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Re: A few questions (fwd)
here the information I sent to David.
cheers elke
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| `, Elke-Caroline Aschenauer =
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---------- Forwarded message ----------
Date: Wed, 7 Mar 2007 15:14:33 -0500 (EST)
From: Elke-Caroline Aschenauer <elke@jlab.org>
To: David Christian <dcc@fnal.gov>
Cc: brooksw@jlab.org, whitlock@jlab.org, lung@jlab.org,
Elke-Caroline Aschenauer <elke@jlab.org>, Elton Smith <elton@jlab.org>
Subject: Re: A few questions
Dear David,
please find below the answers to your questions.
We are happy to give additional information if needed.
The additional documents are attached. I will bring printouts for our
session at 17.00
Regards
elke
>
> Dear Elke,
>
> After yesterday's session, we have a few questions the answers to which
> would help us as we consider what to write in a report. I would
> appreciate it if you could respond today:
>
> 1) What calculation/simulation has been done of the background processes
> that will dominate the rate in the chambers?
please see extra document
>
> 2) It appears that the minimum allowable straw radius is set by a
> maximum allowable rate that is calculated assuming that a dE/dx
> measurement needs to be made in these straws. Is this correct? If not,
> how was the maximum allowable rate estimated?
>
This is actually set by the desire to leave space inside the
straw-tube chamber for other parts of the detector. What was
mentioned was the 30cm long liquid hydrogen target.
For special runs an existing start counter will be installed
and provision has been made for a future upgrade to the Hall D/GlueX
spectrometer to include a vertex detector.
With regard to the rates, the 40KHz is not in any way a limiting
rate in the innermost layer. It was only presented to show that we had
looked at those rates.
> 3) Do you have supporting material available for the cost estimates?
FDC:
====
as preparation for the CD-2 review in summer a very detailed document
was prepared. It gives details of all the individual items contributing to
the overall costs of the FDC and lists the source for the budgeted cost.
see separate document
CDC:
====
Cost estimates for the CDC were made shortly after the prototype
construction was completed. This included the actual cost paid for
straw tubes, and estimates for the "donut" and "feed-through" pieces
that came from both how long it took to make them, and the costs of
pieces when the CLAS region I chamber was built at Carnegie Mellon.
The biggest cost (end plates and shells) came from bids on the CLAS
region I endplates and unfortunately are old. As indicated in the talk,
we are working with JLab on getting more up-to-date numbers based on
the specifications on the endplates.
>
> 4) Since the configuration of magnet steel is being changed, we are
> somewhat concerned with the fact that you do not plan to map the field.
> What drove this decision?
>
The modifications to the magnetic yoke were for two reasons.
First to reduce external stray fields by filling in the yoke gaps and
adding some steel at the downstream end to reduce saturation effects.
The new steel adds 8% to the overall amount.
These changes did not have a significant effect on either the fields or
the forces on the coils.
The second modification was to open up the hole on the upstream end to
match the yoke aperture on the down stream end to improve access for the
cylindrical drift chamber insertion and removal, the barrel calorimeter
installation and removal and to give more access for cabling for both of
these detectors.
This hole enlargement did modify the solenoid field near the upstream
hole and primarily at backward lab angles.
The overall field magnitude was reduced and there are more gradients in
the field.
The magnitude of the Bz integral on the axis thru the solenoid as an
integral was reduced by 15%.
The field reduction taking place almost entirely at backward lab angles
where the particle momentum is much lower and the loss of analyzing
power will not be important.
The gradients in the field will likely require that a field grid be used
in reconstruction.
This field grid to be sued for track reconstruction is planned to be a
TOSCA calculation supported by point field measurements, that is B vs I
measurements at several points, to calibrate in an absolute sense the
geometric field map from TOSCA.
A full field map could be performed on the solenoid but the accuracy of
field grid required , the cost and effort probably do not warrant this
expenditure and the overall absolute accuracy of TOSCA seems as good as
most measured field maps.
The current plan is to rely on the described TOSCA calculation which takes
the above described modifications in account. We also plan to check and
continuously monitor the absolute field with Hall probe measurements
at selected locations inside the magnet.
To verify that the quoted accuracy of the magnetic field of 10^-3 is adequate
to support our design goals detailed studies of the effect of the magnetic
field intensity and gradients on chamber calibration and event reconstruction
are under way.
If we find that increased accuracy would be needed, plans can be added to
map the field.
> Sincerely,
> David Christian
( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
) `\ -
/ '. | +
| `, Elke-Caroline Aschenauer =
\,_ `-/ -
,&&&&&V Jefferson Lab +
,&&&&&&&&: HALL-D 12C / F381 121-A Atlantic Avenue =
,&&&&&&&&&&; Mailstop: 12H5 Hampton, VA 23664 -
| |&&&&&&&;\ 12000 Jefferson Ave +
| | :_) _ Newport News, VA 23606 Tel.: 001-757-224-1216 =
| | ;--' | Mail: elke@jlab.org Mobil: 001-757-256-5224 -
'--' `-.--. | +
\_ | |---' Tel.: 001-757-269-5352 =
`-._\__/ Fax.: 001-757-269-6248 -
+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+
budget_dec_2006.pdf
DCReviewReply.pdf