Transverse beam dynamics issues in the PS

R. Wasef, S. Gilardoni, A. Huschauer, G. Sterbini on behalf of PS-LIU team

LIU Day 11/04/2014

Outline

I. Transverse challengesII. Space Charge at injectionIII. Injection oscillationsIV. Transverse damper and feedbackV. Summary and Conclusions

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Transverse Challenges in the PS

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Acceleration:Transition crossing

Flat top:Electron cloud Transverse instabilities

0 0.5 1 1.5 20

0.05

0.1

0.15

time [us]

e-cl

oud

sign

al [a

.u. ]

Av. intensity = 1.33*1011 ppb

0 0.5 1 1.5 20

2

4

6

time [us]Pi

ck-u

p si

gnal

[a.u

.]

Injection flat bottom:Injection oscillationsSpace charge Headtail instability

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Space Charge at injection

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• Current injection energy: 1.4 GeV

• Typical tune-spread of current operational beam~(-0.2 ; -0.28)

• LHC double batch injection:Long flat bottom: 1.2s

• LIU Budgets: 5% beam loss, 5% emittance growth

• Requests @2GeV: LIU -> ΔQ~(-0.19 ; -0.31) HL-LHC -> ΔQ~(-0.18 ; -0.30)

Current operation area

1.2s

1st Injection 170ms4 bunches 2nd Injection 1370ms

2 bunches

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Space Charge at injection

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• The beam tune-spread is trapped between the 4qy=1 and the integer resonances. The choice of the working point is a compromise between losses and

emittance blow-up

• To respect the LIU budgets of beam loss and emittance growth, ΔQmax≈-0.31

Core of the beam

hallow particles

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Resonance Compensation

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Vertical tune scan

2Qx+Q

y compensation

3Qy com

pensation

Successful implementation of a resonance compensation scheme

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Space Charge at injection

The resonance compensation would empty larger area for the working are, but the 4Qy=25 resonance is still limiting this area.

• Solutions for 4Qy resonance: A study of changing the vertical integer tune shows promising results

to avoid the 4Qy resonance Changing the optics: larger horizontal dispersion & larger vertical

dispersion Longitudinally hollow bunch

LIU Day 11/04/2014

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Injection Oscillations

• At injection of high intensity beams, intra-bunch oscillations were observed.

• No unstable behavior observed• A study revealed that the cause of these

oscillations is indirect space charge.• Problem first observed in 1998.

Explained in 2013• The effect of these oscillations on the

emittance of future beams (HL-LHC:32.5 1011 ppb, LIU :28 1011 ppb) hasto be studied.

• TFB damp it effectively. Effect on the emittance to be studied

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measurement

simulation

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Transverse Damper and Feedback

• The TFB was designed to damp injection orbit errors of 3mm (peak to peak) within 50 turns, to limit the caused emittance growth:

• It also has been used as feedback to dump Headtail instabilities at injection. (Chromaticity should be controlled at 2GeV)

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Injection oscillation

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Transverse Damper and Feedback

• Using the TFB at flattop, it wasable to delay the observed instability by ~10ms

• It could not cure instabilities at transition (700MHz instabilities).These instabilities are not to be expected for LHC beams.

• E-Cloud

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Summary and conclusions

• Injection flat-bottom:

1. Injection oscillations: TFB, effect on the emittance?

2. Space charge: 2GeV injection upgrade, Resonance compensation, studies on going (change of vertical integer, new optics, hollow bunches…etc)

3. Headtail instability: TFB

• Transition instabilities: no limitation expected

• Flat-top:

1. Electron Cloud: TFB

2. Transverse instabilities: TFB

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THANK YOU FOR YOUR ATTENTION!

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Backup slides

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BCMS scheme (48 bunches / PS batch)

LIU upgrades SPS 200 MHz upgrade SPS e-cloud mitigation PSB-PS transfer at 2 GeV

Limitations BCMS scheme SPS: longitudinal instabilities +

beam loading PS: space charge SPS: space charge

Performance reach 2.0x1011p/b in 1.37μm (@

450GeV) 1.9x1011p/b in 1.65μm (in

collision)

HL-LHC

LIU-BCMS

LIU-Std

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Injection oscillations

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simulationmeasurement

max. tune shift in this simulation is approx. 0.01 larger than in the measurement effect very sensitive to the longitudinal distribution

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4th order Resonance

The 4th order resonance seems to be excited by space charge

Maximum detuning due to space charge:Beam 1 : (-.22 ; -.4)Beam 2 : (-.18 ; -.37)Beam 3 : (-.08 ; -.07)Beam 4 : (-.01 ; -.01)

Horizontal tune fixed at 6.23Vertical tune: 6.24->6.3->6.24

6.24

6.3

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Resonance compensation2Q

x+Qy com

pensation3Q

y compensation

Horizontal tune scan