Understanding Phase Advance Optimization

[foshea]

I am trying to understand optimization of the transverse phase advance and I am having trouble. I have attached a sample .ini and .dat file (zipped together) that contains a sufficiently small example.

First, it isn't clear to me if the phase advance is measured from the command, as the manual states, or from after the next element, which is the usual TraceWin convention. In the attached example, what value of N should I give to SET_BEAM_PHASE_ADV so that the phase advance is optimized to the end of drift D4? 7 or 8?

Second, I cannot find any output from TraceWin that will tell me the correct phase advance. The optimizer reaches a really small number, the beam phase advance criterion is in the 1e-11 range, so I think it has reached the target value, but I cannot confirm that anywhere.

In the attached example, I have tried to optimize the lattice such that the x phase advance is 194.324 degrees from beginning to end (and included some twiss parameters, too). When I try to plot the phase advance, I have two options:
A) "Structure" and B) "Beam"

Screenshot 2021-01-12 110535.jpg (6.36 KiB) Viewed 2000 times

When I plot "Beam" I get a significantly different phase advance of 164.595 degrees.
When I try to plot "Structure" I get an error that "Data not yet available"

The manual leads me to believe that "Structure" is the plot that I want, but I don't know how to actually view it. Am I missing a check box somewhere?

[foshea]

Ohh my, it appears that I didn't notice that the units on the phase plot are deg/m. Is there any way to get that plot to show just the phase? I'd rather not integrate it.

[Didier]

Dear Foshea,

First, it isn't clear to me if the phase advance is measured from the command, as the manual states, or from after the next element, which is the usual TraceWin convention. In the attached example, what value of N should I give to SET_BEAM_PHASE_ADV so that the phase advance is optimized to the end of drift D4? 7 or 8?

You're rigth, it's not clear in manual (I'll fix it), because here commmand behavior is not usual and start at the beginning of the command, so first element in included and in your case phase advance is calculated from input of element#1 to output of element#7

Second, I cannot find any output from TraceWin that will tell me the correct phase advance. The optimizer reaches a really small number, the beam phase advance criterion is in the 1e-11 range, so I think it has reached the target value, but I cannot confirm that anywhere.

You have tow ways, the first one is shown during optimisation (see below)

Image0.png (8.23 KiB) Viewed 1991 times

The second way is to place a "LATTICE 7" command in front of your first element to define the periodic structure of your line. Thus, in the tab-sheet "Charts" the phase advance (Beam) plot shows the phase advance of the complete period rather than per element. Using this command, in your example you'll have some message before and after optimisation explaining that is impossible de calculate the kox/y/z. Don't be worry about it, that only means that phase advance calculted from matrix transfer are not possible (see phase advance definition in manuel)

Image2.png (18.84 KiB) Viewed 1991 times

The manual leads me to believe that "Structure" is the plot that I want, but I don't know how to actually view it. Am I missing a check box somewhere?

I don't think so, "Structure" means, phase advance from tranfer matrix without space-charge (another time have a look to phase advance definition)

Ohh my, it appears that I didn't notice that the units on the phase plot are deg/m. Is there any way to get that plot to show just the phase? I'd rather not integrate it.

To have result in deg rather than in deg/m (see option below)

Image1.png (2.47 KiB) Viewed 1991 times

Regards,

Didier