1. ILC Z-pole Calibration Runs Main Linac performance
A. Latina (CERN) K. Kubo (KEK)
LCWS 2016 – Dec , Morioka, Japan

2. Z-pole Calibration Runs
Two scenarios
Option 1: costing beam
Accelerate the beam up to 46 GeV at 31.5 MV/m for the first 13% of the main linac, and then let the beam coast through the rest of the linac at zero gradient
Option 2: uniformly reduced gradient
Uniformly reduce the gradient along the entire main linac to reach 46 GeV energy (G = 4.3 MV/m)
Magnet strength is scaled down, in both cases, to match the beam energy
BBA performance under static imperfections is assessed for the “luminosity” beam at 46 GeV
Performance of the high-energy beam is tested in the ML tuned for the low-energy beam

3. Energy Profile for Z-pole runs

4. Linac and Beam parameters
Laser-Straight Positron Main Linac – Most recent lattice (“2016rc”)
Beam at ML entrance:
E = 15 GeV
Norm. Emittance X: 8.8 μm (DR extraction, 8 μm + 10%)
Norm. Emittance Y: 24 nm (DR extraction, 20 nm + 20%)
Bunch length = 300 micron ; ΔE/E = 1.07% ; Q = 3.2 nC
Static imperfections:
Short-range structure wakefields ; 1 μm bpm resolution
300 μm/μrad RMS quads and structures alignment error
7 μm RMS bpm-to-quad alignment error
0.25% quad strength error

5. Beam-Based Alignment Procedure
The Main Linac divided in 10 bins
10% overlap between bins
36 correctors and bpms per bin
BBA procedure for each bin:
Orbit correction
Dispersion-Free Steering using 2 test beams: (a) injection energy reduced by 5%, (b) accelerating gradients reduced by 5%
100 random seeds

6. BBA Performance, V-axis (46 GeV, luminosity beam)

7. BBA Performance, H-axis (46 GeV, luminosity beam)

8. Emittance profile for opt1 – V-axis (46 GeV, luminosity beam)

9. High-energy beam (for e+ production), V-axis
(high-energy beam for positron generation traveling a ML tuned for low-energy run)
Vertical beam size < 100 micron even in the worst case

10. High-energy beam (for e+ production), H-axis
(high-energy beam for positron generation traveling a ML tuned for low-energy run)
Horizontal beam size < 100 micron even in the worst case

11. ML DFS Simulation, Change final beam energy
Main Linac, initial beam energy 15 GeV, nominal final energy 250 GeV. Old lattice (“2007b”)
Uniform gradient in whole linac
Final energy 250,200,150,100,75, 45 GeV
Set random independent errors　(Gaussian)
Q offset 0.36mm, Cavity offset 0.67 mm, Cavity tilt 0.3mrad, BPM resolution 1 um
DFS correction
Look at emittance growth at the end of linac
(initial emittance = 20 nm)
40 random seeds
K.Kubo

12. Emittance growth vs. final energy
Average of 40 random seeds. Error bar: standard deviation.
K.Kubo

13. High energy beam in ILC Main Linac tuned for low energy
Old lattice (2007) is used. Initial beam energy 15 GeV
For final energy 45 GeV, acc. gradient reduced uniformly in whole linac. Magnet strength scaled down as beam energy.
For high energy beam, final 125~150 GeV, only acc. gradient changed. Magnets are fixed (setting for 45 GeV final beam energy).
Looked at orbit deviation of high energy beam along the linac.
Next slide. ~20 mm vertical orbit deviation for 150 GeV beam
Looked at emittance at the end of linac (final energy 150 GeV).
Vertical emittance 4700 nm (235 times initial emittance, 20 nm)
Mostly due to wakefield. Only single bunch effect included.
K.Kubo

14. Orbit of high energy beam with magnet setting for 45 GeV (Old ILC ML lattice)
ML for final Energy 45 GeV, no error
y vs. s for final Energy 125 GeV, 130GeV and 150 GeV
Initial Energy is 15 GeV in all cases.
K. Kubo
Modified

15. Conclusions & Remarks
ML performance for Z-calibration run has been assessed in the laser-straight main linac lattice
Two options
Coasting beam
Reduced gradient
performance for coasting beam is significantly better
Emittance of the high-energy beam used for positron production is quite degraded
Is it still OK for positron production ?
Other considerations:
Fast kickers should be distributed along the linac to bend the high-energy beam to follow the earth curvature (perhaps all vertical correctors could be fast kickers switching between the two states?)
Lorentz Force Detuning in the structures, is it an issue?

16. Extras

17. Main Linac Architecture
Two type of CMs, Type A consists of nine, 1.3 GHz 9-cell cavities while Type B consists of 8 cavities and a quadrupole magnet package at the center.
An arrangement of Type A Type B Type A makes a ML/RF unit.
A total of 285 (282) ML units for e-linac (p-linac).
Three RF units with a cold-box at the end makes a cryo-string.
Periodic arrangement of cryo-string is interrupted due to insertion of 7.5 m long warm section.
Number of cryo-strings between successive warm section forms a cryo unit. It may compose of 11 to 21 cryo-strings.
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

18. Twiss Functions Along the Linac
V. Kapin, N. Solyak, AWLC ‘14
Transition between cryo unit
Zoomed View
Maximum periodic Twiss function (except at transition) in horizontal and vertical plane are 120 and 140m respectively.
Minimum periodic Twiss function in horizontal and vertical plane are 31 and 40 m respectively.
LCWS'16, Morioka, 5-9/12/2016
Courtesy of Arun Saini

19. Implementation of Earth’s Curvature(1)
Each straight CM is aligned at its center along a line perpendicular to Earth’s radius.
Green blocks represents cryomodules, black block represents BPM while red and blue blocks represent quadrupole mag-net and corrector respectively. Solid black line represents the beam trajectory.
Geometrical kink between the ends of CMs are implemented using special element in LUCRETIA named GKICK while in MAD8 it is done using a combination of thin corrector and dipole with same but opposite kicks.
In curved linac, nominal trajectory is steered though the center of quads using vertical correctors.
Reduce quadrupole kick.
Flag STEER can be set on/off using value 1/0 for
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

20. ILC: Basic Parameters TDR Parameter Lists
LCWS'16, Morioka, 5-9/12/2016
Arun Saini