[FFA_CEBAF_Collab] [EXTERNAL] Re: correction strength requirements

[Brooks, Stephen]

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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