The tables below allow one to estimate the effect of residual or leaked N2 in the STAR TPC gas, which is nominally P10 (90% Ar, 10% methane by volume) at ~2 mbar above the ambient atmospheric pressure with an electric field of ~148 V/cm and a temperature of ~75F=23.9C. (The short answer is that 1000 ppm of N2 reduces the drift velocity by ~1%; diffusion is rather insensitive to it.)
The values were calculated by Roy Bossingham using Magboltz 2, V3.1 (Biagi, 2000) for T=23.9C, P=760 Torr and B, E parallel and near typical values in STAR. Magboltz 2 uses Monte Carlo methods, with the statistics determined by the collisions parameter. The values below were calculated with statistics corresponding to collisions=120, or higher, giving a precision of at least 0.04% in drift velocity and 1.6% in diffusion.
Drift velocity vs E for P10 with 0, 1000 and 10,000 ppm
N2 impurity; for P=760 Torr and E is parallel to B.
E (V/cm) |
E/P (V/cm-Torr) |
V (cm/us) |
|||
N2 (ppm) | |||||
0 | 100 | 1000 | 10,000 | ||
100 | 0.1316 | 5.239 | 5.173 | 4.591 | |
118 | 0.1553 | 5.434 | 5.425 | 5.373 | 4.825 |
128 | 0.1684 | 5.477 | 5.470 | 5.420 | 4.917 |
138 | 0.1816 | 5.487 | 5.490 | 5.424 | 4.968 |
148 | 0.1947 | 5.472 | 5.470 | 5.420 | 4.986 |
158 | 0.2079 | 5.453 | 5.446 | 5.398 | 4.998 |
168 | 0.2211 | 5.393 | 5.401 | 5.367 | 4.997 |
178 | 0.2342 | 5.348 | 5.343 | 5.300 | 4.957 |
188 | 0.2474 | 5.273 | 5.272 | 5.240 | 4.913 |
200 | 0.2632 | 5.189 | 5.152 | 4.870 |
Calculated drift velocity for 0, 100, 1000 and 10,000 ppm N2 in P10 as
a function of E/P for parallel E and B at P=760 Torr and T=23.9C .
E (V/cm) |
E/P (V/cm-Torr) |
Sigma_L (um/sqrt(cm)) |
Sigma_T(B=5 kG) (um/sqrt(cm)) |
||||||
N2 (ppm) | N2 (ppm) | ||||||||
0 | 100 | 1000 | 10,000 | 0 | 100 | 1000 | 10,000 | ||
100 | 0.1316 | 427 | 428 | 427 | 191 | 191 | 206 | ||
118 | 0.1553 | 395 | 391 | 395 | 387 | 209 | 209 | 207 | 224 |
128 | 0.1684 | 379 | 380 | 370 | 378 | 218 | 221 | 220 | 231 |
138 | 0.1816 | 363 | 366 | 367 | 359 | 227 | 222 | 228 | 237 |
148 | 0.1947 | 356 | 354 | 353 | 358 | 240 | 240 | 239 | 249 |
158 | 0.2079 | 341 | 348 | 356 | 347 | 250 | 246 | 245 | 261 |
168 | 0.2211 | 330 | 349 | 354 | 337 | 255 | 255 | 257 | 261 |
178 | 0.2342 | 330 | 343 | 338 | 337 | 260 | 262 | 264 | 271 |
188 | 0.2474 | 339 | 323 | 331 | 329 | 270 | 269 | 267 | 281 |
200 | 0.2632 | 323 | 326 | 323 | 289 | 288 | 290 |
Calculated diffusion for 0, 100, 1000 and 10,000 ppm N2 in P10 as a
function of E/P for parallel E and B at P=760 Torr and T=23.9C .
N2 (ppm) |
V (cm/us) |
Sigma_L (um/sqrt(cm)) |
Sigma_T(B) (um/sqrt(cm)) |
||
B=5.0 kG | B=2.5 kG | B=0.0 kG | |||
0 | 5.472 | 356 | 240 | 346 | 575 |
100 | 5.470 | 354 | 240 | 340 | 562 |
1000 | 5.420 | 353 | 239 | 343 | 566 |
10,000 | 4.986 | 358 | 249 | 363 | 551 |
Calculated drift velocity and diffusion as a function of N2
in P10 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 .