were analyzed by transient heat analysis. Some temperature parameters such as target size and coating thickness were varied to investigate temperature sensitivity. Temperatures were compared each other to find primary variable that affect temperature rising on the x-ray target. The results will be helpful in development high-resolution x-ray tube and related industries.

Estimation for the intensity of beam loss by the optical fiber based Cherenkov beam loss monitor at SACLA

From the issues of radiation safety and radiation damage of accelerator equipments, it is useful to detect the beam loss immediately at high-energy and high intensity particle accelerator facilities. In the undulator section of Spring-8 Angstrom Compact free electron LAser (SACLA) [1], beam loss monitors have been installed in order to control beam losses and to prevent demagnetization of permanent magnets due to electron hitting [2]. Since the commissioning phase of SACLA, this monitor has been successfully working. This beam loss monitor consists of a quartz fiber with 400 μm core diameter and a photomultiplier tube (PMT) which is connected with the upstream end of the fiber. The Cherenkov radiation which is produced in the fiber due to the passing of secondary electrons and positrons (Cherenkov emitters) is detected by the photomultiplier tube. With the detection time of the monitor signals, the position of the beam loss point can be measured. In addition, the use of two monitors with different gains allows measuring intensity of the beam loss over the wide dynamic range. While it is expected that the waveform of the monitor signal corresponds to the spatial distribution of the electron flux or absorbed dose due to the beam loss, if this monitor is used for the beam loss control, it is necessary to calibrate the magnitude of the monitor signal to a value such as the number of electrons or the absorbed dose in order to set an appropriate threshold level. In this study, the electron beam loss was measured by the beam loss monitor and thermo luminescent dosimeters (TLD), and the correlation among the signal of the beam loss monitor, the absorbed dose and electron flux was investigated.

SU‐E‐T‐219: Illustration of Electron Beam Loss of Field Edge Fidelity (Beam Shape) and Uniformity with Air Gap

Purpose: Clinical use of electron beams frequently involves elaborate field shapes and/or matching of edges with adjacent poton fields. Treatment on accasion requires an extended Source Skin Distance (SSD). The optical projection of the field shape on the patient at the extended SSD does not depict the impact of the increased distance on shape and uniformity. The purpose of this presentation is to illustrate some examples of the impact Methods: Shape and dosimetric quantities measured on films exposed cross‐beam at 1 cm depth in plastic water at standard and extended SSD are compared with optical projections of shape and TPS calculations of dosimetric quantities. Results: Small field sizes of low energy electron beams have a small Effective SSD or f‐air and show a greater impact of extended distance on field shape and uniformity. For example, an f‐air value of 0.9 indicates that a net 10 percent of the beam directed towards the measurement point at the standard SSD is scattered away at the extended SSD. The scattering causes an outward bowing of straight edges, a rounding of sharp corners, loss of shape detail and a loss of uniformity of dose. Conclusion: When substantial departure from Inverse Square Law (ISL) is evident in extended SSD Electron Beam calculations it is advisable to evaluate the altered shape and uniformity so that clinical relevance can be judged. Substantial departure from ISL may mean more than a 5 or 10 percent departure from ISL or an air gap of more than 5 or 6 cm. Facilities ought to establish acceptable f‐air and air gap limits or action levels. Careful attention to minimizing air gaps as much as possible minimizes discrepancy between optically projected and actual shape and uniformity.

Investigation of electron beam parameters inside the drift region of plasma cathode electron gun

This paper presents experimental studies for the production and propagation of an electron beam from a single gap pseudospark discharge based plasma cathode electron (PCE) gun. The generated electron beam has been successfully propagated for more than 25 cm in a gaseous environment without application of external guiding magnetic field at different operating conditions. The electron beam losses due to recombination with ions and collision with walls of drift space have been estimated. The electron beam profile has also been analyzed in the drift region of the gun.

Velocity and ejector-jet assisted differential pumping: Novel design stages for environmental SEM

Velocity and ejection pumping are proposed as novel evacuation techniques to assist the static differential pumping already in use in the environmental scanning electron microscope. The gas velocity (or momentum) that accompanies the supersonic jet stream formed through the first pressure limiting aperture is used to initially force the gas out of the system by placing the second pressure limiting aperture at an optimum position in the gaseous jet. By this method, the gaseous particle thickness between the two apertures is minimised and the required pumping speed of the first evacuation stage is also reduced to an absolute minimum. A further improvement is achieved by inserting an appropriately shaped baffle between the two apertures, which shields the second aperture from the gas jet of the first and acts as an ejector-jet pump. The gas leak rate through the second aperture is maintained at an acceptable low level by both systems, even below the static leak rate level when the ejector-jet design is used, in particular. The result of either method has a double benefit, namely, the electron beam loss in the intermediate pumping stage is minimised together with a reduction of pump speed requirements. This translates to best instrument performance and minimal manufacturing costs.

Characteristics of radiation safety for synchrotron radiation and X-ray free electron laser facilities

Radiation safety problems are discussed for typical electron accelerators, synchrotron radiation (SR) facilities and X-ray free electron laser (XFEL) facilities. The radiation sources at the beamline of the facilities are SR, including XFEL, gas bremsstrahlung and high-energy gamma ray and photo-neutrons due to electron beam loss. The radiation safety problems for each source are compared by using 8 GeV class SR and XFEL facilities as an example.

Waveguide detuning caused by transverse magnetic fields on a simulated in‐line 6 MV linac

Due to the close proximity of the linear accelerator (linac) to the magnetic resonance (MR) imager in linac-MR systems, it will be subjected to magnet fringe fields larger than the Earth's magnetic field of 5 x 10(-5) T. Even with passive or active shielding designed to reduce these fields, some magnitude of the magnetic field is still expected to intersect the linac, causing electron deflection and beam loss. This beam loss, resulting from magnetic fields that cannot be eliminated with shielding, can cause a detuning of the waveguide due to excessive heating. The detuning, if significant, could lead to an even further decrease in output above what would be expected strictly from electron deflections caused by an external magnetic field. Thus an investigation of detuning was performed through various simulations. According to the Lorentz force, the electrons will be deflected away from their straight course to the target, depositing energy as they impact the linac copper waveguide. The deposited energy would lead to a heating and deformation of the copper structure resulting in resonant frequency changes. PARMELA was used to determine the mean energy and fraction of total beam lost in each linac cavity. The energy deposited into the copper waveguide from the beam losses caused by transverse magnetic fields was calculated using the Monte Carlo program DOSRZnrc. From the total energy deposited, the rise in temperature and ultimately the deformation of the structure was estimated. The deformed structure was modeled using the finite element method program COMSOL MULTIPHYSICS to determine the change in cavity resonant frequency. The largest changes in resonant frequency were found in the first two accelerating cavities for each field strength investigated. This was caused by a high electron fluence impacting the waveguide inner structures coupled with their low kinetic energies. At each field strength investigated, the total change in accelerator frequency was less than a manufacturing tolerance of 10 kHz and is thus not expected to have a noticeable effect on accelerator performance. The amount of beam loss caused by magnetic fringe fields for a linac in a linac-MR system depends on the effectiveness of its magnetic shielding. Despite the best efforts to shield the linac from the magnetic fringe fields, some persistent magnetic field is expected which would result in electron beam loss. This investigation showed that the detuning of the waveguide caused by additional electron beam loss in persistent magnetic fields is not a concern.

Magnetic decoupling of the linac in a low field biplanar linac‐MR system

The integration of a low field biplanar magnetic resonance (MR) imager and linear accelerator (linac) causes magnetic interference at the linac due to the MR fringe fields. In order to eliminate this interference, passive and active magnetic shielding designs are investigated. The optimized design of passive magnetic shielding was performed using the finite element method. The design was required to achieve no greater than a 20% electron beam loss within the linac waveguide and electron gun, no greater than 0.06 T at the multileaf collimator (MLC) motors, and generate a distortion of the main MR imaging volume of no greater than 300 ppm. Through the superposition of the analytical solution for a single current carrying wire loop, active shielding designs in the form of three and four sets of coil pairs surrounding the linac waveguide and electron gun were also investigated. The optimized current and coil center locations that yielded the best cancellation of the MR fringe fields at the linac were determined using sequential quadratic programming. Optimized passive shielding in the form of two steel cylinders was designed to meet the required constraints. When shielding the MLC motors along with the waveguide and electron gun, the thickness of the cylinders was less than 1 mm. If magnetically insensitive MLC motors are used, no MLC shielding would be required and the waveguide shield (shielding the waveguide and electron gun) became 1.58 mm thick. In addition, the optimized current and coil spacing for active shielding was determined for both three and four coil pair configurations. The results of the active shielding optimization produced no beam loss within the waveguide and electron gun and a maximum MR field distortion of 91 ppm over a 30 cm diameter spherical volume. Very simple passive and active shielding designs have been shown to magnetically decouple the linac from the MR imager in a low field biplanar linac-MR system. The MLC passive shielding produced the largest distortion of the MR field over the imaging volume. With the use of magnetically insensitive motors, the MR field distortion drops substantially since no MLC shield is required. The active shielding designs yielded no electron beam loss within the linac.

TH‐D‐BRB‐08: The Effect of Transverse Magnetic Fields on a Simulated In‐Line 6 MV Linac

Purpose: The linac waveguide is subjected to large magnetic fringe fields in a linac‐MR hybrid system. An investigation is performed to determine the effect of transverse magnetic fields on a simulated in‐line 6 MV medical linac. Method and Materials: The program PARMELA was used calculate the electron beam loss per cavity with the linac waveguide subjected to external transverse fields. BEAMnrc and DOSXYZnrc were used to calculate the effect on 40×40 and 20×20 cm2 field dose profiles and depth dose curves with the linac submersed in a transverse magnetic field. DOSRZnrc was used to determine the heating per cavity as a result of the beam loss and COMSOL was used to determine the resulting cavity resonant frequency changes due to cavity heating. Lastly a calculation of leakage radiation caused by the excessive beam loss was performed using BEAMnrc. Results: The beam loss was calculated to be 5±1 22±1 and 49±1% over nominal for 2 4 and 6 G magnetic fields respectively. The transverse magnetic fields caused a shifting of the electron spatial distribution at the target which resulted in a lateral shift of the dose profiles making 14.4% of all points fail a 1%/1mm acceptance criterion at a 6 G field. Through asymmetric jaw positions the lateral shift in the dose profiles was reduced such that only 0.5% of all points failed. The frequency of the accelerating mode changed by 0.03 Hz due to heating and a total leakage radiation of 0.007% of the radiation field was calculated. Conclusion: The 6 MV linac investigated showed sufficient tolerance to be used in transverse magnetic fields larger than earth's field. The shifts observed in the dose profiles were reduced through asymmetric jaw positions such that only 0.5 % of the points failed a 1 %/ 1 mm criterion at 6 G.

Radiation Shielding Aspects of the SCSS Prototype XFEL Facility

The characteristics of radiation were investigated for a prototype X-ray free electron laser machine with 250-MeV electrons and 49-nm-wavelength light. The doses both inside and outside the shield tunnel including the maze were measured in relation to the electron beam losses and were compared with the empirical formula and Monte Carlo simulations.

Fast electron energy deposition in aluminium foils: Resistive vs. drag heating

The high current electron beam losses have been studied experimentally with 0.7 J, 40 fs, 6 1019 Wcm-2 laser pulses interacting with Al foils of thicknesses 10-200 ?m. The fast electron beam characteristics and the foil temperature were measured by recording the intensity of the electromagnetic emission from the foils rear side at two different wavelengths in the optical domain, ?407 nm (the second harmonic of the laser light) and ?500 nm. The experimentally observed fast electron distribution contains two components: one relativistic tail made of very energetic (Thtail ? 10 MeV) and highly collimated (7° ± 3°) electrons, carrying a small amount of energy (less than 1% of the laser energy), and another, the bulk of the accelerated electrons, containing lower-energy (Thbulk = 500±100 keV) more divergent electrons (35 ± 5°), which transports about 35% of the laser energy. The relativistic component manifests itself by the coherent 2?0 emission due to the modulation of the electron density in the interaction zone. The bulk component induces a strong target heating producing measurable yields of thermal emission from the foils rear side. Our data and modeling demonstrate two mechanisms of fast electron energy deposition: resistive heating due to the neutralizing return current and collisions of fast electrons with plasma electrons. The resistive mechanism is more important at shallow target depths, representing an heating rate of 100 eV per Joule of laser energy at 15 ?m. Beyond that depth, because of the beam divergence, the incident current goes under 1012 Acm-2 and the collisional heating becomes more important than the resistive heating. The heating rate is of only 1.5 eV per Joule at 50 ?m depth. © EDP Sciences and Springer 2009.

Cloaking radiation of moving electron beam and relativistic energy loss spectra

The interaction of ideal and nonideal metamaterial cylindrical cloaks with an electron beam has been studied. The exact solution for energy loss suffered by a fast electron moving inside or outside a cylindrical cloak has been established within a fully relativistic approach. The effect of various imperfect parameters on the efficiency of the cloak has been discussed. It is shown that radiation can be shielded very well by such cloaks when an electron moves either inside or outside of them. The efficiency of nonideal cloaks and the effect of various nonideal parameters on cloak invisibility can be exhibited in the spectra of electron energy loss and radiation emission. This means that the property of a cylindrical cloak can be explored by means of scanning transmission electron microscopy.

Study on the radiation problem caused by electron beam loss in accelerator tubes**Supported by National Natural Science Foundation of China (10135040)

The beam dynamic code PARMELA was used to simulate the transportation process of accelerating electrons in S-band SW linacs with different energies of 2.5, 6 and 20 MeV. The results indicated that in the ideal condition, the percentage of electron beam loss was 50% in accelerator tubes. Also we calculated the spectrum, the location and angular distribution of the lost electrons. Calculation performed by Monte Carlo code MCNP demonstrated that the radiation distribution of lost electrons was nearly uniform along the tube axis, the angular distributions of the radiation dose rates of the three tubes were similar, and the highest leaking dose was at the angle of 160° with respect to the axis. The lower the energy of the accelerator, the higher the radiation relative leakage. For the 2.5 MeV accelerator, the maximum dose rate reached 5% of the main dose and the one on the head of the electron gun was 1%, both of which did not meet the eligible protection requirement for accelerators. We adopted different shielding designs for different accelerators. The simulated result showed that the shielded radiation leaking dose rates fulfilled the requirement.