Available parameters

• First are elements and masses. Each row of the table represents one element. Elements are specified by their periodic table symbols. The masses are expressed in arbitrary units, to be normalised to the sum of 1. The plasma is assumed to consist of the atomic species of given elements at given concentrations, subject to ionisation (namely, the plasma consists of neutrals and positively charged ions).
• The plasma is assumed to be under local thermodynamic equilibrium, subject to the given temperature and electron density. Therefore, the distribution of internal energy of the species is given by Boltzmann statistics, and the ionisation equilibrium is given by Saha equation.
• The plasma volume or mass is required in order to to calculate the absolute concentrations of the species from the charge neutrality equation. The plasma shape and observation conditions (numerical aperture) are necessary as well to calculate radiation transport. Since we consider the plasma to be a one-dimensional light source, the optical path length (l) is its only dimension you need to control. The plasma volume (or mass) is assumed to be proportional to l³. Increasing the value will make the self-absorption effects more evident, while decreasing the value will make the plasma optically thin.
• The wavelength range determines the start and the end of the simulated spectrum. Note: if the spectral range is outside [185; 1700] nm, the spectrum will be calculated for vacuum wavelengths, and for air wavelengths otherwise. The latter are calculated according to Peck & Reeder, JOSA 62, 958 (1972).
• You can either specify the desired wavelength range and let us pick a suitable number of pixels for the implicitly assumed spectrometer observing the plasma or specify the center wavelength, the number of points (which correspond to the detector pixels) and the rest of the spectrometer parameters. Be aware that requesting too many points is not a good idea: around 20000 should be okay for a modern workstation, but if you request 1000 times more, you may make your browser hang your entire machine. We tried to avoid expensive operations on the data returned from the server, but some of them have to be O(N) and eventually the resulting data has to be plotted, which is an unavoidable cost.
• The database priority determines which database of spectral lines to prefer if both of them (NIST and Kurucz) happen to contain a line.
• We assume that the spectral lines in the plasma are subject to Stark broadening. The linear Stark effect caused by electrons inside the plasma is typical for many-electron atoms (ions), thereby the Stark widths of the profiles of the lines are proportional to the electron density (n_e). Since the electron impact Stark broadening parameter is unknown for most of the lines, the default Stark width is used to calculate the Stark width (FWHM) for them: ω = ωdefault/1016 · ne nm.
• The peak recognition limit (α) and line identification limit (β) control the peak and line identification procedure after the spectrum is simulated and lines are empirically assigned to peaks they comprise. The local maxima heights ymax - ymin have to exceed α·(max(y) - min(y)) to be considered as peaks. Lines falling between the local minima of a peak have to exceed β·max(ypeak) to be considered comprising the peak.
• The spectrograph instrumental function can be either a delta function (i.e. no convolution), a rectangle, or a rectangle convolved with (sin x / x)2:

  

• The image intensifier instrumental function can be a delta function, a Gauss profile, a Lorentz profile, or a Lorentz profile with added triangular side bands. The latter has been determined to fit the experimental data obtained in our laboratory the best; your results may vary. The synthetic spectrum is convolved with both instrumental functions as part of the modelling procedure.

  

• The self-absorption checkbox controls whether to simulate the absorption process in plasma in addition to the emission process. It is recommended to leave this checkbox on to get realistic results.

"Advanced" parameters

Use of advanced parameters makes it possible to hand-tune the optical characteristics of the apparatus simulated in the model. This may be needed to make the model spectra precisely agree with the experimental data, but requires more intimate knowledge of the instrumental setup being simulated by the model.

• The center wavelength appears in the middle of the simulated spectrum, but the total wavelength range is determined by the following optical parameters:
• The number of detector pixels directly controls how many points will be generated in the simulated spectrum as well as the wavelength range by affecting the total size of the CCD or CMOS sensor.
• The pixel width is the effective size of each pixel of the (i)CCD or (i)CMOS camera in the focal plane of the spectrograph (wpix,focal). Be aware: if a simple CCD or CMOS camera is used as a detector, you should enter the physical size of the pixel here, but if the ICCD or ICMOS camera is used, the magnification coefficient (k) of the optical system transferring the image from output window of the intensifier to the CCD or CMOS sensor surface should be taken into account to calculate the sensor pixel width in the focal plane: (wpix,focal = wpix/k)

  

• You can set the entrance slit width of the spectrograph. It is usually better to limit it to get better resolution, but in reality this results in much weaker signal.
• By changing the collimator focal length and the objective focal length, you can influence the wavelength range that gets projected on the detector.
• The spectrograph angle α represents the angle between the ray connecting the centers of collimator mirror and the diffraction grating and the ray diffracted into the center of the objective mirror. It is a constant for a given Czerny-Turner spectrograph with a reflective grating.
• Grating width (its physical dimension) and groove density can also be set. The latter strongly affects the observable wavelength range.
• Diffraction order of the grating affects the spectral resolution and observable wavelength range. A higher order means higher resolution and narrower wavelength range.
• The image intensifier resolution is the spatial resolution of the image intensifier of the ICCD (or ICMOS) camera, which is measured in line pairs per mm with the help of the special test targets (for example, USAF 1951). We assume the intensifier instrumental profile width (FWHM) equal to 1.0/resolution (mm). If the intensifier is not used in your system (the image intensifier instrumental function is a delta function), this parameter doesn't matter.

For more information, consult Zaytsev et al., SAB 158, 105632 (2019) or contact the corresponding author of the article.

Interactivity

• On form submission, all parameters are stored in the address bar after the # symbol. It is possible to bookmark the resulting address and reuse the saved parameters this way.
• If the table of identified lines is visible (expanded), clicking on a point on the plot will scroll the document to the row describing the line closest to the click point and highlight it.
• When available, use the Create preset button to save the contents of the form as a named preset inside your browser. The Load preset button will overwrite the form with the saved values. The storage is tied to the scheme and address you're using to access the website, so e.g. http://libs.chem.msu.ru and https://plasma.chem.msu.ru will give you two distinct sets of saved values. If you clear your cookies, your browser will likely remove the presets too.
• It is possible to paste the settings in a plain text format anywhere on the form except in an input element. The description of the settings should consist of pairs of keys and values separated by tab characters or newlines (but not spaces!). Valid keys include element symbols and setting names (like in the address bar). For example:

  elements	Fe Co Ni
  mass_fracts	4 5 6
  Li	100
  Cu	200
  temperature	.9
  

• Double click the label of a checkbox for a species visible in the spectrum to change its colour. Any CSS-compatible syntax is accepted, including named colours (e.g. blanchedalmond), #RGB, #RRGGBB, rgb(r, g, b) (with numbers 0-255 or percentages 0%-100%) and hsl(angle, percentage, percentage).