Design of a high-power NMR probe for low-temperature studies

A low-temperature, high-power NMR probe head design is described which elim inates the problem of electric are discharge commonly experienced during ra diofrequency pulse cycling in a helium environment. A polychlorotrifluoroet hylene (Kel-F) coil former, fitted with a solenoid coil, is heat-shrunk ont o stainless-steel flanges and spot-welded inside a stainless-steel probe he ad assembly connected to a hollow coaxial transmission-line probe shaft, By this means, the sample coil and all high-voltage elements can effectively be isolated in a vacuum, while at the same time permitting good thermal con tact between the sample and cryogenic gas. This design was used in NMR stud ies in the 4.6 K less than or equal to T less than or equal to 77 K tempera ture range for RF pulse durations less than or equal to 50 ms land longer f or low RF amplitudes) and amplitudes up to similar to 60 G. (C) 2000 Academ ic Press.