Who discovered plasma please?

That would be the very first human that saw a lightning bolt.

If you mean who identified and named it, and "harnessed" it, there is more information about it than you will ever need at Plasma (physics) - Wikipedia, the free encyclopedia

Quote:

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This state of matter was first identified in a discharge tube (or Crookes tube), and so described by Sir William Crookes in 1879 (he called it "radiant matter")[1]. The nature of the Crookes tube "cathode ray" matter was subsequently identified by British physicist Sir J.J. Thomson in 1897[2], and dubbed "plasma" by Irving Langmuir in 1928 [3], perhaps because it reminded him of a blood plasma.

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