Cold Test Measurements Research Articles

Design and Cold-Test Measurement of a Novel Metamaterial Assisted Dual-Band Slow Wave Structure

Design and Cold-Test Measurement of a Novel Metamaterial Assisted Dual-Band Slow Wave Structure

Design and RF Characterization of High-Power Ferrule-Loaded Folded Waveguide SWS for mm-Wave TWT

Design and analysis of ferrule-loaded folded waveguide slow wave structure is carried out for a high-power millimeter-wave traveling-wave tube (TWT). The design of the structure is carried out by numerical simulation. A typical structure has been designed and fabricated at the Ka-band, and cold test measurement is carried out for the cold circuit parameters and the results are compared against numerical analysis. To compare the efficacy of the ferrule-loaded folded waveguide structure, a conventional folded waveguide structure is also designed for the same operating bandwidth, and cold circuit parameters are compared. The comparison results shows that the interaction impedance of the ferrule-loaded folded waveguide structure is double compared with the conventional structure at the cost of reduction in cold bandwidth. Furthermore, particle-in-cell (PIC) simulation is also carried out to estimate the output power and gain for both the structures for the same operating band, and the results are compared. The comparison results show that the cross section is reduced by 22% and the overall interaction length is reduced by 50% for the ferrule-loaded FW-SWS compared with the conventional FW-SWS for the same output power of about 500 W.

Development of microfabricated planar slow-wave structures on dielectric substrates for miniaturized millimeter-band traveling-wave tubes

We report the results of the design, simulation, fabrication, and cold-test measurements of millimeter-band 2D planar microstrip slow-wave structures (SWSs) on dielectric substrates. Such structures have a high slow-wave factor, which allows for low-voltage operation and reduction in the size and weight of the device. A low-cost and flexible fabrication technology based on magnetron sputtering and subsequent laser ablation has been developed and is reported in the paper. Microstrip meander-line SWS circuits at V-, W-, and D-bands have been fabricated and characterized. The fabrication of ring-bar planar SWSs by the photolithographic method is also discussed. Experimental measurement of S-parameters of the fabricated structures reveals good transmission properties. Return loss (S11) does not exceed −10 dB and attenuation is about 2 dB/cm in the V-band, 10 dB/cm in the W-band, and 8.5 dB/cm in the D-band.

Cold Circuit Analysis of a Coupled-Cavity Slow Wave Structure for Mm-Wave TWT

An equivalent circuit approach for the analysis of cold circuit parameters such as dispersion and interaction impedance characteristics was used for the design of staggered double slot square-shaped coupled-cavity slow wave structure at millimeter waveband and the results were validated against numerical analysis at Ka -band and $W$ -band. The derived lumped parameters of the square-shaped coupled-cavity slow wave structure (CC-SWS) is different from the reported cylindrical CC-SWS. A typical structure was fabricated at Ka -band and cold test measurement was carried and the results were compared against the proposed equivalent circuit approach. The comparison of results shows that the equivalent circuit is simple but accurate to predict within 3% and 10% accuracy against numerical simulation and cold test measurement for dispersion and interaction impedance characteristics, respectively.

On-Wafer Microstrip Meander-Line Slow-Wave Structure at Ka-Band

A novel configuration for a Ka-band V-shaped microstrip meander-line slow-wave structure (SWS) is reported. The SWS is designed to work at a voltage less than 4 kV and provide a wide bandwidth. Coplanar waveguide (CPW) input–output feed lines and a shielding structure are incorporated to enable fast on-wafer cold test measurements on a CPW probe station without requiring dicing or a metal enclosure. Simulated dispersion characteristics and coupling impedance for the optimized design are presented. The simulated S11 of the entire structure is better than −15 dB over 25–36 GHz. The proposed configuration is fabricated using $4^{\prime \prime }$ Si wafers and standard microfabrication processes. The measured S11 of the entire structure is better than −10 dB over 20–40 GHz. The observed high insertion loss has been explained in detail, and alternative approaches that can reduce the loss have been proposed. The PIC simulation results show that for a 3.6-kV, 50-mA sheet beam, the output power can potentially reach 14.5 W at 34 GHz with a gain of 21.6 dB. A 3-dB bandwidth of about 25% centered at 32 GHz is also indicated.

Orbital Angular Momentum (OAM) of Rotating Modes Driven by Electrons in Electron Cyclotron Masers

The well-defined orbital angular momentum (OAM) of rotating cavity modes operating near the cutoff frequency excited by gyrating electrons in a high-power electron cyclotron maser (ECM)—a gyrotron—has been derived by photonic and electromagnetic wave approaches. A mode generator was built with a high-precision 3D printing technique to mimic the rotating gyrotron modes for precise low-power measurements and shows clear natural production of higher-order OAM modes. Cold-test measurements of higher-order OAM mode generation promise the realization towards wireless long-range communications using high-power ECMs.

Design and Characterization of a W-Band Folded-Waveguide Slow-Wave Structure

A single-section slow-wave structure for a W-band folded-waveguide traveling-wave tube with operating bandwidth of around 4% was designed for delivering the output power of 50 W at the operating voltage of 13.5 kV and operating beam current of 80 mA. The design was carried out using analytical formulations and 3D electromagnetic simulations. The beam-wave interaction analysis was carried out using large signal Lagrangian analysis and particle-in-cell simulation. The folded-waveguide slow-wave structure along with input-output couplers and RF windows were fabricated. Cold test measurements were carried out for dispersion characteristics of the slow-wave structure and voltage standing-wave ratio and insertion loss characteristics of the RF window. The measured cold circuit parameters show close agreement with the analysis.

Ring-Double-Bar Slow Wave Structure for High Power TWTs

The electromagnetic properties of a ring-double-bar (RDB) slow wave structure are investigated. Use of two bars to connect neighboring rings instead of one as in a conventional ring-bar (RB) structure leads to the splitting $E$ - and $H$ -waves, with the $H$ -wave concentrated in thin layers near the rings. This effect leads to the flattening of the dispersion characteristic, similar to that in a helix with longitudinal vanes. Prototype RDB structures have been fabricated, measured, and compared with the conventional helix and RB circuits. Analysis, simulation, and cold test measurements demonstrate that the use of an RDB structure may make it possible to increase the maximum stable operating voltage of wideband traveling-wave tubes to 30–40 kV, enabling an order of magnitude increase in output power without the danger of backward wave oscillation.

Systemic Inflammation Decreases Pain Threshold in Humans In Vivo

BackgroundHyperalgesia is a well recognized hallmark of disease. Pro-inflammatory cytokines have been suggested to be mainly responsible, but human data are scarce. Changes in pain threshold during systemic inflammation evoked by human endotoxemia, were evaluated with three quantitative sensory testing methods. Methods and ResultsPressure pain thresholds, electrical pain thresholds and tolerance to the cold pressor test were measured before and 2 hours after the intravenous administration of 2 ng/kg purified E. coli endotoxin in 27 healthy volunteers. Another 20 subjects not exposed to endotoxemia served as controls. Endotoxemia led to a rise in body temperature and inflammatory symptom scores and a rise in plasma TNF-α, IL-6, IL-10 and IL-1RA. During endotoxemia, pressure pain thresholds and electrical pain thresholds were reduced with 20±4 % and 13±3 %, respectively. In controls only a minor decrease in pressure pain thresholds (7±3 %) and no change in electrical pain thresholds occurred. Endotoxin-treated subjects experienced more pain during the cold pressor test, and fewer subjects were able to complete the cold pressor test measurement, while in controls the cold pressor test results were not altered. Peak levels and area under curves of each individual cytokine did not correlate to a change in pain threshold measured by one of the applied quantitative sensory testing techniques. Conclusions and SignificanceIn conclusion, this study shows that systemic inflammation elicited by the administration of endotoxin to humans, results in lowering of the pain threshold measured by 3 quantitative sensory testing techniques. The current work provides additional evidence that systemic inflammation is accompanied by changes in pain perception.

Broadband 220-GHz Vacuum Window for a Traveling-Wave Tube Amplifier

We present electromagnetic cold-test measurements of BeO ceramic pillbox vacuum windows for a 220-GHz traveling-wave tube amplifier. Transmission and reflection measurements show better than 20 dB return loss over a 25 GHz bandwidth, with band centers in the range of 212-225 GHz. We observe tuning of the window response as the circular waveguide length is changed. High-power testing is performed at 2.5 W, 100% duty at 218 GHz.

Analysis of Ridge-Loaded Folded-Waveguide Slow-Wave Structures for Broadband Traveling-Wave Tubes

An E-plane serpentine folded-waveguide slow-wave structure with ridge loading on one of its broad walls is proposed for broadband traveling-wave tubes (TWTs) and studied using a simple quasi-transverse-electromagnetic analysis for the dispersion and interaction impedance characteristics, including the effects of the beam-hole discontinuity. The results are validated against cold test measurements, an approximate transmission-line parametric analysis, an equivalent circuit analysis, and 3-D electromagnetic modeling using CST Microwave Studio. The effect of the structure parameters on widening the bandwidth of a TWT is also studied.

Inverted Slot-Mode Slow-Wave Structures for Traveling-Wave Tubes

The dispersion and impedance characteristics of an inverted slot-mode (ISM) slow-wave structure computed by three different techniques, i.e., an analytical model based on a periodic quasi-TEM approach, an equivalent-circuit model, and 3-D electromagnetic simulation are obtained and compared. The comparison was carried out for three different slot-mode structures at S-, C-, and X-bands. The approach was also validated with experimental measurements on a practical X-band ISM traveling-wave tube. The design of ferruleless ISM slow-wave structures, both in circular and rectangular formats, has also been proposed and the predicted dispersion characteristics for these two geometries are compared with 3-D simulation and cold-test measurements. The impedance characteristics for all three designs are also compared.

A High Efficiency Launcher and Mirror System for Use in a 110 GHZ TE22,6 Mode Gyrotron

A four-mirror internal quasi-optical mode converter designed for a CPI gyrotron is discussed. Many improved methods were used in designing the mode converter. The launcher was designed and analyzed using the TOL and Surf3d codes developed by CCR. Mirrors 1 and 2 were designed using analytic surfaces to shape the general wavefront curvature of the beam radiated from the launcher. Mirrors 3 and 4 were iteratively designed using improved techniques that produced smooth mirror surfaces. Good agreement was found between theory and low-power cold-test measurements. The fraction of power coupled between the target Gaussian beam and the output of mirror 4, inferred from measurements, was 0.990. The stray radiation from the internal quasi-optical mode converter, inferred from measurements, was only 1.9% of the total power radiated from the launcher. This resulted in a high overall system efficiency of 97.0%, which is greater than previous designs.

RF deflector design and measurements for the longitudinal and transverse phase space characterization at SPARC

The six-dimensional beam phase space at the exit of a photoinjector can be completely characterized by means of an RF deflector and a dispersive system. In this paper we summarize the main features of the use of an RF deflector to measure aspects of the longitudinal and transverse phase space in an ultra-short electron beam. In particular we illustrate these measurements through the simulation of experiments currently under development at the SPARC photoinjector. We also discuss the design procedure followed to design the RF deflector for SPARC. This device is a five-cell structure operating on the π mode at 2.856 GHz. Finally, we report and discuss the cold-test measurement results on a full scale aluminum prototype.

Design and Cold Tests of Asymmetric Quasioptical Resonators

This paper presents the design and test of asymmetric quasioptical resonators for gyrotron applications, where most of the diffraction output coupling comes from the smaller of two mirrors. A computer code based on scalar diffraction theory is used to calculate the resonator losses and the electric field near the mirrors. Resonators with mirror separations approaching confocal have reduced side lobes in the diffraction patterns, which should allow for better power transmission and focusing. Cold tests have been performed at 94 and 141 GHz to measure the quality factor of the asymmetric resonators as a function of mirror separation and mirror misalignment. Typical resonator parameters include 65 cm mirror separation, 1-3% output coupling and 85% of the losses from the small mirror. A half-symmetric resonator with one flat and one curved mirror has also been investigated. The calculated values of Q are in reasonably good agreement with the cold test measurements.

Hemodynamic and metabolic profile in offspring of malignant hypertensive parents.

Malignant hypertension is a serious form of arterial hypertension in which the physiopathological mechanisms include increased activity of the sympathetic nervous system, renin angiotensin system, and endothelium dysfunction. Family history of hypertension is an important predictive factor for hypertension and is associated with metabolic and hemodynamic abnormalities. Studies of these abnormalities in malignant hypertensive offspring have not yet been published. Therefore, we studied 42 offspring of malignant hypertensive parents (OMH group: age, 22+/-7 years; 23 male subjects; 27 white) and 35 offspring of normotensive parents (ONT group: age, 21+/-4 years; 23 male subjects; 25 white). All subjects had blood pressure <140/90 mm Hg. We evaluated body mass index; office blood pressure; 24-hour ambulatory and continuous beat-to-beat blood pressure monitoring (Finapres); biochemical analysis, including total cholesterol and fractions, triglycerides, glucose, and insulin; and hormonal analysis, including plasma renin activity, aldosterone, and catecholamines. The subjects were also submitted to cold pressure test and handgrip measurements. The body mass index was significantly higher in the OMH group (24+/-5 kg/m(2)) than in the ONT group (22+/-4 kg/m(2)). The OMH group showed significantly higher blood pressure and heart rate in office and Finapres measurements (P<0.05). In 24-hour ambulatory monitoring, the OMH group presented higher 24-hour blood pressure and heart rate, higher blood pressure during the night, and higher heart rate variability during the day compared with those of the ONT group. They also presented lower HDL cholesterol, higher levels of plasma insulin and norepinephrine, and higher insulin-to-glucose ratio (P<0.05) than the ONT group. There were no differences in the other biochemical parameters measured. In conclusion, OMH subjects show early hemodynamic, neurohumoral, and metabolic alterations that are typical of hypertensive metabolic syndrome.

Cold test measurements on components of the 1 MW, 140 GHz, CW gyrotron for the stellarator Wendelstein 7-X

For the development of a 1 MW, 140 GHz gyrotron for CW operation which will be installed at the stellarator facility Wendelstein 7-X at IPP Greifswald, a collaboration between different European research institutes and an industrial company has been established. In order to prove the proper functioning of the millimeter wave components installed in the gyrotron — such as the cavity, the waveguide taper and the quasioptical mode converter — these components should be cold tested, preferably before installation. However, due to lack of time as well as long delivery times, this was not possible. Therefore, two units of the quasioptical mode converter and the cavity were fabricated with identical geometry, one of those being used for measurements on the low power test device. To perform these cold tests for tapers and mode converters, the gyrotron cavity output mode has to be simulated. This means that a high order rotating mode (TE 28,8 mode) must be generated at low power. This can be achieved by means of a mode generator consisting of two mirrors and a coaxial cavity with a perforated outer wall. Before applying the mode generator to the components, its proper behavior and the accurate alignment of the system must be verified either by radiation pattern measurements or k-spectrometer measurements. As the coupling through the holes of the k-spectrometer is extremely low, a special vector network analyzer with a dynamic range of at least 100 dB had to be developed. This has been achieved by integration of a phase locked backward-wave oscillator with a line width of 100 Hz and an output power of 10 mW. A non-destructive measurement of the resonance frequency and the quality factor of the cavity does not seem possible. The second cavity will be prepared for the cold measurement by drilling a small radial hole into its wall in the plane of the field maximum. This hole is then used for the input coupling. The accuracy required for this hole is rather critical. The coupling coefficient must be high for sufficient excitation of the rf field, but on the other hand it must neither change the frequency nor the quality factor strongly. The transmission is measured by a probe at the output of the uptaper.

Experimental and theoretical investigations of a 17 GHz RF gun

We report on experimental and theoretical investigations of a 17 GHz RF photocathode electron gun. This is the first photocathode electron gun to operate at a frequency above 2.856 GHz. The 1.5 cell, π mode, copper cavity was tested with 50 ns pulses from a 17.150 GHz klystron amplifier built by Haimson Research Corp. A Bragg filter was used at the RF gun to reduce the reflection of parasitic modes back into the klystron. Coupling hole theory in conjunction with cold test measurements was used to determine the field profile in the RF gun. The particle in cell code MAGIC as well as coupled envelope equations were used to simulate the beam dynamics in the RF gun. With power levels of 4 MW, the on axis electric field at the cathode exceeds 300 MV/m, corresponding to an average accelerating gradient of 200 MV/m over the first half cell of the gun. Breakdown was observed at power levels above 5 MW. Electron bunches were produced by 20 μJ, 1 ps UV laser pulses impinging on the RF gun copper photocathode and were measured with a Faraday cup to have up to 0.1 nC of charge. This corresponds to a peak current of about 100 A, and a density at the cathode of 8.8 kA/cm 2. Multiple output electron bunches were obtained for multiple laser pulses incident on the cathode. Phase scans of laser-induced electron emission reveal an overall phase stability of better than ±20°, corresponding to ±3 ps synchronization of the laser pulses to the phase of the microwave field. A Browne–Buechner magnetic spectrometer indicated that the RF gun generated 1 MeV electrons with a single shot rms energy spread of less than 2.5%, in good agreement with theoretical predictions.

Computational investigation of experimental interaction impedance obtained by perturbation for helical traveling-wave tube structures

Conventional methods used to measure the cold-test interaction impedance of helical slow-wave structures involve perturbing a helical circuit with a cylindrical dielectric rod placed on the central axis of the circuit. It has been shown that the difference in resonant frequency or axial phase shift between the perturbed and unperturbed circuits can be related to the interaction impedance. However, because of the complex configuration of the helical circuit, deriving this relationship involves several approximations. With the advent of accurate three-dimensional (3-D) helical circuit models, these standard approximations can be fully investigated. This paper addresses the most prominent approximations made in the analysis for measured interaction impedance by Lagerstrom (1957) and investigates their accuracy using the 3-D simulation code MAFIA. It is shown that a more accurate value of interaction impedance can be obtained by using 3-D computational methods rather than performing costly and time consuming experimental cold-test measurements.

Geometrical effects in gyrotron coaxial cavities: application to mode selection

A study of the electrodynamical properties of gyrotron coaxial cavities using a conical inner rod has been conducted and compared with cold-test measurements on TE modes over the frequency range 11-14 GHz. On the basis of a geometrical design criterion for resonance of the normal modes, it has been demonstrated that the mode spectrum associated with a purpose-built test coaxial cavity is significantly less dense than that for the empty cavity without the coaxial insert. >