P10: Effect of N2 (Calculated)

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   .