Learn Farsi: تا زمانی که در هیپنوتیزم است، او را رعشه نخواهد گرفت. - As long as he is in hypnosis, a tremor will not overtake him.

This is the accusative experiencer construction. In Farsi, you don't 'have' a tremor; rather, a tremor 'catches' or 'seizes' you. The person experiencing it (u) is the direct object receiving the action, so it takes râ. The tremor (ra'she) is the grammatical subject doing the seizing.

Why is the verb gereftan used here instead of a verb like 'to have' or 'to feel'?

For sudden, involuntary physical or emotional states like a tremor, panic, or sleep, Farsi commonly uses gereftan (to catch/take). The involuntary state 'catches' the person, which is the core of this lesson's experiencer construction.

What is the grammatical structure of nakhâhad gereft?

This is the formal future tense in the negative. It combines the negative present stem of khâstan (to want) conjugated for the third person singular (nakhâhad) with the short infinitive of the main verb (gereft). Since the tremor is the subject, the verb is conjugated for 'it' rather than 'he'.

Does tâ zamâni ke always mean 'as long as'?

It can mean 'as long as' or 'until' depending on the context. Because the main clause here describes a continuous condition (staying free of a tremor) that runs parallel to the time spent in hypnosis, it translates to 'as long as'. If the main clause described a sudden action waiting to happen, it would mean 'until'.