Be Lenses

The beam can be focused by inserting Beryllium compound refractive lenses in the beam path. The focal length can be adjusted for a given X-ray energy by selecting an appropriate number of individual lenses (up to 13) and stacking them. One can switch from one stack to another (up to three) remotely.

Center of location : 3.246 m (translated longitudinally ±0.195m)

The lenses are fabricated by B. Lengele group in RWTH Aachen (http://www.physik.rwth-aachen.de/en/institutes/institute-iib/group-lengeler/)

Updated inventory can be found in g.drive here.

We have sets of Be lenses with thicknesses: 50 um (rarely used because small aperture, only for really hard x-rays), 100 um, 200 um, 300 um, 500 um, 1000 um, 1500 um and 2000 um.

The rayleigh length of this lenses is approx. 3 cm and the focus doesn't blow up that fast far from focus (approx. 1 um bigger at the sample per 1 cm motion of the lenses or 1 um bigger for 1 cm upstream/downstream the sample)

L

CALCULATION:

To calculate the number and type of Be lenses required for certain beamsize and energy we use the following function in xcspython:

Distance from the lenses to the sample is 3.246 m at XCS.

Focal length for certain lenses configuration and energy:

LensFocalLength(LensEffectiveR((200e-6, 300e-6),(2,1)),10,'Be') [LensFocalLength(LensEffectiveR((lensesthickness1,...), (number1,...)), Energy,ID]

Beamsize for certain lenses configuration and energy at a given distance:

crl2.calc.calcBeamFWHM(9,(3,100e-6,1,200e-6),distance=3.246+-0.195)

[crl2.calc.calcBeamFWHM(Energy,(number1,lensthick1,number2,lensthick2....),distance=distance)

For Lens transmission :

LensTransmission(75e-6,800e-6,3,10,'Be') [LensTransmission(effective R ,Beam FWHM , # of Lens, Energy, ID)]

Make sure the focus is not too upstream if there is risk of melting beamline components (usually we set it downstream)

Now we can also use: crl.planSet(E,size), e.g. crl.planSet(9.5,20e-6), which will propose various set of lenses for that size (specifying the achievable range) for downstream focus.

*Note that the C* crystal on the LODCM introduces additional divergence

pack 1 is around 9.5 mm, pack 2 is around 36 mm, pack3 is around 62 mm, out is around 93 mm (m. crl2_y)