<h3id="org5327e8f"><spanclass="section-number-3">2.2.</span> Turning on the Speedgoat Server</h3>
<divclass="outline-text-3"id="text-2-2">
<p>
Connect to the Speedgoat server computer (see Section <ahref="#org5b65cd0">1.7</a>) and run the <code>BLISS SPEEDGOAT SERVER</code> program on the desktop.
</p>
<p>
A terminal window should be displayed, with the last line being:
<h3id="orgaf433a7"><spanclass="section-number-3">2.4.</span> First interferometer reset to be able to use mode B and C</h3>
<divclass="outline-text-3"id="text-2-4">
<p>
After homing all fast jacks, perform an interferometer reset such that \(r_x = 0\), \(r_y = 0\) and \(d_z = \frac{d_{\text{off}}}{2 \cos \theta}\) (i.e. the distance between the crystals is following the theoretical value).
</p>
<p>
Then, make a LUT over the full stroke.
</p>
<p>
And verify that the feedback regulator is working over the full stroke.
<h4id="orgf4ae640"><spanclass="section-number-4">2.6.2.</span> Bragg scan to find \(x\) crystal parallelism</h4>
<divclass="outline-text-4"id="text-2-6-2">
<p>
Measure the rotation of the output beam along the \(z\) axis.
This can be performed by using a position sensor positioned away from the DCM or using an angular metrology (lens + position sensor at the focal plane).
</p>
<p>
Perform a scan in mode C (i.e. closed loop, \(r_x \approx 0\) during the scan), and measure simultaneously the \(R_z\) motion of the output beam.
</p>
<p>
The \(r_x\) offset can be estimated from the data.
This offset is then included in the interferometer data as an offset.
The cosine function can be fitted from the data and the distance offset can be estimated.
</p>
<p>
The accuracy of the results depends on:
</p>
<ulclass="org-ul">
<li>how well the metrology deformations are calibrated</li>
<li>How close the sensor is from the DCM and how well is the y parallelism between the crystals.</li>
<li>How sensitive and accurate is the sensor</li>
</ul>
<p>
If a quadrant photodiode is used, a feedback loop may be performed between the measured \(z\) motion by the photodiode and the vertical \(z\) motion of the piezoelectric actuators.
This means that:
</p>
<ulclass="org-ul">
<li>\(r_x\) and \(r_y\) are regulated from the interferometers</li>
<li>\(d_z\) is regulated from the photodiodes</li>
</ul>
<p>
Then, by plotting the measured \(z\) motion of the crystals by the interferometers as a function of the Bragg angle, it should be possible to estimate the offset between the crystals.
