New possibilities of collectors with azimuthal magnetic field for multistage energy recovery in gyrotrons

The results of modeling a collector with 4-stage recovery of residual electron energy for the SPbPU gyrotron with a frequency of 74.2 GHz and an output power of 100 kW are presented. For spatial separation of electrons with different energies, an azimuthal magnetic field created by a toroidal solenoid is used. An increase of the recovery efficiency and a decrease of the current of electrons reflected from the collector is achieved by reducing the spread of the radial position of the leading centers of electron trajectories at optimal parameters of the toroidal solenoid, as well as by using a sectioned electron beam. The trajectory analysis of the spent electron beam in the collector region showed the possibility of achieving the total efficiency of the gyrotron, close to 80%.

Impact of Work function Engineering in Charge Plasma Based Bipolar Devices

In this paper, we have explored and justified the reason behind the degradation in the cutoff frequency of the bipolar transistors evolved from the charge plasma concept. It has been observed that if the work function difference present between the emitter metal contact and silicon is greater than or equal to 0.68 eV ( ϕ m - ϕ SI = 4.05 eV - 4.73 eV), it results in increment in the base width which is the inverse of the cutoff frequency. On top of this, two dimensional TCAD simulation of the different bipolar devices also demonstrate the same base width widening effect into the intrinsic region which is present between the base region and collector region. Apart from this, if this difference is exactly equal to 0.5 eV ( ϕ m - ϕ SI = 4.23 eV - 4.73 eV) then the base width widening effect can be completely eliminated from the bipolar devices base on the charge plasma.

Development of multistage energy recovery system for gyrotrons

A four-stage depressed collector based on spatial separation of electrons with different energies in the crossed electric and magnetic fields was developed for the experimental SPbPU gyrotron. Modeling of the system of electron energy recovery and analysis of the distributions of electric and magnetic fields in the gyrotron collector region were performed. As a result of the theoretical estimations and the trajectory analysis of the helical electron beam, it is shown that the developed system provides recovery of the residual electron energy necessary to achieve the total efficiency of the gyrotron exceeding 70 %.

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.

Высокоэффективный гиротрон с многоступенчатой рекуперацией остаточной энергии электронов

The results of combined simulation of physical processes in a medium power gyrotron of 4-mm wavelength range are presented. The methods of improving the quality of helical electron beam and the electron efficiency of the gyrotron, based on the optimization of electric field distribution in the near-cathode region, are realized. The design of the collector with 4-stage recovery of residual beam energy, based on the method of spatial separation of electrons in crossed azimuthal magnetic and axial electric fields, was developed. The value of total efficiency of the gyrotron equal to 71.8 % was achieved by improving the quality of the electron beam and by efficient energy recovery in the collector region.

Investigation of 4H-SiC Extraction-Enhanced Vertical Insulated-Gate Bipolar Transistor with Lightly Doped Extractor in Collector Region

This paper proposes a new N-type 4H-SiC extraction-enhanced vertical insulated-gate bipolar transistor (E2VIGBT), which uses a partial Schottky contact to the collector region bottom surface as a carrier extractor to enhance the carrier extraction, so that the switching performance will be improved. TCAD simulation shows that, at an operation frequency of 250 kHz, the E2VIGBT offers a turn-off loss decrease of 69.2% and a total energy loss in a single period reduction of 34.4% when compared with conventional field-stop 4H-SiC IGBTs. With further specific optimization, the proposed structure consumes less energy in a much wider frequency range. The simulation results indicate that this new type of IGBT performs better in high frequency applications.

4H-SiC n-Channel DMOS IGBTs on (0001) and (000-1) Oriented Lightly Doped Free-Standing Substrates

We experimentally demonstrate 4H-SiC n-channel, DMOS Insulated Gate Bipolar Transistors (IGBTs) on 180 µm thick lightly doped free-standing n- substrates with an ion-implanted collector region, and metal-oxide-semiconductor (MOS) gate on (0001) and (000-1) surfaces. The IGBTs show an on-state current of 20A/cm2 at a power dissipation of 300W/cm2. Threshold voltage of 7.5V and 10.5V was obtained on Si-face and C-face respectively. Both IGBTs show a small positive temperature coefficient of the forward voltage drop, which is useful for easy parallelization of devices.