762
M. Dohlus et al.
ECRIS can also be used for charge breeding of ISOL-produced or stopped inflight-produced rare isotopes before post- or re-acceleration [184, 185].
Based on the experience and progress with third generation ECRIS in increasing
beam intensities of highly charged ions in the last decade, proposals to build
next generation ECRIS for microwave frequencies beyond 28 GHz have been
discussed since some years. The 1st fourth generation ECRIS is under construction
now at IMP, Lanzhou, to be operated at 45 GHz, with correspondingly higher
magnetic fields, based on Nb3Sn- instead NbTi- superconducting technology [186].
Expectations are to reach with that fourth generation two to three times higher beam
currents in the future.
With respect to the formation and transport of beams from ECR ion sources, one
has to bear in mind that the extraction system is placed in a region with a superposition of stray fields from the axial coil and the radial hexapole field, affecting
beam formation and beam density distribution. In addition, beams with different
ion charge states have different emittances due to the magnet-field structure, the
production and confinement processes inside the source. The ion-current density is
not uniform within the beam [187–189]. In third generation ECRIS, with higher
magnetic fields and microwave frequencies, beam emittance and low energy beam
transport is an issue [176].
In contrast to cw-operated cyclotrons and superconducting linacs, synchrotrons
require injection at high peak currents within a brief period. Those peak beam
currents of highly charged ions can be delivered from laser ion sources, or by an
EBIS, or by an ECRIS along with an accumulator ring such as LEIR, which uses
fast extraction to provide the requested peak intensities for the LHC [190]. For
the FAIR synchrotrons, high-current short-pulse ion sources are used, which can
deliver many mA (e.g. 15 mA of U 4+ ) of ions in a low charge state [191, 192].
After pre-acceleration and intermediate stripping in the injector linac (Unilac) the
charge state is reached (U 28+ ) which is needed in the booster synchrotron SIS18
(section “Facility for Antiproton and Ion Research (FAIR) at GSI”).
11.5.2.2.2 Charge-Changing Processes
The design of the first stage of a heavy ion accelerator depends on the charge state
delivered from the ion source for the heaviest ion species to be accelerated (highest
A/q-ratio). In accelerator facilities for medium to relativistic energies (some 10–
1000 MeV/u), usually one or two strippers are needed to increase the charge state
of the ions for an efficient acceleration scheme. In a stripper target, the initially
charge-homogeneous beam splits up into several charge components. One gets a
charge state distribution centred on the equilibrium charge state. To optimize the
overall accelerator layout, it is important to know the ion and energy dependence of
the equilibrium charge states and the yield of the charge states as well.
Pioneering theoretical work on these processes was done by Bohr [193]. Bohr
assumed that a fast heavy ion passing a gas stripper retains the electrons which have
orbital velocities which are greater than the ion velocity (Bohr’s Criterion). This
M. Dohlus et al.
ECRIS can also be used for charge breeding of ISOL-produced or stopped inflight-produced rare isotopes before post- or re-acceleration [184, 185].
Based on the experience and progress with third generation ECRIS in increasing
beam intensities of highly charged ions in the last decade, proposals to build
next generation ECRIS for microwave frequencies beyond 28 GHz have been
discussed since some years. The 1st fourth generation ECRIS is under construction
now at IMP, Lanzhou, to be operated at 45 GHz, with correspondingly higher
magnetic fields, based on Nb3Sn- instead NbTi- superconducting technology [186].
Expectations are to reach with that fourth generation two to three times higher beam
currents in the future.
With respect to the formation and transport of beams from ECR ion sources, one
has to bear in mind that the extraction system is placed in a region with a superposition of stray fields from the axial coil and the radial hexapole field, affecting
beam formation and beam density distribution. In addition, beams with different
ion charge states have different emittances due to the magnet-field structure, the
production and confinement processes inside the source. The ion-current density is
not uniform within the beam [187–189]. In third generation ECRIS, with higher
magnetic fields and microwave frequencies, beam emittance and low energy beam
transport is an issue [176].
In contrast to cw-operated cyclotrons and superconducting linacs, synchrotrons
require injection at high peak currents within a brief period. Those peak beam
currents of highly charged ions can be delivered from laser ion sources, or by an
EBIS, or by an ECRIS along with an accumulator ring such as LEIR, which uses
fast extraction to provide the requested peak intensities for the LHC [190]. For
the FAIR synchrotrons, high-current short-pulse ion sources are used, which can
deliver many mA (e.g. 15 mA of U 4+ ) of ions in a low charge state [191, 192].
After pre-acceleration and intermediate stripping in the injector linac (Unilac) the
charge state is reached (U 28+ ) which is needed in the booster synchrotron SIS18
(section “Facility for Antiproton and Ion Research (FAIR) at GSI”).
11.5.2.2.2 Charge-Changing Processes
The design of the first stage of a heavy ion accelerator depends on the charge state
delivered from the ion source for the heaviest ion species to be accelerated (highest
A/q-ratio). In accelerator facilities for medium to relativistic energies (some 10–
1000 MeV/u), usually one or two strippers are needed to increase the charge state
of the ions for an efficient acceleration scheme. In a stripper target, the initially
charge-homogeneous beam splits up into several charge components. One gets a
charge state distribution centred on the equilibrium charge state. To optimize the
overall accelerator layout, it is important to know the ion and energy dependence of
the equilibrium charge states and the yield of the charge states as well.
Pioneering theoretical work on these processes was done by Bohr [193]. Bohr
assumed that a fast heavy ion passing a gas stripper retains the electrons which have
orbital velocities which are greater than the ion velocity (Bohr’s Criterion). This