Storm-trooper, who is a policeman, has energy during trial (7)
I believe the answer is:
tempest
'storm' is the definition.
(tempest is a kind of storm)
'policeman has energy during trial' is the wordplay.
'policeman' becomes 'mp' (abbreviation for Military Policeman).
'has' says to put letters next to each other.
'energy' becomes 'e' (physics symbol as in E=mce).
'during' indicates putting letters inside.
'trial' becomes 'test' (synonyms).
'mp'+'e'='mpe'
'mpe' going within 'test' is 'TEMPEST'.
'trooper who is a' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tempest that I've seen before include "Violent storm (created by Shakespeare?)" , "Shakespearean storm?" , "Big blow" , "An angry storm as in Shakespeare play" , "Bad weather" .)