Download Zoom Draft Proposal

ISIS Second Target Station Project
ZOOM – draft proposal for discussion 06/12/07
Beamline Name: ZOOM
External Co-ordinator:
Prof. J. Lawrence
King’s College,
London.
ISIS Contacts:
Dr. Richard Heenan
Dr. Ann Terry
Email: [email protected]
[email protected]
1. ZOOM - Design Specification:
Sample
Chopper
Bender
4m quadrupole
1m sextupole
<1mm DET
~10mm DET
fast apertures
Telescopic tank
The goal of ZOOM is to reach smaller Q than SANS2d by use of a neutron lens. For
large samples this has significant gains over conventional pinhole collimation using
a very long beam line, which would not in any case be well suited to a pulsed source
due to frame overlap.
A small source aperture is imaged by a large aperture lens, adjacent to the sample,
to a ~mm size focus at a two dimensional detector, at L2 ~ 4 to 12 m. A high count
rate, high resolution central detector is required, which for ease of maintenance (or
to swap detector types) will be mounted either after a thin window or through the
vacuum wall at the end of a ~ 1.5 m diameter telescopic vacuum tank. The entire
tank is on rails inside a shielding tunnel also on rails, so that both may be slid back
to accommodate large sample environments, longer lens assemblies, or to
optionally focus the beam at the sample.
With careful design the technical development and capabilities of ZOOM could be
staged over several years. The initial beam line configuration will depend upon
decisions regarding the lens type to be used, whether polarised beam is optional or
the default, how much of the wavelength band is polarised and how well it is
polarised. It is likely that a bender to filter high energy background will be needed
due to the “open space” around the lens; experience with TS-2 first phase beams
will help to determine this. An initial polarising bender followed by a shorter
polarising quadrupole and/or mirrors could be the default, but would obviously lose
a factor of 2 in flux for conventional SANS.
The simple scheme above, with only static fields, has a 30 mm bore, 4 m long
quadrupole to 99.9% polarise at λ > ~ 10 Å, (with lower polarisation at shorter
wavelengths) and a 50 mm bore, ~ 1 m long, 5 m focal length fixed field sextupole
to focus beam at the detector. At L2 = 10 m, a 1mm pinhole might focus to say a 2
mm spot size, plus tails, at the detector. Using λ = 10 Å at say 5 mm radius on the
detector conservatively gives Qmin = 0.0003 Å-1.
A conventional pinhole instrument might need A1 = 4 mm, L1 = L2 = 20 m, sample
A2 = 2 mm, to give the same Qmin, but with ~ 150 times lower count rate, and a
long, expensive, beam line with frame overlap issues. The inevitable trade off is that
for ZOOM the sample diameter is up to 50 mm so the sample volume is very large,
which may be an issue for some types of science. Smaller samples may be moved
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ISIS Second Target Station Project
ZOOM – draft proposal for discussion 06/12/07
closer to the focus, reducing the length of the vacuum tank and increasing
minimum Q.
Maximum Q would be ~ 0.15 Å-1 with λ = 1.5 Å at 750 mm radius, depending on the
precise detector size or any lateral offset. To reduce the divergence of defocused
shorter wavelengths of the wrong spin state and to attenuate the beam, fast
apertures, capable of moving from 1 up to 50 mm diameter at 10Hz, could adjust
the collimation from “conventional SANS” to “focussing” during the neutron pulse,
as shown schematically below.
At present it is not clear which type of lens would be best, the goal is to focus, as a
minimum requirement, ONLY the longest wavelengths, with shorter wavelengths
being partially focussed, thus expanding the Q range to lower Q. Since there can be
no beam stop this puts greater demands upon the central detector. A coupled cold
moderator is required
Focussing SANS (long λ)
Lens
Sample
Detector
LL
L1
A1
AL
L2
A2
Normal SANS (short λ)
Viable neutron lenses include:
•
•
•
Stack of MgF2 biconcave discs, as at NIST [1] with a factor 3 reduction in
Qmin, and JAERI [2,3],with further recent developments in Munich[4].
Fixed field magnetic sextupole with polarised beam, as JAERI [2,3] where a
50mm bore superconducting device reduced Qmin by a factor of 10. Stray
fields from a broad band pulsed sextupole would likely be unacceptable.
Toroidal mirrors, as used at Julich [5] now moved to Munich, reach Q ~
0.00015 Å-1, but unless stacked replica mirrors can be developed would need
an even larger sample to give effective count rates.
Detailed calculations and likely trial experiments in collaboration with other sources
are required as transmission losses, polarisation, gravity, optical imperfections etc.
all have subtle effects.
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ZOOM – draft proposal for discussion 06/12/07
Outer detectors will be arrays of linear, position sensitive gas tubes which will take
higher count rates but with reduced Q resolution compared to SANS2d.
Suggestions for the central high resolution detector include: wavelength shifting
fibre array with ~ 1mm pixel size; a Gd foil with solid state Si detector (low γ
environment on ZOOM makes this suitable); a position sensitive photomultiplier
with fast scintillators; or perhaps a high count rate ionisation detector (with
integrated circuits inside the gas volume) as is being developed at BNL. For “normal
SANS” or to cross-calibrate detectors, the central detector may be removed and one
of the surrounding gas tube arrays slid into its place.
[1] S.-M.Choi, J.G.Barkera, C.J.Glinkaa, Y.T.Cheng & P.L.Gammel, J.Appl.Cryst.
33(2000)793-796.
[2] T.Oku, H.Iwase, T.Shinohara, S.Yamada, K.Hirota, S.Koizumi, T.Hashimoto &
H.M.Shimizu, J.Appl.Cryst. 40(2007)s408-s413.
[3] S.Koizumi, H.Iwase, J.Suzuki, T.Oku, R.Motokawa, H.Sasao, H.Tanaka,
D.Yamaguchi, H.M.Shimizu & T.Hashimoto, J.Appl.Cryst. 40(2007)s474-s479.
[4] FRM-II Annual Report 2006, p19; H.Frielinghaus et.al. to be published.
[5] B.Alefeld, L.Dohmen, D.Richter & Th.Bruckel, Physica B 283(2000)330-332.
2. ZOOM – Science Case:
ZOOM is a flexible, high count rate SANS instrument which will use novel focussing
devices and detectors to reach smaller Q, to complement SANS2d instrument,
without building an impracticably long beam line. With simple focussing at the
detector ZOOM will match the previously proposed SANS2a at Qmin of 0.001 Å-1 and
with more advanced devices should reach 0.0003 Å-1 ( ~ 2 µm). Although much
smaller Q may be reached using the proposed spin-echo SPIRAL, ZOOM will record
two dimensional scattering patterns from anisotropic systems, and have a wide
simultaneous Q range out to at least ~ 0.15 Å-1, which will better suit kinetic and
dynamic experiments. ZOOM will considerably enhance “conventional SANS” rather
than open up new science areas for “ 5 - 100 micron sized particles” as on LARMOR.
If magnetic lenses are used, then polarised incident beam SANS experiments on
magnetic systems will become possible, again complementing SANS2d. The use of
contrast variation and its large simultaneous Q range will make ZOOM very
powerful. The option to focus the beam to ~ 1 or 2mm at the sample could
enhance long wavelength flux and hence small Q count rates by ~ 5 for
conventional SANS at L2 ~ 4 – 5 m with small samples.
Soft Matter
The soft matter themes relevant to SANS2d will be extended to longer length scales
by ZOOM, for example in areas such as colloidal particles, emulsions, foams,
lamellar fragments, block copolymers, and their interactions with each other and
other macro-molecules or particles. ZOOM is ideal for oriented systems, where
anisotropic scatter covers a wide range of length scales, such as those obtained
under shear, laminar and extensional flow or within complex geometries. Micron
and sub-micron particles and droplets occur in a wide range of systems, often in
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ZOOM – draft proposal for discussion 06/12/07
conjunction with smaller micelles or polymers. In this area the larger samples
required for use with lenses should not be an issue.
Mechanisms of polymer reorganisation and crystallisation may be studied in detail
in conjunction with SAXS by using contrast variation. “Pre-order phases” in
crystallisation kinetics are expected to be larger than the final 100 to 500 Å dspacings. Large scale elastic inhomogeneities in strained polymers, revealed by
deuterium labelling, are currently not well understood.
Responsive polymers in micro-gel networks can change structure dramatically and
reversibly with temperature, pH or chemical stimulus making them ideal for
encapsulation and controlled release situations. The wide Q range of ZOOM down to
smaller Q’s would greatly improve understanding of such systems.
Development of focussed beams to enhance count rates from small sample volumes
in areas such as flow fields, injection moulding, extrusion processing or perhaps
even “microfluidic” confinement would be an exciting prospect, even with sample
channels of ~ 1mm size. Major research programmes are currently under way to
study the rheology, deformation and relaxation of polymers during processing.
Small focus beams would desirably improve count rates from the often small sample
volumes. As the degree of control over polymer architecture by advanced synthesis
methods improves and industrial polymers continue to become more sophisticated,
this area of study will continue to expand. Deuterium labelling is often the only way
to study structure in polymer melts, thus ZOOM would extend the use of neutrons
in this field. In extensional flow LOQ has already been used with 2 mm diameter
beam to study the orientational distributions of flowing strongly scattering
surfactant lamellar phases, many other samples would scatter much more weakly
and would benefit from a sample focussed beam.
Advanced Materials
The longer length scales accessed by ZOOM would expand the range of studies of
void formation, precipitation or magnetic domains in magnetic materials, metals,
alloys and around welds. Material processing and polymerisation using super-critical
fluids in novel high pressure apparatus will benefit from both the Q range and
sample space on ZOOM. Studies of templated and mesoporous materials or directed
assembly using DNA sequences, particularly the early stages of formation or where
oriented anisotropic materials result, would be better suited to ZOOM than to
SPIRAL. For example titania or silica particles templated around surfactants may
self-assemble into larger “crystalline arrays”, spheres, cylinders, hexagonally-packed
rods, etc. which may themselves then assemble into oriented sheets. Learning to
control the geometry of pores and long range aggregation is vital for product
development. Composites and metals containing embedded fibres of carbon or
polymers may be studied by X-rays, but neutrons would supply complementary
information. Amorphous phase separation and crystallisation in glass ceramics
requires an extreme Q range. Polymer intercalated clays are a further example
where anisotropic scatter, wide Q range, good Q resolution and neutron contrast
variation to highlight specific components are all key to good science.
Biology
The longer range hierarchical structure of synthetic and natural fibres, bones, or
scaffolded materials, require the 2D scattering capability of ZOOM. Location of
water is a key use for neutrons, as is the study of samples that are sensitive to X-ray
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damage. For larger proteins or biomolecular complexes the wide simultaneous Q
range available on ZOOM would enhance modelling of molecular shapes. This would
include following the stages of polypeptide aggregation in amyloid plaque
formation and many similar processes of medical importance.
To make best use of focussing to reach the smallest Q’s, samples up to ~ 40 mm
diameter would be required, which in some cases could be restrictive. Focussing at
the sample would provide a realistic method for scanning-SANS (and neutron
transmission) from bio-structures and bio-fibres on a < ~1mm scale, with all the
advantages of contrast variation and still a fairly wide simultaneous Q range to
cover the typically different length scales of both longitudinal and transverse
structure.
Pharmacy
SANS has already helped greatly in the understanding of model drug and gene
delivery systems such as vesicles. Smaller Q on ZOOM would enable better
characterisation of vesicles simultaneously with higher Q data looking at their wall
thickness and local flexibility. Even more exciting is the prospect of using the shape
of S(Q) between small vesicles to probe the interactions between embedded
membrane proteins and say drugs or other vectors which are either free in solution
or are attached to other vesicles. By contrast matching the host vesicles the size
and shape of an embedded protein and perhaps its interaction complex with
antibodies or drugs might be seen at smaller Q.
The growth of small drug crystals and their interaction with polymers or other
additives could be entirely followed using the Q range available on ZOOM. Contrast
variation to match out the drug crystal would then, for suitably dense layers, allow
the thickness and density profiles of polymer stabilisers to be probed.
Environmental science
Many processes in the natural environment feature micron sized particles, which in
themselves may be aggregates of nanoscale objects. Although SPIRAL would be well
suited to studies of strongly scattering samples, ZOOM will be able to study local
interfaces in more dilute systems such as aerosols, more dilute aquatic systems or
the mechanisms of floc and soot formation. Structural data from SANS may help to
relate AFM measurements of local forces in flocs to bulk rheology. Soots may be
studied directly in burning flames or indirectly as aggregates in engine oil, where,
for example, the degradation of lubricating oil in diesel engines is of major
commercial interest.
Polarised neutron option.
The use of magnetic lenses would require a polarised incident beam option,
allowing for polarised incident beam scattering on magnetic materials. This would
allow separation of (potentially weak) magnetic and non-magnetic contributions to
the scattering. This capability is readily applicable to a wide range of nanocrystalline
materials many with direct technological relevance, such as granular and
perpendicular recording media, through to investigations of type-II superconductor
flux lattices.
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3. ZOOM – Business Case:
When ZOOM, SPIRAL & BOUNCE were jointly presented in June 2005 some 40 user
groups responded to an email request for support, of whom virtually all could
suggest good science to do on ZOOM. These groups and others still represent an
immediately viable user community.
It remains clear, given the broad range of scientific applications highlighted above,
that there is also much scope for involvement of new users. Expansion of the ISIS
SANS user base will start as soon as SANS2d is commissioned, with a particular
focus on molecular biology, but also it is hoped for areas such as fibres, pharmacy,
food science, environmental nanoparticles, phase separated alloys and ceramics.
Users of ZOOM would be a broad mixture of UK and European academics from many
fields, both experienced in SANS and not. There is a strong ethic amongst the ISIS
SANS scientists of providing a high level of support to all users, and particularly to
new ones, including assistance and training with data interpretation. If staffing
levels permit, then this support will lead to strong growth of the ZOOM user
community.
Though many users are involved with “near industrial” projects, direct use by
industry will likely be limited due to perceived high cost, and a typical desire for a
fully inclusive service including data collection and interpretation in a short
timescale.
Wherever good SANS instruments have been built in the world, it has been the
experience that demand rapidly saturates. With the exceptional qualities of Q range,
resolution and count rate on offer at TS-2, the usage of ZOOM will be no exception.
4. ZOOM – Development and Skills needs:
Monte-Carlo simulation – of magnetic and optical elements
aberrations and imperfections. This has already been noted by the
The Japanese PHITS code has also made steps in this direction.
identify whether upstream optics could give increased flux from the
source” that is still within the acceptance angle of the lens.
with realistic
McSTAS team.
Also need to
initial “pinhole
Oscillating beam apertures – compact devices to change from 1 to up to 50 mm
diameter, perhaps non-linearly, at 10 Hz, with polarised neutrons. (Various
solutions may be considered from a pair of rotating chopper discs to an oscillating,
multi-leaf Gd foil “camera iris”.)
Broad band polariser – perhaps a magnetic quadrupole or a mirror/filter in
conjunction with a quadrupole. Need extremely high polarisation, as opposite spin
is de-focussed in lens and contaminates SANS signal. The Japanese are interested in
this.
Fixed field magnetic sextupole – at least 50 mm bore with at least 5 m focal
length (i.e. to focus pinhole at 10 m) and good focus. Consider whether it is
possible to tune beam focus by additional fields or windings. Again the Japanese
are working in this area.
MgF2 lenses – Latest developments are stack of parabolic lenses at 70K, Munich
FRM-II reactor.
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ZOOM – draft proposal for discussion 06/12/07
Telescopic vacuum tank - mechanically lock sections at fixed intervals of length,
use inflatable vacuum seals. Normal engineering design process should solve this.
Detector - High count rate, ~ 1mm resolution detector, at least 80 mm diameter,
for λ ~ 1-15 Å
Test Beam. - Development of the above lenses, polarisation devices & detectors
needs a test beam facility, with a > 20m long block house, but perhaps only a
relatively low beam flux from a small view of a cold moderator.
Skills – need staff competent at Monte-Carlo for polarised neutron lenses, and also
to tap into appropriate expertise in magnet design.
5. ZOOM – Other requirements for successful science:
Versions of all standard sample environment, sample changers etc. to cope with
polarised neutrons.
Supplies of much larger fused silica cells than usual SANS for large beam area at
sample (up to 50 mm diameter).
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