In this lab students take measurements on an accelerator beam at the SNS Beam Test Facility using remote access tools. These measurements will be taken "live." It is not a simulated experience. The controls you send remotely will be physically changing magnet currents and moving actuators in the lab in Oak Ridge, TN.
Note your lab group's assigned time on the schedule. All beam measurement demos will take place in the 2-5 pm CST time slot. Contact Kiersten (ruisardkj@ornl.gov) if you have a conflict with your assigned time.
The beam measurement demos will meet in the "Simulation labs" zoom room:
https://msu.zoom.us/j/9506652864
Meeting ID: 950 6652 8647
Passcode: 810895
The Beam Test Facility (BTF) is a replica of the SNS front-end, from beam formation to the first stage of acceleration. It is comprised of:
H- ion source,
a very short low-energy beam transport (LEBT) section which takes the pulsed 65 keV, 40-60 mA beam produced by the ion source and focuses into the RFQ
a radiofrequency quadrupole (RFQ), which accelerates ions from 65 keV to 2.5 MeV while simultaneously capturing the beam into bunches
a medium energy beam transport (MEBT) line that supports 2.5 MeV bunches from the RFQ to the beamstop, including a section of periodic "FODO" lattice.
The MEBT includes diagnostics that sample the beam distribution. The 2.5 MeV medium-energy range is of interest due to the space charge effects on particle motion, which influence beam quality and losses in the high-energy end of the linac.
Watch a video tour of the Beam Test Facility, including components that will be used in class measurements, here:
We will be using the same interface as in the computer labs. The procedures is written up as a Python notebook which we will run in the Jupyter notebook interface on the Radiasoft server: https://jupyter.radiasoft.org/.
This should not be your first visit, but if logging in from a new computer, make sure to use the same email address as last week so that everything is stored in the same persistent workspace.
This lab is not available through the github. Instead, copy the lab from the jupyter server. Navigate to folder USPAS-Instructors/kruisard/ and copy the entire sns-btf-lab folder to your workspace. Open the file "sns-btf-measurement.ipynb" to see the procedure.
Instructions for navigating the python notebook are at the top of the file. You do not have to edit any python code in this lab. There are a few blocks of code used to make plots that illustrate the lab. Make sure to run these cells, but you do not have to change anything.
Section 3E of the lab procedure asks you to compare your measurements against simulated values. As we are not collecting a graded lab report, you are not required to complete this section. The following information is only relevant if you want to work through 3E on your own.
Simulations use the code Opal, which is developed at the Paul Scherrer Institute (PSI). OPAL is used for simulation linacs and electron guns with 3D space charge effects.
Opal runs on the Sirepo interface. A direct link to the simulation is embedded in the lab notebook file.
The lab report asks for a plot to compare simulated and measured beam sizes. This can be done in the program of your choice, but for convenience a python plotting routine is included at the end of the notebook file.