Field Map and phase

[wtam]

I have difficulty understanding the various representations of phase in the FIELD_MAP element. One can the last argument to "0" for relative phase or to "1" for absolute phase. Now, after running the code, under the "Data" tab, there is an "Input_Phase" and a "Sync_Phase". I can see that if I set the last argument to "0" for relative phase, then the set phase will be the "Input_Phase". But I cannot relate the set phase value for a setting of "1" for absolute phase to either the "Input_Phase" or the "Sync_Phase". So, what is "Absolute Phase"?

A more specific question: for bunching, I used a pair of adjust and diag_energy to force zero energy gain through a field map. Then, the resulting "Sync_Phase" will be 90 or -90, which makes sense. But then the resulting "Input_Phase" will depend on the features of the specific field map. Can we simply directly set the "Sync_Phase" so that we don't have to perform an optimization?

[Didier]

Dear wtam,

I understand that the absolute phase flag is a bit confusing. You have to know that in reality whether you put 1 or 0, TraceWin always works in absolute phase. But with 0 it is the phase errors that are absolute and not necessarily the beam itself, whereas with 1, it is the beam. In other words with '0' the input phase is not referenced to the input of the machine. It is a bit complex to explain, but whatever this flag is for transport it is the same thing in both cases.

If you want to set a synchronous phase, you just have to put the command SET_SYNC_PHASE in front of the cavity and replace the value of the input phase by the value of the synchronous phase you want and so the input phase will be automatically adjusted in order to obtain this rigth synchronous phase without optimisation on your part. So no need diag_energy (see below).

SET_SYNC_PHASE
LINA-CMA01-CAV1 : FIELD_MAP 7700 300 -90 19 0.098767 0.098767 0 0 Cavity_field

Regards,

Didier

[wtam]

Dear Didier,

Thank you for the reply.

The SET_SYNC_PHASE command works. How does TraceWin determine the sync phase for a general field map? I have a field map which has a peak and a trough which is not necessarily 180 degree apart w.r.t to the velocity of the beam. I observed that TraceWin references to the 1st peak, what if I want TraceWin to reference to the 2nd peak (the trough)?

I believe the machine phase is the master clock, correct? I believe the "Abs. Phase" under the Data tab is the phase relative to the master clock, correct? Then, when set to "1", what is the relationship of the input phase to abs. phase?

Best regards,
Wai-Ming

[Didier]

What ever the shape of the field, the synchonous phase definition is shown in chapter "Energy gain and synchronous phase" from manual.

I believe the machine phase is the master clock, correct? I believe the "Abs. Phase" under the Data tab is the phase relative to the master clock, correct? Then, when set to "1", what is the relationship of the input phase to abs. phase?

It's just a phase shift! I'm not sure to well understand your question

[wtam]

Dear Didier,

I still want to understand what is Input Phase. I have attached two screenshots. For the case of absolution phase with flag set to "1". What does the "Input_Phase" 35.76754 deg mean? When set to relative phase "0", the "Input_Phase" is 152.54996 deg.

Best regards,
Wai-Ming

[Didier]

The last column is the absolute phase of the beam along the machine.
If "1" the RF phase of the cavity is set to beam phase + Input_phase.
If "0" the RF phase of the cavity is set to Input_phase. But here, phase error comming from beam or cavities are alway transported as le first case.

Both cases should give the same transport, but the first one normally gives input phase values similar to what should actually be put in the command control of a machine for tuning a cavity.

Regards,

Didier

[wtam]

If "1" the RF phase of the cavity is set to beam phase + Input_phase.

What is "beam phase" in this context?
Using the snapshot abs_phase.png as an example, what is the relationship between Input_Phase, Sync_Phase, and Abs. Phase?

Best regards,
Wai-Ming

[Didier]

Abs. Phase is the beam phase
There is not simple relation sheap between RF input phase and sychronous phase (see manual, chapter "Energy gain and synchronous phase").

Regards,

Didier

[wtam]

It is good to know that setting the flag to "1" normally gives input phase values similar to what should actually be put in the command control of a machine for tuning a cavity. Thanks.

Best regards,
Wai-Ming

[wtam]

Dear Didier,

I still have difficulty in understanding the Input_Phase. You have mentioned that:
If "1" the RF phase of the cavity is set to beam phase + Input_phase.
If "0" the RF phase of the cavity is set to Input_phase. But here, phase error comming from beam or cavities are alway transported as le first case.

Referring to the attached snapshots,
When "1", the RF phase of the cavity is 351.68+35.77=387.45
When "0", the RF phase of the cavity is 152.55
They do not match. Could you please explain?

Also, if I have a master clock and I want to determine the phase delay with respect to the master clock in order to achieve the required SYNC_PHASE (as shown in the snapshots), what is the phase delay for the two FIELD_MAPs, FM1 and FM2?

Best regards,
Wai-Ming