s. russenschuck, clic-workshop, wp2-pacman, 4.02.2014 1 r&d projects on rotating coil probe and...

S. Russenschuck, CLIC-Workshop, WP2-Pacman, 4.02.2014

MAGNETIC MEASUREMENT SECTION

1

R&D projects on rotating coil probe

and stretched wire techniques for CLIC / PACMAN

Stephan Russenschuck

for the CERN magnet (measurement) -team

CLIC workshop

4.02.2014

1



Rotating Coil Measurements

Tangential coil Radial flux

Radial coilTangential flux



Series Measurements of the LHC Magnets



Standardized Equipment – Motor Drive Unit

Drive unit for measurements in horizontal (rt) and vertical (cryogenic temp.) position



Standardized Equipment – Rotating Coil Shafts

Shaft for measurements in a vertical cryostat

Shaft R=45 mm, coil length: 130 mm

Shaft R=30 mm, coil length: 1200 mm



Flexible Framework for Magnetic Measurements



Rotating Coil Measurements



The Riemann Lebesque Lemma

8

The Fourier coefficients tend to zero as n goes to infinity (Riemann Lebesque) and they must scale according to the Cauchy theorem for bounded functions

Simulations !



Spread and Noise Floor in Measurements

Compensated

Noncompensated

Radial axes displacement

Torsional deformations

Blind eye?



Challenges

– Sensitivity and tolerances on small shafts

– Bucking ratio

– Vibrations and noise

– Calibration

– Connection PACMAN R&D efforts

– PCB technology for coils

– Rapid prototyping for shaft

– Micro-connectors

– MRU-II (smaller, smoother)

– In-situ calibration

– “Intelligent” post-processing



Architecture

Stretched Wire Experimental Setup



The Single Stretched Wire Method



Measurement system design

Oscillating wire Vibrating wire

Map of Second Wire Resonance

Wire Excitation Frequencies

Stretched wire



Solenoid Center and Axis

Force distribution requires vibration at the second resonance



Solenoid Center and Axis: Transversal Field Profiles

Left: Perfectly aligned. Right: With swing

Therefore: Switch to first resonance, and align (move) the magnet, not the stages



Solenoid Center: Oscillation Amplitudes

Modulus At x sensor At y sensor

For small displacements from the center, the By component is a linear function in x



Linear Regression in the Line Search Procedure



Vibrating wire for magnetic axis Solenoid magnet

Map of Second Wire Resonance

Before alignment After alignment



Vibrating wire for magnetic axis Solenoid magnet

Map of Second Wire Resonance (on 2 mm radius)



Solving Boundary Value Problems I

1. Governing equation in the air domain

2. Chose a suitable coordinate system, make a guess, look it up in a book, use the method of separation, that is, find orthogonal and complete eigenfunctions. Coefficients are not know at this stage

3. Incorporate a bit of knowledge, rename, and calculate field components



Solving Boundary Value Problems II

4. Measure or calculate the field (flux) on a reference radius and perform a discrete Fourier analysis (develop into the eigenfunctions). Coefficients are known here.

5: Compare the known and unknown coefficients

6. Put this into the original solution for the entire air domain



Solving the Boundary Value Problem

Take any 2periodic function and develop according to

For the oscillating wire technique: Use the oscillating amplitudes measured at one position longitudinally as we move the wire such that they become the generators of a cylinder inside the magnet aperture



Optical sensorsPhototransistor Sharp GP1S094HCZ0F

Response of the Phototransistors



Use Wire Displacements

Proposition: We are done if:



Solution of the Wave Equation (Assumptions)



Use Wire Displacements



Solution of the Wave Equation (Steady State)



Check 2: Numerical simulation (FDTD) and the Steady State Solution



Solution of the Wave Equation III

Check: Known longitudinal field or oscillation profiles

Ideas welcome on how to measure the longitudinal profile of the oscillation wire (30 phototransistors, inductive, capacitive)



Solution of the Wave Equation IV

The slackline

The hard-edge (model) magnet



Test Cases

Air coil: Academic worst case LEP-IL-QS The “blue” magnet



The Air Coil

Longitudinal field distribution Longitudinal shape of the wire oscillation



Convergence of the Modal Amplitude Functions



Results for the Air Coil



Results for the Blue Magnet



Conclusion on the Wire Techniques

The classical stretched wire technique is routinely used for axis and gradient measurements

There is still a lot of potential in the oscillating wire technique Because we measure the oscillation amplitude only at one point, we make

in intrinsic error caused by the varying end fields as we move along the circular trajectory

– The method is exact for the hard-edge (model) magnet and consequently for small-aperture magnets excited by rare-earth material

– There is an intrinsic error because we measure only one amplitude. This error can be estimated when the numerical model is available

– Effects from stage misalignment are much larger than the intrinsic error

– We would be exact if it was possible to measure the shape of the wire oscillation



Solution of the Wave Equation (Recall)



Longitudinal field Profiles

Behavior around resonance frequencies



Challenges

– Bandwidth of the system

– Intrinsic error

– Noise at 1 kHz

– Nonlinearities in the physical model

– Tilt and swing alignment of the quadrupole PACMAN R&D efforts

– Measurement of oscillation profiles

– New stages and wire tensioning systems

– Fiducilization

– Software framework (data and task manager)

– “Intelligent” postprocessing (tension, multipoles)

– String of magnets

s. russenschuck, clic-workshop, wp2-pacman, 4.02.2014 1 r&d projects on rotating coil probe and...

Documents

wire slide

resonance slide

position slide

wire experimental setup

line search procedure

wire techniques

coil length

coil shafts shaft