BPM and Profile Monitor Alignment and Calibration

1
BPM and Profile Monitor Alignment and Calibration

• Debbie Harris in consultation with
• Wes Smart
• Peter Prieto
• Virgil Bocean
• Zarko Pavlovich

2
NuMI Beamline Convention

• A Device should report the signed distance of the
  actual beam with respect to the ideal beam.
• For NUMI Beam left positive x (as you look
  downstream)
• For NUMI Beam Up positive y
• Note This is not a universal convention!!!

3
Profile Monitor Alignment

• Correction needed to get from center of foil
  plane (half-way between the middle two files,
  defined as monitor center) to the ideal beam
  position
• Profile Monitors in MI area (PM101-PM112) havent
  moved since December
• Others may have
• moved
• February Alignment
• constants
• ADD these numbers to
• position relative to monitor
• center to get position w/rt
• ideal beam position

4
BPM Alignment

• Remember how BPM works beam goes through BPM,
  induces charge on two plates

• BPM Offsets that need to be applied
• Electronic Offsets
• Electric Center Offset
• Alignment Offset

5
Electric Center Measurement

• Electric center location where when particle
  goes through, charge induced on two plates are
  equal
• Measured by Jim Fitzpatrick on test stand4
  orientations, take the average
• This average is relative to physical center as
  defined by alignment holes
• So imagine to induce equal charge, beam is 1mm in
  positive direction want that to be zero!
• Have to subtract this offset but they are usually
  very small usually lt.1mm, 5 are .1-.3mm

6
Physical Offset w/rt Ideal Beam

• BPMs have 4 alignment holes, know electric cener
  w/rt center defined by these holes
• SAG aligns cylinders of BPMs relative to ideal
  beam position
• SAG measures in beamine positions of cylinders
  w/rt Ideal Beam
• SAG measures (in village) center w/rt cylinder
• If beam goes through center w/rt holes of BPM,
  want it to tell you how far that center is from
  ideal beam ADD this correction! (same as PMs)

7
Electronic Offset

• Forget the BPM what happens if you put equal
  charge into the cables that go the electronics,
  what position does electronics read back? This
  can be due to phase differences, cable lengths,
  etc.
• You want electronics to return 0mm if it gets
  equal charge as input subtract what you measure
  when you put in equal charge!
• These can be large (up to 1.5mm!)

8
What offsets were on when?

• In December and January, electronic offsets were
  in, but not the others. The others (summarized in
  table at right) are to be added
• BUT only MI area ones are sure to be exactly
  correct

9
What happens when you have 2 measurements of the
same thing

• Although there are 23 BPMs (1 view each) and 10
  profile monitors (1 view each) there are only 13
  positions where we have two measurements of the
  same quantity
• Note 4 downstream BPMs, right before target,
  are all redundant with profile monitors

Next Slides consider only the 13 redundant
pairs of measurements
10
Comparison of Corrections
BPM True value measured value electronic
offset BPM Offset (BPM offset
includes electric center correction) Profile
Monitor True Value measured value PM Offset
11
With all known corrections in, how well do BPM
and PMs Agree?
12
What could be wrong here?

• Virgil has done other measurements of the
  electric centers which disagree with Jim
  Fitzgeralds electric center measurements by a
  factor of 10!

Mount If BPM is up or down
13
Still to do

• Understand how Virgils measurements could be
  discrepant by such a huge factor
• Keep going through various offsets and
  corrections with fine-toothed comb

14
What happened for most of Feb. Run?

• Physical and Electric offsets were in right, but
  electronic offsets were in with the wrong sign
  (added, not subtracted). So to get to the right
  position for up to 2PM Feb.22, have to subtract
  2 electronic offset

HPTGT correction -1.4mm!
15
So what did the beam look like for stable running
at that point?

• PM105 off by many wires!
• HTGT also off from 0
• (from E-log, 20 Feb)

16
What happened when BPM entries were corrected
(2/22, 1300-1400)?

• Autotune was run, which tries to set all bpm
  readbacks to 0. BUT cant change position at
  injection, so not all BPMs did read back 0.
• PMs much closer to 0 than they were before, and
  also much closer to BPMs than previously.