sPHENIX HCal discussion

[Stefan Bathe <stefan.bathe AT baruch.cuny.edu>]

Hi John,

The inner HCal prototype has all 48 preamps with 48 thermistors installed and as such is ready for a second thermal test.

Regards,

Stefan

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Stefan Bathe

Professor of Physics
Baruch College, CUNY

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On Jan 6, 2021, at 12:47 PM, Lajoie, John G [PHYSA] <lajoie AT iastate.edu> wrote:

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
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