Status towards Goal 3 (Intensity dependence, - PowerPoint Presentation

Slide1

Status towards Goal 3(Intensity dependence, Wakefield issues)

ATF TB Mtg. 201502

K.Kubo

Slide2

Intensity dependence of IP

b

eam size

Studies using on-mover structures

Beam size at IP

Orbit change

OTR

chamber wake

Some new

reports

Updated

wakefeild

caclulations

Wakefield-Free steering test and Intensity dependent orbit

Simulation of

wakefield

+ orbit jitter, affecting IP beam size

Slide3

IPBSM modulation as function of bunch population. Measured with crossing angle 174 degrees (left) and 30 degrees (right).

Beam Size Depends on

B

unch Intensity

Presented in IPAC14

Slide4

IP beam size growth from measured beam – Cavity BPM center offset

.

Experiment showed factor 6 larger effect than calculation.

This calc. Included cavity BPMs only.

May underestimate

wakefield

. But factor 6 difference seems too much

.

There must be other sources or/and effects than misalignment of

CavBPMs

.

(19 nm/

nC

)

Okugi’s

slide in

proj

. mtg. Feb. 2014

Slide5

Calc. by A. Lyapin

More calculations

Examples of wake calculations

Slide6

Slide this morning, J.

Snuverink

, et.al.

Slide7

Slide this morning, J.

Snuverink

, et.al.

Slide8

J.Snuverink, et.al., LCWS2014

Wake source on mover experiment

-- orbit change

OLD

Slide9

Slide this morning, J.

Snuverink

, et.al.

Slide10

Slide this morning, J.

Snuverink

, et.al.

Slide11

Slide this morning, J.

Snuverink

, et.al.

Slide12

C-band

ref.

No mask Bellows

Masked Bellows

Experiment

55

47~50

7

Calc

32.2

22.6

?

IP beam size vs mover position

experiment and calc.

Effect of wake source at the mover, offset 1 mm, bunch charge 1 nC.

IP beam size

increase (nm/mm/nC)

ATF2 weekly meeting 20130708

　

K.Kubo

Factor 1.7 – 2.2 larger than calculation

consistent wit orbit change measurement

New improved calculation should reduce

t

his discrepancy too.

Slide13

Effect of OTR monitor chamber (beam size monitor in EXT line) to IP vertical beam size was found (June 2014)

IPBSM 174 degrees

N~0.3E10

Slide14

Photo by D. McCormick

OTR monitor View Port Shield

No shield

With shield

by A.

Lyapin

by A.

Lyapin

Remove vertical asymmetry

Reduce position dependent wake

(

factor 0.6)

0.08 V/

pC

/mm

 0.05 V/

pC

/mm

Wakefield of OTR Chamber

Slide15

Before OTR2X position optimization After optimization (174

deg

mode)

100

nm/

nC

 58 nm/

nC

By

Okugi

, 2014.6.23

Removal of all OTRs

121

nm/

nC

 76 nm/

nC

(30

deg

mode)

Okugi

,

2014.6.26 ATF Op. meeting

Dependence reduced by optimizing position or removing chamber

. (similar effect)

(30

deg

mode tend to give stronger dependence than 174

deg

mode.)

Slide by

K.Kubo

in ATF operation meeting Nov 7, 2014

Slide16

Okugi

, 2014. June 6, ATF Operation meeting

IP beam size intensity dependence changed when OTR chamber moved.

Wakefield of 0.3V/

pC

/mm is necessary for explanation.

Calculated

wakefield

is about 0.08 V/

pC

/mm

Slide17

Orbit Change vs. OTR chamber position

(

Okugi

,

2014.10.31 ATF Op. meeting)

About 6-

10 times bigger than expected from calculation (OTR chamber only)

Peak ~

0.05 V/

pC

/mm

Kick

angle/offset

(

urad

/mm)

Wake (average in a bunch)

(V/

pC

/mm)

OTR0

0.374

0.47

OTR1

0.317

0.40

OTR2

0.233

0.30

OTR3

0.240

0.30

(Oct.

28, 2014, one BPM)

(Nov. 11, 2014, many downstream BPMs )

(Kubo, 2014.11.11 owl shift log)

Slide18

E

xperiments compare with calculations

Movable

Wake source

Reference cavit

y

on mover

Used to be different by factor

1.8~2 larger

(Both

IP beam

size and Orbit

)

 About 1.2 now (new calculation)OTR

chamber wake

Factor

4 larger (IP

beam

size) (not very accurate?)

Factor 6~10 larger

(Orbit

)

Need to consider other moving parts.

Will be more accurate calculations soon.

Strong intensity dependence after optimizing cavity and chamber positions

Not understood yet. But some hypothesis.

Possible effect of orbit jitter

Different shape of

wakefiled

, which cannot be compensated by on mover structures.

Slide19

Effect of orbit jitter + wakefield

Large position jitter at high-beta region.

Wakefields

give jittering z-dependent transverse kick.

Jitter at IP is enhanced.

Beam size (of one bunch)

is also enlarged

.

Projected beam size will be even larger.

Jitter enhancement can be detected using IPBPM

IPBSM data selection using BPMs at high beta region will reduce measured beam size.

Slide20

Projected profile (y distribution) at IP

Orbit jitter + Wakefield

5 examples of vertically projected

s

ingle bunch

profile at IP

vertically projected profile of

100 pulses at IP (3 charge/bunch)

Slide21

Recent and near future studiesWake Free Steering experiment, intensity dependence of orbit. More analysis and data taking planned

Use

IPBPM as bunch tilt

monitor?

Can be used, in principle.

Need more quantitative estimation for sensitivity.

Slide22

Summary

Understanding

wakefield

of on-mover

wake source

(

refCav+bellows

)

improved.

Experiments and calculations are (almost) consistent.

Significant improvement in last year, taking care of OTR chamber wake.But, still big discrepancy with calculations.

Efforts to detect intensity dependent orbit and identify yet-unknown wakefield source. (includes wake-free steering study.)

N

o

new

wakefield

sources discovered so far

.

Need to check sensitivity with reasonable BPM resolution

IPBPM will be important for

wakefield

studies too.

Slide23

Wakefield in ILC FF

Effects of transverse wakefield will be much smaller than in ATF2

High energy, short bunch length

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, solving the apparent discrepancies between observations and calculations is still important