University:
Boston University
Course:
CAS PY 105 | Physics 1
Academic year:

2021
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463

Pages:

25
Author:

Luneliomgmw

Langmuir probe theory LP measured currents: I = Ii + Ie + Iph, Ly-α + Ie*, i* + Idust From OML theory (with Maxwellian distribution function, Fahlesson approximation): linear Slo logarithmic Langmuir probe theory LP measured currents: I = Ii + Ie + Iph, Ly-α + Ie*, i* + Idust From OML theory (with Maxwellian distribution function, Fahlesson approximation): U > 0 (electron side) linear ⎛ e(U bias + U float ) ⎞ Ie = ALP n e qe ⎜1 − ⎟ k B Te ⎝ ⎠ Slo logarithmic € Langmuir probe theory LP measured currents: I = Ii + Ie + Iph, Ly-α + Ie*, i* + Idust From OML theory (with Maxwellian distribution function, Fahlesson approximation): U < 0 (ion side) ⎧ v i2 k B Ti ⎪ e U bias + U float ⎨1 − + Ii = ALP n iqi miv i2 16 2πm ⎪ + k B Ti ⎩ 2 ( * vi is relative to S/C speed Slo ) ⎫ ⎪ ⎬ ⎪ ⎭ linear logarithmic Current of any large energy particles becomes constant. Langmuir probe theory LP measured currents: I = Ii + Ie + Iph, Ly-α + Ie*, i* + Idust From OML theory (with Maxwellian distribution function, Fahlesson approximation): U < 0 (ion side) ⎧ v i2 k B Ti ⎪ e U bias + U float ⎨1 − + Ii = ALP n iqi miv i2 16 2πm ⎪ + k B Ti ⎩ 2 ( * vi is relative to S/C speed Slo ) ⎫ ⎪ ⎬ ⎪ ⎭ linear Constant current logarithmic Langmuir probe theory LP measured currents: I = Ii + Ie + Iph, Ly-α + Ie*, i* + Idust From OML theory (with Maxwellian distribution function, Fahlesson approximation): U < 0 (ion side) ⎧ v i2 k B Ti ⎪ e U bias + U float ⎨1 − + Ii = ALP n iqi miv i2 16 2πm ⎪ + k B Ti ⎩ 2 ( * vi is relative to S/C speed Slo ) ⎫ ⎪ ⎬ ⎪ ⎭ linear Constant current logarithmic Langmuir probe theory LP measured currents: I = Ii + Ie + Iph, Ly-α + Ie*, i* + Idust From OML theory (with Maxwellian distribution function, Fahlesson approximation): U < 0 (ion side) ⎧ v i2 k B Ti ⎪ e U bias + U float ⎨1 − + Ii = ALP n iqi miv i2 16 2πm ⎪ + k B Ti ⎩ 2 ( * vi is relative to S/C speed Slo ) ⎫ ⎪ ⎬ ⎪ ⎭ linear Constant current logarithmic Only thermal ion created the current slope LP sweep in the plume Ni/Ne > 10 • Ni/Ne > 10 • Small Vi current if Ne=Ni Significant slope of slow Vi Fitting with co-rotating ion Model parameters [cm-3] Ne : 6.9e+01 Ni : 2.7e+03 [cm-3] 3.0 [km/s] Vi : -2.4 [V] USC: Ni/Ne > 100 LP sweep in the plume • Ni/Ne > 100 • Small Vi Significant slope of slow Vi electron current saturate LP sweep in the plume centre • Electron current saturates due to very low Te. • Ie saturation also indicates the dust-plasma potential is very small. • Again, the ion current slope is due to the small Vi. Significant slope of slow Vi No ion wake Vi < Vco-rotation Ne/Ni << 1 extremely high density in the plume Vi < Vco-rotation Ne/Ni << 1 extremely high density in the plume Dust potential negative Dust effect in a large region! No ion wake RPWS/LP observation shows:  Large Ne and Ni in the Enceladus plume. → Enceladus creates dense plasma.  Ne/Ni << 0.5 (≤ 0.01 in the plume). → Electron attaches to dust.  No Ni wake effect. → Surrounding plasma is not co-rotating.  Vi ~ VKepler < Vco-rotation. Electrons are attached to nm- µm sized dust grains, and the charged dusts drag ions to slower speed. ad << dg << λD, Charged dust participate in collective dynamics using dust distribution of Yaroshenko (2009) Enceladus plume outside plume (E ring) Ne 300 cm-3 80 cm-3 Ni 30,000 cm-3 100 cm-3 Te 2 eV 2 eV USC (≈Ud) -3 V -2 V Nd 95 cm-3 0.25 cm-3 d 0.13 cm 0.98 cm λd 6.04 cm 78 cm Havnes number P= Tp Np aN d = Tp Np ∫ aW (a)da Using Havnes number, the balance condition for the electric current into the dust grains can be expressed as [Barkan et al., 1994]: € relationship between P and Using the relationship of the total charge density of dust ρ d = 4 πε ∫ aW (a)da = q(n i − n e ) Tp Tp q(N i − N e ) P= aN d = Np N p 4 πεU € € Calculation does not depend on dust distribution. Dust is isolated grain E ring plume Color coding = Distance from Enceladus Dust potential is zero Collective dusty plasma Havnes Parameter for our measurements RPWS & MAG J J ⊥ ⊥ • DOY 048: Pass over north hemisphere, 4 Re away • See strong –Bx perturbation in northern hemisphere • Difficult to place this pass in context with more localized S source also suggesting the dust pick up process near Enceladus from Farrell et al MAPS 2011 talk Enceladus plume/E ring studies • Plume detection by B perturbation: Dougherty et al. (2006) • Neutral observations: Waite et al. (2006), Water vapor in the plume • Dust observations: Kempf et al. (2010), CDA submicron sized dust Kurth et al. (2006), RPWS submicron sized dust Jones et al. (2009), Coates et al. (2010), ≤ nano meter sized dust • Dust and Plasma observations: Tokar et al. (2009), high energy ions slowing down Farrell et al. (2010), CAPS & RPWS comparison and suggesting dust pick up • Hybrid simulation study Simon et al. (2011), Kreigel et al. (2011), Enceladus-magnetosphere interaction considering dusty plume can explain mysterious By component. • Nano meter sized dust density estimation by CAPS Hill et al. (talk yesterday), Negative grains density ≈ 103 [cm-3] Rev 62 result Cassini-Saturn-Enceladus angle ~ 180° Dusty Plasma effect in a large region of the E-ring. Vi [km/s] Vi in the equatorial plane (RZ±0.5) [Sakai et al., in preparation] •Clearly much lower than the rigid co-rotation speed. •Vi start to be scattered out beyond ~7RS. •Vi increases with the distance from the planet. Ud < 0 Ud > 0 RS Effect of the dusty plasma in the magnetosphere (suggestion) Gurnett et al. (2007) Goertz (1981) Wahlund et al., (2009) rd << d << λD, Charged dust participate in screening & collective dynamics of ensemble Enceladus far plume Contribution from secondary electrons will make ions colder & slower ! [see also Jacobsen et al., 2009] Hot & co-rotating ions + H+ Cold & slowly drifting ions TW+ < few eV required Consistent with recently ionized ions eH+ W+ Ubias [V] E-ring plasma Hot & co-rotating ions + H+ Cold & slowly drifting ions Ubias [V] Ion transport along plume Minimum required vertical ion speed in the Z direction • RPWS/LP derived ion speeds – The spacecraft velocity vectors for each LP sweep sample position in the XZ plane – Each circle represents the required end position of the ion velocity – The rigid co-rotation velocity vectors • Vz,min >5-10 km/s – Plasma is actively accelerated near Enceladus. k, vs Plasma Speed from Interferometry Phase: d ϕ = k ⋅ d + nπ ∂ϕ ∂ Phase Dispersion: = [k ⋅ d + nπ ] ∂ω ∂ω € Doppler: ω = ω 0 + k ⋅ vs € −1 ⎡ ⎤ ∂ω ˆ ˆ ∂ϕ ⇒ = k ⋅ d d ⎢ ⎥ ⎣∂ω ⎦ ∂k ( ) where v s = (v sc − v plasma ) ∂ω ∂ω 0 ˆ giving = + k ⋅ vˆ s v s ∂k ∂k −1 ⎡ ⎤ ∂ω 0 ˆ ∂ϕ + k ⋅ vˆ s v s = kˆ ⋅ dˆ d ⎢ ⎥ ⎣∂ω ⎦ ∂k   ( ) ( ) ( ) Equating: € Plasma inhom.: € << =1 ⎛ 2π ⎞ v s = cosθ sd d Δf ⎜ ⎟ ⎝ Δϕ [rad] ⎠ ϕ ϕ f f Interferometer results [Wahlund et al., PSS, 2009] 512 fft, 32 averages, 13 such Two δn/n-signature slopes! 42-55 km/s (θsd= 0 assumed) Co-rot: 46-48 km/s, Scales ~100 m 12-14 km/s (θsd= 0 assumed) Keplerian: 11.5 km/s, Scales ~λD

Dust and Low Temperature Plasma of Sature - Langmuir Probe Theory

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