IMPORTANT: size of diamond and goniometer frame for hallD

[Elke-Caroline Aschenauer <elke@jlab.org>]

On Mon, 14 Jul 2008, Richard Jones wrote:

Dear Richard,

Leigh came yesterday to me and showed me also plots from the last studies
from Casa
http://www.jlab.org/~elke/DIMAD-vs-elegant.ppt
His story about the new calculations was by far not as positive.
You can see this also form the plots. In the old studies the beam was not
centered at 0,0 now it is the tails have disappeared but the beam has
become wider. This differences come from nothing else than changing to a
new code, which they claim has been benchmarked against other ones.

As some of this will be presented next week during the CD-3 review I would
like to be a bit more careful and think one more minute about it. I also
think it would be good and run a check with the MC implementing the red
curve as beam profile.

I happy to hear your opinions.
cheers elke




> Date: Mon, 14 Jul 2008 19:44:43 -0400
> From: Richard Jones <richard.t.jones@uconn.edu>
> To: yves roblin <roblin@jlab.org>
> Cc: Hall D beam working group <halld-tagger@jlab.org>
> Subject: Re: size of diamond and goniometer frame for hallD
>
> Yves,
>
> That's great.  The rounder we can make the beam at the radiator the better off we will be, I think.  reducing the
> beam sigma to 0.5mm in x to make it similar to sigma_y at the radiator, keeping it the same at the collimator,
> would be outstanding.  We would have to do more spot moves, but moving the crystal around is relatively quick.
> It also gives us more flexibility in terms of avoiding bad spots on a crystal, less sensitive to large-scale
> deformations of the crystal, and even smaller crystals would be usable.  I would not like to see the spot get
> smaller than 0.5mm in x or y, but making it close to round makes things simpler.  Thanks for the good news of
> these improvements.
>
> Richard Jones
>
> yves roblin wrote:
>
>       Richard,
>
>        Thank you for the information.
>
>
>
>       How small can I make the beam in sigma_x and  not reach a current density that would damage that
>       diamond  (Right now I have sigma_x=1mm and this is what I gave you last year too).
>
>       With our new optics (Double bend achromat), we reduced the emittance by roughly another factor of 2
>       which means  that I can make the beam 40 % smaller for the same quad settings (or relax the quads and
>       keep the beam to whatever size you need). The idea behind a smaller beam is that of course, we would
>       have even less halo.
>
>
>
>       Yves
>
>
>

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