[Halld-pid] ST First Tests

[Elton Smith]

HI Fernando, Mark and Werner,

The order for the SiPMs is out and if a change is going to be made, it 
should be done before Hamamatsu gets started. From Fernando's tests, it 
seems wise to revert to the well-tested 50 um sensors for all 
applications, including the ST. Sasha is planning to contact the 
Hamamatsu rep to find out if and when the switch can be made. The 
decision should be made a soon as possible.

Cheers, Elton.

Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite #16
Newport News, VA 23606
(757) 269-7625
(757) 269-6331 fax

On 7/16/12 10:34 PM, Fernando J Barbosa wrote:
> Hi Mark, Werner,
>
> I have been optimizing and testing the ST readout for the 50 um and 
> 100 um SiPMs. There are 4 SiPMs connected together (current sum) to 
> one readout channel on each of two SiPM PCBs (50 um and 100 um). The 
> sensor capacitance is the same in both cases so one optimization is 
> all that is required for fast risetimes for the group of 4 SiPMs.
>
> The prototype is fully functional but I determined that the micro-coax 
> ribbon cable assembly (connects the readout to the breakout PCB) is 
> not good enough due to cross-talk (primarily due to the connectors on 
> these cable assemblies - a single micro-coax cable assembly provides 
> the power to the electronics, 3 bias supplies, 6 outputs [3 channels 
> w/ 3 for ADCs and 3 for TDCs] and has a thermocouple two-wire output 
> for readout). The readout is temperature compensated via thermistors. 
> The workaround has two coax cables (ADC and TDC), in addition to the 
> micro-coax, which bypass the micro-coax signal connections. So, the 
> final design will change but the current prototype will be useful for 
> tests with ST detector prototype.
>
> I have attached two pics: ST50 is for the 50 um and ST100 is for the 
> 100 um. These were taken with a laser and a diffuser stimulating all 4 
> SiPMs in the group. Some comments:
>
> 1. 50 um - Fast pulses with width of 37 ns (~10%-10%)
> 2. 100 um - Fast pulses with width of 125 ns (~10%-10%), step/kink ~ 5 
> ns after peak.
>
> The leading edge slew rate is about the same for both but the 100 um 
> has a slower recovery w/a kink (the quench resistor on each pixel 
> would need to be ~3x smaller for similar recovery but there are other 
> factors at play, i.e. Geiger current) . I will investigate this a 
> little further but these are definitely characteristics of these SiPMs 
> and I will write a GlueX note soon.
>
> In the meantime, let me know if there is interest in pursuing the 100 
> um further. Even though the rates are expected to be in the KHz range, 
> the long recovery time will likely lead to pileup.
>
> Best regards,
> Fernando
>
>
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