Progress and Plans for R&D and the Conceptual Design of the ILC High Gradient Structures

Gradients and Q□s in the dominant ILC candidate structure have shown steady improvement, reaching 35 — 40 MV/m over the last year using the best techniques of electropolishing, high pressure rinsing and 120... C baking for 48 hours. Progress and plans for these structures are reviewed. Above 40 MV/m, the surface magnetic field encroaches the range of the rf critical magnetic field, believed to fall between 1750 and 2000 Oe, depending on the theory. One way to circumvent the limit is to modify the cavity shape to reduce the ratio of peak magnetic to accelerating field. ° Two candidate shapes have evolved, the Re-entrant shape and the Low-Loss shape. Although field emission is aggravated by higher electric fields, it does not present a brick wall limit because high pressure rinsing at 100 bar eliminates microparticles which cause field emission. Results of single and multicell cavities will be presented. The record field in a single cell re-entrant cavity is now 46 MV/m corresponding to a surface magnetic field of 1750 Oe and a surface electric field of 101 MV/m.