Star-tpc-l mailing list

[James H Thomas <jhthomas AT berkeley.edu>]

Dear Ping,

TPC is a High Voltage structure (28 kV) and so insulation is needed between the inner field cage and the beam pipe, and between the outer field cage and the external mounting frame.    The beam pipe and the external frame, of course, are at ground potential.   The inner field cage lies at a radius of 47.5 cm so air provides the HV insulation between it and the beampipe.  At the outer radius, there is a 5 cm gap between the outer field cage and the external frame for the TPC.  It is filled with N2 gas to provide the HV insulation and isolation between the OFC and ground.  We occasionally have sparks in this 5 cm gap because it is so small.

The most up to date information about the iTPC (the STAR TPC after a major upgrade in 2015) can be found in STAR NOTE - SN0644: The Technical Design Report for the iTPC Upgrade.

Additional details about the old TPC (before upgrade) can be found in the NIM paper and at https://www.star.bnl.gov/public/tpc/tpc.html  (see the hardware link).

The iTPC TDR and the web page are a bit too detailed for easy reading and so I will try to extract some of the information for you (framed by the questions you sent to Gene).  Please give me a day or two to do that homework.  But please do a look at the TDR and web pages to see if they generates additional questions.

 

Cheers,
Jim

--

Jim Thomas

Email: jhthomas AT berkeley.edu

Phone:  USA  (510) 759-4936

Homepage: https://sites.google.com/berkeley.edu/jhthomas

Please don't feel obligated to respond to this message outside of your normal working hours.

On Tue, Dec 3, 2024 at 12:16 PM Van Buren, Gene <gene AT bnl.gov> wrote:

Hi, TPC-ers

I suspect the answers to these questions from some EIC folks can come together more effectively from the TPC group than from myself. Please chime in if you know these.

Thanks,

-Gene

Begin forwarded message:

From: "Wong, Cheuk-Ping" <cwong1 AT bnl.gov>

Subject: Re: STAR TPC tracking parameters

Date: December 3, 2024 at 11:35:41 AM EST

To: "Van Buren, Gene" <gene AT bnl.gov>, "Kiselev, Alexander" <ayk AT bnl.gov>

Hi Gene,

 

Another stupid question about the STAR TPC. The reference said that nitrogen gas or air insulation was used to electrically isolate the TPC field cage from the surrounding ground structures.  Does that mean the nitrogen gas/air between the inner trackers and the TPC?

 

Ping

 

From: Wong, Cheuk-Ping <cwong1 AT bnl.gov>
Date: Tuesday, December 3, 2024 at 11:20 AM
To: Van Buren, Gene <gene AT bnl.gov>, Kiselev, Alexander <ayk AT bnl.gov>
Subject: STAR TPC tracking parameters

Hi Gene,

 

I am trying to simulate the STAR TPC in EicROOT. I need to assign some TPC tracking parameter in the simulation setup. There are 6 TPC tracking parameters.

 

1. transverse dispersion                                   [um/sqrt(cm)]
2. longitudinal dispersion                                [um/sqrt(cm)]
3. transverse intrinsic resolution                  [um]
4. longitudinal intrinsic resolution               [um]
5. radial intrinsic resolution                            [um]
6. vertical pad size                                              [cm]

 

• In EICRoot, the quadrature sum of parameters 1 and 3 determine the spatial resolution in transverse direction, and the same for parameters 2 and 4. 

That is, spatial resolution = sqrt{intrinsic resolution^2 + [dispersion*sqrt(D)]^2 }, where D is the drift distance measured between a point where primary ionization in the gas volume for a particular hit happened and the sensor plane.

• Parameter 4 is product of the electronics frequency and drift velocity
• Parameter 5 is the pad size
• Parameter 6 depends on the size of the TPC and number of hits, that is vertical pad size =(rout-rin)/nHits

 

I tried to extract the parameters from this reference https://arxiv.org/abs/nucl-ex/0301015 . I get the following numbers.

1. transverse dispersion                   230        [um/sqrt(cm)]
2. longitudinal dispersion                360        [um/sqrt(cm)]

6.    “average” vertical pad size         (200-50)cm/(13+32)rows=3.33 [cm]

 

Do you have the numbers of parameters 3-5 that I can use?

 

Cheers,

Ping