Background Vacuum breakdown under intense electromagnetic fields in relativistic backward wave oscillator (RBWO) critically compromises the reliability of high power microwave sources. To meet increasingly demanding power capacity requirements, it is essential to further enhance the performance of resistance to vacuum breakdown. The processes of electron emission and electron beam bombardment are closely associated with the physical interactions at the material surface. Furthermore, studies have indicated that refining the grain size of titanium surfaces may significantly increase their ability to withstand intense electromagnetic field-induced vacuum breakdown.

Purpose Given that surface self-nanocrystallization is a highly effective approach for improving the mechanical properties of metallic materials, particularly through grain refinement at the nanometer scale, this article proposes a novel strategy utilizing surface self-nanocrystallization technology to suppress vacuum breakdown in RBWO under intense electromagnetic fields. Experimental validation was conducted to evaluate the effectiveness of this method in inhibiting vacuum breakdown under such extreme conditions.

Methods This paper employs commercially pure titanium (TA2) as the research object, utilizing ultrasonic peening (USP) and microshot peening (MSP) as two distinct nanoscale surface processing techniques. The nanostructural effects were characterized through scanning electron microscopy coupled with X-ray diffraction analysis. Subsequently, field emission testing apparatus and an X-band RBWO were employed to conduct comparative experiments on field electron emission characteristics and vacuum breakdown performance in high power microwave generation, respectively.

Results USP produces a gradient nanocrystalline layer extending 2−3 μm beneath the surface, with grain size refined to approximately 40 nm. MSP generates a more extensive gradient nanocrystalline layer reaching 30 μm in depth, with surface grains refined to about 48 nm. After undergoing MSP and USP treatment, TA2 exhibits a sequential reduction in the field emission current under the identical electric field; the tail erosion in the output microwave waveforms vanishes, and damage in the high-field region of the slow wave structure is mitigated.

Conclusions The results demonstrate that both MSP and USP treatments successfully refine the surface grain size of TA2 to the nanoscale range of several tens of nanometers, forming a gradient nanostructured layer. Such surface self-nanocrystallization effectively suppresses field-induced electron emission and vacuum breakdown under intense electromagnetic fields. Notably, the USP treatment exhibits particularly pronounced inhibitory effects. This methodology provides technical support for further enhancing the power capacity of high power microwave generators based on RBWO.