Freeman ion source

A method of producing boron ions with an ion source comprising in combination an arc chamber having an extraction slit;

• a straight filament supported within said arc chamber near said extraction slit and aligned therewith;
• means for applying a magnetic field within said arc chamber parallel to said filament;
• a filament power supply adapted to heat said filament to electron-emitting temperatues;
• an arc power supply adapted to maintain an arc discharge within said arc chamber by applying a negative polarity to said filament with respect to said arc chamber;
• an extraction electrode outside said arc chamber and aligned with said extraction slit;
• a power supply adapted to apply a negative polarity to said extraction electrode with respect to said arc chamber, whereby positive ions in said arc discharge may be extracted through said extraction slit;
• said filament having surfaces so arranged that substantially no normal to any said surface passes through said extraction slit, whereby substantially no negative ions formed at said surfaces pass through said extraction slit, said method comprising producing an arc discharge in boron trifluoride between said arc chamber having an extraction slit and said filament contained therein and, in so doing, maintaining said magnetic field parallel to said filament;
• producing boron ions by impact of BF.sub.2.sup.+ and BF.sup.+ on cathode surfaces;
• said surfaces having normals thereto substantially none of which pass through said slit;
• and extracting boron ions through said slit.

A method of enhancing the production of elemental ion species relative to molecular ion species (when using materials such as BF.sub.3, SF.sub.6, UF.sub.6, SiF.sub.4 in an ion source comprising in combination an arc chamber having an extraction slit;

• a straight filament supported within said arc chamber near said extraction slit and aligned therewith;
• means for applying a magnetic field within said arc chamber parallel to said filament;
• a filament power supply adapted to heat said filament to electron-emitting temperatures;
• an arc power supply adapted to maintain an arc discharge within said arc chamber by applying a negative polarity to said filament with respect to said arc chamber;
• an extraction electrode outside said arc chamber and aligned with said extraction slit;
• a power supply adapted to apply a negative polarity to said extraction electrode with respect to said arc chamber, whereby positive ions in said arc discharge may be extracted through said extraction slit) comprising maximizing the area of the surface of said filament for a given cross-sectional area of said filament, maximizing the areas of the surfaces of other metal parts at the potential of said filament, and arranging the said surfaces so that substantially no normal to any said surface passes through said extraction slit.

An ion source for producing a large negative ion flux comprising in combination an arc chamber having an extraction slit;

• a straight filament supported within said arc chamber near said extraction slit and aligned therewith;
• means for applying a magnetic field within said arc chamber parallel to said filament;
• a filament power supply adapted to heat said filament to electron-emitting temperatures;
• an arc power supply adapted to maintain an arc discharge within said arc chamber by applying a negative polarity to said filament with respect to said arc chamber;
• an extraction electrode outside said arc chamber and aligned with said extraction slit;
• a power supply adapted to apply a positive polarity to said extraction electrode with respect to said arc chamber, whereby negative ions in said arc discharge may be extracted through said extraction slit;
• said filament having a smooth concave surface adapted to maximize the cathode surface having normals passing through the extraction slit.