Particle Studio Research Articles

Experimental study of multipactor on dielectric of penetration flange for vacuum chamber

The potential, unexpected occurrence of dielectric multipactor on the dielectric surfaces in high-power radio frequency and microwave components has become a severe constraint in the research and development of space-borne payloads of space vehicles such as satellites and space stations on the ground and their long-term reliable operations in the orbit. In this experimental research, the single-surface multipactor occurring on the dielectric surface of a penetration flange originally designed for a vacuum chamber used in environmental simulation tests of spacecraft is experimentally investigated and compared with the corresponding full-wave simulated results. Under the excitation of periodic pulsed sinusoidal signals, the unusual experimental phenomena of intermittent local jumps of nulling signals in the process of multipactor are repeatedly observed based on an agile nulling experimental system. Taking advantage of the full-wave, three-dimensional (3D) particle-in-cell simulation tool, CST Particle Studio, the entire evolution process of the dielectric multipactor, from its onset to its saturation, is simulated and carefully examined. Combining the results obtained by full-wave 3D particle simulations, some physical explanations and discussion on such phenomena are presented. It is found that under the configuration parameters of pulse signals adopted in this multipactor experiment, the transition of a single-surface dielectric multipactor from its onset to the saturation state can be finished within a single pulse. However, its transition from the saturation state to turning off can last between consecutive pulses in the absence of any high-power radio frequency signals. The obtained result is important for both the theoretical study and the engineering development of high-power dielectric components, providing a new understanding of the dielectric multipactor occurring under the excitation of pulsed high-power electric fields.

Design of an Electron Gun for an 8 MW Peak, 30kW Average Power S-Band Klystron

High Power S-band pulsed klystrons with peak power greater than 6 MW are widely used as RF sources in particle accelerators. This paper presents an electron gun (pierce type) design for such a klystron with an output power of 8 MW peak and 30 kW average with its intended applications in accelerators for food processing. The targeted device is currently under design at CSIR-CEERI and will be developed later on. The results of electron gun simulation through computational codes like Trak, CST particle studio, and Opera are compared to find an optimum design for the electron gun to be fabricated for the klystron.

Investigation of electron optical gun and beam collector for 42 GHz, 200 kW second harmonic gyrotron

This paper presents a design investigation of the Electron Optical Gun (EOG) for a 42 GHz, 200 kW second harmonic gyrotron operating in the TE0, 3 mode. The initial design of MIG is done using established design equations and then optimized through numerical simulations. The different software, such as 2D-Numerical codes EGUN, TRAK and 3D-CST Particle Studio, are used to optimize the design and found good agreement in results obtained from these codes. The sensitivity analysis has also been carried out for the sake of complete design. Furthermore in brief, a design has been done for the un-depressed and Single-Stage Depressed Collector (SDC). In addition, the uneven or uniform beam distribution on collector wall is presented with result comparison of both the collectors. The optimized beam voltage and single-stage depressed collector voltage are 65 kV, 30 kV respectively.

Electrostatic Design and Fabrication a New Tunable Perveance Pierce Electron Gun

The perveance, ${K}$ , one of the Pierce electron gun (PEG) outputs, is completely dependent on geometric features, including the anode-cathode spherical distance, ${D}_{\text {ac}}$ . If the measured ${K}$ is not desirable after assembling, or the center of the cathode is not aligned with the anode axis, the PEG should be disassembled. In this article, with respect to the effects of spherical aberration and thermal velocity, a PEG is designed, simulated by computer simulation technologies (CSTs)-particle studio (PS) software, and manufactured for an ${S}$ -band klystron with ${K} = 1.5\,\,\mu $ and variable ${D}_{\text {ac}}$ . A new part in the PEG is designed that is called the spring film. It can move the cathode ±1 mm in the ${z}$ -direction while the other components are fixed and the vacuum of PEG does not change. The initial design leads to ${D}_{\text {ac }}$ to be 3.6 mm, but since ${K}$ is not expected as what we were looking for, so the desired ${K}$ is obtained by changing ${D}_{\text {ac}}$ , also the other parameters changing with ${D}_{\text {ac}}$ are examined and their values are estimated from the simulation. Finally, it is concluded that with the newly designed electron gun, unlike conventional PEGs, some parameters like perveance, cathode current, cathode lifetime, and body current are not fixed and they can be changed or improved.

Design of the input power coupler for Boron Neutron Capture Therapy Drift Tube Linac

An accelerator-based Boron Neutron Capture Therapy (BNCT) facility has been built at the campus of China Spallation Neutron Source (CSNS). To upgrade it, a Drift Tube Linac (DTL) is designed to provide a 40 mA, 25% duty factor, 10.1 MeV beam for the target. Two opposing power couplers are employed to deliver forward peak power up to 640 kW for the beam and DTL cavity. A new coaxial power coupler with a single Tristan type window is designed to meet the power and coupling coefficient requirements. In this paper, the detailed RF optimization process of the coupler is described. According to the RF simulation results, the multipacting (MP) phenomenon at critical locations is simulated by the CST PS (Particle Studio). Simulations of thermal and mechanical are also carried out, the cooling design to provide a large margin for RF heating is performed based on the simulation results.

Systematic Design Study of the Elliptical Sheet Beam Electron Gun for Terahertz TWT Applications

The design methodology of a sheet beam electron gun has been discussed and, subsequently, used for the design of a gun intended for use in a 0.3 THz traveling wave tube amplifier. The initial gun design parameters have been calculated analytically using a theoretical approach. Then, starting with these calculated parameters, the designed gun is then simulated using a commercial 3-D simulation code “CST Particle Studio” and optimized to get the target beam parameters. The circular-shaped cathode with an elliptically shaped beam-focusing electrode and elliptically shaped anode has been used to produce the good laminar elliptical sheet beam. The effect of varying the several parameters, such as height, width, and distance of focusing electrode, cathode-anode distance, and anode height have been studied to investigate their sensitivity on the target beam parameters. The simulation results predict that the designed sheet beam electron gun produces an elliptical beam with a desired beam cross section of 0.33 mm × 0.066 mm at a beam-waist position of 6.61 mm from the curved cathode emission surface corresponding to the beam parameters of 12 kV beam voltage and 55 mA beam current.

Electromagnetic and Particle-In-Cell Simulation of 5-mW-Long Anode Pulse Magnetron

An electromagnetic (EM) and particle-in-cell (PIC) simulation studies have been carried out to virtual prototype an unstrapped 12 resonator (hole and slot type) 5-MW-long anode magnetron (LAM) with axial extraction symmetrical output (AESO) using 3-D code Computer Simulation Technology, Microwave and Particle Studio (CST-MWS and CST-PS). The “admittance matching theory” and a “length-optimization algorithm” have been used for the selection and optimization of the dimensional parameters of the LAM anode block. The role of AESO has been investigated in the context of mode conversion and output coupling. The designed LAM has a cold frequency of 2.868 GHz with axial mode separation of 268 MHz (9.34% of design frequency). $f_{\pi \prime }/f_{\pi } = 1.093$ and $f_{\pi -1}/f_{\pi } = 0.998$ along with the circuit efficiency of 91.5% have been achieved. The saturated output power is 5.2 MW with an anode voltage of 55 kV and anode current of 205 A. The hot frequency of the LAM is 2.841 GHz with an interaction efficiency of 46.1%. The simulation results have been validated with experimental results of the commercially available E2V LAM tube (M5028).

A 3π Band-Edge Dual Frequency Oscillator Based on a Novel Folded Waveguide Structure

In this article, a $3\pi $ band-edge dual frequency oscillator using a novel half-period staggered folded waveguide (FWG) is proposed. Simulation results from CST Particle Studio show that the half-period staggered FWG could form a stopband at $3\pi $ phase shift with a high coupling impedance, enabling the device operating at two frequencies. A prototype oscillator was then designed and fabricated. The experimental results showed that it was capable of operating at both 89.2 and 94.5 GHz with the maximum output power 148 and 65W, respectively. The testing results are also compared with the simulation.

A Ka-band linearizer TW accelerating structure for the Compact Light XLS project

In the framework of the Compact Light XLS project, we have designed a higher harmonic RF accelerating structure in order to linearize the longitudinal space phase. The design of this compact Traveling Wave (TW) accelerating structure operating on the third harmonic with respect to the linac frequency (11.994 GHz) with a (100-125) MV/m accelerating gradient is presented, together with numerical electromagnetic simulations were carried out by using the numerical codes High Frequency Structure Simulator (HFSS) and CST Particle Studio.

Design and Simulation of Coaxial Magnetron Injection Gun for a 170-GHz MW-Class Gyrotron

This article presents a design of the triode coaxial magnetron injection gun (CMIG) for a 170-GHz MW-class gyrotron. The trade-off equations have been used to initialize the design of gun geometry and beam parameters. The operating mode of gyrotron is TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34,11</sub> at fundamental harmonic. The 3-D electron tracing code CST Particle Studio has been employed to simulate and optimize the CMIG design. An optimum electron beam with transverse to longitudinal velocity ratio α = 1.3 and transverse velocity spread ββ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> = 3.29% has been obtained. The sensitivity analysis of electron gun parameters are also investigated including geometric deviations and misalignments.

CST Particle Studio Simulations of Coaxial Multipactor and Comparison With Experiments

Using CST Particle Studio, we simulate the evolution of the multipactor, beginning with a single seed electron inside a coaxial waveguide. Upon impact with either the outer or inner metallic wall, the primary electron is removed and the emitted secondary electrons are allowed to have a realistic 3-D velocity distribution. It is found that the single electron evolves very quickly into an axisymmetric distribution. The radial distribution of the multipactoring electrons is broad and very different from the infinitesimally thin multipactor electron sheet that was often assumed in previous models. The simulated threshold voltage for the onset of multipactor was compared with published experiments, and the level of agreement was found to depend on the secondary electron yield model chosen.

Clustered-Cavity Approach for the Performance Improvement of aKa-Band Second-Harmonic Gyroklystron Amplifier

The clustered-cavity approach has been discussed to demonstrate the bandwidth enhancement of a previously reported experimental Ka -band, second-harmonic, two-cavity gyroklystron amplifier. A generalized analytical clustered-cavity approach has been developed and then applied to enhance the bandwidth characteristics of a two-cavity gyroklystron amplifier. To validate the analytical results, the device simulation has also been carried out using commercial PIC simulation code, CST Particle Studio. The saturated output power of ~265 kW, the efficiency of ~18.4%, and the gain of ~17.07dB have been obtained in the case of both, cluster-cavity gyroklystron analysis and simulation. The clustered-cavity gyroklystron bandwidth has been achieved as ~56 MHz, which is approximately double that reported using the conventional cavity case, i.e., ~28 MHz. The obtained results show that the bandwidth of clustered-cavity gyroklystron is considerably widened along with the small increment in the RF output power, gain, and efficiency of the device.

Faraday Cup for high current and duty cycle electron LINACs

The design of a Faraday Cup (FC) is presented. The FC is designed to be used at an industrial LINAC test beamline. The present study gives the comprehensive design of FC to minimize the effects of secondary electrons. It also describes the heat dissipation at collector and its cooling design. A 200 mm long FC with aperture diameter of 20 mm and back wall thickness of 30 mm with repeller ring is simulated in CST particle studio software. A repeller ring is optimized for its thickness and axial distance to minimize the escape percentage of secondary charges from FC. The change in the thickness of repeller ring, axial distance and barrier potential greatly influence the escaped percentage. The study incorporates the secondary electron source at back wall of FC with fixed emission of 1.5 × 104 particles having energy 500 eV (10% dispersion) with different angular spread i.e. 0°, 45°, 90°. The escape percentage less than 1% is observed for 7 mm repeller ring-FC distance and 3 mm thickness with barrier potential of −700 V. The optimized design of the repeller ring reduces the physical dimensions of the FC. Moreover, the study also presents the mechanical design and heat transport analysis of Faraday cup. The designed square type channels with water circulating at 20 L/min limits the temperature to 333 K at the surface of the FC. Initial experimental results for thermal design are also presented, showing that temperature rise under 6 MeV, 4 μsec pulse width and 100 Hz repetition rate; is limited to 304 K. The cooling efficiently mitigates the heat load at water flow rate of 7.5 L/min.

Design and simulation of a 1 MeV, 100 mA parallel-fed capacitive coupled cascade industrial accelerator

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.

Nonadiabatic Effects on Beam-Quality Parameters for Frequency-Tunable Gyrotrons

We propose an unconventional electron gun structure in which the emitter is located on a concave cathode surface with a non-uniform electric field. Such a design violates the intuition that an emitter should place close to a uniform electric field to reduce the velocity spread. The commonly employed design guide based on the adiabatic condition predicts a huge velocity spread of 24%, but the simulation using EGUN code and verified with CST particle studio shows a very low spread of 2.8%. Examining the magnetic moment and the kinetic energy of the beam reveals that the electrons experience a relatively long acceleration process due to the much weak electric field. That's why the non-adiabatic effect matters. In addition to the cyclotron compression and the E$\times$B drift, the "resonant" polarization drift plays a crucial role in reducing the overall velocity spread.Simulations show a decent beam quality with the pitch factor of 1.5 and the transverse velocity spread of 2.8% over a wide range of the magnetic field (7.4-8.0 T) and the beam voltage (12-22 kV) with a high structural tolerance. The promising results with the wide working range enable the development of continuous frequency-tunable gyrotrons.

A General Comparison On Impedance Theory And Cst Simulation of Discontinuities

Inhomogeneity of vacuum chamber components is the main source of coupling impedance. Nowadays, wake impedances are mostly predictable by 3D codes and analytical prediction of impedance theories can be helpful as a side solution. On the other hand, some asymmetries in the geometry of components might make troubles and lead to imprecise numerical results in 3D simulations. Analytical approximation of discontinuities, holes and grooves can give us an estimation of expected results and can be used as a benchmark in the case that we do not have any experimental data.To clarify the validity of theoretical expressions, general discontinuities are simulated in CST Particle Studio. The comparison of final results is presented here. At last, Resistive Wall impedance and some general discontinuities of components at ILSF storage ring are compared form the theoretical and simulation point of view.

Radiation from a charged particle bunch in a circular waveguide having areas with corrugated and smooth walls

We analyze the wave field of a charged particle bunch moving in a circular waveguide consisting of two parts: the first one has a corrugated wall and the other one has a smooth wall. It is assumed that the period and the depth of the corrugation are much less than the waveguide radius and wavelengths under consideration. The influence of corrugation on the electromagnetic field is analyzed using the method of equivalent boundary conditions (EBC). The cases of the bunch moving in both directions inside of such a waveguide are considered. We obtain analytical expressions for the main part of the field having discrete spectrum. Figures of a typical mode distribution of radiation are presented. We also perform numerical simulations in software package CST Particle Studio. Comparison of analytical and numerical results confirms the validity of the EBC method.

A multibeam metamaterial backward wave oscillator

Microwave sources transform the kinetic energy of an electron beam into microwaves through the interaction of electrons with a periodic slow wave structure (SWS). A metamaterial (MTM) waveguide is proposed for use in a microwave oscillator instead of a conventional periodic SWS that has been used for a long time to generate high power microwave radiation. MTMs have interesting properties such as the negative refractive index, low group velocity, and below cutoff propagation, among others. In this work, we study the interaction of a multibeam cathode with a set of MTM structures inside a cylindrical waveguide. We developed a structure comprising a number of MTM metallic plates that have periodicity in the axial direction and are repeated in the azimuthal coordinate. Using eigenmode simulations, we obtained negative dispersion around the operating frequency where the group velocity is negative and extremely small. The fully electromagnetic, relativistic particle-in-cell codes MAGIC and CST Particle Studio and the fully electromagnetic software tool CST Microwave Studio were used to obtain the results in this study.

Design and development of thermionic emission microscope for the characterization of multi-beam cathode

Thermionic emission microscope (THEM) is an important analytical research tool to study spatial emission distribution of a thermionic cathode. The criticality of its design and development stems from the need to characterize the inhomogeneous emission nature of the impregnated cathode surface. In this paper the design of lens and deflection plates for studying multi-beam cathode (MBC) is presented. To understand the electron optical performance of THEM, simulations were carried out using the simulation tools 2D-TRAK and Omni TRAK. These results were further validated using another software tool CST Particle Studio. The influence of various parameters of MBC such as protrusion, diameter of button and inter-button spacing have been studied.

Thermal design and simulation of the collector for 140GHz megawatt-class gyrotron on ITER

Thermal co-simulation for the collector of a 140GHz, 1MW gyrotron is achieved in this paper. Thermal losses due to the particle collision in collector from the CST Particle Studio are directly applied to the thermal analysis by the CST Multi-Physics Studio. The convective heat transfer coefficient of copper with different water flow rate has been discussed. In the simulation, the maximum temperature in the collector changes from 419°C to 245°C, which is achieved respectively at the water flow rates from 5m/s to 15m/s. The thermal deformation caused by different temperature distribution in the collector changes from 0.551mm to 0.253mm, which provides physical analysis for the collector.