Summary of the ATF2 project meeting at LAL (Jan.13-15, 2016) Philip Bambade Laboratoire de l’Accélérateur Linéaire Université Paris 11, Orsay, France CLIC workshop 2016 CERN 20 January 2016

Sessions https://agenda.linearcollider.org/event/6939/ Wednesday 13 - Status of beamline alignment, hardware and software at ATF - 19th Technical Board & System Group Coordinator Session Thursday 14 - Status of beam tuning for 37nm beam (Goal-1) - Beam size tuning at the nominal beam intensity, wakefield issues Friday 15 - IP beam stabilization at nanometer level (Goal-2) - Future Plans

Main considerations 1) Beamline hardware maintenance and improvement 2) Focus and maintain small  37 nm beam size (Goal 1) - demonstrate correction of ILC-like chromaticity  40-50 nm routinely - conditions: 10  nominal βx and  1/10 nominal beam charge  consistent with ILC after scaling higher order multipole and wakefield effects - further beam size reductions, e.g. “ultra-low ” optics for CLIC-like chromaticity  multipoles, wakefields, jitter, measurement precision & tuning… - difficulty of beam size measurement at ATF2 compared to ILC/CLIC 3) Beam position jitter  stabilization (Goal 2) - 10 nm stability needed for beam size measurement (Goal 1) - enhanced sensitivity to jitter from wakefield effects at ATF2 - demonstration of two-bunch feedback stabilization in ILC-like conditions (FONT) - nanometer resolution in IP beam position measurement ( stabilization) not yet shown  range 15-30 nm with present triplet of IP-BPMs  not required for ILC/CLIC (only ATF2) 4) R&D for new instruments and methods - Beam halo measurement and collimation - Ground motion feedforward - OTR/ODR

Setup of IPBSM

Concept of IPBSM Modulation depth 𝑀= 𝑁 + − 𝑁 − 𝑁 + + 𝑁 − Small beam size ⇒ large 𝑀 Large beam size ⇒ small 𝑀 Modulation depth 𝑀= 𝑁 + − 𝑁 − 𝑁 + + 𝑁 −

2nd bunch IPBSM measurement 𝑒 − Laser Detector signal Fringe phase ~200 ns Timing of the IPBSM laser is matched to 2nd bunch timing Beam size measurement is done by measuring 100-200 pulses It is not possible to measure the beam size of 1st&2nd bunch at the same time

FONT upstream feedback Vertical steering magnets Extraction line FONT stripline BPMs and kickers Damping Ring

Position jitter at FONTP3 Bar=𝑗𝑖𝑡𝑡𝑒𝑟/ 2 100−1 Jitter source amplitude 𝐽 Position jitter at FONTP3 [μm] 𝜎 Δ𝑦 ′ = 𝜎 Δ𝑦,0 2 + 𝜎 Δ𝑦 2 𝜎 Δ𝑦 /𝐽=12.8 μm 𝜎 Δ𝑦,0 =1.6 μm 𝜒 2 / 𝑁 𝑑𝑜𝑓 =4.0/2 𝜎 Δ𝑦 =1.3 μm Standard deviation = 0.04 μm

Jitter source amplitude dependence Bar = fit error Jitter source amplitude 𝐽 Modulation Standard deviation= 0.03 𝑀= 𝑀 0 exp −2 𝑘 𝑦 2 𝜎 Δ𝑦 2 𝜎 Δ𝑦 𝐽 =131 nm 𝜒 2 / 𝑁 𝑑𝑜𝑓 =3.4/2 ( 𝑘 𝑦 ∼IPBSM laser wavelength) M=0.29+-0.01

IP waist measurements with 0.5 βy optics

IP beam size tuning with 0.5 βy optics

Wakefields measurements compared with calculations Position of Wake sources on movers (IP beam size and Orbit) Reference cavity on mover Larger by factor ~1.4 OTR chamber wake Consistent (Bellows are significant wakefield sources) Strong intensity dependence after optimizing cavity and chamber positions Not understood yet.

Dynamic effects Large orbit jitter and strong wakefield can explain observed intensity dependence. 0.3s orbit jitter and 1.7~2.1 times stronger wake than CavBPM explain intensity dependence of 60~75 nm/nC (previous meeting) Wakefield sources at high beta region are important. Data selection for in IPBSM analysis, using BPM position, was tried but clear improvement could not be seen. For confirmation, we need data of fringe scans with large number of pulses (many scans and/or many pulses/scan) at high intensity (?) See also Kano’s presentation (IPBSM with upstream FONT feedback) Can we use FONT BPMs for data selection?

Wakefield in ILC FF compared with ATF2 Effects of transverse wakefield will be much smaller than in ATF2 High energy, short bunch length (see next slide) Beam pipe aperture will be similar Except for collimators (special care will be necessary) Careful design of beam pipe and structures in the beam line But, understanding the intensity dependence and comparison between observations and calculations are important See http://atf.kek.jp/twiki/pub/ATF/CompareWakeILCAT2/wakecompare-ILCATF-v3.pdf and next slide

Misalignment Orbit jitter ILC ATF2 Dependence Ratio of effect ILC/ATF2 Beam Energy 250 GeV 1.3 GeV 1/E 0.0052 Bunch length 0.3 mm 7.0 mm Shape pf wake ~0.5 Emittance 0.07 pm 12 pm 13 Sum of Beta-function 310 km 58 km 2.3 Total   0.078 Orbit jitter   ILC ATF2 Ratio of effect ILC/ATF2 Beam Energy 250 GeV 1.3 GeV 1/E 0.0052 Bunch Length 0.3 mm 7.0 mm Shape pf wake ~0.5 Sum of Beta-function 310 km 58 km 5.3 Total 0.014

Misalignment ILC ATF2 Dependence Ratio of effect ILC/ATF2 Beam Energy 250 GeV 1.3 GeV 1/E 0.0052 Bunch length 0.3 mm 7.0 mm Shape pf wake ~0.5 Emittance 0.07 pm 12 pm 13 Sum of Beta-function 310 km 58 km 2.3 Total   0.078 Effect of misalignment at ILC with bunch population 2E10 will be similar to that at ATF with bunch population 0.16E10. Effect of betatron oscillation at ILC with bunch population 2E10 will be similar to that at ATF with bunch population 0.03E10. Orbit jitter   ILC ATF2 Ratio of effect ILC/ATF2 Beam Energy 250 GeV 1.3 GeV 1/E 0.0052 Bunch Length 0.3 mm 7.0 mm Shape pf wake ~0.5 Sum of Beta-function 310 km 58 km 5.3 Total 0.014

The results of IPBPM resolution test at Dec 2015 in ATF2 X Convert to residual Beam position prediction Residual value = measured position – predicted position X Measured resolution = 15.0193nm Measured beam charge = 0.5423x1.6nC ~54% beam charge Beam position measurement Norm. Resolution = Geo. factor x RMS of residual Calibration factor = 8.1nm Measured charge Nominal charge x

Participants on-going or recent ATF2 graduate student * ARAKI Sakae, KEK Japan * BAMBADE Philip CNRS LAL IN2P3 France BERGAMASCHI Michele CERN Switzerland * BETT Douglas CERN Switzerland * BLASKOVIC KRALIEVIC, Neven Oxford University U.K * BROMWICH Talitha University of Oxford U.K BURROWS Philip Oxford University U.K FAUS-GOLFE Angeles IFIC - LAL Spain * FUSTER Nuria IFIC Spain * JANG, Si-Won KNU Korea * JEREMIE, Andrea CNRS LAPP IN2P3 France * KANO, Yuya University of Tokyo Japan * KIEFFER Robert CERN Switzerland * KUBO, Kiyoshi, KEK Japan * NAITO Takashi, KEK Japan * OKUGI, Toshiyuki KEK Japan * PATECKI Marcin CERN Switzerland * PLASSARD Fabien CERN Switzerland SCHUETZ Anne DESY Germany * TAUCHI Toshiaki KEK Japan * TERUNUMA Nobuhiro KEK Japan TOMAS Rogelio CERN Switzerland * WALLON Sandry CNRS LAL IN2P3 France WHITE Glen SLAC USA YAMAMOTO Akira KEK & CERN Japan YANG Renjun CNRS LAL IN2P3 France Participants on-going or recent ATF2 graduate student remote participant * speaker