Progress Toward Mini and Micro
Magnetic Undulators
Ololade Oniku, William Patterson, Alexandra Garraud, Evan Shorman, Paul Ryiz, David P. Arnold
University of Florida
Dept. Electrical & Computer Engineering
Interdisciplinary Microsystems Group
Brock Peterson, Florian Herrault, Mark G. Allen
Georgia Institute of Technology
School of Electrical and Computer Engineering
MicroSensors and MicroActuators Group
HBEB
San Juan, Puerto Rico
March 27, 2013
Overview
 State-of-the-art undulator
-
Pole pitch (λu ~ 5-50 mm)
Peak field (B0 ~ 0.1-1 T)
Large total system size
Manual assembly
High costs (material and labor)
 Micromachined Undulator
-
Pole-pitch (λu ~ 5-50 µm)
Peak field (B0 > 0.2 T)
Hard X-rays at lower beam energies
Microfabrication advantages
• Photolithgraphic resolution
• Wafer-level mass production
• More complex patterns (3D?)
2
Overview
3
 Scale-dependent approaches
Thin-Film
Electroplating &
Sputtering
Thick-Film
Micro Powder
Processing
Bulk
COTS Sintered
Magnets
Outline
 Laser-micromachined SmCo “Mini” undulators
 Electroplated CoPt film “Micro” undulators
 Characterization
- Scanning Hall Probe
- Magneto-optical imaging
 Collaborations
- Pulsed-wire characterization (UCLA)
- Photon-generation tests (Michigan)
4
Laser-Cut Magnets Process Overview
Bulk SmCo
~300 µm thick
(unmagnetized)
Laser-cut into comb
structures
Magnetize out-of-plane
Assemble and polish
5
Interlocking Array Segments
 6 single PM comb-arrays assembled
6
Micro-Assembly
7
 Comb array assembly (magnetically self-aligned)
 Top and bottom arrays assembled into frame
 Polished to final thickness
20 mm
SEM of half an undulator
(Period = 500 µm)
Laser-machined SmCo undulator array
with 200-µm thick, 2-mm long poles,
400-µm period and 50 periods
Assembled Prototype Undulator
8
 Undulator assembly
- Two magnet arrays sandwiched with spacers
Estimated ~0.23 T peak B-field
Magnetized and assembled SmCo arrays (400 µm period). The vertical gap between
the PM plates was set at 200 µm.
High-Resolution Field Mapping
 High-resolution Hall effect sensor (1 µm x 1 µm area)
 3-axis stage with 100 nm step size (x, y axes)
 Currently implementing automatic scan height control
Sensor
module
Sample
platform
x- y- and zstages
9
Scanning Hall Probe Stage
1 µm x 1 µm
sensing area
10
Scanning Hall Probe system
 Example field maps at ~100 µm scan height
Peak-to-peak: 0.1 T
Measured period: 400 µm
11
Simulation vs. Experiment
12
 Simulation and experimental data at different heights for a
single array
Simulation
Very good
agreement
Measurement
B0 ~ 0.1 T peak, 100 µm above
Film Magnets Process Overview
13
Electroplate films (CoPt)
5-20 µm thick
Soft magnetic
magnetizing head
Hard magnetic
film (5 – 20 µm)
Pre-magnetize the film
uniformly “UP”
Si substrate
Use magnetizing head to
selectively reverse areas
“DOWN”
Hext
Selective magnetic patterning
using magnetizing heads
Electroplated Co80Pt20 Films
14
 Co-Rich Co80Pt20 on silicon substrates
Top view
Out-of-plane properties:
- Remanent flux density: Br=1.0 T
- Intrinsic coercivity: Hci=330 kA/m (4.1 kOe)
- Energy density: BHmax=134 kJ/m3 (17 MGOe)
30 µm
Cross section
Selective magnetization
15
 Laser-cut magnetizing head from bulk Fe
 Pattern Co80Pt20 using the magnetizing head
 Characterization: magneto-optical imaging and scanning Hall probe
Laser-micromachined Fe magnetizing head
200 µm
200 µm
Electroplated Co-Pt film (5 - 10 µm)
Si substrate
400 µm
Laser-machined
Fe magnetizing head
Magneto-optical image
at surface
Scanning Hall data
100 µm above surface
Selective magnetization
16
 Further down-scaling
200 µm period
120 µm period
65 µm period
Selective magnetization: complex patterns
Magnetizing mask (Fe sheet)
Magnetic pattern
17
Magnetic Properties of L10 CoPt
18
 L10 CoPt (50:50 ratio) on silicon substrates
 Annealed @ 700 °C
 Coercivity ~2.5x higher than Co80Pt20 films
500 µm
Out-of-plane properties:
- Remanent flux density: Br=1.15 T
- Intrinsic coercivity: Hci=800 kA/m (10 kOe)
- Energy density: BHmax=220 kJ/m3 (28 MGOe)
Magnetic Properties
19
 Micromagnets compared to bulk
Sputtered NdFeB
40 μm
(collaborator)
Plated L10
CoPt 15 μm
Plated
Co80Pt20
15 μm
UCLA: pulsed-wire measurements
 Magnetic characterization of the full undulator
Side view
Schematic of the setup
20
UCLA: Pulsed-wire measurements
21
 Undulator
- full length = 20 mm
- period = 400 µm
- gap = 200 µm
 Wire
- diameter = 25-50 µm
 Hanging mass ~ 30-80 g
Electron “kick” but no detectable undulations
 Work in progress
- estimation of the displacement of the e-beam
Michigan: Photon-generation tests
eprofile
Fiducial Array
(100µm W wires,
1.25 mm
spacing)
~140 cm
110 cm
Micro-Undulator on
Hexapod
(400 µm gap, 2 cm long)
5 cm
Magnet
(0.75T)
Light shield/
Laser block
Deflected (25 µm Al)
Direct detection
X-ray camera
(Andor)
LANEX or Filter Pack
(300 µm Mylar
+ 2 µm Al)
Electron
Beam
e- spec
22
F/20 OAP Beam
(~100 TW, ~22 µm spot)
Gas cell (10mm)
Michigan: Photon-generation tests
 Initial results indicate that:
- e-beam is not mono-energetic enough (dE/E > 10%)
 New gas cells have been fabricated
- 10 mm gas cell: monoergenetic shots at ~400 MeV
3 consecutive shots
23
Ongoing Efforts
 Halbach magnetization patterns for higher magnetic fields
 Further development of electroplated L10 CoPt and FePt
(50:50 ratio) for superior magnetic properties
 Exploration of limits of selective magnetization using
magnetizing heads
- Goal: 50-µm period undulator
 Collaboration with UCLA and Michigan for lasermicromachined undulator characterization
- Open to other collaboration opportunities
24
Acknowledgments

14
AXiS Project #N6601-11-1-4198
Uniform Magnetization
Patterned Magnetization
26
Towards shorter laser-machined undulators
 Undulator with shorter periods successfully fabricated
Magnetized and assembled SmCo arrays:
(a) 300-µm period
(b) 250-µm period
(c) 230-µm period
27
Summary of Designs
28
Undulator
period (#)
Undulator
gap
Magnetic
material
400 µm
(50)
200 µm
Laser-cut
Bulk SmCo
0.25 T
1
0.010
50 µm
(50)
20 µm
Plated
L10 CoPt
0.13 T
2
0.00065
1
measured with the SHP
2 estimated from simulation
B-field
(peak, midgap)
K
(cm.T)