Thanks to Mac, Steve C., and Larry for replies to my questions
about the gas system. My tone seems to have struck M&S, and perhaps
others, as too harsh, judging by the tone of the reply I got. I
apologize for this, because I am not trying to bait anyone, but rather
am feeling nervous about getting the system on which we have all worked
so hard to run successfully. My first message went to a restricted
group of people I thought were directly interested in the questions, but
the reply went to the whole mailing list, which is fine, too. I'll post
this to the whole list as well, hoping that we can continue to have a
useful, preferrably amicable, discussion.
Note that those of us JLab Users out in the provinces may not be
quite up to date on thinking and planning at the Lab. Since the flow of
information in our direction is not exactly torrential, we sometimes
must ask for information. Doing so in this semi-public forum, instead
of picking up the phone, necessarily exposes us to the risk of looking
silly. On the other hand, the public discussion does serve us all as a
way to distribute information more efficiently.
1) The Tigon (Tygon?) gas lines in Regions Two and Three. M&S
inform us that the Tigon exhaust lines in Region Three will be replaced
with nylon before recirculation starts. I'm glad to hear it. Larry
informs us that the Region Two Tigon is used just for blowing dry air on
the circuit boards. Great, my questions were answered.
I agree with Larry that Kadyk and Vav'ra have much more complete
discussions of chamber aging than Blum&Rolandi, but I happened to have
the book handy when I was looking for the data.
2) Chaotic routing of gas lines. OK maybe that wording was a
bit harsh. As I said, it is a small point. But it is a mess right now.
I'm worried about how the upstream end of the magnet will look by the
time Region One, the minitoroid, the target, and all the signal cables
are hooked in. M&S say that by February there will be stainless steel
everywhere except between the manifolds and the chambers, where there
will be nylon. I was talking about the part between the manifolds and
the chambers. Region Two has numerous lines in place already, and they
are the ones which to me look dangerously exposed. So let me ask: is
there a plan to protect these lines or not? And if so, what is it? And
if not, I think we need to do something more than what is there now. My
real motive in asking this is to determine what we need to do for Region
One, for which the gas-line situation will be similar. This is
something which I personally care about.
Perhaps we need to establish who will have responsibility for
this interface-point between the chambers and gas system. If JLab wants
to handle it in isolation from us Users, fine, but let's be clear about
it. I believe we should work together as much as possible to integrate
our separate components into a working whole.
3) Control of gas in the Hall. First I have to say that there
are 18 equally important chambers in this apparatus, and the only envy
some of us little guys feel is for the ease and luxury the big guys have
with so much room to work! There are elements of the gas system I was
not aware of, like the over and underpressure bubblers on Level 2. I did
not see this panel when I was looking around on Level 2 last week. This
is just what I was hoping for with my points (d) and (iv). The fact
that both bubblers are in the exhaust line is fine, of course.
On the point of monitoring flow to the sectors, it seems we are
heading towards a consensus. My 5 minute conversation with Mac in the
Hall did not constitute a consensus to me, but a step in that process.
We certainly don't have a design yet, nor a plan for who will impliment
the design. Larry and Sebastian also agree that we want to monitor
sectors individually; on that point I think we have consensus. The
"plan" of searching for leaks by manual on/off switching of the valves
seems to be off the table. Mac and I spoke and agreed that at a minimum
we want to monitor gas coming out of the chambers. I still believe we
really want a way to monitor both gas in and gas out of the sectors. I
perfectly understand the point of not wanting an unnecessary
flow-dependent pressure drop in the lines. However, our flow rates are
constant, to a good approximation, so any drops in the line are
basically "DC offsets" in pressure which can be including in our
set-points of the pressure monitors. That's why I said "who cares?"
about pressure drops in my first letter. To simply monitor the output
flow from a chamber requires only a tiny head of mineral oil: if we were
to use Steve's clever mason-jar design, with its high flow capacity, a
1/16" head of oil would introduce a pressure drop of only 0.02 psi. It
would be flow rate independent, would it not? And the number is very
small, leading for Region One to a force on the gas seal of about 0.2
pounds per linear inch.
As for the "low impedance" flow tubes which we all (I think)
seem to like, I have a question: who knows what the impedances of
typical flow tubes are? My Matheson catalog does not give a spec for
this quantity. Is there another type of rotameter-like design which has
demonstrably lower impedance? I have heard of such things by hearsay,
but never seen them personally. Without more information about this I
don't know how to go further. I am ready and able to build some of the
components we need, but we need to decide as a group what we want to do.
What shall we build: bubbler panels and/or flow tube panels? Where
should they fit in the hall? Who will organize the rack space? Will the
plumbing be nylon or stainless? Who will take responibility for the
construction?
My urgent, insistent tone on this derives from the fact that we
have very little time, given everything else we are doing and the
proximity of the holidays, to do something. Maybe I'm all wet on this,
and JLab has thought this all through fully and I am just out of the
loop. But if so, I have never seen a design report that goes through
all these arguments for the in-hall part of the gas ssytem. The outside
experts from Cornell and Fermilab may have blessed solutions to all
problems already. Nor do I recall any discussions at our meetings (I
could have forgotten them, of course). So I hope you all read this in
the nervous but amicable spirit in which it is offered, and keep the
discussion going.
Regards, Reinhard.