Advanced Gyrotron Project

Gyrotrons are the most powerful source of electromagnetic radiation in the subterahertz frequency range. Recent advances in gyrotron development have unlocked a wide range of applications in scientific and technological studies.

Introduction to the Gyrotron

The gyrotron is an electron tube device that consists of an electron gun,an open-ended cavity resonator, an internal mode converter, a vacuum window, and a collector. The tube is installed in a superconducting magnet in order to produce high-speed cyclotron motion of electrons. Electron beams are emitted from a cathode, accelerated with high voltage, and injected into the cavity. In the cavity, the energy of the gyrating electrons is transformed into the energy of electromagnetic waves owing to the cyclotron resonance maser. The oscillation frequency depends on the cyclotron frequency of the electrons; therefore, it can be changed with the magnetic field strength in the cavity. The excited wave is formed into a Gaussian-like beam with the mode converter, and radiated through the vacuum window. In the FIR UF, on the basis of the achievements of the gyrotron study, a project for the development of advanced gyrotrons has been promoted for application in various studies.Representative results are shown here.

Gyrotron with an internal mode converter,- Gyrotron FU CW G Series

We commenced the development of CW gyrotrons equipped with a converter to produce a Gaussian beam. We can apply these devices in a wide variety of scientific research areas.

Gyrotron FU CW GV
Infrared image of the temperature increase caused by the radiation beam from the Gyrotron FU CW GI.

FU CW GII:

  • Demountable tube
  • Second harmonic osc.
  • Frequency: 395GHz
  • Application: DNP/NMR

FU CW GIII (A second-harmonic oscillation efficiency of 4% was realized using a specially designed electron gun. Continuous operation for over ten hours was achieved):

  • Sealed-off tube
  • Second harmonic osc.
  • Frequency: 395GHz
  • Power: 0.4kW
  • Application: Pulsed ESR

FU CW GI (The first gyrotron of this series):

  • Demountable tube
  • Fundamental harmonic osc.
  • Frequency: 203GHz
  • Power: 0.5kW
  • Application: Direct measurement of positronium hyperfine splitting

FU CW GIV:

  • Sealed-off tube
  • Second harmonic osc.
  • Frequency: 395GHz

FU CW GV:

  • Sealed-off tube
  • Fundamental harmonic osc.
  • Frequency: Stepwise tunable from 160 – 270GHz
  • Power: ~1kW
  • General purpose applications are possible

Compact gyrotrons – Gyrotron FU CW C Series

Using innovative designs for making gyrotron tubes compact, along with a compact magnet and rackmounted power supplies, we realized compact gyrotron systems. Each system can be installed within a 3 m2 floor space and a height of 1.5 m.

FU CW CI:

  • Demountable tube
  • Frequency tunable
  • Fundamental harmonic osc.:107-205GHz,150-320W
  • Second harmonic osc.:290-396GHz,10-30W
  • Applications:Studies on magnetic resonance and DNP-NMR

FU CW CII:

  • Sealed-off tube
  • Fundamental harmonic osc.:203GHz,0.8kW
  • Internal mode converter(Gaussian-like radiation)
  • Operation with rack-mounted power supplies

Development of a high-power pulse gyrotron

A high-power pulse gyrotron mounted on a 12-TSC magnet is under development for use on LHD in the National Institute for Fusion Science.

Using a gyrotron, the ion temperature of a fusion plasma can be measured up to 100million degrees. For this application, more than 100kW is required.

Target power of a high-power gyrotron
The optimum frequency is 300~400 GHz.
A high power exceeding 300 kW is required.

We have achieved the target output power of 300kW for the desired frequency of 303 GHz at the fundamental harmonic.
The long-range transmission test of the gyrotron output with a corrugated waveguide system has been performed.

Stabilization of power

A gyrotron operating system which is under development.

The stabilization of the output power over a long time interval is necessary for the application of the gyrotrons. A highly stable oscillation within a power fluctuation of 0.6% was realized by PID feedback control. We are also developing a computer-control system which can automatically operate the gyrotron.

Continuous frequency tunability

The observed oscillation frequency changes in the Gyrotron FU CW XA.

The continuous frequency tunability is very important for the application of the gyrotrons. We realized a 400-GHz-band gyrotron with a frequency tunability greater than 4 GHz using the mechanism of backward wave oscillation. In FIR-UF, we have developed a multifunction gyrotron in which the oscillation frequency can be continuously changed in different frequency bands.

Development of high-performance electron guns

For the advancement of the gyrotrons, high-performance electron guns are needed to emit electrons as a generator of electromagnetic waves. We developed high-performance electron guns using an original design methodology.