Dear Didier,
I'm a bit confused to how to set the field amplitudes for each cell initially. The field amplitudes will affect the acceleration of the particle and the arrival time to the cell centers. My guess is that GenDTL uses Superfish to compute the electric fields to get the field amplitudes. If so, is the electric fields is calculated cell by cell or by a whole tank? I am concerned about whether the electric field distribution on z axis computed cell by cell is consistent with that computed for the entire tank at once. Thank you in advance.
Best regards,
Warson
Field amplitude
Re: Field amplitude
Dear Warson,
I'm not sure I understand your question. What I can tell you is that the amplitude of the electric field is an input to the calculation performed by SuperFish. It's up to you to define it via GenDTL GUI for each cell, bearing in mind that it can vary from one cell to another but only to a certain extent depending on the post-coupler you have. Obviously, the calculation of the transport of the synchronous particle will depend on the electric field calculated in the cell and will therefore define the geometry of the cell and, of course, the following cellule geometry as a function of the acceleration obtained. For each cell, it's an iterative process that allows you to obtain the desired field amplitude because the geometry of the cell also depends on the field.
I'm probably not being very clear, just tell me.
Regards,
Didier
I'm not sure I understand your question. What I can tell you is that the amplitude of the electric field is an input to the calculation performed by SuperFish. It's up to you to define it via GenDTL GUI for each cell, bearing in mind that it can vary from one cell to another but only to a certain extent depending on the post-coupler you have. Obviously, the calculation of the transport of the synchronous particle will depend on the electric field calculated in the cell and will therefore define the geometry of the cell and, of course, the following cellule geometry as a function of the acceleration obtained. For each cell, it's an iterative process that allows you to obtain the desired field amplitude because the geometry of the cell also depends on the field.
I'm probably not being very clear, just tell me.
Regards,
Didier
Re: Field amplitude
Dear Didier,
Thanks for your answer. In the design process, does GenDTL input the geometry of the first cell into Superfish, calculate the electric field distribution of this cell, and adjust the geometry of the cell through multiple iterations to achieve the required E0 and synchronous phase? Then this process is repeated for the design of the second cell and so on. Alternatively, does GenDTL input the geometry of the entire tank (including all cells) into Superfish to obtain the electric field distribution of the entire tank, then modify the geometry of the first cell and input the entire tank geometry (including other cells) into Superfish for further calculations, and so on?
Best regards,
Warson
Thanks for your answer. In the design process, does GenDTL input the geometry of the first cell into Superfish, calculate the electric field distribution of this cell, and adjust the geometry of the cell through multiple iterations to achieve the required E0 and synchronous phase? Then this process is repeated for the design of the second cell and so on. Alternatively, does GenDTL input the geometry of the entire tank (including all cells) into Superfish to obtain the electric field distribution of the entire tank, then modify the geometry of the first cell and input the entire tank geometry (including other cells) into Superfish for further calculations, and so on?
Best regards,
Warson
Re: Field amplitude
Dear Warson,
Yes exactly.
Now if the Eo is the same for all the tank, there's no point in simulating the whole tank, you'll find the same thing. If the Eo cell by cell is not constant because, for example, you want a ramp, yes, that could be of interest, but you'd need 3D code, because the local frequency variation that allows the field to be varied relies on the post-couplers.
That said, you can also enter the frequency shift required in each cell to obtain a ramp, for example, and so consider that a simulation of the complete tank is no longer of interest either.
In any case, GenDTL provides the file you need to simulate the tank.
One last point, most of the DTLs in the world were calculated with much more approximation by calculating only one cell out of 5 and by extrrapolating the geometry of the others. GenDTL normally provides really very good accuracy, which has been proven on Linac4 and ESS, both of which were designed using GenDTL.
Regards,
Didier
Code: Select all
In the design process, does GenDTL input the geometry of the first cell into Superfish, calculate the electric field distribution of this cell, and adjust the geometry of the cell through multiple iterations to achieve the required E0 and synchronous phase? Then this process is repeated for the design of the second cell and so onNow if the Eo is the same for all the tank, there's no point in simulating the whole tank, you'll find the same thing. If the Eo cell by cell is not constant because, for example, you want a ramp, yes, that could be of interest, but you'd need 3D code, because the local frequency variation that allows the field to be varied relies on the post-couplers.
That said, you can also enter the frequency shift required in each cell to obtain a ramp, for example, and so consider that a simulation of the complete tank is no longer of interest either.
In any case, GenDTL provides the file you need to simulate the tank.
One last point, most of the DTLs in the world were calculated with much more approximation by calculating only one cell out of 5 and by extrrapolating the geometry of the others. GenDTL normally provides really very good accuracy, which has been proven on Linac4 and ESS, both of which were designed using GenDTL.
Regards,
Didier
Re: Field amplitude
Dear Didier,
Thank you again. Since the electric field is calculated cell by cell, can the electric field in the gap within a cell be solved using electrostatic method? For example, for Alvarez DTL, Dirichlet boundary conditions are set at both ends of the cell (at the center of DT), and the Laplace equation of the electric potential is solved using finite element method. The geometry is like this:
Best regards,
Warson
Thank you again. Since the electric field is calculated cell by cell, can the electric field in the gap within a cell be solved using electrostatic method? For example, for Alvarez DTL, Dirichlet boundary conditions are set at both ends of the cell (at the center of DT), and the Laplace equation of the electric potential is solved using finite element method. The geometry is like this:
- solution.png (242.19 KiB) Viewed 220 times
Warson
Last edited by 
warson on Thu 31 Oct 2024 01:15, edited 1 time in total.
warson on Thu 31 Oct 2024 01:15, edited 1 time in total.
Re: Field amplitude
Dear Didier,
I still have another question. The field distribution depends upon the detailed cavity geometry. How do you know the relative electric field strength for each cell before the DTL design (the geometry of the cavity is unknown yet)? Is it entirely based on experience?
Best regards,
Warson
I still have another question. The field distribution depends upon the detailed cavity geometry. How do you know the relative electric field strength for each cell before the DTL design (the geometry of the cavity is unknown yet)? Is it entirely based on experience?
Best regards,
Warson
Re: Field amplitude
Dear Warson,
I don't quite understand your question. In fact, I set a field law, Eo(n), and the synchronous phase loi, Ps(n), to design my DTL in GenDTL. I know from experience how to set them to have acceptable phase advances (mainly depending on Eo(n) and Ps(n)) and longitudinal acceptance (mainly depending on Ps(n)) for the beam I have to accelerate and transport in good condition.
Then, once the design has been carried out by GenDTL, I check that it's going correctly in particle simulation and often things have to be readjusted and sometimes iterated.
Regards,
Didier
I don't quite understand your question. In fact, I set a field law, Eo(n), and the synchronous phase loi, Ps(n), to design my DTL in GenDTL. I know from experience how to set them to have acceptable phase advances (mainly depending on Eo(n) and Ps(n)) and longitudinal acceptance (mainly depending on Ps(n)) for the beam I have to accelerate and transport in good condition.
Then, once the design has been carried out by GenDTL, I check that it's going correctly in particle simulation and often things have to be readjusted and sometimes iterated.
Regards,
Didier
Re: Field amplitude
Dear Didier,
Thank you very much. What I mean is that the field amplitude of the gaps cannot be set arbitrarily since these field distribution may not be realized in the cavity. To exaggerate, for example, in the first gap, the field amplitude is set to 1 MV/m, and in the second gap, the field amplitude is set to 100 MV/m and so on. The relative field amplitude of these gaps still needs to be based on experience.
Best regards,
Warson
Thank you very much. What I mean is that the field amplitude of the gaps cannot be set arbitrarily since these field distribution may not be realized in the cavity. To exaggerate, for example, in the first gap, the field amplitude is set to 1 MV/m, and in the second gap, the field amplitude is set to 100 MV/m and so on. The relative field amplitude of these gaps still needs to be based on experience.
Best regards,
Warson