Measuring Electron Beam Currents
I was involved (in the 1990s) in designing Gas mass spectrometers and the preferred method for dealing with the curved ionic "beam" (due to gas atomic/molecular mass and the applied magnetic flux density) was an earthed plate with a slot in it - the curved beam (when at the correct radius due to the precise mass) went thru the slot and hit an electrode which directly fed a transimpedance amplifier.

Some amount of series resistance was tried (mainly because it was felt the transimedance amplifer might be protected by it) but it neither made it more reliable (it was fairly reliable anyway) nor seemed to reduce the effectiveness of the amplifier.

So, the two methods that appeared to work equally good are transimpedance amplifiers and a regular inverting amplifier using op-amps. I can't say if other methods work based on my direct experiences.