“Magnetic Measurements for Particle Accelerators” International Master in Hadronteraphy, Pavia, 10 May 2013 [email protected]Page 1/65 M A G N ETIC M EA SU REM EN T LA B O R A TO R Y cern .ch /m m Contents 1 – Rotating coils 2 – Stretched wire Magnetic Measurements for PACMAN Marco Buzio, TE/MSC/MM
Magnetic Measurements for PACMAN Marco Buzio, TE/MSC/MM. Contents 1 – Rotating coils 2 – Stretched wire. Main PACMAN WP 2.2 goal - PowerPoint PPT Presentation
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
“Magnetic Measurements for Particle Accelerators”International Master in Hadronteraphy, Pavia, 10 May 2013 [email protected]
Page 1/65 MAGNETIC MEASUREMENT LABORATORY cern.ch/mm
Contents
1 – Rotating coils
2 – Stretched wire
Magnetic Measurementsfor PACMANMarco Buzio, TE/MSC/MM
“Magnetic Measurements for Particle Accelerators”International Master in Hadronteraphy, Pavia, 10 May 2013 [email protected]
Page 2/65 MAGNETIC MEASUREMENT LABORATORY cern.ch/mm
Main PACMAN WP 2.2 goal
Development of a rotating coil system (single scanning coil and/or coil train) integrated on the PACMAN test stand in bldg. 169 and aimed at field quality (strength, harmonics, direction) measurements of CLIC quadrupoles.
Magnetic measurement of the axis: if possible absolute, otherwise in relative (fixed-coil) mode with ultra-high bandwidth and resolution.
This implies, within the 3-years span: a dedicated FAME system with an optimized PCB coil(s), FDI, FFMM script etc…. Metrological qualification, cross-checks with other instruments, with documented calibration and test procedures
“Magnetic Measurements for Particle Accelerators”International Master in Hadronteraphy, Pavia, 10 May 2013 [email protected]
Page 3/65 MAGNETIC MEASUREMENT LABORATORY cern.ch/mm
• Workhorse of CERN instrumentation park: most accurate and cost-effective method• Size, effective surface, number of turns, resistance, assemblies … must be adapted to the specific
requirements of each magnet no commercial solution, in-house R&D• Main parameter: total area exposed to flux change Ac, which determines the peak
induced voltage (limited by electronics, typically 5 or 10 V)
Search coils
AAA
C dAt
dAdtd
dtdV d BvnBnB
VC
A
NT
B n
A
Faraday’s law (total derivative) fixed-coil,time-varying field
coil rotating, translatingor deforming (wire)
BvABABA
tV
c
c
c
c
Fixed coil in a time-varying field
Coil rotating at angular speed in stationary, uniform field
Coil translating at speed v in stationary field with gradientB
• the number of turns available for coils (→ signal level) r2
• Signal level grow with linked flux variation → rn-1 (e.g. radial coil), rn (stretched wire)(field/gradient strength, rotation/translation speed, length, etc. being equal)
S/N ratio for quadrupole measurement may vary with r3 r4
…. BUT: small magnets are easier to flip around …
nn
rn
r
nnT
n rrnLN
12
e.g.: radial coil, n>1
rrn
n
n )()(
“Magnetic Measurements for Particle Accelerators”International Master in Hadronteraphy, Pavia, 10 May 2013 [email protected]
Page 8/65 MAGNETIC MEASUREMENT LABORATORY cern.ch/mm
Coil bucking
• The accuracy of higher harmonics measured by individual coils may be affected by geometry errors• Solution = coil bucking (or compensation): suitable linear combinations of coil signals cancel out the
sensitivity to the main (and lower) harmonics robustness to mechanical imperfections• Example: in a perfect quadrupole, average gravity-induced sag on a radial coil flux error including
mainly B1 and B3 components. A four-coil series/anti-series combination cancels out B2 sensitivity error-free harmonic measurement
“Magnetic Measurements for Particle Accelerators”International Master in Hadronteraphy, Pavia, 10 May 2013 [email protected]
Page 9/65 MAGNETIC MEASUREMENT LABORATORY cern.ch/mm
Effective coil width
• The flux corresponding to a given coil position can be obtained in various ways (flipping or rotating the coil, pulsing the field from zero)
• L can be considered as known from mechanical measurements• General case: unless B(s) or w(s) are constant and can be taken out of the integral sign, the flux cannot
be obtained from average width and average field:
• Define: effective width (NT gets lumped in for convenience) = average of width weighted with the field
eff
Bd
A
eff
L
T wLBLwBdssBswNeff
)()(0
1)()(
)()(
01
01
01
L
L
L
L
L
L
dsswdssB
dssBsw
Bd)(
)()(
)(1
0
0
0
effeff
L
L
Teff
L
wLA
dssB
dssBswNw
dssBL
B
considerations made here for a dipole field hold true for other components as well
“Magnetic Measurements for Particle Accelerators”International Master in Hadronteraphy, Pavia, 10 May 2013 [email protected]
Page 10/65 MAGNETIC MEASUREMENT LABORATORY cern.ch/mm
Linac4 harmonic coil test bench
• Developed for small-aperture Linac4 permanent-magnet and fast-pulsed quads• Æ19 mm, 200~400 mm long quadrupole-bucked coils (difficult measurement: S/N Æaperture
3 !)• Harmonic measurements in DC (continuously rotating coil) or fast-pulsed (stepwise rotating) mode. • small size flipping the magnet around allows elimination of many systematic errors• in-situ calibration technique to improve accuracy despite geometrical coil imperfections
“Magnetic measurements of the Linac4 diagnostic line dipole – first results”Page 12/7
MAGNETIC MEASUREMENT LABORATORY cern.ch/mm
PCB coil-related R&D themes
1. general improvement of multi-layer PCB coils: track density (currently only ~1/3 of conventional coils), layer referencing and alignment (currently ~0.1 mm)
2. optimization of track layout to minimize sensitivity to production errors
3. improvement of the existing Æ8 mm rotating PCB coil shaft: mechanical stiffness of the assembly (materials, geometry, resins …), alignment and stability of ball bearings, scaling above and below Æ8 mm (e.g. is it possible Æ4 mm for CLIC, Æ20 mm for Linac magnets, or even more ?)
4. development (as suggested by Stephan) of a more compact Mini Rotating Unit MRU-II, i.e. about 10-12 contacts instead of the current 76, better adapted to small coils, with less angular vibrations
5. PCB-based quench antennas (with compensation)
6. micro PCB connectors for multi-strand wire coils (as suggested by Olaf, to replace the existing micro-soldered connectors that only Lucette knows how to make)
7. large scale PCB fluxmeters: upper limits of current printing, pressing and assembly techniques + new possibilities offered by ELTOS; alternative architectures e.g. multiple mass-produced short boards + suitable inter-board connections
8. quality assurance of PCB fluxmeters: AC measurement of coil width, R/L measurement, calibration of magnetic equivalent coil area and coil distance inside reference magnets
9. micron-level precision coils for high order analog bucking (e.g. integrated circuit - scale fluxmeters)
10. Joe di Marco-style, polyvalent PCB sandwich coil shaft (flexible design, may be very practical for very large diameter rotating systems). Advanced materials (foams, honeycombs etc … for higher stiffness-to-weight ratio)
11. electronic acquisition systems: correction of side effects of high resistance load coils (input impedances, automatic resistance measurement and off-line correction, noise and offsets)
12. software tool to facilitate the design of new PCB coils, bypassing traditional CAD: from geometry specifications (e.g. straight/arc/straight or more realistic continuously varying curve) layer design Gerber format file
13. other techniques alternative to PCB: circuits printed on flexible rolls, inkjet circuit printers
“Magnetic measurements of the Linac4 diagnostic line dipole – first results”Page 13/7
MAGNETIC MEASUREMENT LABORATORY cern.ch/mm
Single Stretched Wire
B stage
Reference quadrupole
A stage
“Magnetic measurements of the Linac4 diagnostic line dipole – first results”Page 14/7
MAGNETIC MEASUREMENT LABORATORY cern.ch/mm
Classical Single Stretched Wire
• DC operation: nominal field level• AC operation : enhanced sensitivity at very low
field levels (e.g. 1 A in LHC cryomagnets),elimination of DC offset (stray fields, remanent …)
A B C
iterativeaxis finding
Gxdy, Gydxfield direction (roll)
field harmonics
S0, pitch, yaw
“Magnetic Measurements for Particle Accelerators”International Master in Hadronteraphy, Pavia, 10 May 2013 [email protected]
Page 15/65 MAGNETIC MEASUREMENT LABORATORY cern.ch/mm
1528.09.2005
2
8 wirelTwg
Sag
As tension measurement is affected by friction problems and gauge accuracy, the SSW system measures the fundamental frequency of the wire, which depends uponh its mechanical properties
wT
lf
wire21
Shape of stretched wire with / without magnetic forces