1. ILC Main Linac Lattice Updates and LET Performance for Nominal Misalignments
Arun Saini, N. Solyak
Fermi National Accelerator Laboratory
ALCWS’16, Morioka, Japan, 4-9th December 2016
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

2. Outline Layout of ILC Main Linac Implementation of Earth’s Curvature
Low Emittance Transport and Alignment Tolerances
Straight Linac
Curved Linac
Recent Updates
Summary
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

3. ILC schematics Damping Rings Polarised electron source
Polarised positron source
Ring to Main Linac (RTML)
e- Main Linac (incl. bunch compressor)
Beam Delivery System (BDS) & physics detectors
e+ Main Linac (incl. bunch compressor)
Beam dump
Total length (500 GeV)
30.5 km
SCRF ML (RTML)
22.2 km
RTML_BC
2.8 km
Positron source
1.1 km
BDS / IR
4.5 km
Damping Rings
3.2 km
In this presentation I will discuss only electron linac
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

4. 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

5. 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
Arun Saini

6. Curved Linac
A key feature of ILC linac is that it follows Earth’s Curvature
It simplifies helium transport at 2K
Incorporation of Earth’s Curvature requires:
A dispersion matching with upstream (bunch compressor) and downstream (beam delivery section).
Suppression of periodic dispersion resulting from the Earth’s curvature.
Earth’s curvature in lattice can be switch on/off using a flag named CURVE (1/0)
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

7. 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

8. Implementation of Earth’s Curvature(2)
Matching of the curved main linac with straight sections (zero dispersion) at both ends and dispersion suppression between the cryo-units are performed using additional kicks implemented using a flag BUMPS.
Things to do to switch on/off Earth’s curvature:
Straight Linac: CURVE = STEER = 0
BUMPS= 0
Curved Linac : CURVE = STEER = 1
BUMPS= 1
Flags are available in file: ilc007.ML_common.xsif
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

9. Curved Linac: Dispersion Function
Zoomed view
Optimal period dispersion is achieved by minimizing its value at every defocusing quads.
Maximum dispersion in linac is below 3mm.
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

10. LET Studies for ILC Main Linac
Beam tracking studies is performed using LUCRETIA
A Gaussian distribution of 10k macro particles distributed in 4s are tracked through the lattice.
Nominal Straight Linac
Nominal Curved Linac
No emittance growth in straight linac.
Initial abrupt emittance in curved linac is consequence of initial matching.
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

11. Nominal ILC main linac: Trajectory
Straight Linac
Curved Linac
Sudden changes in vertical beam trajectory occurs at transition between cryo-units and at both ends of the linac.
Maximum excursion of vertical beam trajectory is ~0.5 mm.
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

12. Alignment tolerances in Linac
Vertical (y) plane
BPM Offset w.r.t. Cryomodule
300 μm
Quad offset w.r.t. Cryomodule
Quad Rotation w.r.t. Cryomodule
300 μrad
Cavity Offset w.r.t. Cryomodule
Cryostat Offset w.r.t. Survey Line
200 μm
Cavity Pitch w.r.t. Cryomodule
Cryostat Pitch w.r.t. Survey Line
20 μrad
BPM Resolution
1.0 μm
Nominal
Pure Transverse
Pitch/ Tilt.
Misalignment is applied only in ‘Y’ plane.
Short range wake fields are included in analysis.
One to One steering is applied
50 Machines are used.
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

13. Random Misalignment implementation
Random misalignments of elements are distributed in range of +/- 3s
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

14. Misalignment Tolerances Studies
Straight Linac
Emittance growth without and with correction
Distribution of Emittance after corrections
Maximum normalized RMS Emittance without correction is ~4E+06.
After one to one steering correction, max. emittance dilution is limited to 2500 nm
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

15. Misalignment Tolerances Studies
Curved Linac
Emittance growth without and with correction
Distribution of Emittance after corrections
Final mean emittance growth after one to one steering is ~500nm.
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

16. Straight v/s Curved Linac
Mean Emittance Growth for 50 seeds
No Correction
After One to One Correction
Curved and straight linac shows same order of emittance growth without and with correction.
Effectiveness of one to one steering is largely outlined by BPMs alignment.
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

17. Curved Linac: Trajectory
Beam trajectories without and with correction
Golden trajectories after correction
Maximum excursion of beam trajectory without correction is 30mm.
After applying one to one correction, excursion of beam trajectories are limited in +/- 3 s of BPMs offset.
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

18. Curved Linac: Mean trajectory
Element misalignments result in an increase in amplitude of beam trajectory along the linac.
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

19. Emittance growth in curved linac
Recent Updates
ILC2016 Lattices has been released. New requests had been incorporated in lattice.
(M.Woodley presentation)
ILC2016b lattice is not matched for the Earth’s Curvature:
Emittance growth in curved linac
A significant emittance growth in nominal curved linac (no misalignment).
Need to perform a dispersion matching between:
Bunch compressor and Main Linac
Main linac End to following section.
Suppression of dispersion due to Earth’s curvature
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

20. Summary
Earth’s curvature has been implemented in ILC main linac lattice.
Developed several routines and scripts to implement Earth’s curvature in optics.
LET studies have been performed.
Curved linac and straight linac shows similar sensitivity against misalignment errors.
One to one steering scheme reduces the emittance growth. However, its performance is largely outlined by BPMs offset.
Study with more rigorous emittance compensation scheme to validate that emittance growth in main linac remains in allotted budget.
Incorporation of Earth’s curvature for ILC2016 b lattice and performing a LET study.
Correlated Misalignment Studies.
Next Steps
LCWS'16, Morioka, 5-9/12/2016
Arun Saini

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