11 Application of Accelerators and Storage Rings
749
ring. Use of a H − linac injector for a compressor ring or RCS now needs to be
re-evaluated and other schemes also considered.
11.4.3.3 Direct Proton Injection from a Pulsed Proton Linac to a Fast
Cycling Synchrotron
In a new scheme, a proton linac replaces the H − linac and a ring with only one type
of lattice cell is assumed, as a H − injection insertion isn’t needed. A more stable,
higher current, lower emittance linac beam is realised and intra-beam and injection
stripper losses are avoided. The RCS, compressor or FFAG ring is fed directly from
the proton linac, using a two plane, multi-turn injection scheme, as proposed for a
heavy ion fusion research project in 1998 [133]. Direct proton injection is similar for
all three rings. A tilted, corner, electrostatic septum unit is set at a long drift section
centre point. The septum wires have an effective 1 mm thickness and are at a 40–60 ◦
angle, θ, to the horizontal. Control of closed orbits at the septum is via vertical and
horizontal bump magnets. Correlated painting is used, with closed orbits reduced
during injection to reach the design emittances.
Basic parameters are input beam and ring emittances, angle θ, ring betatron tunes,
Twiss parameters, space charge levels, and positions and directions, at the septum
output, of the incoming beam centre and the ring’s closed orbit. The ring lattice
parameters may be kept constant during the injection or varied, to minimise injection
beam losses. Evolution of beam distributions under the non-linear space charge
forces, during and after injection, was simulated in the study [133]. Emittances were
found to continue to grow after injection and evolve towards a stationary state so, to
avoid loss, the late beam-septum separations were increased. A maximum number
of turns injected without loss, for F = 10–20, and (εh εv) ring and (εh εv) inj the
respective products of ring and injected emittances, was found to be approximately:
N inj = (1/F) (εh εv) ring /(εh εv) inj .
Ring circumference and straight sections must be large enough to achieve the
required injected beam. RAL studies [134] have compared combined function,
DFD and FDF triplet, and dFDFd and fDFDf, pumplet lattice cells. Magnets d
and D provide vertical focusing (horizontal defocusing) and f and F give opposite
focusing. Doublet cells are avoided as beam waists aren’t at an injection straight
centre. RCS pumplet cells are similar to those proposed for FFAGs [135], but their
fields are linear and their magnets all have positive bends. The bending radii are thus
larger and magnetic fields much reduced. For equal bending and corrector lengths,
triplet and pumplet cells have the same length. Pumplets are preferred as the Twiss
parameters are lower and hence the magnet apertures smaller. Ring designs use only
one type of pumplet lattice cell (dFDFd or fDFDf), and a low dispersion in the
injection straight section is advantageous.
An ISIS upgrade considers replacing the present ring by a large emittance, 0.6–
1.8 GeV pumplet RCS. A fDFDf cell is preferred to a dFDFd as it has lower β(h)
values and dispersion. The 12 cells have a 26.0 m mean and a 12.5 m bend radius,
and a 0.686 T maximum on-axis magnetic field. Assumed is a 70% chopped, 0.1 A
749
ring. Use of a H − linac injector for a compressor ring or RCS now needs to be
re-evaluated and other schemes also considered.
11.4.3.3 Direct Proton Injection from a Pulsed Proton Linac to a Fast
Cycling Synchrotron
In a new scheme, a proton linac replaces the H − linac and a ring with only one type
of lattice cell is assumed, as a H − injection insertion isn’t needed. A more stable,
higher current, lower emittance linac beam is realised and intra-beam and injection
stripper losses are avoided. The RCS, compressor or FFAG ring is fed directly from
the proton linac, using a two plane, multi-turn injection scheme, as proposed for a
heavy ion fusion research project in 1998 [133]. Direct proton injection is similar for
all three rings. A tilted, corner, electrostatic septum unit is set at a long drift section
centre point. The septum wires have an effective 1 mm thickness and are at a 40–60 ◦
angle, θ, to the horizontal. Control of closed orbits at the septum is via vertical and
horizontal bump magnets. Correlated painting is used, with closed orbits reduced
during injection to reach the design emittances.
Basic parameters are input beam and ring emittances, angle θ, ring betatron tunes,
Twiss parameters, space charge levels, and positions and directions, at the septum
output, of the incoming beam centre and the ring’s closed orbit. The ring lattice
parameters may be kept constant during the injection or varied, to minimise injection
beam losses. Evolution of beam distributions under the non-linear space charge
forces, during and after injection, was simulated in the study [133]. Emittances were
found to continue to grow after injection and evolve towards a stationary state so, to
avoid loss, the late beam-septum separations were increased. A maximum number
of turns injected without loss, for F = 10–20, and (εh εv) ring and (εh εv) inj the
respective products of ring and injected emittances, was found to be approximately:
N inj = (1/F) (εh εv) ring /(εh εv) inj .
Ring circumference and straight sections must be large enough to achieve the
required injected beam. RAL studies [134] have compared combined function,
DFD and FDF triplet, and dFDFd and fDFDf, pumplet lattice cells. Magnets d
and D provide vertical focusing (horizontal defocusing) and f and F give opposite
focusing. Doublet cells are avoided as beam waists aren’t at an injection straight
centre. RCS pumplet cells are similar to those proposed for FFAGs [135], but their
fields are linear and their magnets all have positive bends. The bending radii are thus
larger and magnetic fields much reduced. For equal bending and corrector lengths,
triplet and pumplet cells have the same length. Pumplets are preferred as the Twiss
parameters are lower and hence the magnet apertures smaller. Ring designs use only
one type of pumplet lattice cell (dFDFd or fDFDf), and a low dispersion in the
injection straight section is advantageous.
An ISIS upgrade considers replacing the present ring by a large emittance, 0.6–
1.8 GeV pumplet RCS. A fDFDf cell is preferred to a dFDFd as it has lower β(h)
values and dispersion. The 12 cells have a 26.0 m mean and a 12.5 m bend radius,
and a 0.686 T maximum on-axis magnetic field. Assumed is a 70% chopped, 0.1 A