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Davlenie ionizovannogo gaza
V samyh vneshnih sloyah zvezd veshestvo nahoditsya preimushestvenno v atomarnom sostoyanii (ionogda dazhe zametny molekuly). V nedrah zvezd s povesheniem temperatury sleduet ozhidat' ionizacii veshestva s prevrasheniem ego v plazmu, to est' sostoyaniya, kogda elektrony mozhno rassmatrivat' kak svobodnye chasticy, bezotnositel'no k ionnym ostatkam. Hotya predstavlenie o sovokupnosti zaryazhennyh chastic kak o ideal'nom gaze vryad li verno dazhe v principe, glavnaya trudnost' pri vychislenii davleniya svyazana ne s oblastyami polnosti ionizovannoi plazmy, a s perehodnym sloem, to est' s chastichnoi ionizaciei veshestva. Pomimo togo, chto chislo chastic v takih oblastyah neizvestno, ono (eto chislo chastic) ves'ma bystro menyaetsya s temperaturoi i plotnost'yu, vliyaya ves'ma znachitel'no na termodinamicheskie proizvodnye.
Pri raschetah stroeniya zvezd, dlya opisaniya chastichno ionizovannoi plazmy chasto ispol'zuyut himicheskoe predstavlenie (iz-za etoi analogii vsyu sistemu uravnenii sostoyaniya tak zhe nazyvayut himicheskoi kartinoi). Pri etom tak zhe sushestvenno predpolozhenie o ideal'nosti komponent - elektronov i ionov (Zametim, chto ispol'zovanie statistiki vyrozhdennyh elektronov ne yavlyaetsya narusheniem predpolozheniya o ideal'nosti v strogom smysle etogo slova - ved' real'nogo vzaimodeistviya - sily prityazhenyai ili ottalkivaniya - mezhdu vyrozhdennymi elektronami net!). Interesuyushuyu nas "himicheskuyu" reakciyu ionizacii vypishem dlya vodoroda
![](https://images.astronet.ru/pubd/2004/01/27/0001196386/structure/physics/pressure/../../../tex_symb/leftrightarrow.gif)
![](https://images.astronet.ru/pubd/2004/01/27/0001196386/structure/physics/pressure/../../../tex_symb/gamma.gif)
Usloviem ravnovesiya dlya takoi reakcii yavyaletsya usloviya minimuma svobodnoi energii
F (vybor imenno svobodnoi energii svyazan s tem, chto svobodnaya energiya
yavlyaetsya termodinamicheskim potencialom v peremennyh T i ).
Etot minimum nuzhno naiti po otnosheniyu k chislu chastic raznogo sorta (n0
- neitral'nyh, n+ - ionizovannyh) i pri uslovii sohraneniya
chisla chastic, to est'
![](https://images.astronet.ru/pubd/2004/01/27/0001196386/structure/physics/pressure/images/eqi1.gif)
i sohraneniya obshego chisla yader (v nashem sluchae vodoroda). Takim usloviem minimuma yavlyaetsya uslovie stacionarnosti, to est' ravenstva nulyu proizvodnyh s uchetom ogranichenii, perechislenyh vyshe. Takim obrazom my poluchaem
![](https://images.astronet.ru/pubd/2004/01/27/0001196386/structure/physics/pressure/images/eqi2.gif)
Chastnye proizvodnye svobodnoi energii po chislu chastic nazyvat himicheskim potencialom dannogo sorta chastic. Interesuyushee nas uravnenie Saha yavyaletsya ni chem inym, kak zapisannym cherez koncentracii i energii sostoyanii dannoe uslovie ravnovesiya. Otmetim takzhe, chto svobodnaya energiya elektronov mozhet uchityvat' statistiku vyrozhdennogo elektronnogo gaza - eto menyaet konkretnoe vyrazhenie dlya uravneniya Saha, no ne menyaet uslovie ravnovesiya.
Inogda byvaet polezno vvesti eshe parametr vyrozhdeniya
, ispol'zuya vyrazheniya (snova spravedlivye vo vseh sluchayah, vyrozhdennyh ili net
elektronov)
![](https://images.astronet.ru/pubd/2004/01/27/0001196386/structure/physics/pressure/images/eqi3.gif)
Togda v sluchae klassicheskogo elektronnogo gaza, parametr vyrozhdeniya opredelyaetsya v vide
![](https://images.astronet.ru/pubd/2004/01/27/0001196386/structure/physics/pressure/images/eqi4.gif)
gde i - tak nazyvaemaya teplovaya
dlina volny chasticy sorta i, ili
![](https://images.astronet.ru/pubd/2004/01/27/0001196386/structure/physics/pressure/images/eqi5.gif)
Eksponenta ot parametra vyrozhdeniya imeet dovol'no "prozrachnyi"
smysl - eto dolya zanyatogo fazovogo prostranstva. V etom vyrazhenii gi
- statisticheskaya summa dlya dannogo sostoyaniya. Dlya elektronov eta velichina ravna
dvum. Esli chastic "slishkom mnogo" i oni zanimayut vse vozmozhnye pozicii
v fazovom prostranstve (s samymi nizhnimi energiyami), to takoe sostoyanie stanovitsya
vyrozhdennym. V etom sluchae velichina opredelyaetsya
po drugomu, cherez integral Fermi
![](https://images.astronet.ru/pubd/2004/01/27/0001196386/structure/physics/pressure/images/eqi6.gif)
Okonchatel'no, uravnenie Saha imeet vid
![](https://images.astronet.ru/pubd/2004/01/27/0001196386/structure/physics/pressure/images/eqi7.gif)
gde - raznica energii mezhdu ionizovannym
i neitral'nym sostoyaniem vodoroda.
Posle resheniya sistemy ionizacionnyh uravnenii Saha dlya vseh vozmozhnyh stadii ionizacii i elementov (sistema uravnenii obrazuetsya za schet togo, chto v kazhdoe uravnenie vhodit obshee chislo elektronov), mozhno poluchit' chislo chastic pri dannoi temperature i plotnosti, i vospol'zovat'sya formuloi dlya davleniya ideal'nogo gaza.
V.A.Baturin
Publikacii s klyuchevymi slovami:
Sverhnovye - zvezdy - sverhgigant - neitronnye zvezdy - krasnyi gigant - buryi karlik - diagramma Gercshprunga-Ressela - belyi karlik - Evolyuciya zvezd - termoyadernye reakcii - vyrozhdennyi gaz - gidrostaticheskoe ravnovesie - konvekciya - luchistyi perenos - glavnaya posledovatel'nost' - evolyucionnyi trek zvezdy - karliki
Publikacii so slovami: Sverhnovye - zvezdy - sverhgigant - neitronnye zvezdy - krasnyi gigant - buryi karlik - |