[mesa-users] approx13
Bill Paxton
paxton at kitp.ucsb.edu
Wed May 14 17:54:42 EDT 2014
Hi Ken,
Hardwired nets are a challenge! It is much easier to screw them up than to get them right. But if you really need to squeeze out the last bit of performance, then they are required. So, as background, is approx20.net just too big for you to use? Really? If so, then it will be possible (with some work on my part) to create a smaller net like frank's approx13. let me know.
-b
On May 14, 2014, at 2:09 PM, Ken Shen wrote:
> Hi all. I've been trying to construct a nuclear network in MESA that mimics Frank Timmes's approx13, which is an alpha-network that contains 4He, 12C, 16O, 20Ne, etc. up to 56Ni. It contains the 12x2 (a,g) and (g,a) forward and reverse reactions linking each adjacent isotope (e.g., 12C(a,g)16O); 3 heavy-ion forward reactions (12C+12C, 12C+16O, 16O+16O); and 8x4 (a,p)(p,g) forward and reverse p-catalyzed alpha-captures starting at 24Mg(a,p)(p,g)28Si. These hardwired reactions assume the intermediate isotopes (e.g., 27Al) are in equilibrium with the reactions that involve them.
>
> MESA (version 5596) gives me an error when I don't include protons in the network (why is that?), so I've added them in, but no reactions link directly to them, so their mass fraction should stay zero (and does). I've attached the naive .net file I came up with, based off approx_base.net, at the bottom of the email.
>
> The problem is that this network doesn't give the correct burning results. At T = 3e9 K and rho = 1e7 g/cm^3, a pure 12C composition results in epsilon = 1.8e19 erg/(g*s), which is about 4 orders of magnitude too low. I eventually stumbled across a fix, which is to include neutrons in the isotope list. As with protons, neutrons don't show up explicitly in the network and their mass fraction stays constant at zero, but the burning goes up to the correct value.
>
> Furthermore, with neutrons and protons included in the isotopes list, a pure 16O composition at the same T and rho yields epsilon = 6.3e17. Adding 1H to the list (again, not part of the actual network) yields epsilon = 7.3e17.
>
> Any enlightenment out there?
>
>
> ! Naive approx13.net file
> add_isos(
> prot
> he4
> c12
> o16
> ne20
> mg24
> si28
> s32
> ar36
> ca40
> ti44
> cr48
> fe52
> ni56
> )
>
> add_reactions(
>
> ! triple alpha
> r_he4_he4_he4_to_c12
> r_c12_to_he4_he4_he4
>
> ! C/O burning
> r1212 ! c12 + c12 -> ne20 + he4, includes na23+p channel
> r1216_to_mg24 ! c12 + o16 -> mg24 + he4
> r1216_to_si28 ! c12 + o16 -> si28
> r1616a ! o16(o16a)si28
> r1616ppa ! o16(o16p)p31(pa)si28
> r1616ppg ! o16(o16p)p31(pg)s32
> r1616g ! o16(o16g)s32
> r1616p_aux ! o16(o16p)p31
>
> ! alpha links with both (a,g) and (a,p)(p,g)
>
> ! o16
> ! from c12 by (a,g)
> r_c12_ag_o16
> r_o16_ga_c12
>
> ! ne20
> ! from o16 by (a,g)
> r_o16_ag_ne20
> r_ne20_ga_o16
>
> ! mg24
> ! from ne20 by (a,g)
> r_ne20_ag_mg24
> r_mg24_ga_ne20
>
> ! si28
> ! from mg24 by (a,g)
> r_mg24_ag_si28
> r_si28_ga_mg24
>
> ! from mg24 by (a,p)(p,g) via al27
> rmg24ap_to_si28 ! mg24(ap)al27(pg)si28
> rsi28gp_to_mg24 ! si28(gp)al27(pa)mg24
> rmg24ap_aux ! mg24(ap)al27
> ral27pg_aux ! al27(pg)si28
> rsi28gp_aux ! si28(gp)al27
> ral27pa_aux ! al27(pa)mg24
>
> ! s32
> ! from si28 by (a,g)
> r_si28_ag_s32
> r_s32_ga_si28
>
> ! from si28 by (a,p)(p,g) via p31
> rsi28ap_to_s32 ! si28(ap)p31(pg)s32
> rs32gp_to_si28 ! s32(gp)p31(pa)si28
> rsi28ap_aux ! si28(ap)p31
> rp31pg_aux ! p31(pg)s32
> rs32gp_aux ! s32(gp)p31
> rp31pa_aux ! p31(pa)si28
>
> ! ar36
> ! from s32 by (a,g)
> r_s32_ag_ar36
> r_ar36_ga_s32
>
> ! from s32 by (a,p)(p,g) via cl35
> rs32ap_to_ar36 ! s32(ap)cl35(pg)ar36
> rar36gp_to_s32 ! ar36(gp)cl35(pa)s32
> rs32ap_aux ! s32(ap)cl35
> rcl35pg_aux ! cl35(pg)ar36
> rar36gp_aux ! ar36(gp)cl35
> rcl35pa_aux ! cl35(pa)s32
>
> ! ca40
> ! from ar36 by (a,g)
> r_ar36_ag_ca40
> r_ca40_ga_ar36
>
> ! from ar36 by (a,p)(p,g) via k39
> rar36ap_to_ca40 ! ar36(ap)k39(pg)ca40
> rca40gp_to_ar36 ! ca40(gp)k39(pa)ar36
> rar36ap_aux ! ar36(ap)k39
> rk39pg_aux ! k39(pg)ca40
> rca40gp_aux ! ca40(gp)k39
> rk39pa_aux ! k39(pa)ar36
>
> ! ti44
> ! from ca40 by (a,g)
> r_ca40_ag_ti44
> r_ti44_ga_ca40
>
> ! from ca40 by (a,p)(p,g) via sc43
> rca40ap_to_ti44 ! ca40(ap)sc43(pg)ti44
> rti44gp_to_ca40 ! ti44(gp)sc43(pa)ca40
> rca40ap_aux ! ca40(ap)sc43
> rsc43pg_aux ! sc43(pg)ti44
> rti44gp_aux ! ti44(gp)sc43
> rsc43pa_aux ! sc43(pa)ca40
>
> ! cr48
> ! from ti44 by (a,g)
> r_ti44_ag_cr48
> r_cr48_ga_ti44
>
> ! from ti44 by (a,p)(p,g) via v47
> rti44ap_to_cr48 ! ti44(ap)v47(pg)cr48
> rcr48gp_to_ti44 ! cr48(gp)v47(pa)ti44
> rti44ap_aux ! ti44(ap)v47
> rv47pg_aux ! v47(pg)cr48
> rcr48gp_aux ! cr48(gp)v47
> rv47pa_aux ! v47(pa)ti44
>
> ! fe52
> ! from cr48 by (a,g)
> r_cr48_ag_fe52
> r_fe52_ga_cr48
>
> ! from cr48 by (a,p)(p,g) via mn51
> rcr48ap_to_fe52 ! cr48(ap)mn51(pg)fe52
> rfe52gp_to_cr48 ! fe52(gp)mn51(pa)cr48
> rcr48ap_aux ! cr48(ap)mn51
> rmn51pg_aux ! mn51(pg)fe52
> rfe52gp_aux ! fe52(gp)mn51
> rmn51pa_aux ! mn51(pa)cr48
>
> ! ni56
> ! from fe52 by (a,g)
> r_fe52_ag_ni56
> r_ni56_ga_fe52
>
> ! from fe52 by (a,p)(p,g) via co55
> rfe52ap_to_ni56 ! fe52(ap)co55(pg)ni56
> rni56gp_to_fe52 ! ni56(gp)co55(pa)fe52
> rfe52ap_aux ! fe52(ap)co55
> rco55pg_aux ! co55(pg)ni56
> rni56gp_aux ! ni56(gp)co55
> rco55pa_aux ! co55(pa)fe52
>
>
> )
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