A Study into the Long-term Stability of Front End X-ray BeamPosition Monitor Support Columns at Diamond Light Source

C. Houghton, C. Bloomer, L. Bobb, D. Crivelli, H. Patel and J. Melton, Diamond Light Source, Oxfordshire, UKABSTRACT
Sand-filled steel columns are used at Diamond Light Source to support front-end X-ray beam position monitors. This approach is chosen due to the relatively large thermal massof the sand being considered useful to reduce the rate at which expansion and contraction of the column occurred as the storage ring tunnel temperature varied, particularly
during machine start-up. With the higher requirements for mechanical stability for the upcoming Diamond-II upgrade, there is now a need to assess and quantify the current
system’s impact on X-ray beam movement. A study of thermal and mechanical stability has been carried out to quantify the stability performance of the front end X-ray beam
position monitor’s columns and the impact that column motion may have on the X-ray beam position measurement. Measurements have been made over a range of different
timescales, from 250Hz up to 2 weeks. The measured stability of the support column is presented, showing that it meets our Diamond-II stability requirements. A comparison of thestability of the column with and without a sand filling is presented.

Short-Term Stability

Measurement systems/devices used:•••

Laser interferometry system (in grey),laser source mounted to the top of theX-ray Beam Position Monitor (XBPM)
vessel.
Four piezoelectric accelerometers(blue squares) placed on the floor,
column base, column top and XBPM
mounting plate.
Seven thermal sensors (circles); redfor column thermal sensors, purple forair thermal sensors and green for asensor bolted to the floor.

The steel column's height was tracked forweeks with and without sand, accounting
for environmental factors like airtemperature, pressure, and humidity.

•••

A drawing of the XBPM and its support
column, with the locations of the differentdevices.

•Long-Term Stability
During a typical week, the electron beam is turned off to allow for machine development,
during this time the machine cools, this can be seen clearly on the height change of thesteel column.

The horizontal transmissibility ratio of the XBPM support
column bottom plate to the XBPM mounting plate••The change in the support column height measured with and without sand filling thecolumn••••

Horizontaltransmissibility ratio
similar both with andwithout sand up to∼120 Hz.
Amplification of motion
above 30 Hz in bothdatasets.
Fewer damping
troughs without sand
140 Hz and 166 Hz
suggesting larger
amplification. at thesefrequencies
Vibration of the bottomof the column and topof the XBPM
mounting plate go outof phase at 84 Hz,
indicating a resonanceof the system.

With sand transmissibility
ratio is close to one acrossthe frequency range,
except for a peak at 50
Hz-70 HzNew relatively large peaks
at 167 Hz and 193 Hz
without sand, suggestingthat the sand works todampen theseresonances.

Minimal difference between the steel column with and without sand
Variation in column height with sand ~6.5µm
Variation in column height without sand ~8.4µm
Over 11 days empty column sees a variation of column height of 10µm

The vertical transmissibility ratio of the XBPM support
column bottom plate to the XBPM mounting plate

CONCLUSION

The change in the support column height and the average column temperature measured
with (top) and without (bottom) sand filling the column•••

The mechanical stability of an XBPM support column has been assessed and results
show that sand-filled steel columns effectively maintain the required thermal andmechanical stability for supporting front-end X-ray beam position monitors at DiamondLight Source. Through laser interferometry and accelerometer measurements, both shortterm and long-term stability were examined, highlighting the negligible impact of sand on
high-frequency mechanical stability and its beneficial role in reducing vertical column
variations over extended periods. These findings verify the columns’ suitability for theupcoming Diamond-II upgrade, ensuring accurate and reliable X-ray beam position
measurements. The current sand-filled steel columns are sufficiently stable to meet theDiamond-II requirements and will remain during the upgrade.

Clear correlation between support column height and average column temperature.
User beam returned to the machine at ≈ 200 Hrs.
The column temperature takes 5 hours to return to the level before the beam dump
when it is filled with sand.

For more information, please contact Claire Houghton at claire.houghton@diamond.ac.uk