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Background Information | Background Information | |
Jovian Trapped Particle Radiation Models |
In the following, we present a brief review of the main characteristics of the Jovian trapped particle radiation belts and the engineering models that are used to evaluate mission fluences and doses.
The Jovian magnetosphere is normally described in terms of three major regions [Dessler, 1983]:
Also, the passage of Ulysses spacecraft through the Jovian magnetosphere revealed stable pancake-shape pitch angle distributions for protons inside ~ 17 Rj. The same mission showed that the equatorial proton omni-directional flux decreases approximately exponentially with magnetic equatorial distance and is nearly longitudinally symmetric [Aglin et al, 1997].
The population of energetic electrons is limited mainly by absorption by the satellites and the Jovian ring rather than by radiation losses.
Low energy electrons contribute to spacecraft surface charging. High energy electrons can cause dielectric charge buildup that may lead in turn to destructive arcing. Electrons also contribute to ionising doses through direct energy deposition and bremsstrahlung effects.
High energy protons are the main contributors to ionising dose deposition in shielded components. They also dominate Single Event Upset (SEU) rates. Lower energy protons (up to 10 MeV) contribute to Non-Ionising Energy Loss (NIEL) dose that affects Charged-Coupled Devices (CCD) and other detectors.
Model |
Energy range (MeV) |
Coordinate range (Rj) |
Magnetic field models | Reference |
---|---|---|---|---|
Proton models | ||||
D&G83 | > 0.6 | L <= 12 | D4 (Smith et al, 1976) | Divine & Garrett, 1983 |
Salammbo | 1 - 1000 | L <= 6 |
Internal: O6 (Connerney, 1993)
External: Khurana (1992,1997) |
Bourdarie & Sicard, 2006 |
Electron models | ||||
D&G83 | > 0.06 | L <= 16 (in) L > 16 (out) |
D4 (Smith et al, 1976) | Divine & Garrett, 1983 |
GIRE | 0.5 - 30 | 8 <= L <= 16 | VIP4 (Connerney et al, 1998) | Garrett et al, 2003 |
Salammbo | 1 - 600 | L <= 9.5 |
Internal: O6 (Connerney, 1993)
External: Khurana (1992,1997) |
Bourdarie & Sicard, 2006 |
Ion models | ||||
JOSE HIC | 6-200 MeV/nucl | 2.8 to > 30 | N/A | Jun, 2005 |
JPL-Heavy Ion | 5-40 MeV/nucl | 5 ≤ Radius ≤ 25 Rj | N/A | JPL Publication 11-16, 2011 |
For energies below model validity range (see Table 1), flux values are extrapolated and subsequently used in other SPENVIS applications (e.g. SHIELDOSE).
4.1 The Divine and Garrett model The model developed by Divine and Garrett is the only global model available today and is based on data collected by the Pioneer and Voyager flybys of Jupiter combined with earth-based observations [Divine and Garrett, 1983]. For the electrons, it covers the whole range from the surface of the planet to the tail of the magnetosphere while for the protons it applies from the surface to L = 12. The energy spectrum for electrons and protons includes energies higher than 0.06 and 0.6 MeV respectively.
The magnetic field used is based on the D4 model derived from Pioneer Helium vector magnetometer data [Smith et al , 1976]. Note that this model performs fine for radial distances inside Io's orbit but it fails for higher distances due to effects of the plasma torus.
Though GIRE covers the equatorial plane of Jupiter, it can be extended by assuming the pitch-angle distribution provided by the Divine and Garrett model. It applies for electrons with energies from 0.5 to 30 MeV [Bourdarie & Sicard , 2006].
Also, the more recent VIP4 magnetic field model was used [Connerney et al, 1998]. However, it has the same spatial limitations as the D4 model.
The spatial range of the model extends from the surface to L = 9.5 for the electrons and L = 6 for the protons. It includes electrons and protons with energies from 1 to 600 MeV and 1 MeV to 1 GeV respectively.
In order to have a more accurate picture of the radiation belts outside Io's orbit, the O6 model [Connerney, 1993] is used to describe the inner magnetic field. In addition, an external field model from Khurana is used, providing more realistic field lines for large distances [Khurana, 1992,1997].
The spatial range of the model extends from the surface to L = 9.5 for the electrons and L = 6 for the protons. It includes electrons and protons with energies from 1 to 600 MeV and 1 MeV to 1 GeV respectively.
The heavy ion model integrated in JOSE is the HIC model developed by Garrett et al. [Jun 2005][Evans, 2008].This version of the HIC model uses data from 31 of the 35 Galileo orbits of Jupiter. The HIC model covers radial distances of 2.5 Rj to well past 30 Rj and defines three heavy ion populations: carbon, oxygen, and sulphur. The HIC model is composed of two cases: the average and the worst case. However, until now, only the average model is publicly available and consequently is the only one implemented in JOSE.
In order to have a more accurate picture of the radiation belts outside Io's orbit, the O6 model [Connerney, 1993] is used to describe the inner magnetic field. In addition, an external field model from Khurana is used, providing more realistic field lines for large distances [Khurana, 1992,1997].
The JPL Jovian equatorial heavy ion radiation environment model has been based on data from the Galileo HIC experiment. The data covered the period from 1995 to 2003 and included orbits C03 through J35 (excluding J5, J13 and A34) and the heavy ion range from 6C to 28Ni. The model defines the fluxes for oxygen (5-40 MeV/nucl), carbon (5-40 MeV/nucl) and sulphur (6.3-40 MeV/nucl) between ~5 and 25 RJ. Average differential flux spectra for these three components are presented in terms of energy for selected radial bins. A simple fit has been developed in terms of energy and radial distance that allows interpolation of the fluxes at intermediate values of the two variables. As the model is based on averages over pitch angle from Galileo, which primarily orbits in the jovian equatorial plane, the model is considered valid for approximately 2-3 RJ above or below that plane between 5-25 RJ. The model defaults to the ambient GCR levels for carbon, oxygen and sulphur values for fluxes below 10-6(cm2 s sr MeV/nuc)-1 for carbon and oxygen and 10-8 (cm2 s sr MeV/nucl)-1 for sulphur.
The model is constructed from two components: a tabular radial function, F0,j(R), and a double power law energy fit, as in the equation below.
Fj | differential flux in units of (#/cm²/s/sr/(MeV/nucl)) |
Fo,j(R) | flux constant at a given radius, fit from the data. |
E | Energy in MeV/nucl |
R | radial position (Jovian Radii) |
Aj,Bj | power law constants fit to the data |
E0,j | energy constant fit to the data (MeV/nucl) |
j | subscript indicating the ion species: carbon, oxygen or sulphur |
The Spenvis implementation makes no attempts to propagate the equatorial fluxes to higher latitudes, nor to follow field lines to determine the corresponding equatorial radius that the field line crosses. Instead, the radial distance of the orbital location is used to access the JPL model and the corresponding equatorial fluxes for that radius are returned. It is left as an exercise for the user to assess the validity of higher latitude results.
To provide the integral spectrum, the the Spenvis implementation employs a numerical integration of the differential spectrum and adds the corresponding ISO 15390 GCR integral flux spectrum as the integration constant, or 9.02E10-4, 8.36E10-4 and 2.75E10-4 (cm2 s sr)-1 for carbon, oxygen and sulphur, respectively.
Bourdarie S. and Sicard A., Jupiter environmental modelling, ONERA technical note 120 issue 1.2, ESA contract 19735/NL/HB, FR 1/11189 DESP, October 2006
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Connerney, J. E. P. et al, New models of Jupiter's magnetic field constrained by the Io flux tube footprint, J. Geophys. Res., 103, 11929-11939, 1998.
Dessler, A. J. (Ed.), Physics of the Jovian magnetosphere, Cambridge University Press, New York, 1983
Divine N. and Garrett H. B., Charged particle distribution in Jupiter's magnetosphere, J. Geophys. Res., 88, 6889-6903, 1983
Drake F. D. and Hvatum H., Non-thermal microwave radiation from Jupiter, Astron. J., 64, 329, 1959
Garrett H. B. et al, Galileo Interim Radiation Electron Model, Jet Propulsion Laboratory, California Inst. of Technol., JPL 03-006, Pasadena, CA, 2003
Khurana K., A generalized hinged-magnetodisc model of Jupiter's nightside current sheet, J. Geophys. Res., 97, 6269-6276, 1992
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Mauk B. H., Energetic ion characterestics and neutral gas interactions in Jupiter's magnetosphere, 109(A9), A09S12, doi:10.1029/2003JA010270, 2004
McIlwain, C. E., Coordinates for mapping the distribution of magnetically trapped particles, J. Geophys. Res., 66, 3681-3691, 1961
Rogers J. H.,The giant planet Jupiter, Cambridge University Press, Cambridge 1995
Sicard A. and Bourdarie S., Physical electron belts model from Jupiter's surface to the orbit of Europa, J. Geophys. Res., 109, 2004
Smith E., Davis L. and Jones D., Jupiter's magnetic field and magnetosphere, in Jupiter (Gehrels T. ed.), University of Arizona press, Tucson, 788-829, 1976
Garret H.B., Kokorowski M., Kang S., Evans R.W., Cohen C.M.S., The Jovian Equatorial Heavy Ion Radiation Environment, JPL Publication 11-16, November 2011.
Jun I., Henry B. Garrett and Robin W. Evans, "High-Energy trapped Particle Environments at Jupiter: an update", IEEE Transactions on Nuclear Science, vol. 52, No. 6, 2005.
Evans R. W., H.B. Garrett, I. Jun, C.M.S. Cohen, E.C. Stone,and S.J. Drouilhet, "Galileo Heavy Ion Radiation Model: Update to the HIC model", AGU poster, 2008.