Collisionless anisotropic electron heating and turbulent transport in coronal flare loops

Transcription

1 Collisionlss anisotropic lctron hating and turbulnt transport in coronal flar loops K.-W. L and J. Büchnr 5 April 2011 Outlin: 1. HXR obsrvation and standard flar modl 2. Linar stability analysis (multi-fluid disprsion) 3. Collisionlss transport and anisotropic lctron hating (PIC simulation) 4. Summary

2 1. HXR obsrvation and standard flar modl Accompanid looptop and footpoint HXR sits Synchronization of missions (Masuda t al Natur)

3 Charactristics and consquncs of standard modl 1. Standard modl infrs an fficint lctron acclration in corona: from T=2*10 6 K to T=2*10 8 K (Masuda t al.1994) 2. Strong rturn currnt (lctrons) in flar loops ar ndd for charg nutrality (Emsli 1980; van dr Oord 1990; Zharkova t al. 1995). Th dnsity of rturn currnt lctrons must b comparabl or smallr than th ambint plasma dnsity (Fltchr 2005; Zharkova & Gordovskyy 2005) Challngs 1. Numbr problm: lctron bams last minuts N=1*10 39 lctrons must b acclratd (Brown t al. 2009) 2. Stability of lctron bam propagation: bam and rturn currnt n=10 9 cm -3 flow at a spd U=3*10 9 cm s -1 would caus many instabilitis. Can this lctron bam propagat down to chromosphr (Brown 2009; Fltchr 2005) Thortical and computational invstigation of th transport ar rquird!

4 Altrnativ modls/suggstd solutions 1. Proposd nw modl (Fltchr t al. 2008) Larg-scal Alfvén wavs and turbulncs of wav cascading ar gnratd by rconnction in th corona thy acclrat lctrons in chromosphr. Long lasting (minuts) footpoint HXR radiation is gnratd by lctron r-acclration mchanism in chromosphr. 2. Proposd combind modl (Brown t al. 2009) Local R-acclration Thick Targt Modl (LRTTM) : it combins Alfvén wav acclration and th collisional thick targt modl in chromosphr. This modl still assums a bam propagating from looptop acclration cit hnc it automatically xplains th synchronization of missions and flar ruption. Elction bams from looptop acclration sit is a common assumption in all solar flar modls. Howvr th tmporal span of injction is still an opn qustion but not th scop of this work. W intndd to invstigat th stability and turbulnt transport proprtis of th propagating bams.

5 / 10 1 / 10 5 ; / / m N m N m N G B m m Ion RC Bam pi p i Currnt-fr Rturn Bam Plasma ) ( ) ( 1 ; 2 Ion d t RC d Bam d RC Bam RC RC Bam Bam total i RC Bam V V V V N N N T N T T kv T T kv T B x 100G

6 (L and Buchnr 2011)

7 Multi-fluid Disprsion Diagram (paralll and obliqu propagation)

8 3. Collisionlss transport and anisotropic lctron hating (PIC simulation) Simulation stup B x 100G Bam Elctron Background B x L x 128 ; N 512 D x Elctron Bam Rturn-currnt Elctron Background Ion Priodic boundaris in X and Y L x 512 ; N D x 2048

9 Elctric and magntic fild prturbations t p

10 Elctric and magntic fild prturbations t p

11 Elctric and magntic fild prturbations t p

12 spctrum of fild prturbation at linar and nonlinar stags

13 Bam rlaxation and anisotropic lctron hating

14 Flow turbulncs and prpndicular momntum N Py Pn n1 1 2 ion

15 Th prpndicular hat flux Thrmal nrgy flux Bulk kintic nrgy At ; At ;

16 Th prpndicular hating rat and hat flux

17 Landau damping coms into play at simulation lat stag T p

18 with background magntic fild B x 100G 9kV 4. 9kV 2kV 5.4kV 23.2MK 62.6MK 1kV 4kV 11.6MK 46.4MK 2kV 2.78kV 23.2MK 32.3MK 1kV 2.02kV 11.6MK 23.4MK 1. Bam vlocity is rducd but still propagat stably. Th rturn currnt lctrons did not totally dstroy th injctd lctron bam. 2. Th original isotropic lctron bams bcom anisotropic in th lat stag of volution.

19 4. Discussions 1. Th initial bam plasma rturn currnt systm can b wll dscribd in multi-fluid rgim. Th linar stability analysis is prformd for idntifying th unstabl mods. 2. Th nonlinar volution of instabilitis ar prformd in a 2D EM PIC simulation. Anomalous drift rlaxation and anisotropic lctron hating ar found. 3. By calculating th prpndicular momntum and prpndicular hat flux it is found that th long lasting prpndicular lctron hating is causd by th turbulnt dflction of th pr-hatd paralll lctrons. This turbulnt dflction vntually gnrats anisotropic lctron hating. 4. Considring th Landau damping ffct which coms into play significantly only at th simulation lat stag th lctron bam is abl to propagat in th flar loops. This ffct is manifstd by th combind ffct of bam vlocity rlaxation and lctron hating.