ILC Quadrupole package for the Main Linac
1. General ILC Layout is shown in Fig.1
Fig.1. General ILC layout
The number of superconducting CM and quadrupoles used in ILC is shown below.
#Quad
Electron Linac
# CM
Main e- linac
960
280
BC (5-15 GeV)
60
20/60*
e-Source (~ 5 GeV)
20
10*
Lost e-Energy (3.23GeV)
13
5*
Total
1053
~355
* My guess. Lattice file is not ready yet.
Positron Linac
Main e+ linac
BC (5-15 GeV)
e+Source (~ 5 GeV)
#CM
#Quad
960
60
20
280
20/60*
10*
1040
~350
2. The quadrupole package consists of: BPM/Quad/Corrector(X and Y). Two
possible configurations for correction dipole are shown in fig.2. In TDR-like
configuration vertical and horizontal correction dipoles are built-in with quad. In
ILC proposal they can be separated. Every second quad package has vertical
corrector only
ILC
Preliminary
Fig.2. Quadrupole package
3. Quadrulpole package location.
Baseline Configuration considers quadrupole package placed in the middle of the
cryomodule. Another discussed proposal is to place quad package in the separate
cryomodule. It will simplify assembly, testing and better for upgrading ILC to a higher
energy. Possible layout in separate cryostat is shown below.
4. Quadrupole Strength.
Quad strength is defined by quad spacing, required phase advance and beam
energy. In BDC Main Linac lattice configuration:
Quad spacing: 1 Quad/4CM for Energy = 15 – 250 GeV
Phase advance (X/Y) = 75°/ 60°
For flexibility quad should provide optics with phase advance 90° up to E=250 GeV.
Strength in this case is defined from equation:
2 eG  L

,
s
Energy
where s-quad spacing, L-quad length, G-gradient. For s=48m, L=0.666m, Gradient
scales as:
E = 15-250 GeV, s=48m:
T 
 Energy 
G    40 * 
m
 250GeV 
In case of lattice with quad spacing 1Q/3CM (RF unit) we have
E = 15-25 GeV, s=36m:
T 
 Energy 
G    54  
m
 250GeV 
For 1TeV ILC (500GeV/linac) the required gradient (maximum) G = 60 T/m,
assuming that higher energy (250-500GeV) will accept larger quadrupole spacing
(1QM/6CM).
5. Correction quadrupoles
Corrector will bend beam in vertical plane to transport beam along earth curvature and correct
Maximum beam offset of about +-3mm. Field integral is defined as:
 2 y s 
 
s
R

H  L T  m  Energy(GeV )  
0.3
Where s-quad spacing, R=6400km - earth radius, y – quad offset need to correct. Here is 90°
phase advance.
The maximum field integral ~0.075 [Tm] to correct 3mm beam offset at E=250 GeV and deflect
beam in vertical plane along earth surface (field strength needed for deflection is only ~10%.of
strength needed for beam/quad offset correction). There is one correction coil for vertical beam
in every magnet package and one for horizontal beam deflection in every second package.
1. Specifications (reference from TESLA TDR):
Quad
Beam pipe diameter
Inner coil diameter
Coil length
Gradient, max
Operating T
Nominal Current
Max Field at conductor
N turns/pole
Inductance
Field quality
Skew quadrupole
Higher harmonics
Alignment error (angle)
Dipole coil
Beam pipe diameter
Length (if separate)
Max Current
Temperature
Max Field at conductor
Max Field at axis
Inductance
78
90
626
60
2
100
3.6
1007
~3.2
mm
mm
mm
T/m
K
A
T
H
3.e-4
1.e-3*
0.1 mrad rms
78
350
40
2
3.6
0.074
~29
mm
mm
A
K
T
T
mH
*Tolerances for higher harmonics are probably looser. Need to check.
7. Preliminary dimensions:
2. Questions, Issues
o How many different magnet types need to cover energy (strength) range 5
to 500 GeV?
o Combined or separated Quad / corrector. Problems if combined. Distance
if separated.
o Iron dominated quads. Pros and Cons. Maximum field.
Some remarks from Vladimir Kashikhin:
1. It seems better to place BPM between Quadrupole and Dipole Corrector for separate corrector
option. In this case 66 mm BMP space eliminates overlapping fields and possible unwanted cross
magnetization effects.
2. I estimated Dipole Correctors with lengths 150-200 mm, but we can reduce it up to 100 mm
with center field increase from 0.3 T to 0.45 T and with proper ends design.
3. We need to know the distance between magnet package and nearest SCRF to estimate fringing
fields.
4. We can accommodate the 100mm (future goal) -150 mm length increase (option 2) with
corresponding main quadrupole strength increase from 60 to 75 T/m and length decrease to 520
mm (516+150=666 mm). It is possible because of better magnet performance [absence outer
dipole coils (extra space), better mechanical stability (absence dipole structure), closer iron core].
5. We need pros/cons of placing magnets in the center or cryomodule or separately in separate
cryostat:
- center position Pros: compact design, quadrupole position mechanically stable relatively SCRF, common
cryostat
and cooling with SCRF,...
Cons: Mechanical coupling when position magnet adjusted also moves SCRF, larger number of
cryomodule types,...
- separate magnet module Pros: easy management of SCRF/magnet modules along lattice, quick and cheap replacement,
small number of spares, easy upgrade for higher energy or better performance, smaller fringing
fields in SCRF area, better BBA having movable magnet support structure.
Cons: extra space, extra support structure with moving table,...
6. We need to have scenarios of magnet operation.
For example: power quadrupole up to maximum, after that bending dipole, then horizontal
dipole, then adjust +/-20% quad strength for BBA procedure, then playing with correctors in +/5 microns
quadrupole center motion, quench, repeat, ...?
and the quadrupole center should be stable +/-1 micron ?
Best regards,
Vladimir
P.S. I am digging out strand magnetization to estimate very roughly these effects and Vadim will
control this process working on BDS magnets.