Spectrometer Solenoid Field Mapping: Thoughts on Mapping Analysis & Results Major caveat: Everything in this talk is highly preliminary Data arrived on Saturday whilst travelling!

Why map MICE magnets? 1.Alignment of the experiment 2.Gain confidence in OPERA maps and calculations 3.Understand hysteresis effects 4.Field representation in software

(Thoughts on) Analysis See Maria’s talk for a report on the mapping campaign Lots of surveys have been done that we’ll need to use quite extensively to get to grips with our uncertainties – For the purpose of this talk, assuming that mapper alignment is “good enough” w.r.t. geometric centre – Surveys won’t change what we do, but do add a complicated extra step!

The things we want to know… 1.Garbage check! 2.Linearity of field with current a)With/without Virostek plate 3.Residual magnetic field a)With/without Virostek plate 4.Hysteresis a)Should only occur with Virostek plate (but see point 3) 5.Magnetic axis/coil fits

A rudimentary look at some data: “Run 5”, 95% of 240MeV currents No Virostek plate On-axis probe Largest radius

A rudimentary look at some data: “Run 5”, 95% of 240MeV currents No Virostek plate Compare on-axis field with calculation Rough guess to approximately align calculated magnet with measured magnet Calculation a bit high…

A rudimentary look at some data: “Run 5”, 95% of 240MeV currents No Virostek plate Can also compare over all radii DataBiot-Savart calculation

FITTING FIELD MAPS (From June 6 th analysis meeting – only uses simulated data!)

UpstreamDownstream S PECIFYING A MAGNET Key: A coil Position of upstream edge Inner radius Current in coil Conductor This is a generic magnet, it’s not meant to look like the SS or AFC. We can model any magnet we want!

F ITTING A FIELD MAP Mixing/Scaling fit procedure: 1.Take data in cylindrical co-ordinates a)In this case using a pre- calculated map based on SS. 2.Make two detailed field maps with parameters that “bracket” our best guess at the real paramters 3.Minimise for “best fit” parameters: a)Mixing of the detailed field maps b)Length scale of the detailed field maps c)Field scale of the detailed field maps Two methods: Mixing/scaling fit Full 20+ parameter coil fit – takes FOREVER for SS

F ITTING A FIELD MAP Mixing/Scaling fit procedure: 1.Take data in cylindrical co- ordinates a)In this case using a pre- calculated map based on SS. Again, a generic magnet Spectrometer Solenoid parameters

F ITTING A FIELD MAP Mixing/Scaling fit procedure: 2.Make two detailed field maps with parameters that “bracket” our best guess at the real parameters Original magnet “Long, thin” bracketing magnet “Short, fat” bracketing magnet

F ITTING A FIELD MAP Mixing/Scaling fit procedure: 2.Make two detailed field maps with parameters that “bracket” our best guess at the real parameters

F ITTING A FIELD MAP Mixing/Scaling fit procedure: 3.Minimise for “best fit” parameters: a)Mixing of the detailed field maps b)Length scale of the detailed field maps c)Field scale of the detailed field maps

A SIDE : I NTERPOLATING FIELDS How well does this work? (weakest link) Lesson: Make sure the bracketing fields are calculated on a finer grid than the data! 1e-15

F ITTING A FIELD MAP Few grid points Many grid points

F ITTING A FIELD MAP zoomed y-scale

F ITTING A FIELD MAP zoomed y-scale

I MPROVEMENTS TO COME : Need to account for longitudinal offset + two rotations This is included in the 20+ parameter fit, but is far too slow for the SS map Adding Fourier-Bessel fit to account for residual field (green plots) will improve our map further. Also helps account for Virostek plate longitudinal offset + in/out of screen rotations