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TOF II Justification

TOF II Justification. Chris Rogers Imperial College 18 May 2006. Overview. TOF2 resolution justification The need for longitudinal emittance Detector resolution vs emittance resolution Some parts of this talk may come up in the CM Plenary. Energy Loss through LH2. PDG. PDG.

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TOF II Justification

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  1. TOF II Justification Chris Rogers Imperial College 18 May 2006

  2. Overview • TOF2 resolution justification • The need for longitudinal emittance • Detector resolution vs emittance resolution • Some parts of this talk may come up in the CM Plenary

  3. Energy Loss through LH2 PDG PDG • In material beam s(E) changes because of • Energy straggling (dominant) • Width of energy loss distribution • Curvature of dE/dx • Muons with lower energy lose more energy than the reference particle • This is longitudinal emittance growth that we should measure

  4. RF Bucket 40o Phase Energy straggling switched OFF Energy straggling switched ON Contours in total energy Position of reference particle z=0 z=0 • I plot t-tRF vs E-Eref for a single muon over a long beamline • In longitudinal phase space, muons are contained in an “RF bucket” • Optical “aberrations” cause emittance growth over ~ 10s of cells • Random effects (energy straggling) from passing through material cause muons to get knocked out of the RF bucket • This is also longitudinal emittance growth z=275 metres z=190 metres

  5. Longitudinal beta function (Periodic SFoFo) ~Periodic (“matched”) b// Deliberately unmatched b// Energy straggling switched OFF Repeating structure made up of 4 x 2.75 m SFoFo lattices b// [m] • Set up the beam so that the longitudinal phase space structure is periodic over a MICE 2.75 m cell • Define “longitudinal beta function” b// ~ s(t)/s(E) • Choose b// ~ 0.025 ns/MeV for periodic “matched” b// • Compare with a non-periodic structure • Deliberately introduce a mismatch by choosing b// ~ 0.05 ns/MeV initially LH2

  6. Longitudinal Emittance (Periodic SFoFo) Optical aberrations Energy Straggling • Slightly small s(E) ~ 10 MeV, s(t) ~ 0.25 ns • Much larger and I start falling out of the bucket • I haven’t cut on muons inside the bucket for this plot • Two effects to be measured • Growth due to optical “aberrations” (quite significant) • Growth due to energy straggling • Alternatively count directly the number of muons in the RF bucket

  7. RF @ 90o Phase (Periodic SFoFo) z=0 b// with RF at 40o b// with RF at 90o • MICE default is to have RF at 90o phase • Then there is no “bucket” • May be possible to run at 40o in MICE V • But can still measure emittance growth due to energy straggling z=40 metres

  8. MICE Channel • Much harder to match • MICE is fundamentally not periodic due to pz loss • (RF @ 40o) • Difficult to prevent emittance growth • No RF cavities in the tracker/matching section • But I should be able to do better than this with some more faff

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