Patent ID: 8324592

Claim:
An ion source comprising: a plasma chamber having a length; a cathode in the plasma chamber for generating a plasma in the chamber; a magnetic field generator to produce a magnetic field in said chamber extending in a magnetic field direction along said length; said plasma chamber having a front plate defining an ion extraction slit having a center and extending lengthwise of said plasma chamber, whereby charged particles in a plasma formed in said chamber can be extracted through the slit in an extraction direction along an extraction axis through said center of said slit, said magnetic field direction and said extraction axis defining a central plane in said chamber; said ion source further including a first control electrode in said plasma chamber located asymmetrically relative to said central plane and at a first control position along said length of said chamber; a second control electrode in said plasma chamber located asymmetrically relative to said central plane and at a second control position, displaced from said first control portion, along said length of said chamber; and respective first and second control terminals connected to said first and second control electrodes for applying respective bias voltages to said first and second control electrodes.