[FFA_CEBAF_Collab] [EXTERNAL] RE: correction strength requirements

[Berg, J Scott]

And operationally, we certainly ran some correctors at their limits.

-Scott

> -----Original Message-----
> From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org> On Behalf Of
> Brooks, Stephen via FFA_CEBAF_Collab
> Sent: Friday, August 5, 2022 11:24 AM
> To: ffa at cebaf <ffa_cebaf_collab at jlab.org>; Jay Benesch <benesch at jlab.org>
> Subject: [FFA_CEBAF_Collab] [EXTERNAL] Re: correction strength requirements
> 
> The main reason for dipole (horizontal and vertical) correction is
> misplacements of magnets when installed.
> 
> +/-0.25mm is a reasonable assumption for the alignment errors after survey
> into place.  Suppose the largest gradient in any FFA magnet we're
> considering is 60 T/m.  Then the dipole corrector field should be
> 
> 0.25mm * 60 T/m = 15mT = 150 Gauss
> 
> In CBETA, I remember we actually managed more than this, about 300 Gauss.
> This headroom is useful in case we need to do multi-orbit correction (send
> different orbits in different directions).
> 
> The quad correction will be set by magnet quad errors and temperature
> variation.  Suppose we correct the quads to +/-0.1% gradient during tuning
> (I've done this here in my office, CBETA managed +/-0.05 but with easier
> magnets).  Then, the gradient correction required for that is
> 
> 0.1% * 60 T/m = 60 mT/m
> 
> You'll also have a temperature coefficient of around 0.1% per degree(C), so
> may want to provide 2x or 3x this value in case the temperature is off by a
> degree for some reason.
> 
> We did something very like this for CBETA, air cooled (not even a fan), so
> I think it's possible to do here.  Although we might want to take advantage
> of the water channels in the PM aluminium casing to also cool the
> windowframe inner coils a bit.
> 
>      -Stephen
> 
> ________________________________________
> From: FFA_CEBAF_Collab <ffa_cebaf_collab-bounces at jlab.org> on behalf of Jay
> Benesch via FFA_CEBAF_Collab <ffa_cebaf_collab at jlab.org>
> Sent: 05 August 2022 11:11
> To: ffa at cebaf
> Subject: [FFA_CEBAF_Collab] correction strength requirements
> 
> Colleagues,
> 
> I vaguely remembered that no meeting is scheduled after waiting in the zoom
> room.   I was going to ask a question today: How much correction capability
> is required of the external "picture frame" aka Panofsky magnets?  I threw
> together a design with 23 cm square clear bore and low current density in
> the conductor, 1 A/mm^2.  Dipole 70 G.  Quad 5.5 G/cm aka 55 mT/m.  Current
> density could easily be increased to get 100 G, ~1% of permanent magnet
> dipole.  Quad is another matter.   What's a reasonable target?
> 
> Bore is relatively large because there needs to be mounting and alignment
> gear for the permanent magnets inside it.  Even if the correctors are ~10
> cm shorter than the permanent magnets (PM), so alignment is handled in 5 cm
> at each end, there will still need to be a rigid support under the PM
> within the corrector.   Likely a box beam of some sort for stiffness.
> 
> Jay
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