Electron drift properties for P10 can be estimated with Magboltz 1 [Steve Biagi, 1995]. The particular version used here was interfaced to Garfield [Rob Veenhof, 1995] for use in gas detector simulations. The plots were calculated by R.Bossingham; similar ones appear in SN0408.

As a function of "reduced field" (electric field divided by pressure,
**E/P**), drift velocity is shown in the figure below for several
alignments of **E** and **B**.

** Electron drift velocity in P10 at 297K
and 1 bar with B=5 kG. The left-hand plot is for B aligned 0,
15, 30, 45, 60, 75 and 90 deg. from E, left to right.**

For the high E region (right-hand plot), the alignments are 0 and 45 deg., left to right. The low drift velocities for E/P ~ 2 are typical of the region

between the ground-wire and anode-wire planes, accounting for a shift of the "effective detection planes" further from the central membrane.

In the TPC drift volume, **E** is nearly aligned with **B**, and
large enough (**E/P**~ 0.19) that the drift velocity **V** is
beyond saturation (**dV/dE**<0). This allows active regulation of
drift time using **E**, compensating for factors such as
variations in the argon-methane ratio or low levels of contaminants.

Away from the anode wires, a log scale (right-hand plot) is more
appropriate, showing that **V** is nearly constant for **E/P** ~
1.5-5 V/cm-Torr. Most of the shift of the effective detection planes
occurs in this region.

The figure below shows the electron drift velocity in P10 **V** vs.
**E/P** on a linear scale. The main drift region of the TPC
corresponds to **E/P** ~ 0.19 V/cm-Torr, slightly to the right of
the saturation peak for **E** and **B** parallel. In the
higher-field region within ~500 um of the anode wires, **V**
increases with **E/P** linearly, or almost as the inverse of the
distance to the wire.

**Electron drift velocity in P10 for lower and higher
E, left and right, respectively. The left curve
is for E and B parallel;
they are at 45 deg.for the right-hand curve (merging at high E/P).
**

For calibration purposes, another important property of P10 is the
Lorentz angle, allowing an estimate of the size of the **ExB**
effect near the anode wires. Finally, for completeness, plots of the
Townsend and attachment coefficients also appear below.

** Lorentz angles (left) and diffusion (right) in P10
at 297K and 1 bar, with B=5 kG aligned 0, 15, 30, 45, 60, 75
and 90 deg. from E. **

For increasing angle: Lorentz angles and transverse diffusion (*'s) increase; longitudinal diffusion (open circles) decreases.

**
Townsend coefficients (left) and attachment coefficients (right) in
P10 at 297K and 1 bar.
**

Page created by Roy Bossingham;
maintained by .

Last modified on June 29, 2000