sPHENIX HCal discussion

["Lajoie, John G [PHYSA]" <lajoie AT iastate.edu>]

Hi John, 

Thanks  - I agree that your list sounds like the right things to do next, and 
if we can get Rob to comment that would help. 

That calculator is fun!  Did you know that a 10x10x10 cm^3 enclosure of 1mm 
balsa wood enclosing 200 Watts will have an internal temperature of 78.56C? 
There goes my afternoon..... 😊

Joking aside, the box calculator is nice but it's like you have two 
enclosures in serial - the first is the iHCAL, the second is the gap between 
the iHCAL and the cryostat? 

Let's NOT bring up the SiPMs again - that's not the point of what we are 
trying to do and it took us a lot of time and discussion to separate the 
issues. 

John

John Lajoie
he, him, his
Professor of Physics
Iowa State University
 
(515) 294-6952
lajoie AT iastate.edu

-----Original Message-----
From: John Haggerty <haggerty AT bnl.gov> 
Sent: Wednesday, January 06, 2021 10:48 AM
To: Lajoie, John G [PHYSA] <lajoie AT iastate.edu>
Cc: sphenix-hcal-l AT lists.bnl.gov
Subject: Re: iHCAL thermal testing

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://urldefense.com/v3/__https://www.powerstream.com/temperature-rise-in-an-electronics-enclosu__;!!P4SdNyxKAPE!WKOKC5U6ZdTpbzBcYoeUVYBen0VuD_dbEAaS-JvPjHeK50ZceeE6IdbnsK5NONChgKE6_aMJOuw$
>  
> re.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