This Letter uncovers five distinct charge transport modes and their transitions in dual-energy electron beam diodes. We via first-principle particle-in-cell (PIC) simulations establish that the specific mode (e.g., space-charge oscillations) and the current transmitted characteristics are essentially governed by the interplay between the electron beam energy and the injected current density. The effective space-charge-limited (SCL) current (lower than the conventional SCL threshold) is unveiled due to the coupled interactions between two electron beams. A generalized analysis is conducted for $n$-component electron beams, and a theoretical piecewise function for the transmitted current density is proposed, which agrees well with the PIC results under designed conditions. The discovery provides a mechanistic picture of multiple electron beam transport in diodes, paving the way for novel designs of high-performance modern vacuum electronic devices.

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• Electron emission
• Plasma oscillations
• Plasma transport
• Space charge in beams
• Low-temperature plasma
• First-principles calculations in plasma physics
• Particle-in-cell methods
• Scaling methods