The UCMJ says:

10 U.S. Code § 855 - Art. 55. Cruel and unusual punishments prohibited

U.S. Code

Notes

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Punishment by flogging, or by branding, marking, or tattooing on the body, or any other cruel or unusual punishment, may not be adjudged by any court-martial or inflicted upon any person subject to this chapter. The use of irons, single or double, except for the purpose of safe custody, is prohibited.

(Aug. 10, 1956, ch. 1041, 70A Stat. 56.)

(note: does not mention plasma swords)