MISTRAL

Soft X-ray microscope beamline

The full-field Transmission X-ray Microscopy beamline MISTRAL is one of the seven phase-I beamlines at ALBA. It is devoted to cryo nano-tomography in the water window and multi-keV spectral regions (E= 270 eV–2600 eV) for biological applications. In addition, spectroscopic imaging (a series of 2D images over a range of X-ray wavelengths) at several interesting X-ray absorption edges can be performed.

The Transmission X-ray Microscope (TXM) works from 270 eV to 1200 eV. A single-reflection elliptical glass capillary condenser focuses monochromatic light on to the sample, which is at cryo-temperature. The transmitted signal is collected by an objective Fresnel Zone plate (of 25 or 40 nm outermost zone widths) and a magnified image is delivered to a direct illumination CCD camera. The routinely expected spatial resolution in 2D is 30 nm and ~50 nm for tomographies. An upgrade of the microscope to higher energies (i.e. Zernike phase contrast at 2600 eV) is planned, as well as the development of correlated fluorescence visible light microscopy.

Facilities for sample cryo-preparation as well as software reconstruction and analysis will be available for the users.

Design & Construction Phase: 2007-2010

1. A first tender exercise for the procurement of the optical components of the beamline was launched in spring 2007. Contracts with companies were signed in summer/autumn 2007. The PGM was awarded to FMB, the mirror vessels, slits and WB diagnostic was awarded to Cinel, mirrors to SESO and gratings to Jobin Yvon. Another tender exercise was launched in spring 2008 for the end-station. The cryo-Transmission X-ray Microscope was awared in September 2008 to Xradia.

2. The Plane Grating Monochromator (PGM) from FMB was installed in October 2009 (see picture below). The optics (2 VLS gratings and a plane mirror) were installed in April 2010.

3. Mirror vessels, slits and diagnostics were installed at the beginning of April 2010 by Cinel. Mirrors will be installed the first week of May 2010.

4. The cryo-TXM factory acceptance tests will be done during the first week of June 2010. The installation by Xradia is expected in September 2010.

5. The TXM was installed mid-September 2010.

6. The BL was completed and ready for commissioning in February 2011.

Commissioning Phase 2011

The Front End was opened for the first time on March 18th.

The beamline started the official commissioning phase on October 18th 2011 for approx. 1.5 months until Christmas 2011. After a period of machine shutdown, the commissioning will restart on January 24th.

Staff

Scientist Responsible: Eva Pereiro

Mechanical Engineer: ------------------

Beamline Technician: Ricardo Valcárcel (shared with CLAESS)

Software Engineer: Antonio Milán (shared with CIRCE beamline)

Visiting scientist: Salvador Ferrer

Post-doc: Andrea Sorrentino

People that have contributed to the optics design: Malcolm Howells & Josep Nicolás

People that have worked at the BL: Daniel Bacescu (Mechanical Engineer), Maria Brzhezinskaya (Scientist)

Beamline Characteristics

MISTRAL		Comment
Microscope type	TXM
Current Status	under commissioning	open for users in 2012
Source	bending magnet
Energy range	270-2600 eV	TXM: 270-1200 eV available; upgrade to 2600 eV planned.
Energy resolution	up to E/DE=5*10³
Zone plates available	25 nm and 40 nm
Sample format	TEM round grid (3.05 mm)
Tomography capability	yes
Tilt range	± 65º
Cryo capability	yes
Detector type	PIXIS-XO: 1k * 1k, pixel size = 13um
X-ray magnification	adjustable range depending on objective used (1500-3000 mm from sample)
Image contrast capability	amplitude contrast	Zernike phase contrast planned for outside the water window energy range
X-ray fluorescence	no
Light microscope	for sample alignment only	integration of a fluorescence light microscope planned
Filter sets for light fluorescence microscope	no
Raw data format	file format: XRM, raw data, HDF5, TIFF file size per image: ~4 MB
Data analysis software capabilities available	ImageJ, IMOD, PRIISM, XMIPP.
Preparation Lab	Bio-lab (safety level 2). Plunge freezing preparation available.	under construction

Technical Description of BL Optics

Polychromatic radiation will be delivered by a bending magnet. A VLS Plane Grating Monochromator (PGM) will fill with light an elliptical glass capillary, which will, in turn, focus the light on to the sample. The transmitted signal will be collected by an objective Fresnel Zone Plate and a magnified image will be delivered to an X-ray CCD.

The following sketch shows the optical layout of the optics. A Kirkpatrick-Baez system focus light vertically (VFM) on to the entrance slit (Sin) and horizontally (HFM) on to the exit slit (Sout) of the vertically dispersive PGM. The monochromator will work in standard imaging conditions with a constant slit-to-slit magnification in the dispersive plane of 1/cff = 1/2.25. It is constituted by a plane mirror PM and two varied line spacing gratings (VLS G), covering the whole energy range. An elliptical cylinder mirror (VRFM) will refocuse the beam vertically onto the exit slit. The source is demagnified 3 times horizontally and 3*2.25 times vertically at the exit slit position.

Mistral layout