X-ray Protein
micro-crystallography
It is sometimes difficult to grow crystals larger than a few
tens of microns. Many experiments carried out on the ESRF ID13 micro-focus
beamline have shown that good data can be collected from crystals as small
as 20 x 20 x 10 microns, but that a lack exists in diffractometers able
to handle efficiently these small crystals. A collaborative project has
been set between the EMBL and the ESRF to bring protein micro-crystallography
to the same efficiency level as standard crystallography. TopPage
Designed
to handle crystals down to 5 µm size
Crystals from 5 to 200 µm size
can be REMOTELY mounted, centred on the rotation axis and aligned with
the beam. A high resolution video-microscope is used to view both the sample
and the beam size and shape. The beam position can be checked at any time
on a mouse click, even when a sample is mounted.
TopPage
Accepts
on site freezing or pre-frozen samples
The samples are mounted on a motorized arc. Non frozen
samples are frozen directly in the cryo-stream as they are mounted. Mounting
of frozen sample (loop + vial) is facilitated by the "cryo back feature
of the motorized cryo-stream head. After the sample is mounted on the arc,
ALL THE OPERATIONS ARE REMOTELY CONTROLLED .
TopPage
Fast
& High precision PHI axis
The PHI axis is a spindle directly coupled to a high resolution
incremental encoder, it is driven by a gear box free torque motor.
- Sphere of confusion radius at sample position: 1 µm
- Precision: ±1 mDeg @ 10 Deg/s
- Maximum rotation speed: 180 Deg/s
TopPage
High
resolution video-microscope with viewing coaxial to the beam
The video-microscope is used to
view the sample and the beam display scintillator. Because the camera looks
in the direction of the beam, the sample can be aligned with the beam WITHOUT
PARALLAX ERROR.
- Sub-micron resolution, diffraction limited objective lens
(N.A. = 0.28)
- High resolution 3CCD colour camera
- Motorized zoom (X1 to X10; field 1.6 x 2.1 mm down to 0,16 x 0,21
mm)
- Condenser lighting with polarizer
- Motorized analyser
TopPage
Beam viewing
scintillator*
The scintillator is a 3 mm3 fluorescent single crystal
that can be set in the beam, at the exact position of the sample
(in the cryo-stream).
The beam can be displayed at any time even while a sample is mounted
(In this case the sample is slightly shifted away from the scintillator).
The scintillator allows the user to evaluate the beam shape, quality and
position. The resolution is only limited by the video-microscope.
TopPage
Remote
computer aided sample alignment
After the sample has been mounted on the arc, all the operations
are controlled remotely:
Assisted sample centring in the PHI axis
Automatic beam position marking
Assisted sample alignment with the beam
TopPage
Beam
definition aperture from 10 to 200 µm
The aperture is positionned at 25 mm
from the sample and mounted on a high repeatability YZ units. The aperture
is mounted on a small individual support that is held by magnets on the
YZ units. This allow the user to change the aperture size in seconds. The
alignment of the aperture is done using an integrated software tool providing
fast 1D and 2D scans. To avoid damages, the aperture is withdrawn and hidden
during the sample loading and unloading phases.
TopPage
Low
X-ray background
Most of the beam path is shielded by
molybdenum tubes to reduce the air scattering. A capillary/aperture unit
is set just after the beam definition aperture. The free beam path
in the air is then shortened to the distance between the cleaning aperture
(set at the end of the capillary) and the beamstop (typically 10 mm). The
capillary/aperture unit is mounted on a small support that is held
by magnets on YZ units. Alignment features described in the beam definition
aperture chapter (above) are available.
TopPage
PC
Controlled Standalone instrument
The electronics is packaged in a 19" 9U rack and installed
near the micro-diffractometer. The rack is connected to a Window NT PC
by two optical fibres. A video cable links the video-microscope to the
PC frame grabber card. The control program is written in Visual Basic.
A device server allows some devices (like the PHI axis) to be controlled
by a host computer.
The Installation of the micro-diffractometer is easy and fast, usually
one day is enough to set and align the instrument.
TopPage
User
friendly GUI
The main GUI window is divided in three
parts. The first one is for the monitor camera that gives a general view
of the micro-diffractometer (useful to have a global view from the control
hutch). The second window shows the video-microscope view, and the third
one is dedicated to the control commands of the micro-diffractometer.
To facilitate the task of the users, the control
is divided in six phases: "Sample Loading, Sample Centring, Beam Marking,
Sample Alignment, Remote and Sample Unloading". For maximum clarity, only
the useful controls are available for a selected phase .The Remote phase
is selected so that a host computer can take the control of the micro-diffractometer
for data collection.
The full access to the system is possible through
a number of "device windows" (menu access). Device parameters are password
protected.
TopPage
Remote
control Device Server
When the remote phase is selected, the
GUI is locked out, and some devices like the PHI axis can be controlled
by a host computer.
Basic motion commands and high level commands
like "angular scans with shutter control" are then available.
TopPage
Tuning
and diagnostic tools
Tuning and diagnostic tools are key features that allow fast
setting, and easy quality control of the instrument.
1) PHI axis scans for diagnostics: the following parameters can be
plot as a function of the PHI angular position (220 microseconds sampling
period):
- Following error
- Shutter command signal
- Beam intensity using the internal photo diode (to set the shutter
open/close delays)
2) Beam Definition aperture scans: linear and 2D scan of the YZ units
using the internal photo diode. They are used to align the aperture in
the beam.
3) Capillary/beamstop unit scans: (As above)
TopPage
Compatible
with future automatic sample feeding systems
An automatic sample changer for prefrozen sample is under development.
It will be integrated as soon it will be available.
TopPage
New Version
Many features of the micro-diffractometer
have been highly appreciated by the users. A version designed for more
general use is under development. It will accept larger detectors (up to
30 x 30 cm overall size) with a minimum sample to detector distance of
5 cm. It will be compatible with MAD experiments (Adjunction of a fluorescence
detector) and can be provided with an automatic sample changer for pre-frozen
samples.
TopPage
More information:cipriani@embl-grenoble.fr
TopPage
|
