Quickstart
This section presents a concise user’s guide to ExPRES.
Configuration File
An ExPRES run is configured through a configuration file (in JSON format). Examples of configuration files (and the associated results files) are available from the ExPRES section of the MASER data repository for Io-, Europa- and Ganymede-controlled emissions, and for various observers.
These routine simulation files are configured for using the JRM09 [CKO+18] magnetic field model (or ISaAC [HBZG11] for some of them), the CAN81 [CAN81] current sheet model, and an electron energy of 3 keV. The position of the Active Flux Tube (AFT) for Io is based on the (corrected) lead angle model of [HCZ08], whereas for Europa and Ganymede the AFT is the same as the flux tube connected to the moon. The file names are built automatically by ExPRES. The easiest option to build your configuration file is to update an existing one.
Updating a Configuration File
You can download a configuration file to get a template (please be sure to take one using the JRM09 magnetic field model [CKO+18], for up-to-date description). There are many items and options in this file. Here are the main ones.
Setting the temporal axis
The temporal axis is configured in the TIME
section. The start time (MIN
keyword) and end time (MAX
keyword) should be provided in minutes relative to the simulation run time origin. The time sampling step is computed
from the number of time steps (NBR
keyword). The absolute time reference of the simulation run given in the
OBSERVER
section, with the SCTIME
keyword. Hence, in most cases, MIN
should be set to 0.
Setting the spectral axis
The spectral axis is configured in the FREQUENCY
section. The lower and upper bounds (MIN
and MAX
keywords)
are given in MHz. The sampling interval is cimputed from the number of spectral step (NBR
keyword). The spectral
axis can use either a Linear
or Log
scale (TYPE
keyword values). It is also possible to use a customised
spectral axis.
Setting the observer
The observer defines the place, from which the observation will be done. Basic users only need to use a limited set of
parameters. In this short guide, we present the Pre-Defined
type of observer (set in the TYPE
keyword). If you
need to change the central body (PARENT
keyword), it is recommended to use a configuration file using the
desired central body. The name of the observer (SC
keyword) should then be a name known by ExPRES. The current
list of known observers is: Cassini
, Juno
, Earth
, Voyager1
, Voyager2
. The time origin of the
simulation run is set with the SCTIME
keyword, with the format: YYYYMMDDhhmm
, with YYYY
is the year, MM
the month, DD
the day, hh
the hour, mm
the minute, all 0-padded. The other parameters are not used in this
case.
Setting the output parameters
The CDF
sub-section of SPDYN
defines the parameters that will be provided in the resulting CDF file. Each
parameters can be selected/deselected setting its value to true
/false
. In most cases, setting Theta
keyword
(opening angle of the emission cone in the direction of the observer) to true
is the minimal recommended setup.
Note that the more options are set, the bigger is the output file.
Setting the plasma model parameters
The main set of parameters that can be adjusted is the plasma density model at the source. This is done
through the DENS
sub-section of BODY
. The default model parameters, in case of the Io-controlled emissions,
are an Ionospheric model (based on [HTK98]) and an Io torus model (based on
[Bag94]).
Setting the radio source parameters
The SOURCE
section defines the radio source parameters. There may be several sources in the configuration file.
The parameters are:
TYPE
: here,attached to a satellite
, which means that the magnetic field lines used will be those connected to a moon.SAT
: ifTYPE="attached to a satellite"
, then provide the name of the moon (which also needs to be defined as aBODY
)aurora_alt
: sets the altitude (in Planetary radius) of the UV aurora (altitude below which electrons are lost by collision with the atmosphere)NORTH
: emission will be produced in the northern hemisphereSOUTH
: emission will be produced in the southern hemisphereWidth
: width of the beaming hollow cone (in degrees)current
:In most cases it should be set to
Transient (Alfvenic)
, which calculates self-consistently the beaming angle using the Cyclotron maser Instability (CMI) and a loss cone distribution functionIt can also be set to
Constant
, so that the beaming angle will not be calculated using the CMI, but will be set at a chosen values (see next parameters)
Constant
: ifCurrent="Constant"
then provide here the value in degree (80.0 for example)Accel
: the energy of the resonant electrons (in keV)Refraction
: to take into account refraction in the source’s vicinity
Running ExPRES Online
The code is available for Run-on-Demand at Observatoire de Paris: https://voparis-uws-maser.obspm.fr/client/
Short workflow to use this interface:
Click on Job List (top left)
In Job List for, select ExPRES
Click on + Create New Job (top right)
In config choose the configuration file (.json) you want to run. The other parameters (runId, slurp_mem and Add control parameters have to be left as there are)
Click on Submit, and wait for a response. It will first marked as Queued and then as Executing. It will last a few tens of second to a few minutes (depends on how many time/frequency steps and how many cdf-output parameters you asked for).
Then it will be marked as Completed,
In > Job Results you will be able to download resulting files.
If the Job is marked as Error, something went wrong during the simulation. Then, look at the > Job Details, and check the stdout and stderr sections.
For more details see the Run-on-Demand page.