SBIR-STTR Award

High-brightness electron beams are needed for improved power production and reliability of microwave tubes operating in the 80GHz - 300GHz range. At these frequencies, the beam size becomes sufficiently small that beam emittance begins to play a more significant role in the beam dynamics, intensifying thermal management issues and efficiency constraints. To properly model beam formation off the cathode, the intrinsic emittance of the emission due to effects such as material preparation and surface finishing, must be captured in new models. Secondary generation on gun surfaces, particularly on intercepting grids, can lead to thermal tails on the beam and beam halos. Moreover, impact ionization of background gas can enhance beam halos and lead to cathode erosion or poisoning over time, thereby limiting emission life. We propose to develop validated, improved secondary emission and ionization algorithms within the MICHELLE code for modeling high-brightness beam generation, acceleration, and transport. Specifically, these models will capture the non-ideal effects that could lead to beam brightness degradation in electron beam sources commonly used in millimeter-wave tubes. Support for user-control of the new algorithms will be implemented within the MICHELLE interface module in the Analyst finite-element package. Specializations of the Analyst adaptive mesh refinement and optimization functionality will also be developed to improve the capability to design high-brightness guns.

Benefit:
The most substantial benefit of the proposed work is to provide the vacuum electron device and accelerator designers a validated and integrated capability to model high brightness beam components that not only includes improved physics models, but also to have these models incorporated into a design environment. Arguably the most capable and most widely used simulation tools for electron gun and collector design by the US Vacuum Electronics community is the NRL/SAIC MICHELLE code housed within the STAAR Analyst design environment. The proposed effort directly implements the improved capabilities into these tools, and this would provide immediate access to the community when the new capabilities are developed.

Keywords:
emittance-dominated, emittance-dominated, secondary emission, ionization, electrostatic PIC, MICHELLE, millimeter-wave tube, surface finish, high-brighness beam

Millimeter-wave tubes that operate in the 80 to 300 GHz range are important sources of microwave power for future communication, remote sensing, and electronic warfare applications. Effective computer design and optimization capabilities are required to develop these tubes due to their small size, stringent mechanical and beam tolerances, and very high brightness, emittance-dominated electron beams. The objective of the Phase 2 project is the development of new physics and modeling capabilities within the Analyst/MICHELLE design system that enables virtual prototyping and optimization of microwave tube components involving high-brightness beams. The Phase 2 work will build upon prototype extensions to the secondary emission and impact ionization models developed during the successful Phase 1 project. The emission and ionization models in MICHELLE will be modified in the Phase 2 project based upon the Phase 1 studies. Additional development will be done in MICHELLE and Analyst to dramatically lower design/optimization times through extension of existing parallel processing support and improvements to the modeling infrastructure.

Benefit:
The proposed work will leverage the a successful existing design framework, yielding a unique integrated software suite for high-brightness beam devices. These capabilities will enable more rapid development of robust millimeter wave tubes, lowering the cost of these devices for both military and commercial applications and improving the competitiveness of the US tube industry in the worldwide marketplace.

Keywords:
High-Brightness Electron Beam, millimeter-wave tube, MICHELLE, secondary emission, Primary Emission, Impact Ionization