Plasma

Characteristics

A plasma particle has these characteristics according to our model:

• Coordinates \(x\) and \(y\), stored as x_init + x_offt and y_init + y_offt [Offset-coordinate separation].
• Momenta \(p_x\), \(p_y\) and \(p_z\), stored as px, py and pz.
• Charge \(q\), stored as q.
• Mass \(m\), stored as m.

Shape

From the interpolation/deposition perspective, a plasma particle represents not a point in space, but a 2D Triangular-Shaped Cloud (TSC2D).

These clouds always (partially) cover an area the size of \(3x3\) cells: the one where their center lies and eight neighouring ones.

Todo

DOCS: WRITE: write a nicer formula for the weights of each cell.

lcode.weights(x, y, grid_steps, grid_step_size)

Calculate the indices of a cell corresponding to the coordinates, and the coefficients of interpolation and deposition for this cell and 8 surrounding cells. The weights correspond to 2D triangluar shaped cloud (TSC2D).

The same coefficients are used for both deposition of the particle characterictics onto the grid [Deposition] and interpolation of the fields in the particle center positions [Plasma pusher].

lcode.deposit9(a, i, j, val, wMP, w0P, wPP, wM0, w00, wP0, wMM, w0M, wPM)

Deposit value into a cell and 8 surrounding cells (using weights output).

lcode.interp9(a, i, j, wMP, w0P, wPP, wM0, w00, wP0, wMM, w0M, wPM)

Collect value from a cell and 8 surrounding cells (using weights output).

The concept is orthogonal to the coarse plasma particle shape [Coarse and fine plasma]. While a coarse particle may be considered to be a component of an elastic cloud of fine particles, each individial fine particle sports the same TSC2D shape.