# Presentation: 466528

## Inelastic X-ray Scattering at NSLS-II 

**IXS Program, and Current Project Beamline Design**
**Yong Cai**
**With contributions by John Hill, Xianrong Huang, Zhong Zhong, Scott Coburn (NSLS-II)**
**Alfred Baron (RIKEN), Yuri Shvyd’ko (APS), ****Alex Babkevich and Nigel Boulding (Oxford-Danfysik)**

- IXS@NSLS-II Workshop, February 7-8, 2008

**Notes:**
Good Morning, my name is Yong Cai.

This talk is about the Inelastic X-ray Scattering  beamline for the NSLS-II project. And it has been the work of a number of individuals, including John Hill, XianRong Huang, Scott Coburn, Alfred Baron of RIKEN, Yuri Shvyd’ko from the APS, and two other gentlemen, Alex Babkevich and Nigel Boulding from Oxford-Danfysik who did the design study for us. Like me, XianRong has just joined the project. You will hear more from him about the R&D effort for achieving the 0.1meV resolution in his talk.

## IXS: Current Status

- A powerful (but weak) probe offering energy and momentum resolved information on dynamics and excitations in condensed matter systems
- Practical applications with highly successful state-of-the-art implementation at ESRF, SPring-8 and APS
- Broad areas of applications, including but not limited to the followings:
**Lattice dynamics **– Phonons in solids, vibration modes and relaxation processes in disordered systems: routinely operational at ~1meV resolution with ~109 photons/sec at ~20keV using symmetric backscattering crystal optics
**Charge dynamics **– Plasmon in simple metals, complex electronic excitations in strongly correlated systems: best resolution at ~50meV with ~1011 photons/sec at ~10keV for the most demanding experiments
**Element specific applications **– Chemistry and materials science, materials under extreme conditions of pressure and temperature: x-ray Raman scattering, x-ray emission and absorption spectroscopy by partial fluorescent yield at low resolution (~300meV or lower)

## IXS Opportunities at NSLS-II

- Key scientific drivers identified thru community inputs (CDR, user workshops)
**0.1-meV scientific case: *****filling the gap between high and low frequency probes***
- Visco-elastic crossover behaviors of disordered systems and fluids
- New modes in complex fluids and confined systems
- Collective modes in lipid membranes and other biomolecular systems
-  **1-meV scientific case:**
- Relaxation processes in disordered systems (glasses, fluids, polymers ...)
- Phonons in single crystals, surfaces, thin films, high pressure systems, small samples
- Exotic excitations in strongly correlated systems
**10~50-meV (including lower resolution) scientific case:**
- Non-resonant and resonant inelastic scattering on charge dynamics
- X-ray Raman scattering, x-ray emission and absorption spectroscopy by partial fluorescent yield combined with small beam for small samples of micrometer scale, high pressure, high fields, low and high temperature ...
- High flux experiments with low(er) energy resolution

## Scientific Mission of the Project Beamline

**Develop advanced instrumentation that enables IXS experiments at extremely high resolution of ****0.1 meV**** at ~10 keV – *****a key goal for NSLS-II.***** **
**Why 10keV, as opposed to 20keV or higher?**
- Technical merits: higher brightness and flux for NSLS-II
- Scientific merits: better momentum resolution for a given solid angle, or the same momentum resolution for larger solid angle
- Counting efficiency: a complex issue, sample and optics dependent, requirecareful evaluation
- Possible scheme based on highly asymmetric backscattering optics proposed by Yuri Shvyd’ko working at 9.1keV, require considerable R&D(more from Xianrong Huang and Zhong Zhong’s talks)
- What are the alternatives?

**Notes:**
Clearly, the scientific mission for this beamline within the project scope is to develop advanced instrumentation that would enable IXS experiments at extremely high resolution of 0.1meV. Right now in the world at other high-energy synchrotrons, the best one can do is about 1meV using x-ray photons of above 20keV. What we try to accomplish here therefore represent an order of magnitude improvement from what is available today.  And we want to do this with 10keV x-ray photons.

There are a few scientific reasons for using 10keV x-ray photons for IXS experiments. The most important of these is that we will have higher scattering cross section compared with 20keV photons. The absorption length will also match better to the small sample volume especially for high-pressure experiments using diamond anvil cells. There are also technical reasons. The most obvious is that the brightness and flux are higher at 10keV for NSLS-II. The x-ray optics will be more efficient as well as we will see from XianRong’s talk. 

The outcome of this effort would allow us to bridge, at least partially, the dynamical gap between the existing scattering probes. We will be able to measure 10 times more precisely how atoms in materials respond to external perturbation.  

Clearly, this is an ambitious goal, which is beyond state-of-the-art technology.  But we believe that we have a credible plan that will lead us towards that. 

Having the experimental capability to do inelastic scattering experiments with 0.1meV resolution will immediately benefit a few classes of experiment. I list two classes here that are identified in the breakout session during the July workshop. 

## Specifications and Requirements 

**Radiation source**
- Provide flux > 1010 phs/s/0.1meV at 9.1 keV, to provide > 109 phs/s/0.1meV at sample, require beamline overall efficiency > 10%
- Essential source size and divergence stability, vibration and thermal stability for achieving the 0.1meV resolution (more from XianRong Huang’s talk)
**Beamline and Endstations**
- Two end stations, one with 0.1meV and the other with 1meV resolution
- Primary beam energy at 9.1 keV to match scheme for achieving 0.1meV resolution
- Beam energy tunable over 7~12 keV for added flexibility (e.g., other refractions)
- Energy scan range: order of 0.1 ~ 1eV, appropriate for the excitations to be studied
- Momentum resolution: 0.1 ~ 0.4nm-1 at 9.1keV
- Momentum range: up to 80 nm-1 to cover typical BZ sizes, ~120o at 9.1 keV
- Spot size: ≤ 10 μm (H) x 5 μm (V), required for high pressure experiment
- Sample environments: crystal alignment capability, handling of small samples of micrometer scale, high pressure, low and high temperature (4-800K), ..., etc.** **

**Notes:**
In order to serve the scientific mission which I have just outlined, here is a list of specifications and requirements that we are going to need. 

For the beamline and endstations:
We are designing the beamline to be compatible with two endstations even thought the 1meV endstation is outside the project scope. The first endstation will have the 0.1meV resolution, and the second one the 1meV resolution.
The primary beam energy is chosen at 9.1keV because of the scheme for achieving the 0.1meV resolution using highly asymmetric cut Si optics, but we would like
To retain some flexibility in case other scheme is needed. Therefore, the beamline energy is tunable over 7~12keV.
Energy scan range should be appropriate for the excitations to be studied, and is in the range of 0.1~1eV.
High momentum resolution of up to 0.1nm-1 will be required for studies of disordered systems in the forward scattering direction. This corresponds to an angular acceptance of 10mrad at 9.1keV for the analyzer.
Momentum scan range should be up to about 80nm-1 in order to cover typical BZ sizes for small single crystals. This corresponds to  a scattering angle of ~120 deg at 9.1keV.
Beam spot size we aim to achieve is 10 x 5 microns. This is required mainly by high-pressure experiments using diamond anvil cells.
Flux at sample should be greater than 109 phs/sec over the 0.1meV band width. This is essential for experiments on lattice dynamics in order to obtain sufficient counting efficiency.

Clearly the radiation source should provide more than 1010 phs/sec over the 0.1meV band width. This is assuming that the beamline overall efficiency is better than 10%. Our current estimate is that we will be able to achieve at least 30%.

Essential source size and divergence stability requirements are those needed to achieve the 0.1meV resolution. You will hear from XianRong’s talk that these requirements are not more stringent compared to other project beamlines. The default facility standard of 10% stability will be sufficient for our purpose.

## Overall Beamline Layout

**Overall Beamline Layout**

_**1.0meV Endstation***_
-  CDDW HRM (0.7meV)
-  CDW Analyzers (0.7meV)
-  larger q range (~80nm-1)
- * (not in the project scope)

_**0.1meV Endstation**_
-  CDDW HRM (0.1meV)
-  CDW Analyzers (0.1meV)
-  0.1nm-1 q resolution
-  limited q range

_**FOE**_
-  HHL DCM
-  VFM / VCM

- KB

- KB

- HRM

- HRM

- DCM

- VFM VCM

**Beamline occupies a high-****β**** straight section**

- R-wall: 28.3m
- Walkway: 60.8m

**Notes:**
Here is the layout of the beamline. It will be located in a high-β long straight section. The current design includes three hutches, one for the high heat-load optics, and two for the experimental stations. 

In terms of the optical layout, the DCM is the first optics that intercepts the white beam from the undulator. This is then followed by a vertically focusing or collimating mirror before the beam is delivered to the experimental stations. The high-resolution monochromator is considered to be part of the endstation due to the required R&D work, and is placed upstream of the KB mirrors. The KB mirrors focus the beam onto the sample. 

The HRM will be based on the so-called CDDW scheme proposed by Yuri Shvyd’ko, which we will hear more from XianRong’s talk. The analyzer will be based on the CDW or the CDDW scheme. This optical layout will in principle be the same for both endstations. They differ only in the energy resolution and the momentum scan range. Although the 1meV endstation is not in the project scope, it may be possible that we could use the prototype developed from the R&D program here. 

In the following, I will walk thru with you the details of the beamline design beginning from the insertion device.

## Optical Scheme for 0.1meV

- CDDW mono to achieve 0.1meV with ~100μrad angular acceptance
- Multilayer mirror to achieve 5~10mrad angular acceptance for CDW/CDDW analyzer

- Δ*θ**e** = *~ 5μrad
*E* = 9.1keV for Si(800)
- Δ*E *= 0.1 meV, φ = 89.6°

**Notes:**
Now we come to the interesting part of the beamline, that is the 0.1meV spectrometer design. This slide shows the side view of the overall layout of the spectrometer embedded in the beamline optics that I have just described. This design is based on a novel scheme proposed by Yuri Shvyd’ko using highly asymmetric cut Si crystal optics that promises to deliver the 0.1meV resolution. 

The main components of the spectrometer requiring the scheme to work include the high-resolution monochromator, and the analyzer. 

Without going into the details of how the scheme actually works, which I will come to in the next couple of slides, I would just like to point out a couple of features here:

Firstly the so-called CDDW scheme for the high-resolution mono has a very large angular acceptance of about 100microrad, which is 5 times bigger than the natural divergence of the undulator beam. We could therefore afford to focus the beam with a demagnification factor of up to 5:1 before the mono in order to reduce the length of all the crystals within the scheme, thereby minimizing the impact of the engineering challenges that we may face in designing the monochromator.
Secondly, since the required angular acceptance of the analyzer is in the range of 5-10 mrad for sufficient counting efficiency, limited only by the momentum resolution we want to achieve, the same angular acceptance of the scheme for the analyzer would mean that we will need a collimating or focusing mirror with a demagnification factor of 50:1 at least. It is possible to achieve this with multilayer mirrors. If we can achieve the required angular acceptance with a focus beam on the analyzer crystal, there will be no need for a multi segment analyzer as shown in the schematic here. We could also use the CDDW scheme for the analyzer.

Although this scheme is novel and shows promise, it has not been demonstrated to work at 0.1meV. It therefore requires substantial R&D effort as you will hear more from XianRong’s talk. Nevertheless, it offers a unique opportunity for NSLS-II to build a fundamentally new instrument and certainly the first of this kind in the world for IXS.

## Multilayer Mirror for Analyzer

- ~10 cm

- CDDW analyzer with  ~0.1mrad acceptance

- We hope the beam here is a slightly focused beam with divergence  ~0.1mrad and beam height ~50 μm

- E = 9.1 keV

- We hope the mirror length to be ~10 cm. It can be either a (1) laterally graded multilayer or (2) a parabolically / elliptically bent periodic multilayer

**Multilayer Mirror for Analyzer**

**Requirements:**
- 100:1 demagnification (from 10mrad to 0.1mrad)
- 10mrad angular acceptance
- Greater than 50% efficiency
- Possibility for parallelization of data collection

## Conceptual Beamline Layout

**Multilayer mirror with 100:1 demagnification to provide 10mrad (vertical) angular acceptance for analyzer ******** ~10m arm length**

## Experimental Floor Layout

**Experimental Floor Layout**

- 25m

- ~61m   + 2m (possibly)

- ~53m

- Space may be sufficient for only one end station based on current scheme and 10mrad angular acceptance for analyzer
- Another ~8m may be required for a second end station with 5mrad angular acceptance for analyzer, space for mirrors and phase plates

- BM line

- ID line

## Insertion Device

**U20 (IVU), or U14 (SCU) on a high-****β**** straight section **Figure of Merit: Flux / meV – provide flux > 1010 phs/s/0.1meV at  9.1 keV

| Name | U20 | U14 |
| --- | --- | --- |
| Type | IVU | SCU |
| Period (mm) | 20 | 14 |
| L (m) | 3.0 | 2.0 |
| No. Periods | 150 | 143 |
| Bmax (T) | 0.97 | 1.68 |
| Kmax | 1.81 | 2.20 |
| Tot. Power (kW) | 8.024 | 16.08 |
| On-axis PD (kW/mrad2) | 62.65 | 103.7 |

- * U20: baseline device

**Notes:**
First of all, the insertion device. The design has been based on the U19 undulator, even though we know that the baseline device now is the U20. The difference in performance is very small. For convenience, we will continue to use U19 throughout this talk. 

We chose the U19 because it is the best device in the baseline in terms of brightness and flux at 9.1 keV for NSLS-II. It delivers just about 1010 phs/sec over 0.1meV bandwidth at 9.1keV.  Since IXS is a photon hungry experiment, the figure of merit is the flux per meV. If there is another device that offers more photons, we would like to take it. The U14 (SCU) discussed in the CDR for example can be a good candidate.

## Insertion Device Optimization

**Optimize to maximize flux at 9.1keV: magnet period vs length vs minimum gap**Until superconducting devices become an option, the U20-5m seems to be the best option

| Basic Undulator Parameters  | #1 | #2 | #3 | #4 | #5 |
| --- | --- | --- | --- | --- | --- |
|  | Baseline | Proposed | Proposed | Proposed | Proposed |
| Name  | U20-3m | U22-6m | U21-4.5m | U20-4.5m | U20-5m |
| Type  | PMU | PMU | PMU | PMU | PMU |
| Period (mm)  | 20 | 22 | 21 | 20 | 20 |
| Length (m)  | 3 | 6 | 4.5 | 4.5 | 5 |
| No. of Periods  | 150 | 272 | 214 | 225 | 250 |
| Minimum gap (mm) | 5 | 7.5 | 7.5 | 7 | 7 |
| Bpeak (T) | 0.969 | 0.725 | 0.85 | 0.88 | 0.88 |
| Keff | 1.81 | 1.4893 | 1.66671 | 1.64336 | 1.64336 |
| Minimum 5th harmonic energy, linear mode (eV)  | 8099.45 | 9210.20 | 8518.10 | 9091.00 | 9091.00 |
| Total power (kW)  | 8.024 | 8.955 | 9.244 | 9.922 | 11.02 |
| Power density (kW/mrad2) | 62.65 | 84.32 | 78.15 | 85.02 | 94.47 |
|  |  |  |  |  |  |
| Performance at 9.1keV, 5th harmonic (for 9.3m high-β straight, beta_x=20.8, beta_y=2.94) |  |  |  |  |  |
|  |  |   |  |  |   |
| Brightness (phs/sec/mrad2/mm2/0.1%BW) | 4.68E+20 | 4.60E+20 | 4.25E+20 | 4.90E+20 | 5.42E+20 |
| Total Flux (phs/sec/0.1%BW) | 8.00E+14 | 1.06E+15 | 1.01E+15 | 1.20E+15 | 1.35E+15 |
| Brightness ratio with baseline: | 1.00 | 0.98 | 0.91 | 1.05 | 1.16 |
| Flux ratio with baseline: | 1.00 | 1.33 | 1.26 | 1.50 | 1.69 |

**Notes:**
Other optimizations we are considering include optimizing the magnet period length to maximize the flux at 9.1keV. The example shown here for the U17 suggests that we could gain a factor of 2 more flux compared to the U19 for a 6m long device with a similar strength of magnetic field. 

Further upgrade includes putting in multiple devices. For example with 2 U19 or 3 U14 on a long straight section. As inelastic scattering experiment generally requires long counting time, one spectrum can take up to a day. A factor of 2 gain in the incident flux is a significant gain.

Even with one U19 device, comparison with other facilities on a per meV bandwidth basis shows that NSLS-II is about the same as BL35XU at SPring-8 at ~10keV. With conventional optics, BL35XU achieves the 1meV resolution at energies above 20keV. NSLS-II will still be better by a factor of 2 at the source. We could therefore say that NSLS-II will be the best source in the world for IXS!

## Extended Long Straight

- It is possible to obtained one 15m extended long straight by extending one 9.3m high-β straight and shortening two adjacent 6.6m low-β straights of the current lattice
- Preliminary solution indicates that it would be possible to put in two U20-5m devices with refocusing magnet. Potentially more than triple (3.38 times) the flux compared to one U20-3m baseline device
- There are accelerator issues (tune shift compensation, radiation shielding) and cost impact.

- βx = 18.5, βy = 3.5 for extended LS
- βx = 0.8, βy = 0.8 for short straights

## Straight Section

**High-****β**** straight section (9.3m) is required for a long device**
**Additional benefits associated with a high-****β**** compared to a low-****β**** straight section :**
- Bigger horizontal source size but smaller horizontal divergence, leading to smaller horizontal photon beam size  shorter horizontal mirrors
- Lower power load within the central cone of the photon beam delivered to the first optics  heatload is more manageable for first optics, even for two U19 undulators.
**Important:** Flux within the central cone remains the same!
-      Photon beam size and power (one U19, at 9.1keV) thru angular aperture of 4(H)x4(V).

| Distance, m | K | Low-β |  |  | High-β |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
|  |  | Aperture (HxV), μrad2 | Beam Size (HxV), mm2 | Power, W | Aperture (HxV), μrad2 | Beam Size (HxV), mm2 | Power, W |
| 30 | 1.713 | 79.2 x 22.8 | 2.4 x 0.7 | 118 | 29.2 x 20.0 | 1.0 x 0.6 | 38 |
| 30 | 0.981 |  |  | 65 |  |  | 21 |

**Notes:**
For the straight section, we require the longer high-β straight in order to put in multiple devices. Although the source brightness of the high-β is lower than the low-β straight, there are other benefits associated with the high-β straight that we think are good for the beamline: 

The High-β straight has a bigger horizontal source size, but a smaller horizontal divergence. This results in a smaller horizontal photon beam size. One could therefore use shorter horizontal mirrors.
Due to the smaller photon beam size, the power delivered within the central cone to the first optics is also smaller for the high-β straight section. We show here the power calculated at 30m from the source thru an aperture defined by 4σ x 4σ of the photon source size. The power is a factor of 3 less for the high-β straight section. The heatload without filters for one U19 is only 38W with K at 1.713 for the 5th harmonic.  Even if we put in two U19 devices, the heatload is still quite manageable.

It is important to realize that the flux within the central cone for the high-β straight section remains the same. 

## First Optics Enclosure (FOE)

- DCM: cryogenic cooled Si(111).
- FEA analysis on first crystal of DCM shows < ±5 μrad slope error at 115W heat load
- For high-β straights, thermal effect would be less a problem (lower heat load).

- Cooled fixed mask

- Bremsstrahlung collimator

- Blade BPM

- White beam slit

- DCM

- Diamond window

- Cooled flu. screen

- White beam & Bremsstrahlung stop

- Quadrant BPM

- VFM

**Notes:**
This is the layout of the first optics enclosure. As I mentioned earlier, we would like to move the X-Y (white beam) slit into the front end.

For the DCM, our preference is to use cryogenic cooled Si crystals. FEA analysis showed that water-cooled Si is not a viable option because of the large heat-load induced slope errors in the crystal.

Water-cooled diamond crystal is another possibility, but is less preferable due to the poor quality of the crystal. There are also concerns from mounting strain and the small size of the crystals available in the market. 

The issue of concern here is the vibration caused by cryogenic cooling of Si crystals. We will pay close attention to that during engineering design of the DCM.

## Beamline Collimating and Focusing Optics

- Candidate: Bimorph mirrors

- Supplied by SESO
- Multiples of 150mm in length
- Each segment can be bent independently  (2 electrodes for cylindrical and 4 electrodes for elliptical)
- Bimorph can in principle correct its own tangential polishing slope errors and also correct for tangential errors introduced by other optics
- KB bimorph pair can in principle correct for sagittal and tangential errors
- Small beam size allows short mirrors with small incident angle (2.5mrad) and Si substrate for high reflectivity at 9.1keV

**Notes:**
For collimating and focusing optics, we will use state-of-the-art technology where necessary. Possible candidates are the bimorph mirrors. There are bendable mirrors and can be made to any required length. The bimorph can in principle correct tangential slope errors of its own and errors induced by other optics. 

Due to the smaller beam size of the high-β straight, we could use small incident angle of 2.5mrad with Si substrate to obtain highest possible reflectivity at 9.1keV.

## Shadow Ray Tracing with FEA Results

| Case | Model , LN2 cooled DCM(εx = 0.55nm-rad) | Spot size , μm(No distortion) | Flux, ph/sec (No distortion) | Spot size, μm(W/ distortion) | Flux,  ph/s/eV (W/ distortion) |
| --- | --- | --- | --- | --- | --- |
| 1 | Lo-β, K=0.981, 1 U19-3m, 22W | 2.0 x 1.8 | 1.50 x 1013 | 2.1 x 2.1 | 1.49 x 1013 |
| 2 | Hi-β, K=0.981, 1 U19-3m, 7W | 7.0 x 1.8 | 1.49 x 1013 | 7.0 x 2.0 | 1.49 x 1013 |
| 2a | Same as 2, but water cooled | 7.0 x 1.8 | 1.49 x 1013 | 16 x 7.4 | 1.51 x 1013 |
| 3 | Lo-β, K=1.714, 1 U19-3m, 71W | 2.0 x 1.9 | 2.88 x 1013 | 2.3 x 4.2 | 2.81 x 1013 |
| 3a | Same as 3, but hot spot at 125K | 2.0 x 1.9 | 2.88 x 1013 | 2.1 x 0.5 | 2.92 x 1013 |
| 3b | Same as 3, but 2 U19-3m, 115W | 2.0 x 2.0 | 5.80 x 1013 | 2.9 x 5.9 | 5.14 x 1013 |
| 4 | Hi-β, K=1.714, 1 U19-3m, 22W | 7.1 x 1.9 | 2.81 x 1013 | 7.0 x 3.4 | 2.79 x 1013 |

**Notes:**
We have done Shadow ray tracing studies to examine the performance of the beamline optics. The generic layout without concerning the details of high-resolution mono includes the undulator source, the high-heat load DCM and the mirrors. The studies include the FEA results for the first crystal of the DCM. The outcome is quite satisfactory. The focus spot size is within the target. The flux at the sample is well over 1013 phs/sec over 1eV bandwidth, particularly if we run the undulator with K at 1.714 the 5th harmonic.

## 0.1meV Endstation Layout

**Features**
- Pre-focusing (up to 5:1) to reduce length of collimator (C) crystal for 0.1meV HRM
- KB mirrors after HRM for micro focusing to ≤ 10(H) x 5(V) μm2
- Temperature scan of energy transfer
- Analyzer(s) based on the CDW or CDDW scheme with multi-layer focusing mirror(s) to achieve 10(H)x5(V) mrad2 angular acceptance
- High (0.1nm-1) momentum resolution in forward scattering, limited scan range
- Extremely clean energy resolution function

| Instrument | Intensity at Sample |
| --- | --- |
| NSLS-II, 3m U19 | > 1x109 ph/sec/0.1meV (estimate) |
| APS, 5m U30 |    1x109 ph/sec/1meV |
| SPring-8, 4.5m U32 |    5x109 ph/sec/1meV |

**Notes:**
So by now, we can summarize the main features of the 0.1meV resolution endstation as follows. 

## 1meV Endstation Layout

**Features**
- Pre-focusing (up to 2:1) to reduce length of collimator (C) crystal for 0.7meV HRM
- KB mirrors after HRM for micro focusing to ≤ 10(H) x 5(V) μm2
- Temperature scan of energy transfer
- Analyzer(s) based on the CDW or CDDW scheme with multi-layer collimating mirror to achieve 10(H)x5(V) mrad2 angular acceptance
- Large momentum scan range (up to 80nm-1) for single crystal studies, require phase plates
- Extremely clean energy resolution function

| Instrument | Intensity at Sample |
| --- | --- |
| NSLS-II, 3m U19 | > 1x1010 ph/sec/1meV (estimate) |
| APS, 5m U30 |    1x109 ph/sec/1meV |
| SPring-8, 4.5m U32 |    5x109 ph/sec/1meV |

- A natural step in achieving 0.1meV resolution

**Notes:**
The 1meV resolution endstation will be similar in many ways, except that it will be optimized to do the 1meV science, where the larger momentum transfer range is required. This approach is a natural choice given that to achieve 0.1meV resolution, we would have to prove that the scheme works for 1meV. We would know this already sometime next year the earliest.

## Schedule Summary

-  2008~2011: Design phase, interaction with BAT, actively pursue 0.1meV R&D
-  2011~2013: Construction phase, long lead-time procurements to begin in final design stage
-  2014: Integrated testing phase, to be ready to take beam

## Outstanding Issues

**Multiple undulators on extended straight for more flux **(depends on AS design)tuning compensation for beam dynamics, heat load on second undulator, cost impact
**CDDW scheme to achieve 0.1meV HRM: Substantial R&D effort required **(proof of scheme by end 2010, final design phase)
**Multilayer mirror to achieve 10mrad angular acceptance for CDW / CDDW analyzers:  **(proof of scheme by early 2010, preliminary design phase)
**Risks with current approach and mitigation strategies:**1meV is promising, 0.1meV remains a major challenge, aggressively pursue the R&D and seek alternatives
**Possibility to combine two end stations into one:** energy resolution tuning
**Parallel data collection: **multiple analyzers, area detector
*Your inputs are important!*

**Notes:**
So what are the outstanding issues?