Traveling Wave Tube Amplifier Research Articles

Wide Band High Gain Modified-Folded-Wave-guide Slow Wave Structure for Millimeter Wave Traveling Wave Tube Amplifier in 6G and Beyond Back-haul Communications

Abstract Millimeter-wave technology is crucial in telecommunications as it enables higher bandwidths and faster data transfer. V-band represents frequencies ranging from 50 to 75 GHz and is used for short-range back-haul communication, defense radar, inter-satellite communications, and space debris detection. Folded wave guide slow-wave structures (FWG-SWS) are an excellent choice for V-band amplifiers due to their wide bandwidths, large gain, and ease of fabrication using modern lithographic processes. This article presents a modified folded wave-guide slow-wave structure (MFW-SWS) for V-band traveling wave tube amplifiers (TWTAs) desirable for multi-gigabit 6G and beyond back-haul communications. The MFW slow-wave structure is an FWG-SWS variant that supports an increased RF phase velocity, accommodating additional SWS length for much-improved amplification. The dispersion analysis effectively provides a 15\% operational bandwidth ranging from 64-74 GHz with a reduced phase velocity of three-tenths the speed of light apt for enhanced beam-wave interactions. The two-section SWS has independent attenuators designed to provide over 20 dB attenuation throughout the functional bandwidth effortlessly. Additional wave-guide transitions are introduced to achieve the best attenuation characteristics. Along the axis of the SWS, a square beam tunnel is employed to support a 26 kV round electron beam with a beam current of 70 mA. To contain the electron beam within the beam tunnel, this study used a focusing mechanism with a constant magnetic field of 0.25T, which is highly appropriate for miniaturization and large-scale implementation in 6G back-haul towers. Particle-in-cell (PIC) simulations were performed using the CST (Computer Simulation Technology) Studio Suite, and a gain of over 26 dB with an output power of 50 W was successfully attained across the operational bandwidth.

Integrated Couplers of THz Radiation for Helical Slow-Wave Structures.

We have designed an integrated device that couples input and output coaxial horn antennas with a self-assembled helical slow-wave structure cradled in a v-groove on a silicon-on-insulator wafer. These devices will potentially enable the characterization of cold parameters and beam-wave interaction in slow-wave structures on a wafer level, i.e., without having to dice and package individual devices. In addition, such vertically integrated antennas and helical slow-wave structures may form the basis of compact and low-cost traveling-wave tube amplifiers operating at THz frequencies.

Dual Frequency Enhancement of the Supernanogan Multi-Charged Ion Source at TRIUMF ISAC Facility

In 2008, a Supernanogan ECR ion source from PANTECHNIK was introduced in addition to an in-house developed microwave ion source and a surface ion source to complement the TRIUMF Offline Ion Source (OLIS) facility to provide highly charged ions to ISAC experiments. Originally, it employed a 400 W Travelling Wave Tube Amplifier (TWTA) for RF heating, but less than 50 W was enough to produce all the multi-charged beams required by the experiments. A 50 W solid-state amplifier was added for redundancy purposes, but we found a significant improvement when both were switched on at the same time. When properly optimized for the dual frequency, less than ten times the total power is needed to produce a similar charge state distribution with more current than the single frequency. The beam stability and the ability to extract higher charged ions also improved with the dual frequency enhancement. The simulation studies, operational experience, and results are discussed in this paper.

Design for an 18 GHz Open Hexapole Electron Cyclotron Resonance Ion Source

Responding to a request by the user community for higher beam intensities, an upgrade of the Argonne National Laboratory ECR2 ion source is in progress. The upgrade has three main constraints: 1) The overall source architecture as defined by the solenoid coils cannot change, 2) radial access to the plasma chamber has to be maintained, and 3) the amount of time the source can be shut down for hardware installation is < 2 months. A new NdFeB open hexapole is projected to produce a 1.19 T wall field (r = 38.1 mm) with six radial slots (6.35 mm x 91.2 mm) allowing solid material access and ∼120 l/s of pumping to the plasma chamber. The axial magnetic fields will be enhanced with a vanadium permendur plug and optimization of the iron resulting in a magnetic field at injection Binj of 2.4 T, magnetic field at center Bmin of 0.4 T, and magnetic field at extraction Bext of 1.0 T and magnetic gradients Bgrad of 5.9 T/m for 14.5 GHz and 7.4 T/m for 18 GHz. The plasma is currently heated with multiple-frequency RF provided by two traveling wave tube amplifiers (TWTA) operating between 11 and 14.5 GHz and capable of providing 1100 W total power. The new magnetic structure will support 18 GHz operation with RF provided by a new TWTA.

Quality Control of Doppler Spectra from a Vertically Pointing, S-Band Profiling Radar

Abstract This study describes a novel combination of methods to remove spurious spectral peaks, or “spurs,” from Doppler spectra produced by a vertically pointing, S-band radar. The University of Massachusetts S-band frequency-modulated, continuous-wave radar (UMass FMCW) was deployed to monitor the growth of the CBL over northern Alabama during the VORTEX–Southeast field campaign in 2016. The Doppler spectra contained spurs caused by high-voltage switching power supplies in the traveling wave tube amplifier. In the original data-processing scheme for this radar, a median filtering method was used to eliminate most of the spurs, but the largest ones persisted, which significantly degraded the quality of derived radar moments (e.g., reflectivity, Doppler velocity, and spectrum width) and hindered further analysis of these data (e.g., hydrometeor classification and boundary layer height tracking). Our technique for removing the spurs consists of three steps: (i) a Laplacian filter identifies and masks peaks in the spectra that are characteristic of the spurs in shape and amplitude, (ii) an in-painting method then fills in the masked area based on surrounding data, and (iii) the moments data (e.g., reflectivity, Doppler velocity, and spectrum width) are then recomputed using a coherent power technique. This combination of techniques was more effective than the median filter at removing the largest spurs from the Doppler spectra and preserved more of the underlying Doppler spectral structure of the scatterers. Performance of both the median-filter and the in-painting methods is assessed through statistical analysis of the spectral power differences. Downstream products, such as boundary layer height detection, are more easily derived from the recomputed moments. Significance Statement This manuscript describes a novel combination of image and signal processing techniques used to recover meteorological observations from corrupted Doppler radar spectra. This successful recovery of meteorologically significant information illustrates the importance of retaining Doppler spectra when practical. In seeking solutions to data quality issues, the atmospheric science community should remain cognizant of promising techniques offered by other disciplines. We present this data rescue study as an example to the meteorological community.

Rotational spectroscopy of methyl tert-butyl ether with a new Ka band chirped-pulse Fourier transform microwave spectrometer.

Chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is a powerful tool for performing broadband gas-phase rotational spectroscopy, and its applications include discovery of new molecules, complex mixture analysis, and exploration of fundamental molecular physics. Here we report the development of a new Ka band (26.5-40 GHz) CP-FTMW spectrometer that is equipped with a pulsed supersonic expansion source and a heated reservoir for low-volatility samples. The spectrometer is built around a 150 W traveling wave tube amplifier and has an instantaneous bandwidth that covers the entire Ka band spectral range. To test the performance of the spectrometer, the rotational spectrum of methyl tert-butyl ether (MTBE), a former gasoline additive and environmental pollutant, has been measured for the first time in this spectral range. Over 1000 spectroscopic transitions have been measured and assigned to the vibrational ground state and a newly-identified torsionally excited state; all transitions were fit using the XIAM program to a root-mean-square deviation of 22 kHz. The spectrum displays internal rotation splitting, nominally forbidden transitions, and an intriguing axis-switching effect between the ground and torsionally excited state that is a consequence of MTBE's extreme near-prolate nature. Finally, the sensitivity of the spectrometer enabled detection of all singly-substituted 13C and 18O isotopologues in natural abundance. This set of isotopic spectra allowed for a partial r0 structure involving the heavy atoms to be derived, resolving a structural discrepancy in the literature between previous microwave and electron diffraction measurements.

Оптимизация полосы пропускания в лампе бегущей волны О-типа террагерцового диапазона

For developing terahertz O-type traveling wave tube amplifiers, as a rule, models are used that take into account only interaction of electron beam with electromagnetic wave in slow-wave system, without considering influence of areas occupied by electron gun and collector on these processes. However, if resonance occurs within volumes occupied by electron gun and collector, then this may lead to distortion of the slow-wave system bandwidth, thereby degrading the device performance. Reflectors using can significantly improve this situation, as thanks to reflectors, electromagnetic waves don't pass inside these areas, and absorbing layer inside them suppresses the resonance possibility. As a result, the device becomes more stable and efficient as an electromagnetic wave amplifier. This paper presents the numerical simulation results of processes in terahertz TWT model, including the entire device volume without exceptions, based on the Finite-Difference Time-Domain (FDTD) method for Maxwell equations and the Particle-In-Cells (PIC) method for calculating electron beam dynamics.

Electroplating on Unconventional Ultra-Compliant Substrates for Travelling Wave Tube Amplifiers

We report gold electroplating on ultra-compliant substrates comprising helical slow wave structures (SWSs) for traveling wave tube amplifiers (TWTAs) [1]. The novel ultra-compliant substrates are composed of edge-tethered tri-layer metal ribbons with a helical geometry of microscale diameter. After electroplating with gold, we obtain overall thicknesses of a few um. We discuss different controllable electroplating conditions that influence thickness, uniformity, roughness, and related properties of deposited gold films on helical ribbons. In addition to increasing conductance of the electroplated helical ribbons, electroplating stabilizes the helix at its equilibrium diameter, with the pitch predicted by Prakash et al.[1].Our method of fabrication of ultra-compliant helical ribbons starts with defining strips of width 5 µm to 10 µm by optical lithography, metal evaporation, and lift-off, deposited on Si substrates coated with a sacrificial layer of Ge or GeOx,. We use Cr/Au/Cr tri-layers to create an inherent stress gradient that causes the strip to self-assemble into a helix, after etching with XeF2 for selective removal of a sacrificial layer. Diameter and pitch of the released helices are controlled by varying the thickness, the elastic modulus, the residual stress, and the in-plane geometry of the deposited tri-layer metal strips. The gold electroplating process uses a sulphate-based gold solution in a two-electrode electrochemical setup with the helix as the cathode and a platinized mesh as the anode [2]. We deposit gold to a thickness of a few um, using a pulsed current source with variable parameters. Direct current can also be used with smaller deposition times. Our results demonstrate the application of electroplating to unconventional ultra-compliant helix of nanoscale dimensions. Reference [1] Divya J. Prakash,., Matthew M. Dwyer, Marcos Martinez Argudo, Mengistie L. Debasu, Hassan Dibaji, Max G. Lagally, Daniel W. van der Weide, and Francesca Cavallo. 2020. “Self-Winding Helices as Slow-Wave Structures for Sub-Millimeter Traveling-Wave Tubes.” ACS Nano, 2021, 15, 1229-1239. doi:10.1021/acsnano.0c08296.[2] Max G. Lagally, Anjali Chaudhary, Daniel van der Weide, Divya J. Prakash, and Francesca Cavallo, Improved Self-assembly of Helices via Electrodeposition on Freestanding Nanoribbons for TWT Application, provisional US patent application (P220249US01)Work supported by U.S. AFOSR-Award No FA9550-22-1-0086.

Demonstration of a PCM-Focused Sheet Beam TWT Amplifier at G-Band

A sheet beam traveling-wave tube (TWT) amplifier focused by periodically cusped-magnetic (PCM) fields has been successfully developed. The amplifier produces <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 115 W of peak power at 212.4 GHz with a voltage of 25.8 kV. The output power is more than 100 W from 210.2 to 213.6 GHz. The measured transport current is about 106 mA accounting for 81.5% of the total current. The high-efficiency circuit design, along with the novel coupling structure, makes it possible to greatly reduce the required current, enabling the use of the PCM focusing. As a result, large power and a wide band have been achieved in a compact volume with an overall weight of less than 1.8 kg. The results demonstrate a significant breakthrough in developing the sheet-beam amplifier at terahertz frequencies. Although a single-section circuit without the attenuator is used at this stage, we have verified all the key technologies. The measured results are in good agreement with the design.

Staggered-Vane Traveling-Wave Tube (SVTWT) Amplifier for High-Power V-Band Applications: Design, Fabrication, and Test

As a part of the plan to deploy a wideband high-power module (HPM) to very high-throughput satellite (VHTS) network systems, Communications and Power Industries LLC (CPI) has been developing a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}$</tex-math> </inline-formula> -band high-power traveling-wave tube (TWT) amplifier. The power amplifier is designed with a staggered-vane TWT (SVTWT) circuit and a circular beam, operating at beam voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{E}_{\textit{k}}\text{)} =$</tex-math> </inline-formula> 18–20 kV and beam current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{k}}\text{)} =$</tex-math> </inline-formula> 400–500 mA with the perveance of 0.168 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula> P. Within the development program, three prototypes have been built and tested so far—the first two prototypes only include simple features in their circuit configuration, excluding servers and complex tuning elements. The signal amplification process in the novel beam–wave scheme was demonstrated with the first prototype, showing 35 dBm of output power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{P}_{\text{out}}\text{)}$</tex-math> </inline-formula> with 10–15 dB of small-signal gain and 4 GHz of 1-dB bandwidth (47.2–51.2 GHz). <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{P}_{\text{out}} =$</tex-math> </inline-formula> 57 dBm (500 W) and 24 dB of small-signal gain (SSG) were demonstrated over 4.2 GHz (47.2–51.4 GHz) of 1-dB bandwidth with the second prototype. During the RF test, the tube operated at the continuous wave (CW) mode (100% of duty cycle) with extra external cooling fans. The third prototype is designed with more complex features, including servers, mode anode, and multistage depressed collector (MDC). Its test results showed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{P}_{\text{out}} =$</tex-math> </inline-formula> 54 dBm (250 W) and 24 dB of SSG over 5.2 GHz (47.2–52.4 GHz) of 1-dB bandwidth, running at CW mode with extra external cooling fans.

A Broadband Analog Predistortion Linearizer Based on GaAs MMIC for Ka-Band TWTAs

In this article, a Ka-band broadband analog predistortion (APD) microwave monolithic integrated circuit (MMIC) with independent tunability based on a 0.15 μm GaAs pHEMT process is proposed, which can be cascaded in front of traveling wave tube amplifiers (TWTAs) to improve their linearity. The influence of different diode sizes on the parameters of Schottky diodes is analyzed and used to design the gain and phase nonlinear branches. The broadband APD MMIC is realized based on a dual-branch vector synthesis design and nonlinear frequency adjust module (NFAM). The independent tunability and broadband characteristics of the APD MMIC are verified by simulated and measured results with an error of less than 5%. Furthermore, a Ka-band 60 W TWTA is linearized by the APD MMIC, and the gain and phase compressions are reduced from 8 dB and 50° to within 3 dB and 12°, respectively. The third-order intermodulation (C/IM3) is greater than 28 dBc and noise power ratio (NPR) is greater than 15.7 dBc at 3 dB output power backoff (OPBO) over the operating band of 25.1~27.5 GHz, indicating that the APD MMIC can improve the nonlinearity of TWTA effectively under broadband signals.

Performance of SWIPT-Enabled FD TWR Network With Hardware Impairments and Imperfect CSI

Cooperative communication with energy harvesting capability increases network coverage and provides a green and sustainable solution for future wireless technologies. In this article, we analyze the performance of a two-way relay network, where bidirectional information exchange between two nodes takes place via simultaneous wireless information and power transfer-enabled relay node, operating in full-duplex (FD) mode over generalized Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> fading channels. Different nonlinear power amplifier (NLPA) models, such as solid-state power amplifier, traveling wave tube amplifier, and soft envelope limiter, are considered at the relay node. The effect of practical constraints, such as imperfect channel state information (CSI) and transceiver hardware impairments (HIs), is considered. Further, we consider the impact of residual self-interference (RSI) due to imperfect successive interference cancellation in the FD mode. For performance analysis, the closed-form expressions of outage probability (OP), asymptotic OP, system throughput, energy efficiency, ergodic capacity, and asymptotic ergodic capacity are derived. The diversity order of the considered network is evaluated. Further, the impact of imperfect CSI, NLPA, HIs, RSI, and other parameters are highlighted on the system performance. The performance of FD and half-duplex mode is also compared. Monte Carlo simulations confirm the accuracy of the derived closed-form expressions.

The Effects of γ-Radiation on the Physical and Electrical Properties of Silicone Encapsulation for Electronic Power Conditioners

Since the electronic power conditioner (EPC) is a crucial part of a space traveling-wave tube amplifier (STWTA), its reliability issue must be considered. The most effective way to prevent insulation breakdown is potting. Silicone elastomers are commonly used as an encapsulant for the EPC because of their good physical and electrical properties. The properties of the encapsulant and the interfaces change under the influence of γ-radiation, which may result in the failure of the potted modules. In this work, a comprehensive evaluation methodology is proposed for silicone-based potted modules, where besides physical and electrical properties, the effect of γ-radiation on the encapsulated interface is also considered. The results show that with the increase of the irradiation dose, the crosslinking density, hardness, elastic modulus, volume resistivity, dielectric constant, and storage modulus are increased by 301.6%, 76.3%, 289.7%, 396.1%, 5.0%, and 589.8%, respectively. In contrast, the elongation at break and dielectric loss factor are decreased by 83.8% and 57.8%. In addition, the tensile strength and breakdown strength first increase and then decrease, while the coefficient of thermal expansion of the interface shows the opposite trend. Since the interface bonding state does not change and the electric field strength of the tip decreases slightly with an increasing dielectric constant, the average value of the partial discharge inception voltage increased slightly.

Генерация темных импульсов огибающей в модифицированной схеме шумотрона

The generation of dark envelope pulses with a duration of about 10 ns is obtained in a modified noisetron circuit consisting of two nonlinear amplifiers: a multicavity drift klystron and a travel-ing wave tube (TWT), captured by a delayed feedback circuit. The drift klystron operates in the output power saturation mode, and the TWT amplifier operates in the nonlinear cross mode, in which there are two N-shaped sections on the amplitude characteristic of the lamp, and the phase shift dependence on the signal power at the traveling wave tube entrance is highly nonlinear. It is shown that an increase in the chaotic signal power in a ring leads not only to a decrease in the average repetition period of dark envelope pulses, but also to the formation of bound states of dark and anti-dark envelope pulses.

The Effect of Thermal and Moisture Stress on Insulation Deterioration Law of Ionic Contaminated High-Voltage Printed Circuit Board of Electronic Power Conditioner

Since the electronic power conditioner (EPC) is a crucial part applied of a Space Travelling-wave Tube Amplifier (STWTA), the reliability issue must be considered. Of all the failure modes of an EPC, the insulation failure of an EPC in thermal and moist environments is the most serious, and needs special attention. By investigating the influence of contamination, humidity, and temperature on surface insulation resistance (SIR) and surface discharge, we focused on the determination of the insulation failure boundary in an EPC. Considering real working conditions, we used the typical circuit applied in the EPC as the test object. The insulation deterioration phenomenon under different thermal and moisture stress was studied. The results show that: (1) SIR of the samples did not change with contamination levels when the relative humidity (RH) was below 70%. When RH was higher than 75%, the SIR began to vary with temperature and ionic contaminant concentration. (2) Even if the samples were not contaminated (the ionic contamination concentration was less than 1.56 μg/cm2), the deterioration of the SIR still occurred at 85 °C/90% RH. (3) The insulation failure boundary caused by surface discharge, and the degree of electrical erosion were related to humidity, pollution, voltage and temperature. To improve the failure caused by insulation, encapsulation was used. Experiments showed that encapsulation is an effective protection method to prevent insulation deterioration.

Performance analysis and precoder design for IRS-assisted MIMO system with non-linear power amplifiers

In this work, a point-to-point intelligent-reflecting-surface (IRS) assisted single input single output (SISO) model is first developed and later modified to the multiple-input multiple-output (MIMO) case. For the SISO case, the transmitter or the access point (AP) is assumed to be equipped with a non-linear memory-less power amplifier (PA). A PA is assumed to be present for each data stream at the AP or base station (BS) side for the MIMO case. For both cases, three different types of PAs (A) Soft envelope limiter (SEL), (B) Solid-state power amplifier (SSPA), and (C) Travelling wave tube amplifier (TWTA) are considered. A Bussgang decomposition of the transmitted signal is then utilized for further analysis. A modified channel model is conceived for the AP-IRS-User equipment (UE) link based on the reflecting IRS elements’ radar cross-section (RCS). For the SISO system, both perfect and imperfect geometries of IRS elements with uniformly distributed element size errors are considered. An approximate closed-form expression for the upper bound on the above system’s spectral efficiency (SE) with ideal IRS elements is derived. The expression of the SE for two special cases of (A) Infinitely large IRS and (B) Ideal PA is deduced. Approximate closed-form expressions of various quality parameters for the IRS-assisted MIMO system with ideal and non-ideal PAs are also derived and verified numerically. Maximum ratio transmission (MRT) based precoder for this system is designed assuming that the information about the BS-UE link, BS-IRS-UE link, and the non-linear PA statistics is available at the BS. A closed-form expression for the SE of this system with this precoder is then derived and verified for various parametric situations.

Amplification of THz waves by beam-wave interaction in self-assembled helical slow-wave structures with single and double chirality

We investigate the interaction between an electron beam and a THz guided electromagnetic wave in a helical slow-wave structure formed by self-assembly of a conductive ribbon. We have previously shown the controlled fabrication of this slow-wave structure and its potential to form the basis for widely deployable millimeter-through-THz traveling-wave tube amplifiers. The process allows the fabrication of helical slow-wave structures with single and double chirality. Here, we use three-dimensional simulations to perform a comparative analysis of beam–wave interaction in self-assembled gold helices with single and double chirality. First, the structures are modeled without the electron beam (cold helices) to calculate the distribution of the electric field generated by the high-frequency wave. We perform simulations of cold helices by using Computer Simulation Technology Microwave Studio. Second, we evaluate the interaction between an electron beam and the THz travelingwave by using a particle in cell simulator in Computer Simulation Technology Particle Studio. Simulation studies show that a switch in chirality in the middle of self-assembled helices generates a reflected wave that boosts beam–wave interaction. We demonstrate that this efficient energy exchange will potentially provide high gain in THz traveling-wave tube amplifiers based on self-assembled helices.

Simulation Design of G-Band FWG TWT Amplifier Enhanced by π-Mode Extended Interaction

This article studies and summarizes the operating characteristics of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${G}$ </tex-math></inline-formula> -band folded waveguide traveling wave tube (TWT) amplifier enhanced by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -mode extended interaction cavities. Compared with conventional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${G}$ </tex-math></inline-formula> -band TWTs, the proposed amplifier can at once obtain a higher gain in a shorter interaction circuit length and ensure a proper operating bandwidth. The key of the design is introducing the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -mode multigap resonant cavity with alternating wide and narrow slots, which will improve the working performance of the whole device by shortening the length of the interaction circuit, enhancing its interaction effect, and improving its gain of unit length. In this design, the operation bandwidth is expanded by stagger tuning technique. In addition, the influence of cavity loss is examined so that the optimal performance is achieved. The PIC simulation results show that when the operating voltage is 21 kV and the operating current 80 mA, the maximum average output power of the designed TWT amplifier is 65.78 W at 217.4 GHz, which is corresponding to the maximum gain and efficiency of 37.38 dB and 3.9%, respectively. The gain per unit length is 12.64 dB/cm and the 3-dB bandwidth is 3.5 GHz.

Design and Cold Test of a G-Band 10-kW-Level Pulse TE01-Mode Gyrotron Traveling-Wave Tube

Overall design and cold test of a G-band gyrotron traveling-wave tube (gyro-TWT) amplifier are presented. This gyro-TWT aims at achieving a goal of 10-kW pulse output power in the range of 210–220 GHz. It is operated in a circular TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode at the fundamental cyclotron harmonics, which is driven by a 50-kV, 3-A gyrating electron beam. Low velocity spread diode-type magnetron injection gun (MIG), multichannel TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode input coupler, broadband metasurface output window, and lossy material loaded beam–wave interaction circuit are simulated and partially measured. Particle-in-cell (PIC) simulation shows that the designed gyro-TWT can achieve a saturated output power over 10 kW in the range of 210–228 GHz with a beam velocity spread of 2.29%.

Experiment of two-frequency heating for production of multiply charged ion at compact ECR ion source

Several research and developments have been performed at a compact ECR ion source (Kei3) with a fixed magnetic field at HIMAC. The Kei3 is a testing machine for application of Kei series developed for high-energy carbon-ion radiotherapy. It is difficult for Kei3 to produce ions that are heavier than carbon ion because it uses the same magnetic field distribution as the Kei series. In order to improve the beam current of multiply charged ions such as neon and argon, the two-microwave-frequency heating method was tested in the Kei3. Microwaves are introduced into the plasma chamber with a WR-90 rectangular waveguide. A traveling wave tube (TWT) amplifier made by the NEC (LD79X75A1) is used as the microwave source. The frequency band is 9.75-10.25 GHz and the maximum output power is 750 W. The WR-75 waveguide is also introduced from the upper part of the upstream vacuum chamber and installed on top of the existing the WR-90 waveguide. A TWT amplifier manufactured by the Xicom (XTRD-300IJ) was used as a microwave source for the two-microwave-frequency heating. The frequency band is 10-18 GHz and the maximum output power is 300 W. A beam test with oxygen, neon, and argon was performed in order to confirm the effect of two microwave frequency heating. In this test, we focused on O6+, Ne7+, and Ar9+ ions. We measured the dependence of the XTRD-300IJ microwave frequency and the microwave power of the LD79X75A1 on a charge state distributions.