Transcript • Sample simulation

• Sample simulation
Basic Picture
Complexity 1: Geometry
Complexity 2: more than 1 scatterers
Complexity 3: more than 1 scattering
mechanisms
• How to handle a scatterer with
competing scattering mechanisms
Complexity 4: sample forms
• Single crystal
• Polycrystal
• Amorphous
Sample simulation framework
• Sample assembly
– Scatterers
• Scattering kernels
– (Phonon dispersion…)
Sample simulation framework - motivation
An extensible sample simulation framework has been constructed. It is
designed with the following issues in mind:
•
•
•
separation of physics and geometry. A clean separation of geometrical
and physics properties will increase flexibility and extensibility.
composite sample assembly. A sample is not alone. Usually it is inside
some kinds of container. A sample simulation needs to take into
account a collection of scatterers including sample and other objects.
composite scatterer. Currently available sample simulation usually
focus on one kind of scattering mechanism. A full simulation should
take into account all possible scattering mechanisms with similar
scattering strength.
Sample simulation UML
Sample simulation - algorithm
•
The ScattererContainer is a container of scatterers. When a neutron
comes in, it gathers the information of the position, orientation, and
shape of all scatterers and passes the information to a PathFinder. A
PathFinder will figure out the path of a particle through those shapes
given the position and moving direction of the particle. With those
information at hand, ScattererContainer will randomly choose a
scatterer, and ask the scatterer to respond to the neutron event.
•
Now the ball is on the scatterer's court. He is a container of scattering
kernels. One of those kernels will be randomly picked and asked to
respond to the neutron event. A scattering kernel has all information
about the physics, and will figure out which direction the neutron should
go and report back to the hosting scatterer. And then the scatterer will
report back what he knows to ScattererContainer, where the fate of the
neutron will be finally decided.
Sample Assembly
Collection of scatterers
Aluminum Can
Fcc Ni Sample
Shape
Collection of
scattering kernels
Coherent inelastic
phonon scattering kernel
Shape
Collection of
scattering kernels
Incoherent inelastic
phonon scattering kernel
A test case: simulation of an inelastic
scattering experiment with bcc Tungsten
Instrument setup: general
Neutron
Source
Sample
Detector
Instrument setup 1: all ideal
Neutron
Source
Monochromatic
(all neutrons are in
the same state)
New
Sample
Bcc Tungsten polycrystal
sample with only cohernt
inelastic phonon scattering
New
Detector
Ideal detector that records
neutron intensities as a function
of Q, the momentum transfre, and
E, the energy transfer
McStas
E(meV)
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Q (Angstrom^-1)
• 1st Brillouine Zone: optical branch is partially missing
• Higher Brillouine Zone: sharp dispersions
Instrument setup 2: ARCS source
Neutron
Source
Simulated neutrons
at sample position of
ARCS instrument
New
Sample
Bcc Tungsten polycrystal
sample with only cohernt
inelastic phonon scattering
New
Detector
Ideal detector that records
neutron intensities as a function
of Q, the momentum transfre, and
E, the energy transfer
McStas
ARCS neutrons at sample
Moderator
(McStas)
Guides,
Choppers
(McStas)
Neutron
recorder
(new)
E(meV)
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Q (Angstrom^-1)
• dispersions not as sharp
• large smearing due to long tail of energy distribution of
incident neutrons
Energy resolution of Fermi chopper
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
ARCS neutrons
at sample
(New)
I(E) monitor
(McStas)
Instrument setup 3: ARCS source and detector
Neutron
Source
Simulated neutrons at
sample position of
ARCS instrument
New
Sample
Bcc Tungsten polycrystal
sample with only cohernt
inelastic phonon scattering
New
Detector
ARCS detector. Reduction is
done to reduced the detector
data to I(Q,E)
New
E(meV)
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Q (Angstrom^-1)
• more smearing due to sample size, detector size
A test case: simulation of an inelastic
scattering experiment with fcc Ni
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Simulation result. Monochromatic
source. Ideal detector
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Simulation result.broadening due to
Fermi chopper included
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Simulation result.broadening due to
Fermi chopper, sample, and detector
included