Re: collimator extension

[Richard Jones <richard.t.jones@uconn.edu>]

Jim, my answers below. -rtj
> Richard
>
> There is a lot I do not understand about running in Hall b and how 
> that effects halld. I do not know if I agree or disagree with you but 
> I do know I do not understand your arguments.
>
> I will try  explain what I do not understand.
>
> "There will be a hot spot at the front of the collimator that may 
> require some time before personnel access to the equipment there will 
> be permitted."
>
> Is there any knowledge about how long one needs to wait before entering?
> Will this be a few hours at Hall-D or a few Days?
This is a good question for radcon.  There will be a continual 5W 
irradiation of that spot during high-intensity running.  My guess is 
that this is a reasonably low value, but may be tagged as a "hot spot" 
with the yellow and purple rope.  I think protocol will require is to 
have the area "swept" by a "ARM" before we will be able to go into that 
area at all.
> "I don't think that we want to have to wait for a downtime period 
> before we can check what is going on when we find the tagging 
> efficiency starts to slide." How does letting you switch between no 
> collimator, wide collimator,  and normal collimator help to diagnose 
> why the tagging efficiency is degrading?
Suppose that the active collimator says that the beam is centered, but 
we see dropping tagger efficiency.  One explanation is that the beam 
emittance is degrading, or the virtual focus is bad.  We can find that 
out by removing the collimator and allowing a larger fraction of the 
beam to pass.
>
> "I can also imagine run periods where the machine beam quality is 
> degraded and we might want to run with reduced polarization and 
> increased beam time on target.  This is not infrequent during 6GeV 
> running during the present era, and I guess it will happen during the 
> 12 GeV era as well."
>
> How does this cycle typically look like? Does the beam divergence, 
> size, position stability just change? Do the bad periods last minutes, 
> hours, or days?
All of the above.  Experimentalists sometimes groan when the operator 
calls and says, "I just want to tune something up in the XXX, give me a 
few minutes." (where XXX is somewhere in the machine or switchyard).
>
> If it takes only a few hours to gain access then you could build a 
> collimator with inserts which would let you change the diameter in a 
> short access. This would only make sense if the dose is not too high 
> and the time for access not too long. I have no knowledge concerning 
> the time scales.
Generally diagnosing something like this is going down through a list of 
possibilities, where collimation is only one of them.  Of course, if you 
always know what is wrong then having remote access to switch things in 
and out is less necessary, because the number of times you need to do it 
are few.
>
> I assume that when the passive collimator moves the  active collimator 
> is stationary.
No, they are pinned together.
>
> I assume the wide collimator would then have 5mm diameter to match the 
> active collimator.
That would be a good choice, I think.
>
> Are there issues with Radcon about removing the collimator?  Do we 
> need an interlock?
Should ask them about that.  My guess is that a current interlock at the 
photon beam dump is going to be installed anyway, and this will be 
sufficient.
>
> Jim
>
>
>
>
>
> Richard Jones wrote:
>> Jim,
>>
>> It's ok if you disagree.  Those are my arguments.  I cannot make them 
>> any more convincing by talking about them.
>>
>> Richard Jones
>>
>>
>> Jim Stewart wrote:
>>>
>>> Sorry Richard but I don't really follow this. Can you call me at 757 
>>> 269 5470 some time? I think this is something which will be 
>>> infinitely easier to discuss over the phone.
>>>
>>> Jim
>>>
>>> Richard Jones wrote:
>>>> Jim,
>>>>
>>>> The short answer is because that is what we had in Hall B, and we 
>>>> found it very useful when there were problems with the beam line.  
>>>> There will be a hot spot at the front of the collimator that may 
>>>> require some time before personnel access to the equipment there 
>>>> will be permitted.  I don't think that we want to have to wait for 
>>>> a downtime period before we can check what is going on when we find 
>>>> the tagging efficiency starts to slide.  I can also imagine run 
>>>> periods where the machine beam quality is degraded and we might 
>>>> want to run with reduced polarization and increased beam time on 
>>>> target.  This is not infrequent during 6GeV running during the 
>>>> present era, and I guess it will happen during the 12 GeV era as 
>>>> well.  Basically it is a means to switch between conservative and 
>>>> optimal running conditions for GlueX physics.
>>>>
>>>> Richard Jones
>>>>
>>>>
>>>> Jim Stewart wrote:
>>>>> Hello Richard
>>>>>
>>>>> Maybe you explained this to me already but can you tell me why we 
>>>>> need to switch between no collimator, normal collimator, and "wide 
>>>>> aperature" collimator remotely?
>>>>>
>>>>> Jim
>>>>>
>>>>
>>>
>>
>