Intrabeam Stripping Loss Estimate Intrabeam Stripping Loss Estimate - - PowerPoint PPT Presentation

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Intrabeam Stripping Loss Estimate Intrabeam Stripping Loss Estimate for the ProjectX IC2 Linac for the ProjectX IC2 Linac

J.-F. Ostiguy

APC/Fermilab

• stiguy@fnal.gov

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Preliminaries Preliminaries

• V Lebedev suggested that intra-beam stripping might

account for the unexplained losses at SNS.

• He performed an estimate for both SNS and PrX
• His results suggest that we need to pay attention.
• I wrote a simple program to produce an intrabeam

stripping estimate from TraceWin (can easily be adapted to TRACK).

• Agreement with Valeri's estimates is very good.
• We will request that an intrabeam stripping loss

estimate be integrated in TraceWin.

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H- Stripping Cross -Section (V. Lebedev) H- Stripping Cross -Section (V. Lebedev)

Stripping cross-section is essentially constant in the range 2.0x10-4 < β < 3 x 10-3 Velocities are expected to be in that range for SNS

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From Valeri Lebedev's Talk From Valeri Lebedev's Talk

Transverse and long rms beam sizes in the lab frame Transverse and long rms velocities normalized w/r c, in the lab frame. Fractional particle losses per unit of distance: Assumes: Gaussian distribution and σstripping = constant

¾stri

pp i ng

Stripping cross-section

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How this calculation was performed How this calculation was performed

• IC2 CW lattice (2.5 MeV – 3 GeV) : as of Apr 17
• Estimate requires only knowledge of 2nd order moments &

synchronous energy

• Tracking done using TraceWin/Partran

(200k particles with SC – not necessary … just experimenting with Partran)

• We could/should also be able to use the TraceWin envelope
• calculation. This was not done because TraceWin does not

currently provide all the necessary moments (Twiss functions) in a convenient form (this will be fixed).

• Wrote a short program (python) which uses a partran *.out file

(similar to TRACK beam.out) as input.

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PrX- Relative Velocities in the Beam Frame PrX- Relative Velocities in the Beam Frame

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PrX- Beam Sizes In the Laboratory Frame PrX- Beam Sizes In the Laboratory Frame

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PrX - Fractional Particle Loss Along the Linac PrX - Fractional Particle Loss Along the Linac

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PrX - Power Loss/unit length Along the Linac PrX - Power Loss/unit length Along the Linac

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Comparison with Lebedev's Results Comparison with Lebedev's Results

Local loss rate

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Conclusions Conclusions

• Assuming the IBS model is adequate, the predicted

power loss caused by H- stripping due is marginally manageable in the current lattice.

• Further studies and experimental results from SNS will

be helpful to gain more confidence about the validity of the model.

• We need to explore loss reduction by a factor
• f 2x – 3x.
• Reducing focusing may be difficult without changing

distance between elements due to constraints on phase advances … etc.