Detection of Energetic Particles by a Network of HF Propagation Paths in Alaska

Transcription

1 Dtction of Enrgtic Particls by a twork of HF Propagation Paths in Alaska A.Y. Wong* HIPAS Obsrvatory, Fairbanks, AK and Dpt of Physics and Astronomy, UCLA *With th assistanc of G. Rosnthal, J. Pau, E. ichols of UCLA March 15, 2001 Abstract. A ntwork of horizontal propagation paths of HF radiation is proposd to dtct ionization paths cratd by nrgtic particls nar th arth s surfac. Cohrnt phas mthod is snsitiv to suddn changs in ionization in any portion of a long path lngth. Rcognizing that th flux of magntic monopols is low and that a larg viwing rgion is ncssary to incras th probability of obsrvation I am proposing an lctronic ntwork using commrcial cll-phon stations in th ntir stat of Alaska (Fig.1, 2). Th rasons for prforming th xprimnt in Alaska ar: th rmotnss of th Alaska rgion mans that th lvl of background nois is significantly lowr than that in th lowr forty-ight stats; th climat in Alaska dos not giv ris to thundrstorms in most rgions, thrby rducing th amount of xtranous ionization which can confus our dtction schm; most of th infrastructur is alrady prsnt at th UCLA HIPAS Obsrvatory (Wong, 1999;

2 locatd in th cntral rgion of Alaska as a rsult of our mor than twnty yars of prforming communication xprimnts on th intraction of lctromagntic wavs with th ionosphr (fig 3, 4). Th cntral ida of our concpt consists of snding a cohrnt HF wav from a vrtical antnna locatd at HIPAS Obsrvatory, which propagats uniformly in all horizontal dirctions. Rcivr sits locatd at various cllular stations throughout Alaska ar usd to rcord this signal in amplitud and phas. Ths rcivr sits (fig 1) all hav vry accurat timing providd by T-1 lins. Th phas stability is on part in Thrfor vry small incrmntal chang in phas can b dtctd. Rcivrs ar locatd at distancs from 30 km up to 500 km. All data ar rcordd continuously in a digital mod at th 1 MHz rat and any suddn chang in th ordr of millisconds or lss will nsur that th data will b rtaind prmanntly and xamind first on a local computr. This procdur avoids th accumulation of an ovrwhlming amount of unintrsting background data. Only ths pr-scrnd data ar thn snt forward in batch formats to a cntral tlscinc cntr using th cll station links. Th data from all stations will b xamind and corrlatd. Th us of xisting cll stations for data gathring and intrmittnt transfr gratly lowrs th cost of this largscal xprimnt. Th ntwork can b calibratd by th short burst of ionization gnratd by a 300-Joul lasr (Wurkr, 2001) at th HIPAS Obsrvatory on dust particls. A 2.7 m rotating mirror at HIPAS can b usd to focus a lasr bam to impact on dust particls at a hight of 100 km. Th rsulting lctron population lin dnsity of nl < 10 8 cm 2 is xpctd to caus a dtctabl chang in th phas of a propagating HF signal. Th propagation of lctromagntic wavs through a mdium containing lctrons will suffr a chang of phas givn by th following quation (Wong, 1980):

3 L ( k k ) φ = dx. 0 vacuum plasma Assuming constant n through lngth L, w hav: whr ω p = k vacuum 4πn 2 m = 1/ 2 1/ 2 p 2 ω ω φ = L c ω, ω, and c = 5.6x10 4 n 1/ 2 (rad/s) Th minimum dtctabl chang in phas is xpctd to b 0.1 dgr, which corrsponds to a chang in th lin dnsity (~n L) of 6x10 3 cm -2. According to th layout of th rciving stations this dtction systm is xpctd to covr an ara of approximatly 500 km in radius. Anytim an nrgtic particl falls into this ara, it will caus ionization dtctabl by this mthod. According to th thortical work by Wick t al (2000) taking th uppr flux bound of monopols as cm -2 sc -1 sr -1 (Amanda, Baikal and Macro) and considring a rgion with a radius of 500 km, an uppr limit of 5 vnts/sc is stimatd. Evn if this wr an optimistic stimat our dtction systm is dsignd to obsrv 5 vnts/yar, which can put th flux 10 7 tims lowr. Wick also stimatd that th ionization in th lowr atmosphr will giv a lin dnsity nl ~ 10 5 cm 2 which is wll abov th snsitivity limit of our dtctors. Th lin dnsity might b highr if w considr th impact of th monopol on th arth s surfac. Th matrial dnsity is highr and givs ris to scondary lctron mission and transition radiation. This might rsult in a larg lctron showr in th km hight rang w ar dtcting. W ar currntly prforming computr modling of such vnts.

4 In our proposd xprimnts th vnts ar discriminatd according to th spd of occurrnc. Background vnts cannot in gnral produc such a larg lin dnsity within tns of microsconds nar th arth s surfac. W hav also considrd th duration of th lctron lin dnsity at such low hights. Th ionization balanc quations for th concntrations of th lctrons and - of th ngativ ions tak th form (Gurvich, 1978): d dt d dt = q i + ν = ν a ion ν d ν a α i + ν d ( + α ) ( + ) whr q i is th total intnsity of th ionization producd by th xtrnal sourc, ν ion is th frquncy of th molcul ionization by th fast lctrons, ν a is th frquncy of lctron attachmnt to th molculs, and ν d is th lctron dtachmnt frquncy. Undr th conditions of th lowr ionosphr, an important rol is playd by th attachmnt of lctrons to oxygn molculs in tripl collisions ν k. According to Phlps (1969), k a 1 O2 O = xp( ) cm / T s. For th lctron dtachmnt frquncy, important procsss in th ionosphr ar photo dtachmnt, dtachmnt in collisions with molculs, and associativ dtachmnt: ν d =ν ph + ' k6 O + k7o + k 2 8 Th rat of chang in th lctron population is qual to th diffrnc btwn rats of dtachmnt and attachmnt. With + - = + and ν a, ν d >> α I +, w can xprss th nt lctron dnsity + ν d ν a + ν d

5 Dpnding on th xcitd stats of molculs and th nrgy rlasd from th intraction btwn monopols and atmosphr and ground a rat of chang of lctron dnsity btwn microsconds is possibl. Rfrncs Gurvich A.V., onlinar Phnomna in th Ionosphr, Springr-Vrlag,.Y., Wick, S., Confrnc papr, RADHEP 2000, UCLA, ovmbr 16, 2000 Wong, A.Y., onlinar Intractions of Elctromagntic Wavs with th Auroral Ionosphr, 13 th Topical Confrnc on Radio Frquncy Powr in Plamas, Annapolis, MD, AIP Confrnc Procdings 485, p 18-34, April, 1999 Wong, A.Y., Introduction to Exprimntal Plasma Physics, UCLA Publication, 1980 Wurkr, R.F., Privat communication, This nw Lidar facility is bing put togthr by R. F. Wurkr. Acknowldgmnt This work is supportd by SDSU foundation.

6 Figur 1: Location of commrcial communications rcivr sits in Alaska. Figur 2: Artist concption of th xprimntal arrangmnt. HIPAS is in th cntr of th array radiating a cohrnt signal. Th radiation pattrn of ach rcivr is shown as an ovrlapping shad. Th arth s magntic fild is rprsntd by vrtical magntic fild lins.

7 Figur 3: Antnna arrays at th HIPAS Obsrvatory, Fairbanks, Alaska. Th frquncis usd rang from HF to Lasr rgims. Figur 4 Schmatic showing th various diagnostics usd in an xprimnt to invstigat th intraction of lctromagntic wavs with th ionosphr.

8 Figur 5 Schmatic showing a calibration procdur using a lasr to ioniz dusts at a hight of 100m. Th lctrons gnratd will caus phas shift in th cohrnt signal dtctd by th rcivr.