Intrabeam Stripping Loss Estimate Intrabeam Stripping Loss Estimate for the ProjectX IC2 Linac for the ProjectX IC2 Linac J.-F. Ostiguy APC/Fermilab ostiguy@fnal.gov JFO - 20100430
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. JFO - 20100430
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 JFO - 20100430
From Valeri Lebedev's Talk From Valeri Lebedev's Talk Fractional particle losses per unit of distance: Assumes: Gaussian distribution and σ stripping = constant Transverse and long rms beam sizes in the lab frame Transverse and long rms velocities normalized w/r c, in the lab frame. ¾ stri Stripping cross-section pp i ng JFO - 20100430
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 2 nd 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. JFO - 20100430
PrX- Relative Velocities in the Beam Frame PrX- Relative Velocities in the Beam Frame JFO - 20100430
PrX- Beam Sizes In the Laboratory Frame PrX- Beam Sizes In the Laboratory Frame JFO - 20100430
PrX - Fractional Particle Loss Along the Linac PrX - Fractional Particle Loss Along the Linac JFO - 20100430
PrX - Power Loss/unit length Along the Linac PrX - Power Loss/unit length Along the Linac JFO - 20100430
Comparison with Lebedev's Results Comparison with Lebedev's Results Local loss rate JFO - 20100430
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 of 2x – 3x. ● Reducing focusing may be difficult without changing distance between elements due to constraints on phase advances … etc. JFO - 20100430
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