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Messages - Ji-Gwang Hwang

MHz-bandwidth magnets are widely used in Hadron machines as well as therapy machines for a fast switching (for machine projection) and a fast kicker magnet. This is also necessary to inject or extract beams to/from a ring. But these kickers are using a ferrite core since this can achieve the field requirement.
   M.J. Barnes:

Recent progress in material research, particularly on Magnetic Alloy, allows accessing that bandwidth (a few MHz) for the core, which is used for a magnetic-alloy-loaded cavity.
   C. Ohmori:

 Hello Laura,

It is good to hear that you did the test with accelerometers. In general, the sensitivity of the accelerometers (depending on the model and frequency) is an order of magnitude better (less than 100 nm) than the BPMs (~ 1 um). This could explain the discrepancy between the two monitors.

If the vibration amplitude is changing daily (especially more in summer), the cooling system would be the source since the water flow/pressure is variating to fight against the temperature raising in the tunnel or circumstance. But I am not sure whether the cooling water could drive the 50 Hz noise. In my case, the compressor of the chiller was working with that frequency which is equivalent to the frequency of the main powerline in Germany.

Best regards

Ji-Gwang Hwang
We have recently opened a doctoral student position to work on beam diagnostics/dynamics:


Feel free to ask any questions.

Ji-Gwang Hwang
 Dear Laura

It is a bit different issue but I have observed the 50 Hz ground motion in our optical table with a vibration sensor. We found that the source was small chillers installed onto a vibration damped carriage. The 50 Hz noise disappeared (please see the attached figure) when the chillers are off for the summer shutdown.
It may possible to check the motion with a vibration sensor. Then, it would be clear that the motion is real or artefact.

Best regards

Ji-Gwang Hwang
Similar work has been done in Metrology Light Source for a primary radiation source standard but with a different approach (scraping from high-current to a single electron and cooled photodiode).

See Figure 12 c of Publication in PRST-AB:

It looks like the previous measurement from MLS has a better signal-to-noise ratio.
What would be the advantage to use the high-efficiency PMT?
Need help? / Re: Coupling Synchrotron Radiation into Fiber
September 17, 2021, 11:56:25 AM
 Dear Johannes

Our group had the idea to couple SR light into an optical fiber to convey the light to a fast photodiode (with an active area of 200 um^2) and we tried a proof-of-principle using a liquid light guide (something like: at an optical table with SR since the liquid cable has a large inlet aperture, high transmission, and a large numerical aperture (for easy coupling).

In the test, the transmission was okay and input coupling was easy since that light guide has a large aperture.
But it is difficult to get proper outcoupling optics for the small active area. Due to the large NA, the light is quickly diverse and then it demands a lens close to the output port of the light guide. But this leads to a small magnification that causes the loss of a lot of light intensity. I guess this is the same issue for the streak camera.

Best regards

Ji-Gwang Hwang