Tennessee Code Title 24. Evidence and Witnesses § 24-4-106

(a) The clerk of the court may take probate of witnesses' attendance at any time between the commencement and the final decision of the cause, either in vacation or in term time. The clerk may at that time pay any witness the fees for which the state is liable under §§ 40-17-201 -- 40-17-210, or any witness fees due and may accept an assignment from the witness for all such fees paid. The clerk may take credit in the settlement of the clerk's accounts for all such fees advanced represented by a valid assignment.

(b) In criminal cases, with the approval of the judicial cost accountant and at the request of the district attorney general, the state may advance travel expenses as set out in §§ 24-4-102, 40-17-206 and 40-17-208, to witnesses designated by the district attorney general. The judicial cost accountant shall prescribe the procedures which shall be followed in making travel advances as set forth above.