The ERL in a SRF linac was demonstrated for the first
time at Stanford University. The high-energy electron beam
was returned to the linac at a decelerating phase [4]. This is
also the first instance of the ‘same-cell’ energy recovery
technique. Another experimental demonstration of an ERL in
a very different configuration took place at Los Alamos. In
that case, the accelerator was a normal-conducting linac, and
the beam energy recovery was done in a dedicated separatecell
[5]. The RF power recovered from the decelerating
structure was coupled to the accelerating structure through
resonant bridge couplers, however, the efficiency of this
operation was only about 70%. The examples given above
show another divergence of approach, that of SRF linacs and
copper (normal-conducting) linacs, however this work is
aimed exclusively at superconducting ERLs.