[Isotope-prod] Optimization question

[George Neil]

You really don't get significant conduction cooling through the foil in 
these 400 micron thick windows.  Almost all the cooling comes from the 
N2 gas flow.  That being said a narrower dimension leads to superior 
strength so that thinner foils/less energy deposit can occur.

George


On 7/1/2016 10:04 AM, Joseph Grames wrote:
> Be mindful that linear rastering leads to dwell times at the end points, albeit closer to your heat sink.
>
> Joe
>
> ----- Original Message -----
> From: "Pavel Degtiarenko" <pavel at jlab.org>
> To: isotope-prod at jlab.org
> Sent: Friday, July 1, 2016 10:00:07 AM
> Subject: Re: [Isotope-prod] Optimization question
>
> A logical extension (and simplification) of the previous argument
> regarding the circular beam rastering: linear rastering.
>
> We could improve thermal and mechanical conditions for all windows, and
> make beam currents up to 5-10 mA accessible, if we switch from the
> circular shape of the raster and the window to the one-dimensional (say,
> vertical) narrow slit shape. We can make the window's horizontal
> dimension small, I guess it could be down to 3-5 mm, and the vertical
> dimension reasonably large (few cm). The narrow beam (say, 200 micron
> sigma) is rastered vertically with some reasonable frequency (say, tens
> of hertz). The power deposited in such window will be spread vertically,
> and it will have a very short thermal conduction path to the cold mass
> of the window holder, both to the left and to the right. The solution
> improves thermal parameters for the window dramatically, and at the same
> time the mechanical stresses in the window are also expected to be
> decreased, as the window span holding vacuum becomes much smaller than
> in the circular case.
>
> Such scenario may actually end up requiring comparable or even smaller
> volume of the target gallium than the present beam sizes - need some
> simulations for a real comparison.
>
> Best regards,
> Pavel
>
> On 06/22/2016 03:48 PM, Pavel Degtiarenko wrote:
>> I'd like to revisit one optimization question that was standing from
>> the very beginning.
>>
>> We assume presently that minimizing volume of the isotopically pure
>> target is paramount in this problem and we have to design windows,
>> radiators, and targets that would survive extremely high power
>> densities, to the limits of impossible. But there might be an optimal
>> overall solution, in which the target volume is few times larger than
>> the absolute minimum. The target itself, and the Cu67 separation
>> process would be more expensive (most likely less than linearly). But
>> the cost increase would be compensated by avoiding risky and therefore
>> expensive engineering solutions. So may be the optimum solution would
>> be using larger diameter targets and windows that could be cooled
>> easier. I would suggest to consider for the proposal finding the beam
>> diameter that we know could be run safely, base all estimates on that,
>> and include further optimization as one of the goals of the proposal.
>>
>> One of the solutions to consider could be a circular beam rastering
>> when beam position at the target goes in circles at a constant radius.
>> The target does not fill the whole cylinder volume, but is placed in a
>> cylindrical layer, say, 5-10 mm thick, with the core of the cell made
>> of the same material as the whole cell. The Ga/Zn target volume then
>> goes linearly (not quadratically) with increasing radius, so that
>> might be a comfortable variant for the optimization.
>>
>> Best regards,
>> Pavel
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