Electron Linac Optimisation for Short RF and Beam Pulse Lengths

New applications of electron linacs require better use of the space available and the success of the SLED RF compression method renews the interest for the conventionnal E-coupled TW accelerating structure which has the required short filling time. We propose to use the less conventionnal backward-wave H-coupled TW accelerating structure which allows an higher shunt impedance. A unit of acceleration could include a 37 MW TH 2094 klystron, with SLED feeding through a 3 db hybrid coupler including a load in the fourth arm, two 6 meter long backward TW structures with thickened irises near the acceleration axis. Output loads could be avoided. The choice of the H-coupled 4 π/5 mode and the cell shapes and properties are analyzed. Conclusion stresses the advantages as simplicity and also the limits of this optimization.