Masafumi Fukunari

Replacement of chemical rocket launchers by beamed energy propulsion

Microwave Rocket is a beamed energy propulsion system that is expected to reach space at drastically lower cost. This cost reduction is estimated by replacing the first-stage engine and solid rocket boosters of the Japanese H-IIB rocket with Microwave Rocket, using a recently developed thrust model in which thrust is generated through repetitively pulsed microwave detonation with a reed-valve air-breathing system. Results show that Microwave Rocket trajectory, in terms of velocity versus altitude, can be designed similarly to the current H-IIB first stage trajectory. Moreover, the payload ratio can be increased by 450%, resulting in launch-cost reduction of 74%.

Rocket Propulsion Powered Using a Gyrotron

This paper presents a review of a beamed energy propulsion rocket, the Microwave Rocket, which produces propulsive thrust from millimeter-wave beams transferred from the ground. The thrust is generated through millimeter-wave discharge driven in a cylindrical thruster. As a high-power millimeter-wave generator, a Gyrotron is promising as the beam source. The salient benefit of Microwave Rockets is the resultant drastic cost reduction of mass transportation into space. We have already conducted launch experiments and have achieved continuous thrust generation under multi-pulse operation. Recently, a long-distance beam transfer system has been developed. Ignition tests have been conducted. The physics of the millimeter-wave discharge remain unclear. Additional studies using experimentation and calculations must be conducted to optimize the thrust generation.

High power test of a wideband diplexer with short-slotted metal half mirrors for electron cyclotron current drive system

The wideband high power diplexer has been developed for combining and fast switching of high power millimeter waves generated by a dual frequency gyrotron. The actual diplexer was tested at the frequency band of 170 GHz in low power. After adjusting a resonant frequency of diplexer for the gyrotron frequency, the evacuated wideband diplexer with short-slotted metal half mirrors was tested at an incident power of about 150 kW, a pulse duration of 30 ms and a frequency band of 170.2–170.3 GHz. Any discharge damage was not observed in the diplexer.

Thrust performance and plasma generation of microwave rocket with microwave beam space transmission system

Summary form only given. Experiments of microwave beamed energy propulsion using 1 MW-class, 170 GHz gyrotron and a microwave beam space transmission system comprising of a transmission mirror system and a receiving system are described1. The transmission mirror system was designed to expand the radius of an incident beam from 20.4 to 120 mm to suppress beam divergence due to diffraction. Two types of receiving system, a mirror type and a tapered-tube type, were developed. The receiving systems were equipped on the thruster to focus the expanded beam and guide it into the thruster. The characteristics of the transmission mirror system and the two receiving systems were examined using a low-power 170 GHz generator. In the high-power experiments using gyrotron, plasma propagation in the thruster was successfully observed through an acrylic window by fast-framing camera using the transmission mirror system and both receiving systems. Additionally, the pressure histories in the thruster were measured, and the propagation velocity of the shock wave as well as the thrust impulse were deduced. As a result, thrust impulse using the mirror-type receiving system is higher than that of the tapered-tube type. Moreover, it was also found that plasma exhausted from the thruster remains for several milliseconds, and the microwave beam was cut off by remaining plasma at high pulse repetition frequency, in the order of 200 Hz. The phenomenon has important role to optimize the thruster design and operation parameter of the gyrotron for the microwave rocket.

Millimeter‐wave Driven Shock Wave for a Pulsed Detonation Microwave Rocket

A shock wave driven by millimeter wave ionization can be applied into a pulsed detonation engine as a Microwave Rocket. A high pressure induced inside the thruster generates the thrust, thus the shock wave propagation driven by the plasma is important. In this study, to obtain a different propagating structure, the beam profile was transformed from a Gaussian into a Ring and a Flat‐top profile by using a pair of phase correcting mirrors. As a result, the shape of the propagating plasma was changed into a no‐center shape in case of the Ring beam, and it was changed to a wider shape in case of the Flat‐top beam. The propagating velocity of the ionization front of the Flat‐top beam was much lower than that of the Gaussian due to the lower peak power density, and a higher plateau pressure and higher thrust impulse were generated by the Flat‐top beam.

Numerical analysis of plasma structure observed in atmospheric millimeter-wave discharge at under-critical intensity

Atmospheric millimeter-wave discharge at intensity on the order of 1 GW/m2, which is lower than the critical intensity for breakdown by one order, was computed numerically using a tuning parameter to reproduce a wavelength-scale discrete plasmoid structure in a propagating ionization front observed in experiments. In this structure, the plasmoids line up along the E field of the incident beam in the same pitch of 0.9λ. Computational results showed that the structure appears when the electron number density in the plasmoid is greater than the cutoff density of 2.5 × 1020/m3. Interference among an incident wave and reflection waves from a plasmoids produces fringes around the plasmoid. Neighboring plasmoids come to the enhanced point, which is placed at a distance of 0.9λ from the plasmoid center. This knowledge related to the structure is expected to be correct irrespective of the plasma modeling because the revealed forming mechanism is dependent only on the geometrical interference between the incident and reflection.Atmospheric millimeter-wave discharge at intensity on the order of 1 GW/m2, which is lower than the critical intensity for breakdown by one order, was computed numerically using a tuning parameter to reproduce a wavelength-scale discrete plasmoid structure in a propagating ionization front observed in experiments. In this structure, the plasmoids line up along the E field of the incident beam in the same pitch of 0.9λ. Computational results showed that the structure appears when the electron number density in the plasmoid is greater than the cutoff density of 2.5 × 1020/m3. Interference among an incident wave and reflection waves from a plasmoids produces fringes around the plasmoid. Neighboring plasmoids come to the enhanced point, which is placed at a distance of 0.9λ from the plasmoid center. This knowledge related to the structure is expected to be correct irrespective of the plasma modeling because the revealed forming mechanism is dependent only on the geometrical interference between the incident a...

Electromagnetic Modeling of a Complex-Cavity Resonator for the 0.4-THz Second-Harmonic Frequency-Tunable Gyrotron

Complex-cavity resonator with mode conversion is a promising way of improving mode selection properties of a terahertz gyrotron. In this paper, enhancement of the frequency tunability of the second-harmonic 0.4-THz gyrotron by using the complex-cavity resonator is considered. Results of detailed numerical study of the cold-cavity electromagnetic parameters are presented. Using the results of cold-cavity simulations, start-oscillation currents for different modes are calculated.

Strong yellow emission of high-conductivity bulk ZnO single crystals irradiated with high-power gyrotron beam

We report the strong yellow emission of bulk ZnO single crystals irradiated with the high-power gyrotron beam. Hydrothermally grown bulk crystals with high conductivity are irradiated at room temperature with up to 60-W output of a sub-terahertz gyrotron wave source. During gyrotron irradiation, the high-conductivity crystals exhibit intense emissions with a peak of around 2 eV (600 nm) and a longer-wavelength tail. The sample temperatures were also elevated from room temperature to above 1000 K by irradiation. However, when heated up to 1250 K using a heater without irradiation, the ZnO crystals do not exhibit similar visible emissions. We then use the generalized Plancks radiation in non-equilibrium states as an explanation of our experimental observations. The emission peak intensity can be enhanced by the gyrotron-induced non-equilibrium states, and the emission peak position can be related to the Urbach energy. With high intensities in the visible wavelengths, the emissions of the irradiated crystal...

Controllability Study of Propagating Mode Content by an Angle-Adjustable Mirror of a Miter-Bend in EC H&CD Transmission Line

A miter-bend-type mode converter, which has an angle-adjustable mirror, is proposed to control the transmission mode content in the electron cyclotron heating and current drive transmission line. This component excites the higher order mode by injecting a tilted radio frequency beam into a waveguide using the angle-adjustable mirror. A mock-up model of the converter was developed to evaluate the principle of the mode conversion. The experimental result of the mock-up representing the ratio of LP01 mode and LP11 mode was successfully controlled by 10% as the theoretical prediction.

A study of transmission mode conversion miter-bend for EC H&CD transmission line

A mode conversion miter-bend with angle controllable mirror was developed. By changing mirror angle, RF beam angle in the miter bend is controlled and transmission mode contents (LP01 and LP11 modes) are controlled. The miter bend was tested at 170 GHz mW-class low power RF system. The dependence of miter bend mirror angle and ratio of LP01 and LP11 modes was acquired. The concept of mode conversion system was validated.