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1/70. Field Mapping. V. Blackmore CM38 23rd February 2014. 2/70. There is a lot of information in these slides, and not enough time to say it all. A lot of this will be revisited in future analysis meetings.

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field mapping

1/70

Field Mapping

V. Blackmore

CM38

23rd February 2014

slide2

2/70

There is a lot of information in these slides, and not enough time to say it all. A lot of this will be revisited in future analysis meetings.

I have added notes to most slides (if you download the .ppt version), so they should be understandable “offline.”

As for now, we’ll see just how far we get...

contents

3/70

Mapped Currents

Contents

Survey plots presented at CM37.

Today:

Coordinate systems

Effect of the shielding plate

Linearity of field with current

Residual magnetic field

Probe Jitter

Hysteresis

Magnetic axis fits

4

17

24

29

41

  • Runs cover the above currents, plus:
  • 0A measurements (residual field)
  • 30A individual coil measurements (superposition)
  • With and without Virostek plate

48

50

A lot of data

coordinate systems

4/70

Coordinate Systems

Until the end of this talk...

the mapper co ordinate system

5/70

The “Mapper” Co-ordinate System

Mapper: Movement example video*

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video *

“Spectrometer Solenoid”

*Thanks to F. Bergsma

“Upstream” end and Virostek Plate

Hall probe card

Probes numbered from 0 to 6 in order of increasing radius

Probe “0” on axis

“Conveyor belt”

“Carriage”

the mapper co ordinate system1

6/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

the mapper co ordinate system2

7/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

Tick!

In file for :

Record probe number,

the mapper co ordinate system3

8/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

Tick!

In file for :

Record probe number,

the mapper co ordinate system4

9/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

Tick!

In file for :

Record probe number,

the mapper co ordinate system5

10/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

Rotate!

Tick!

Start new file for :

Record probe number,

the mapper co ordinate system6

11/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

Reverse!

the mapper co ordinate system7

12/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

Tick!

In file for :

Record probe number,

the mapper co ordinate system8

13/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

Tick!

In file for :

Record probe number,

the mapper co ordinate system9

14/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

Rotate!

Tick!

Start new file for :

Record probe number,

the mapper co ordinate system10

15/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

Forward!

etc. etc.

the mapper co ordinate system11

16/70

The “Mapper” Co-ordinate System

Mapper: Movement example video

  • To avoid changing too many variables at once, all of the data (until it says otherwise) is in the “mapper co-ordinate system.”
  • No survey corrections (as described at CM37) have been applied.

Mapper: Rotation example video

  • Each data “set” is taken over the same range of in the same number of steps, and similarly for
  • Each is recorded in a separate data file
  • I do combine these files
  • I do rotate , and keep (see “backup slides”)
  • is what the mapper reports

Forward!

etc. etc.

the shielding plate

17/70

*

Mapper m

Mapper at this side

The Shielding Plate

Compare identical measurements with and without the shielding (“Virostek”) plate

“Identical”: Same currents

*Photographs gratuitously stolen from S. Virostek’s talk at CM36

spot the shielding plate

18/70

Spot the Shielding Plate

Let’s play

  • “On-axis” probe, plotting (i.e. ) w.r.t. mappers recorded position at 4 angles of
  • Measurements at 50% current, Solenoid Mode (will come back to linearity)
spot the shielding plate1

19/70

Spot the Shielding Plate

Let’s play

  • 150mm probe, plotting (i.e. ) w.r.t. mappers recorded position at 4 angles of
  • Measurements at 50% current, Solenoid Mode (will come back to linearity)
spot the shielding plate2

20/70

Spot the Shielding Plate

Let’s play

  • 150mm probe, plotting w.r.t. mappers recorded position at 4 angles of
  • Measurements at 50% current, Solenoid Mode (will come back to linearity)
spot the difference

21/70

Spot the Difference:

Let’s play

  • is interpolated along the -axis
  • Compare at fixed -points
  • From the field changes quickly
  • “Noise” in this region probably due to rapidly changing field

Probably due to rapidly changing field (?)

mm

mm

spot the difference again

22/70

Spot the Difference (Again)

Let’s play

Field increased by shielding plate

Would guess the centre of the shielding plate is here!

T at mm

T at mm

Field decreased by shielding plate

spot the difference1

23/70

Spot the Difference:

Let’s play

mm

Probably due to rapidly changing field (?)

mm

field linearity

24/70

Field linearity

With no shielding plate, field should belinear with current.

With shielding plate, field may benon-linear with current

without the shielding plate

25/70

Without the shielding plate…
  • (Black) 100% current in Flip Mode
  • (Red) 80% current in Flip Mode
  • Scale up 80% measurements and compare…
without the shielding plate1

26/70

Without the shielding plate…
  • (Black) 100% current in Flip Mode
  • (Red) 80% current in Flip Mode
  • Scale up 80% measurements and compare…
  • First impression is good.
without the shielding plate2

27/70

Without the shielding plate…

Scaled down field measurement

Majority of differences are where field is changing

T

Scaled field is slightly larger (difference <0)

with the shielding plate

28/70

With the shielding plate…

Scaled by 1.25

Scaled down field measurement

T

Larger difference at large

This region was previously negative

Majority of differences are where field is changing, now looks more systematic

residual field

29/70

Residual field

We do have data sets that allow us to naively look at the residual field

Q: Does the residual field change depending on the previous operating current?

residual field measurements

30/70

Residual Field Measurements

No intermediate measurements carried out between these pairs of data

  • Every day of measurements began/ended (or both) with a field map at “0A”
  • Can compare measurements at 80/100% field and 0A.
  • Still using “mapper co-ordinates”
  • Order of measurements does matter

Intermediate Flip Mode runs (not interspersed with 0A data). Shielding plate removed 15th—16th June.

Colour-coded dots are meant to help those viewing later

7th 10th june

31/70

7th—10th June:

On-axis probe only

Previously at 80% Sol. Mode

Ran at 80% Solenoid Mode, then turned everything off and took a well-deserved weekend break

0A, so line should be flat – but is it?

7th 10th june1

32/70

7th—10th June:

On-axis probe only

Previously at 80% Sol. Mode

Scaled 80% SM measurements for general shape comparison only.

Not very flat – but there are welds, which will

be magnetic (hence suffer residual field). Possibly correlates with mapper carriage movement?

10th 11th june

33/70

10th—11th June:

On-axis probe only

Previously at 3.6% Sol. Mode

Ran at 10A (3.6%) Solenoid Mode, then went home for the night

The next morning, at 0A

10th 11th june1

34/70

10th—11th June:

On-axis probe only

Previously at 3.6% Sol. Mode

3.6% SM scaled for shape comparison only

Similar to before?

10th 11th june2

35/70

10th—11th June:

On-axis probe only

Previously at 3.6% Sol. Mode

3.6% SM scaled for shape comparison only

Similar to before?

Yes!

11th 13th june

36/70

11th—13th June:

On-axis probe only

Previously at 100% Sol. Mode

Now it gets interesting:

After the previous slide’s 0A run, ran at 100% SM.

The next day took a 0A measurement…

11th 13th june1

37/70

11th—13th June:

On-axis probe only

Previously at 100% Sol. Mode

100% SM scaled for shape comparison only

Much flatter!

More obvious when compared to previous 0A measurements…

(Does make mapper carriage movement argument moot)

11th 13th june2

38/70

11th—13th June:

On-axis probe only

Previously at 100% Sol. Mode

100% SM scaled for shape comparison only

The only thing that happened between

and is a 100% field run.

19th 19th june

39/70

19th—19th June:

On-axis probe only

Previously at 100% Sol. Mode

80% SM (no shielding plate) scaled for shape comparison only

All bar consistent here

: Several Flip Mode runs, shielding plate removed, then back to 80%SM followed by 0A measurement.

7th 19th june

40/70

7th—19th June:

On-axis probe only

Shielding plate differences

80% SM (w/ & w/o shielding plate) scaled for shape comparison only

probe jitter

41/70

Probe Jitter

What kind of error bars should we be imagining on the previous plots?

Look at the “flat” regions of the 0A measurements and see what variation there is in probe readout.

region of interest m

42/70

Region of Interest: m

Probe at 90mm sees more residual field that the others

180mm probe has a large spike here

  • Consider dotted region
  • Is approx flat in all 0A measurements
  • Should have a negligible residual field
  • Use , June 13th 0A measurement, as it is “flattest”
  • Compare with measurement from June 14th (not previously shown)
  • Calculate mean and standard deviation in this ROI
mean residual

43/70

Mean Residual

Probe at 90mm sees more residual field that the others

  • Mean residual is different after powering magnet
  • Only probe 5 (mm) is consistent with zero
  • Probe 3 sees consistently higher fields, but it should be consistent with other probes
mean residual1

44/70

Mean Residual
  • Mean residual are all consistent with 0 (including probe 3)
  • Noisiest -axis probes are 2 and 4
  • Mean residual are all consistent with 0
  • Noisiest -axis probes are also 2 and 4
mean residual2

45/70

Mean Residual
  • Mean residual are all consistent with 0 (including probe 3)
  • Noisiest -axis probes are 2 and 4
  • Mean residual are all consistent with 0
  • Noisiest -axis probes are also 2 and 4
probe jitter comparison

46/70

Probe Jitter Comparison

Composite of previous 3 slide’s plots

probe jitter comparison1

47/70

Probe Jitter Comparison
  • G
  • Exceptions are probes 2 and 4 in and
  • No measurements without SS present, so residual field effects are difficult to quantify
  • There are other ‘uncertainties’ to consider, but this is a start!
hysteresis

48/70

Hysteresis

Q: Do we achieve the same field when we approach it from below the operating current and above the operating current?

hysteresis1

49/70

Hysteresis
  • Ideally, requires consecutive four measurements with the shielding plate
    • 0% solenoid/flip
    • 80% solenoid/flip mode
    • 100% solenoid/flip mode
    • 80% solenoid/flip mode
  • We have 0%80%, and 0%100%, but do not have 100%80%
    • Mapping takes a long time
    • Time taken by shielding plate installation and removal
  • Judging by changes in residual field, likely there will be a (very) small hysteresis effect
    • Should make this measurement when mapping final SS
finding the magnetic axis first pass

50/70

Finding the Magnetic Axis (First pass)

The mapper moves about by ~ 1mm in (x,y) as it travels through the magnet

To first approximation, ignore this movement and use mapper co-ordinates to get an estimate of the magnetic axis

finding the magnetic axis

51/70

Finding the Magnetic Axis

Simulation, 1 coil

  • At each measured point along , get all measurements of and
  • In regions of , these should form lines passing through the magnetic axis
  • Fit a line to and find where it crosses the -axis
  • Fit a line to and find where it crosses the -axis
  • Plot these points as a function of
  • Test on a 1-coil ‘magnet’
  • Use G (from probe jitter) in the fits

Fit

Bx or By

Magnetic axis

x or y

finding the magnetic axis1

52/70

Finding the Magnetic Axis:

Simulation, 1 coil

1e-12m

finding the magnetic axis2

53/70

Finding the Magnetic Axis:

Simulation, 1 coil

1e-12m

real magnets

54/70

Real magnets

100% Solenoid Mode, w/ Shielding Plate

Note: No survey information has been applied to the data before the fits, and the mapper does wiggle around!

real magnets axis

55/70

Real Magnets: -Axis

field shape

Shielding plate

Region 1

Region 2

No shielding plate

is not well behaved in this region

real magnets axis region 1

56/70

Real Magnets: -Axis (Region 1)

field shape

0.5mm

Probably just the carriage moving about

Mapper carriage moves around by ~ 1mm, so axis is consistent with zero

real magnets axis region 2

57/70

Real Magnets: -Axis (Region 2)

Shielding plate alters

(see slide 19)

field shape

~0.8mm

Mapper carriage moves around by ~ 1mm, so axis is consistent with zero

real magnets axis1

58/70

Real Magnets: -Axis

field shape

Shielding plate

Region 1

Region 2

No shielding plate

real magnets axis region 11

59/70

Real Magnets: -Axis (Region 1)

field shape

1mm

This is the upstream end, so the shielding plate should have no effect. Shape matches, but is offset...

real magnets axis region 21

60/70

Real Magnets: -Axis (Region 2)

field shape

1mm

Shielding plate makes a difference

slide61

61/70

Real Magnets: -Axis (again)

field shape

What happens in here?

Region 3

region 3

62/70

Region 3

100% Solenoid Mode, w/ Shielding Plate

0.03T

region 31

63/70

Region 3

100% Solenoid Mode, w/ Shielding Plate

1T

region 32

64/70

Region 3

100% Solenoid Mode, w/ Shielding Plate

0.06T

region 33

65/70

Region 3

100% Solenoid Mode, w/ Shielding Plate

0.5T

region 34

66/70

Region 3

100% Solenoid Mode, w/ Shielding Plate

0.03T

region 35

67/70

Region 3

100% Solenoid Mode, w/ Shielding Plate

0.015T

region 36

68/70

Region 3

100% Solenoid Mode, w/ Shielding Plate

0.5T

conclusions next steps
Conclusions & Next Steps
  • We looked at the survey info at CM37, and have now looked at the raw data.
  • The shielding plate does its job.
  • Fields are probably linear, though the residual field needs understanding
  • Residual field changes ‘oddly’ depending on its previously powered state.
  • Hall probe measurement noise is difficult to quantify given the residual field, but estimate G.
  • More data is needed to look at hysteresis effects seriously
  • The magnetic axis is approximately centred on zero, but this requires a significant uncertainty analysis and combination with the survey info to confirm.
  • Next steps:
    • Evaluation of uncertainties
    • Cross-calibration of Hall probes
    • Refinement of magnetic axis fits
    • Field fits using 2-model scaling technique
    • Evaluation of difference between fitted and measured fields (Fourier-Bessel fits)
    • “Real magnet” model  MAUS
  • More to come at analysis meetings!
back up slides
Back-up Slides

A. Interpolation reliability

B. Mapper co-ordinate transforms

interpolation reliability

A1/1

Interpolation reliability

4 measurements with different rotations of the mapper disc

Interpolated line

mapper co0rdinate transformations

B1/4

Mapper co0rdinate transformations

Bz

By

z

0

1

2

3

4

5

6

y

phi

Direction of mapper travel (x) is out of page

mapper co0rdinate transformations1

B2/4

Mapper co0rdinate transformations

Bz

By

z

1

2

3

4

5

6

0

0

1

2

3

4

5

6

y

phi

Direction of mapper travel (x) is out of page

Start by working in POLAR co-ordinates (Br, Bphi, Bz)

mapper co0rdinate transformations2

B3/4

Bz

By

Mapper co0rdinate transformations

z

0

1

2

3

4

5

6

y

phi

Direction of mapper travel (x) is out of page

This will be true regardless of how we rotate the disc

Start by working in POLAR co-ordinates (Br, Bphi, Bz)

mapper co0rdinate transformations3

B4/4

Bz

By

Mapper co0rdinate transformations

From polar co-ordinates, get to Cartesian components for probe by:

z

0

1

2

3

4

5

6

y

phi

Direction of mapper travel (x) is out of page

For “MICE” co-ordinates:

ad