SICS manual for the SANS I instrument
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Instrument settings

Beam shutter

Every instrument area in the SINQ neutron guide hall is controlled by the Local Beam Controlsystem (LBC). It uses fixed installed barriers to prevent entry to the area around the active beam during experimental work. If the user carries out his work in accordance with the operating instructions, he will be protected from direct beam radiation. A danger zone which is subject to the LBC interlocking system has two beam shutters

the neutron guide main shutter which only can be opended by the radiation safety officer
and a secondary shutter to close the beam at the instrument separately from the others if more then one instrument is build up at the same neutron guide.

The secondary shutter for the instrument is the one the user can handle. Normally the secondary shutter can only be operated if the experimental area (yellow fence) of the instrument is locked. The shutter can then be opened and closed by a button on the key box at the entrance door of the instrument area and also by the SICS command shutter which has the following syntax:

shutter: without parameter yields the actual status of the shutter which can be shutter is open, shutter is closed, or Enclosure is broken. The last status message is returned if the LBC system wouldn't allow to open the beam. If this message is returned the shutter is closed.
shutter close: closes the secondary beam shutter.
shutter open: opens the secondary beam shutter.

Neutron velocity selector

The neutron velocity selector is a high-speed rotor. Blades inserted in the rotor are only transparent for neutrons which manage pass the rotor in a time intervall defined by the rotation speed of the selector. Thus neutrons in a certain speed range (wavelength range) are selected. The wavelength distribution of neutrons is also dependent of the tilt angle between the rotation axis and the neutron beam. Extensive time-of-flight measurements have been done to determine the wavelength λ and resolution Δλ/λ as a function of selector speed and tilting angle. The dependency of the wavelength λ [nm] on the rotation speed ν [RPM] can well be described by

λ(ν,ξ)= A(ξ)/ν+B(ξ)

where A(ξ) ans B(ξ) are parameters depending on the tilting angle ξ. The experimentally determined relationships A(ξ) and B(ξ) are

B(ξ)= 0.0122+3.61x10^-4ξ+3.14 x10^-4ξ² +3.05x10^-5ξ³ +9.32x10^-7ξ⁴

The wavelength resolution Δλ/λ of the selector should be independent of the rotation speed and only be dependent of the tilting angle ξ. However, this is only true for long collimations. For short collimation lengths a slight dependency of the resolution on the rotaion speed could be measured. Also the shape of the resolution function is than not necessarily triangular. If the wavelength resolution of the selector is not so important for the refinement of your data analysis you can use the values given in the following table for the dependency of the wavelength resolution Δλ/ λ on the tilting angle ξ.

ξ	Δλ/λ	A(ξ)	B(ξ)
-15	0.12	19812	0.0218
-10	0.115	17774	0.0182
-5	0.095	15493	0.0163
0	0.1	12716	0.01097
5	0.155	9342	0.0269
10	0.3	5293	0.0869

A high speed-device like a velocity selector has to account for gyroscopic forces when moving the device. In praxis this means that the selector must be stopped before the tilt angle can be changed. Furthermore there are forbidden areas of rotation speeds. In these areas the velocity selector is in destructive resonance with itself. For controlling the neutron velocity selector three command are available: nvs , nvswatch, and lambda which are described below.

lambda: The name of the variable alone prints the current wavelength in nm.
lambda rot <value>: calculates the rotation speed for the wavelength given by <value>.
lambda wl <value>: calculates the wavelength for the rotation speed given as parameter <value>.
drive lambda <newval>, run lambda <newval>: The lambda variable can be driven using the normal drive and run commands.
nvs status: Prints a status summary of the velocity selector.
nvs list: Displays rotation speed and tilt angle of the velocity selctor.
nvs [rot=<newval>] [tilt=<newval>]: This command sets a new tilt angle and/or rotation speed for the velocity selector. Either one or both of the keywords tilt or rot may be given, followed by a number.
nvs rotinterest: Enables printing of status messages about the current state of the selector when it is driven.
nvs loss: Starts a loss current measurement on the velocity selector and prints the result.

The commands described so far cover the actual handling of the velocity selector. During a measurement users might want to use further functions such as:

Monitor the rotation speed of the velocity selector.
Log the rotation speeds of the velocity selector.
Initiate error handling when the velocity selector fails to stay within a predefined tolerance of rotation speeds.

Now, these are tasks usually connected with sample environment devices. Now, the SICS programmers have been lazy. Moreover they wanted to avoid duplicating code (and bugs). Consequently, they tricked the velocity selector to be a sample environment device as well.

This means besides the actual velocity selector object (in this case called nvs) there exists another object for monitoring the velocity selector. The name of this device is the name of the velocity selector object with the string watch appended. For example if the velocity selector has the SICS name nvs, the monitor object will be nvswatch. The commands understood by the watch object are fully decribed in the section about sample environment devices. Please note, that all driving commands for the watch object have been disabled. Driving can only be achieved through the velocity selector object or the lambda command.

Positioning an attenuator

att

prints the current positioned attenuator.

att <val>

positions attenuator <val>. Allowed attenuator numbers are 0, 1, 2, 3, 4 and 5.

0 : square 50 mm x 50 mm slit, attenuation = 1

1 : circular 41 x diameter 0.4 mm slit, attenuation = 1/485

2 : circular 9 x diameter 2 mm slit, attenuation = 1/88

3 : circular 20 mm diameter slit, attenuation = 1/8

4 : circular 30 mm diameter slit, attenuation = 1/3.5

5 : circular 15 mm diameter slit, attenuation = 1/??

Change the collimation

coll: prints the current collimation length.
coll <val>: sets the collimation <val>. Allowed collimation lengths are 1, 1.4, 2, 3, 4.5, 6, 8, 11, 15 and 18.

Positioning the detector

The detector can be moved via three motors named detectorx , detectory, and detectorrotation. These motors can be driven by the run or drive commands described in the Section called Drive commands. The commands how to change motor parameters like Precision, SoftZero etc. are described in the Section called SICS motor handling. The axes of the detector motors are defined as:

detectorx

An increasing value moves the detector away and a decreasing value towards the sample position.

detectory

moves the detector laterally by a maximum of 480 mm in order to increase the accessible q-range at any detector position.

detectorrotation

rotates the detector around its vertical axis to reduce parallaxes effects.

	Warning
	The BerSANS software package for the primary data reduction does not handle the detector rotation.

Instead of driving the motors individually one can refer to all motors as a whole by the dt command. The command dt without other parameters will yield a listing of the current position of the detector:

						dt 
Status listing for dt 
dt.x = 18800.048828 
dt.y = 0.004000 
dt.phi = 0.414000

To move the detector you can call dt with parameters defining the new position of the motors, e.g.

						dt x = 800 y = ++100 phi 0

The = sign is not mandatory and can be left out. The command above drives the motor detectorx to the position 800, the motor detectory to a position 100 mm further into y-direction, the motor detectorrotation to position 0. All the three movements are done parallel. Relative movements can be performed by preceding an -- or ++ to the motor position. The whole set of parameters valid for the dt command is described in the the Section called Special SANS commands about special SANS commands.

Positioning the beam stop

The beam stop can be adjusted by two motors named beamstopx and beamstopy. They can be driven by the run or drive commands which are described in the Section called Drive commands. The commands how to change motor parameters like Precision, SoftZero etc. are described in the Section called SICS motor handling. The axes of the beam stop motors are defined as:

beamstopx: moves the beam stop horizontally.
beamstopy: moves the beam stop vertically.

Instead of driving the motors individually one can refer to both motors as a whole by the bs command. The command bs without other parameters will yield a listing of the current position of the beam stop:

						bs 
Status listing for bs 
bs.x = 0.300000 
bs.y = 2.500000

To move the beam stop you can call bs with parameters defining the new position of the motors, e.g.

						bs x = 2 y ++10

The = sign is not mandatory and can be left out. The command above drives the motor beamstopx to the position 2 and the motor beamstopy to a position 10 mm further into y-direction. Both movements are done parallely. Relative movements can be performed by preceding an -- or ++ to the motor position. The whole set of parameters valid for the bs command is described in the the Section called Special SANS commands about special SANS commands.

Additionally to the commands for the movement of the two beam stop axes a few other commands have been established:

bsout

moves the beam stop out of the detection area, so that there is nowhere a shadow of the beam stop on the detector. This position is outside the software limits of the motors in the area of the beam stop magazines. In this area an uncontrolled movement could lead to a collisioni with the magazines. Therefore one can not move the beam stop anymore with the bs command after calling bsout, because the motors are fixed automatically.

bsin

releases the beam stop motors and moves them back to the previous position. After calling bsout you have to call first bsin to continue with the movement of the beam stop with the bs command.

bsfree

is a manager command, which releases the beam stop motors, if they are still in the bsout-position. This command should only be used when something went wrong with the SICS server during the time the beam stop was in bsout-position.

bschange [<val>]

allows the user to change the size of the beam stop. Four different sizes are available and can be selected by the parameter <val>. Valid values for <val> are:

1 for beam stop size of 40 mm x 40 mm

2 for beam stop size of 70 mm x 70 mm

3 for beam stop size of 85 mm x 85 mm

4 for beam stop size of 100 mm x 100 mm

The bschange command automatically recognizes the actually used beam stop size, puts it into the empty magazine and picks up the new beam stop. bschange automatically closes the instrument beam shutter, if it was open, but it doesn't reopen it again afterwards. Calling bschange without a parameter returns the number of the actually used beam stop size.

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