The closer spacing of diffraction rings in electron diffraction when electrons travel at higher speeds is primarily due to their shorter de Broglie wavelength. The de Broglie wavelength of a particle is inversely proportional to its momentum, and since momentum increases with speed, higher-speed electrons have shorter de Broglie wavelengths.
The spacing of the diffraction rings in electron diffraction is determined by the interference of the electron waves as they pass through a crystalline sample. The shorter de Broglie wavelength of higher-speed electrons means that the waves are more tightly packed, resulting in a smaller angular separation between the diffraction rings on the screen.
It's important to note that the spacing of the diffraction rings is not directly related to the time it takes for the electrons to reach the screen or any repulsive forces between the electrons. The phenomenon of diffraction arises from the wave nature of electrons, and the spacing of the diffraction pattern is primarily determined by the wavelength of the electron waves.