The OPAL Discussion Forum

[Daniel Winklehner <winklehn AT mit.edu>]

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