Electrons, accelerated by electric fields and focused by magnetic fields to scan across a phosphor-coated screen.
Electrons.
The CRT was bulky, hot, and heavy, used large amounts of power, and was prone to disruptions of glare and magnetic and electrical fields
To create an electron cloud that can be shaped into a beam.
Thomson. William Crookes and others early experimented with the cathode ray tube, and thus discovered the electron.