What is the purpose of the suppressor grid in a pentode tube?

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electron tube Elements of the simplest electron tube, the diode.

In a pentode vacuum tube, the suppressor grid is positioned between the screen grid and the anode plate. Its primary purpose is to prevent the passage of secondary electrons between these two components.12

Because the suppressor grid is maintained at the same potential as the cathode, it creates an electrostatic field that repels electrons emitted from the plate surface back toward the plate. This action suppresses the negative effects of secondary emission, which otherwise could interfere with the tube's performance, thereby allowing the pentode to provide greater amplification compared to a tetrode.13