Jian-Bo Jin

Self-consistent nonlinear investigation of an outer-slotted-coaxial waveguide gyroton traveling-wave amplifier

A nonlinear self-consistent simulation code is employed to investigate the behavior of the outer-slotted-coaxial waveguide gyrotron traveling-wave amplifier (gyro-TWA). The influences of the velocity pitch, frequency, and input power of the electron beam on efficiency, output power, and saturated gain are simulated and discussed in detail. It is predicted that this design with 95 GHz, TE/sub 3,1/ will yield a peak output power of 264.3 KW, a peak efficiency of 33.7%, and saturated gain of 44.2 dB.

Coaxial-waveguide gyrotron amplifier operating with high power and ultrahigh gain in Millimeter and submillimeter waves

A coaxial-waveguide gyrotron-traveling wave amplifier is proposed, which may be suitable for the operation in the spectrum of the short millimeter and submillimeter waves with good mode selectivity, high power, and ultrahigh gain. An example is presented in terms of the linear gyrokinetics and nonlinear simulations. Theoretical results show that tens of kilowatts with ultrahigh gain up to 67 dB might be achieved for the operation of the coaxial-waveguide mode TE/sub 28,16/ in the fundamental cyclotron harmonic at the frequency of 140 GHz. The power enhancement by a tapered magnetic field is discussed.

Nonlinear theory of a cyclotron autoresonance maser (CARM) amplifier with outer-slotted-coaxial waveguide

A self-consistent nonlinear theory for the outer-slotted-coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier is presented, which includes the characteristic equation of the wave, coupling equation of the wave with the relativistic electron beam and the simulation model. The influences of the magnetic field, the slot depth and width are investigated. The interesting characteristic of the device is that the mode competition can be efficiently suppressed by slotting the outer wall of the coaxial waveguide. A typical example is given by the theoretical design of a 137 GHz outer-slotted-coaxial-waveguide CARM amplifier by utilizing an electron beam with a voltage of 90 kV, current of 50 A, velocity pitch angle of 0.85 and a magnetic field of 43.0 kG. The nonlinear simulation predicts a power of 467.9 kW, an electronic efficiency of 10.4% and a saturated gain of 46.7 dB, if the electron beam has no velocity spread. However, the axial velocity spread deteriorates the device; for example, if the axial velocity spread is 2%, the peak power decreases to 332.4 kW with an efficiency of 7.4% and a saturated gain of 45.22 dB. Simulation shows that the efficiency of the outer-slotted-coaxial-waveguide CARM amplifier may be increased from 10.4% to 29.6% by tapering the magnetic field.

Nonlinear simulation of power enhancement of an electromagnetic-wave-wiggler free-electron laser by employing a tapered axial guide magnetic field

Three-dimensional (3-D) simulations are presented to demonstrate the power enhancement in an electromagnetic-wave-wiggler free-electron laser by employing a tapered axial guide magnetic field. Results show that the power of 93 kW, which was obtained in a recent experiment, could be increased up to 350 kW by using a proper taper of the axial guide magnetic field. In contrast to a linear conclusion, the efficiency enhancement is not as remarkable as expected, if the taper of the axial guide magnetic field begins close to or after the position where the system has run to saturation. The power enhanced by properly tapering the guide magnetic field is stronger than that which occurs when the guide magnetic field is at resonance but untapered. The device could not operate normally if the guide magnetic field was too weak to focus the electron beam.

Efficiency Enhancement of Coaxial-Cavity Electron Cyclotron Resonance Maser by Tapering Guide Magnetic Field

A coaxial-cavity cyclotron resonance maser (CRM) oscillator with tapered guide magnetic field is proposed. It is shown that the transmission quality can be improved by tapering the guide magnetic field. Simulation indicates that the efficiency of a millimeter-wave gyrotron oscillator may be reached up to 38.7% by optimizing the tapered magnetic field.

Power enhancement of a Doppler-frequency-up-shift scattered wave by a relativistic electron beam drifting in a reversed, tapered axial guide magnetic field

A transverse-electric (TE) wave with a Doppler-upshift frequency may be excited when a backward wave is scattered by a relativistic electron beam. Credible three-dimensional nonlinear simulations are presented to demonstrate the power enhancement of the scattered wave by making use of a properly reversed, tapered axial guide magnetic field. The influences of the taper slope and the taper starting point of the reversed axial guide magnetic field on the power of radiation fields are discussed. Simulations show that the peak power of 93 kW at a wavelength of 3 mm observed in a recent experiment could be increased up to 500 kW through the proposed method. Compared to the case of a tapered positive guide magnetic field, the method studied in the present paper is more effective to enhance the power of the scattered wave.

Nonlinear Analysis of Relativistic Motion of Electrons in Self-Amplified Spontaneous Emission Free-Electron Laser in Ultraviolet and X-Ray Spectral Regions

The free-electron laser (FEL) based on the self-amplified spontaneous emission (SASE) is an effective candidate of the coherent optical sources at wavelengths in ultraviolet and x-rays. It requires a relativistic electron beam with extremely high quality and extremely stable transmission. In this paper we analyze the dynamic behavior of the relativistic electron in that device by calculating the entropy-like quantity. Results show that if there is no adiabatic field of the wiggler, the electron beam may have great fluctuation in velocity space and diverge in configuration space.

Parameter optimum in a free-electron laser

In this paper the beam transmission of a millimeter wave free-electron laser (FEL) experiment is investigated. The simulation results show a total loss of 34% of the electron beam current in the Group-I orbits regime, which is far smaller than the previous simulations, but no loss of the e-beam current is found in the Group-II orbits regime and the reversed guide magnetic field regime. The influence of the initial transverse velocity of the electron beam on the output power for the reversed guide magnetic field regime is also investigated.

Proposal of a coaxial-cavity gyrotron with tapered guide magnetic field

In this paper a gyrotron with tapered guide magnetic field is proposed. The transmission quality of the electron beam in this device is investigated and found to be improved. Simulations show the electronic efficiency of the FZK gyrotron experiment might be increased up to 38.7% by tapering the guide magnetic field.

Effect of Initial Pitch-Angle of Electrons on Output Power of Free-Electron Laser with a Reversed Guide Magnetic Field

A nonlinear simulation is presented to the output power of the MIT free-electron laser experiment, which is in agreement with the measured data. It is found that the initial pitch-angle of the electrons substantially influences the output power and should be optimized carefully.