ILC Z-pole Calibration Runs Main Linac performance A. Latina (CERN) K. Kubo (KEK) LCWS 2016 – Dec 5-9 2016, Morioka, Japan

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

Energy Profile for Z-pole runs

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

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

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

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

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

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

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

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 20161201 K.Kubo

Emittance growth vs. final energy Average of 40 random seeds. Error bar: standard deviation. 20161201 K.Kubo

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 20161206

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. 20160213 K. Kubo Modified 20161206

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?

Extras

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

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

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

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