STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA

decelerated beam energy. A spectrometer in the injector region was used to measure
the injected energy and the magnet which deflects the beam to the dump was used
to measure the decelerated beam energy.
2.3 Transporting Beam to the Energy Recovery
Dump
The CEBAF-ER experiment started in earnest on March 25, 2003 using a
56 MeV injector setup and by the following day energy recovered beam was suc-
cessfully transported to the beam dump. That in itself satisfied the primary goal of
the experiment - to demonstrate the feasibility of energy recovery on a large-scale
machine and at high energy.
The experiment started by balancing the linac energy as described in Sec-
tion 2.2.4. After the linac energies were balanced, the RF ganged phases in the
south linac were returned to their nominal settings to accelerate the first pass beam.
The arc 2 optics, with the spreader and recombiner set to match the beam into the
north linac for deceleration, were then loaded into the machine.
2.3.1 Setting the Path Length
To achieve good performance with energy recovery, the decelerated pass must
be exactly 180 ◦ out of phase with respect to the accelerating pass. Operationally,
the proper path length differential was achieved in the following way [35]: first, note
that the energy of the first pass beam through arc 1 is
E (1)
A1 = Einj + ENL cos θNL
33
(2.2)
where Einj is the injected beam energy, ENL is the energy gain through the north