Measurement of AC Ion Current from Ionizer by Using Faraday Cage
AC ionizer with high frequency became more common in semiconductor industries. Neutralization mechanism of such equipment is, however, not well understood because the measurement of extremely small ion current is interfered by AC induction. Our attempt is to use the Faraday cage that is directly connected to an AC ionizer. At frequencies of 1 Hz and 10 Hz, clear pulse shape ion currents were measured. The amounts of transported charges increase with both applied voltage and pressure. The effect of pressure is more significant than voltage. At higher frequency, the measured current changes from pulse to sinusoidal shape. From the delay time of 1 kHz, the average air velocity between the needle and Faraday cage was calculated. From DC corona measurement inside the nozzle, it became clear that the portion of transported charge to the Faraday cage is quite small.
A Low-Voltage Microwave Plasma Ionizer With Reduced Electric Overstress Due to Displacement Current Coupling From a High-AC Voltage Source
A low-voltage microwave plasma ionizer was proposed as an ac-type ionizer. A structure to improve the ionizing performance and stability of the plasma ionizer was proposed. A dedicated source module was also designed to generate microwave power for the ionizer. The ionizing performance of the proposed ionizer was experimentally investigated using a charged plate monitor, and the factors required to achieve good performance were found. The risk of electric overstress due to displacement current coupling from the ac voltage source in the ionizer was then investigated. It was experimentally confirmed that the proposed microwave plasma ionizer has a much lower risk of electric overstress at a close distance than a conventional ac-type corona ionizer.
Long Ceramic Beam Tubes for Accelerator Magnets
The ceramic beam tubes for the fast and abort kickers and the bucker and pinger magnets used at Fermilab must meet a number of exacting requirements. The tubes must be long and sufficiently straight so as not to limit magnet design. They must have wall strength capable of withstanding the atmospheric and mechanical forces encountered during construction and operation. Vacuum tight ceramic to stainless steel transitions must be of reasonable cost; they must also withstand high temperature processing and remain vacuum tight to the 10/sup -9/ Torr range. To remove the possibility of static charge buildup each tube must have a surface coating of indium oxide applied to the inner wall. This thin coating is difficult to achieve and requires the most careful attention to detail. The methods used at Fermilab to achieve these goals are presented in this paper.