The tables below were calculated by Roy Bossingham using **Magboltz
2, V3.1** (Biagi, 2000) for typical values of interest to STAR:
T=23.9C, P=760 Torr and **B**=5.0, 2.5 and 0.0 kG, with additional
values to help with interpolation. **E** values were most
concentrated around **E**=148 V/cm, and were parallel to **B**
in all cases.

The drift velocity and diffusion constant are functions of the ratio
of **E** over density; to find the drift velocity and
single-electron diffusion at fixed **B**, general values of
the drift length **L** and small changes from the input values
of (cm)**E** (V/cm), **P** (Torr) and **T** (K):

- Use
**(E/P) * (T / 297.04 K)**for the "E/P" column. - Look up the appropriate value (note that, for parallel
**E**and**B**in**Magboltz**,**Sigma_T**is a function of**B**, but drift velocity and**Sigma_L**are not). - Scale
**Sigma_L**and**Sigma_T**by**sqrt[L * (760 Torr / P) * (T / 297.04 K)]**to get the diffusion in um.

**Magboltz 2** uses Monte Carlo methods, with the statistics
determined by the **collisions** parameter. Statistics were used
corresponding to **collisions=120**, or higher, giving a precision
of at least 0.04% in drift velocity and 1.6% in diffusion.

**
Drift velocity in P10 vs E for P=760 Torr and E parallel to B,
from a rather global viewpoint.
The STAR TPC normally operates just beyond the peak in
the right-hand plot.
**

**
Diffusion in P10 vs E for P=760 Torr and E parallel to B.
**

**
Drift velocity and longitudinal diffusion in P10 vs E for P=760 Torr
and E parallel to B.
The plotted parameters are close to the operating conditions
for the STAR TPC drift volume.
**

**
Transverse diffusion in P10 vs E for P=760 Torr and E parallel to B.
The plotted
parameters are close to the operating conditions for the STAR TPC drift volume.
**

Blum and Rolandi define the variable D, which is proportional to the
transverse diffusion squared and a function of **E** and **B**;
they plot it for the special case of P9 (relevant to Aleph) and E=110
V/cm. D(0)/D(B) becomes a straight line at sufficiently high **B**
(higher than in STAR, however). As the lefthand plot below shows,
D(0)/D(B) varies smoothly and slowly with **B^2** and **E**,
making it useful for interpolation. However, as the righthand plot
shows, Blum and Rolandi's P9 plot does not apply especially well to
STAR's operating conditions.

**
Transverse diffusion in P10 vs E for P=760 Torr and E parallel to B.
The plotted
parameters are close to the operating conditions for the STAR TPC drift volume.
**

E(V/cm) |
E/P(V/cm-Torr) |
V(cm/us) |
Sigma_L(um/sqrt(cm)) |

50 |
0.0658 | 3.427 | 618 |

75 |
0.0987 | 4.628 | 499 |

100 |
0.1316 | 5.239 | 427 |

118 |
0.1553 | 5.434 | 395 |

128 |
0.1684 | 5.473 | 377 |

138 |
0.1816 | 5.487 | 363 |

148 |
0.1947 | 5.472 | 356 |

158 |
0.2079 | 5.453 | 341 |

168 |
0.2211 | 5.397 | 342 |

178 |
0.2342 | 5.345 | 331 |

188 |
0.2474 | 5.281 | 325 |

200 |
0.2632 | 5.189 | 323 |

250 |
0.3289 | 4.802 | 298 |

375 |
0.4934 | 3.968 | 261 |

500 |
0.6579 | 3.410 | 239 |

750 |
0.9868 | 2.839 | 222 |

1000 |
1.3158 | 2.573 | 219 |

1500 |
1.9737 | 2.380 | 219 |

2000 |
2.6316 | 2.340 | 218 |

3000 |
3.9474 | 2.360 | 211 |

4000 |
5.2632 | 2.410 | 217 |

6000 |
7.8947 | 2.828 | 246 |

8000 |
10.5263 | 3.385 | 243 |

12000 |
15.7895 | 4.552 | 219 |

16000 |
21.0526 | 5.631 | 201 |

24000 |
31.5789 | 7.713 | 172 |

32000 |
42.1053 | 9.699 | 157 |

**Calculated drift velocity [cm/us] and longitudinal diffusion
[um/sqrt(cm)] in P10 for parallel
E and B at P=760 Torr and T=23.9C . Values are nearly
independent of the magnitude of B.**

B (kG) |
||||||||||

E(V/cm) |
E/P(V/cm-Torr) |
5.0 |
4.375 |
3.75 |
3.125 |
2.5 |
1.875 |
1.25 |
0.625 |
0.0 |

50 |
0.0658 | 162 | 268 | 592 | ||||||

75 |
0.0987 | 168 | 282 | 583 | ||||||

100 |
0.1316 | 191 | 296 | 569 | ||||||

118 |
0.1553 | 209 | 314 | 562 | ||||||

128 |
0.1684 | 218 | 240 | 258 | 290 | 322 | 377 | 446 | 529 | 560 |

138 |
0.1816 | 227 | 267 | 337 | 452 | 571 | ||||

148 |
0.1947 | 240 | 253 | 277 | 306 | 346 | 390 | 463 | 531 | 575 |

158 |
0.2079 | 250 | 287 | 352 | 468 | 554 | ||||

168 |
0.2211 | 255 | 276 | 299 | 324 | 351 | 416 | 469 | 542 | 566 |

178 |
0.2342 | 260 | 302 | 371 | 494 | 577 | ||||

188 |
0.2474 | 270 | 314 | 379 | 487 | 575 | ||||

200 |
0.2632 | 289 | 392 | 571 | ||||||

250 |
0.3289 | 325 | 433 | 580 | ||||||

375 |
0.4934 | 396 | 486 | 589 | ||||||

500 |
0.6579 | 460 | 534 | 610 | ||||||

750 |
0.9868 | 514 | 574 | 620 | ||||||

1000 |
1.3158 | 533 | 583 | 592 | ||||||

1500 |
1.9737 | 537 | 566 | 580 | ||||||

2000 |
2.6316 | 541 | 550 | 561 | ||||||

3000 |
3.9474 | 503 | ||||||||

4000 |
5.2632 | 478 | 498 | 498 | ||||||

6000 |
7.8947 | 432 | ||||||||

8000 |
10.5263 | 385 | 386 | 388 | ||||||

12000 |
15.7895 | 317 | ||||||||

16000 |
21.0526 | 282 | 280 | 284 | ||||||

24000 |
31.5789 | 231 | ||||||||

32000 |
42.1053 | 201 | 203 | 203 |

**Transverse diffusion [um/sqrt(cm)] in P10 (calculated)
for parallel E and B at P=760 Torr and T=23.9C .**

Page created by Roy Bossingham;
maintained by .

Last modified on June 29, 2000 .