DESCRIPTION

XALOC aims to provide the present and future Structural Biology groups with a flexible and reliable tool to help in finding solutions for structures of macromolecules and complexes. The beamline copes with a broad variety of crystal sizes and unit cell parameters, and allows both wavelength dependent and independent experiments.

Endstation of XALOC  Optical hutch of XALOC

 

USER ACCESS STATUS

The Call for proposals for 2019 cycle will open in July for XALOC beamline:

  • Opening: July 2nd, 2018
  • Deadline: September 10th, 2018

Call for Proposals for 2019-I cycle for BL13-XALOC will cover all the year for BAG proposals

Continuous access to XALOC is currently available, see the users call information page

Remote data collection is fully operative

Important note: During 2018, ALBA will also cover the dewar transport (only for remote access experiments).

To submit a proposal go to:
http://useroffice.cells.es/

More information about the Call:
http://www.cells.es/en/users/call-information

More information about funding rules:
https://www.cells.es/en/users/user-funding

 

Check the Preparing you Experiment page to see relevant information about administrative steps and technical requirements!

NEW: XALOC now supports both SPINE (EMBL/ESRF) pucks and Unipucks, which allow fast sample interchange.

Please include the reference to the beamline paper in your publications containing data collected at XALOC beamline:

 J. Juanhuix, F. Gil-Ortiz, G. Cunı, C. Colldelram, J. Nicolas, J. Lidon, E. Boter, C. Ruget, S. Ferrer and J. Benach, "Developments in optics and performance at BL13-XALOC, the macromolecular crystallography beamline at the Alba Synchrotron", J. Synchrotron Rad.  21, 679–689 (2014).

DOI:10.1107/S160057751400825X

 

STATUS

The beamline is under user operation from 18 July 2012. Three calls for proposals have been completed so far.

 

TECHNICAL SPECIFICATIONS

Photon Energy (Wavelength) range  5-22 keV   (2.4-0.58 A)
Flux at sample > 2·1012 photons/s/250mA at sample (measured)
Energy resolution (DE/E) 2·10-4
Beam size at sample (FWHM) Adjustable 50-300 (H) x 6-100 (V) μm2
Beam divergence at sample (FWHM) < 0.5 x 0.1 mrad(HxV)

 

The beam size will be fitted to the crystal dimensions by (a) adjusting the focus of the mirrors along the beam path, and (b) having two beamline operation modes: focused and unfocused.

In the unfocused configuration, one or both mirrors are removed from the photon beam path, resulting in a very limited beam divergence, less than 0.03 mrad vertically. This mode can be especially useful for large macromolecular complexes with large unit cell parameters. In the focused configuration both mirrors can focus the beam to 50×6 µm2 FWHM (H×V) on small or microcrystals, while at the same time retaining a small and useful vertical divergence (0.1 mrad). In addition, the mirrors allow variable focusing (de-focusing) if matching the size of the X-ray beam to the dimensions of the crystals, or if focusing at the detector (which can be placed at any distance between 80 mm to 1300 mm from sample) is required. In this case, the beam size at the position of the sample can range from 50×6 µm2 up to 300×300 µm2 (H×V). In order to avoid x-ray beam deformations caused by the optics when defocusing, slope errors of the mounted mirrors have been reduced to 70 nrad RMS and the monochromator crystal can work close to the zero-expansion temperature of Silicon (124 K).

 

ENDSTATION

The end-station is based on two positioning tables that support the detector and the diffractometer (and the beam-conditioning elements). Both tables have been developed in-house. 

 

Beam conditioning elements 

These are the elements immediately in front of the sample, they consist of 12-foil attenuators, x-ray position monitors, slits, slow and fast shutters, and a kapton window.

  • Position monitors: both 4-quadrant CVD diamond (DECTRIS)
  • 12-foil attenuators (ESRF type)
  • Fast shutter (FPS400 CEDRAT)
  • Slits (JJ-Xray ESRF type)

 

Diffractometer (MD2M - Maatel) 

Where the sample is to be rotated for data collection. The system includes a high accuracy omega axis (and a mini-kappa) and an on-axis viewing system. 

  • On-axis viewing system 
  • 2 μm sphere of confusion
  • mini-kappa
  • XYZ movable beam stop (in-house design)

 

Automatic Sample Changer (CATS - IRELEC)

The 6-axis robotic arm is used to manipulate both cryosamples and room-temperature crystallization plates. The Dewar is able to store a maximum of 108 cryosamples. 

  • Robotic arm to mount/unmount SPINE pins
  • The liquid N2 Dewar is able to store up to 108 samples
  • Ability to scan Greiner, MRC and Fluidigm crystallization plates
  • Barcode reading
  • Supports EMBL/ESRF and Unipuck standards


Detector 

The main data collection detector is capable of recording up to 12 images per second. 


Fluorescence detector

XFlash Detector 410-SA - Bruker to allow anomalous scattering experiments.

 

PILATUS 6M - Dectris

  • 424 x 435 mm active area, 6 Mpixels
  • 1 Million counts dynamic range (20 bits)
  • Delivery May 2011
  • Virtually noise free


Cryostream: 700 series - Oxford Cryosystems

  • 100K to 400K operation
  • 0.1 K stability

 

SOURCE

  

LAYOUT

Channel-cut Si(111) + KB focusing mirrors

The main XALOC optical elements are: a diamond window (not shown in figure); a removable diamond filter (which could also be used as a Laue monochromator); a channel-cut monochromator; and a Kirkpatrick-Baez (KB) focusing system.

Layout of XALOC Layout of XALOC

Monochromator

Type   Si(111) channel-cut, cryocooled
Gap between crystals 6 mm
Absorbed power <100 W (in working conditions)
460 W (in worst-case conditions)
Bragg axis resolution (measured) <1 µrad (<0.2 arcsec)
Bragg axis stability (measured) <1 µrad/1 hour


KB Mirrors

Vertical Focusing Mirror Horizontal Focusing Mirror
Type Elliptically bent mirror Elliptically bent mirror
Substrate Si Si
Coating material Si, Rh, Ir Si, Rh, Ir
Angle of incidence 4.1 mrad 4.1 mrad
Optical length  300 mm 600 mm

RMS slope error (bent, measured) <0.1 µrad <0.1 µrad

 

Other optical elements include white beam attenuators, slits, photon shutter, fluorescent screens and x-ray beam positioning monitors.