1 Experience at ATF To get a low emittance beam Junji Urakawa KEK Circumference: m Arc Cell Type: FOBO Number of Arc Cells: 36 Energy: GeV Tunes: / Extracted Vertical Emittance:  y ≈ 10 pm-rad,  y ≈ 25 nm-rad Natural Emittance : 1nm

22 ATF Introduction E=1.28GeV, N e =2x10 10 e-/bunch 1 ~ 20 bunches, Rep=3.125Hz X emit=2.5E -6 ( at 0 intensity) Y emit=1.25E -8 ( at 0 intensity) Emittance status

3 DRLBW44 Optics

4 Arc Cell QF2SFSDCombined Function Bend (QD)QF1ZVZH BPM Phase Advance Per Cell: 120.3° / 48.5° Phase Advance Between BPMs: 11.6° / 10.7° Each quadrupole has an independent trim Each sextupole has an independent skew quadrupole trim

5 Damping rings for JLC/NLC/(ILC) will need to achieve very low vertical emittance –less than 5 pm (not normalized) 2pm for ILC –roughly factor 2 smaller than so far achieved in electron storage rings (2004) Vertical emittance is an alignment issue –vertical quadrupole misalignments lead to vertical steering which gives vertical dispersion –vertical sextupole misalignments couple horizontal dispersion and betatron motion into the vertical plane Vertical emittance is highly sensitive to misalignments –around 30 µm rms sextupole misalignment will generate 5 pm emittance in otherwise perfect lattice –similar sensitivity in JLC/NLC damping rings Effective correction relies on good performance and understanding of diagnostics BBA can help –“BBA at the KEK ATF”, M. Ross et al, EPAC Why BBA?

6 Sextupole Alignment Vertical emittance after skew correction based on measured beam offset in sextupoles. Includes orbit distortion ~ 100 um.

77 ATF Damping Ring BPM Electronics: single pass detection for 96 BPMs DC-50MHz BW, base line clip & charge ADC, min. resolution ~20µm

88 Spectrum of DR BPM Signal peak at ~ 1GHz

99 BPM electronics improvement Electronics: 40MHz - 1GHz BW, base line clip & low noise LF amp min. resolution ~2µm

10 Resolution Improvement Min. resolution ~ 2µm Estimated Resolution [  m] Bunch Intensity [electrons/bunch] Old first circuit (estimated by beam) Improved second circuit (estimated by calibration pulser)

11 Vertical orbit Improvement

12 Vertical dispersion Improvement

13 X to Y coupling Improvement

14 Laser wire beam size monitor in DR 14.7µm laser wire for X scan 5.7µm for Y scan (whole scan: 15min for X, 6min for Y) 300mW 532nm Solid-state Laser Fed into optical cavity

15 Beam profile by Laser wire  e 2 =  meas 2 -  lw 2  =  e 2 – [  (  p/p)] 2  :measured by Q-trim excitation

16 Emittance by Laser wire < 0.5% y/x emittance ratio Y emittance =4pm at small intensity

17 BPM Offset Measurement Technique make a closed local bump at target BPM use quadrupole or sextupole (skew quad) trims (ΔQ) make grid scan of bump amplitude and trim setting for each bump value make difference orbit w.r.t. to trim=0 fit difference orbits for kick (k) at quadrupole or sextupole for each bump value fit kick vs trim: k = f (ΔQ) = m ΔQ+b - m is offset from magnetic center - for some trajectory through the magnet, m = 0 plot fitted offset vs absolute reading of target BPM - horizontal intercept is BPM offset

18 Measurement Challenges intrinsic BPM resolution (intensity dependent; e-/bunch, 40 5  10 9 e-/bunch) orbit averaging intensity dependent position calibration monitor intensity stability during acquisition beam losses in ring cause fluctuating BPM readings acquisition: bump/trim range selection (too big … losses; too small … resolution) analysis: monitor and cut on relative intensity (stored/injected) energy drift add energy error to horizontal orbit fits time (single-turn orbit acquisition at 3 Hz machine rate; 20 orbit averaging; 5 bump steps; 5 trim settings; 100 BPMs; x and y) automate data acquisition (  8 minutes/magnet for a single plane)

19 Improved BPM Electronics (2003)

20 Possible Sextupole-Systematic Error Sources SF SD differential saturation IRIR I L  I R ILIL

21 BPM Performance Measurements of changes in the closed orbit are subject to systematic and random errors –BPM dependence on current –changes in beam energy –BPM noise All relevant effects need to be understood to extract meaningful results from BBA data Model Independent Analysis provides a simple but powerful tool for identifying systematic effects –collect a data set consisting of a large number of orbits, with no deliberate changes in machine settings –analyze the data set to identify correlated changes in BPM readings –correlated changes arise from different sources orbit changes energy changes current changes –uncorrelated changes indicate BPM noise

22 Current Dependence What affects the systematic current dependence? Effect of calibration Effect of changing the duty cycle Variation over 24 hours Red boxes = current correlation, no calibration: Black boxes = correlation with calibration Red boxes = current correlation, reduced duty cycle: Black boxes = correlation, full duty cycle Red boxes = current correlation, March 7: Black boxes = correlation, March 6

23 Good, Bad, Ugly Bad Fit Good Fit

24 Fits to BBA Orbits Green line = MIA modes 1-4 Points = measured difference orbits

25 Dispersion Correction First attempt RMS reduced from 2.3 mm to 1.6 mm Second attempt (after using BBA results to steer through sextupoles) RMS increased from 3.7 mm to 6.5 mm - as predicted! black boxes = measured dispersion before correction red boxes = measured dispersion after correction red line = predicted dispersion after correction black boxes = measured dispersion before correction red boxes = measured dispersion after correction red line = predicted dispersion after correction

26 ATF achieved ~4pm vertical emittance More challenges to reach ~1pm simulation: BPM offset error should be < 0.1 mm. (“BBA”) --> εy ~ 2 pm DR BPM upgrade (SLAC,FNAL,KEK) Magnet re-alignment, < 30 μm. --> εy ~ 1 pm Measured in DR Single bunch

27 Goal: Generation and extraction of low emittance beam (ε y < 2 pm) at the nominal ILC bunch charge A major tool for low emittance corrections: a high resolution BPM system –Optimization of the closed-orbit, beam-based alignment (BBA) studies to investigate BPM offsets and calibration. –Correction of non-linear field effects, i.e. coupling, chromaticity,… –Necessary: a state-or-the-art BPM system, utilizing a broadband turn-by-turn mode (< 10 µm resolution) a narrowband mode with high resolution (~ 100 nm range) DR-BPM Upgrade (FNAL/SLAC/KEK)

28 Narrowband Mode Resolution Triggered at turn #500,000 ~200 ms position data per shot (1280 narrowband mode BPM measurements). 126 tap box car filter to reject 50 Hz: ~ 800 nm resolution removing modes with hor./ vert. correlation: ~200 nm resolution DR BPM upgrade - Hardware Overview -

Stored Beam – 10 minute time scale; ATF lifetime ~ few minutes DR BPM resolution improvement by digital read-out system (SLAC, FNAL, KEK) beam position read-out vs. beam intensity: scattered plot : existing analog circuit. line plot : digital read-out introduced for test. εy ~ 1 pm への挑戦 Digital read-out Analogue read-out

30 The ATF Damping Ring / 96 BPMs were upgraded. Planning to upgrade all (96) BPMs.

31 ILC シンポジウム, 物理学会 2008 春 Fast Ion Instability -observed at ATF in Bunch

32 ILC シンポジウム, 物理学会 2008 春 Study on the Fast Ion Instability (KEK,DESY,SLAC,KNU) 2007/Dec~ Under tuning…

Gas Injection system in ATF-DR Continuous gas leak into the beam chamber. We can control the leak rate of N 2 gas. Pressure range: Pa ~10 -3 Pa.

34 Multi-bunch Turn-by-turn monitor The beam blowup at tail bunches was measured by the laser wire in ATF, which is assumed coming from FII effect. In order to observe the individual beam oscillation in the multi-bunch beam, multi-bunch turn-by-turn monitor has been developed. This monitor consists of front end circuits(amplifier and filter) and DPO7254 scope. The scope can store the waveform up to 2ms with 100ps time resolution. The preliminary results shows the different oscillation amplitude of the tune-X and the tune-Y for the 1st and 2nd bunches at just after injection. Tune-X Tune-Y 1st 2nd When one bunch from many bunches is kicked, we hope other bunches have almost no oscillation.