STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
STUDIES OF ENERGY RECOVERY LINACS AT ... - CASA
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3.4.2 Backleg Region<br />
The backleg region consists of six 90 ◦ FODO cells. In addition to matching the<br />
beam to the undulator, the FODO lattice provides the additional freedom to vary<br />
the betatron phase advances [58]. This feature was implemented to allow control<br />
of BBU through modification of the recirculation phase advance and is discussed<br />
in detail in Section 6.2. The optical cavity chicane provides −0.5 m of momentum<br />
compaction, so that from the linac to undulator, the compaction is (+0.2 − 0.5)<br />
−0.3 m. Following the optical cavity chicane, a six quadrupole telescope is used to<br />
match the transverse beam envelopes to the undulator.<br />
Note that during experimental studies of BBU, the performance of the Driver<br />
itself, without lasing, was studied.<br />
3.4.3 Energy Recovery Transport<br />
Following the undulator, a six quadrupole telescope is used to match the trans-<br />
verse beam envelopes to the second recirculation arc. The endloop is the same as the<br />
first, except that in addition to trim quadrupoles and sextupoles, there is a family<br />
of octupoles to provide tunable momentum compactions through third order.<br />
Following the undulator the electron bunch remains short, however there is a<br />
significant momentum spread induced by the lasing process. The transport following<br />
the undulator is designed to cleanly transport a beam with up to 10% full relative<br />
momentum spread and provide adequate energy compression so as to prevent adia-<br />
batic antidamping from generating a prohibitively large momentum spread.<br />
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