Electron Beam Source of Nanotube for Free Electron laser

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It is well known that an electron beam with low emittance and low energy spread is emitted from a tip of metal/semiconductor needle by field emission. These characters of the field emitter are favorable for a free electron laser (FEL). In this study carbon nano-tubes (CNTs) were synthesized by three methods of arc discharge, laser ablation and chemical vapor deposition (CVD). Some of them were investigated for the field emission experiment.A single multiwalled CNT on a W needle gave the current of 〜9 μA and a mass of entangled CNTs emitted electrons with current of 2.5 mA which is 〜100 times as high as that of usual W needle cathode. The SEM images of CNTs in pre-/post-experiment suggested that the entangled tubes were frayed by the high electric field and then electrons were emitted mainly from the tip of each CNT. Especially the entangles CNTs coated on a stainless tube with a very small amount of resin presented similar high current with a fluctuation of <4 %. However the current decreased to 〜600 to 40 μA when the electrodes with a hole at the center were set in order to extract the electron beam. It was attributed to the arrival of most of the elements to the first electrode. In the further studies, the geometrical optimum design of the electrodes will improve the current and the focusing property of the electron beam for FEL. Besides the field emission experiment, other remarkable results were obtained such as the first success of forming nano-products including CNT by ultraviolet laser of XeCl excimer and finding the superior transmission filter of polyethylene sheet including CNT in the far-infrared.