I can't think of a single-word equivalent for carcéral in the physical sense - except something like 'prison' used adjectivally - as in 'he was given a prison sentence'. There is a more formal word for this: 'he was given a custodial sentence'. 'Prison environment' would be fine in some contexts, but over-the-top (=excessive, sometimes abbreviated to 'OTT') in others:
:up: "I am doing a study of criminals in a prison environment"
:down: "The judge told me I had to spend 5 years in a prison environment' ;-)
PS - re my 'in the physical sense': I had in mind the Spanish (Fr also?) cárcel, as I hadn't met the word carcéral before, so I meant a one-word adjective that means 'pertaining to a dungeon-like room'.