observation of octupole driven resonance phenomena with space charge

Elias Métral, COULOMB’05, Senigallia (AN), Italy, September 12-16, 2005

1/29

OBSERVATION OF OCTUPOLE DRIVEN

RESONANCE PHENOMENA WITH SPACE CHARGE

AT THE CERN PROTON SYNCHROTRON

Invited talk (40 min, 29 slides)Invited talk (40 min, 29 slides)

E. MétralE. Métral M. Giovannozzi, M. Martini, R. Steerenberg M. Giovannozzi, M. Martini, R. Steerenberg (CERN), G. Franchetti, I. Hofmann (GSI)(CERN), G. Franchetti, I. Hofmann (GSI)withwith

2 measurement campaigns: 14-18 October 2002 22-29 September 2003


2/29

Mechanism anticipated by G. Franchetti & I. Hofmann, which involves Space charge tune spread Nonlinear (octupole) resonance Synchrotron motion

INTRODUCTION

Qx

Qy

hQ

vQ Regime where continuous loss occurs Due to longitudinal motion

Qx

QyvQ

hQ

Regime of loss-free core-emittance blow-up

Particles diffuse into a halo

xQ xQ

yQyQ Regime of loss-free core-emittance blow-up

Regime where continuous loss occurs Due to longitudinal motion

254 xQ

See Giuliano’s talk on Tuesday


3/29

EXPERIMENTAL SETUP

Time [ms]

170180

300 1200

Injection

1st profile measurement with a Fast Wire Scanner

(20 m/s)

Last profile measurement

Powering of the octupole

1 octupole pulsed with -3

3 m 1.215 IK m 7.11x m 2.22y

310

Profile measurement in H

Profile measurement in V m 6.11y

m 6.12x m 3.2xD


4/29

OTHER BEAM AND MACHINE PARAMETERS

Parameter Value Unit

Circumference 628 m

Horiz. / vert. beam pipe diameter 14 / 7 cm

Superperiodicity 10

Kinetic energy 1.4 GeV

Vert. tune 6.12

Horiz. tune 6.24 < Qx < 6.32

# of bunches 1

# of protons per bunch ~ 1012

Bunch length (4σ) ~ 180 ns

Horiz. / vert. normalised rms emittances ~ 5 / ~ 2.5 mm mrad

Rms momentum spread ~ 1.410-3

Horiz. / vert. rms beam sizes ~ 7 / ~ 4 mm

Derived horiz. / vert. SC tune shifts ~ - 0.075 / ~ - 0.125

Synchrotron period ~ 1.5 ms


5/29

FIRST MEASUREMENT CAMPAIGN: 14-18 OCTOBER 2002 (1/3)

Loss dominated regime Emittance growth dominated regime

A 40octI

xQ

G. Franchetti et al.,PRSTAB, 6, 124201 (2003)


6/29

6.27xQ

[ms] Time

1010bN

Octupole ON (40 A)

170 300 1200

50% of losses



7/29

Conclusions of the data analysis by Ingo&Giuliano

Emittance growth in good agreement with predictions

Losses not yet completely explained

Re-do measurements in 2003

Use the “real” nonlinear model of the PS machine instead of the constant focusing approximation



8/29

SECOND MEASUREMENT CAMPAIGN: 22-29 SEPTEMBER 2003 (1/21)

Octupole turned on at 300 ms, measurements at 1200 ms

0

0.5

1

1.5

2

-100 -50 0 50 100

Octupole current [A]

Rel

ativ

e ch

ang

es

I/ini (Qx=6,28)

epsx/ini (Qx=6,28)

I/ini (Qx=6,29)

epsx/ini (Qx=6,29)

Vert. emittance equal (here only) to

the horiz. one


9/29

A 20octI

xQ

6.265


6.25

G. Franchetti et al.,ICFA workshop, Bensheim,

Germany, October 2004


10/29

Qx=6.285

1

1.1

1.2

1.3

1.4

1.5

180 380 580 780 980 1180

Time [ms]

Re

lati

ve

ch

an

ge

s

epsx/ini

epsy/ini

Octupole ON

Emittance growth dominated regime

A 20octI


1 standard deviation

of 5 measurements

Precision of the emittance measurements ~10%


11/29

Qx=6.285

7

7.2

7.4

7.6

7.8

8

8.2

180 380 580 780 980 1180

Time [ms]

Ho

rizo

nta

l rm

s b

eam

siz

e [m

m]

From Gaussian fit

Rms computation

A 20octIOctupole ON



12/29


180 ms

1200 ms


13/29


30 20 10 10 20 30POSITIONmm

200

400

600

800

1000

HORIZONTAL PROFILE 1st profile and Gaussian fit


14/29


30 20 10 10 20 30POSITIONmm

200

400

600

800

1000

HORIZONTAL PROFILE Last profile and Gaussian fit


15/29

Qx=6.265

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

180 380 580 780 980 1180

Time [ms]

Re

lati

ve

ch

an

ge

s

epsx/ini

epsy/ini

Octupole ON

Beam loss dominated regime

A 20octI



16/29

Qx=6.265

5.9

6.1

6.3

6.5

6.7

6.9

7.1

7.3

7.5

180 380 580 780 980 1180

Time [ms]

Ho

rizo

nta

l rm

s b

eam

siz

e [m

m]

From Gaussian fit

Rms computation

A 20octIOctupole ON



17/29


180 ms

1200 ms


18/29


30 20 10 10 20 30POSITIONmm

200

400

600

800

HORIZONTAL PROFILE 1st profile and Gaussian fit


19/29


30 20 10 10 20 30POSITIONmm

200

400

600

800

HORIZONTAL PROFILE Last profile and Gaussian fit


20/29


180 ms

1200 ms

Undershoot due to the measurement

device


21/29


50 100 150 200 250 300 350 400TIMEns

2

4

6

8

LONGITUDINAL PROFILE1st profile and Gaussian fit


device


22/29


100 200 300 400TIMEns

2

4

6

8

LONGITUDINAL PROFILELast profile and Gaussian fit


device


23/29


From Gaussian fits of previous profiles

Integrated intensity of previous profiles

Octupole ON

G. Franchetti et al.,ICFA workshop, Bensheim,

Germany, October 2004


24/29


0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

6.245 6.25 6.255 6.26 6.265 6.27 6.275 6.28 6.285 6.29 6.295 6.3 6.305 6.31 6.315 6.32

I/iniepsx/iniI/ini w/o OCTepsx/ini w/o OCTI/ini w/o OCT, deb.epsx/ini w/o OCT, deb.epsy/ini w/o OCT, deb.

A 20octI

xQ


25/29


Debunched beam with octupole OFF

Qx=6.315

Qx=6.245


26/29


Qx=6.315

Qx=6.245

Debunched beam with octupole OFF


27/29


20 15 10 5 5 10 15 20POSITIONmm

200

400

600

800

1000

VERTICAL PROFILE 1st profile and Gaussian fit

Same kind of vertical distributions

observed in the previous measurements (due to

PSB and/or injection process)


28/29


20 15 10 5 5 10 15 20POSITIONmm

200

400

600

800

1000

VERTICAL PROFILE Last profile and Gaussian fit


29/29

By lowering the working point towards the resonance 4 Qx = 25, a gradual transition from a regime of loss-free core emittance blow-up to a regime dominated by continuous beam loss has been observed, as expected by Ingo&Giuliano

Emittance growth in good agreement with predictions

Beam losses now better explained than in 2002 (using the nonlinear model of the PS machine instead of the constant focusing approximation)

The observed maximum losses (~30%) are still larger than predicted (~8%)

HOWEVER, with octupole OFF ~20% of maximum beam losses are already observed! May explain the difference

CONCLUSION

observation of octupole driven resonance phenomena with space charge

Documents

onesecond measurement

measurement campaigns

h profile measurement

octupole1 octupole

octupole analogous

emittance measurements

emittance equal

continuous loss