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Funding Information: This work has received funding from the EMPIR programme (projects 16NRM05 and 20SIP01) co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme and the Portuguese National Funding Agency for Science, Research and Technology in the framework of the project UIDB/FIS/ 00068/2020. Publisher Copyright: © 2023 The Author(s) Recently, a new type of ionization vacuum gauge was introduced, which was proposed as a reference and transfer standard in the range of 10-6 Pa to 10-2 Pa because of its excellent stability and linearity. In contrast to present models of ionisation vacuum gauges, all electrons have a well-defined path length through the ionisation space. This even allows one to predict the sensitivity for a gas species provided that the ionisation cross section of the gas molecules for electrons between 50 eV and 200 eV is known. Following the development of this gauge we investigated its metrological performance in terms of linearity, resolution, repeatability, reproducibility, transport and long-term stability, disturbances by magnetic fields, influence of the surrounding earth potential and so on. The gauge demonstrated excellent metrological properties and is indeed suitable as an accurate reference and transfer standard, but can also provide important economic benefits to manufacturers and users. publishersversion published

An effective design for cold cathode named as the interdigitated field electron emission driving-secondary electron emission (FEE-SEE) cathode is proposed in this article. The cathode consists of an FEE region and an SEE region, which integrates the advantages of the field emission and secondary emission on the M-type device. The excellent FEE performance of the directional single-wall carbon nanotubes (SWCNTs) with an effective method of directly imprinting the SWCNTs sludge on a substrate is studied for obtaining higher primary excitation current. Meanwhile, the cathode prebunch technique is implemented by imposing a fivefold azimuthal variation on the SEE cathode of a ten-cavity magnetron, which could prebunch the electrons into the desired mode at birth to enhance stability and speed startup time. A 3-D particle-in-cell simulation analysis is used to predict a novel cold cathode magnetron with high output power of 3144 W with 6.2% efficiency enhancement with reference to the conventional thermionic cathode applied to the 2450-MHz magnetron. Its startup time is about 100 ns with excellent stability and pure output spectrum.

A model of a thermionic cathode in a planar diode in which the Poisson and Vlasov equations are solved in 3-D assuming an infinite magnetic field is presented. We explore how 2-D work function variations across the cathode surface may affect the transition between temperature-limited and space-charge-limited flow, commonly known as the “knee” of the Miram curve. We study a variety of work function distributions, both realistic and idealized, and demonstrate how emission from the lowest work function regions dominates the total anode current even when such regions make up a relatively small fraction of cathode area. Our model also illustrates the ability of cathodes to reach the full Child–Langmuir current despite the presence of a sizeable nonemitting region. We find that as the length scale of these work function variations decreases, the Miram knee grows sharper, indicating improved cathode performance.

This paper presents a conceptual design of the compact SC230 superconducting cyclotron that accelerates a beam of protons to 230 MeV and is intended for proton therapy and biomedical research. SC230 is an isochronous four-sector cyclotron based on a shell-type magnet with a magnetic field in the center of 1.7 T. Superconducting coils will be enclosed in a cryostat; all other parts of the cyclotron are warm. Acceleration is carried out at the fourth harmonic mode of the accelerating high-frequency (HF) system consisting of four resonators located in the cyclotron valleys. The accelerator employs an internal Penning-type hot cathode source. Extraction is carried out using an electrostatic deflector located in the gap between the sectors and two passive magnetic channels.

This work reviews the progress in the area of high current density electron emitters, specifically for use in high frequency and high-power microwave vacuum electron devices. The review is divided into two subsections: 1) thermionic cathodes and 2) field emission cathodes. The thermionic cathode section includes the discussion on the M-type, MM-type, Scandate and the CPD cathodes. CPD cathode promises better usability in a practical device as compared to the Scandate cathodes which are limited by emission nonuniformity, poor resistance to poisoning/ion bombardment and low life. With the increasing demand for miniaturized and high power VEDs in the near future, the development of high current density field emission cathodes is of immediate interest to the VED community. The Spindt, CNT, and graphene-based emitters are the potential candidates in the field emitters section. Graphene-based film cathodes, when compared to the Mo/Si FEAs and the CNTs, offer larger emission area as well as high current carrying capability. This review includes the evolution of the emission capabilities of the emitters, state-of-the-art performances, and possible future developments.

As the performance of vacuum electron devices is essentially governed by the properties of their cathodes, developing efficient and durable thermionic cathode is necessary and highly desired to meet the boosting requirements of vacuum electron devices. This review summarized the progress made in the past decades with a detailed discussion on the occurred various thermionic cathodes and their features, and the understandings of the correlation between the emission properties and the composition, where structure and synthesis method are well illustrated. Furthermore, dispenser cathodes with novel structures and emission mechanism are highlighted to indicate the recent achievement in this area of research, and Sc-cathode is considered as a promising candidate for the next-generation vacuum electron devices due to the greatly improved efficiency. However, challenges still exist to meet the ever-growing demands of thermionic cathode with collaborative requirement of high performance, easy fabrication and inadequate reproducibility.

A self-consistent model of steady-state electron flow in a planar crossed-field diode with a thermionic cathode is presented. Our formulation is a generalization of the classic work of Fry and Langmuir, to include a constant magnetic field B of arbitrary strength parallel to the electrode surfaces. Some effects of the magnetic field on the electron flow are illustrated in an example.

A zero-dimension plasma model of thermionic hollow cathodes is here derived. The equations of conservation of mass, current and power are solved within the insert and orifice regions. The model introduces some elements of novelty compared to prior literature such as the inclusion of the electron current collected on the orifice lateral walls, and ion and electron currents collected on the orifice plate walls in the overall balance equations. Estimation of the power deposited on walls due to electron and ion bombardment in both insert and orifice regions are performed, thus, enabling comparisons among different geometrical configurations and operating regimes. The model results are compared against published experimental data and a thorough investigation of the model response to variation of geometrical and operational condition of a sample cathode are presented. A power budget, which includes power consumption and power deposition, of a sample thermionic cathode is also discussed.

Silicon carbide (SiC) nanostructures were synthesized on a silicon (Si) substrate that served as a thermionic cathode. Nanosheets, nanograins, and high-aspect-ratio nanostructures formed on the thermionic cathodes, depending on the synthesis parameters. The calculated work functions of thermionic cathodes ranged from 4.48 eV to 4.83 eV. It can be observed that the work function is attributed to the geometrical characteristics, such as the aspect ratios and the surface-area-to-volume ratios of SiC nanostructures. Among the nanostructures, using SiC nanowire structures (M200SC3) resulted in the greatest reduction in the thermionic cathode’s work function, which was 0.36 eV. This reduction is attributed to the sharp-tip structures having high aspect ratios, which is a strong field enhancement factor to the electron emission. This study suggests that the presence of SiC nanostructures on a thermionic cathode can potentially enhance electron emission in a thermionic energy converter (TEC) system.

The study of a diffuse vacuum arc (DVA) is of interest in connection with the developing methods of plasma processing of the spent nuclear fuel (SNF). This type of discharge can provide a high degree of ionization of the vapors of the cathode material in the absence of droplets and multiply charged ions. This work is devoted to the study of the ion composition of the arc discharge plasma at a consumable hot gadolinium cathode by analyzing the optical and mass spectra of ions. The plasma ion composition is determined at a discharge current of 50 A, arc voltage ranging from 4 to 14 V, and cathode temperature ranging from 1.9 to 1.95 kK. The obtained data, together with the data recorded using the condensation probe method, showed that at an arc voltage of 5 to 6 V a plasma is generated with an ionization degree close to 100%, which contains more than 95% of singly charged ions among all the charged states.

Highlights • Line-focus X-ray tubes are suitable for clinical microbeam radiation therapy (MRT). • A modular high-voltage supply safely enables high electron beam powers. • An electron accelerator was designed to generate an eccentric focal spot. • We simulated a peak-to-valley dose ratio above 20 for single-field MRT. • Microbeam arc therapy spares healthy brain tissue compared to single-field MRT., Background and purpose Microbeam radiotherapy (MRT) is a preclinical concept in radiation oncology with arrays of alternating micrometer-wide high-dose peaks and low-dose valleys. Experiments demonstrated a superior normal tissue sparing at similar tumor control rates with MRT compared to conventional radiotherapy. Possible clinical applications are currently limited to large third-generation synchrotrons. Here, we investigated the line-focus X-ray tube as an alternative microbeam source. Materials and methods We developed a concept for a high-voltage supply and an electron source. In Monte Carlo simulations, we assessed the influence of X-ray spectrum, focal spot size, electron incidence angle, and photon emission angle on the microbeam dose distribution. We further assessed the dose distribution of microbeam arc therapy and suggested to interpret this complex dose distribution by equivalent uniform dose. Results An adapted modular multi-level converter can supply high-voltage powers in the megawatt range for a few seconds. The electron source with a thermionic cathode and a quadrupole can generate an eccentric, high-power electron beam of several 100 keV energy. Highest dose rates and peak-to-valley dose ratios (PVDRs) were achieved for an electron beam impinging perpendicular onto the target surface and a focal spot smaller than the microbeam cross-section. The line-focus X-ray tube simulations demonstrated PVDRs above 20. Conclusion The line-focus X-ray tube is a suitable compact source for clinical MRT. We demonstrated its technical feasibility based on state-of-the-art high-voltage and electron-beam technology. Microbeam arc therapy is an effective concept to increase the target-to-entrance dose ratio of orthovoltage microbeams.

The results of investigations of a low-pressure hollow-cathode glow discharge with a hot filament (thermionic cathode) inside the cavity are presented. The current-voltage characteristics (CVCs) of the discharge and the dependences of the current delivered to the thermionic and hollow cathodes on the discharge burning voltage are obtained at different gas pressures and filament currents. It is shown that the major fraction of the current is transferred in the thermionic cathode circuit. For interpretation of the CVCs, a model is accepted, which uses a generalized coefficient (rather than a conventionally utilized secondary-emission coefficient), which includes not only the cathode bombardment with ions but also the emission current induced by an external source. An estimation is made of the discharge parameters. The model is shown to be quite consistent with the experiment.

In this article, the design and simulation of an electron injector based on a thermionic RF-modulated electron gun for particle accelerator applications is presented. The electron gun is based on a gridded thermionic cathode with the geometry based on a Pierce-type configuration. Both theory and numerical simulation were used to explore the relationship between the bunch length and the charge. The reasons for the pulse widening were also analyzed. The beam dynamics simulations showed that a minimum pulselength of 106 ps could be achieved with a bunch charge of 33 pC when the driving RF frequency was 1.5 GHz. The average transverse emittance was about 17 mm·mrad from the particle-in-cell simulations. Operating at a higher RF frequency did not significantly reduce the micro pulselength.

Analysis of temperature-limited flow, space-charge-limited flow, and the transition between them using a simple planar diode with a thermionic cathode, in which the cathode surface has spatially nonuniform emission properties, is presented. Our theoretical results, which are derived from a model based on solutions to the Vlasov and Poisson equations, compare well with the results of particle-in-cell simulations. We find that the location and the shape of the knee in the anode current versus temperature characteristic (Miram or “rollover” curve) are significantly affected by non-uniformities in the space-charge density in the A–K gap, but are relatively unaffected by the electron motion parallel to the electrode surfaces. In particular, emission from an actively emitting region is strongly affected by the forces (or lack thereof) exerted by the space-charge of the electrons emitted by their neighbors. Perhaps, most remarkably, we find that the limiting current reaching the anode is approximately given by the classical 1-D Child–Langmuir law, even if a significant fraction of the cathode surface is non-emitting.

Irradiation of polymeric materials is a modern method of modifying their final properties (for example, improvements in mechanical, thermal and chemical properties). The main used types of radiation to modify polymers include ionic and ionizing radiation. Due to its properties, ionization beta (electron) radiation is the most widely used. The interaction of ionizing radiation with polymeric materials manifests as radiation cross-linking, which is a result of recombination of migrating polymer radicals into the amorphous region. In this type of radiation, electrons are generated under high vacuum using a hot cathode. Electrons emitted from the cathode are then accelerated in the electrostatic field that arises between the cathode and the anode. The depth of penetration into the material rises with increasing energy of electrons. This study examines the influence of ionizing beta radiation on the flammability index and ignition temperature of thermoplastic materials.

The article shows the results of research on the destruction of the thermionic cathode of an arc plasma torch when inserting hafnium and zirconium along the trace of the spot of a gas-discharge arc by means of electronic metallography with spectral analysis in the control region. The depth of penetration of the spot into the metal of the cathode insert was determined due to the discrete mechanism of action on the metal at the time of attachment. The erosion rate of zirconium oxide films was experimentally established, the extension of the operating life substantiated while mechanisms for its increase were revealed, and two types of arc contact with a hafnium or zirconium insert - the "contracted" and "diffused" ones - were offered. The theoretical operating life of the cathode is calculated.

Pseudospark (PS) discharge is a low-pressure gas discharge characterized by a rapid breakdown phase with the generation of a high current density electron beam, which is over 100 times higher than a thermionic cathode. The PS-sourced beam can also transport a long distance without the need for an external guiding magnetic field. Such features are attractive as beam sources in terahertz wave generation. At high frequency, the conventional vacuum electron devices suffer a quick drop in the power level due to the small cross-section of the beam tunnel and the limit of current density from a thermionic cathode.

Plasma current start-up and pre-ionization is an important motivation in Taban tokamak. The plasma current start-up has been successfully achieved using a central solenoid and a pre-ionization system and the experimental conditions have been optimized. Two distinct schemes were used to start-up the plasma current. Hot cathode emitter and electron cyclotron resonance (ECR) was used as the pre-ionization system. ECR pre-ionization circuit of 2.45 GHz magnetron was modified for long duration pulse mode. The transient plasma parameters were measured during discharge as a function of time in different conditions, while a toroidal field of 0.1 T with 4 ms flat-top was being applied. The experimental results showed that the plasma current could be started up by both ECR and hot cathode emitter. In the optimum conditions, a plasma current of 7.5 kA has been achieved with pulse duration of ~ 0.7 ms using the electron cyclotron pre-ionization system. Under such circumstances, the X-ray emission, as well as, the impurity level was minimized.

Hot cathode ionization gauges are intended to be the only in-situ diagnostic for neutral gas pressures in the vacuum vessel of ITER. The development bases on the well established ASDEX pressure gauge. The upper measuring limit for ITER is required to be at least 20 Pa in hydrogen at a magnetic flux density of up to 8 T. The objective of the presented study is to find parameter and design settings that allow to satisfy this specification. At the same time, the sensitivity shall be high and only weakly dependent on the magnetic field strength. Gauge parameters, specifically the electron emission current, the electrode potentials and the transparency of the acceleration grid, were varied consecutively to assess their impact on the calibration characteristics. The ratio of ion to electron current as a function of pressure and magnetic flux density was obtained for each parameter set. A monotonic progression of the signal in dependence of the pressure was proven even up to 30 Pa. This was achieved by a low grid transparency and high electric field strength at the cathode. While the former leads to a lower sensitivity, which is unfavorable for measurements in the low pressure range, this can be compensated by a higher electron current.

Purpose In this study, the authors performed a numerical investigation on the heating of a hot cathode with a conical tip by atmospheric arc, taking into account of the two temperature sheath effect for the first time. Design/methodology/approach The Schottky effect at cathode surface is considered, which is based on the analytic solution of a one-dimensional sheath model. The unified model allows one to predict the cathode-plasma heat transfer. Findings The total heat flux to cathode surface is smaller than its components’ heat flux due to electron back diffusion is as large as that due to ion flux with the increase of cathode length the total heat transported to the cathode body has an obvious decrease. Originality/value It is found that two kinds of solution exist for the cathode with a 140° conical tip; however, only one stable solution exists when the conical angle is reduced to 130°.

The results of investigation of pulsed burning modes of a non-self-sustained arc discharge with a combined hot-and-hollow cathode are presented. The principal discharge characteristics are measured at the currents up to 350 A and discharge burning voltages up to 200 V within the working pressure range 0.2–1 Pa. It is shown that an increase in the working pressure gives rise to an increase in the discharge current as a result of gas amplification, resulting from an improvement in the processes of fast electron energy utilization during gas ionization. The maximum resulting discharge current in a nitrogen atmosphere at a pressure of 0.8 Pa is found to be 550 A at the discharge burning voltage up to 200 V and the maximum pulsed power up to 80 kV. The concentration of plasma in the center of the ≈0.2 m3 chamber is found to be about 4·1017 m–3 at the density of the ion current from plasma approximately 6.5 mA/cm2 and the discharge pulsed power 18 kW.

CeB6-based quaternary rare-earth hexaboride single crystals Ce1-x-yLaxPryB6 (x = 0.1–0.4, y = 0.1–0.4) with Φ 5 mm × 35 mm were grown via the optical floating zone technique. The crystal structure, atomic composition and thermionic emission properties of Ce1-x-yLaxPryB6 single crystals were systematically studied. The results of XRD and X-ray Laue diffraction reveal that these single crystals are grown along the direction. The X-ray rocking curve analysis shows that the lowest full-width at half-maximum (FWHM) of Ce1-x-yLaxPryB6 single crystals is only 0.036° for Ce0.4La0.4Pr0.2B6 single crystal, whose atomic structure is revealed and the lattice spacing is 0.414 nm. The maximum thermionic emission current density of 114.21 A/cm2 at 1600 °C and minimum effective work function of 2.62 eV at the same temperature are also belonged to Ce0.4La0.4Pr0.2B6 single crystal, which indicates that it has great application prospects as a promising hot cathode material.

Composite metal oxide-coated tungsten cathodes were formulated as efficient and reliable thermo-electron sources for vacuum ultraviolet ionizers. Cathode suspensions were prepared by adding...

The design and construction studies of Alborz tokamak have been conducted since 2012 in the Department of Energy Engineering and Physics, Amirkabir University of Technology, Iran. Recently, this device has been assembled and initial tests are currently in process. In the present study, the overall configuration, major components, design features as well as the main engineering parameters of this tokamak have been investigated. First, all the magnetic field systems and configurations have been presented in detail. Afterward, the mechanical properties of the vacuum vessel and the designed system to reach the desirable vacuum environment for plasma generation have been addressed. The pre-ionization systems, including hot cathode and ECR methods were also evaluated. Based on the obtained engineering design aspects, it can be argued that Alborz tokamak is in an acceptable condition for the initial phase of its operation to achieve a 20 kA plasma current with 20 ms duration.

As the cathode with the highest electron emission capability in the thermionic cathode, the scandate cathode has attracted more and more attention in recent years, especially the scandia doped tungsten matrix scandate cathode. Experimental studies show that scandia doped tungsten matrix scandate cathodes with submicron microstructures exhibit excellent emission capacity, and the pulse emission current density in the space-charge region can be over 35 A cm−2 at 850 °Cb. In the direct current (DC) condition with temperature compensation, the emission current density could reach 25 A cm−2 at 850 °Cb. The device lifetime is over 3700 h after operating at 950 °Cb with the DC loading of 40 A cm−2. The emission mechanism of the scandate cathode including the effect of the surface structure and composition on the work function of the cathode are systematically reviewed.

The Novosibirsk FEL facility has three FELs installed on the first, second, and fourth orbits of the multiturn energy recovery linac (ERL). The first FEL covers the 90–240 μm range of wavelengths at an average radiation power of 0.5 kW with a pulse repetition rate of 5.6 or 11.2 MHz and a peak power of 1 MW. The second FEL operates in the 40–80 μm range of wavelengths at an average radiation power of 0.5 kW with a pulse-repetition rate of 7.5 MHz and a peak power of around 1 MW. These two FELs are the world’s most powerful (in terms of average power) sources of coherent narrow-band (less than 1%) radiation in their wavelength ranges. The third FEL was commissioned in 2015 to cover the 5–20 μm range of wavelengths. The Novosibirsk ERL is the world’s first and only multiturn ERL. Its distinctive features include a normally-conductive 180 MHz accelerating system, a direct current (DC) electrostatic electron gun with a control grid and thermionic cathode, three operating modes of the magnetic system, and a compact (6 × 40 m) design. The Novosibirsk FEL facility has been in operation for users of terahertz radiation since 2004.

The plasma electron beam (P-ebeam) with a cold cathode has various advantages, including longer cathode life, easier beam diameter control and lower vacuum pressure, as compared to the thermionic electron beam with a hot cathode. The present paper is concerned with investigation of a novel metal additive manufacturing process using the P-ebeam based on powder bed fusion. The proposed process is composed of preheating, deposition and re-melting steps. An experimental system with some desired features is newly developed. Preheating and deposition characteristics are examined to estimate appropriate operation conditions. Fabrication characteristics of the process are elucidated through multi-layer deposition experiments.

This paper presents the results of the formation of deep modified layers in AISI 5140 alloy steel using a high-intensity repetitively pulsed nitrogen ion beam. An arc generator with a hot cathode provided the DC nitrogen plasma flow. A plasma immersion approach was used for high-frequency, short-pulse very intense nitrogen ion beam formation. A grid hemisphere with radii of 7.5 cm was immersed in the plasma. Negative bias pulses with an amplitude of 1.2 kV, a pulse duration of 4 μs, and a pulse repetition rate of 105 pulses per second were applied to the grid. The substrates were implanted at various temperatures ranging from 450 to 650 °C with 1.2 keV nitrogen ions using a very-high current density up to 0.5 A/cm2 ion beams. The work explores the surface morphology, elemental composition, and mechanical properties of deep-layer modified AISI 5140 alloy steel after 60 min of low ion energy, very-high-intensity nitrogen ion beam implantation.

We designed an electron linear accelerator (LINAC) for High Energy Electron Radiography (HEER) studies, which consists of two different guns, either a thermionic cathode or a photocathode RF gun, for diagnosing different targets. In this paper, we present the simulation studies and optimization of the LINAC based on an S-band thermionic RF gun. The LINAC is capable of generating sub-picosecond electron pulses with low energy spread (0.13%) and large micro-bunch charge (143 pC). The beam dynamics of the LINAC is studied and optimized by different beam dynamics simulation codes. The entrance hole induced field distortion in the alpha magnet is also reported. The space charge effects are studied by the General Particle Tracer (GPT) code. The results showed that the space charge forces had a significant influence on beam dynamics in such a low energy LINAC.

The high-quality LaxCeyPr1-x-yB6 (x = 0.6–0.8, y = 0.1–0.3) single crystals have been firstly grown by optical floating zone melting method. The crystal structure, mechanical and thermionic emission properties of the as-grown single crystals were characterized by X-ray single crystal diffractometer, SEM, XRD, X-ray Laue diffraction. Subgrain-boundary-free [100] LaxCeyPr1-x-yB6 single crystal with a good crystalline integrity and homogeneous element distribution is obtained. The Lattice constant of LaxCeyPr1-x-yB6 single crystal is lower than that of the LaB6 single crystal. The lowest FWHM of 162.0 arcsec belongs to the La0.6Ce0.3Pr0.1B6 single crystal. The highest thermionic emission current density of 105.10 A/cm2 and the lowest work function of 2.562 eV indicate that La0.6Ce0.3Pr0.1B6 single crystal is a very promising thermionic cathode material.

The effect of back-bombardment (BB) electrons is considered one of the main obstacles for extensive use of thermionic RF guns (T-RF). The 10 hexaboride materials named (Ca, Sr, Ba, La, Ce, Pr, Nd, Sm, Eu, and Gd) B6 are investigated in this paper to survey the effect of the cathode material on reducing BB electrons and compare them with LaB6 (which is widely used as a thermionic cathode). A numerical model was used to conduct this paper. Besides the numerical calculations, an experiment has been performed to determine the work functions of CeB6 and LaB6. The results from the numerical calculations revealed that (Ba, Ca, and Nd) B6 are less affected by BB electrons: 42%, 50%, and 59%, respectively, compared with LaB6, for low beam current applications. In contrast, for high beam current duties, (Nd, Ce, and Sm) B6 have minimum influence by BB electrons compared with other hexaborides. The study concluded that BB electrons are strongly affected by the properties of the cathode material, especially thermionic emission and material density. Moreover, the study suggests that it is worthwhile to prepare BaB6, CaB6, NdB6, and SmB6 as cathode materials, then to subject them to a real experimental test using T-RF gun to compare their performance and BB effect against LaB6.

A plasma gun for forming a plasma stream in the open magnetic mirror trap with additional helicoidal field SMOLA is described. The plasma gun is an axisymmetric system with a planar circular hot cathode based on lanthanum hexaboride and a hollow copper anode. The two planar coils are located around the plasma source and create a magnetic field of up to 200 mT. The magnetic field forms the magnetron configuration of the discharge and provides a radial electric insulation. The source typically operates with a discharge current of up to 350 A in hydrogen. Plasma parameters in the SMOLA device are Ti ~ 5 eV, Te ~ 5–40 eV and ni ~ (0.1–1) × 1019 m−3. Helium plasma can also be created. The plasma properties depend on the whole group of initial technical parameters: the cathode temperature, the feeding gas flow, the anode-cathode supply voltage and the magnitude of the cathode magnetic insulation.

In this paper, a novel X-ray tube, which uses a photocathode as an electron emission source, is first introduced. The X-ray tube with photocathode can use an external light source to control the output of photoelectrons, thereby controlling the characteristics of the emitted X-rays. Compared with the traditional X-ray tube with hot cathode, the X-ray emitted by the photocathode X-ray tube is completely modulated by the external light source. Therefore, X-rays can achieve instant on-off and arbitrary pulse waveform emission, and have extremely high time resolution. The basic characteristics of the photocathode X-ray tube was tested. By using the developed X-ray tube and LED light source, preliminary X-ray communication experiments have been carried out. The results show that the digital signal restoration with a frequency of up to 1MHz can be achieved. Except for X-ray communication, the developed photocathode X-ray tube can also have important applications in many fields such as radiation calibration and scintillator afterglow measurement.

In secondary education, cathode-ray tubes (CRTs) are often the first choice when it comes to investigating the behavior of electrically charged particles in electric and magnetic fields. While CRTs offer some advantages, mainly from a practical point of view, they are on the whole ill-suited for an inquiry-based approach since they provide very limited room for modification or hands-on experimentation. Therefore, a 3D-printable plasma electron gun has been developed, which is at the same time modular, inexpensive, and easily accessible. The main objective is to provide teachers and students with an easy-to-operate electron beam source that allows conducting experiments on beam generation, beam focusing, and beam deflection as a hands-on activity in a classroom setting. From a technical point of view, this can be achieved by substituting the hot cathode as standard electron source by a plasma cathode electron gun, which can be operated at fore-vacuum pressure and in reactive gases. We provide a proof of concept that a low-cost 3D-printed plasma electron source is feasible and that beam generation can be accomplished.

UID/FIS/00068/2019 The EURAMET EMPIR project “16NRM05 - Ion gauge” aims to develop an ionisation vacuum gauge suitable as a reference vacuum standard. In such a gauge the electron trajectories and their kinetic energy inside the ionisation volume should be well defined and stable. In the search for a suitable design, a series of simulations on different ionisation gauge concepts that have the potential to meet stringent stability requirements have been carried out. Different software packages were used for this purpose. This paper focuses on the design aspects and the performance of the different ionisation gauge concepts that have been investigated by simulation. Parameters such as ionisation gauge sensitivity, ion collection efficiency and electron transmission efficiency, have been determined as a function of emission current, pressure and electron source alignment. publishersversion published

Although accelerator technology has matured sufficiently, state-of-the-art x-ray linacs for radiotherapy and cargo-scanning capture merely 30%--50% of the electrons from a thermionic cathode, requiring a higher cathode current and leaving uncaptured electrons to cause problems such as back bombardment on the cathode leading to a shortening of cathode life. Any solution to increase capture should be effective, simple, reliable, compact, and low cost in order to be adopted by the industry. To address this, we present the design of a 6 MeV high capture efficiency S-band electron linac that captures 90% of the initial dc beam. This linac does not require any extra parts that would increase the cost as the high efficiency is achieved via a low-field amplitude in the first bunching cell to decrease the number of back-streaming electrons, to velocity bunch the electron beam, and recapture back-streaming electrons. Under the low field amplitude, any electrons launched at decelerating phases travel backward with low speeds, thus most of them can catch the next rf cycle, and get reaccelerated/recaptured. As the electron speed is low, the cell length is also shorter than existing linacs. Such a short field is achieved by the use of asymmetric cells with differential coupling to the side-coupled cells. Our novel design has implications for all commercial high current thermionic gun linacs for increasing beam current and increasing cathode lifetime.

X-ray has been widely used in medical diagnosis and other fields with the non-destructive merit. Recently, the cold cathode X-ray source based on field emission, which are different from traditional hot cathode X-ray source, have overcome the limitations of traditional X-ray source due to their small size, addressable, and integrated characteristics, making CT imaging methods can be further developed. Especially X-ray sources using ZnO nanowires as cold cathodes can densely integrate a large number of X-ray sources into flat panel devices. When we use this flat X-ray source to light up multiple sources to scan an object at the same time, small source spacing will cause inevitable projection aliasing. Therefore, we propose an image restoration algorithm for projection aliasing, and use the method of projection rearrangement to remove projection aliasing. In addition, we estimated the spectrum of the flat-panel X-ray source by solving the spectral model parameters from the attenuation data of materials of different thicknesses, and used the spectral information to simulate the effect of the proposed image restoration method on the new photon counting detector. The results of simulation experiments show the effectiveness of this method and the potential of this new imaging mode.