P10: Effect of Deviations in the Methane:Argon Ratio (Calculated)

The STAR TPC nominally operates with 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 tables below give some idea of the effect of small deviations from a perfect mixture.

The tables below were calculated by Roy Bossingham using Magboltz 2, V3.1 (Biagi, 2000) for parameters relevant to STAR: T=23.9C and P=760 Torr, with B and E parallel and concentrated near common values. Magboltz 2 uses Monte Carlo methods, with the statistics determined by the collisions parameter. The tables 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 P9, P10 and P11 at P=760 Torr, with E parallel to B.

 

Transverse diffusion vs E for P9, P10 and P11 at B=5 kG and P=760 Torr, with E parallel to B.

 

E
(V/cm)
E/P
(V/cm-Torr)
V
(cm/us)
Sigma_L
(um/sqrt(cm))
Sigma_T(B=5 kG)
(um/sqrt(cm))
    P9 P10 P11 P9 P10 P11 P9 P10 P11
100 0.1316 5.119 5.239 5.322 426 427 423 200 191 184
118 0.1553 5.246 5.434 5.568 393 395 391 220 209 197
128 0.1684 5.271 5.477 5.648 371 379 374 227 218 207
138 0.1816 5.250 5.487 5.685 373 363 362 239 227 221
148 0.1947 5.230 5.472 5.692 357 356 357 249 240 224
158 0.2079 5.183 5.453 5.685 352 341 350 261 250 233
168 0.2211 5.102 5.393 5.639 344 330 333 273 255 243
178 0.2342 5.049 5.348 5.602 325 330 332 279 260 253
188 0.2474 4.978 5.348 5.539 336 339 327 297 270 263
200 0.2632 4.880 5.189 5.469 319 323 321 296 289 269

Calculated drift velocity and diffusion in P9, P10 and P11 as a function
of E/P for parallel E and B at P=760 Torr and T=23.9C .

 

Drift velocity vs methane fraction at E=148 V/cm and P=760 Torr, with E parallel to B.

 

Transverse diffusion vs methane fraction at B=5 kG and P=760 Torr, with E parallel to B.

 

F
(% CH4)
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
6.0 4.201 377 311    
7.0 4.593 377 287    
8.0 4.935 364 270 379 614
9.0 5.230 357 249 363 594
10.0 5.472 356 240 346 575
11.0 5.692 357 224 335 556
12.0 5.876 353 217 324 530
13.0 6.040 349 211    
14.0 6.147 350 203    

Calculated drift velocity and diffusion as a function of methane content F
(100%-F argon) for parallel E and B at E=148 V/cm, P=760 Torr and T=23.9C .

 


Page created by Roy Bossingham; maintained by   .
Last modified on June 29, 2000   .