10 The Largest Accelerators and Colliders of Their Time
651
The layout of the Long Straight Section between Q7L and Q7R is mirror
symmetric with respect to the IP. The right side of IR7 is shown in Fig. 10.23.
This allows the symmetrical installation for the collimators of the two beams and
minimizes the space conflicts in the insertion. Starting from Q7 left, the quadrupole
Q6 (made of six superconducting MQTL modules) is followed by a dog-leg
structure made of two sets of MBW warm single bore wide aperture dipole magnets
(two warm modules each). The dogleg dipole magnets are labeled D3 and D4 in the
LHC sequence with D3 being the dipole closer to the IP. The Primary Collimators
are located between the D4 and D3 magnets, allowing neutral particles produced in
the jaws to point out of the beam line, and most charged particles to be swept away.
The inter-beam distance between the dogleg assemblies left and right from the IP is
224 mm, i.e. 30 mm larger than in the arc. This increased beam separation allows a
substantially higher gradient in the Q4 and Q5 quadrupoles which are made out of
six warm MQW modules. The space between Q5 left and right from the IP is used
to house the secondary collimators at adequate phase advances with respect to the
primary collimators.
The Q4 and Q5 quadrupoles left and right from the IP are powered in series. The
warm dual-bore MQW quadrupole cannot be powered with different currents for
each magnet aperture because the field quality is degraded to an unacceptable level
even for a small imbalance in the field of the two apertures. The current must be
equal or of opposite value in the bores to provide a good field quality. In order
to obtain the required flexibility for the optics, two different kinds of powering
schemes are used for the Q4 and Q5 quadrupole units. The magnets are identical,
but in the MQWA type magnet the field is identical in both apertures, while in
the MQWB type magnet, the field is opposite for both apertures. Each Q4 and Q5
assembly is made of five MQWA and one MQWB module. The nominal gradient of
the MQWB unit is limited to 29.6 T/m while it can reach 35 T/m in the MQWA
unit. This powering scheme breaks the exact antisymmetry by 29% providing
enough flexibility to satisfy all the optics constraints. Again, Q5AL+Q5AR and
Q5BL+Q5BR respectively are powered in series. As a by-product, this freedom in
the straight section allows the trim strength needed in the DS to be limited so that
regular MQTL’s can be used.
In IR3, the most difficult constraint was to generate a large dispersion function
in the straight section. Since the layout of the DS cannot be changed in IR3 this
constraint means that the natural dispersion suppression generated in the DS is
over compensated. To this end Q6 and Q5 were moved towards each other by a
substantial amount, thus shrinking the space granted to the dog-leg structure D4D3. It was therefore necessary to add a third MBW element to D3 and D4 in IR3.
Apart from this IR3 and IR7 are identical.
10.6.2.8 LSS4
IR4 houses the RF and feed-back systems as well as some of the LHC beam
instrumentation.
651
The layout of the Long Straight Section between Q7L and Q7R is mirror
symmetric with respect to the IP. The right side of IR7 is shown in Fig. 10.23.
This allows the symmetrical installation for the collimators of the two beams and
minimizes the space conflicts in the insertion. Starting from Q7 left, the quadrupole
Q6 (made of six superconducting MQTL modules) is followed by a dog-leg
structure made of two sets of MBW warm single bore wide aperture dipole magnets
(two warm modules each). The dogleg dipole magnets are labeled D3 and D4 in the
LHC sequence with D3 being the dipole closer to the IP. The Primary Collimators
are located between the D4 and D3 magnets, allowing neutral particles produced in
the jaws to point out of the beam line, and most charged particles to be swept away.
The inter-beam distance between the dogleg assemblies left and right from the IP is
224 mm, i.e. 30 mm larger than in the arc. This increased beam separation allows a
substantially higher gradient in the Q4 and Q5 quadrupoles which are made out of
six warm MQW modules. The space between Q5 left and right from the IP is used
to house the secondary collimators at adequate phase advances with respect to the
primary collimators.
The Q4 and Q5 quadrupoles left and right from the IP are powered in series. The
warm dual-bore MQW quadrupole cannot be powered with different currents for
each magnet aperture because the field quality is degraded to an unacceptable level
even for a small imbalance in the field of the two apertures. The current must be
equal or of opposite value in the bores to provide a good field quality. In order
to obtain the required flexibility for the optics, two different kinds of powering
schemes are used for the Q4 and Q5 quadrupole units. The magnets are identical,
but in the MQWA type magnet the field is identical in both apertures, while in
the MQWB type magnet, the field is opposite for both apertures. Each Q4 and Q5
assembly is made of five MQWA and one MQWB module. The nominal gradient of
the MQWB unit is limited to 29.6 T/m while it can reach 35 T/m in the MQWA
unit. This powering scheme breaks the exact antisymmetry by 29% providing
enough flexibility to satisfy all the optics constraints. Again, Q5AL+Q5AR and
Q5BL+Q5BR respectively are powered in series. As a by-product, this freedom in
the straight section allows the trim strength needed in the DS to be limited so that
regular MQTL’s can be used.
In IR3, the most difficult constraint was to generate a large dispersion function
in the straight section. Since the layout of the DS cannot be changed in IR3 this
constraint means that the natural dispersion suppression generated in the DS is
over compensated. To this end Q6 and Q5 were moved towards each other by a
substantial amount, thus shrinking the space granted to the dog-leg structure D4D3. It was therefore necessary to add a third MBW element to D3 and D4 in IR3.
Apart from this IR3 and IR7 are identical.
10.6.2.8 LSS4
IR4 houses the RF and feed-back systems as well as some of the LHC beam
instrumentation.