What's the rf cavity phasing for?

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jmc2000
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Joined: Sun May 08, 2011 2:51 pm

What's the rf cavity phasing for?

Post by jmc2000 » Mon Apr 30, 2012 7:48 pm

rf cavity phasing ... summit to do with preparing for the bunch intensity increase above 1.4x10^11 and possibly to 1.6x10^11?

It all looks very mysterious to me...

Kasuha
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Joined: Tue Dec 15, 2009 1:22 pm

Re: What's the rf cavity phasing for?

Post by Kasuha » Mon Apr 30, 2012 11:27 pm

RF cavities are oscillation chambers taking care of accelerating the beam and keeping the beam in bunches. Their oscillation frequency corresponds with spacing between beam buckets - imaginary places where a bunch can be stored (normally only small part of about 32000 buckets is filled with protons). If a proton in the beam bunch is too ahead within the bucket, it gets a slight backwards kick, if it's too behind it gets a slight forward kick from the cavity oscillation. Phasing may have something to do with attempting to correctly synchronize these cavities with the beam and with shaping their oscillation to achieve the best acceleration and the least "seeping" of protons between beam buckets.

adam_jeff
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Joined: Thu Nov 18, 2010 3:07 pm

Re: What's the rf cavity phasing for?

Post by adam_jeff » Thu May 03, 2012 8:21 am

That's right. The complication is that the beam itself places a 'load' on the cavities which changes the shape of the oscillation slightly. That's why when you increase the intensity you have to tweak the phase of the cavities to allow for the extra 'beam load'.

adam_jeff
Posts: 49
Joined: Thu Nov 18, 2010 3:07 pm

Re: What's the rf cavity phasing for?

Post by adam_jeff » Thu May 03, 2012 8:23 am

Oh and the extra complication is that the LHC operates 'above transition' meaning that particles with more energy actually take longer to go round - you have to give an extra FORWARDS kick to the leading particles, and a backwards kick / less forwards kick to the trailing particles... accelerators are pretty weird sometimes.

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