Keywords:
electromagnetics, multistageCollector
Multistage Depressed Collectors (MDCs) are used to recover energy from a spent beam in linear type microwave tubes such as traveling wave tubes (TWTs) and klystrons. VSim provides the capability to simulate these collectors shaped with arbitrarily complex geometries and depressed with different time-dependent voltage profiles to optimize the recovery efficiency of a design. To demonstrate this capability, we show in this example a 4-stage depressed collector. One can adjust the depressed potentials at each electrode individually to see how the performance of the collector is affected.
This simulation can be performed with a VSimMD or VSimPD license.
The Multistage Collector example is accessed from within VSimComposer by the following actions:
The Setup Window is now shown with all the implemented physics and geometries, if applicable. See Fig. 452.
The simulation geometry consisting of an S-band 4-stage depressed collector is imported into the computational engine from CAD files in stl format. One can easily create new geometry using any CAD program and output or convert the CAD files into stl files for a new simulation design. The detailed import method is provided in the input file. The spent beam profile is taken from a TWT simulation provided by Prof. H. Song at University of Colorado at Colorado Springs.
An optimized design for a MPM module can be found in reference [1]. Users can set preferred spent beam profiles by employing different emission methods or import data in dat format as in this example. A main feature of this input file is that the depressed voltage profiles are time-dependent and are stabilized with a new external circuit model based on special feedback algorithms only available in VSim. Interested users may refer to the publication for more a detailed description and validation. In addition, the convergence of this example is carefully tested.
In this example, the Z coordinate is the direction aligned with the beam axis of the MDC, and the 4 different voltages can be easily assigned at the input panel. Since it is a time domain simulation, the Dey-Mittra algorithm is employed and the accuracy is second-order for the complex boundaries.
After performing the above actions, continue as follows:
After performing the above actions, continue as follows:
The results are then read from the Data Overview in the Visualize Window:
The potential of each of collector surfaces is recorded using a history. To visualize these values as shown in Fig. 455, do the following:
The depressed voltages or beam current/radius can be varied in the input panel for testing runs. One can also change the grid cell numbers to see the convergence of the simulations.