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Re: Feedthru material



Hello all,

I performed extensive tests at BNL and for the CLAS feedthroughs quite a 
while ago on Delrin, Noryl and a polycarbonate material (I can go though 
my notes but I don't recall the specific name at the moment or maybe I 
don't really want to recall because it was terrible).

The glass-filled polycarbonate material showed considerable surface 
current leakage after a relatively short time of operation which even 
tripped the HV supply. This was unacceptable. Note that most 
manufacturers provide only data on bulk arc resistance (that's the 
standard), not surface arc resistance (I think for obvious reasons).

Delrin and Noryl have excellent electrical properties but Delrin is soft 
and difficult to machine and for tight tolerances. We chose Delrin for 
the BNL detectors because Noryl was very expensive (at the time) and 
new. We chose Noryl for the CLAS drift chambers feedthroughs and these 
have proved to be very reliable over ~ 15 years of operation. I should 
also note that the CLAS feedthroughs were also injection molded with a 
specially designed metal trumpet because of the geometry of the detector 
and to reduce the electric field gradients at the wire entrance into the 
gas volume (=expensive feedthroughs).

Best regards,
Fernando



Curtis A. Meyer wrote:
> Hi Tim -
>
>  there were a number of concerns raised about Delrin and ageing. Noryl 
> is a safe
> material for a chamber. As per the glass filled poly carbonate, we 
> will need to do
> a bit of research.
>
>   I think that we can arrange a time on Wed. or Thur. we just need to 
> get the relevant
> people on board.
>
>  Curtis
> Tim Whitlatch wrote:
>> Hi Curtis,
>>
>> The delrin is cheaper as well as glass filled polycarbonate. We 
>> should have a meeting Wednesday or Thursday to discuss info we 
>> received from vendors recently.
>>
>> Tim
>>
>> Curtis A. Meyer wrote:
>>> Hi Tim -
>>>
>>>   probably the main reason that we went with Noryl was that it was 
>>> cheap, could
>>> be bought in rods, and had been safely used in drift chambers before 
>>> without aging
>>> or out-gassing issues. I think the latter reason puts some limits on 
>>> what we can choose
>>> for material.
>>>
>>>     Curtis
>>> Tim Whitlatch wrote:
>>>> Hi Curtis,
>>>>
>>>> If another material other than Noryl is used, what are the 
>>>> electrical requirements?
>>>>
>>>> 20V/mil dielectric strength?
>>>> Max dielectric constant?
>>>>
>>>> Tim
>>>>
>>>
>>>
>>
>
>
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