Help! There's no beam!

If you are not finding any signal from your sample, here is a checklist of things to track down where the problem could be.

Is there beam in the I0 ion chamber? If not:

• Make sure the hutch is closed and the shutters are open (green indication on the hutch panel)
• Ensure that there is beam in CESR and that it is not currently injecting
• Make sure the mono and the undulator are both at the same energy
• Try tuning the mostab knob (see below); especially for the Si(311) mono, the intensity is quite sensitive to the tuning

Is beam in I0 but not I2?

• Make sure the fast shutter is open by typing 'opens' in spec
• Ensure that the incident energy is not above the mirror cutoff (generally 16 keV)
• Check that there is no attenuation in front of I2
• Check that the JJ slits are centered on the beam
• Try tuning the mostab to optimize counts in I2 (see below), it is generally much more sensitive to tuning than I0

Is there beam in I2 but not the detector?

• Check that the sample is actually in place and aligned in the beam
• Check that the incident energy is above the absorption edge
• When using the Vortex:
  • Make sure the detector is pointed at the sample and can see fluorescence
  • Ensure that the electronic window is set correctly on the detector
• When using DAVES:
  • Make sure the emission energy is set to something reasonable ('do goHome.mac' can often help here)
  • Double check that the cryostat cap is oriented correctly (large window facing the analyzers), if applicable
  • Check that the helium bag is inflated and in the right place
  • Ensure that the reflected beam is within the ROI

Tuning for X-Rays

At a given energy, the mostab can be used to maximize the flux getting to the sample. Tuning the mostab knob left or right adjusts the angle of the second monochromator crystal and thus can be used to control the amount of beam that passes through the mono. The sensitivity of the intensity to the mostab tuning depends on the Darwin width of the reflection off the monochromator; thus, when using the Si(311) mono the intensity will be more sensitive to the mostab than when using the Si(111). When tuning, it is generally best to monitor the signal in the I2 ion chamber so that flux at the sample is maximized. If you do not find any intensity even after tuning, go to the Help Finding Beam page.

-- ChrisPollock - 17 Dec 2022