Low Velocity Spread Research Articles

Design and Cold Test of a G-Band 10-kW-Level Pulse TE01-Mode Gyrotron Traveling-Wave Tube

Overall design and cold test of a G-band gyrotron traveling-wave tube (gyro-TWT) amplifier are presented. This gyro-TWT aims at achieving a goal of 10-kW pulse output power in the range of 210–220 GHz. It is operated in a circular TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode at the fundamental cyclotron harmonics, which is driven by a 50-kV, 3-A gyrating electron beam. Low velocity spread diode-type magnetron injection gun (MIG), multichannel TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode input coupler, broadband metasurface output window, and lossy material loaded beam–wave interaction circuit are simulated and partially measured. Particle-in-cell (PIC) simulation shows that the designed gyro-TWT can achieve a saturated output power over 10 kW in the range of 210–228 GHz with a beam velocity spread of 2.29%.

Design and Simulation Investigations of W-Band Second Harmonic Periodically Dielectric-Loaded Gyro-TWT

ABSTRACT In this article, the complete design and beam-wave interaction studies of W-band gyro-TWT amplifier have been presented. The gyro-TWT has been designed to operate at second harmonic TE 02 mode to reduce the magnetic field requirement. A triode-type magnetron injection gun has been designed and optimized for low-velocity spread using E-GUN. A novel, mode selective input coupler with a gradually tapered slotted waveguide has been used to feed the desired TE 02 mode and suppress the reflection and spurious oscillations at the input end (upstream). To abridge the absolute instability of the operating mode and backward wave oscillations caused by spurious modes, a periodic lossy dielectric-loaded RF structure has been adopted. The particle-in-cell simulation of the amplifier predicted a peak RF output power of ∼500 kW with ∼3.6 GHz bandwidth, ∼20% efficiency, and ∼32.2 dB saturated gain for the DC input of 100 kV, ∼25 A with 4% axial velocity spread and velocity ratio of 1.22. Further, to extract the output power with minimum reflection, a double-disc window has been studied. An undepressed curved collector is also designed using E-GUN and its simulation predicted a maximum heat wall loading of ∼0.39 kW /cm2.

Design and Experiment of a 200-kW Q-Band Gyro-TWT

In this article, the design and experimental verification of a 200-kW ${Q}$ -band gyrotron traveling wave tube (gyro-TWT) amplifier are presented. A low-velocity spread magnetic injection electron gun (MIG), a new type of multichannel TE01 mode input coupler, and a broadband double-disk output window are adopted in the design to improve the performance of the gyro-TWT. At the same time, the lossy ceramic ring-loaded high-frequency interaction circuit is constructed to provide the required loss for stable operation, and the potential oscillations are effectively suppressed. Saturated peak power of 208 kW and 12.5-kW average output power are measured at 47 GHz by hot test, corresponding to a saturated gain of 50.2 dB, an efficiency of 29.4%, and a −3-dB bandwidth of 5.5 GHz.

Design and Experiment of a High Average Power Ku-Band TE01 Mode Gyro-TWT

A high power Ku -band TE01 mode gyrotron traveling wave tube amplifier (gyro-TWT) is designed and experimented in this paper. The emphasis is put on the gyro-TWT with a high average power. In the design process, a low average velocity spread magnetron injection electron gun and a wideband multichannel TE01 mode input coupler are adopted. At the same time, a high average power curved collector is also applied. To suppress the potential gyro-backward wave oscillator interactions, a new type lossy ceramic rings and lossy ceramic pieces hybrid loaded structure is used in the high-frequency interaction circuit of gyro-TWT. In hot test, the developed Ku -band TE01 mode gyro-TWT is driven by a 70-kV 23-A helical electron beam and produce a ~31.5 kW maximum saturated output average power at 16.2 GHz, corresponding to a saturated peak power of ~450 kW (7% duty ratio), a saturated gain of ~40.5 dB, an efficiency of ~28%. The measured 3-dB bandwidth is ~2.1 GHz. The gyro-TWT is found to be zero-drive stable at these operating points.

Simulation of high-efficiency gyrotron with the system of multistage energy recovery

The results of simulations of helical electron beam formation and collecting, as well as high frequency wave-particle interaction processes, in the moderate-power experimental gyrotron with the frequency of 74.2 GHz are presented. Various methods of beam quality and electron efficiency improvement via optimization of electric and magnetic field distributions in the cathode region were realized. In the optimal operating regime with high pitch ratio and low velocity spread, the electron efficiency of about 46 % was calculated for the gyrotron with the magnetron injection gun including a control electrode and a cathode with sectioned emission. In the gyrotron collector region, a system of 4-stage electron energy recovery was used for enhancement of total efficiency of the device. By improving the quality of the electron beam and efficient energy recovery in the collector region, the total efficiency of the gyrotron equal to 71.8% was achieved.

Investigation on the optimal magnetic field of a cusp electron gun for a W-band gyro-TWA

High efficiency and broadband operation of a gyrotron traveling wave amplifier (gyro-TWA) require a high-quality electron beam with low-velocity spreads. The beam velocity spreads are mainly due to the differences of the electric and magnetic fields that the electrons withstand the electron gun. This paper investigates the possibility to decouple the design of electron gun geometry and the magnet system while still achieving optimal results, through a case study of designing a cusp electron gun for a W-band gyro-TWA. A global multiple-objective optimization routing was used to optimize the electron gun geometry for different predefined magnetic field profiles individually. Their results were compared and the properties of the required magnetic field profile are summarized.

Characteristics of a KA-band third-harmonic peniotron driven by a high-quality linear axis-encircling electron beam

We employ a high-quality linear axis-encircling electron beam generated by a Cuccia coupler to drive a Ka-band third-harmonic peniotron and develop a self-consistent nonlinear calculation code to numerically analyze the characteristics of the designed peniotron. It is demonstrated that through a Cuccia coupler, a 6 kV, 0.5 A pencil beam and an input microwave power of 16 kW at 10 GHz can generate a 37 kV, 0.5 A linear axis-encircling beam, and it is characterized by a very low velocity spread. Moreover, the electron beam guiding center deviation can be adjusted easily. Driven by such a beam, a 30 GHz, Ka-band third-harmonic peniotron is predicted to achieve a conversion efficiency of 51.0% and a microwave output power of 9.44 kW; the results are in good agreement with the Magic3D simulation. Using this code, we studied the factors influencing the peniotron performance, and it can provide some guidelines for the design of a Ka-band third-harmonic peniotron driven by a linear electron beam and can promote the application of high-harmonic peniotrons in practice.

Genetic Algorithm-Based Shape Optimization of Modulating Anode for Magnetron Injection Gun With Low Velocity Spread

The magnetron injection gun (MIG) is an important component in the gyro-traveling wave tube (gyro-TWT). The electron velocity spread induced to the mismatch of the electric and magnetic fields influences the performance of gyro-TWT. To improve electron beam quality, we designed a modulating anode with curved geometry. And the multi-objective genetic algorithm was employed to optimize the curved geometry. An electron beam with a velocity ratio of 1.05 and low transverse velocity spread of 0.31% in a MIG for a Q-band gyro-TWT is obtained. Compared with the previous design with a transverse velocity spread of 1.17%, the electron beam performance got improved. And the thermal analysis and parametric sensitivity were done. The curved MIG can stably provide an electron beam with a transverse spread lower than 0.8%.

Computational Design and Optimization of a Magnetron Injection Gun

The magnetron injection gun (MIG) is an important component in a gyro-travelling wave tube. To improve the efficiency of the MIG design process, a design tool based on ANSYS Workbench combining with other commercially available software, has been developed. The design process for a Q-band triode MIG is described. A pitch factor of 1.004 and low axial velocity spread of 1.54% were achieved. The results of design tool were validated by EGUN and by numerical calculation.

Double-beam magnetron injection gun

A double-beam magnetron injection gun was used to improve the output power of gyrotrons. A double-beam magnetron injection gun can output two relativistic electron beams, which is a better way to raise the current of the magnetron injection gun without reducing the quality of electron beams. Compared with the double-anode magnetron injection gun with the same output current, the double-beam magnetron injection gun can reduce velocity spread and improve the quality of electron beams, because of its smaller influence of the space charge. Using the software MAGIC, a double-beam magnetron injection gun with a modest velocity ratio and a low velocity spread of electron beams was designed.

Simulation and Experiment of a Ku-Band Gyro-TWT

Design techniques and experimental results are presented on a Ku-band TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode gyro-traveling wave tube. The hot test of this amplifier gives more than 153-kW output power, 2.3-GHz bandwidth (14%), 41-dB saturated gain, and 20% efficiency driven by a 63 kV, 12-A electron beam with a pitch angle (v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sub> ) of 1.2, and velocity spread of 5%. A linear polarized TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode input coupler is used to introduce the input power. The stability of the amplifier from oscillation, including both the operating TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode and the backward wave TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> mode, has been investigated with linear codes, nonlinear selfconsistent theory, and 3-D PIC CHIPIC simulation. To suppress the potential gyro-backward wave oscillator interactions, the high frequency circuit is loaded with lossy ceramic rings. The lossy structure is optimized by nonlinear theory and 3-D PIC simulation. A low velocity spread magnetron injection gun is designed with a new structure.

低速度零散的双阳极磁控注入电子枪设计

低速度零散的双阳极磁控注入电子枪设计

Analysis and design of a double-anode magnetron injection gun for 1THz gyrotron

Based on the electron optics theory, through a massive numerical calculation by programming, a double-anode magnetron injection gun (MIG) for a 1THz gyrotron is designed. The method of calculation and design of MIG is expounded, and the problem that high magnetic compression ratio in THz gyrotron(compression ratio of 125 in electron gun for 1THz gyrotron in this paper)could lead to the reversal of direction of electron flow is also detailedly analyzed and simulated. Through simulation and optimization, an MIG with a modest velocity ratio of the beam (=1.3) and a low velocity spread (8%) is designed.

Numerical Simulation of a Double-anode Magnetron Injection Gun for 110 GHz, 1 MW Gyrotron

A 40 A double-anode magnetron injection gun for a 1 MW, 110 GHz gyrotron has been designed. The preliminary design has been obtained by using some trade-off equations. The electron beam analysis has been performed by using the commercially available code EGUN and the in-house developed code MIGANS. The operating mode of the gyrotron is TE22,6 and it is operated in the fundamental harmonic. The electron beam with a low transverse velocity spread (\( \delta {\beta_{ \bot \max }} = 2.26\% \)) and the transverse-to-axial velocity ratio of the electron beam (α) = 1.37 is obtained. The simulated results of the MIG obtained with the EGUN code have been validated with another trajectory code TRAK. The results on the design output parameters obtained by both the codes are in good agreement. The sensitivity analysis has been carried out by changing the different gun parameters to decide the fabrication tolerance.

Magnetron injection gun for a broadband gyrotron backward-wave oscillator

The magnetron injection gun is capable of generating relativistic electron beam with high velocity ratio and low velocity spread for a gyrotron backward-wave oscillator (gyro-BWO). However, the velocity ratio (α) varies drastically against both the magnetic field and the beam voltage, which significantly limits the tuning bandwidth of a gyro-BWO. This study remedies this drawback by adding a variable trim field to adjust the magnetic compression ratio when changing the operating conditions. Theoretical results obtained by employing a two-dimensional electron gun code (EGUN) demonstrate a constant velocity ratio of 1.5 with a low axial velocity spread of 6% from 3.4–4.8 Tesla. These results are compared with a three-dimensional particle-tracing code (computer simulation technology, CST). The underlying physics for constant α will be discussed in depth.

Experimental verification of low-velocity spread axis-encircling electron beam

We have experimentally demonstrated a low-velocity spread, axis-encircling electron beam using a comparatively simple Pierce-type electron gun and single cusp magnetic field based on a recent theory [Jeon et al., Appl. Phys. Lett. 80, 3703 (2002)] developed with the assumption of small orbit gyration before the magnetic cusp, in which every physical property has been analyzed and the possibility of zero percent axial velocity spread was concluded. The velocity ratio and the axial velocity spread were measured to compare the theory with varied operation conditions of the electron gun. These results agree well with our hypothesis.

Crystallisation of ion beams in the rf quadrupole storage ring PALLAS

The crystallisation of laser-cooled Mg+ ion beams circulating in the table-top rf quadrupole storage ring PALLAS at a velocity of the order of 2800 m/s (beam energy 1 eV) is reviewed. Emphasis is given to the description of the experimental techniques that were required for this first realisation of crystalline beams. The equivalence of the equations of motion for rf electric and magnetic confinement and thus for PALLAS and high-energy storage rings is pointed out. The phase transition is indicated by the detection of a sudden collapse of the transverse beam size, by the low velocity spread, and by the exceptional stability of the crystalline state, persisting for more than3000 revolutions or 106 focusing periods without any cooling.

Cooling and bunching of ion beams for collinear laser spectroscopy

A greatly increased sensitivity in collinear laser spectroscopy experiments has been achieved by the application of new on-line ion cooling and bunching techniques. Cooling of a low-energy ion beam to low emittance and low velocity spread is shown to increase the peak efficiency while bunching the beam results in highly efficient background suppression.

Analysis of Axis-Encircling Electron Beam Using a Single-Cusp Magnetic Field

The characteristics of an axis-encircling electron beam using an annular Pierce-type electron gun are calculated analytically. The analytical calculation is carried out by considering the initial canonical angular momentum spreads at the cathode and the crossing of the electron beam with the magnetic flux line before the magnetic cusp. The analytically calculated characteristics of an axis-encircling electron beam such as the axial velocity spread, the velocity ratio, the Larmor radius, and the guiding center radius are in good agreement with the simulated result obtained using an electron trajectory program. In this comparison, a 30 kV, 1.0 A electron beam is used with a peak magnetic flux density of 4.38 kG using the magnetic field with a single cusp. The result obtained by this analysis also shows that the electron beam with a fairly low axial velocity spread of less than 1% can be realized by employing a suitable distance between the cathode and magnetic cusp.

Study on velocity spread for axis-encircling electron beams generated by single magnetic cusp

The physical characteristics of an annular Pierce-type electron gun are investigated analytically. The electron gun is used in conjunction with a nonadiabatic magnetic reversal and adiabatic compression region to produce an axis-encircling beam. Typical magnetic field profiles that can generate zero velocity spreads are obtained from the analytical calculation, taking into account initial canonical angular momentum spreads at the cathode and the crossing of the beam trajectory and magnetic flux line before the magnetic cusp. Using this magnetic fields, a fairly low axial velocity spread of less than 1% is achieved by an electron trajectory program [W. B. Hermannsfeldt, Electron Trajectory Program (Stanford Linear Acceleration Center, Stanford, CA, 1979)], which agrees well with that by analytical estimation.