4. The Experiment

4.1 First

All the sample equipment you applied for will be at the instrument around 10am on the day you begin. It is your responsibility to get the sample record sheet from the DAC (Data Acquisition Central) and put it in the box on the side of the instrument. If there is something wrong on the sample sheet you must inform your local contact. First, the sample has to be placed in the beam, for the different sample environments see that respective heading. All equipment has a note saying how far down the center of the beam is, to make it easy for you to put your sample at the right height.

4.2 Safety

The safety system is composed of an electrical and a mechanical system. Your local contact will go through the safety system with you.

4.3 Computer introduction

The OSIRIS computer is a Digital Alpha workstation running OpenVMS. There are four desktops on the computer: data monitor is used to monitor the experiment and run all the command files; osimgr is reserved for the instrument responsible; Analysis for analysis; and User is for the user to do with what ever he wants.

Since VMS might not be familiar to all users, we start with some VMS commands. To find out where your are your can type either where or show def and then to change your directory simply type set def directory. Directories are always written within square brackets, you either type the full name or if you want to go down to dir1 you need only type [.dir1] and if you want to go up one step you can use [-]. You create a new directory by writing create/directory [.name]

If you open a new window you will be in the [osiris] area. If your name is Smith and you want to change directory to your directory you would type

set def [.users.smith] 

set def [osiris]

set def [-.-]

If you want to print a postscript file, this is most easily done by using one of the plaser scripts. The printer in the DAC is number 2 and if you want to print to it just type plaser2 fil.ps. The printer on the 3rd floor in R3 (photo copier room) is number 1.

organisation

The area you work in on osiris is osiris$disk0:[osiris]. Programmes being developed are in [.alpha], and other programmes are in [.programmes]. In [osimgr.tcb] are all the files with the Time Channel Boundaries. They contain tcb files which should not be changed by the user. These files should only be edited by the ochange command.

OSIRIS data that is directly accessible are in the areas OSIRIS$DISK1:[OSIMGR.DATA] and OSIRIS$DISK0:[OSIMGR.DATA]. You access these areas via the logical name osiris_data. OpenGenie is configured to automatically search these directories.

your files

Users should only keep files in the [osiris.users] directory and on scratch$disk:[osiris]. The files in [osiris.users] will be saved for the current cycle but if the disk space is needed they will be deleted during the next cycle. When you have finished you experiment, copy the files you want to save to your own account on user$disk. If you have not got an account the computer support will help you get one.

4.4 Setting up to run

Running the experiment and most of the sample environment is controlled by the computer.

d-spacing

To begin with you need to decide what d-spacing range you want to measure. You can choose from the values in table d-range

drange range 

$ cset c_ph6 3180
$ cset c_ph10 5056
$ load [osimgr.tcb]l2.tcb 

Sample environment

There is usually one temperature sensor on the sample, and another in the cryostat/furnace. They are connected to the EuroTherm in the cabin. The right side of it (temp) is used for controlling the cryostat and the left side (temp1) for controlling a furnace.

All CAMAC (Computer Aided Measurement And Control) parameters are checked and changed with the two commands cshow and cset

Depending on your sample environment, there are different values that you want to set, see section SE. The temperature is controlled by setting either heater or temp depending on what equipment you use. For the cryo-magnet he magnetic field is set with the command file magset value where values is the field in Tesla.

When you eg use the orange cryostat or furnace, to set the temperature, you typically type

$ cset temp/value=50/range=10/control

$ cset temp/devspec=number

The heating power is set in percentage of the maximum voltages, (which is set by hand on the physical heater, also done by your local contact), with the parameter max_power. To see what power is presently used cshow power/enq. Note that if you are controlling on temp1 and not temp you just replace temp1 for temp

4.5 Collecting data

The current status of your experiment can be read on the dashboard. If there is no dashboard on your screen you can start one with the command stat on and conversely you turn it of with on replaced by off. There is a "windowed" version of the dashboard, which is started with the command dash if you prefer that.

If e.g. temp is not display in the dashboard you can "turn it on" by

cset temp/disp.

4.6 Command files (VMS)

You are now ready to write down your whole experiment in a command file. A command file would typically look like this:

$ Set Verify
$
$ cset max_power 10
$ cset temp/value=200/range=10/control
$ cset temp1/value=200/range=10/control
$
$ drange 1 
$ change title """new title"""
$ begin
$ waitfor 30 uAmps
$ end
$
$ drange 2 
$ change title """new title"""
$ begin
$ waitfor 30 uAmps
$ end
$
$ cset max_power 30
$ cset temp/value=500/range=10/control
$ cset temp1/value=500/range=10/control
$
$ drange 1 
$ change title """new title"""
$ begin
$ waitfor 30 uAmps
$ end

4.7 Finally

When you have finished your experiment the sample needs to be taken out of the beam. As soon as you have taken it out you should measure the induced radioactivity and act according to table radiation