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In the first stage of the REX-ISOLDE linac the ions are
accelerated from 5 keV/u to 300 keV/u by a 4-rod RFQ. In
order to match the beam from the RFQ into the
acceptance of the IH (Interdigital-H-type)-structure a
section consisting of two magnetic quadrupole triplet
lenses and a rebuncher is required. A feature of the
REX-ISOLDE-IH resonator is the possibility to vary the
final energy between 1.1 and 1.2 MeV/u by adjusting the gap voltage
distribution via two capacitive plungers and by adjusting the
rf-power fed into the resonator. The lower final energy of the IH-structure
is important for deceleration of the ions down to 0.8 MeV/u,
since the deceleration from 1.2 MeV/u down to 0.8 MeV/u through
the 7-gap resonators would perform a non-acceptable phase spread
at the target.
The high-energy section (0.8 - 3.0 MeV/u) of the linac
consists mainly of three 7-gap resonators. These spiral
resonators are designed and optimised for synchronous
velocities of β
= 5.4%, 6.0% and 6.6%. Each resonator has a single
resonance structure, which consists of a copper half
shell and three arms attached to both sides of the
shell. All linac structures are operated at 101.28 MHz.
In the spring of 2004 an additional 9-gap IH structure, operating at a frequency of 202.56 MHz was installed in the high-energy section of the linac. This provides ions accelerated to 3.0 MeV/u.
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Resonance frequency = 101.28 and 202.56 MHz(T=10 ns)
Duty cycle = 10 % Design transmission = 90% Time structure: EBIS pulse = 50µs Repetition rate = max. 50Hz Bunch length at target = 0.3ns (2.2 MeV/u) 13ns (0.8 MeV/u (cw)) |