FAQ: Proposing FACET Experiments



What beam diagnostics are available in FACET that I can access when running my experiment?

The following paper gives a summary of the available beam diagnostics in FACET:


It describes:

1). Beam Position Monitors
2). Toroidal Current Monitors
3). Energy Spectrometers
4). Transition Radiation Monitors

The following URL describes a transverse deflecting x-band RF cavity system for measuring the bunch length and longitudinal bunch structure of the FACET beam:

The following URL describes how OTR (opical tranition radiation) screens work:

The following URL descibes how a YAG (yitterium aluminum garnet) crystal is use as the basis of an x-ray spectrometer and profile monitor:

The following URL describes a cherenkov spectroemter system:


How much space can I get for my experiment?

The following URL takes you to a page where the beamline is described. Look for the Solid Edge drawings. These show the optical tables where the FACET experiments are installed. There are four different experimental setups and the two tables are a toal of 24 feet in length. In principle an absolutely outstanding proposal could use the entire space (although this is extremely unlikely!). We make every effort to accommodate all experiments and if this requires de-installing existing experiments, we can do it. It's usually a question of resolving scheduling difficulties, minimizing risk and being able to do the work safely.



How much help can I expect from SLAC after my experiment is approved?

You will need to develop your plan for the experiment with assistance from people at FACET and also other users. We will typically ask for your plan and then identify areas where perhaps there can be improvement. It is likely that the plan will need to be revised based on our feedback. There is no problem in giving us plans with assumptions and questions as we will work with you to improve it.

(More details on plans and procedures can be found here:

You are also likely to need help with the hardware. We will organise and perform the installation, sometimes with your assistance depending on the tasks (e.g. tasks that require an "expert" such as installation of a rubidium oven or alignment of optics with a class 4 laser may be better performed by experimenters with experience from their home institutions). All long-haul cables are installed by SLAC staff as are gas lines. Vacuum work is typically done by SLAC staff. We can also review the design and advise and assist as required.


What is the energy spread of the FACET beam?

Experimentally it has been ~0.8% uncompressed to ~1.4% fully compressed (RMS), full width ~4% compressed with a complicated looking distribution. We measure the energy spread with the "sYAG": 

The simulation expectation for the 7mm R56 chicane optics are ~1% RMS fully compressed with <2% full width.

Follow up question: What would be the ratio of correlated energy spread to uncorrelated?
It depends on the compression, fully compressed there should be none of course, but we leave in some for 2-bunch operations.


How stable is the beam energy?

Long-term it is kept stable by the feedbacks.
For fast pulse-by-pulse uncorrelated jitter, buffered BPM data indicates a few % (I.e. <10%).


What beam parameters can I expect from the FACET facility?

​The nominal FACET beam parameters are listed in the following URL:

We record what was delivered to experiments in our reports (which get sent to DOE):

Specific questions may be answered in the FAQ you are reading separately.


What type of research can I do at FACET?

​The following URL gives a description of some of the research that can be done or is being done at FACET. Topics include:

   Plasma Wakefield Acceleration

   THz Radiation

   Plasma focusing

   Dielectric Wakefield Acceleration

   Ultrafast Process in Magnetic Solids

   Bunch length Diagnostic development.



Some already published results are in the following URL:






How can I request additional time for an existing experiment?

Existing experiments have their progress reviewed on an annual basis by the SAREC committee at the request of the FACET Division Director.

This typically requires a short presentation to the SAREC committee at an annual FACET & Test Facilities User Meeting. The presentation should describe the progress and future plans for the experiment (future plans should be at least a third of the presentation to justify continuation).

​Existing experiments don't need to resubmit a proposal unless there has been sufficient change to merit it being considered a new experiment or test beam. We recommend emailing points of contact within the facilities for case-by-case guidence on what is "sufficient".

Where can I go to get an overview of the FACET proposal process?

New proposals will be solicited every year. Proposals are peer reviewed by the SLAC Accelerator Research Experimental Program Committee (SAREC). Successful proposals will be offered beam time within a year of the proposal submission deadline. Users register after the proposal has been accepted and complete web-based training prior to arrival.

The following URL describes the FACET proposal process:


What is SAREC?

SAREC is the SLAC Accelerator Research Experimental Program Committee and it reviews all experimental proposal for FACET (and other research accelerators at SLAC). The following URL the charge of the SAREC committee and its most recent committee members.

Not to be confused by SAREK who was Spock's father in the late 60's science fiction TV series "Star Trek".


What do I have to do if I have a brand new FACET proposal?

The following URL describes the process for new FACET proposals: