A compact X-band backward traveling-wave accelerating structure

Very high-energy electrons(VHEEs)are potential candidates for FLASH radiotherapy for deep-seated tumors.We proposed a compact VHEE facility based on an X-band high-gradient high-power technique.In this study,we investigated and realized the first X-band backward traveling-wave(BTW)accelerating structure as the buncher for a VHEE facility.A method for calculating the parameters of single cell from the field distribution was introduced to simplify the design of the BTW structure.Time-domain circuit equations were applied to calculate the transient beam parameters of the buncher in the unsteady state.A prototype of the BTW structure with a thermionic cathode-diode electron gun was designed,fabricated,and tested at high power at the Tsinghua X-band high-power test stand.The structure successfully operated with 5-MW microwave pulses from the pulse compressor and outputted electron bunches with an energy of 8 MeV and a pulsed current of 108 mA.

Calculation of Start-Oscillation-Current for Lossy Gyrotron Traveling-Wave Tube (Gyro-TWT) Using Linear Traveling-Wave Tube (TWT) Parameter Conversions

The start-oscillation-current of a gyro-TWT (gyrotron traveling-wave tube) determines the stable operating current level of the device. The amplifier is susceptible to oscillations when the operating current level is higher than the start-oscillation current. There are several ways of calculating the start-oscillation current, including using the linear and nonlinear theory of a gyro-TWT. In this paper, a simple way of determining the start-oscillation current of lossy gyro-TWT is introduced. The linear TWT parameters that include the effects of synchronism, loss, and gain, were converted to gyro-TWT parameters to calculate the start-oscillation-current. The dependence on magnetic field, loss, and beam alpha was investigated. Calculations were carried out for a V-band gyro-TWT for both operating and competing modes. The proposed method of calculating the start-oscillation current provides a simple and fast way to estimate the oscillation conditions and can be used for the design process of a gyro-TWT.

Design, fabrication, and testing of low-group-velocity S-band traveling-wave accelerating structure

To implement the Tsinghua Thomson Scattering X-ray Source upgrade plan and the Very Compact Inverse Compton Scattering Gamma-ray Source (VIGAS) program, a new 1.5-m traveling-wave accelerating structure was designed to replace the old 3-m SLAC-type structure with the aim of increasing the accelerating gradient from15 to 30 MV/m. The new type of structure works in the 3π/4 mode with a comparatively low group velocity varying from 0.007c to 0.003c to increase the accelerating gradient at a given power. An elliptical iris was employed to reduce the surface field enhancement. The filling process of the low-group-velocity structure was analyzed using a circuit model. After fabrication, the structure was precisely tuned using the non-contact tuning method, followed by detailed low-power radiofrequency measurements. The structure was first installed and utilized at a beamline for the terahertz experiment at Tsinghua University. After 120 h of conditioning, it is now operating at a gradient of 24.2 MV/m and a 20.7-MW input power, with the klystron operating at its full power. It is expected to generate an accelerating gradient of 30 MV/m when the klystron power is upgraded to 30 MW in the near future.

Fabrication,tuning,and high-gradient testing of an X-band traveling-wave accelerating structure for VIGAS

X-band high-gradient linear accelerators are a challenging and attractive technology for compact electron linear-accelerator facilities.The Very Compact Inverse Compton Scattering Gamma-ray Source(VIGAS)program at Tsinghua University will utilize X-band high-gradient accelerating structures to boost the electron beam from 50 to 350 MeV over a short distance.A constant-impedance traveling-wave structure consisting of 72 cells working in the 2π/3 mode was designed and fabricated for this project.Precise tuning and detailed measurements were successfully applied to the structure.After 180 h of conditioning in the Tsinghua high-power test stand,the structure reached a target gradient of 80 MV/m.The breakdown rate versus gradient of this structure was measured and analyzed.

Design and development of high linearity millimeter wave traveling-wave tube for satellite communications

The linearity of the traveling-wave tube is a very important characteristic for a modern communication system. To improve the linearity of the traveling-wave tube at no expense of the saturated output power and overall efficiency, a modified pitch profile combined with a small adjustment of operating parameters is proposed. The optimal design of the helix circuit is evaluated theoretically by a large signal analysis, and the experimental test is also carried out to make a comparison of performance between the novel and original designed traveling-wave tubes. The experiments show that the saturated output powers and efficiencies of these two tubes are close to each other, while the linearity of the traveling-wave tube is obviously improved. The total phase shift and AM/PM conversion at saturation of the novel tube, averaged over the operating band, are only 30.6°/d B and 2.5°/d B, respectively, which are 20.1°/d B and 1.6°/d B lower than those of the original tube, respectively. Moreover, the third-order intermodulation of the novel tube is up to 2.2 d Bc lower than that of the original tube.

A novel slotted helix slow-wave structure for high power Ka-band traveling-wave tubes

A novel slotted helix slow-wave structure （SWS） is proposed to develop a high power, wide-bandwidth, and high reliability millimeter-wave traveling-wave tube （TWT）. This novel structure, which has higher heat capacity than a conven- tional helix SWS, evolves from conventional helix SWS with three parallel rows of rectangular slots made in the outside of the helix tape. In this paper, the electromagnetic characteristics and the beam-wave interaction of this novel structure operating in the Ka-band are investigated. From our calculations, when the designed beam voltage and beam current are set to be 18.45 kV and 0.2 A, respectively, this novel circuit can produce over 700-W average output power in a frequency range from 27.5 GHz to 32.5 GHz, and the corresponding conversion efficiency values vary from 19% to 21.3%, and the maximum output power is 787 W at 30 GHz.

A staggered double vane circuit for a W-band traveling-wave tube amplifier

Based on the combination of a staggered double vane slow wave structure （SWS） and round electron beam, a 200-W W-band traveling-wave tube （TWT） amplifier is studied in this paper. The main advantages of round beam operation over the sheet beam is that the round beam can be formed more easily and the focus requirement can be dramatically reduced. It operates in the fundamental mode at the first spatial harmonic. The geometric parameters are optimized and a transition structure for the slow wave circuit is designed which can well match the signal that enters into and goes out from the tube. Then a TWT model is established and the particle-in-cell （PIC） simulation results show that the tube can provide over 200-W output power in a frequency range of 88 GHz-103 GHz with a maximum power of 289 W at 95 GHz, on the assumption that the input power is 0.1 W and the beam power is 5.155 kW. The corresponding conversion efficiency and gain at 95 GHz are expected to be 5.6% and 34.6 dB, respectively. Such amplifiers can potentially be used in high power microwave-power-modules （MPM） and for other portable applications.

Effect of traveling-wave magnetic field on dendrite growth of high-strength steel slab: Industrial trials and numerical simulation

The dendrite growth behavior of high-strength steel during slab continuous casting with a traveling-wave magnetic field was studied in this paper. The morphology of the solidification structure and composition distribution were analyzed. Results showed that the columnar crystals could deflect and break when the traveling-wave magnetic field had low current intensity. With the increase in current intensity, the secondary dendrite arm spacing and solute permeability decreased, and the columnar crystal transformed into an equiaxed crystal. The electromagnetic force caused by the traveling-wave magnetic field changed the temperature gradient and velocity magnitude and promoted the breaking and fusing of dendrites. Dendrite compactness and composition uniformity were arranged in descending order as follows:columnar-toequiaxed transition (high current intensity), columnar crystal zone (low current intensity), columnar-to-equiaxed transition (low current intensity), and equiaxed crystal zone (high current intensity). Verified numerical simulation results combined with the boundary layer theory of solidification front and dendrite breaking–fusing model revealed the dendrite deflection mechanism and growth process. When thermal stress is not considered, and no narrow segment can be found in the dendrite, the velocity magnitude on the solidification front of liquid steel can reach up to 0.041 m/s before the dendrites break.

Directed transport of coupled Brownian motors in a two-dimensional traveling-wave potential

Considering an elastically coupled Brownian motors system in a two-dimensional traveling-wave potential, we investigate the effects of the angular frequency of the traveling wave, wavelength, coupling strength, free length of the spring, and the noise intensity on the current of the system. It is found that the traveling wave is the essential condition of the directed transport. The current is dominated by the traveling wave and varies nonmonotonically with both the angular frequency and the wavelength. At an optimal angular frequency or wavelength, the current can be optimized. The coupling strength and the free length of the spring can locally modulate the current, especially at small angular frequencies. Moreover, the current decreases rapidly with the increase of the noise intensity, indicating the interference effect of noise on the directed transport.

Fault locating for traveling-wave accelerators based on transmission line theory

Radio-frequency(RF)breakdown analysis and location are critical for successful development of high-gradient traveling-wave(TW)accelerators,especially those expected to generate high-intensity,high-power beams.Compared with commonly used schemes involving dedicated devices or complicated techniques,a convenient approach for breakdown locating based on transmission line(TL)theory offers advantages in the typical constant-gradient TW-accelerating structure.To deliver such an approach,an equivalent TL model has been constructed to equate the TW-accelerating structure based on the fun-damental theory of the TL transient response in the time domain.An equivalence relationship between the TW-accelerating structure and the TL model has been established via analytical derivations associated with grid charts and verified by TL circuit simulations.Furthermore,to validate the proposed fault-locating method in practical applications,an elaborate analysis via such a method has been conducted for the recoverable RF-breakdown phenomena observed at an existing prototype of a TW-accelerating-structure-based beam injector constructed at the Huazhong University of Science and Technology.In addition,further considerations and discussion for extending the applications of the proposed method have been given.This breakdown-locating approach involving the transient response in the framework of TL theory can be a conceivable supple-ment to existing methods,facilitating solution to construction problems at an affordable cost.

An Open Rectangular Waveguide Grating for Millimeter-Wave Traveling-Wave Tubes

Millimeter-wave traveling-wave tube （TWT） prevails nowadays as the amplifier for radar, communication and electronic countermeasures. The rectangular waveguide grating is a promising all-metal interaction circuit for the millimeter-wave TWT with advantages of high power capacity, fine heat dissipation, scalability to smaller dimen- sions for shorter wavelengths, compact structure and robust performance. Compared with the traditional closed structure, the open rectangular waveguide grating （ORWG） has wider bandwidth, lower cut-off frequency, and higher machining precision for higher working frequencies due to the open transverse. It is a potential structure that can work in the millimeter wave and even Terahertz band. The rf characteristics including dispersion and interaction impedance are investigated by both theoretic calculation and software simulation. The influences of the structure parameters are also discussed and compared, and the theoretical results agree well with the simula- tion results. Based on the study, the ORWG will favor the design of a broadband and high-power millimeter-wave TWT.

Design of a re-entrant double-staggered ladder circuit for V-band coupled-cavity traveling-wave tubes

The re-entrant double-staggered ladder slow-wave structure is employed in a high-power V-band coupled-cavity traveling-wave tube. This structure has a wide bandwidth, a moderate interaction impedance, and excellent thermal dissipation properties, as well as easy fabrication. A well-matched waveguide coupler is proposed for the structure. Combining the design of attenuators, a full-scale three-dimensional circuit model for the V-band coupled-cavity traveling- wave tube is constructed. The electromagnetic characteristics and the beam wave interaction of this structure are investigated. The beam current is set to be 100 mA, and the cathode voltage is tuned from 16.8 kV to 15.8 kV. The calculation results show that this tube can produce a saturated average output power over 100 W with an instantaneous bandwidth greater than 1.25 GHz in the frequency ranging from 58 GHz to 62 GHz. The corresponding gain and electronic efficiency can reach over 32 dB and 6.5%, respectively.

Design of a Novel Folded Waveguide for 60-GHz Traveling-Wave Tubes

The 60-GHz traveling-wave tube （TWT） prevails nowadays as the amplifier for the satellite communication and electronic countermeasures. The folded waveguide （FW） is a promising all-metal slow-wave structure （SWS） for the 60-GHz TWT with advantages of robust performance, fine heat dissipation, considerable power and bandwidth. A novel FW periodically loaded with rectangular grooves is analyzed for the purpose of gaining higher power and gain. The rf characteristics are investigated by numerical simulation, and the nonlinear large- signal performance of such a TWT is analyzed by a 3I） particle-in-cell code MAGIC. Compared with normal circuits, relatively higher continuous-wave power （40-56 W） and similar bandwidth （5 GHz） are predicted by simulation. Meanwhile, the designed operation voltage is 10.5 kV, which keeps the low-voltage advantage of the popular helix TWT competitor. The novel FW will favor the design of a broadband and high-power 60-GHz TWT

An open-styled dielectric-lined azimuthally periodic circular waveguide for a millimeter wave traveling-wave tube

An open-styled dielectric-lined azimuthMly periodic circular waveguide （ODLAP-CW） for a millimeter-wave traveling-wave tube （TWT） is proposed, which is a modified form of a dielectric-lined azimuthally periodic circular waveguide （DLAP-CW）. The slow-wave characteristics of the open-styled DLAP-CW are studied by using the spatial harmonics method, which includes normalized phase velocity and interaction impedance. The complicated dispersion equations are numerically solved with MATLAB and the results are in good agreement with the simulation results obtained from HFSS. The influence of structural parameters on the RF properties is investigated based on our theory. The numerical results show that the optimal thickness of the metal rod can increase the interaction impedance, with the dielectric constant held fixed. Finally, the slow-wave characteristics and transmission properties of an open-styled structure are compared with those of the DLAP-CW. The results validate that the mode competition is eliminated in the improved structure with only a slight influence on the dispersion characteristics, which may significantly improve the stability of an open-styled DLAP-CW-based TWT, and the interaction efficiency is also improved.

Integrated Design of a Compact and Lightweight S-Band Traveling-Wave Tube Amplifier for a New Class of Microwave Power Module

A new class of compact and lightweight S-band 1 kW traveling-wave tube (TWT) is being developed for a microwave power module (MPM) that will be used for phased antenna array radar applications. The proposed S-band MPM provides a tenfold peak power increase compared to state-of-the-art S-band MPMs. In this paper, the design of the vacuum power booster TWT part of the MPM is presented. The compact and lightweight S-band TWT is driven by a 6 kV, 0.9 A electron beam. The amplifier is predicted by large-signal simulations to generate over 1 kW at S-band with 25 dB saturated gain and over 40% efficiency. The stability from unwanted oscillations has been investigated. To suppress the oscillations, the helix circuit has been coated with carbon composite material. The coaxial input and output antennas have been fabricated. For efficiency enhancement, a multi-stage depressed collector (MDC) has been designed using a 3D particle-in-cell (PIC) simulator, VORPAL. The collector design makes use of a current loop based on a feedback mechanism for effective design process. The integrated designs of a helix circuit, an electron gun, a periodic permanent magnet (PPM), antennas, and a collector are presented.

On the functions of astrocyte-mediated neuronal slow inward currents

Slow inward currents are known as neuronal excitatory currents mediated by glutamate release and activation of neuronal extra synaptic N-met hyl-D-aspartate receptors with the contribution of astrocytes.These events are significantly slower than the excitatory postsynaptic currents.Parameters of slow inward currents are determined by seve ral factors including the mechanisms of astrocytic activation and glutamate release,as well as the diffusion pathways from the release site towards the extra synaptic recepto rs.Astrocytes are stimulated by neuronal network activity,which in turn excite neurons,forming an astrocyte-neuron feedback loop.Mostly as a consequence of brain edema,astrocytic swelling can also induce slow inward currents under pathological conditions.There is a growing body of evidence on the roles of slow inward currents on a single neuron or local network level.These events often occur in synchro ny on neurons located in the same astrocytic domain.Besides synchronization of neuronal excitability,slow inward currents also set synaptic strength via eliciting timing-dependent synaptic plasticity.In addition,slow inward currents are also subject to non-synaptic plasticity triggered by long-la sting stimulation of the excitatory inputs.Of note,there might be important regionspecific differences in the roles and actions triggering slow inward currents.In greater networks,the pathophysiological roles of slow inward currents can be better understood than physiological ones.Slow inward currents are identified in the pathophysiological background of autism,as slow inward currents drive early hypersynchrony of the neural networks.Slow inward currents are significant contributors to paroxysmal depolarizational shifts/interictal spikes.These events are related to epilepsy,but also found in Alzheimer's disease,Parkinson's disease,and stroke,leading to the decline of cognitive functions.Events with features overlapping with slow inward currents(excitatory,N-methyl-Daspartate-receptor mediated currents with astrocytic contribution) as ischemic currents and spreading depolarization also have a well-known pathophysiological role in worsening consequences of stroke,traumatic brain injury,or epilepsy.One might assume that slow inward currents occurring with low frequency under physiological conditions might contribute to synaptic plasticity and memory formation.However,to state this,more experimental evidence from greater neuronal networks or the level of the individual is needed.In this review,I aimed to summarize findings on slow inward currents and to speculate on the potential functions of it.

Altered synaptic currents,mitophagy,mitochondrial dynamics in Alzheimer's disease models and therapeutic potential of Dengzhan Shengmai capsules intervention

Emerging research suggests a potential association of progression of Alzheimer's disease(AD)with alterations in synaptic currents and mitochondrial dynamics.However,the specific associations between these pathological changes remain unclear.In this study,we utilized Aβ42-induced AD rats and primary neural cells as in vivo and in vitro models.The investigations included behavioural tests,brain magnetic resonance imaging(MRI),liquid chromatography-tandem mass spectrometry(UPLC-MS/MS)analysis,Nissl staining,thioflavin-S staining,enzyme-linked immunosorbent assay,Golgi-Cox staining,transmission electron microscopy(TEM),immunofluorescence staining,proteomics,adenosine triphosphate(ATP)detection,mitochondrial membrane potential(MMP)and reactive oxygen species(ROS)assessment,mitochondrial morphology analysis,electrophysiological studies,Western blotting,and molecular docking.The results revealed changes in synaptic currents,mitophagy,and mitochondrial dynamics in the AD models.Remarkably,intervention with Dengzhan Shengmai(DZSM)capsules emerged as a pivotal element in this investigation.Aβ42-induced synaptic dysfunction was significantly mitigated by DZSM intervention,which notably amplified the frequency and amplitude of synaptic transmission.The cognitive impairment observed in AD rats was ameliorated and accompanied by robust protection against structural damage in key brain regions,including the hippocampal CA3,primary cingular cortex,prelimbic system,and dysgranular insular cortex.DZSM intervention led to increased IDE levels,augmented long-term potential(LTP)amplitude,and enhanced dendritic spine density and length.Moreover,DZSM intervention led to favourable changes in mitochondrial parameters,including ROS expression,MMP and ATP contents,and mitochondrial morphology.In conclusion,our findings delved into the realm of altered synaptic currents,mitophagy,and mitochondrial dynamics in AD,concurrently highlighting the therapeutic potential of DZSM intervention.

New Traveling-Wave Antenna Resonating at 6 GHz Based on Artificial Transmission Line Metamaterial Structures for RF Portable Devices

Design of new metamaterial (MTM) traveling-wave antenna with “d-formed” left-handed structure is proposed. The proposed MTM structure is designed at a height of 0.8 mm from the ground plane with almost 2 GHz bandwidth. The most interesting feature of the design is the ability of enhancing the gain and total efficiency of the antenna without negative effects of the other important parameters like bandwidth. By using the “d-shaped” MTM structure and printed planar technique, the bandwidth of the MTM traveling-wave antenna is significantly increased at a resonant frequency of 6 GHz and also a foot print area reduction of the antenna structure is provided. Antenna size is 7.2 × 5 × 0.8 mm3. The proposed antenna is suitable for RF portable devices operating at 6 GHz.

Current perspectives of viral hepatitis

Viral hepatitis represents a major danger to public health,and is a globally leading cause of death.The five liver-specific viruses:Hepatitis A virus,hepatitis B virus,hepatitis C virus,hepatitis D virus,and hepatitis E virus,each have their own unique epidemiology,structural biology,transmission,endemic patterns,risk of liver complications,and response to antiviral therapies.There remain few options for treatment,in spite of the increasing prevalence of viral-hepatitiscaused liver disease.Furthermore,chronic viral hepatitis is a leading worldwide cause of both liver-related morbidity and mortality,even though effective treatments are available that could reduce or prevent most patients’complications.In 2016,the World Health Organization released its plan to eliminate viral hepatitis as a public health threat by the year 2030,along with a discussion of current gaps and prospects for both regional and global eradication of viral hepatitis.Today,treatment is sufficiently able to prevent the disease from reaching advanced phases.However,future therapies must be extremely safe,and should ideally limit the period of treatment necessary.A better understanding of pathogenesis will prove beneficial in the development of potential treatment strategies targeting infections by viral hepatitis.This review aims to summarize the current state of knowledge on each type of viral hepatitis,together with major innovations.

Lift-Off Effect of Koch and Circular Differential Pickup Eddy Current Probes

A flexible or planar eddy current probe with a differential structure can suppress the lift-off noise during the inspection of defects.However,the extent of the lift-off effect on differential probes,including different coil structures,varies.In this study,two planar eddy current probes with differential pickup structures and the same size,Koch and circular probes,were used to compare lift-off effects.The eddy current distributions of the probes perturbed by 0°and 90°cracks were obtained by finite element analysis.The analysis results show that the 90°crack can impede the eddy current induced by the Koch probe even further at relatively low lift-off distance.The peak-to-peak values of the signal output from the two probes were compared at different lift-off distances using finite element analysis and experimental methods.In addition,the effects of different frequencies on the lift-off were studied experimentally.The results show that the signal peak-to-peak value of the Koch probe for the inspection of cracks in 90°orientation is larger than that of the circular probe when the lift-off distance is smaller than 1.2 mm.In addition,the influence of the lift-off distance on the peak-to-peak signal value of the two probes was studied via normalization.This indicates that the influence becomes more evident with an increase in excitation frequency.This research discloses the lift-off effect of differential planar eddy current probes with different coil shapes and proves the detection merit of the Koch probe for 90°cracks at low lift-off distances.