Two-dimensional leapfrog scheme for trajectories of relativistic charged particles in static axisymmetric electric and magnetic field

A method for the calculation of two-dimensional particle trajectories is proposed in this work. It makes use of the cylindrical symmetry and the simplification of the static electric field, so that there should be no systematic error for the centered large-orbit rotations nor for the acceleration or deceleration in a uniform electric field. The method also shows a lower error level than the standard Boris method in many cases. Typical applications of this method are for example, electron microscopes, electron guns and collectors of gyro-devices as well as of other vacuum tubes, which can be described in axisymmetric cylindrical coordinates. Besides, the proposed method enforces the conservation of canonical angular momentum by construction, which is expected to show its advantages in the simulation of cusp electron guns and other components relying on non-adiabatic transitions in the externally applied static magnetic field

Novel High-Frequency Electric Field Sweeping Concept for High-Power Gyrotron Collectors

Future fusion power plants will require for plasma heating and noninductive current drive high-power gyrotrons, each of which generates 2 MW of continuous-wave microwave power, while another 2 MW in the spent electron beam is dissipated as heat on the collector wall. In today’s 1-MW continuous-wave gyrotrons, collector coils superimpose an ac (10–50 Hz) magnetic field to sweep the hot spots of spent electrons over a large area. However, to double today’s power, it will also be critical to reduce the hot spot dwell time preventing significant increase of material fatigue. This can be achieved by increasing the sweeping frequency. However, a higher frequency magnetic field would hardly penetrate the metallic collector vessel due to eddy currents. Instead of magnetic field, sweeping with electric fields is proposed for the first time. The presented mechanism is capable to apply several orders higher sweeping frequency to reduce the periodic variation of temperature, and thus, the device lifetime can be extended

Generation of 1.5MW-140GHz pulses with the modular pre-prototype gyrotron for W7-X

In anticipation of an Electron Cyclotron Resonance Heating system upgrade for the stellarator Wendelstein 7-X, a 1.5 MW – 140 GHz continuous-wave gyrotron is under development. In order to provide a first experimental verification of the scientific RF and electron beam optics design of the gyrotron with ms pulses, the Karlsruhe Intitule of Technology has developed a short-pulse pre-prototype gyrotron. In this work, we present details regarding the construction of the pre-prototype as well as measurements from the first experimental campaign delivering up to 1.6 MW in short pulses

Gyrotron multistage depressed collector based on E × B drift concept using azimuthal electric field. II: Upgraded designs

Multistage Depressed Collectors (MDCs) are nontrivial for high-frequency gyrotrons. A basic conceptual design of an E x B MDC using azimuthal electric fields was proposed in Part I of this series. In the present work, several upgraded design proposals based on the basic one will be elaborated. These proposals will significantly reduce the back-stream of electrons, which was the main drawback of the basic design proposal. Another upgraded design proposal will shrink the length and maximal radius of the MDC to be only a fraction of its full-length version. A conceptual design of the final MDC proposal will be given at the end

Toward the First Continuous Wave Compatible Multistage Depressed Collector Design for High Power Gyrotrons

The multistage depressed collector (MDC) is essential to significantly increase the overall efficiency of the gyrotron. To date, a short pulse (SP) MDC prototype system has been manufactured and is currently under test. The long-term goal that makes the most sense is to use MDCs on 2-MW fusion gyrotrons in continuous wave (CW) operation. To achieve this, a CW MDC system based on the same physical principle as the SP system is designed and analyzed for the first time. The highlights of this design are the sweeping systems to keep the thermal loading within an acceptable limit when the MDC is operated in CW. In the present analysis, the expected performance and size of the new CW MDC design are compared with that of the SP MDC prototype and with the corresponding single-stage depressed collectors (SDCs) as a reference. In addition, the effects of thermal expansion in CW operation are analyzed and discussed

Mechanical Design of the Short Pulse E×B Drift Two-Stage Depressed Collector Prototype for High Power Gyrotron

Multistage depressed collector (MDC) technology is capable of significantly increased overall tube efficiencies of vacuum electronic devices compared to conventional single stage depressed collectors (SDC). The spent electron beam sorting as used for TWT and klystron collectors is not effective in the high stray magnetic field of gyrotrons. For that reason, many new design approaches based on E×B drift concept have been theoretically investigated during the last years at KIT. The mechanical design for the first MDC for a high power gyrotron is finalized and the production started end of 2020. In this work, the fundamentals of the mechanical design and the cooling principle of the electrodes are presented

Mechanical Design of the Short Pulse E×B Drift Two-Stage Depressed Collector Prototype for High Power Gyrotron

Multistage depressed collector (MDC) technology is capable of significantly increased overall tube efficiencies of vacuum electronic devices compared to conventional single stage depressed collectors (SDC). The spent electron beam sorting as used for TWT and klystron collectors is not effective in the high stray magnetic field of gyrotrons. For that reason, many new design approaches based on E×B drift concept have been theoretically investigated during the last years at KIT. The mechanical design for the first MDC for a high power gyrotron is finalized and the production started end of 2020. In this work, the fundamentals of the mechanical design and the cooling principle of the electrodes are presented