The role of ion bombardment in field emission current instability is clarified experimentally by varying the emission current level and pressure over a wide range. It is found that bombarding ions sputter-off adsorbed gas molecules on the emitter surface and this causes field emission current fluctuation. This current fluctuation caused by ion bombardment is larger than that caused by gas molecule migration when the product of the pressure and the emission current is higher than 7×10-12 PaA. The relative fluctuations turn out to be the logarithm of the product of the pressure and the emission current. The ions are mainly generated close to the emitter due to electron collisions with residual gas.
A scattering-type cell projection method is proposed and its characteristics
are estimated by simulation and experiment. In this method, a mask consisting of thin
scatterers and apertures is used to shape an electron beam. Thus, this method has
advantages over the conventional cell projection method. First, a high aspect ratio
is not necessary to fabricate the mask. Thus, the mask pattern is easily fabricated
and its experimental dimensional accuracy is better than 0.2 µ m. Second,
the simulated heat deposition on the mask drastically decreases. In addition, simulation
and experiment show good contrast of over 105 related to using a limiting aperture to
intercept scattered electrons. As a result, this method is considered to be a key
technology in future electron beam lithography systems.
The magnetic limiter and helical divertor geometry predicted by vacuum magnetic field calculations has been confirmed by measurements with various probe and calorimeter arrays in Heliotron-E. The effect of modification of these configurations with auxiliary magnetic fields or a material limiter on the edge plasma profile is studied. The relation of the edge plasma properties with the main plasma parameters (density, heating power, etc.) are described. The amount of total heat loss to the divertor region is almost the same as that of the heating power. The edge plasma density is approximately proportional to the core plasma density.
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