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

A low-temperature, high-power NMR probe head design is described which eliminates the problem of electric are discharge commonly experienced during radiofrequency pulse cycling in a helium environment. A polychlorotrifluoroethylene (Kel-F) coil former, fitted with a solenoid coil, is heat-shrunk onto stainless-steel flanges and spot-welded inside a stainless-steel probe head 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 contact between the sample and cryogenic gas. This design was used in NMR studies in the 4.6 K less than or equal to T less than or equal to 77 K temperature range for RF pulse durations less than or equal to 50 ms land longer for low RF amplitudes) and amplitudes up to similar to 60 G. (C) 2000 Academic Press.