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-- PeterKammel - 09 Aug 2008

Garfield Studies

Main Goals of Studies



  • optimize HV cathode
  • optimize grid
  • study performance, signals, resolutions

Detailed outline of work

  1. Introduction
  2. pTPC and cTPC geometry and Garfield Models
    1. pTPC (wire and plane model)
    2. cTPC (wire and plane model)
  3. Gas properties
    • generate H2, D2, 1%, 5%, 30K, 300K datasets and display differences in main properties)
    • compare main properties to literature
  4. pTPC studies
    1. Basic field configuration for fall run (compare wire/plane model)
    2. Drift properties
      • investigate grid losses as function of field/distance compared to analytical equations
      • predict drift variations
    3. Signals
      • define sensitive regions on plane
      • understand signal shapes, direct/indirect
      • study risetime as function of pad-grid distance
      • try to determine grid feedthrough for different field/geometry parameters
  5. cTPC studies
    1. Optimize field configuration for several models
      • Constant field, critical field on edges
    2. Drift properties
      • Standard drift properties
      • Table of drift times in fiducial grid
    3. Signals
      • Signal generation, shape for different geometry/distance choices
      • Grid transparency
  6. Misc other studies (we have to decide whether they are worth the effort)
    1. Simulate realistic tracks: SRIM interface allows dE/dx input, angular distribution could be simulated.

Noah's studies

Peter's studies

I performed some studies expanding on Noah's input file describing the pTPC. The relevant files are

file description
pt.in Garfield input file
cell.1 Cell description
pt1.pdf Graphic output
pt1.zip Text output
The sections are briefly explained below.


This is Noah's file. For some reason one has to load cell.1 twice to get reasonable field calculations.
pt1_cell.txt contains the wire table.


The overall fields are shows on page 2 and 3 (in pt1.pdf). Page 4 has the cut through the horizontal midplane. Page 5 shows the field on a path from the leftmost upper cathode frame (displayed as funtion of y), which is a critical high field region.


The gas is generated if the flag new_gas=True, otherwise it is read in from gas.gas. I.e. one should overwrite gas.gas with the gas file currently in use. In the gas generation I included some approximate clusters. Next time, we should throw that out and rely on heed. Various gas properties are displayed on p.6-11. We should check the more important ones versus literature.


The drift section studies the drift lines and isochrons (to check for timing differences) p.12. The closeup p.13 indicates some troubles in the Garfield calculation and emphasizes that the padplane approximation via wires distorts the drift behaviour between grid and pads. This should be studied with an alternative model using a plane. The drifttime vs. location table is contained in pt1_drift.txt and should be displayed with ROOT, to check for corrections and observable effects. The last part of the drift section defines a do loop with high statistics to find drift lines missing the sense wires. Again that has to be repeated with a plane and distance and field should be changed to generate misses according to the equations presented by Luke ( original reference).


Signals are generated at 3 different distances to the pad plane. The tracks are horizontal and correspond to MIPS. E.g. p. 14 shows the clusters generated by a track and p. 15 the signal averaged over several tracks. While this is not a realistic situation, it is a first approach to get the point response of the chamber and to check whether the grid transparency is properly calculated by Garfield. Again this exercise has to be repeated for a pad plane geometry. At the moment I don't understand the large induced signal component and have not systematically looked for amplitude vs. y of the signal. The very different signal shape for a vertical track is indicated in p.21,22.

Analytical calculations

I started a little mathematica notebook on wire grid field calculation, transparency etc. The TPC model is not correct yet. Nevertheless a few useful plots already exist. See


Topic attachments
I Attachment History Action Size Date Who Comment
Unknown file format1 cell.1 r1 manage 6.2 K 2008-08-09 - 16:18 PeterKammel  
Unknown file formatin pt.in r2 r1 manage 5.9 K 2008-08-09 - 18:51 PeterKammel  
PDFpdf pt1.pdf r2 r1 manage 1275.6 K 2008-08-09 - 18:51 PeterKammel  
Compressed Zip archivezip pt1.zip r1 manage 53.7 K 2008-08-09 - 16:17 PeterKammel  
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