NIMROD Jaws

Nimrod jaws are a set of 6 jaws which work in concert to limit the beam of neutrons reaching the sample (see Jaws Manager for more). The 6 jaws are ordered 1 nearest the beam and 6 nearest the sample.

The parameters, with reference to the diagram in Jaws Manager, are:

Letter	Parameter	Value	Notes
c	Collimator position	0 mm	No collimator so beam tapered from moderator
j1	Jaw 1 position	6458 mm	Distance from moderator
j2	Jaw 2 position	8072 mm	Distance from moderator
j3	Jaw 3 position	12072 mm	Distance from moderator
j4	Jaw 4 position	15450 mm	Distance from moderator
j5	Jaw 5 position	17235 mm	Distance from moderator
j6	Jaw 6 position	19691 mm	Distance from moderator
s	Sample position	19691 mm	Note that the sample is assumed to be at the final jawset
w	Width of moderator	user set
h	Height of moderator	user set
x	Width at sample	user set
y	Height at sample	user set

Setup

The control files for the nimrod jaws are part of the galil motor set up and are per instrument. There is an example in ...\EPICS\support\motorExtensions\master\settings\nimrod_jaws\*.cmd which would need to be copied to C:\Instrument\Settings\config\<instrument host name>\configurations\galil. IOC System tests also exist for the logic.

Jaw centres

The jaws on NIMROD are not centred with respect to the beam, i.e. all jaws being at a centre of (0, 0) will not actually let the beam through. This is due to some of the jaw sets being mounted off-centre during installation.

The expected centres of each jaw set are:

Jaw set	Horizontal	Vertical
1	-0.135	-1.5
2	-0.126	-1.457
3	-0.205	-9.634
4	0.159	-1.460
5	-0.303	-0.801
6	-0.378	-9.507

The numbers above correspond to the jaws being centred around the beam in “real” coordinates as opposed to motor coordinates.