Record-breaking high power coherent radiation at a subterahertz frequency region from a gyrotron utilizing second harmonic resonance modes was attained with a simple cavity. In order to aim at high power and high frequency simultaneously, the oscillation mode was selected carefully enough to realize stable radiation free from mode competition. The cavity radius was determined from the viewpoints of the oscillation frequency, the coupling coefficient between the electron beam, and the rf-electric field. The cavity length was also optimized for the highest perpendicular efficiency. In addition, a new electron gun which is capable of generating a thin laminar beam for a large current was introduced. Consequently, single mode second harmonic radiation with powers of 52 and 37 kW at frequencies of about 349 and 390 GHz, respectively, was achieved.

Development of a Novel High Power Sub-THz Second Harmonic Gyrotron

A “Sandwich” type of neutron shielding composite filled with boron carbide reinforced by carbon fiber

We report the design and experimental demonstration of a frequency tunable terahertz gyrotron at 527 GHz built for an 800-MHz dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP-NMR) spectrometer. The gyrotron is designed at the second harmonic ( $\omega = {2}\omega _{c}$ ) of the electron cyclotron frequency. It produces up to 9.3-W continuous microwave (CW) power at 527.2-GHz frequency using a diode type electron gun operating at ${V} = {16.65}$ kV, ${I}_{b} = {110}$ mA in a TE11,2,1 mode, corresponding to an efficiency of ~0.5%. The gyrotron is tunable within ~0.4 GHz by combining voltage and magnetic field tuning. The gyrotron has an internal mode converter that produces a Gaussian-like beam that couples to the HE11 mode of an internal 12-mm i.d. corrugated waveguide periscope assembly leading up to the output window. An external corrugated waveguide transmission line system is built including a corrugated taper from 12- to 16-mm i.d. waveguide followed by 3 m of the 16-mm i.d. waveguide The microwave beam profile is measured using a pyroelectric camera showing ~84% HE11 mode content.

Second Harmonic 527-GHz Gyrotron for DNP-NMR: Design and Experimental Results

In this review paper, we present the recent progress in the development of a series of gyrotrons at the Research Center for Development of Far-Infrared Region, University of Fukui, that have opened the road to many novel applications in the high-power terahertz science and technology. The current status of the research in this actively developing field is illustrated by the most representative examples in which the developed gyrotrons are used as powerful and frequency-tunable sources of coherent radiation operating in a continuous-wave regime. Among them are high-precision spectroscopic techniques (most notably dynamic nuclear polarization-nuclear magnetic resonance, electron spin resonance, X-ray detected magnetic resonance, and studies of the hyperfine splitting of the energy levels of positronium), treatment and characterization of advanced materials, and new medical technologies.

Gyrotrons for High-Power Terahertz Science and Technology at FIR UF

In this paper, we present and discuss experimental results from a microwave sintering of a silica-glass ceramic, produced from a silica xerogel extracted from a sago waste ash. As a radiation source for the microwave heating a sub-millimeter wave gyrotron (Gyrotron FU CW I) with an output frequency of 300 GHz has been used. The powders of silica xerogel have been dry pressed and then sintered at temperatures ranging from 300°C to 1500°C. The influence of the sintering temperature on the technological properties such as porosity and bulk density was studied in detail. Furthermore, X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy have been used in order to study the structure of the produced silica glass-ceramics. It has been found that the silica xerogel crystallizes at a temperature of 800°C, which is about 200°C lower than the one observed in the conventional process. The silica xerogel samples sintered by their irradiation with a sub-millimeter wave at 900°C for 18 minutes are fully crystallized into a silica glass-ceramic with a density of about 2.2 g/cm3 and cristobalite as a major crystalline phase. The results obtained in this study allow one to conclude that the microwave sintering with sub-millimeter waves is an appropriate technological process for production of silica glass-ceramics from a silica xerogel and is characterized with such advantages as shorter times of the thermal cycle, lower sintering temperatures and higher quality of the final product.

Rapid Sintering of Silica Xerogel Ceramic Derived from Sago Waste Ash Using Sub-millimeter Wave Heating with a 300 GHz CW Gyrotron

Boron carbide (B4C) is one of advanced materials and is being used in a wide rage of applications. The unique feature of this material is its large neutron-absorbing cross-section. Some of its most prominent applications are controlling rods in nuclear reactors and radiation protection. 24 GHz microwave processing for B4C ceramics were performed under flowing argon gas using the sintering system. Sintering at the high temperature (up to 2200°C) was achieved using thermal insulation system consists of fiber-board, boron nitride powder, and boron nitride case. The sintered samples were achieved 90 % of theoretical.

High Temperature Thermal Insulation System for Millimeter Wave Sintering of B4C

Sintering at high temperature (up to 2200/spl deg/C) was achieved. Boron carbide has been sintered to 83% of theoretical density without carbon or sintering aides by using a 24 GHz gyrotron as a radiation source. The densification of B/sub 4/C was occurred at 2000/spl deg/C. However the densification showed the plateau at the temperature 2100/spl deg/C. The SEM shows the sintering process for small pores occur at the early stage of sintering below the temperature 2100/spl deg/C. These results suggest the green specimens which doesn't have large pores, make more dense sintered pellets below 2100/spl deg/C.

Ceramics sintering using a 24 GHz gyrotron system

Boron carbide (B4C) is one of advanced materials and is being used in a wide rage of applications. The unique feature of this material is its large neutron-absorbing cross-section. Some of its most prominent applications are controlling rods in nuclear reactors and radiation protection. 24 GHz microwave processing for B4C ceramics were performed under flowing argon gas using the sintering system. The sintered samples were characterized by the density, the shrinkage and SEM micrographs of fracture surface. Above the temperature of 2000°C, the shrinkage and the grain grows were observed.

http://ieeexplore.ieee.org/iel5/6213246/6220476/06220598.pdf

Ultra high temperature sintering by using 24 GHz gyrotron

Boron carbide (B/sub 4/C) is one of advanced materials and is being used in a wide rage of applications The unique feature of this material is its large neutron-absorbing cross-section Some of its most prominent applications are controlling rods in nuclear reactors and radiation protection 24 GHz microwave processing for B/sub 4/C ceramics were performed under flowing argon gas using the sintering system The sintered samples were characterized by the density, the shrinkage and SEM micrographs of fracture surface Above the temperature of 2000/spl deg/C, the shrinkage and the grain grows are observed

http://ieeexplore.ieee.org/iel5/9723/30686/01422298.pdf

High power millimeter and submillimeter wave material processing

Summary form only given, as follows. We report a sintering experiment of alumina (Al/sub 2/O/sub 3/) and B/sub 4/C ceramics by using a compact gyrotron system. A 2.5 kW, 24 GHz compact gyrotron is used as a microwave radiation source.

https://ieeexplore.ieee.org/iel5/8704/27557/01228739.pdf

A. Eremeev

Papers

High Temperature Thermal Insulation System for Millimeter Wave Sintering of B4C

Ceramics sintering using a 24 GHz gyrotron system

Ultra high temperature sintering by using 24 GHz gyrotron

High power millimeter and submillimeter wave material processing

Sintering of high-quality ceramics using a compact gyrotron system