NEUTRON GENERATOR ION SOURCE PULSER

Apparatus for producing a pulsed high voltage source for use with a pulsed neutron generator in a logging tool in a borehold, the apparatus comprising: (a) means for receiving a high voltage supply (16;48); (b) field effect transistor means comprising at least a pair of field effect transistors (51 to 53 and 54 to 58) serially connected between said high voltage receiving means and ground; (c) an output terminal between the two transistors of said at least one pair or field effect transistor means, said output terminal being adapted to be connected by a conductor (50) to provide pulsed high voltage to a neutron generator (20); and (d) control pulse forming means (70) connected to the gates of the or each respective two transistors, said pulse forming means forming control pulses selectively switching said transistors off and on in timed sequence to thereby connect the output terminal to said high voltage receiving means.