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Independent power supplies or families power supplies ??

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Independent power supplies or families power supplies ??

Post  hardy on Fri Jun 27, 2014 12:51 am

Hi there,

For the new ESRF II project, the question is to decide whether each magnets will have its independent power supply (which means about 1000 power supplies) or group the magnets by families and feed one family with one power supply (hence reducing the power supply from 1000 down to about 15 ...).
Pros for independent PS: a lot of flexibility for beam dynamics
Cons: expecting huge problems of reliability, infant mortality problems, fans maintenance, etc.
Alba (Spain), Diamond LS (UK), APS (Chicago), etc use independent PS.
What is your experience ? Whatever is your system (family or independent), would you do the same for a next accelerator ? What is the weak points of your system ? Can you provide me any statistics of failures ? I am of course ready to share ESRF data to feed the discussion !

All the best,

Laurent Hardy
ESRF Operation Manager

hardy

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Re: Independent power supplies or families power supplies ?? -> have both :-)

Post  AndreasLuedeke on Mon Jun 30, 2014 8:12 am

Hi Laurent,
we have about 600 independent magnet power supplies at the Swiss Light Source.
Our 177 quadrupole power supplies have independent PS, but the dipoles (36) are in series as well as the sextupoles (9 families of 24 or 12 magnets).
Since we have three types of dipoles (14deg, 8deg and 14deg "super-bends"), we have a couple of extra windings on the dipoles with correction PS.
While the sextupoles are cabled in families, we have 12 sextupoles (from one family) with extra coils for a sextupole correction with individual PS, too. This provides us with the desired flexibility for the optics.

The data on the number of beam outages caused by magnet power supplies at the SLS can be found in Figure 2 of the article:
Accelerator Reliability Reporting at the SLS (IPAC pre-press release)
It appears to me that our number for the magnet PS are quite good, in particular if you consider the large number.
But only about a third of our power supplies will dump the beam if they fail: a broken corrector likely just stops the orbit feedback; a failure of a Booster PS just stops top-up.

If you want to have the full flexibility in combination with the maximum MTBF, then I would suggest our sextupole solution.
The total number of PS becomes even larger for that solution, but if one of the sextupole correction PS fails it won't dump the beam:
the individual PS have a small effect on the beam and the first order effects of a missing sextupole correction can be compensated by other sextupole correction PS.

Of course there are some limitation. The power supply for the family is fully coupled with the sextupole correction PS. This can be solved if the PS of the family is very slow and
the regulation of the sextupole correction PS is fast.

Another possibility is the "hot spare option": if you have like eight power supplies in one rack, then only seven are connected to magnets and the eighth can be configured
to replace any of the other seven. This does not affect the MTBF, but it reduces the time to recover (MTTR): one mouse click and you have a replacement power supply ready to use.
The defective power supply can be fixed on the next working day, without additional beam interruptions.
If I remember correctly then such "N+1 redundancy power supplies" have been developed for the ILC/ATF-2 project.

Kind Regards
Andreas

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Location : Paul Scherrer Institute, Villigen, Switzerland

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