The meaning of uz

[chiehjen]

Hi,
I am new to WarpX. Please help me with a very basic question: I want to output the velocity of each particles, is that ux,uy,uz ?

For example, I use spatial resolution for an aluminium target about 30nm, the e- momentum is distributed as:

electrons.species_type = electron
electrons.injection_style = NUniformPerCell
electrons.num_particles_per_cell_each_dim = 1 1 # 8 8
electrons.momentum_distribution_type = "maxwell_boltzmann"
electrons.theta = 8.6e-11*temp/mass_e

where temp=300 and mass_e=0.511.

My diagnosis is:

diag2.particle_fields_to_plot = z uz
diag2.particle_fields_species = electrons p aluminium
diag2.particle_fields.z(x,y,z,ux,uy,uz) = z
diag2.particle_fields.uz(x,y,z,ux,uy,uz) = uz

and I use the default "do average=1".

However, when I check the output uz, it's much higher than it should be (before laser hit the target, the thermal velocity of e- at room temperature should be 10^-2 in 1/c unit, but I got something at order 1 instead). And the value of uz seems to depend on the number of macro particle per cell also (in any case, the uz is too high for all results using 1 up to 64 marco particle per cell).

My question is: what uz actually means? Is it still (Lorentz factor)*v/c for each physical particle as stated in the introductory document or there is some macro-particle stuff involved?

Thank you in advance.