## Smilei users | 241 Members | |

github.com/SmileiPIC/Smilei | 4 Servers |

Sender | Message | Time |
---|---|---|

21 Feb 2024 | ||

doubleagentdave | but not if dr is reduced | 12:07:11 |

doubleagentdave | What was the intended behaviour of timestep_over_CFL in AM geometry? | 12:07:35 |

doubleagentdave | If it's not 1/sqrt(dx2 +dr2) maybe the guide on the website needs to be adjusted. | 12:09:15 |

doubleagentdave | just so it's not used in the AM geometry | 12:10:00 |

doubleagentdave | Anyway, I can use it properly now I know that I was setting up dt wrongly using that input. | 12:12:21 |

doubleagentdave | I'll try something like 0.9/(1/dx +1/dr) | 12:15:12 |

z10f | Hello, in the benchmark `benchmarks/tst3d_04_laser_wake.py` you will find a laser initialised in a 3D simulation through python functions and the laser block. Since the laser is propagating from x=0, you need to specify the profiles for By and Bz in the coordinates y,z of that plane. You need to adapt this procedure to your case, by changing the laser with the one you wish to use. However you will need to specify the laser only as function of r (it's a cylindrical grid), taking into account the axes defined as here https://smileipic.github.io/Smilei/Understand/azimuthal_modes_decomposition.html#conventions-for-the-namelist and specifying the laser profile through `space_time_profile_AM` described here https://smileipic.github.io/Smilei/Use/namelist.html#lasers | 12:15:23 |

z10f | The CFL condition hard coded in that message is not exact, since there is no exact expression for a CFL in this geometry (which depends also on the number of modes) | 12:16:30 |

z10f | so I don't recommend to specify a dt through the CFL | 12:16:45 |

z10f | use directly `timestep` | 12:16:50 |

z10f | or it will be difficult to tune it and understand what is happening | 12:17:04 |

doubleagentdave | Thanks | 12:19:44 |

z10f | you're welcome, let us know if the problem persists | 12:20:12 |

beck-llr | Sanjeev Kumar: i had not realized your j0 was a function of r. I thought it was only (x,t). In that case you ll have to follow to general procedure indeed. | 12:32:54 |

Sanjeev Kumar | In reply to @beck-llr:matrix.orgthanks | 12:54:28 |

abigailjames | Hi again. Could someone advise on applying a linear chirp to a laser pulse. So far I've found that I need to use the Laser() rather than the gaussian2d() but can shape the beam using the temporal and spatial profiles. However the chirp is also a temporal profile. Ideally I want to have a gaussian beam with a chirp of a specified amount. I thought I could maybe use the trapezoidal temporal profile and set the slope1 to be the duration of the laser pulse and then the plateau and slope2 to zero but it's not really working. I've achieved it in other code by applying a conditional statement to the laser wavelength and I've worked out how much the omega value needs to shift by but it's not clear how I can control the amount of shift over the duration of the pulse. And advice or direction is appreciated! | 17:27:24 |

@yb12bine:matrix.tu-darmstadt.de removed their display name Carolin Elisabeth Goll (TUDa). | 17:51:03 | |

z10f | Hello, there a chirp argument implemented in some Laser Profiles https://smileipic.github.io/Smilei/Use/namelist.html#chirp_profile , but not everyone uses this definition | 18:57:21 |

z10f | an alternative way is to use a strategy similar to `benchmarks/tst3d_04_laser_wake.py` . The laser is injected from xmin in that namelist, so since it is a 3D simulation you need to specify the Bz(y,z,t) and By(y,z,t) at the border x=0 through python function, so you have virtually full control of the laser profile | 18:59:00 |

z10f | Maxwell's equations will take care of the other components while the laser is injected and propagated | 18:59:19 |

z10f | note that in that in that namelist you specify a time profile as `time_envelope = tgaussian(center=2**0.5*laser_fwhm, fwhm=laser_fwhm)` | 18:59:47 |

z10f | but it's not mandatory | 18:59:51 |

z10f | you can use any 1D function for the temporal profile, knowing that 0 is the start of the simulation | 19:00:13 |

z10f | the final result is `return a0 * w * math.exp( -invWaist2*r2 ) * time_envelope( omegat/omega ) * math.sin( omegat )` , so you can add your phase yielding the desired chirp | 19:01:16 |

z10f | playing with the delay of this phase you can control the chirp along the laser pulse | 19:01:37 |

z10f | since you specify the y,z,t profiles you can virtually add even spatio-temporal couplings | 19:02:05 |

z10f | * you can use any 1D function of t for the temporal profile, knowing that t=0 is the start of the simulation | 19:04:56 |

22 Feb 2024 | ||

Kcharbo | Hello smilei team, I was wondering for the AMCylindrical particle boundary conditions, does removal mean that any particles that cross the r=0 axis are removed? Or are they only removed at r=R where R is the radius of the cylinder? | 00:09:16 |

beck-llr | Hi. There is no particle boundary at r=0 since particle live in a 3d geometry. Particle BC are applied only when they cross Rmax. | 06:35:23 |

Kcharbo | Okay got it, thanks!! | 08:32:25 |

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