11 Application of Accelerators and Storage Rings
747
RCS to deliver neutron target beam powers of 205 (410) kW, at 25 (50) Hz. Despite
the extent of the study, the project was not approved.
Now, Japan’s Proton Accelerator Research Complex, J-PARC [126] has a 3 GeV
RCS for a spallation neutron source as a part of a larger facility. The initial phase had
a 25 Hz, 0.18 GeV, H − linac with a 25 Hz, 3 GeV RCS, for a 0.5 MW beam power,
but the H − linac energy has been raised to 0.4 GeV to double the beam power. The
348.3 m circumference RCS has three superperiods, and uses novel, MA (magnetic
alloy) loaded cavities for its harmonic number 2, RF system.
A RCS based, spallation source, the CSNS, is being built in China. It has a
81 MeV, H − injector linac and a 25 Hz, 120 kW, 1.6 GeV, proton synchrotron
[127]. Later linac energies of 134 and 230 MeV will allow beam powers of 240 and
500 kW, respectively. The 41.5 m long H − linac has a 324 MHz, RFQ and DTL. An
initial hybrid lattice of doublet straights and FBDB arc cells has been replaced by
an all triplet lattice.
ISIS experience showed the importance of reliable 50 Hz, ion sources, long-life
H − stripping foils, RF shields for ceramic vacuum chambers, glass bonding for
ceramic sections, low loss fast extraction, and quick release for flanges and water
fittings. H − charge exchange injection is a key issue and includes painting smooth
beam distributions, reducing proton foil traverses (to limit foil temperatures), collecting foil stripped electrons, and locating a momentum and a betatron collimation
system, allowing hands-on and “active” maintenance, for improved reliability and
availability. Anti-correlated is preferred to correlated painting, as the latter produces
some large amplitude protons in both transverse planes, which may be lost via
coupling. Every fifth, RCS pulse is now diverted, at 10 Hz, to a new target station,
which has become a major development.
A sub-tunnel within a main ring tunnel may reduce air activation near the
collectors. Fractional loss design levels are set at ≈10 −3 at collimators and 10 −4
elsewhere in the ring, with the latter leading to a beam loss of <1 W/m. A RCS needs
rectangular vessels to avoid vertical loss of any un-trapped beam, which spirals
to protective momentum collectors, set in a high, normalized dispersion region.
Rectangular vessels also aid transverse halo collection. Betatron collectors may be
in three adjacent straights, with three long secondary units placed at 17 ◦ , 90 ◦ and
163 ◦ , transverse, betatron phase shifts after a primary scatterer.
Beam density limitations due to Liouville’s Theorem are circumvented in charge
exchange injection. Two designs are available for low-loss H − injection systems for
RCS rings. In one, the merging of the H − ions and the circulating protons occurs
at a ring dipole and, in the other, at the centre of an orbit chicane of four fixed and
eight variable dipoles, in a very low dispersion region (SNS scheme) [128]. The
former does not need an injection chicane, or an injection septum unit, or horizontal
painting magnets, but it is not as flexible as the latter for longitudinal painting.
Both injection schemes aim to scrape the H − beam (~±10σ) in the input line
at ±5σ and set the beam centre at 5σ (~5 mm) from the adjacent, stripping foil
edges. Input steering errors (of one polarity) result in some H − ions missing the foil.
Partially stripped H o atoms appear in a range of quantum states [129] and, together
with unstripped H − ions, diverge from the protons in the region’s bend field, and
747
RCS to deliver neutron target beam powers of 205 (410) kW, at 25 (50) Hz. Despite
the extent of the study, the project was not approved.
Now, Japan’s Proton Accelerator Research Complex, J-PARC [126] has a 3 GeV
RCS for a spallation neutron source as a part of a larger facility. The initial phase had
a 25 Hz, 0.18 GeV, H − linac with a 25 Hz, 3 GeV RCS, for a 0.5 MW beam power,
but the H − linac energy has been raised to 0.4 GeV to double the beam power. The
348.3 m circumference RCS has three superperiods, and uses novel, MA (magnetic
alloy) loaded cavities for its harmonic number 2, RF system.
A RCS based, spallation source, the CSNS, is being built in China. It has a
81 MeV, H − injector linac and a 25 Hz, 120 kW, 1.6 GeV, proton synchrotron
[127]. Later linac energies of 134 and 230 MeV will allow beam powers of 240 and
500 kW, respectively. The 41.5 m long H − linac has a 324 MHz, RFQ and DTL. An
initial hybrid lattice of doublet straights and FBDB arc cells has been replaced by
an all triplet lattice.
ISIS experience showed the importance of reliable 50 Hz, ion sources, long-life
H − stripping foils, RF shields for ceramic vacuum chambers, glass bonding for
ceramic sections, low loss fast extraction, and quick release for flanges and water
fittings. H − charge exchange injection is a key issue and includes painting smooth
beam distributions, reducing proton foil traverses (to limit foil temperatures), collecting foil stripped electrons, and locating a momentum and a betatron collimation
system, allowing hands-on and “active” maintenance, for improved reliability and
availability. Anti-correlated is preferred to correlated painting, as the latter produces
some large amplitude protons in both transverse planes, which may be lost via
coupling. Every fifth, RCS pulse is now diverted, at 10 Hz, to a new target station,
which has become a major development.
A sub-tunnel within a main ring tunnel may reduce air activation near the
collectors. Fractional loss design levels are set at ≈10 −3 at collimators and 10 −4
elsewhere in the ring, with the latter leading to a beam loss of <1 W/m. A RCS needs
rectangular vessels to avoid vertical loss of any un-trapped beam, which spirals
to protective momentum collectors, set in a high, normalized dispersion region.
Rectangular vessels also aid transverse halo collection. Betatron collectors may be
in three adjacent straights, with three long secondary units placed at 17 ◦ , 90 ◦ and
163 ◦ , transverse, betatron phase shifts after a primary scatterer.
Beam density limitations due to Liouville’s Theorem are circumvented in charge
exchange injection. Two designs are available for low-loss H − injection systems for
RCS rings. In one, the merging of the H − ions and the circulating protons occurs
at a ring dipole and, in the other, at the centre of an orbit chicane of four fixed and
eight variable dipoles, in a very low dispersion region (SNS scheme) [128]. The
former does not need an injection chicane, or an injection septum unit, or horizontal
painting magnets, but it is not as flexible as the latter for longitudinal painting.
Both injection schemes aim to scrape the H − beam (~±10σ) in the input line
at ±5σ and set the beam centre at 5σ (~5 mm) from the adjacent, stripping foil
edges. Input steering errors (of one polarity) result in some H − ions missing the foil.
Partially stripped H o atoms appear in a range of quantum states [129] and, together
with unstripped H − ions, diverge from the protons in the region’s bend field, and