Experimental Program in ATF

• Brief Introduction of present ATF/ATF2• Low Emittance Study

• Fast Ion Study

N. Terunuma, KEKLER11, Heraklion, Crete, Greece, 2011/Oct/4

Challenging goals for ATF/ATF2

An important technical challenge of ILC is the collision of extremely small beams of a few nanometers in vertical size.

ATF/ATF2 will address the development of the techniques for following issues:

1.Achieve the small vertical emittanceATF-DR 4 pm 2 pm (ILC) or 1 pm

2.Demonstrate the ILC final focus opticsachieve the 37 nm vertical beam size at the IP

3.Stabilize the the beam position in a few nanometer level at the IP.

The ATF international collaboration is strongly promoting these activities.

Photo-cathode RF gun(Multi-bunch electron source)

S-band Linac

Previous EXT line (~Jun.2008)

ATF2 beam line (ILC Final focus test system)

Damping Ring~140 m

KEK Accelerator Test Facility (ATF)Energy: 1.3 GeV, Repetition: 1.56 HzIntensity: 1x1010 e-/bunch (max. 2x1010), 1~20 bunches/pulseEmittance: Design, 1 nm(H)/ 10 pm(V), Achieved 4 pm(V)

ATF2 Overview

Damping Ring

Focal Pointy~37nm

Extraction beamlineFinal Focus (FF) SystemDamping

Ring

y~10pm

Use a low emittance beam extracted from DR ~10 pm 37 nm vertical beam size

Low Emittance Studies toward 2 or 1 pm

Low emittance tuning in ATF Damping Ring

Review off Old Experiences + Plans

2011.10.

Kiyoshi Kubo (KEK)

History of Low Emittance in ATF DR• There were great efforts to achieve low vertical emittance

since DR commissioning.– From the end of 2000 to 2002, we observed the lowest vertical

emittance in DR about 10 pm.• After improvement of hardware, with software and simulation

works, we constantly achieved lower than 5 pm at low intensity (N 0), and lower than 8 pm at high intensity (N~1E10)., which was lower than “designed” emittance. (2003)

• Since then, basically no farther improvement till 2008.– We have not really pursued lower emittance. – Emiitance became larger.

• Re-start low emittance studies from 2009 (or late 2008)– Emittance recovered

• For further improvement– BPM electronics replaced. (finished in 2010)– Re- alignment (in this summer) K. Kubo(KEK)

Vertical emittance measured by Laser Wire (April 16, 2003)

by Y.Honda

Laser wire monitor is still the most accurate emittance monitor in ATF DR. But the measurement is time consuming.We use X-ray synchrotron radiation profile monitor as a real time monitor.

K. Kubo(KEK)

Measured vertical emittance (2009 Dec)XSR=8.56±0.46 pm, IF=8.43±1.79 pm,LW00 =3.50±1.78 pm, LW01=2.00±1.61pm under the poor laser intensity

DR Emittance Summary (single bunch)

2009 autumI=4-5x109

2009 springI=5-6x109

in EXT

in EXT

= Toward the 2(or1) pm emittance =Simulation - correction(1)

Three consecutive corrections:

Simulate actual procedureMonitor:

BPM (total 96)

Corrector:

Steering magnets (47 horizontal and 51 vertical)

Skew Qauds (trim coils of sextupole magnets, total 72)

• COD correction• Vertical COD-dispersion correction• Coupling correction

K. Kubo(KEK)

= Toward the 2(or1) pm emittance = Old simulation of ATF DR emittance tuningERRORS: (tried to reproduce actual condition, not confirmed)• Misalignment of magnets: as measured

+ random 30 micron offset

+ random 0.3 mrad. rotation• BPM error : offset 300 micron wrt nearest magnet, rotation 0.02 rad.

measured misalignment

K. Kubo(KEK)

Simulation - correction(2)

(a) COD correction: using steering magnets, minimize

and , :x(y): horizontal (vertical) BPM reading.

(b) V-COD-dispersion correction: using steering magnets, minimize

y: measured vertical dispersion.

r : weight factor = 0.05

(c) Coupling correction: using skew quads, minimize

x(y): horizontal (vertical) position change at BPM due to excitation of a horizontal steering magnet.

Two horizontal steering magnets were used (Nsteer=2). About (n+1/2) phase advance between the two.

K. Kubo(KEK)

Emmitace, dispersion and coupling of each stageCOD corrected

Dispersion corrected

K. Kubo(KEK)Rms of vertical dispersion C_xy

_y

_y _y

_y

C_xy Rms of vertical dispersion

Simulated vertical emittance

Corrections Average Ratio of target (11pm)

COD 23 pm 20%

+ Dispersion 16 pm 51%

+ Coupling 5.8 pm 91%

COD+Dispersion+coupling

COD+Dispersion

COD

y (pm)

Num

ber

of e

ntrie

s

Distribution from 500 random seeds

Original goal

K. Kubo(KEK)

For lower emittance BPM offset error should be small (~100 m)

K. Kubo(KEK)

Magnet alignments (< 30m) are important,(only) if BPM offset error is small

and for very low emittance

K. Kubo(KEK)

Quad strength error should be small (<0.5%)

Emittance, 90% random seeds are lower than that.(A few seeds give extremely large emittances which make plots of average useless.)

K. Kubo(KEK)

Low emittance study SUMMARYSimulation:• BPM offset error should be (w.r.t. nearest magnet) small.

– Beam based alignment measurement using good BPM system will make it possible.

– Then, εy ~ 2 pm will be achieved. (if offset error < 0.1 mm)• Magnet re-alignment, RMS < 30 μm.

– Then, εy ~ 1 pm will be achieved.– Realistic alignment model?

• Quad strength error should be 0.5% or smaller– It may have been achieved already, but not confirmed.– Beam based optics measurement (Orbit Response Matrix) with good BPM

system make it possible.What we need:• Good BPM system, which we have now. TBT analysis will be planed.• Good alignment.• Good software tools, etc.

– Make measurements and analysis faster.– New correction methods?

• Good emittance monitor.

K. Kubo(KEK)

DR BPM Upgrade for 2 pm emittanceThe original read-out system designed for the single path position measurement has a 10 m resolution.

Upgraded BPM readout system: FNAL-KEK collaboration

•Broadband turn-by-turn mode (< 10 µm resolution)

•Injection 1,000 turns•Extraction 64 turns

•Narrowband mode with high resolution (~ 100 nm range)

•160 ms, 500,000 turns after injection

Installed in 2010 for all DR BPMs (96)

Downmix box at the beamline

BPM digitizer station

The most accurate emittance monitor in ATF DR.

14.7µm laser wire for X scan 5.7µm for Y scan

But the measurement is

time consuming.(scan: 15 min for X, 6 min for Y)

Laser Wire with Optical Cavity (DR)

300mW 532nm Solid-state Laserfed into optical cavity

Multi-bunch separated measurement

Zone plate

image of 1ms exposure

SR X-ray beam line

x = 48.2 ± 0.5 [m]y = 6.4 ± 0.1 [m]

Real-time monitor for emittance tuning in DRX-Ray Telescope using Zone Plate at 3.2KeV magnification : 20

– Non destructive measurement

– High resolution (< 1m)– 2D direct imaging of the electron beam

– Exposure time (1 ms ~ 20 ms)

X-ray SR Monitor (XSR)

Alignment: present situationDisplacement was measured after the 3.11 earthquake (Enlarged image)

after earthquakeRough alignment in May

•1.5 mm wider(N-S) than the original design. When??•New design was defined as wider but same circumference.

Alignment work should be continued: DRAfter earthquake, aligned in June, aligned in summer

- 2.0

mm

+2.0 mm

Horizontal Longitudinal

all

B

Q

Sx

- 2.0

mm

+2.0 mm

Recovery of beam in DR (x1010 e/bunch)A stored beam was delivered to the dump of ATF2.No critical damage on the accelerator was found.

6/1 6/3 6/8 6/10 6/13 6/17 6/24 6/30

0.5x1010

1.0x1010

3 trains

XSR

read

y

Compton2-mirror

FON

T

3 trains

Cavity BPMsFFTB moverHAPS

Freq. A

djust

V-emittance

(XSR

) ~30pm

DR rough alignment for checkout was continued in daytime.

Insp

ectio

n of

the

radi

atio

n sa

fety

Status of the Fast Ion Study at ATF

Devices for FII study

One Path

One Path

One Path & multi-turn

Superposition of multi-turn

Superposition of multi-turn

Exa

mp

le:

mu

lti-b

un

ch b

ea

m s

ize

, 2

00

9m

ay1

9

0.4x1010/bunch0.3x1010/bunch0.1x1010/bunch

Lower emittance < 10 pmGood base vacuum pressureHigh intensity Laser Wire Monitor

Need clear signals!

2009

~10 pm

2004

Bunch Number

Bunch Number

Clear FII was measured in 2004.Most of the machine time was assigned for the study of the low emittance multi-bunch beam.

After the ITRP’s cold LC selection, The target of R&D was shifted to the development of the ATF2 (ILC final focus) instruments.

Several years later, the needs for low emittance were raised again but not enough time for tuning a beam and instruments.

Fast Ion Study at ATF

FII study on 2007/3/13-14(2)

5mA/20bunches 10mA/20bunches 20mA/20bunches

We measured emittance of each bunch in a 20-bunch beam in the DR with a laser-wire monitor. No clear emittance blow-up along a train was observed up to 20mA/train. One of the reason may be the bigger vertical emittance compared with the data taken in 2004.

70 pm

0

20 pm

Fast Ion Study at ATF

We need followings for this study…

•Low emittance beam < 10 pm Now, the 2 pm emittance study is started. Situation for the FII study becomes better and better!

Difficulties are in the coexistence with other R&D programs…

•Stable multi-bunch beamNot enough tuning time for multi-bunch beam because of too much single-bunch programs

•Good multi-bunch emittance monitorIncrease the LW signal is required. Under working.

We will try to resume the study under above boundary.

Summary

The KEK-ATF has challenging goals to develop the key technology for ILC.

One of them is the achievement of 2 (or 1) pm vertical emittance. This study has been started.

We are continuing the alignment work to recover the machine from the earthquake and also to realize the 2 pm low emittance beam. The fast ion study will be resumed too.