The OPAL Discussion Forum

[douguoliang <douguoliang AT impcas.ac.cn>]

Thank you for your reply,  Daniel.

Thank you for reminding me that TTF is a problem I did not consider before. 

Firstly, OPAL can't get the phase of when the bunch crossed the gaps in the case of 3D E-field(maybe it can?) . But I noticed the theta of bunch position  at the end of each turn. I think it can represent the slip phase to a certain extent, but the changes in the whole acceleration process are small, not more than 3 degrees(Figure1,2).

Secondly,  I did the test of scanning phase to select the best acceleration phase. And I set the initial phase in opal based on the maximum energy gain per turn. The initial phase in opal differs by 6 degrees from the initial phase calculated theoretically.

I think there are some errors due to my parameter settings in the simulation process. However, I am not sure whether the current energy gain error of about 10% is abnormal. Can you give the approximate error range according to your experience in 3D electric field simulation?

	Douguoliang
douguoliang AT impcas.ac.cn

---- Replied Message ----

From Daniel Winklehner<winklehn AT mit.edu> Date 11/10/2022 23:07 To douguoliang<douguoliang AT impcas.ac.cn> ,
opal<opal AT lists.psi.ch> Subject RE: [Opal] the Energy gain per turn with 3D RF E-field

Hi Guoliang Dou,

 

The energy gain in a cyclotron will never be as high as the peak field of your cavity.

 

Did you consider the transit time factor (TTF) and, more importantly, the bunch phase? In OPAL, you can 1. plot the phases of when the bunch crossed the gaps and 2. do a phase scan to find what cavity phase would get you close to the desired energy gain, at least in the first turn. What is your designed synchronous phase? What is the isochronicity of your cyclotron magnetic field?

 

Another option for debugging your problem is to start with the built-in RF Cavities, set the parameters to match your 3D model as much as you can, and check what you get.

 

Your CST field seems a bit jumpy as well. You might consider increasing the resolution.

 

Best,

   Daniel

 

 

 

From: opal-request AT lists.psi.ch <opal-request AT lists.psi.ch> On Behalf Of douguoliang
Sent: Thursday, November 10, 2022 9:32 AM
To: opal <opal AT lists.psi.ch>
Subject: [Opal] the Energy gain per turn with 3D RF E-field

 

Hi, all

 

I'm using 3D electric field to simulate the straight-sector cyclotron. But I found that there is a certain difference between the energy gain and the design value.

 

Before that, the 3D E-field files is exported from CST. The peak voltage value in the model is 160kV, so I set the ESCALE to 0.75 to make it consistent with the design peak voltage of 120kV. And I also have set the right PHIINT.

 

From the OPAL's output ,I can get the energy gain per turn. And from the CST, I can get the gap voltage by the curve integral(Figure 1). I found that from OPAL's output that the energy gain per turn is less than the energy of the CST gap voltage. So, I convert the energy gain per turn into the gap voltage actually felt by the particles according to the particle charge and gap numbers. We can see that the trends are consistent but there is a difference of about 10kV between them(Figure 2) .

 

I checked the 3D E-field file before input OPAL and the 3D electric field file at t=0 output using DUMPEMFIELDS command. But there is nearly no difference between them(Figure 3,4,5). 

 

So I don't know what is the reason for such a difference, can anyone help me to answer it?

 

The all figures are in the attachment.

 

Best regards, 

Guoliang Dou

	douguoliang
douguoliang AT impcas.ac.cn

 

Attachment: Figure1.png
Description: PNG image

Attachment: Figure2.jpg
Description: JPEG image