[Isotope-prod] Optimization question

[Pavel Degtiarenko]

The effect of conduction does not depend on thickness as both energy 
deposited and energy conducted are proportional to the thickness. In 
large thin windows N2 cooling prevails because the conduction path is 
too long and the area is large for N2 cooling. If we shorten the path by 
a factor 20-50, the conduction will do the job. It all can be checked 
numerically of course.

Pavel

On 07/01/2016 10:09 AM, George Neil wrote:
> 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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