BEAMLINES SOPHISTICATED SYSTEMS CONSTRUCTED FROM SIMPLE BUILDING - - PowerPoint PPT Presentation

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BEAMLINES SOPHISTICATED SYSTEMS CONSTRUCTED FROM SIMPLE BUILDING BLOCKS An introduction to beamline engineering

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BEAMLINES SOPHISTICATED SYSTEMS CONSTRUCTED FROM SIMPLE BUILDING BLOCKS An introduction to beamline engineering Outline What are we dealing with? Basic beamline functions and generic solutions. Heatload Management Vacuum Supports Positioning

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What comes out of the Front End (looking towards the machine)

Radiation from Dipole magnet downstream of straight section Radiation from Dipole magnet upstream of straight section Undulator beam

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What is delivered to the beamline (high power front end) Aperture in Front End defining the beam. 4mm diameter diamond window

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• 0.002
• 0.0015
• 0.001
• 0.0005

0.0005 0.001 0.0015 0.002

• 0.002
• 0.0015
• 0.001
• 0.0005

0.0005 0.001 0.0015 0.002 100-110 90-100 80-90 70-80 60-70 50-60 40-50 30-40 20-30 10-20 0-10

Power frofile for a single u27 undulator @200mA at the primary slits

20 40 60 80 100 120 1 2 3 4 5 6 7 8 9

20 40 60 80 100 120

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Power Comparisons New upgrade beamlines UPBL11 8 metres of undulator u27 gap 1mm gives max power density 385 Watts/mm2 Total power through the Front End approx 4 kWatts Laser welder 8 KW can welder metal tubes seams at 60m/min

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How do we process these beams? Slits/Absorbers Windows Optics Outline What are we dealing with? Basic beamline functions and generic solutions. Heatload Management Vacuum Supports Positioning

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How do we process these beams? Slits 4 Independent blades each capable of intersecting the entire beam. Power in Q

Maximum temperature Proportional to k thermal conductivity Proportional to Q Dependant on geometry Wall temperature Dependant on exchange coefficient (Flowrate) Fluid temperature Proportional to flow rate and Q Choose Copper (high thermal conductivity) Water cooling (turbulent flow)

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How can this fail? Simple approach: The surface should not melt! More conservative approach: The thermal induced stress should not exceed 2 x thermal yield strength of the material. Choice of ―Glidcop‖ a dispersion strengthened copper which maintains high yield stress even after brazing With optimized cooling geometry gives a maximum power absorption of 50W/mm length of absorber

Choice of material Melting temp oC Conductivity W/mK Diamond

3550 900-2300

Copper

1084 401

Aluminium

660 237

Stainless Steel

1400 12-45

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Initial Primary Slit design

Why was it so big?

q Power absrbed per mm of absorber = Qsinq If we have power densities of 1000 W/mm then q should be less than 2.8 degrees

Q W/mm

Present High Power Slits y z y z

Grazing angle 1.8 degrees

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How do we process these beams? WINDOWS Window, attenuators and CRLs can be treated the same. h t

In the central zone this can be approximated to a 1 dimensional problem Assuming copper at constant temperature (20C) Qabsorbed = -kAdT/dx  Qabs/mm = k x t x DT x 2/h  DT = h Qabs/mm/2kt

Materials and thicknesses Example a.0.3mm diamond in u27@11mm absorbs 28W/mm if h =6mm then temperature = 140oC Example b 0.3mm aluminum in u27@11mm absorbs 41W/mm if h =6mm then temperature = 1180oC

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In real conditions

• Beam is not linear approx 3mm horizontally x 1mm vertically.
• Copper cooling block is not constant temperature
• Material is not isotropic

HP attenuators

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Typical attenuator foils that are now used Not to forget our initial problem! CVD diamond Pyrocarbon Pure aluminium CVD diamond coated with high z material

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How do we process these beams? OPTICS

• Monochromators
• Mirrors

The difference: size of the projected beam on the optical surface. Monochromator Mirror

Angle of incidence (Bragg Angle) 4-70 degrees Typical Footprint 3mm x 3mm Power density up to 100 W/mm2 Total power up to 300W Angle of incidence (Bragg Angle) 0.1 to 0.3 degrees Typical Footprint 3mm x 500mm Power density up to 1 W/mm2 Total power up to 800W

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Mirrors How do we process these beams? OPTICS Mirror cooled by In/Ga baths. In/Ga is a ―safe‖ mercury. Liquid metal for good flexible thermal contact

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Results

temperature along mirror

20.00 25.00 30.00 35.00 40.00 45.00 100 200 300 400 500 distance along mirror (mm) temperature deg C 200mA 160mA 160mA width corr

Deformation of mirror

0.00E+00 5.00E-07 1.00E-06 1.50E-06 2.00E-06 2.50E-06 3.00E-06 3.50E-06 4.00E-06 4.50E-06 50 100 150 200 250 300 350 400 450 distance along mirror deformation (m) 200mA corrected 200mA 160mA 160mA corrrected 200mA 160mA width corr 160mA width corr 200mA

If the mirror is inserted in the white beam part will be reflected and part will be absorbed. The absorbed beam will heat up the surface of the mirror and also the bulk of the mirror. The temperature of the surface can be calculated and varies according to above graph. It will vary with different currents in the machine.. From these temperatures the deformation of the surface can be calculated and corrected using a bender. End effect outside useful beam Primary Slits Secondary slit

How do we process these beams? OPTICS

T Mairs et al Upgrading Beamline Performance : Ultra Stable Mirror Developments at ESRF 18

The New ESRF Generic Mirror Solutions

Final choice for ESRF ID24_MH1—Specific horizontally deflecting mirrors ID24 ―Smart‖ section mirrors Water cooling on top of side Clamps for cooling absorbers and Indium foil interface

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Monochromators How do we process these beams? OPTICS Optimised cooling as seen before.

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Monochromators

Aim is to keep this region as flat as possible

Thermal conductivity (w/mK) vs temperature 200 400 600 800 1000 1200 1400 1600 1800 70 120 170 220 270 320 temperature (K)

Why liquid nitrogen

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After the monochromator the heatload problem disappears PHEW! Outline What are we dealing with? Basic beamline functions and generic solutions. Heatload Management Vacuum Supports Positioning But we still have

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VACUUM

Vacuum is not the specialisation of the mechanical engineers working on beamlines, but vacuum chambers are used everywhere. Some figures: ESRF subsystem length vacuum chambers vacuum level Booster 300 metres 10-8mbar Storage Ring 32 cells x 26m =844 metres 10-11mbar Front Ends 47 x 20m = 940 metres 10-9mbar Beamlines 47 x 20-100m = 1500-2500metres 10-6 – 10-10mbar Vacuum Regimes Rough Vacuum: Atm (1000mbar) - 10-2mbar Process Vacuum: 10-2mbar - 10-4mbar High Vacuum: 10-5mbar - 10-9mbar Ultra-High Vacuum: < 10-9mbar Generally beamlines operate in the high vacuum region. But why?

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Beamline Vacuum requirements Maximum transmission of photons Vacuum level transmission for 1 metre at energy mbar 2keV 4.5keV 7keV 12keV 20keV 1000 0% 0.5% 25% 76% 93% 100 0.2% 59% 87% 97% 99% 10 55% 95% 98% 99% 100% 1 94% 99% 99% 100% 100% 0.1 99% 100% 100% 100% 100% Cleanliness Surfaces are free from contaminents

• to avoid damage i.e. mirrors, crystals etc
• for the science of the surface.

Practical considerations.

• need to minimise vibrations (no mechanical movements ion pumps)
• minimise maintenance (ion pump lifetime  vacuum <10-7mbar)

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Standardisation at ESRF Decision taken in 1990 to use CF flanges with copper gaskets

Conflat flanges Stores 316LN Beamlines 304L is OK Gaskets Stores machined copper Bolts Stores silver plated For rough pumping

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Some chambers at ESRF

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Outline What are we dealing with? Basic beamline functions and generic solutions. Heatload Management Vacuum Supports Positioning One of the most common jobs to do for our colleagues in MEG ― I have got to go and draw a support!‖ Not an interesting job but very important for the performance of the beamline.

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Why are the supports so important?

Stability of the beam from the machine is given as 10% of its divergence

Sample Optics Machine

Microbeam: ideally neither the beam or the sample should move more than 10% of its size I.e.<1-2mm

We do not want to amplify the instabilities in the beam. It is important that all the optical elements and the sample are correctly supported

What do we mean by a good support?

• ESRF site already shows movements
• f the order of 1 micron. Weekends

and nights are better.

• The support should not amplify these

levels.

• The support should not resonate with

―normal‖ driving sources. Water flow, LN2 flow, electronic fans, chillers etc.

• ―Support‖ is not just the vacuum

chamber but is also the internal mechanics.

The ideal support?

Distance floor to instrument inposed

Distance instrument to support should be minimised

Not an optimised support

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Improvement from previous version

BM29 in 2008 Metallic frame Cryostat (gas?) cooled mono BM23 in 2011 Celith and marble + airlocks LN2 cooled mono

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Improvement from previous version

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Carbon Fibre Support

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For sensitive instruments Granite base glued to the floor Height adjustment using high rigidity wedges Minimal movement or movements that can be blocked after movement

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Outline What are we dealing with? Basic beamline functions and generic solutions. Heatload Management Vacuum Supports Positioning

Simplictically there are three ways of moving mechanics at ESRF Pneumatic cylinders Piezo cells Screwdrives

Used on attenuators, beamviewers, valves, transfocators etc. Used on monochromators, mirros for fast and/or vary accurate movements

Simplictically there are three ways of moving mechanics at ESRF Pneumatic cylinders Piezo cells Screwdrives

Used on attenuators, beamviewers, valves, transfocators etc. Used on monochromators, mirros for fast and/or vary accurate movements

96% of movement are actuated using some form of screw. Different accuracies are available

What do we mean by precision etc. Some definitions

Minimum Incremental Motion The smallest motion a device is capable of delivering reliably. Not to be confused with resolution claims, which are typically based on the smallest controller display increment and which can be more than an order of magnitude more impressive than the actual motion output.

There is always a compromise between speed/resolution/repeatability etc

What do we mean by precision etc. Some definitions Various errors or qualities can be added by the guiding elements

UPBL4 Dmirr Double white beam mirror with variable incidence angle . Water cooled with optimised smart profile and In/Ga cooled 2nd mirror

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High load z movement no guiding

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The Rolls Royce

UPBL4 Dmirr Double white beam mirror with variable incidence angle . Water cooled with optimised smart profile and In/Ga cooled 2nd mirror

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The construction of an experiment is also a combination of a set of building

• blocks. If the building blocks are right a sophisticated experiment can be built in

2 weeks!