| 摘要 |
PURPOSE:To dispense with an electrode for expelling secondary electrons and an external power source, by arranging a radial type permanent magnet to the beam inlet part of a Faraday cup for monitoring an ion beam current to provide secondary electron suppressing function to said cup. CONSTITUTION:The whole of a Faraday cup is arranged in a beam line vacuum container insulated from others and connected to the ammeter 4 placed in the open air through a current introducing terminal 3 and an ion beam current is measured by said ammeter 4. Ion beam 5 to be measured is collected in the cup and collides with the wall surface of the cup at this time to form a secondary electron 6 and a part of the electron 6 goes to the inlet direction of the cup. Herein, if a line 7 of magnetic force of about 10 gauss is formed within the plane almost vertical to the ion beam by a radial type permanent magnet 2, a Larmor radius becomes small than the inlet radius of the cup with respect to the passing electron and the electron is trapped in a form wound around the line of magnetic force. Since the magnetic field of the permanent magnet 2 has a cup shape, said magnetic field can not escape from the inlet of the cup.
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