1

Experience at ATFTo get a low emittance beam Junji Urakawa

KEK

Circumference: 138.56 mArc Cell Type: FOBONumber of Arc Cells: 36Energy: 1.279 GeVTunes: 15.192 / 8.542Extracted Vertical Emittance: y ≈ 10 pm-rad, y ≈ 25 nm-rad

Natural Emittance : 1nm

22

ATF Introduction

E=1.28GeV, Ne=2x1010 e-/bunch 1 ~ 20 bunches, Rep=3.125HzX emit=2.5E-6( at 0 intensity)

Y emit=1.25E-8( at 0 intensity)

Emittance status

3

DRLBW44 Optics

4

Arc CellQF2 SF SD Combined Function Bend (QD) QF1 ZV ZH

BPMBPM

Phase Advance Per Cell: 120.3° / 48.5°Phase Advance Between BPMs: 11.6° / 10.7°Each quadrupole has an independent trimEach 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 2002.

Why BBA?

6

Sextupole Alignment

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

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

77

ATF Damping Ring BPMreference

plane

referenceplane

EBW

referenceplane

19.5 mm

ceramics

button (SUS304)

flange (A3003)HIP transitiontop block (Ti)

SMA connector

pin (Kovar)brazing (Ag-Cu)

brazing (Al)

Button BPM for Damping Ring

ø24mm

70mm

Button electrode assemblycross section of BPM camber

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

40

45

50

55

60

65

107 108 109 1010

DR

BP

M(M

B30

R)

spec

trum

[dB

V]

Freqency [Hz]

DR button BPM beam signal spectrum out from 40m RG223/u cable

99

BPM electronics improvement

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

ch 1

ch 2

ch 3

ch 4

calibration pulse

HPF 50MHz LPF1000MHzATT

LPF135MHz

Gain change

RF amp 40 ~ 1000MHz Gain 28.5dB 25dBm output

LF amp DC~ 155MHz Gain 15dB 19dBm output

Microwave diode detector 600 ~ 1000MHz

RF combiner

4-way splitter

-20dB

Improved BPM Circuit ( simplified diagram )

single bunch

multibunch

ch 2

ch 3

ch 4

SMA

SMA

SMA

SMA

SMA

QLA

QLA

QLA

QLA

gain change control flat

ch 1

ch 2

ch 3

ch 4

signal from BPM signal to charge ADC

1010

Resolution Improvement

Min. resolution ~ 2µm

1

10

100

108 109 1010 1011

Estim

ated

Res

olut

ion

[

m

]

Bunch Intensity [electrons/bunch]

Old first circuit(estimated by beam)

Improved second circuit(estimated by calibration pulser)

1111

Vertical orbit Improvement

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

0 20 40 60 80 100

Y orbit before BPM improvement (26Nov2002)

Y C

.O.D

. [m

m]

BPM number

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

0 20 40 60 80 100

Y orbit after BPM improvement (20May2003)

Y C

.O.D

. [m

m]

BPMnumber

1212

Vertical dispersion Improvement

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

0 20 40 60 80 100

Y dispersion before BPM improvement (26Nov2002)

Y d

ispe

rsio

n [m

m]

BPMnumber

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

0 20 40 60 80 100

Y dispersion after BPM improvement (20May2003)

Y d

ispe

rsio

n [m

m]

BPMnumber

1313

X to Y coupling Improvement

-200.0-150.0-100.0

-50.00.0

50.0100.0150.0200.0

0 20 40 60 80 100

dY by ZH2R 26Nov2002

dY[m

icro

n]

BPMnumber

-200.0-150.0-100.0

-50.00.0

50.0100.0150.0200.0

0 20 40 60 80 100

dY by ZH4R 26Nov2002

dY[m

icro

n]

BPMnumber

-200.0-150.0-100.0

-50.00.0

50.0100.0150.0200.0

0 20 40 60 80 100

dY by ZH2R 20May2003

dY[m

icro

n]

BPMnumber

-200.0-150.0-100.0

-50.00.0

50.0100.0150.0200.0

0 20 40 60 80 100

dY by ZH4R 20May2003

dY[m

icro

n]

BPMnumber

1414

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 LaserFed into optical cavity

1515

Beam profile by Laser wire

e2 = meas

2 - lw2

= e2 – [(p/p)]2 :measured by Q-trim excitation

1616

Emittance by Laser wire

< 0.5% y/x emittance ratio

Y emittance =4pm at small intensity

1 10-9

1.2 10-9

1.4 10-9

1.6 10-9

1.8 10-9

2 10-9

0 2 109 4 109 6 109 8 109 1 1010

X emittance by LW

X emittance (single bunch)emitt_x

X e

mit

tanc

e

Bunch Intensity

0.5% coupling Calculation

LW X emit(single 16APR03)0

2 10-12

4 10-12

6 10-12

8 10-12

1 10-11

0 2 109 4 109 6 109 8 109 1 1010

Y emittance by LW

Y emittance (single bunch)Y emittance (15bunch projected)emitt_y

Y e

mit

tanc

eBunch Intensity

0.5% coupling Calculation

LW Y emit(single 16APR03)LW Y emit(15 bunch 6JUN03)

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; 20 μm @ 1010 e-/bunch, 40

μm @ 5109 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)

0 20 40 60 80 1000

5

10

15

20

25

30

35

Quadrupole BBA Offset Fit Error (m)

BBA Offset Fit Errors: old and new BPM electronics

old BPMs (rms= 28.2 um)new BPMs (rms= 9.0 um)

0 20 40 60 80 1000

2

4

6

8

10

12

14

16

18

20

Sextupole BBA Offset Fit Error (m)

BBA Offset Fit Errors: old and new BPM electronics

old BPMs (rms= 51.8 um)new BPMs (rms= 42.6 um)

20

Possible Sextupole-Systematic Error Sources

SF SD

differentialsaturation

IR

IL IR

IL

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 DependenceWhat 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 1-4Points = measured difference orbits

25

Dispersion CorrectionFirst attemptRMS 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 pm2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 2 109 4 109 6 109 8 109 1 1010

Vertical Emittancey emittance (run B)y emittance (run D)simulation (0.4% coupling)

y e

mit

tan

ce [

10-1

2]

bunch intensity [electrons/bunch]

GLC Design

Measured in DR

Single bunch

27

Goal:Generation and extraction of

low emittance beam (εy < 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

30

20 / 96 BPMs were upgraded.

Planning to upgrade all (96) BPMs.

31ILC シンポジウム , 物理学会 2008春

Fast Ion Instability -observed at ATF in 2004-

Bunch

32ILC 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

0

2 10-6

4 10-6

6 10-6

8 10-6

1 10-5

1.2 10-5

0 10 20 30 40 50 60

GasInject-subtract-071210

CCG 1CCG 2CCG 3CCG 4CCG 5CCG 0

y = 1.7802e-7 + 2.206e-7x R= 0.9985

Delt

a-P

(P

a),

CC

GFlow Controller %

• Continuous gas leak into the beam chamber.• We can control the leak rate of N2 gas.• Pressure range: 10-7 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.

0.0 100

1.0 10-11

2.0 10-11

3.0 10-11

4.0 10-11

5.0 10-11

0 5 10 15 20

Vertical Emittance of Multibunch

Y_emittance(00mode, 1.6E9intensity)Y_emittance(00mode, 3.7E9intensity)Y_emittance(01mode, 6.3E9intensity)

Ver

tica

l E

mit

tan

ce o

f ea

ch b

un

ch

Bunch Number

1.6x109

3.7x109

6.3x109

GLC Design

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 iskicked, we hope other bunches have almost no oscillation.