Analysis of a Symmetric Terahertz Dielectric-Lined Rectangular Structure for High Gradient Acceleration

We study, using computational methods based on analytic theory as well as a PIC code, the wakefields set up in a seven-zone symmetric rectangular THZ structure, and find that for overall transverse x/y dimensions 2.121 mm×0.6 mm, two 5-GeV drive bunches (3 nC, with x/y/z dimensions 0.3/0.3/0.12 mm³ as available at SLAC) will set up an axial wakefield ∼350 MV/m in the witness channel, with a transformer ratio ∼18-20. The symmetry of the structure ensures not only that small transverse forces are imposed on the witness bunch, but also that the two components of transverse force are equal and opposite at the bunch location so as to enable dynamical stabilization in an accelerator comprising many modules. Transverse forces on the drive bunch tails may allow bunches to move ∼0.5-1 m without suffering excessive erosion.