Test construction of a large current low voltage CW ion source for ion implantation

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The performance characteristics of the newly constructed Hall accelerator for low voltage CW operation (HALOC) were investigated. Hydrogen gas pressure, magnetic field, and drain current of the power supply determine the HALOC performance. Effects on the extracted hydrogen beam current, energy profiles, V-I characteristics, energy efficiency and so on were investigated in the experiments. Parameter ranges were from 0.93 to 10.6 (Pa) for pressure, 0 to 190 (Gauss) for magnetic field, and 0.1 to 3.0 (A) for drain current. The beam was extracted by appling positive voltage to intermediate electrodes while the anode and two cathodes were grounded. A beam of about 3 A could be extracted successfully for an acceleration voltage of 600 V, for several hours. Particularly, a very stable beam could be extracted by using a Baratron pressure control system. The ignition of the beam could be achieved merely by increasing the pressure to about 0.1 Torr without the use of filaments. Efficiency of current extraction ranges form 70 to 90%. The analyses of the energy profiles by means of a multi-grid analyzer show a very sharp peak around 300 V for an acceleration voltage of 600 V, and the ratio of half width to the peak voltage is less than 0.1. The average energy obtained from the energy profile ranges from 260 to 360 V, depending on the operation conditions, resulting in an energy efficiency between 30 to 70 %. From the above results, It can be seen that the HALOC could have successfully generated a large hydrogen beam current of 3 A, and very stably with a very sharp peak in the energy profile, and continuously for several hours. (So far total running time is about 100 hours.) The 30-70 % energy efficiency meets the requirements posed for HALOC. Further research to further decrease the beam energy, say, down to 100 V, and the extraction of other gas ions (oxygen, in particular) are needed.