BPM and Profile Monitor Alignment

BPM and Profile Monitor Alignment Debbie Harris in consultation with Wes Smart Peter Prieto Virgil Bocean

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!!!

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) haven’t 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

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

Electric Center Measurement • Electric center: location where when particle goes through, charge induced on two plates are equal • Measured by Jim Fitzpatrick on test stand—4 orientations, take the sum • This offset is measured 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 <.1mm, 5 are .1-.3mm

Physical Offset w/rt Ideal Beam: • BPM’s have 4 alignment holes, know electric cener w/rt center defined by these holes • SAG aligns cylinders of BPM’s 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 PM’s)

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!)

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…

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!

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)

What happened when BPM entries were corrected (2/22, 13:00-14:00)? • Autotune was run, which tries to set all bpm readbacks to 0. BUT can’t change position at injection, so not all BPM’s did read back 0. • PM’s much closer to 0 than they were before, and also much closer to BPM’s than previously.

BPM and Profile Monitor Alignment