Summary

Thin electrostatic septa are the most critical elements of the main ring extrac-tion system and the beam splitting stations at Fermilab. 1p2 Operating experience since the first extracted beam in 1972 has indica-ted several improvements needed over the original septa for both extraction (single cathode) and beam splitting (double cathode) A second generation of septa, now being im-plemented, is described here. Original Fermilab Septa These consist of several modules (4 for beam splitter and 5 for extractor) placed in line to give the required lo-foot length. The modules are accurately aligned inside an aluminum box with a thin stainless steel vat uum skin. It was eventually learned that the alignment is degraded when the vacuum skin is welded on. A typical effective thickness is. 030 ” although the aligyment before welding is accurate to.OOl”. The resulting extraction efficiency for slow spill is limited to about 90%. The wire plane consists of.002 ” tung-sten wires with a. 050 ” spacing. The wires are tensioned on an accurately machined aluminum frame. Each wire is hard-soldered to a coil spring on both ends and tensions are individually set at 300 grams. Since one lo-foot septum contains 2400 wires, the assembly is very tedious. Both failure at the solder joints and beam-induced wire breakage have been seri-ous problems, resulting in shorted septa. The welded vacuum skin makes disassembly for repair inefficient. Second Generation Septa The septa now being implemented at Fermilab are characterized by: 1.;2 one-piece wire support frame, 10 feet long. 2. A simplified wire fastening tech-nique. 3. Improved wire material. 4. Retracting springs to automatically extract broken wires from the high field region. 5. One-piece hollow titanium cathodes, 10 feet long. 6. Decoupling of the frame from the vacuum box to preserve straightness. Frame The wire support frame is machined from a single piece of type 300 cast aluminum tool ing plate. Flatness of the wire plane is *Operated by Universities Kesearch>issocia-tion under contract with the U.S. Energ