Rotating Coils PACMAN meeting 14 04 14 Printed

Rotating Coils PACMAN meeting 14. 04. 14 Printed Circuit Coils – Future developments Rotating Coils - Giordana Severino – 14. 04. 2014

Rotating coils measurement systems are developed to characterize the magnetic field quality of magnets in accelerators facilities. The field harmonics are computed knowing the rotating coil’s precise geometry. The process of bucking allows improving the measurement accuracy. Rotating Coils - Giordana Severino – 14. 04. 2014

Rotating coils Useful background information Using an angular encoder w Rotating Coils - Giordana Severino – 14. 04. 2014

Rotating coils Useful background information Rotating Coils - Giordana Severino – 14. 04. 2014 Radial coil: Harder to build for small dimension, better the tangential coil A rotating coil (loop of wires) measures the variation of the intercepted magnetic flux multipole coefficients Bn(ref) and An(ref) are called normal and skew multipole coefficients

Tangential coil Vertical dipole Rotating Coils - Giordana Severino – 14. 04. 2014 Horizontal dipole Quadrupole

Tangential coil: Blind eye Rc = coil central radius D = Opening angle Rotating Coils - Giordana Severino – 14. 04. 2014

Rotating coils Motion related issues Vibration motion causes spurious harmonics in the coil signal Torsion motion Minimize (errors) Effect “Bucking method” Coil system whose sensitivity to the (n -1)- th harmonic is zero Vibration Rotating Coils - Giordana Severino – 14. 04. 2014 Coil system whose sensitivity to the n- th harmonic is zero Torsion

Rotating coils Bucking Analog bucking: Digital bucking: The Bucking Ratio is the ratio of the harmonic n in the absolute and compensated measurements It is the «quality check» for bucking For a quadrupole it should be tipically 100 Rotating Coils - Giordana Severino – 14. 04. 2014

Rotating coils Example: How to calculate the gain factor Rotating Coils - Giordana Severino – 14. 04. 2014

Rotating coils Sensitivity Factor General: Tangential: Radial: Calibrated parameters (coil central radius, axial tilt, magnetic surface) Ø Construction drawings Rotating Coils - Giordana Severino – 14. 04. 2014 a, R 2, and R 1

Rotating coils Fabrication problems Handmade systems: Time of fabrication is long, wiring is a complicated process. Connectors Manual coil winding facility Rotating Coils - Giordana Severino – 14. 04. 2014

Printed circuit rotating coils The PCB coil is based on the same principle as classic rotating coil. PCB coils are made up by multiples layers boards on which are printed the coil loops traces on both sides. Rotating Coils - Giordana Severino – 14. 04. 2014

Ideal PCB coil A perfect PCB coil: accuracy implies high stiffness and straightness of the coils excellent knowledge of traces (windings) localization. Coils fabrication should also be easy and low-cost, so that coil parameters (type, length, number of turns, radius, etc. ) can be customized to the magnet requiring test. Rotating Coils - Giordana Severino – 14. 04. 2014

Printed circuit rotating coils Rotating Coils - Giordana Severino – 14. 04. 2014 The trace continues in loops of increasing width on the reverse side (dashed line) following the original traces and maintaining the same chirality to complete a winding:

Printed circuit rotating coils Dipole and Quadrupole bucking Quadrupole and Dipole Bucking DQB(1+3) Also only Dipole bucking DB (1+2+3+4) Rotating Coils - Giordana Severino – 14. 04. 2014

Printed circuit rotating coils Sensitivity factor One method to compute it is: L length of a given wire R reference radius The (-1) j gives the sign of the current flow of each wire and the (xj, yj) are the locations of the wires with respect to the rotation axis. Multiple layers: The position of traces in not well known… Hard to calculate with high precision Rotating Coils - Giordana Severino – 14. 04. 2014

Printed circuit rotating coils Opening angle Tangential coils: Determinate the distances between traces according to the opening angle: Rotating Coils - Giordana Severino – 14. 04. 2014

Printed circuit rotating coils Sensitivity factor Comparison between tangential coil and pcb tangential coil (one layer) at probe radius of 16 mm and 32 mm Rotating Coils - Giordana Severino – 14. 04. 2014

Printed circuit rotating coils To sum up: Advantages… The number of turns can be increased by adding identical layers (PCB stack) Precise trace positioning (<10 μm) Sensitivity comparable to traditional designs (with 32 or more layers) Manufacture large series quickly, reproducibly, cheap Makes practical high-order compensation schemes (B 1=B 2=B 3=B 4=0) Rotating Coils - Giordana Severino – 14. 04. 2014

Printed circuit rotating coils … and inconvenients Coil Resistance is High [k. W]: consequent instrumentation required Cost of production when producing few coils Human error on multiple layers assembly (stack of double layer) Stiffness of the structure too low, flexible during rotation much harder to calibrate Rotating Coils - Giordana Severino – 14. 04. 2014

Printed circuit rotating coils … and inconvenients Fabrication errors: Rotating Coils - Giordana Severino – 14. 04. 2014

Some PCB coils-related R&D themes ü General improvement of multi-layer PCB coils: track density (currently only ~1/3 of conventional coils) ü Optimization of track layout to minimize sensitivity to production errors Rotating Coils - Giordana Severino – 14. 04. 2014

Some PCB coils-related R&D themes Improvement of the existing 8 mm rotating PCB coil shaft: mechanical stiffness of the assembly (materials, geometry, resins …) alignment and stability of ball bearings, scaling above and below 8 mm ü ü Development of a more compact Mini Rotating Unit MRU-II Rotating Coils - Giordana Severino – 14. 04. 2014

Some PCB coils-related R&D themes ü ü Micro PCB connectors for multi-strand wire coils : Standard for all number of Brins Easy to use Avoid human errors PCB fluxmeters : upper limits of current printing pressing and assembly techniques new possibilities offered by ELTOS Rotating Coils - Giordana Severino – 14. 04. 2014

Some PCB coils-related R&D themes ü ü Polyvalent PCB sandwich coil shaft advanced materials (foams, honeycombs etc … for higher stiffness-to-weight ratio) Software tool to facilitate the design of new PCB coils, bypassing traditional CAD: from geometry specifications layer design Gerber format file ü Other techniques alternative to PCB: circuits printed on flexible rolls, inkjet circuit printers ü Other tasks…. Rotating Coils - Giordana Severino – 14. 04. 2014

Scientific Planning for 2014 Rotating Coils - Giordana Severino – 14. 04. 2014