Field Map and phase

[Didier]

Dear Wai-Ming,

For case '0':
Cav1 : Input phase = 152.54°
Cav2 : input phase = -142.87°

For case '1':
Cav1 : Input phase = 11.67° + 35.76°
Cav2 : input phase = -363.36° + 116.98°

Regards,

Didier

[wtam]

Dear Didier,

For case '0':
Cav1 : Input phase = 152.54°
Cav2 : input phase = -142.87°
Cav2 - Cav1 = -295.41

For case '1':
Cav1 : Input phase = 11.67° + 35.76° = 47.43
Cav2 : input phase = -363.36° + 116.98° = -246.38
Cav2 - Cav1 = -293.81

Questions:
(1) Why do you call these "input phase"? I thought these are "RF phase of the cavity".
(2) For Cav2 in Case '1', how do you determine that the sign to be negative for "-363.36"?
(3) Although the difference, Cav2 - Cav1, is the same for both case '0' and case '1', why are the values for the "RF phase of the cavity" not the same? I understand that setting the flag to '0' or '1' will lead to different Input Phase, but I thought with the above adjustment, the RF phase of the cavity should be the same.

Best regards,
Wai-Ming

[Didier]

Dear Wai-ming,

(1) Yes it's RF phase
(2) I's a tipo, read +363.36°
(3) First difference is not exactly the same and I see no reason why they should be the same.

Regards,

Didier

[wtam]

Dear Didier,

Ultimately, my question is that, when I send a beam down the beam line, what is the phase difference between Cavity1 and Cavity2?

I imagine that when I send a beam down the beam line, I have to assign a phase for Cavity1 and a phase for Cavity2 according to the design. The phase difference between Cavity1 and Cavity2 must be the same for the case of Absolute and the case of Relative ---- because it is the same design.

You have shown me how to interpret "input phase", "abs phase", and "RF phase of cavity" for both of the cases. But when I try to calculate the phase difference between Cavity1 and Cavity2, I am not able to get the same value no matter what I do with these phase calculation. Please see attachment.

Or could you please simply show me how to calculate the phase difference between Cavity1 and Cavity2 for both cases of Absolute and Relative?

Thanks and best regards,
Wai-Ming

[Didier]

Dear Wai-Ming,

Relative phase:
E = E(z)*cos(phiE), E is field see by the beam
PhiE= "Input_phase".
If for your both cavities, you set the same synchronous phase with small field amplitude (ke), then phiE1=phiE2 and if you select phys_sync-90° & 90° phiE1 = phiE2 +180°

Abosulte phase:
E = E(z)*cos(phiE+phiB)
PhiB = "Abs phase", corresponding to the time of flight of the beam.

Knowing that, I'll calculate the relation between both cases tomorrow.

Regards,

Didier

[Didier]

Ok, I'm really not able to use your example, I don't knwo why so I made bellow another one.

absolute.png (12.63 KiB) Viewed 4973 times

relative.png (10.81 KiB) Viewed 4973 times

The phases are calculed like that:
P_abs + P_beam = P_relative
cav1: -129.84 + 30.238 = -99.60
cav2: 1.617 + 978.778 = 980,3954 = -99,60

I hope it's much more clear and now you can calculate the phase differences, if you want.

Regards,

Didier

[wtam]

Dear Didier,

Thank you and I really appreciate that you made another model to show me. Now I know it is probably a problem with my edz data file. Two questions:
(1) could you please send me your model and field data file?
(2) When you use SET_SYNC_PHASE, behind the scene is it an optimization to target a certain energy gain at the exit of the field map?
(3) The field map I used (attached) has one peak and one trough. I believe it might be the reason for not having the same RF phase for cavity for the two cases of Absolute and Relative. In this case, how is the input phase being defined or calculated?

Best regards,
Wai-Ming

[Didier]

Dear Wai-Ming,

(1) Attached here, test.zip, all files of my last example including field_map file.
(2) SET_SYNC_CHANGE will find the RF phase (input phase in data tab-sheet) given the wanted synchronous phase.
(3) No, mine is very similar

test.zip

(12.24 KiB) Downloaded 252 times

Regards,

Didier

[wtam]

Dear Didier,

My problem with absolute and relative phase is resolved. Thank you. But I still need to understand what does the "input phase" mean. Using the relative case of your example, the Input_Phase is -99.6, Sync_Phase is -90, and the field map length is 300mm. For a Sync_Phase=90, does it mean that the fields goes to zero when the synchronous particle arrives at the first peak (z=98mm)? or at the middle (z=150mm)? or at the second peak (z=202m)? I am not able to relate these numbers. Could you please show me?

Thank you.

Best regards,
Wai-Ming

[Didier]

Dear Wai-Ming,

As I already say, the synchronous phase is clearly defined in manual (see picture bellow)
In equation (A2), phi0 is input phase and syncronous phase is given by equation (A5).
This is the model used in TraceWin, other software, other models and currently we are working on another model, which may be better if we consider the actual acceptance of a cavity. But in any case, there will not be a simple relationship between input phase and phase synchronous phase.

phaseS.png (44.38 KiB) Viewed 4960 times

Regards,

Didier