The properties of the needed motors and detectors are described above, but several practical problems have to be solved to get the instrument working. Since the idea of the MoWaSt setup is to install all hardware within only a few hours at a syn-chrotron, a lot of effort has been taken to keep the setup as simple as possible for the user. In the following section major problems of implementation and their solutions are described.
3.4.1 Computer network
To reduce cabling during build-up of the setup at a beamline, the control computer and all motor controllers are installed in the experimental hutch. This allows to reduce the cabling to only a few meters, testing of all motors after installation, easy setting of motor limits and rough alignment of the setup, e.g. with the help of an adjustment laser. In beam operation mode it is of course not possible to run the setup from inside the experimental hutch. Therefore a computer network is installed at the beamline, where one network cable is needed to connect the instrument control computer with its clients. The desktop of the instrument control computer is exported via network to a client computer in the control room. In Figure 3.17 one out of several possibilities for the MoWaSt beamline network is sketched.
MoWaSt
IP: 192.168.0.1 @ eth1 Router IP local: 192.168.0.254 DHCP server @ local & wlan
IP uplink: DHCP Experimental
Hutch Control room
eth0 eth1
Otto
IP: DHCP (192.168.0.2) @ eth0
local wlan
eth0
MoWaSt-printer IP: DHCP (192.168.0.100)
MoWaSt-clientx IP: DHCP @ local & wlan (192.168.0.200-192.168.0.220)
Beamline network
Figure3.17: Layout of the instrument network. Only one network cable is needed to run the system from the control room. All other cabling is done in the experimental hutch.
This way of connecting the computers at the beamline provides several
addi-tional advantages: As we will see later (3.4.2) it allows for the synchronization between the SPEC motor-control-software and the CCD acquisition software. If the network is additionally connected to the native beamline network, it is possible to run beamline provided hardware in the MoWaSt’s SPEC session. The MoWaSt control computer can be used as file server for all computers in the network and only one beamline provided IP-address is needed for all computers of the setup.
At the same time the network can be used for a lot more, e.g. license server for simulation software or interface for additional motor controllers. To make use of this flexibility and modularity it is recommended to have some knowledge of computer networks and Linux configuration. Helpful references here are [Lin, Sou]
and the links and newgroups therein.
3.4.2 CCD - Motor synchronization
To be able to take CCD frames depending on motor positions of the MoWaSt setup and to be able to scan with the CCD as detector, it was necessary to implement the possibility of sending trigger events from the SPEC instrument control software to the CCD. To realize that, we chose to include the CCD into the SPEC software in a way that is easy to implement, modular and feasible within a few weeks. We are again using the network capabilities for the SPEC software. In Figure 3.18 the connections for the different parts of the CCD setup are described.
Figure3.18: Sketch showing the connections between SPEC, Winview and the hardware The Princeton Instruments LCX-1300 CCD is controlled by the ST-133 con-troller, which is connected via TAXI interface to a PCI interface card accessible
un-der Windows XP with the WinView CCD acquisition software. A stand-alone-setup of the CCD thus consists of the windows PC connected to the ST-133 controller, which has access to the CCD. This software package provides a dynamically load-able library (dll) usload-able by any Microsoft .net programm. We chose to programm a small UDP server application (Microsoft .net Visual Basic), which is able to control the most common features of the WinView software through the winx32lib.dll (see Appendix A.1 for source code). As described above (see section 3.3.1) the LCX-1300 chip has a full frame architecture and thus needs an external shutter. We chose to include a UNIBLITZ (Rochester, NY, USA) XRS6 fastshutter into the setup. It has a 6mm wide aperture, which can be closed magnetically with a Pt/Ir-alloy blade (x-ray transmission 10−14 up to 20keV) within 3.2msec with up to 50 repetitions per second. It is controlled by a VCM-D1 UNIBLITZ controller. As sketched in figure 3.18 this controller is connected to the ST-133 CCD controller via a standard BNC cable using a TTL (5V, active-high) signal as trigger event for opening and closing the shutter. As an option it is possible to open and close the fastshutter directly from SPEC via a RS232 connection and with the help of a small macroset called fastshutter.mac. This allows opening the shutter perma-nently during point detector operation of the system. In CCD operation mode of the system the UDP server is accessed by a SPEC macroset (see Appendix A.1 for source code) representing the client side.
3.4.3 SDD implementation
As described in section 3.3.2 an energy dispersive silicon drift detector system can be used to detect fluorescence photons during scanning. Although the SPEC soft-ware supports low level communication to multi channel analyzers (MCA) such as the Roentec SDD, neither user-friendly commands nor a standardized data display was available.
Again a macroset was developed to access the roentec detection system via all standard SPEC commands, to allow user-friendly configuration of the detection system, to provide a rough energy calibration and to display and save the MCA data in reproducible manner. The source code of this set of macros can be found in appendix A.2. Since all MCA devices need a comparable software environment, it was possible to adapt the Roentec macroset for the silena Si(Li) detector at the ID22 beamline.