This paper presents a review of the experimental achievements related to the development of high-power gyrotron oscillators for long-pulse or CW operation and pulsed gyrotrons for many applications. In addition, this work gives a short overview on the present development status of frequency step-tunable and multi-frequency gyrotrons, coaxial-cavity multi-megawatt gyrotrons, gyrotrons for technological and spectroscopy applications, relativistic gyrotrons, large orbit gyrotrons (LOGs), quasi-optical gyrotrons, fast- and slow-wave cyclotron autoresonance masers (CARMs), gyroklystrons, gyro-TWT amplifiers, gyrotwystron amplifiers, gyro-BWOs, gyro-harmonic converters, gyro-peniotrons, magnicons, free electron masers (FEMs), and dielectric vacuum windows for such high-power mm-wave sources. Gyrotron oscillators (gyromonotrons) are mainly used as high-power millimeter wave sources for electron cyclotron resonance heating (ECRH), electron cyclotron current drive (ECCD), stability control, and diagnostics of magnetically confined plasmas for clean generation of energy by controlled thermonuclear fusion. The maximum pulse length of commercially available 140 GHz, megawatt-class gyrotrons employing synthetic diamond output windows is 30 min (CPI and European KIT-SPC-THALES collaboration). The world record parameters of the European tube are as follows: 0.92 MW output power at 30-min pulse duration, 97.5% Gaussian mode purity, and 44% efficiency, employing a single-stage depressed collector (SDC) for energy recovery. A maximum output power of 1.5 MW in 4.0-s pulses at 45% efficiency was generated with the QST-TOSHIBA (now CANON) 110-GHz gyrotron. The Japan 170-GHz ITER gyrotron achieved 1 MW, 800 s at 55% efficiency and holds the energy world record of 2.88 GJ (0.8 MW, 60 min) and the efficiency record of 57% for tubes with an output power of more than 0.5 MW. The Russian 170-GHz ITER gyrotron obtained 0.99 (1.2) MW with a pulse duration of 1000 (100) s and 53% efficiency. The prototype tube of the European 2-MW, 170-GHz coaxial-cavity gyrotron achieved in short pulses the record power of 2.2 MW at 48% efficiency and 96% Gaussian mode purity. Gyrotrons with pulsed magnet for various short-pulse applications deliver Pout = 210 kW with τ = 20 μs at frequencies up to 670 GHz (η ≅ 20%), Pout = 5.3 kW at 1 THz (η = 6.1%), and Pout = 0.5 kW at 1.3 THz (η = 0.6%). Gyrotron oscillators have also been successfully used in materials processing. Such technological applications require tubes with the following parameters: f > 24 GHz, Pout = 4–50 kW, CW, η > 30%. The CW powers produced by gyroklystrons and FEMs are 10 kW (94 GHz) and 36 W (15 GHz), respectively. The IR FEL at the Thomas Jefferson National Accelerator Facility in the USA obtained a record average power of 14.2 kW at a wavelength of 1.6 μm. The THz FEL (NOVEL) at the Budker Institute of Nuclear Physics in Russia achieved a maximum average power of 0.5 kW at wavelengths 50–240 μm (6.00–1.25 THz).

/pdf/state-of-the-art-of-high-power-gyro-devices-and-free-5avfirj4z9.pdf

State-of-the-Art of High-Power Gyro-Devices and Free Electron Masers

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

Powerful sources of coherent radiation in the sub-terahertz and in the terahertz frequency range of the electromagnetic spectrum are necessary for a great and continuously expanding number of applications in the physical research and in various advanced technological processes as well as in radars, communication systems, for remote sensing and inspection etc.. In recent years, a spectacular progress in the development of various gyro-devices and in particular of the powerful high frequency (sub-terahertz and terahertz) gyrotron oscillators has demonstrated a remarkable potential for bridging the so-called terahertz power gap and stimulated many novel and prospective applications. In this review paper we outline two series of such devices, namely the Gyrotron FU Series which includes pulsed gyrotrons and Gyrotron FU CW Series which consist of tubes operated in a CW (continuous wave) or long pulse mode, both developed at the FIR FU Center. We present the most remarkable achievements of these devices and illustrate their applications by some characteristic examples. An outlook for the further extension of the Gyrotron FU CW Series is also provided.

Development and Applications of High—Frequency Gyrotrons in FIR FU Covering the sub-THz to THz Range

This report gives an update of the worldwide experimental achievements in the development of long-pulse gyrotron oscillators for fusion plasma heating, plasma diagnostics and materials processing. In addition, this work gives a short overview of the present development status of coaxial-cavity multi-megawatt gyrotrons, gyrotrons for technological and spectroscopy applications, relativistic gyrotrons, quasi-optical gyrotrons, cyclotron autoresonance masers, gyro-amplifiers, gyro-BWO's, free electron masers and of vacuum windows for such high-power mm-wave sources.

/pdf/state-of-the-art-of-high-power-gyro-devices-and-free-1mmeiw5vph.pdf

State-of-the-Art of High Power Gyro-Devices and Free Electron Masers. Update 2011. (KIT Scientific Reports ; 7606)

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

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

An increase in the frequency of microwave used for the processing of materials has a great potential for the applications We developed the material heating system by using a 300GHz gyrotron This system are consisted of a 300 GHz, 35 kW, CW gyrotron with a cryogen free 12 T superconducting magnet, a corrugated circular waveguide and an applicator The circular corrugated waveguide (id = 635cm) with a corrugated period and depth of 254 /spl mu/m have been designed The applicator have been designed both volumetric heating by uniformly distributed microwave and surface heating by a focused wave beam

http://ieeexplore.ieee.org/iel5/10504/33267/01572569.pdf

Development of the material processing system by using a 300 GHz gyrotron

The Japanese prototype fast breeder reactor MONJU developmental project is of prime importance in the establishment of the commercialized fast breeder reactor technology in Japan. This work presents new results obtained by the 3D hexagonal transport nodal code NSHEX, which for the first time has been applied to MONJU criticality analysis in whole core simulation and up to 70 energy groups. Significant energy-group approximation effect on k eff caused by the collapsing into coarse energy-group structure has been found and then confirmed separately using the Monte Carlo analysis. On the basis of the presented applied results, a method of transport correction evaluation, based on 70 energy-group approximation can be recommended instead of the conventional few-group method that assumes inter-independency of energy-group approximation and transport effect.

https://www.tandfonline.com/doi/pdf/10.1080/18811248.2004.9715512

Transport Criticality Analysis of FBR MONJU Initial Critical Core in Whole Core Simulation by NSHEX and GMVP

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.

Junichi Ishibashi

Papers

High Temperature Thermal Insulation System for Millimeter Wave Sintering of B4C

Development of the material processing system by using a 300 GHz gyrotron

Transport Criticality Analysis of FBR MONJU Initial Critical Core in Whole Core Simulation by NSHEX and GMVP

Ceramics sintering using a 24 GHz gyrotron system

3D transport theory method based on MOC for analyzing integral data of transmutation