Particle-in-cell (PIC) codes enable high-performance simulations of plasma dynamics, providing accurate modeling of electron and ion interactions in realistic configuration of fusion devices. Such codes have very long execution times even if they are parallelized using MPI so the need to optimize them is critical. Vector processors can improve performance and parallel execution for many types of applications. This paper studies BIT1, a representative PIC code, to assess the benefit from Vector/SIMD architectures using automatic and manual vectorization. We provide an extensive evaluation study on x86 and RISC-V platforms and improve BIT1 code to enable better vectorization and increase its performance. Our findings show that a portable solution (with minor code updates) enhances the performance using the out-of-the-box compiler's auto-vectorization capabilities on x86 by 76 % and on RISC-V by 2× using auto or manual vectorization with 2 MPI ranks.