sPHENIX HCal discussion

[John Haggerty <haggerty AT bnl.gov>]

John et al.,

Sorry I couldn't stay to discuss this but here are a few more comments 
based on what I did hear:

Things to do next:

1- make sure all the preamps are actually powered and reading their 
thermistors
2- make sure the preamp thermistors are actually attached somewhere we 
want to know the temperature
3- stick a temperature sensor on the hottest IB component (I guess 
that's the LDO)
4- take another couple hours of data

I'm not sure whether it makes sense to try to thermally isolate the 
sector completely from the environment, we should kick this around a bit 
more, and I'll talk to Rob about it; he has a good feeling for thermal 
issues.

I'm no expert on thermal management, but I've played around with things 
like this:

> https://www.powerstream.com/temperature-rise-in-an-electronics-enclosure.htm

to see if what we observe seems consistent with what we expect, and it 
seems to me to make sense to provide an air inlet so we have a 
controlled way for air to enter the sectors rather than relying on 
random leaks.  I think the only way we could do better would be to 
thermally attach the interface board to a cooling plate which would be 
in thermal contact with the sector structure (making the entire IHCAL 
the heat sink), but I sort of doubt it's warranted based on what we've 
seen so far.

Edward asked about the pattern of temperatures, which I think does not 
measure what we want to know, because I'm not sure what the thermistors 
are in contact with (air? aluminum? the preamp?), so I would not draw 
any conclusions without another test (which will also have more of 
them).  I should add that trying to get excellent and long-lived thermal 
contact to thermocouples or thermistors is not so easy; glue tends to 
give way, the sensors are small, and it's not so easy to get the SiPM 
temperatures even in the EMCAL, and it's harder in the HCAL.

I think there is no path to cooling the SiPM's, so we're going to have 
to learn to live with the noise at room temperature, which is less good 
for the IHCAL the the OHCAL, since the neutron dose is less than the 
emcal according to Jin's simulation, but it's not order of magnitude 
less like the OHCAL, but we can only do what we can do.

On 2021-01-05 15:33, Lajoie, John G [PHYSA] wrote:
> Hi John H,
>
> Thanks for showing the slides on the iHCAL thermal tests today, it's
> great to get that rolling. It makes sense that you see temperatures
> similar to the oHCAL sectors.
>
> What I am having a hard time getting my brain around is what sort of
> tests we have to do to convince ourselves that we are OK, and whether
> or not the thermal solution that has been designed for the iHCAL is
> adequate (or needed?).  As I see it there are two things we need to
> address:
>
> - The LDO's on the boards at the end of the sector don't like to get
> too hot. I think you saw a 60C peak? Obviously with the colling tube
> and vanes in the bay that will help somewhat but can we put a
> thermistor on the LDO's?
>
> - The iHCAL is in a different situation than the oHCAL. The oHCAL can
> just radiate all it's heat out the back, while the iHCAL is sandwiched
> between the EMCal and the cryostat.  A standalone sector test that
> shows temperatures similar to the oHCAL is fine, but what happens when
> it is installed? I really don't know how to answer this question. It
> may be that all the heat is transferred to the frame and exits though
> the end rings, but I'd feel more comfortable with an expert telling me
> that was a valid assumption.  In particular I don't want to find we
> present some sort of heat load to the cryostat.
>
> I absolutely do NOT want to over complicate the iHCAL thermal testing.
> Before we go further, is there some additional expertise at BNL that
> we could tap into to sanity check our approach?  If we could get some
> input that would better define the key tests we have to do we could
> save a lot of time.
>
> Regards,
>
> John
>
> John Lajoie
>
> he, him, his
>
> Professor of Physics
>
> Iowa State University
>
> (515) 294-6952
>
> lajoie AT iastate.edu

---
John Haggerty
haggerty AT bnl.gov
cell: 631 741 3358