magnetic measurements plans for ornl ppu · 2 jdm, mt | mag. meas. plans for ornl ppu. 9/18/2020...

Magnetic Measurements Plans for ORNL PPU

Joe DiMarco and Mike TartagliaPPU Magnetic Field Measurement Design Review18 September 2020

Measurement Plan Outline

9/18/2020jdm, mt | Mag. Meas. Plans for ORNL PPU2

• Hall Probe field mapping to validate the magnetic model (“as-built”)• Salient Regions of Interest (Focus here is on the Chicane Dipoles)

1. “Good Field Region”2. D2 Foil Region 3. D3 Shield and Foil Region4. Fringe Field Regions

• Induction coil probe measurements• Chicane Magnets

1. Characterization of magnets with straight integral rotating coil probe – measured field can be used to validate model and support calculation of integral field along beam path.

2. Measurement of actual field integral using a short rotating coil precisely positioned along beam path

• Beam Dump Septum Dipole3. Single Stretched Wire (SSW) measurement in circulating beam region 4. Curved, Single Multi-turn Flatcoil to measure dipole and gradient integrals and harmonic

field quality

Hall Probe Field Mapping

9/18/20203

• Available Technology– New IB1 precision motion stages for probe positioning (~.001”)

• Multiple power supplies with LCW cooling capability– Laser Tracker position determination integrated into meas’mts– 3-axis Hall probes with well defined geometry and calibrations

• Can be made to work at the 10-4 level, 10-3 is less challenging– Multiple vendors (CERN/Amsterdam, Metrolab)

• Both are readily integrated to our EMMA framework– Readily fabricated into precision arrays– Simultaneous readout of multiple channels– Existing inventory of single high sensitivity 3-axis probes

jdm, mt | Mag. Meas. Plans for ORNL PPU

PRODUCT


Semi-Customizable, Used at FAIR (2017)

T-control for high precision

MODEL


“GOOD FIELD REGION”


D2 and D3 are slightly different, but they are both within a rectangular envelope of X={-0.12, 0.12} and Y={-.06, .06} [m]

Ideal field map (centered on X=Y=0) provides information about the field strength and variations with {x,y,z} coordinates – let’s take a look at those to get a sense of the scale of variations:Focus on the corners and central axis, and variations with X at certain Z and Y values with the largest excursions

“GOOD FIELD REGION” Position Dependence


“Good Field” on the boundaries at a set of nominal currents

“GOOD FIELD REGION” Measurements

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• We need to measure at the level of 10 G in a ~1-2.5 kG level main field, in three axes• 10-3 Should be achievable, 10-4 is desired and possible, But not obviously necessary• Array design:

– Stages can issue triggers for simultaneous readout of probes– Probe array can move in a continuous scan along Z– Stages can move at 50 mm/sec (calibrated rate)

• A 5 m range will take 100 seconds at this rate, may want to go slower• Continuous motion avoids vibration• Stage repositioning would be needed (1 m range in Z), so it would be done in steps

– E.g., A linear array of 12 probes spaced 2 cm apart *3 scans to cover the good field boundaries and central axis region – about 15 minutes of actual scan time (may want to have some overlap of regions to cross-check readings)

• Not obvious we need more points, but seems they could be obtained pretty quickly– CERN solution availability is unknown; also number of sensors may be an issue– Metrolab has a customizable product (Hall Magnetic Camera) that seems mature and is

ideally suited, reasonably affordable and can meet our schedule (and has internal temperature control for better precision)

– There are ways to ensure control of geometry and rigidity; need some mechanical engineering, and thought about inspection and survey details.

9/18/2020jdm, mt | Mag. Meas. Plans for ORNL PPU

“FOIL REGIONS”


D2 Foil Region: requirements are not any more challenging than good field region

(for tilt, need Bz to ~ 100 G out of By ~ 1 kG)With a small local region like this, any issues could be studied with a scan using a single 3-axis high sensitivity (0.2 T) Hall probe

“FRINGE REGIONS”


Fringe Region: requirements are not any more challenging than good field region; modeling with local iron will be needed!

200mm diameter, 7m lengthCarbon fiber cylinder3x (8’ x 8” dia. x 0.25” wall)

G10 end plugs with 1” hollow shaft for feed-through of signals (not shown in sketch).

3 dipole windings across diameter of probe (red in sketch), 40 turns each. Sandwiched between carbon fiber sheets (black) to form probe plane. Combined for bucking of dipole field.

3d printed ‘D’ supports (or machinable foam) within tube to support probe plane (not shown in sketch).

Supported at ends – entire CF structure rotates – could rest on roller surfaces if necessary because of sag.

Induction coil probe measurements1. Chicane Magnets – long straight integral probe


Approx. field region of interest (orange square) x = [-120mm, 120mm] y = [-60mm, 60mm] Measured

harmonic fields exactly represented by cylindrical expansion in the dashed range

20mm corners are outside cylindrical representation – probe can be repositioned as needed to measure these fields

jdm, mt | Mag. Meas. Plans for ORNL PPU13

Chicane dipole integral probe (continued)

9/18/2020

Support

Carbon Fiber Tube OD: 7.87”

Chicanes on Stand A –Large Diameter Integral Probe


200mm diameterprecision machined diameter cylinder

Rotating within CF tubeLength 200mm (?)

G10 end plugs with 1” diameter, supported within CF outer tube by 3-D printed bearing supports

Local encoder and slip-rings. Flexible drive shaft (“FERRET” type probe)

Windings are only on surface of cylinder (“saddle type” coil ) – PCB flex circuit conformed to cylindrical surface. In the sketch, red signifies turns of the main, small angle coil sensitive to all harmonics and green the bucking coil which suppresses the main dipole.

2. Chicane Magnets – short probe


Probe will be sensitive to radial field only (no sensitivity to longitudinal fields). Sum fluxes along path as function of angle to get flux vs angle over the whole integral

Probe ends designed so that a small overlap between probe positions largely compensates for the harmonic-order-dependent sensitivity that changes over the 2-3 mm winding end.

Probe would be precisely moved by stages on test stand with 2um accuracy – magnet would be off to the side of the test stand as for Hall probe measurements. An additional rotational stage would control the yaw of the probe wrt beam path.

Chicane Magnets – short probe (continued)


Stretched between motion stagesmoves with 1 micron accuracy

• Simple geometry • Can be ‘arbitrarily long’

Integral Magnetic Strength: SSW can resolve ~1e-5Tm

Stage assemblies

DAQ cart

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Single Stretched Wire (SSW)

3. Beam Dump Septum Dipole – circulating beam region


Measure strength with SSW at this location with magnet at 0A and at currents corresponding to 1 and 1.3GeV

Should be able to measure field at the level of fraction of Gauss-m (sufficient for requirements)

Overhead view of magnet

jdm, mt | Mag. Meas. Plans for ORNL PPU18

Integral strength in circulating beam area

9/18/2020

Single Multi-turn Flatcoil (SMF) on stiff strongback.Curved shape matching beam trajectories.

SMF slides on stationary surface within the magnetat center of gap

Translated precisely at each end by the Aerotech stages on the test stand to achieve high-accuracy dipole and gradient integral measurements.

Use Litz wire with return wire stationary inside magnet –which allows small moves to generate large signals (small moves help determine the local field with negligible impact from harmonics)

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Stationary multi-turn return wire that completes loop

Like a curved, multi-turn version of SSW

Can use mechanical or magnetic feature as reference so that SMF can be positioned accurately at “x=0” (beam location) for integral dipole field measurements.

(e.g. to achieve 10 units (0.1%) in the presence of 1000 units/inch gradient, need 0.25mm position localization)

4. Septum magnet- Dipole and gradient field integrals (and homogeneity) in gap


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Stationary multi-turn return wire(s)

• Return wire(s) stationary at innermost part of C.• Extending far enough out ends so that return loop sees no field with motion of SMF• Have more than one SMF – neighboring SMFs connected in series opposition when

desired to give full Loop (LMF) which rejects dipole. • Use independent multiple wires in same structure to measure along multiple or

different beam trajectories of interest.

Single Multi-turn Flatcoil


• Creating a Loop of MultiturnFlatcoil can buck dipole and get harmonics profileOR can just measure local field vs position and fit (though in the latter case larger dynamic range is required of integrator).

+/- motion flux integrals

𝜑𝜑+𝜑𝜑−

Can determine integrated gradient, 𝐿𝐿𝑚𝑚𝑔𝑔(for step D), from

𝜑𝜑+ + 𝜑𝜑− = 𝐿𝐿𝑚𝑚𝑔𝑔𝐷𝐷2

with errors from (local) multipole harmonics of

𝑏𝑏4𝐷𝐷2

2𝑅𝑅2+𝑏𝑏6𝐷𝐷4

3𝑅𝑅4+ ⋯

Errors are small for D small compared to R

Can determine integrated dipole, 𝐿𝐿𝑚𝑚𝐵𝐵1 (for step D), from

𝜑𝜑+ − 𝜑𝜑− = 2𝐿𝐿𝑚𝑚𝐵𝐵1𝐷𝐷

with errors from (local) multipole harmonics of

𝑏𝑏3𝐷𝐷2

3𝑅𝑅2+𝑏𝑏5𝐷𝐷4

5𝑅𝑅4+ ⋯

Again errors are small for small D

Accurate positioning to beam center locationin aperture would be needed

Integral strength and gradient


SUMMARY


Hall Probe Measurements• Commercial precision Hall probe options exist• Straightforward integration into our measurement software• Precise calibrations can be made to meet 10-3 requirement• Details of probe array design TBD• Mechanical control of probe angles needed• Precise Motion is possible, with Laser Tracker readout

Inductive Coil Measurements• Full length large diameter rotating coil for the chicane magnets• Short large diameter rotating coil, precisely positioned through beam path in chicane

magnet• Single Stretched Wire system measurement in circulating beam region of dump dipole• Curved, Single Multi-turn Flatcoil to measure integrals and harmonic field quality in dump

dipole• The measurement systems seem fairly straightforward to design and build, and should

provide the necessary validation of magnetic models and independent measurements of field integrals of strength and harmonics.

magnetic measurements plans for ornl ppu · 2 jdm, mt | mag. meas. plans for ornl ppu. 9/18/2020...

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