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The paper describes experiments on the injection of an electron beam into a gas at the gas dynamic trap (GDT) and develops a technique for creating a starting plasma with parameters sufficient for its subsequent heating by neutral beams. It is found that a relatively thin electron beam is capable of ionizing plasma in the entire volume of the trap, and the plasma turbulence it excites is capable of accelerating some of the electrons to energies tens of times higher than the initial energy of the beam. It is shown that, in contrast to early experiments on tabletop open traps, collective beam relaxation under GDT conditions occurs in the vicinity of the entrance magnetic mirror. Since the electron cyclotron frequency in this region significantly exceeds the plasma frequency, it is necessary to study the mechanism of a beam-plasma discharge under these conditions. As a first step along this path, we measure the radial diffusion coefficient of fast particles, as well as the rate at which they gain energy.

The paper presents the results of a study of the operating modes of a technological electron gun used in installations for electron beam welding. The design of an electron gun, which is part of the ELA-15I power complex, is considered, and the results of modeling the accelerating gap for a new design gun with an accelerating voltage of 120 kV are presented. The current-voltage characteristics of the gun operation were experimentally obtained at different temperatures of the main LaB6 cathode. For this, the beam current was recorded at different values of the control electrode potential. A mathematical model of the accelerating gap was implemented, which makes it possible to analyze the shape of the electron beam in the region of the first lens. Using a mathematical model, the shapes of the electron beam were calculated for various operating modes of the gun, and the characteristic transverse size of the beam in the crossover was determined. The beam diameter and the angle of convergence in the area of focusing the beam on the product were determined experimentally. Conclusions were made about the equality of the crossover diameters of the full-scale and mathematical models, as well as about the sufficient coincidence of the experimental and calculated volt-ampere characteristics. The design of the accelerating gap of the ELA-15 gun was optimized with an increase in the accelerating voltage from 60 kV to 120 kV. The optimization results are shown for the original and modified design in the form of a comparison of the patterns of the distribution of the electrostatic field strength and a comparison of the current-voltage characteristics.

In this paper, the electric field intensity of the electrode structure of the thermally emitted electron gun of UTEM is simulated, and the relation between the electric field intensity distribution and the electrode plate is analyzed. Using the electronic optics software, the optical system of the electron gun is simulated, the performance parameters of the electron gun are obtained, and the advantages and disadvantages of the whole optical system are analyzed. The research results of this paper can provide a reference for the design and simulation of similar electron gun.

We report on the characterization of the response of windowless silicon avalanche photo-diodes to electrons in the 90-900 eV energy range. The electrons were provided by a monoenergetic electron gun present in the LASEC laboratories of University of Roma Tre. We find that the avalanche photo-diode generates a current proportional to the current of electrons hitting its active surface. The gain is found to depend on the electron energy $E_e$, and varies from $2.147 \pm 0.027$ (for $E_e = 90$ eV) to $385.8 \pm 3.3$ (for $E_e = 900$ eV), when operating the diode at a bias of $V_{apd} = 350$ V.} This is the first time silicon avalanche photo-diodes are employed to measure electrons with $E_e < 1$ keV.

This work aims to review the enhancement of electrical conductivity and field electron emission (FEE) properties of ultrananocrystalline diamond (UNCD) films as a function of gold ion implantation content. Au has been employed in UNCD films as an implanted species as well as an interlayer between diamond film and substrate. In the initial part of the review UNCD films are briefly introduced. The focus is on their FEE properties and multiple strategies employed for enhancing these properties using ion-implantation with the goal to obtain a better cathode material. A comparison of the characteristics of the UNCD films implanted with Au and other species after studying the modification of the microstructure and emission properties of the Au-implanted UNCD films is then provided. Subsequently, the use of a thin Au coating on silicon substrates covered by UNCD or hybrid granular structured diamond films is discussed. The Si diffusion through the Au-Si eutectic interface results in a SiC layer. This facilitates the nucleation of diamond clusters, thereby suppressing the development of the carbon layer which is amorphous and electrically resistive, resulting in improved FEE characteristics. Finally, in the third and final part, the combined effects of Au-ion implantation (including multi-energy Au ion implantation) and Au-interlayer is discussed. Based on the obtained results, the catalytic activity of gold for improving the electrical conductivity and the FEE properties of diamond films is highlighted.

A new and simple type of electron gun is presented. Unlike conventional electron guns, which require a heated fllament or extractor, accelerator and focusing electrodes, this gun uses the collimated electron microchannels of an inertial electrostatic conflnement (IEC) discharge to achieve the same outcome. A cylindrical cathode is placed coaxially within a cylindrical anode to create the discharge. Collimated beams of electrons and fast neutrals emerge along the axis of the cylindrical cathode. This geometry isolates one of the microchannels that emerge in a nega- tively biased IEC grid. The internal operating pressure range of the gun is 35-190 mTorr. A small aperture separates the gun from the main vacuum chamber in order to achieve a pressure difieren- tial. The chamber was operated at pressures of 4-12 mTorr. The measured current produced by the gun was 0.1-3 mA (0.2-14 mA corrected measurement) for discharge currents of 1-45 mA and discharge voltages of 0.5-12 kV. The collimated electron beam emerges from the aperture into the vacuum chamber. The performance of the gun is unafiected by the pressure difierential between the vacuum chamber and the gun. This allows the aperture to be removed and the chamber pressure to be equal to the gun pressure if required.

This work aims to characterize the novel DRX Plus 3543C detector in terms of detective quantum efficiency (DQE) using both a mobile x-ray system called Carestream DRX Revolution Nano and a traditional x-ray system (Carestream DRX Evolution). We used the commercial system DRX Revolution Nano, equipped with a new x-ray source based on CNT technology and field emission (FE) as the electron emitter (cathode). An innovative aspect of this device is its intrinsic selection of the focal spot size. We tested the system using three IEC-specified beam qualities (RQA3, 5 and 7) in terms of modulation transfer function (MTF), normalized noise power spectra (NNPS) and DQE as defined in the IEC 62220-1-1:2015. We compared the results obtained using DRX Revolution Nano and DRX Evolution with correlation and with Bland-Altman plots to study their agreement. RQA3 MTF is slightly lower than the RQA5 and 7 curves between 0.5 and 2.5 cycles mm-1. We measured MTF values of about 0.6 at 1 lp mm-1 and about 0.28 lp mm-1 at 2 lp mm-1. The NNPS curves show a decreasing trend with the energy regarding the DRX Revolution Nano. On the other hand, the DRX Evolution NNPS curve at RQA3 is greater than the one at RQA5, but the one at RQA5 is less than the one at RQA7. The DQE(0) ranged between about 0.82 (DRX Evolution at RQA3) and 0.54 (DRX Evolution at RQA7). As expected, the squared Pearson's correlation coefficients between the two x-ray tubes were always in an optimal agreement, and Bland-Altman plots confirmed a substantial equivalence between the two physical characterizations of the wireless detector. In conclusion, we can show that the dynamic focal selection of the system equipped with CNT does not play a substantial role in image quality compared to a traditional system in terms of physical characterisation of the detector in our measurement conditions.

Cherenkov radiation forms a wave front in a direction that depends on the density of the medium and the velocity of charged particles; therefore, ordinary electron bunches do not generate coherent radiation unless they are sufficiently compressed. In this work, we present the generation of a quasi-monochromatic THz pulse using an electron bunch with a periodic structure generated from a small rf gun. A coherent THz pulse was generated by matching the tilt angle of the electron bunch and Cherenkov radiation angle with a rf deflector. Furthermore, we attempted to render the THz pulse quasi-monochromatic by adding a periodic structure to the electron bunch using a multi-slit. Finally, using several band-pass filters, we successfully confirmed that the quasi-monochromatic operation was performed at frequencies of 0.2 and 0.3 THz.

The construction of indigenous parallel-fed capacitive coupled cascade accelerators for industrial electron beam processing has been taken up at accelerator division of NSTRI at Iran atomic energy organization. This machine has been previously developed by Radiation Dynamics Inc. (RDI), IBA Industrial and High Voltage Engineering Europa B.V. (HVE) companies. Parallel-fed capacitive coupled cascade generators are reliable and high current sources of DC accelerators with many scientific, medical and industrial applications. We have selected this mechine because of some superiorities of that in comparison with many existing accelerators. These superiorities are as follows: compactness, simplicity, cheapness, having typically higher amount of beam current, wide range of beam energy and addressing many areas of applications. In this article, the main parts of a 1MeV, 100mA parallel-fed cascade industrial accelerator have been analyzed, designed and simulated. These parts are the electron gun, accelerating tube, voltage multiplier column (VMC) and some of the other components of the VMC. The electron gun is of a diode type with the Pierce configuration. Two electron guns with different cathode shapes have been designed and compared with each other. The intended cathode is a Dispenser type with a tungsten heater and porous tungsten matrix wich is impregnated with LaB6 and works in ambient vacuum of 10–7 Torr. The required current in our accelerator is about 100mA. For the next step, the accelerating tubes with different electrode geometries have been designed, simulated and compared with each other and the best geometry has been selected. For the VMC, we have tried to achieve a low ripple output DC voltage. The VMC has been analyzed and simulated with PSpice simulation software and optimum values of different parameters were achieved. We have tried to get the optimum values of the PSpice simulations by a mechanical design in CST Particle studio. At the end, the parameters of the mechanically designed VMC had a good accordance with the results from PSpice.

A superconducting electron linac (e-Linac) photo-fission driver is under construction at VECC for the upcoming rare isotope beam facility called ANURIB. The first stage consists of an injector linac based on 1.3 GHz superconducting radio frequency technology designed for accelerating 10 MeV, 2 mA CW electron beam. An rf modulated thermionic electron gun (E-Gun) has been developed and tested for this injector linac. The E-Gun will allow continuous beam operation up to 300 keV with around 3 pC charge per pulse at 650 MHz. Electron beam with RF modulation is extracted from the gun and intensity, energy, size of the DC beam as well as trans-conductance of the electron source are measured. The design of some major components for the electron gun and low energy beam transport line is discussed and results of beam tests are presented.

Recent research indicates that ultrafast electron diffraction and microscopy (UED/M) have unprecedented potential in probing ultrafast dynamic processes, especially in organic and biological materials. However, reaching the required brightness while maintaining high spatiotemporal resolution requires new design of electron source. In order to produce ultrashort electron beam with extreme high brightness, a 1.4-cell RF gun is being developed to reach higher acceleration gradient near the photocathode and thus suppress the space charge effect in the low energy region. Simulation of the 1.4-cell RF photocathode gun shows considerable improvement in bunch length, emittance and energy spread, which all lead to better temporal and spatial resolution comparing to traditional 1.6-cell RF photocathode gun. The results demonstrate the feasibility of sub-ps temporal resolution with normalized emittance less than 0.1 πmm·mrad while maintaining 1 pC electron pulse.

At the PBP-CMU Electron Linac Laboratory, high-brightness electron beams are produced from the radio-frequency (RF) linear accelerator (linac) system that consists of a thermionic RF electron gun, an alpha magnet, a traveling-wave linac structure, quadrupole magnets and steering coils. Several diagnostic devices are installed in the accelerator system to characterize electron beam properties. In this work, we study on measurement of electron beam energy downstream the RF gun using the alpha magnet equipped with energy slits in the vacuum chamber and a current transformer. Calibration of the energy slits’ posit ions for various stepper motor encoder numbers was conducted before installing the slits in the magnet’s vacuum chamber. The calibration result was imported into the energy calculation software that links to the stepper motor encoder and the energy value will then be automatically calculated. Moreover, dynamic simulations using a software ASTRA were performed to investigate electron’s trajectories in the alpha magnet’s field with different initial electron positions and angles. The results from this study will be used to estimate the result and accuracy of energy measurement using the alpha magnet. It was found that, for different initial horizontal and vertical positions at the alpha magnet entrance, the energy of electron will be measured to be lower than its actual energy by around 0.5% and the measured energy will decrease when the initial position is moving away from the middle point. In case of horizontal particle’s angle, the error of energy measurement increases up to 1% at the angle of 3° before the beam hitting the alpha magnet chamber. For the vertical particle’s angle, the electron that has the initial angle less than or larger than 1.5° will hit the vacuum chamber.

The next generation of advanced light sources requires photons with large average flux and high brightness, which needs advanced electron gun matched with excellent photocathode materials. K2CsSb photocathode has the advantages of high quantum efficiency, long lifetime and instantaneous response. This study introduces the design of a set of K2CsSb photocathode preparation systems and detailed preparation process of K2CsSb photocathodes, including sequential deposition process and co-deposition process, and finally develops a K2CsSb photocathode. The influence of laser power on the quantum efficiency is also investigated.

To increase the quantum efficiency (QE) of a copper photocathode and reduce the thermal emittance of an electron beam, a drive laser with oblique incidence was adopted in a BNL type photocathode rf gun. The disadvantageous effects on the beam quality caused by oblique incidence were analyzed qualitatively. A simple way to solve the problems through wavefront shaping was introduced and the beam quality was improved.

The Beijing X-ray Energy Recovery Linac (BXERL) test facility is proposed in Institute of High Physics (IHEP). In this proposal, the main linac requires the injector to provide an electron beam with 5 MeV energy and 10 mA average current. An injector based on DC gun technology is the first candidate electron source for BXERL. However, the field emission in the DC gun cavity makes it much more difficult to increase the high voltage to more than 500 kV. Another technology based on a 217 MHz normal conducting RF gun is proposed as the backup injector for this test facility. We have designed this RF gun with 2D SUPERFISH code and 3D MICROWAVE STUDIO code. In this paper, we present the optimized design of the gun cavity, the gun RF parameters and the set-up of the whole injector system. The detailed beam dynamics have been done and the simulation results show that the injector can generate electron bunches with RMS normalized emittance 1.0 πmm·mrad, bunch length 0.77 mm, beam energy 5.0 MeV and energy spread 0.60%.

The length of electron beam from a photocathode RF gun is determined by a spectrometer, according to the relative energy spread induced by the bunch length during the acceleration in a linac. For a photocathode RF gun, different laser injected phase and beam charge are studied. The compression is changed for the different laser phases, as from 10° to 30°, and the bunch length is lengthened due to the strong longitudinal space charge force, caused by the increased charge.

This work looks at a new type of electron linear accelerator. Compared with the traditional electron linac, it has only two main parts: a klystron and an accelerating tube, without the electron gun element. This new kind of linac could perform just like its predecesors but reduce cost and space. The preliminary design and simulation have been accomplished. In this paper, an overview discussion about the performance tests and some improvements to increase the beam current are presented.

Electron guns are used in the accelerators of the European XFEL and FLASH. They are operated at 1.3 GHz. The RF peak power is 5 MW at 650 us pulse width and 10 Hz repetition rate. In order to understand the multipacting that occurs during conditioning, it was simulated in the RF window type that is used for the electron gun in the XFEL. The reduction in secondary emission yield associated with conditioning was taken into account. Since the RF windows are tested with high power on a test stand before their use, without the electron gun, measurement results are available which are compared with the simulation results. The main advantage of the simulation compared to the measurement is that the locations of multipacting can be determined in the RF window. This could be helpful for the development of high-power RF components in the future, in order to detect pronounced multipacting resonances even before production and to avoid them by design changes., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

ELI-NP is a linac based gamma-source in construction at Magurele (RO) by the European consortium EuroGammaS led by INFN. Photons with tunable energy and with intensity and brilliance well beyond the state of the art, will be produced by Compton back-scattering between a high quality electron beam (up to 740 MeV) and a 515 nm intense laser pulse. Production of very intense photon flux with narrow bandwidth requires multi-bunch operation at 100 Hz repetition rate. A total of 13 klystrons, 3 S-band (2856 MHz) and 10 C-band (5712 MHz) will power a total of 14 Travelling Wave accelerating sections (2 S-band and 12 C-band) plus 3 S-band Standing Wave cavities (a 1.6 cell RF gun and 2 RF deflectors). Each klystron is individually driven by a temperature stabilized LLRF module for a maximum flexibility in terms of accelerating gradient, arbitrary pulse shaping (e.g. to compensate beam loading effects in multi-bunch regime) and compensation of long-term thermal drifts. In this paper, the whole LLRF system architecture and bench test results, the RF reference generation and distribution together with an overview of the synchronization system will be described., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The effects of a transverse magnetic field on an in-line side-coupled 6 MV linear accelerator are given. The results are directly applicable to a linac-MR system used for real-time image guided adaptive radiotherapy. Our previously designed end-to-end linac simulation incorporated the results from the axisymmetric 2D electron gun program EGN2w. However, since the magnetic fields being investigated are non-axisymmetric in nature for the work presented here, the electron gun simulation was performed using OPERA-3d/SCALA. The simulation results from OPERA-3d/SCALA showed excellent agreement with previous results. Upon the addition of external magnetic fields to our fully 3D linac simulation, it was found that a transverse magnetic field of 6 G resulted in a 45 +/- 1% beam loss, and by 14 G, no electrons were incident on the target. Transverse magnetic fields on the linac simulation produced a highly asymmetric focal spot at the target, which translated into a 13% profile asymmetry at 6 G. Upon translating the focal spot with respect to the target coordinates, profile symmetry was regained at the expense of a lateral shift in the dose profiles. It was found that all points in the penumbra failed a 1%/1 mm acceptance criterion for fields between 4 and 6 G. However, it was also found that the lateral profile shifts were corrected by adjusting the jaw positions asymmetrically.

The Laser Undulator Compact X-ray source (LUCX) is a test bench for a compact high brightness X-ray generator, based on inverse Compton Scattering at KEK, which requires high intensity multi-bunch trains with low transverse emittance. A photocathode RF gun with emittance compensation solenoid is used as an electron source. Much endeavor has been made to increase the beam intensity in the multi-bunch trains. The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects, so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough. A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform. In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance. With the uniform driving laser and the unbalanced RF gun, the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 μmm mrad to 3.66 μmm mrad.

The beam produced by a thermionic RF gun has wide energy spread that makes it unsuitable for direct usage in photon sources. Here in the present work, we optimize the extracted beam from a thermionic RF gun by a compact economical bunch compressor. A compact magnetic bunch compressor (Alpha magnet) is designed and constructed. A comparison between simulation results and experimental measurements shows acceptable conformity. The beam dynamics simulation results show a reduction of the energy spread as well as a compression of length less than 1 ps with 2.3 mm-mrad emittance.

In the present work, we examined the patterns of the electron beam motion when controlling the transverse with respect to the axis of the beam homogeneous magnetic field created by the coils of the deflection system the electron gun. During electron beam processes, the beam motion is determined the process type (welding, surface modification, etc.), the technological mode, the design dimensions of the electron gun and the shape of the processed samples. The electron beam motion is defined by the cumulative action of two cosine-like control signals generated by a functional generator. The signal control is related to changing the amplitudes, frequencies and phases (phase differences) of the generated voltages. We realized the motion control by applying a graphical user interface developed by us and an Arduino Uno programmable microcontroller. The signals generated were calibrated using experimental data from the available functional generator. The free and precise motion on arbitrary trajectories determines the possible applications of an electron beam process to carrying out various scientific research tasks in material processing.

Recent investigations that are presented here illustrate the initial results that were obtained from a modified technique for holding the CNT on a W clean blunt tip. Field Electron Emission (FEE) has been investigated for single walled carbon nanotube (SWCNT) mounted on tungsten tip under (~10−8 mbar) vacuum conditions. The measurements recorded presented results showed that the CNT mounted on the W tip could emit electron current of at (0.7 V/μm) and reach up to (24 μA) of emission current at normal emission conditions. Such electron field emission tip was fabricated by electrolytically etching the high purity tungsten wire of (0.1 mm) in diameter in NaOH of (0.1) Molar solution, then mounting the single-walled carbon nanotube on the tip to be nearest to the tin oxide-coated and phosphorus glass anode. Such process was possible to be carried out under the microscope. A field electron microscope with a tip-screen separation at (~10mm) was used to characterize the electron emitter. The system was evacuated to an ultra-high vacuum level obtained after initial backing the system at up to (~180 °C) overnight. The emission characteristic has been investigated employing the I-V characteristics with Fowler-Nordheim plots and recording the emission images

A carbon nanotube (CNT) possesses various benefits as a field electron emitter. Multi-walled CNT (MWNT) have exhibited high brightness and the field emission (FE) current is stable even under poor high-vacuum condition of 10−6 – 10−7 Pa without ion pumping. In this study, we have experimentally manufactured a compact composite field emission scanning electron microscope (FE-SEM) and X-ray microscope (XRM) with a single isolated MWNT electron source. An electron beam from a MWNT was focussed and accelerated by a Butler electrostatic lens. Stable SEM images were observed at a Butler voltage V but = 1.5 kV and accelerating voltage V acc 15 kV with a focussed probe current I foc = 61 pA. The spatial resolution of the SEM, which was estimated from 80 – 20 % edge profile of polystyrene latex spheres, was about 9 nm. XRM images were acquired by 30-min exposure at V but = 1.5 kV and V acc 17 kV. A spatial resolution of about 200 nm was obtained for XRM. The present results prove the high performance of the compact FE-SEM and XRM using a single isolated MWNT electron source at 10–7 Pa.

RF deflectors can be used for bunch length measurement with high resolution. This paper describes a completed S-band traveling wave RF deflector and the bunch length measurement of the electron beam produced by the photocathode RF gun of the Shanghai DUV-FEL facility. This is the first time that such a transverse RF deflector has been developed and used to measure the bunch length of picosecond order in China. The deflector's VSWR, is 1.06, the whole attenuation 0.5 dB, and the bandwidth 4.77 MHz for VSWR less than I. I. With a laser pulse width of 8.5 ps, beam energy of 4.2 MeV, and bunch charge of 0.64 nC, the bunch lengths for different RF input power into the deflector were measured, and an averaged rms bunch length of 5.25 ps was obtained. A YAG crystal is used as a screen downstream of the deflector, with the calibrated value of 1 pix = 136 mu m.

An RF deflecting cavity used for bunch length measurement has been designed and fabricated at Tsinghua University for the Thomson Scattering X-Ray Source. The cavity is a 2856 MHz, π-mode, 3-cell standing-wave cavity, to diagnose the 3.5 MeV beam produced by photocathode electron gun. With a larger power source, the same cavity will again be used to measure the accelerated beam with energy of 50 MeV before colliding with the laser pulse. The RF design using MAFIA for both the cavity shape and the power coupler is reviewed, followed by presenting the fabrication procedure and bench measurement results of two cavities.

Recent progress in the accelerator structure studies at SLAC is reported. This paper covers the room temperature accelerator structures for the ILC e+/e− sources; RF structures for some photon science projects including RF deflectors and the LCLS RF gun; the high gradient accelerator R&D in a global CLIC collaboration for the future multi-TeV linear colliders.

In China, polymer radiation processing has become one of the most important processing industries. The radiation processing source may be an electron beam accelerator or a radioactive source. Physical design of an electron beam facility applied for radiation crosslinking is introduced in this paper because of it's much higher dose rate and efficiency. Main part of this facility is a 10 MeV travelling wave electron linac with constant impedance accelerating structure. A start to end simulation concerning the linac is reported in this paper. The codes Opera-3d, Poisson-superfish and Parmela are used to describe electromagnetic elements of the accelerator and track particle distribution from the cathode to the end of the linac. After beam dynamic optimization, wave phase velocities in the structure have been chosen to be 0.56, 0.9 and 0.999 respectively. Physical parameters about the main elements such as DC electron gun, iris-loaded periodic structure, solenoids, etc, are presented. Simulation results proves that it can satisfy the industrial requirement. The linac is under construction. Some components have been finished. Measurements proved that they are in a good agreement with the design values.

Laser amplification using a 12 µm mid-infrared free-electron laser (MIR-FEL) was observed at the Institute of Advanced Energy (IAE), Kyoto University. A 25 MeV electron beam of 17 A peak current was used for the lasing experiment. A beam loading compensation method with an RF amplitude control in the thermionic RF gun was used to extend the macropulse duration against the backbombardment effect in the thermionic RF gun. As a result, an electron beam with a 4 µs duration was generated. A laser output with an intensity 50 times as high as the spontaneous emission intensity was observed. FEL gain was estimated to be 16% from the exponential growth of the laser output signal, and a cavity loss of 2.8% was estimated from the decay of the laser output signal. Three-dimensional (3D) FEL simulation was also performed to achieve the gain saturation in our FEL device.

RF deflecting cavity can be used for bunch length measurement and is designed to diagnose the beam produced by the photocathode electron gun which was built at Tsinghua University for the Thomson scattering experiment. Detailed discussion and calculation for measuring the 3.5 MeV bunch and another with further acceleration to 50 MeV, which is under development, are presented. A standing-wave deflecting cavity working at 2856 MHz is designed and the power feeding system has been planned.

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.

Measurement of emittance for a space-charge dominated electron beam from a photocathode rf gun is performed by employing the multislit-based method at Accelerator Laboratory of Tsinghua University. We present the design considerations on the multislit system and the experimental results, with special attention to the study of space charge induced emittance growth. The experimental results are in reasonable agreement with the PARMELA simulations.

We study the field emission (FE) property of a nanometer-scale gap structure in a palladium strip, which was fabricated by hydrogen absorption under high-pressure treatment. A vigorous cracking process could be accompanied by extensive atomic migration during the hydrogen treatment. A three-dimensional finite-difference time-domain particle-in-cell method is adopted to simulate the electron emission in a surface-conduction electron-emitter display (SED) device. Examinations of conducting characteristics, FE efficiency, the local field around the emitter, and the current density on the anode plate with one FE emitter are conducted. The image of a light spot is successfully produced on a phosphor plate, which implies that the explored electrode with nanometer separation possesses a potential SED application. Experimental observation and numerical simulation show that the proposed structure can be used as a surface conduction electron emitter and has a high FE efficiency with low turn-on voltage and a different electron emission mechanism. This study benefits the advanced SED design for a new type of electron source.

We fabricated a Bayard–Alpert-type ionization gauge using a screen-printed field electron emitter with carbon nanotubes (CNTs) as an electron source. Vertically aligned CNTs grown on Si substrates by thermal chemical vapor deposition was used as the source material for CNT paste to make the screen-printed field emitter. The fabricated gauge responded linearly to the pressure in the range from 10-4 to 10-8 Torr, and exhibited a sensitivity of 13 Torr-1, which is competitive with the commercial gauge using a hot-filament electron source. The ion current of the gauge also showed good stability for more than 15 h, indicating the high quality of the electron emitter. This work demonstrated the feasibility of the vacuum electronic device using the CNT field emitter.