View source for MMS Hot Plasma Composition Analyzer

[[File: hpca_overview.png |200px|thumb|right|HPCA density, velocity, and energy spectra for H+, He+, He++, and O+ ions.]]

The MMS HPCA measures the distribution of hydrogen, helium, and oxygen ions using an electrostatic analyzer.  SPEDAS provides command line and [[GUI]] access to HPCA data.

For more information on the HPCA instrument, please see the HPCA Data Products Guide:

https://lasp.colorado.edu/mms/sdc/public/datasets/hpca/ ([https://lasp.colorado.edu/mms/sdc/public/datasets/hpca/10160.13-MMS-HPCA_SCI_ALG_UM_20160310_0.pdf 10160.13 MMS HPCA SCI ALG UM 20160310])


For basic command line access see:
<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 2px 10px; margin-left: 5px; overflow:hidden;">
/projects/mms/examples/basic/mms_load_hpca_crib.pro

/projects/mms/examples/basic/mms_load_hpca_burst_crib.pro
</div>



==HPCA moments==

[[File: hpca_moments.png |200px|right|HPCA ion moments: H+ density, O+ temperature, and He+ velocity]]

To load and plot HPCA moments for MMS1 on March 7, 2016:

<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 2px 10px; margin-left: 5px; overflow:hidden">
MMS>  mms_load_hpca, probes='1', trange=['2015-10-16', '2015-10-17'], '''datatype='moments''''

MMS>  tplot, ['mms1_hpca_hplus_number_density', 'mms1_hpca_oplus_scalar_temperature', 'mms1_hpca_heplus_ion_bulk_velocity']
</div>



==HPCA spectrograms==

[[File: hpca_espec.png |200px|right|HPCA H+, O+, He+, and He++ energy spectrograms]]

To load and plot HPCA energy spectrograms for MMS1 on March 7, 2016:

<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 2px 10px; margin-left: 5px; overflow:hidden">
MMS>  mms_load_hpca, probes='1', trange=['2015-10-16', '2015-10-17'], '''datatype='ion''''

MMS>  mms_hpca_calc_anodes, fov=[0, 360], probe='1'

MMS>  tplot, ['mms1_hpca_hplus_flux_elev_0-360', 'mms1_hpca_oplus_flux_elev_0-360', 'mms1_hpca_heplus_flux_elev_0-360', 'mms1_hpca_heplusplus_flux_elev_0-360']
</div>



==SPEDAS derived products==
[[File: hpca_spd_moments.png |200px|right|HPCA H+ density, velocity, and pressure tensor]]
[[File: hpca_spd_spec.png |200px|right|HPCA ]]
[[File: hpca_slice_contour.png |150px|right|2D slice of HPCA H+ data for 1/2 spin]]
[[File: hpca_slice_bins.png |150px|right|2D slice of HPCA H+ data for 1/2 spin showing bin width in energy and angle]]

Moments and spectrograms can be calculated from the full 3D distributions using general SPEDAS routines.  This allows for various options, such as energy and angle ranges, to be set manually for the calculation.

For example usage see:

<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 2px 10px; margin-left: 5px; overflow:hidden;">
/projects/mms/examples/advanced/mms_part_products_crib.pro
</div>


===Moments===

When producing moments all data products are calculated simultaneously for a particular input.  Spacecraft potential and magnetic field are specified via supplementary tplot variables.


===Specrograms===

Angular spectrograms are calculated in spacecraft and field-aligned coordinates.  Phi (azimuth) and theta (elevation) spectra are calculated in spacecraft coordinates.  Gyrophase (azimuth) and pitch angle (co-lat) spectra are calculated in field-aligned coordinates.  Magnetic field and ephemeris data are specified via supplementary tplot variables.  Energy spectrograms are also available.



===2D slices===
Slices of full 3D particle data can be visualized as smooth contours or by angle/energy bin.

For example usage see:
<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 2px 10px; margin-left: 5px; overflow:hidden;">
/projects/mms/examples/advanced/mms_slice2d_hpca_crib.pro
</div>

==Visualizing 3D Distribution Functions==
{{Main|ISEE_3D}}

[[File: Hpca_isee_3d.PNG |200px|right|3D visualization of HPCA H+ data for 1/2 spin.]]

SPEDAS can also be used for visualizing MMS 3D distribution functions from HPCA using the ISEE_3D tool, developed by the Institute for Space-Earth Environmental Research (ISEE), Nagoya University, Japan.

For example usage see:
<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 2px 10px; margin-left: 5px; overflow:hidden;">
/projects/mms/examples/advanced/mms_isee_3d_crib_basic.pro
</div>


====Example====

Load data into tplot
<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 0px 10px; margin-left: 5px; margin-right: 5px;">
MMS> trange = ['2015-10-20/05:56', '2015-10-20/05:58']

MMS> mms_load_hpca, probe='1', trange=trange, data_rate='srvy', datatype='ion'
</div>


Load the data into standard structures
<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 0px 10px; margin-left: 5px; margin-right: 5px;">
MMS> dist = mms_get_dist('mms1_hpca_hplus_phase_space_density', trange=trange)

MMS> data = spd_dist_to_hash(dist) ;convert structures to isee_3d data model
</div>


Load the magnetic field (cyan vector) and velocity (yellow vector) support data
<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 0px 10px; margin-left: 5px; margin-right: 5px;">
MMS> mms_load_fgm, probe=1, trange=trange, level='l2'

MMS> mms_load_hpca, probe=1, trange=trange, data_rate='srvy', datatype='moments'
</div>


Once the GUI is opened, select PSD from Units menu
<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 0px 10px; margin-left: 5px; margin-right: 5px;">

MMS> isee_3d, data=data, trange=trange, bfield='mms1_fgm_b_gse_srvy_l2_bvec', velocity='mms1_hpca_hplus_ion_bulk_velocity'
</div>

==Working with the Data in IDL structures==
To get the data out of a tplot variable and into an IDL structure, use get_data:

<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 0px 10px; margin-left: 5px; margin-right: 5px;">
MMS> get_data, 'mms1_hpca_azimuth_angles_per_ev_degrees', data=azimuth_angles

MMS> help, azimuth_angles, /structure

Structure <2283cae0>, 5 tags, length=624902264, data length=624902262, refs=1:

X               DOUBLE    Array[4843]

Y               DOUBLE    Array[4843, 63, 16, 16]

V1              UINT      Array[16]

V2              DOUBLE    Array[16]

V3              UINT      Array[63]

</div>


In this example, it's not clear which of the indices of azimuth_angles.Y corresponds to azimuths and which corresponds to anodes. To find out, use print_tinfo:


<div style="border: 1px solid LightGray; background-color:#F9F9F9; padding: 0px 10px; margin-left: 5px; margin-right: 5px;">
MMS> print_tinfo, 'mms1_hpca_azimuth_angles_per_ev_degrees'

Variable: mms1_hpca_azimuth_angles_per_ev_degrees

Structure <2aedf1c0>, 5 tags, length=158709648, data length=158709646, refs=1:

   X               DOUBLE    Array[1230]

   Y               DOUBLE    Array[1230, 63, 16, 16]

   V1              UINT      Array[16]

   V2              DOUBLE    Array[16]

   V3              UINT      Array[63]

Data format: [Epoch_Angles, mms1_hpca_energy_step_number, mms1_hpca_polar_anode_number, mms1_hpca_azimuth_index]

v1: mms1_hpca_azimuth_index

v2: mms1_hpca_polar_anode_number

v3: mms1_hpca_energy_step_number

</div>