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Field Mapping. V. Blackmore CM38 23rd February 2014. Mapped Currents. Contents. Survey plots presented at CM37. Today: Effect of the shielding plate Linearity of field with current Residual magnetic field Probe Jitter Hysteresis? Magnetic axis fits.

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Field mapping

Field Mapping

V. Blackmore

CM38

23rd February 2014


Contents

Mapped Currents

Contents

Survey plots presented at CM37.

Today:

Effect of the shielding plate

Linearity of field with current

Residual magnetic field

Probe Jitter

Hysteresis?

Magnetic axis fits

  • Runs cover the above currents, plus:

  • 0A measurements (residual field)

  • 30A individual coil measurements (superposition)

  • With and without Virostek plate

A lot of data


Co ordinate systems
Co-ordinate Systems

Until the end of this talk...


The mapper co ordinate system
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
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
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
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
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
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
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
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
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
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
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
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

  • are what the mapper reports

Forward!

etc. etc.


The shielding plate

*

Mapper m

Mapper at this side

The Shielding Plate

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

“Identical”: Exactly the same points taken at the same currents

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


Spot the shielding plate
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
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 difference
Spot the Difference

Let’s play

This region has been temporarily censored

Huge spikes!

Are we being naïve?


Working spike hypothesis
Working Spike Hypothesis

We’re being a little bit naïve, but nevertheless…

  • The mapper does not return to exactly the same place each time

  • Have 4 measurements of with and without the plate (i.e. 4 orientations of )

Difference taken as: w/o plate with plate


Working spike hypothesis1
Working Spike Hypothesis

We’re being a little bit naïve, but nevertheless…

  • The mapper does not return to exactly the same place each time

  • Have 4 measurements of with and without the plate (i.e. 4 orientations of )

Difference taken as: w/o plate with plate


Working spike hypothesis2
Working Spike Hypothesis

We’re being a little bit naïve, but nevertheless…

+1.4377T

And a careful observer will see…

  • This plot just shows , so the actual difference taken could be more complicated.

  • This theory will be clearer when we consider the survey information as well.

  • But consider the scales – overall small effect.

m

m

+1.34994m


Spot the difference again
Spot the Difference (Again)

Let’s play

A real feature

A consequence of being purposefully naïve


Spot the difference again1
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


Field linearity
Field linearity

With no shielding plate, field should belinear with current.

With shielding plate, field may benon-linear with current*

but there’s no data to test this theory with ‘naïvely’

(i.e. with the exact same measurement grid)


Without the shielding plate
Without the shielding plate…

  • (Red) 100% current in Solenoid Mode

  • (Black) 80% current in Solenoid Mode

  • Scale up 80% measurements and compare…


Without the shielding plate1
Without the shielding plate…

  • (Red) 100% current in Solenoid Mode

  • (Black) 80% current in Solenoid Mode

  • Scale up 80% measurements and compare…

  • Looks good at first glance!


Without the shielding plate difference
Without the shielding plate (difference)

This is the 100% measurement scaled down to a level that fits on the y-axis (for comparison with the bumps)

This looks like more than just the earlier “spikes”


Without the shielding plate difference1
Without the shielding plate (difference)

Everything is ‘perfect’ in the centre coil

probe

and mm are -out of phase.

See the same story for Flip Mode


Hysteresis
Hysteresis

The obvious follow-up question is…

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

No ‘naïve’ data to test this with.

Important: This does not mean we won’t know, it just relies on a more in-depth analysis!


Residual field
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
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.

  • Non-naïve measurements, not taking differences

  • 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
7th—10th June:

On-axis probe only

Previously at 80% Sol. Mode

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

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


7th 10th june1
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
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
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
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
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
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
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
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
7th—19th June:

On-axis probe only

Shielding plate differences

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


Probe jitter
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.