The accumulation of helium and/or hydrogen in nuclear materials may cause performance deterioration of the materials.In order to provide a unique tool to investigate the He-and/or H-caused problems

such as interaction of helium with hydrogen and defects

formation of gas bubbles and its evolution

and the related effects

we designed a low energy（≤20 keV） cold cathode Penning ion source

which will be interfaced to a 200 kV transmission electron microscope（TEM）

for monitoring continuously the evolution of micro-structure during the He+ or H+ ion implantation.Studies on discharge voltage-current characteristics of the ion source

and extraction and focusing of the ion beam were performed.The ion source works stably with 15–60 mA of the discharge current.Under the gas pressure of 5×10–3 Pa and 1.5×10–2 Pa

the discharge voltage are about 380 V and 320 V

respectively.The extracted ion current under lower gas pressure is greater than that under higher gas pressure

and it increases with the discharge current and extraction voltage.The ion lens consisting of three equal-diameter metal cylinder focus the ion beam effectively

so that the beam density at the 150 cm away from the lens exit increases by a over one order of magnitude.For ion beams of around 10 keV

the measured beam density is about 200 nA·cm–2

which is applicable for ion implantation and in situ TEM observation for many kinds of nuclear materials.