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    User name Jin Huang

    Log entry time 16:19:35 on July 06, 2010

    Entry number 330483

    This entry is a followup to: 330348

    keyword=Optics Check: LHRS reconstruction of Ta foil vz, before and after adding bending magnets

    Seamus asked about what's the shift in tg_y corresponding to last log.
    Therefore I analyzed two Ta runs to quantify the shift : 6.5mm towards
    beam right on LHRS tg_y.
    
    Data selected:
    * Run 1776: 2 pass run with BPMA=BPMB=~(0,0)mm. Septum was in APEX
    polarity. Beam was bended before entering target. Cenral 1% dp cut.
    * Run 1170: 1 pass run with BPMA=BPMB=~(0,0)mm. Septum was in PREX
    polarity. Beam was straight through. Sieve was in. elstoc dp scan @0%
    
    For run 1776, tg_y peak at -6.0mm, while run 1170 peak at +0.5mm.
    Therefore there are -6.5mm shift on tg_y in current configuration (+tg_y
    is to beam left). I think there are two contributions:
    1. Change septrum from PREX polarity to APEX one. However, I overheard
    various study by John and Yi suggest the effect is small.
    2. Add variable beam bending magnet upstream of target, which shift both
    beam direction and hit position on target. If we ignore effect 1, then
    beam was shifted 6~7mm towards beam right at Ta target. (correct
    direction for bending magnet)
    
    Just to clarify optics conventions:
    * vz was constructed with assumption beam went straight through after BPMs
    * y direction in beam is vertical. y direction in spectrometer target
    coordintate system is horizontal. Ex. tg_y is in Hall horizontal plane
    (HALL x-z plane).
    * +vz is downstream. +tg_y is to away beam side direction relative to
    LHRS central line @ 5 degree.   
    


    A copy of this log entry has been emailed to: riordan, vasulk, schuster@slac.stanford.edu, ntoro@stanford.edu, bogdanw, yqiang



    Figure 1 : Last column is shift on tg_y