D22 manual

This manual describes the characteristics and the use of D22, the latest small-angle neutron scattering instrument at the ILL.

An up-to-date version of this help file is available on the instrument computer. There is also help about emergency procedures (use restricted to experienced local contacts and instrument responsibles or technicians). Technical information about D22 can be found in the D22 yellow pages in ILL's WWW server.

See also the D22 documentation and the D22 Short Manual.

• 1. Instrument features
• 2. Technical data
• 3. Data acquisition and MAD
• 3.1. GEORGE
• 3.2. Log files
• 3.3. Other programs can also be activated on D22.
• 4. Neutron velocity selector
• 5. Attenuators and entrance diaphragms
• 6. Collimation
• 7. Multidetector
• 8. Sample position
• 9. Monitor
• 10. Printing
• 11. Digital voltmeter
• 12. Circulating baths
• 13. Orange cryostats
• 14. Power supply (e.g. for controlling a magnetic field)

The main features of D22 are:

• high brilliance of the second (horizontal) cold source
• high performance selector (peak transmission 94 %)
• high dynamic q-range (q_max/q_min up to 50)
• large (96 x 96 cm) detector with 16K pixels of 0.75 x 0.75 cm²

D22 is the small-angle neutron scattering (SANS) facility with the highest flux at the sample in a wavelength range of 0.4 to more than 4 nm. This is due to a brillant source (horizontal cold source of the ILL), a high-tec velocity selector of short rotor length (25 cm) and high transmission, the relatively large beam cross-section of 55 x 40 mm of the guide H512, and a shortest guide-to-sample distance ("collimation length") of 1.4 m.

The lengths of the neutron guide sections are chosen such that the solid angle seen by the sample decreases by a factor of two for every section removed in front of the sample.

D22 possesses the largest area detector of all small-angle scattering instruments (active area 96 x 96 cm), with a pixel size of 7.5 x 7.5 mm, i.e. 16K resolution elements. The detector can be moved laterally by 50 cm inside an evacuated tube of 2.5 m diameter and 20 m length. In a setting optimized for a maximal dynamic Q-range - Q is the momentum transfer, (4pi/lambda) sin theta, with lambda, the wavelength and 2 theta, the full scattering angle -, a q_max/q_min ratio of as much as 50 can be reached; this is unequaled at least by reactor-based SANS instruments.

The VME memory card will be able to store 8 MB of data, i.e. 128 frames of 16K of 4 byte words allowing for excellent time-resolved measurements.

D22 will perform most experiments better than previous instruments; Its larger dynamic q range, higher flux and larger storage memory provide a substantial improvement for experiments on unique samples that cannot be prepared identically for successive experiments. This may be decisive for measurements on new polymer materials, for example. Many experiments on weakly scattering samples (e.g. defects in Si, highly diluted proteins) will become accessible or largely improved by the increased flux.

• Beam Tube: H512 (horizontal cold source)
• Monochromator: Dornier velocity selector, max. speed 28300 rpm
• Incident wavelength: 0.45 < λ < 2.0 nm (0.3 < λ < 1.2 nm, selector angle = -9 deg.)
• Wavelength resolution: 10% for selector angle = 0 deg.
• Collimation: 8 guide tube sections of 55 x 40 mm;
• Source-to-sample distances: 1.4, 2, 2.8, 4, 5.6, 8, 11.2, 14.4, 17.6 m
• Max. flux at specimen: 1.23x10⁸ cm^-2 s^-1 at 20000 rpm (0.64 nm), 1.4 m collimation (gold foil measurement by S. Million 24-Feb-1995)
• Detector: 2-dimensional ³He detector with 128 x 128 pixels of 7.5 x 7.5 mm
• Max. counting rate: 200 KHz
• Electronic noise: ca. 2 Hz on whole detector
• Sample-to-detector distances: 1.3 < L < 18 m
• Horizontal detector offset: -5 to 50 cm
• Rotation about vertical axis: 0 to 22 deg.
• q-range: 1.5x10^-3 nm^-1 < q < 10 nm^-1
• Sample environment: compatible with D11 and D17
  • automatic, temperature-controlled sample changer, 10 to 22 positions
  • electromagnets up to 2 Tesla
  • cryostats (4 to 300 K)
  • Couette shear cell (sample volume 4.5/7.5 ml, max. G = 12000 s^-1)

The data acquisition itself is controlled by an instrument-specific version of the program MAD (Multidetector Acquisition of Data) written by Michel Roure; there is a specific WWW document for  MAD, and online help is also available on the instrument computer.

The most important MAD commands are:

• ATTenuator In/Out/Change
• CHAnger position
• CHEck file.ext
• COLlimation n
• DET n
• HELp
• PARameter (sub-menu)
• PAUSE
• QUIT
• RESUME
• RUN [preset_value] [preset_type] [ntimes] [save/nosave]
• STArt file.ext
• STOP SAVE/NOSAVE
• TEMperature n (Kelvin)
• UNIX (system command)
• WAIT n (seconds)
• WAVelen n (Angstroms)

The preset type in the RUN command is M (monitor) or T (time).

A GEORGE pad is available for controlling D22 via a graphical MAD-IDL user interface based on LAMP

There is a new location and name structure of log files: [/users/d22/]logfiles/madyymmdd.log, e.g. mad010307.log. The command "more mad.log" automatically points to the current log file. For info: The old location and name structure of log files was LOG_FILE/MAD.LOG.Dec.27. Old log files get compressed and stored in subdirectories yymm, e.g. 0307, of /users/d22/logfiles.

DTI is a package to drive and control the 'illptc' temperature controller.

MSP displays the status of the measurement. It requires a video terminal.

NSW controls log printer output and storage of instrument log files. More information on NSW is found in MAD help.

SACHA is an interactive program for creating MAD command_files not yet available in a UNIX version.

TRANSFER allows one to manually force transfer of data files to the central data base.
Command syntax:
    transfer
or
    transfer start number
to start from a given run.

PCP (known from the VMS version of MAD) is no longer in use. There are the commands STOP, PAUSE, and RESUME now.

A DORNIER velocity selector is used to choose the neutron wavelength. The value of the wavelength depends on the rotation speed (2800 to 28300 rpm) and on the tilt angle of the selector around its vertical axis (-10 to +10 deg).

Allowed values of the wavelength (as of 4-Feb-2002) are:

• 4.6 to 11.5 A (10920 to 28300 RPM)
• 14.9 to 21.9 A (5700 to 8400 RPM)
• 23.5 to 27 A (4625 to 5300 RPM)

Currently forbidden values (as of 4-Feb-2002) for the wavelength (and rotation speed) are:

• below 4.6 A (above 28300 RPM)
• 11.5 to 14.9 A (8400 to 10918 RPM)
• 21.9 to 23.5 A (5300 to 5700 RPM)
• above 27 A (below 4625 RPM)

These values can be checked by

 MAD> PAR SEL

It takes less than 6 minutes to accelerate the selector from 3200 to 28000 rpm, but the MAD program introduces delay times to allow the selector temperature to equilibrate.

According to our silver behenate measurements of 5-Feb-2002, we use the following values for the selector at tilt angle 0 °:

wavelength (Å) = (120003 / rpm) + 0.1734

We advise you to use a sample of Silver Behenate in order to calibrate the wavelength. The d₀₀₁ of silver behenate is 58.38 Å, i.e. q₀₀₁ = 0.1076 Å^-1.

A measurement time of the order of 200 s is normally sufficient.

Reference: T.C. Huang et al. "X-ray Powder Diffraction Analysis of Silver Behenate, a Possible Low-Angle Diffraction Standard" (1993) J. Appl. Crystallogr. 26, 180-184.

Selector supervision program

The window of the selector program (Anatole) on the supervision PC can be made visible by permanently pushing the "ALT" key while typing the "TAB" key (-->|) until the word "selector" appears in the central rectangle. Then release both keys.

Normally, the selector program runs in VAX mode, controlled by the MAD program. It then serves only to check the running conditions, speed etc. In LOCAL mode (normally reserved for the instrument reponsibles), the different buttons can be used for controlling the selector. The most important of them is the CONTROL button. Clicking on it opens a dialog box allowing one to enter a speed value to be confirmed by clicking the OK button or by pushing ENTER.

Manual setting of selector speed

• In the rightmost cabinet of the process controller, switch the selector control box to MANUAL.
• Change the speed preset to the desired RPM value by pushing the buttons above and below the digits. The correct speed value can be found using the WAV command in MAD. Be sure to choose allowed speed values. Forbidden values are obtained by PAR SPEED in MAD.
• Push the AUTOMATIC button (don't use RESET)

There are three attenuators available on D22:

• 1; attenuation factor 147
• 2; attenuation factor 902
• 3; attenuation factor 2874

The attenuators are "sieves" consisting of gadolinium or cadmium plates with 88 holes of about 0.4, 0.2, and 0.1 mm diameter, respectively, at a distance of 5 mm. The smallest holes are drilled in 0.25 mm Gd, the others in 1 mm Cd.

Furthermore, there are four round entrance apertures (1 mm Cd) in the attenuation box (in the D22 casemate)"

• 4; diaphragm diameter 5 mm
• 5; diaphragm diameter 10 mm
• 6; diaphragm diameter 20 mm
• 7; diaphragm diameter 30 mm

Attenuators and apertures are changed with the ATT C n command in MAD.

Caution: ATT out removes the aperture like it does with an attenuator! There is no combination of such an aperture with an attenuator.

Remotely controlled entrance slits

In front of the neutron guide crossing the "casemate" wall, and after the beam monitor and attenuator, there is a remotely controlled beam-defining aperture. The control box for this unit is in the instrument electronics cabin, below the ones controlling the detector and sample movements. All four movements are regrouped in one box. The four slits move independently; they only cover half of the beam cross section. The end switch positions are:

• left: 117 (open) to 14 (half-closed)
• right: 119 to 13
• top: 182 to 49
• bottom: 169 to 39

("Left" and "right" refer to the aperture control unit in the electronics cabinet).

Closing the left slit to a value of 80 removes faster neutrons and leads to a reduction in the otherwise unexplained increase in the background near the beamstop that cannot be subtracted using the normal transmission values.

With the aperture sufficiently closed, the free neutron flight path becomes 19.1 m, since the neutron guide insert crossing the casemate wall is no longer seen by the neutrons.

The incoming beam on D22 is defined by a rotating collimation system consisting of 8 sections. Each section has three tubes; the first contains a neutron guide of cross section 40 mm (wide) x 55 mm, the second is internally covered with B4C and carries an antiparasitic aperture wider than the beam, the third one is unused and foreseen for optional neutron-optical elements.

The 8 sections have decreasing lengths seen in neutron direction and yield free neutron flight paths of:

Every piece of neutron guide that is inserted in front of the sample increases the solid angle of the virtual source, i.e. the end of the neutron guide, by about a factor of two. This is no longer true for short wavelengths where the divergence angle of the guides becomes larger than the critical angle of reflection.

Antiparasitic apertures, laser and halogen light.

The collimation ends with a setup of standard size vacuum tubes. The O-rings between them can hold antiparasititic B4C/Cd apertures of different sizes. Normally, a large iris aperture (30 mm diameter) should be used as the last one before the sample aperture. A smaller iris aperture is advisable in cases where low background is desired, and when the collimation distance is long and/or the sample aperture is small.

The first tube section is equipped with a silicon wafer serving as a mirror for light; it is, however, transparent for neutrons. A laser diode and a halogen bulb shine on the centre of the mirror. Their direction can be made co-axial to the incoming neutron beam, thus faciltitating the setup of the sample in the beam.

D22 is equipped with a 128 x 128 pixel 3He multidetector (pixel size 8 mm x 8 mm), running at a tension of + 1515 V. The detector is made up of 128 linear sensitive Reuter-Stokes detector tubes of 8 mm diameter allowing for a count rate of 100 kHz each at 10 % dead-time loss.

Beamstops

Five different beamstops are available on D22:

1. 4 x 4 cm
2. 5 x 6 cm
3. 5.5 x 7 cm
4. 7 x 8.5 cm
5. 8 x 10 cm

These can be chosen by the MAD BEAMstop n command, where n is the number of the beamstop to be used. The command BEAMSTOP without a number indicates the beamstop currently in use. Changing the beamstop takes place in 6 steps. At the end of the exchange procedure, the new beamstop is automatically moved to the old BX and BY values.

The beamstop should only be changed at a detector position where it can be visually controlled, e.g. at 3.5 m.

The beamstop is moved by the MAD commands BX and BY in absolute units (mm); it is roughly centred for BX = 0., BY = 0. BX and BY can be on one command line. There is no specific short command (yet) to remove the beamstop completely for transmission measurements (use BY -500 instead), nor to move it back to the previous position; always note BX, BY values before moving the beamstop. They are also found in the summary lines printed after the end of every run.

The beamstop movement is independent of the lateral detector position and of the detector rotation.

Technical information:

The beamstop arm moves down to y = -620 mm for depositing a beamstop and moving to the next, pick-up takes place at about -605 mm, and a safe height for moving the beamstop above the "shelves" is -500 mm. The X positions of the shelves are at 132, 192, 261, 342 and 432 mm (as of 12-Mar-2004).

Before doing this for repairing a wrong beamstop value indication, try the MAD PAR BEAM command.

Dead time

In first-order, dead-time effects can be corrected assuming that the whole detector behaves like a single detector with a dead time of 2.06 microsec. Corrected counts per cell are obtained by

I(x,y,true) = I(x,y,measured) / (1 - n'*tau)

where n' is the observed overall detector count rate and tau the detector dead time.

The D22 sample position is equipped with a sample table that has an electrical lifting device carrying up to 400 kg. The sample table is fixed to the floor by screws. The vertical movement has an incremental encoder. In order to make sure that the value read has a meaning, the lifting device must be initialized my moving it to its lowest position (end switch). Then, the "sample" card in the VME crate must be reset. Quit MAD before doing that and run MAD again after the reset. You should also quit the 2-D on-line program running on the supervision Macintosh. The encoder reading is set to 0 whenever the VME crate is reset!

The neutron beam is at about 1465 mm from the floor, i.e. 700 mm above the top of the sample table which is 765 mm high.

The distance of the nominal sample position from the aluminum plate closing the VAT gate valve is 274 mm, and that from the aluminum surface of the nose cone with the 80 mm sapphire window is 23 mm.

The distance between the bottom of the bottom plate of the sample changer and the top of the sample table is 494 mm for the 22-position rack plate,

The sample height is now shown in mm like the other movements (except the detector distance: m). Typical height values for the sample table are

• about 56.6 mm (coder 1350) with the sample changer on top of all stages (see below) in place

• about xxx mm (coder 6920) with the Orange Cryostat on top of all stages in place

On the round base plate of the lifting device are normaly mounted

• a translation table moving +/- 100 mm along the neutron beam

• a translation table moving +/- 50 mm across the neutron beam

• a rotation stage of 1/200 deg. precision

When the sample changer is being used, connect the encoder and motor cable of the second translation stage to it. Make sure that this translation stage is in central position before exchanging the cables

The beam monitor of D22 is situated in the casemate before the attenuation module.

The high tension supply ("MONITEUR") in the electronics cabinet uses a green HT cable and a black signal cable both marked "1" plugged in in the back of the unit.

The easiest command for printing is normally "pri your_file". The first time a user issues the pri command on the worksation or a X terminal, pri will call "myprinter" that will prompt for the default terminal. If myprinter should not work, you can make the following definition:

setenv SAS_PRINTER dj1_d22.

Recently, a similar commad (plo) was introduced to allow one using a separate printer for colour plots. plo calls myplotter.

Other printers that are available can be obtained in the "System" field of the "toolchest" under "Printer Manager".

Two digital voltmeters (Keithley) are available on D22.

They can be addressed by the MAD commands par ieee1 (for defining parameters) and ieee1 (for reading).

Temperatures measured with a PT100 probe can be read out with a display unit that also supplies a 0-20 mA output for the range -20 to +100 C. This output can be interpreted using the programs Y=MX+B on the Keithley models 196 or 2000 :

Model 2000:

• Push buttons DCI and "auto range"
• Push buttons SHIFT and DCV
• Set the value M in Y=MX+B by entering the digits 5.5 K (5500) using up/down buttons; push ENTER
• Set the value B in Y=MX+B by entering the digits -10; push ENTER
• Use up/down buttons to set UNITS to DEG; push ENTER

Model 196:

• Push buttons DCA and "auto range"
• Push button PROGRAM. Push buttons 3 and then 4 to choose program 34 (select M and B)
• Set the value M in Y=MX+B by entering the digits 5.5 K (5500) using up/down buttons; push ENTER
• Set the value B in Y=MX+B by entering the digits -10; push ENTER
• Push button PROGRAM on the voltmeter model 196. Push button 4 to choose program 4 (MX + B)
• Switch program Y=MX+B on by toggling (push an up/down button); push ENTER

The value thus shown on the voltmeter model 2000 screen can be read by MAD using the commands

• par ieee21 3 2 (for switching the voltmeter to DC Ampere mode, range 300 mA
• ieee2 (whenever you want to use this command)

The model 196 voltmeter requires ieee1.

Direct reading of a PT100 probe is also possible using the values M=2.5974 and B=-259.74 with par ieee1 1 2 1 or par ieee2 1 2 1 (for switching on the voltmeter to Ohm mode, precision 300 Ohm).

NB:
The resistance of a PT100 (in Ohms) is 100 + 0.385 * temperature (deg.C). Therefore, temperature = (resistance-100) / 0.385 = 2.5974 * resistance - 259.74.

D22 possesses two Haake baths, a model N8 and a model F4-K. The temperature can be controlled by the MAD command BATH value (deg.) using a digital-to-analogue interface. The offset and slope values to be used in the PAR BATH commands are

• N8: 0.2 100.
• F8-K: 0.66 98.5

The N8 can also be controlled by an RS232 interface. The bath uses the cable for the ILL temerature controller and requires an adapter that is 9-pin male on one end and 25-pin female on the other.

The commands for setting the temperature and the line speed are included in the Setup menu of the GEORGE control pad.

Another way of interacting with the bath is using DTI:

• DTI h con (to see the configurations)
• DTI se contr haake (to define the bath)
• DTI sh t (or just DTI to read the temperature)
• DTI se[t] t[emp] <value> (to set the temperature to a value in °C)</value>

The baths can use the reading of an external PT100 probe for regulating the sample temperature. The actual temperature can be output as 10 mV/deg. and read on the digital voltmeter:

This output can be interpreted using the programs Y=MX+B on the Keithley models 196 or 2000 :

Model 2000:

• Push buttons DCI and "auto range"
• Push buttons SHIFT and DCV
• Set the value M in Y=MX+B by entering the digits 100. using up/down buttons; push ENTER
• Set the value B in Y=MX+B by entering the digit 0. push ENTER
• Use up/down buttons to set UNITS to DEG; push ENTER

Model 196:

• Push buttons DCA and "auto range"
• Push button PROGRAM. Push buttons 3 and then 4 to choose program 34 (select M and B)
• Set the value M in Y=MX+B by entering the digits 100. using up/down buttons; push ENTER
• Set the value B in Y=MX+B by entering the digit 0; push ENTER
• Push button PROGRAM on the voltmeter model 196. Push button 4 to choose program 4 (MX + B)
• Switch program Y=MX+B on by toggling (push an up/down button); push ENTER

The value thus shown on the voltmeter model 2000 screen can be read by MAD using the commands

• par ieee2 1 0 4 (for switching the voltmeter to DC Volt mode, range 300 V
• ieee2 (whenever you want to use this command)

The model 196 voltmeter requires ieee1.

The standard orange cryostats for small-angle scattering can be used on D22. Michel Bonnaud, the D17 technician, takes care of them (bonnaud@ill.fr; Tel. 7779).

With the sample stick of cryostat 55, the distance between the lowest copper shield and the centre of the sample is 124 mm.

D22 possesses a new generation (ILLSEC) temperature controller.

The Midec SK 80-30 stabilized power supply of D22 can be controlled by a DAC or by an RS232 power supply controller (Midec PSC232).

As soon as a control plug is connected to the back side of the power supply, the front panel control is switched off.

Simplified DAC commands in MAD are "AMP value" for the current and "VOLT value" for the voltage. The DAC commands use channels 1 (0) and 2 of the DAC output for the current and voltage, respectively. You should first set a maximum voltage, e.g. 60 Volts, and then select a current, e.g. 20 Amps. The magnet can then be switched off and on by toggling between a current of 0 Amps and the desired value.

RS232 commands can be sent after setting the RS232 parameters in MAD: par rs232 4800 LF PSC232.

The most important commands are:

CH [x], where [x] is a channel number, e.g. 0, to be set on the PSC232.
SOurce:Voltage:Maximum [x], where [x] is a voltage value
SOurce:Current:Maximum [x]
SOurce:Voltage [x]
SOurce:Current [x]
SOurce, Voltage, Current and Maximum can be abbreviated as SO, V, C and M.

These commands are sent with the MAD RS232 command, e.g. RS232 SO:C 25.