A REDUCED GRADIENT OUTPUT DESIGN FOR SLAC'S XL4 X-BAND KLYSTRON*

X-band klystron work began at SLAC in the mid to late 1980's to develop high frequency (4 times the SLAC Sband klystron), high power RF sources for the linear collider designs under consideration at that time. This work culminated in the current workhorse X-band RF source, the XL4. To date 26 XL4 tubes have been built. The XL4 4-cell disk loaded traveling wave output structure has a high operating gradient. A new 6-cell structure has been designed to reduce breakdown and to further improve the klystron's robustness. Initial simulations show the 6-cell design reduces the gradient roughly 25% and that the structure is stable. A physical XL4 will be retrofitted with the new output cavity and hot tested in the near future.