Microgenerators that could extract energy from the environment would be very attractive for powering some types of microsystems. One approach uses a mechanical resonant element to transfer seismic vibrations into useful motion. A novel configuration for an electromagnetic microgenerator and an electrostatic microgenerator has been modelled and confirmed by experiments at a small macroscopic scale. This design allows the possibility of a ‘stacked’ array to increase the output. However it is concluded, as with other studies, that few applications are plausible with the outputs that can be achieved. A power output of 6 nW is predicted for a typical single-element electromagnetic microgenerator but at a very low voltage. The electrostatic form delivers more useful voltage but, at the small scale, its reactive impedance is much too high for useful power delivery.
A high performance core snubber using Fe-based soft magnetic alloys composed of ultrafine grain structure cores has been developed to protect an ion source accelerator from electrical breakdowns. Dimension of each core is 900 mm in outer diameter, 400 mm in inner diameter, and 25.4 mm in thickness. Basic characteristics of the core has been investigated and confirmed that the core has a saturation magnetic flux density of 1.35 T with a high relative permeability of about 3500 for a high frequency pulse of 1 MHz. A total magnetic flux of the core snubber is 0.15 Wb with 13 cores and a biasing current. The size of the core snubber could be reduced to about 1/3 from the conventional one composed of Ni–Zn ferrite cores.
The high power ion beams used in the next generation thermonuclear fusion reactors require high current negative ion beams accelerated to high energy, with high efficiency. One way to meet these requirements is to merge multiple low current density H− beamlets into a single high current beam. The feasibility of a high current merging preaccelerator was demonstrated in this experiment by merging 19 beamlets of H− ions distributed over a circular area 80 mm in diameter from a Japan Atomic Energy Research Institute negative ion source. H− ions were extracted at a current density exceeding 10 mA/cm2 at the ion source which operates at 0.13 Pa (1 mTorr), with a low arc power density (70 V×250 A). Spherically curved grids (with built-in magnetic electron suppression) were used in the preaccelerator to focus the extracted beamlets into a single 104 mA, 100 keV beam. The merged beam has a diameter of 23 mm and a converging angle of ±30 mrad at the beam envelope. The rms emittance of the 104 mA merging beam was 1.00 π mrad cm, which is a condition acceptable to the electrostatic quadropole accelerator for further acceleration.
dc voltage holding characteristics were investigated to obtain a data base for designing high-energy and high-power ion sources of neutral beam injectors. We confirmed that the voltage holding characteristics almost obey the clump theory in the experimental gap length of up to 50 mm. The magnetic field in the gap lowered the breakdown voltage in a gas discharge region higher than a pressure of 10−3 Torr. The breakdown voltage of 30% was reduced by seeding cesium on the electrode with one order higher density than that of actual ion source at the pressure region of lower than several mTorr.
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