Electron Beam Extraction Research Articles

Surface-barrier detector with smoothly tunable thickness of depleted layer for study of ionization loss and dechanneling length of negatively charged particles channeling in a crystal

A new method for the experimental study of ionization loss of relativistic negatively charged particles moving in a crystal in the channeling regime using a semiconductor surface-barrier detector with smoothly tunable thickness of the depleted layer is proposed. The thickness of the depleted layer in a flat semiconductor detector can be smoothly regulated by the value of the bias voltage applied to the detector. Therefore, the energy distribution of the ionization loss of relativistic particles which cross the detector and move in the channeling regime in the detector crystal can be measured along the path of the particles by varying the bias voltage of the detector and the dechanneling length can be found. Available literature data on experimental and theoretical researches of the dechanneling length are reviewed. The significant disagreement between the experimental and theoretical data is noted. Comparison of experimental data obtained by the detector-target with smoothly tunable thickness of the depleted layer with calculations can help to develop theoretical description of the dynamics of motion of negatively charged particles channeling in a crystal. A better understanding of the dechanneling length properties can be useful in the production of positrons and other particles such as neutrons by an electron beam in crystals, as well as in the development of crystalline undulators, and in the crystal-based extraction of electron beams from a synchrotron.

Ultrafast laser pulse stretching via dispersive materials including high dispersion orders

Ultrafast laser systems typically employ complicated systems for varying their pulse length (duration) such as an ultrafast IR mode-locked laser used at the Schlesinger Compact Accelerator Center at Ariel University. The laser is an Astrella manufactured by Coherent generating an 800nm pulse. The pulse duration can be varied from 10 ps to 35 fs using a remote-controlled grating-based compressor. In order to measure the time duration of the pulse, an automated compact autocorrelator was designed and developed. The laser is mainly used to extract electrons from a photo-cathode using dual BBO frequency tripling system, providing a UV (266nm) ultra-short pulse. The electrons are formed into a beam, which is used to generate a THz FEL. Using an fs-level UV pulse, the extracted electron beam is unstable, resulting in high space-charge effects, high emittance values, and lowered radiation power dramatically. For this reason, we aim to stretch the UV pulse to a ps level. We study here an applicative method that uses dispersive materials. This method is convenient, compact, and can be easily installed. However, ultrafast lasers can suffer from high dispersion orders. Therefore, we study the contribution of the third and fourth orders of dispersion using analytical and numerical methods. Furthermore, our analysis takes into account the self-phase modulation effect when intense lasers are used. An experimental measurement is executed to confirm our numerical results, and a comparison between the experimental and simulation results is presented.

A cryogenically cooled 200kV DC photoemission electron gun for ultralow emittance photocathodes.

Novel photocathode materials like ordered surfaces of single crystal metals, epitaxially grown high quantum efficiency thin films, and topologically non-trivial materials with dirac cones show great promise for generating brighter electron beams for various accelerator and ultrafast electron scattering applications. Despite several materials being identified as brighter photocathodes, none of them have been tested in electron guns to extract electron beams due to technical and logistical challenges. In this paper, we present the design and commissioning of a cryocooled 200kV DC electron gun that is capable of testing a wide variety of novel photocathode materials over a broad range of temperatures from 298 to 35K for bright electron beam generation. This gun is designed to enable easy transfer of the photocathode to various standard ultra-high-vacuum surface diagnostics and preparation techniques, allowing a full characterization of the dependence of beam brightness on the photocathode material and surface properties. We demonstrate the development of such a high-voltage, high-gradient gun using materials and equipment that are easily available in any standard university lab, making the development of such 200kV electron guns more accessible.

DNA irradiating system with 35-keV electron beam

This work aims to design the experimental system for investigating the effect of low energy electron irradiation on DNA by means of particle tracking and mechanical strength simulations. The electron beam produced with a DC accelerator having uniform kinetic energy of 35keV and the current of 10nA is used as a source of primary electrons. Two situations of DNA irradiation, in vacuo and in ambient, are studied. For both cases, the main objective is to choose appropriate materials to serve as the windows for the in vacuo sample cell and the vacuum window for ambient electron beam extraction. Silicon nitride with varied thickness has been proposed to be used as the electron exposing window for the sample cell and has been examined in Geant4 particle tracking simulation and SolidWorks mechanical strength test while titanium (Ti), beryllium (Be), and high-density polyethylene (HDPE) are considered to be used as the vacuum window and the properties are studied with the same method. The optimal materials are used to construct the system where electron beam is irradiated on a DNA sample. The interaction of electrons with the DNA and its damages is performed with the Geant4-DNA simulation. Based on our limiting conditions, it is found that the DNA double strand breaks can only be observed when the DNA sample is irradiated inside the vacuum part of the accelerator unit.

Analytical study of FEL oscillator saturation state based on longitudinal ponderomotive bucket

Free Electron Laser(FEL) oscillator is the main working mode to produce infrared and THz wavelength range radiation. At FEL saturation state, the interaction between electron beams and radiation becomes nonlinear. Saturation power can be solved by numerical simulation of macro particle motion in longitudinal phase space or by semi-analytical formulae analogous to conventional laser system from previous study. While in this paper, the motions of macro-particle are depicted with analytical formulae in the assumption that energy transfer is mainly from captured electrons of ponderomotive bucket. Then corresponding electron beam extraction efficiency can be achieved due to initial and final state of electron beams. Therefore laser power is confirmed through equilibrium situation inside resonator cavity. These simple analytical formulae can be used to optimize output laser power and offer a better understanding in FEL oscillator saturation. Taking small signal gain regime as an example, the optimum FEL efficiency is obtained at gain to loss ratio around 4.1. This agrees well with the results of three-dimension simulation.

First design of a crystal-based extraction of 6\xa0GeV electrons for the DESY II Booster Synchrotron

A proof-of-principle experimental setup for the extraction of 6 GeV electrons from the DESY II Booster Synchrotron using the channeling effect in a bent crystal is elaborated. Various aspects of the experimental setup were investigated in detail, such as the particle beam dynamics during the extraction process, the manufacturing and characterization of bent crystals, and the detection of the extracted beam. In order to optimize the crystal geometry, the overall process of beam extraction was simulated, taking into account the influence of radiation energy losses. As result it is concluded that the multi-turn electron beam extraction efficiency can reach up to 16%. In principle this crystal-based beam extraction technique can be applied at any electron synchrotron in order to provide multi-GeV electron beams in a parasitic mode. This technique will allow to supply fixed-target experiments by intense high-quality monoenergetic electron beams. Furthermore, electron/positron crystal-based extraction from future lepton colliders may provide an access to unique experimental conditions for ultra-high energy fixed-target experiments including searches for new physics beyond the Standard Model.

Testing of the Ti foil with TiN coating as an exit window of a pulsed electron accelerator

Increasing the efficiency of electron beam extraction from a vacuum diode is an urgent problem for the practical use of accelerators. In the general case, the given problem is reduced to decreasing the mass thickness (g/cm2) of the exit window membrane while ensuring sufficient mechanical properties. The paper presents the results of testing an exit window 85 mm in diameter with a 25 μm Ti membrane and a 0.8 μm TiN coating. When tested, the coated membrane exhibited mechanical characteristics comparable to those of a 60 μm Ti membrane, which deteriorated upon repeated pumpings of the accelerator chamber volume due to the appearance of cracks in the coating. The energy loss of the electron beam in the exit window of the accelerator was decreased by 18%, as compared to the Ti 60 μm membrane. The use of a 25 μm Ti membrane with a 0.8 μm TiN coating provided 16 J per pulse energy output of more than 104 pulses of the electron beam (50–275 keV) with a repetition rate of 1–10 pulses per second. The obtained results will be used to further improve the electron beam extraction systems in the field of high-pressure applications.

Efficiency of electron beam extraction to the atmosphere in an accelerator based on ion-electron emission

The use of a modern element base makes it possible to create power supplies with a transition from a direct mode of generation of an auxiliary discharge to a pulse-periodic mode with a pulse repetition rate at the level of several tens of kHz. This allows for a more flexible adjustment of the discharge parameters, keeping the average value of its current, but changing its amplitude with a corresponding change in the pulse duty cycle. In this work, using an electron accelerator based on ion-electron emission, generating a wide-aperture electron beam, we research the effect of auxiliary discharge generation mode (direct and pulse-periodic) on the efficiency of electron beam extraction into the ambient atmosphere. It is shown that, in a direct mode of electron beam generation at an accelerating voltage of 150 kV, the beam extraction coefficient does not exceed 0.25. The possibility of increasing the extraction coefficient to K = 0.55 at the same accelerating voltage of 150 kV was demonstrated without making changes to the design of the accelerator, but switching to a pulsed-periodic mode of emission plasma generation.

Longitudinal phase space improvement of a continuous-wave photoinjector toward X-ray free-electron laser application

The electron source still remains a major challenge for continuous-wave (CW) X-ray free-electron lasers (FELs). In this paper, we study the feasibility of an injection line based on a DC and superconducting radio-frequency (SRF) combined photocathode injector. We present a detailed investigation on the longitudinal phase space evolution of the electron beam along the injection line. We also analyze the main issues determining the high-order energy spread and current skewness. Based on the analysis, we propose to use a harmonic cavity as the buncher for the injection line. Simulation shows that an extracted electron beam with a normalized RMS emittance of 0.37 μm, an RMS bunch length of 1.0 mm, a high-order RMS energy spread of 2.75 keV, and a current skewness of 0 can be obtained at the bunch charge of 100 pC. This study is meaningful to the design of the injection lines for short-wavelength CW FELs, including those based on normal-conducting very-high-frequency (VHF) guns or DC guns.

Experimental, analytical, and computational investigation of mesh grid thermal physics in an electron gun with dispenser cathode.

Gridded electron guns are key components of various electron beam based vacuum tubes. Mesh grids may be utilized for electron beam extraction and control. As part of the electron beam may be intercepted by the mesh grid, heating occurs, which could translate into performance degradation of the vacuum tube or even failure. This paper introduces an analytical model based on first physics principles for mesh grid heating in an electron gun, toward generating the upper bound for the intercepted electron beam power. 3D simulations and exploratory experiments for mesh grid heating in an electron gun directionally confirm the predictions of the analytical model. This analytical approach may be leveraged further when the upper bounds of mesh grid heating in electron guns are needed, as well as for adjusting mesh grid topology to increase its robustness against electron beam heating.

Test Beams of the LPI Accelerating Complex Pakhra

In this paper, we report the characteristics of the generated beams, the extracted electron beam and the beam of secondary electrons/positrons, of the LPI accelerator complex Pakhra as of November 2019 for testing and calibrating detectors used in large accelerator and astrophysical experiments. At energies of 250–500 MeV of the electron beam ejected into Hall 1 from the S-25R synchrotron, its energy resolution is δ ~ 1% and the intensity can be changed by collimators in the range of 103–1010 s–1. The quasi-monochromatic beam of secondary electrons produced in Hall 2 typically has an energy in the range of 50–300 MeV, a corresponding energy resolution of δ = 14–2%, and an intensity of ~ 102 s–1. The performed simulation of the characteristics of the secondary positron beam allowed selecting the optimal geometry of the setup and showed good agreement with the experimental data obtained later.

Design and Implementation of a SoC Embedded Waveform Acquisition System for Surveillance and Diagnostics of Pulsed Magnet Power Supplies

Pulsed magnet power supply systems used for electron beam injection and extraction have been developed for the Taiwan Photon Source (TPS) and the Taiwan Light Source (TLS). Control systems for these supplies have been implemented with well-functioning operations interfaces. To accomplish higher reliable operation, advanced real-time diagnostic toolkits for pulsed magnet power supplies had to be developed. A SoC (System-on-Chip) embedded waveform acquisition system has been designed, implemented and applied to inspect pulsed magnet power supplies during routine operation. This waveform acquisition system not only operates at the 125 MS/s sample rate, 50 MHz bandwidth and 14 bits resolution, but supports also the EPICS software framework for complete system integration. The acquired current waveforms can be immediately extracted specific characteristics to examine the status of pulsed magnet power supplies. In this paper, we summarize the design, implementation and real-time data analysis of the SoC embedded waveform acquisition system for the pulsed magnet power supplies.

Obtaining of High-Power Electron Beams in a Plasma Anode Source Powered by the Marx Generator with Matched Loads

Experiments have been carried out to obtain high-power microsecond electron beams with high energy using an electron beam source with an explosive emission cathode and a plasma anode. The beam was formed and transported in a longitudinal magnetic field. The voltage source was the Marx generator with stages based on artificial long lines with matched loads connected to them. The possibility of realization of operation modes of the electron beam source with quasi-constant values of the accelerating voltage and current without highcurrent arc discharge formation in the interelectrode gap is demonstrated. Electron beams with circular and rectangular cross sections of ~100–200 cm2 with current up to 1–1.5 kA and duration of 5 μs were obtained at a quasi-constant accelerating voltage of 200 kV. The rotation of the beam around its axis was recorded. The possibility of electron beam extraction through a foil window into the atmosphere has been tested.

Functional test of electron beam extraction for pulse electron irradiator

Function test of electron beam extraction for pulse electron. The functional test of pulse electron beam extraction has been performed. The purpose of the functional test is to know the magnitude of the current and the distribution of the extracted electron beam. The plasma current detection system consists of three Rogowski coils mounted on output cables of Ignitor Discharge Power Supply (IDPS), Arc Discharge Power Supply (ADPS) and Faraday Cup (FC), while the voltage and pulse width are observed using an Oscilloscope. From the measurement results obtained that the spot and plasma currents are 11,24 A and 119,65 A. At the extraction voltage of 3 kV obtained the maximum extraction current are 13,1 A and 6,7 A for the position of FC near the ignitor electrode and in the middle of the grid respectively. It can be concluded that the pulsed electron beam can be extracted by the distribution of the beam near the ignitor electrode higher than in the middle position of the grid.

Numerical studies on electron beam quality optimization in a laser-driven plasma accelerator with external injection at SINBAD for ATHENAe

Nowadays the electron beams produced in plasma-based accelerators (PBAs) are of sufficient energy for multi-GeV applications. However, to allow PBAs to be usable for demanding applications such as Free-Electron Lasers, the quality and stability of plasma-accelerated beams have to be improved. We present numerical studies on acceleration of an RF-generated electron beam with a charge of 0.8 pC and initial mean energy of 100 MeV to GeV energies by a laser-plasma accelerator. This acceleration scheme is planned to be tested experimentally within the framework of the ATHENAe (Accelerator Technology HElmholtz iNfrAstructure) project at the SINBAD (Short INnovative Bunches and Accelerators at DESY) facility at DESY, Hamburg. Electron beam injection, acceleration and extraction from the plasma are investigated through start-to-end 3D simulations. The effect of the injection phase on the accelerated beam quality is investigated through tolerance studies on the arrival-time jitter between the electron beam and the external laser.

Straw Chambers for the NA64 Experiment

The aim of this work is to describe the characteristics and properties of the particle-tracking detectors created at the Joint Institute for Nuclear Research by the glued straw tube technology for the NA64 experiment on the extracted electron beam of the CERN SPS. The physical task of the experiment is to search for phenomena of the dark sector and dark matter.

Triggering of ionization oscillations in hollow cathode discharge by keeper electrode

The keeper electrode was believed to be beneficial for improving the hollow cathode performance. However, this paper shows that it can also be hazardous to the discharge if not treated properly. Interactions between the extracted electron beam and the keeper electrode were revealed in an experiment regarding the hollow cathode discharge in the magnetic field environment. It was found that when the electron beam was wider than the keeper orifice, non-negligible electron current was irreversibly lost on the cold keeper wall, inferring from the escalated floating potential of the keeper with respect to the cathode potential. This loss triggered the high-amplitude ionization oscillations in the cathode plume that were highly coherent with the potential fluctuations of keeper itself. The magnetic field that was parallel to the cathode axis could restrict electron diffusion onto the keeper surface and greatly restrain the triggering. Based on the discovered triggering mechanism, several suggestions regarding the cathode design and thruster-cathode coupling were given.

Adjustable pulse width and high repetition frequency electron beam extraction from vacuum arc plasma

We investigate the generation of high repetition frequency electron beam from vacuum arc plasma source, which consists of Cu cathode and hollow anode. The frequency and pulse width of the extraction pulse power supply based on MOSFET can be adjusted continuously. A self-trigger circuit is designed to immediately reignite DC arc after its extinguishment and guarantee the discharge duration time and stability. The experimental results show that the repletion frequency and pulse width of the electron beam are controlled by the extraction pulse voltage parameters. With a certain discharge current, the beam current increases with the increasing extraction voltage and shows a saturation limit up to 1A. However, the extraction voltage with too high pulse frequency or pulse width is not conducive to the stability of the beam current.

Two-stage laser-driven plasma acceleration with external injection for EuPRAXIA

The EuPRAXIA (European Particle Research Accelerator with excellence In Applications) project aims at producing a conceptual design for the worldwide plasma-based accelerator facility, capable of delivering multi-GeV electron beams with high quality. This accelerator facility will be used for various user applications such as compact X-ray sources for medical imaging and high-energy physics detector tests. EuPRAXIA explores different approaches to plasma acceleration techniques. Laser-driven plasma wakefield acceleration with external injection of an RF-generated electron beam is one of the basic research directions of EuPRAXIA. We present studies of electron beam acceleration to GeV energies by a two-stage laser wakefield acceleration with external injection from an RF accelerator. Electron beam injection, acceleration and extraction from the plasma, using particle-in-cell simulations, are investigated.

Characteristics of an electron beam extracted from a microwave electron cyclotron resonance plasma cathode

Under ultra-low pressure, an electron beam is generated by the microwave electron cyclotron resonance plasma with a permanent magnet. By means of the Hall coil and Miller ampere meter, two electron current signals at the end of the extraction anode (Ia) and the sample holder (Is) were measured. The influences of discharge power, gas pressure, and accelerating voltage on the electron beam current Is were analyzed. The experimental results indicated that the extracted electron current can reach 75.1 mA at a gas pressure of 1.4 × 10-3 Pa, an accelerating voltage of 8 kV, and an orifice size of 3 mm in diameter. In order to estimate the focusing properties of the electron beam by the beam-focusing coil, the influence of the coil current on the size of the electron beam spot on the sample holder was presented and discussed. The intrinsic mechanism of electron beam extraction and propagation is revealed by numerical simulation.