1. 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 CERN January 2016

2. 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

3. 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  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 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

4. Setup of IPBSM

5. 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 −

7. 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 pulses
It is not possible to measure the beam size of 1st&2nd bunch at the same time

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

9. Position jitter at FONTP3
Bar=𝑗𝑖𝑡𝑡𝑒𝑟/ −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

10. 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=

11. IP waist measurements with 0.5 βy optics

12. IP beam size tuning with 0.5 βy optics

13. 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.

14. 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?

15. 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
and next slide

16. 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

17. 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

22. 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
= nm
Measured beam charge
= x1.6nC
~54% beam charge
Beam position measurement
Norm. Resolution = Geo. factor x
RMS of residual
Calibration factor
= 8.1nm
Measured charge
Nominal charge x

23. 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