Hard X-Ray Wiggler Sources at NSLS-II
Oleg Chubar
X-ray source scientist, XFD, NSLS-II
Workshop on Preparation of High-Pressure Beamline Proposal
April 29, 2010
1 BROOKHAVEN SCIENCE ASSOCIATES
Wiggler Impact on NSLS-II Electron Beam Parameters
Two main phenomena associated with the process of Emission of Photons by relativistic Electrons
in High-Energy Electron Storage Rings:
- Radiation Damping (associated with classical emission) tends to reduce Electron Beam Emittance
- Quantum Fluctuations (due to discreteness of the emission “events”) result in the increase
of Electron Beam Emittance and Energy Spread
The “equilibrium” Electron Beam Emittance and Energy Spread is determined by the balance of these
two phenomena.
Basic Parameters of Electron Beam at NSLS-II
Energy 3 GeV
Max. Current 0.5 A
Bare Lattice With With
(without DW) 3 x 7 m DW 8 x 7 m DW If used in dispersion-free
Horizontal Emittance [nm] 2 0.9 0.5 straight sections at NSLS-II,
high-field wigglers would
Relative Energy Spread 0.5 x 10-3 0.89 x 10-3 1.0 x 10-3 further reduce e-beam
Horizontal RMS Size [μm]* 64 / 204 43 / 137 33 / 107 emittance, however would
Horizontal RMS Divergence [μrad]* increase energy spread
31 / 9.8 21 / 6.6 17 / 5.1
Vertical RMS Size [μm]* 4.6 / 8.2 2.9 / 5.2 2.9 / 5.2
Vertical RMS Divergence [μrad]* 4.3 / 2.4 2.7 / 1.5 2.7 / 1.5
* - Low-Beta section / High-Beta section values 2 BROOKHAVEN SCIENCE ASSOCIATES
Spectral Brightness of NSLS-II Sources
3 BROOKHAVEN SCIENCE ASSOCIATES
Spectral Flux of NSLS-II Sources
4 BROOKHAVEN SCIENCE ASSOCIATES
Wiggler Comparisons: Brightness
NSLS-II e-beam
assumed:
I = 0.5 A
εx = 0.55 nm
εy = 8 pm
5 BROOKHAVEN SCIENCE ASSOCIATES
Wiggler Comparisons:
Flux per Unit Horizontal Angle
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Wiggler Comparisons:
Peak Flux per Unit Solid Angle
7 BROOKHAVEN SCIENCE ASSOCIATES
DW Reference Magnetic and Mechanical Design
Magnetic Design with Side Magnets: 90 mm Period, 1.85 T Peak Field at 12.5 mm Gap (T. Tanabe)
3D Magnetic Model (with reduced number of periods) Calculated Magnetic Field (RADIA)
Side Magnets
Fixed-Gap Conceptual Mechanical Design (proposal of E.Gluskin and E.Trakhtengerg, APS)
3.5 T SC Wiggler of MAX-Lab
The Structure (E. Wallen, Max-Lab)
RADIA model with reduced number of periods
Peak Magnetic Field vs Horizontal Position
Period: 61 mm
Magnetic Gap: 10 mm
Vertical Magnetic Field on the Axis Peak Magnetic Field vs Vertical Position
Example of Commercially-Available Multi-Pole SCW
Figure courtesy of Nikolay Mezentsev (BINP, Novosibirsk, Russia)
Power Output of NSLS-II IDs
Power per Unit Solid Angle
In Horizontal Median Plane In Vertical Median Plane
Total Power:
PDW90≈ 67 kW
PSCW60≈ 34 kW
11 BROOKHAVEN SCIENCE ASSOCIATES
Spectral-Angular Distributions of Emission from
2 x 3.5 m Long DW90 in “Inline” Configuration
Angular Profiles of DW Emission
at Different Photon Energies
Spectral Flux per Unit Solid Angle Horizontal Profiles
FWHM Angular Divergence of DW Emission Vertical Profiles
1/g ≈ 170 μrad
Wiggler Magnetic Fields and Electron Trajectories
DW90 Magnetic Field (RADIA) SCW60
DW90 Modeling Magnetic Field Zoom
Typical perturbations due to
imperfect magnets: ΔB/Bmax~3 x 10-3
(magnet specs: ΔBr/Br <10-2)
Horizontal Trajectory: Angle
Suggested Tolerance for
Horizontal Trajectory in DW:
|x| < 120 μm
(max. allowed deviation from Horizontal Trajectory: Coordinate
“straightness”: 20 μm)
Example of SCW Parametric Optimization
(for SOLEIL High Pressure Beamline)
Spectral Flux Per Unit Horizontal and Vertical Angles
from Wigglers with Different Periods and Peak Fields
at the Constraints on the Total Emitted Power Pmax = 30 kW, and the Total Length L 2 m
E = 2.75 GeV, I = 0.5 A, Sinusoidal Field
Photons/s/0.1%bw/mr2 at = 50 keV W/mr2 at 20 keV < < 100 keV
x max = 8 mr x max = 8 mr
x min = 2 mr x min = 2 mr
u 35 mm, Np 44 u 44 mm, Np 42 “Technology Limits” Data taken from:
Bmax 2.85 T Bmax 2.6 T - presentations by N.Mezentsev (BINP) and S.Kubsky (ACCEL)
F 1.6 x 1015 Ph/s/0.1%bw/mr2 F 1.2 x 1015 Ph/s/0.1%bw/mr2 - hybrid wiggler simulations by O.Marcouille
SOLEIL, 2005
In-Vacuum Wiggler W50
On-Axis Flux 3D Magnetic Model
per Unit Solid Angle (reduced number of periods)
[Ph/s/0.1%bw/mrad2]
Photon Energy: 50 keV
Pmax = 25 kW; L = 2 m
O. Marcouille
EPAC2008
Approx. “Technology Curves”
CAD Drawing
On-Axis Magnetic Field
Magnetic Force vs Gap
Example of Spectral Performance of Optimized SCW
(for SOLEIL High Pressure Beamline)
Spectral Flux per Unit Horizontal and Vertical Angles
Ptot 20 kW for all structures Ptot 30 kW, L 2 m for all structures
Wiggler for NSLS-II High Pressure Beamline could be similarly optimized to provide
maximal flux (per unit solid angle) in users’ spectral domain of interest, while satisfying
all accelerator physics constraints.