## 2 Instrumental Concept and Performance
### Sample Positioning  
Horizontal sample alignment is achieved with a linear translation stage (LS-180, Physik Instrumente GmbH & Co. KG, Karlsruhe, Germany) with a maximum load of 100 kg, an operating displacement of 508 mm at a maximum speed of 150 mm s\({}^{-1}\), and a bidirectional repetition accuracy of \(\pm 0.1\) mm. The linear stage is driven by a two-phase bipolar half-coil stepper motor (model PK-258-02B, Oriental Motor, Tokyo, Japan). The position is monitored with a linear optical encoder with RS-422 quadrature signal transmission (LIA-20, Numerik Jena, Jena, Germany). The entire setup will be placed on an optical breadboard based on a lifting table, which ensures the vertical sample alignment. The control unit was built according to ESS specifications ensuring compatibility with ESS control standards. Figure 5 shows the corresponding circuit diagram for the custom built crate. The translation stage is labeled with \"AXIS 1\". For testing purposes, a two-axis goniometer was also integrated (motor top, motor bottom, encoder top, and encoder bottom). However, in the framework of the foam cell SE, this goniometer is not used.  
Figure 4: Evolution of the temperature of a tetradecyltrimethylammonium bromide (C\({}_{14}\)TAB, \(c=3.5\) mM) foam in the foam cylinder without (**a**) and with (**b**) aluminum foil cover. The temperature was monitored using three Pt-100 temperature sensors at positions depicted by the inset. The setpoint of the water bath thermostat was adjusted to 50 °C at the beginning of the experiment and was reached after ca. 8 min.  
The custom built 19-inch crate is equipped with 24 V (BLOCK Transformatoren-Elektronik GmbH, Verden, Germany) and 48 V (Mean Well Enterprises, New Taipei City, Taiwan) power supplies. The latter one provides power for the motors while the first one provides the power for the control unit. The control unit is based on an Ethernet fieldbus system (EtherCAT, Beckhoff Automation GmbH & Co. KG, Verl, Germany). An embedded PC (CX5130) is connected to a potential distribution terminal (EL9189) and a stepper motor terminal (EL7041), which ensure the motor movement. A digital input terminal (EL1808) and a digital output terminal (EL2819) are connected, sending and reading the motor positions. Additionally, an incremental encoder interface terminal (EL5101) is added to read the encoder signal out.  
The embedded PC communicates with the hardware of the linear stage via the Twin-CAT 3 software. This signal is forwarded to the Experimental Physics and Industrial Control System (EPICS) [35], which will be the unified control software for beamline devices at the ESS and is able to control the devices and monitor their state. The EPICS is used by the Networked Instrument Control System (NICOS) [36], which offers a graphical interface for users and is the outermost layer of the instrument control structure at  
Figure 5: Circuit diagram of the motion control crate. Beside the translation stage, a two-axis goniometer is also controlled by this crate.  
the ESS. Further details regarding instrument control and data streaming are described elsewhere [37].  
From 2015 until 2019, the ESS operated a dedicated testbeamline at the Helmholtz-Zentrum Berlin, also known as V20 [38; 39]. Here, a fully workable environment, mimicking a future ESS instrument, was built up for testing and development. The linear stage was successfully tested at this instrument, proving the compatibility with the ESS standards in terms of control, interaction with other devices, and data logging.  
The integration of the peripheral SE components into NICOS also allows programmable measurements with automated changes between the three foam cells and the measurement height along each cell, varying temperature, and gas flows.