AC dipole for LHC Mei Bai Collider Accelerator Department Brookhaven National Laboratory.

AC dipole for LHCAC dipole for LHC

Mei BaiMei Bai

Collider Accelerator DepartmentCollider Accelerator Department

Brookhaven National LaboratoryBrookhaven National Laboratory

LARP, 2005LARP, 2005

What’s ac dipole and its technique for beam What’s ac dipole and its technique for beam diagnosticdiagnostic

AC dipole: a dipole magnet with oscillating field. AC dipole: a dipole magnet with oscillating field. By driving the ac dipole at a frequency at the vicinity of beam betatron By driving the ac dipole at a frequency at the vicinity of beam betatron

frequency, a coherent oscillation can be excited. The size of this excited frequency, a coherent oscillation can be excited. The size of this excited coherent oscillation is proportional to the strength of the ac dipole. coherent oscillation is proportional to the strength of the ac dipole. The closer the ac dipole frequency to the beam The closer the ac dipole frequency to the beam betatronbetatron frequency, the stronger the driven coherent oscillation frequency, the stronger the driven coherent oscillation

The technique of using an ac dipole to achieve a long lasting The technique of using an ac dipole to achieve a long lasting coherent oscillation coherent oscillation in the hardon machine was first developed in the in the hardon machine was first developed in the Brookhaven AGS. The technique was also tested the CERN SPS using a Brookhaven AGS. The technique was also tested the CERN SPS using a transverse dampertransverse damper

The Brookhaven AGS beam experiment also demonstrated The Brookhaven AGS beam experiment also demonstrated the the beam beam emittanceemittance can be restored can be restored if the excitation of ac if the excitation of ac dipole gets ramped up/down adiabatically. dipole gets ramped up/down adiabatically.


AC dipole applications: Linear Optics measurementAC dipole applications: Linear Optics measurement

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Use the coherent oscillation driven by an ac dipole to measure the betatron functions and phase Use the coherent oscillation driven by an ac dipole to measure the betatron functions and phase advances between bpms advances between bpms


AC dipole applications: Linear Optics measurementAC dipole applications: Linear Optics measurement

Measured phase advances

Measured betatron functions


Driven coherent oscillation with non-zero couplingDriven coherent oscillation with non-zero coupling

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AC dipole applications: Linear coupling AC dipole applications: Linear coupling measurementmeasurement

Driven oscillation amplitude with horizontal ac dipole

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AC dipole applications: Linear coupling AC dipole applications: Linear coupling measurementmeasurement

The measured ratio of amplitudes for horizontal (top) and vertical (bottom) AC dipole excitation with different skew quadrupole settings.

Skew quadrupole strengthSkew quadrupole strength

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AC dipole applications: Non-linear resonance AC dipole applications: Non-linear resonance measurementmeasurement Non-linear resonance driving termNon-linear resonance driving term

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Normal form with driven coherent oscillationNormal form with driven coherent oscillation

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Normal form of particle motion under the influence of an ac dipole, R. Tomas, Phys. Review ST-AB, Vol. 5, 054001

R. Bartolini and F. Schmidt, LHC Project Note 132, 1998

Spectral line @ (1-j+k, m-l) resonance @ (j-k, l-m)


AC dipole applications: Non-linear resonance AC dipole applications: Non-linear resonance measurementmeasurement

First 3First 3rdrd order resonance driving term measurement in RHIC with ac dipole order resonance driving term measurement in RHIC with ac dipole

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Why AC dipole for LHCWhy AC dipole for LHC

Critical to measureCritical to measure Linear optics measurement including beta* measurement Linear optics measurement including beta* measurement Non-linearity could be a concern for high energy collider’s Non-linearity could be a concern for high energy collider’s

luminosity and being able to measure the non-linear luminosity and being able to measure the non-linear resonance will be criticalresonance will be critical

Other transverse beam parameters Other transverse beam parameters Disadvantage of using transverse kickerDisadvantage of using transverse kicker

Long lasting coherence is critical for the transverse Long lasting coherence is critical for the transverse measurements. However, it is hard to maintain coherent measurements. However, it is hard to maintain coherent oscillation induced by a kicker due to the tune spreadoscillation induced by a kicker due to the tune spread

The budget for emittance growth in LHC is rather limitedThe budget for emittance growth in LHC is rather limited Large amplitude coherence is desired for measuring the non-Large amplitude coherence is desired for measuring the non-

linearity. However, to kick the beam to high amplitude may linearity. However, to kick the beam to high amplitude may require a very strong kickerrequire a very strong kicker

The ac dipole technique has been tested in SPS using the The ac dipole technique has been tested in SPS using the SPS transverse damperSPS transverse damper


SummerySummery

AC dipole has demonstrated to be a powerful tool to induce AC dipole has demonstrated to be a powerful tool to induce long lasting coherent oscillation which is necessary for long lasting coherent oscillation which is necessary for measuring the machine optics parameters as well as measuring the machine optics parameters as well as studying the non-linear behavior of the beam. It has been studying the non-linear behavior of the beam. It has been routinely applied in the Brookhaven RHIC to measure the routinely applied in the Brookhaven RHIC to measure the phase advances as well as betatron functions. phase advances as well as betatron functions.


Active non-destructive technique: AC dipoleActive non-destructive technique: AC dipole

Amplitude of driven coherent oscillation in a linear machineAmplitude of driven coherent oscillation in a linear machine

O. Berrig, W. Hoflem, R. Jones, J. Koopman, J-P. Koutchouk, F. Schmidt, SL-Note-00-062 MD, Nov. 2003

M. Bai et al., Physical Review E. Vol 5, (1997)

Beam becomes unstable if m=z

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Driven coherent oscillation with non-linear detuningDriven coherent oscillation with non-linear detuning


Active non-destructive techniques: AC dipoleActive non-destructive techniques: AC dipole

Adiabatic excitation allows the particles in the beam to follow Adiabatic excitation allows the particles in the beam to follow the external driving force so that the beam distribution gets the external driving force so that the beam distribution gets restored after the excitation.restored after the excitation.

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Ac dipole driven coherent oscillation in the Brookhaven AGS Ac dipole driven coherent oscillation in the Brookhaven AGS


Active non-destructive techniques: AC dipoleActive non-destructive techniques: AC dipole

Beam size measurement results of the beam Beam size measurement results of the beam experiment with ac dipole in the Brookhaven AGSexperiment with ac dipole in the Brookhaven AGS

Experimental results in the Brookhaven AGS

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after excitation

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AC dipole for LHC Mei Bai Collider Accelerator Department Brookhaven National Laboratory.

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Transcript of AC dipole for LHC Mei Bai Collider Accelerator Department Brookhaven National Laboratory.