What is SLAC?


“Welcome to SLAC National Accelerator Laboratory! We are glad you have joined our team as we explore the ultimate structure and dynamics of matter and the properties of energy, space and time – at the smallest and largest scales, in the fastest processes and at the highest energies. Here, scientists, engineers, technicians and support professionals work together to conduct world-class research in high-energy physics, X-ray science, structural biology, chemistry, materials and energy sciences, advanced accelerator physics and particle astrophysics/cosmology.”

This was an email I received from SLAC’s on boarding team the day before I left Australia. Finally, I would be starting my new job at SLAC! Most people I’ve told about my job as “Beam Line Operations Engineer” have been left with a confused look on their face, so let me try to explain…

SLAC vaguely stands for Stanford Linear Accelerator and it is a government owned, university operated facility. I am an employee of Stanford University, of SLAC and of the United States Department of Energy. An Aussie working for the American government!??!?! No wonder the visa took so long to come through…

Let’s start with Stanford University. It was established in 1891 when education was free, but now as one of the most prestigious universities in the country, you can expect to pay upwards of $50,000 just to study here for one year. Here’s some fun facts from my initial day of training on campus:

  • 16,000 students & 17,000 staff (of which I am one!) Don’t ask me why there are more staff than students
  • Last year, there were 145,000 applications for only 2,000 job postings (i.e. everyone and their dog wants to work here)
  • As staff, I get to travel on most of the Bay Area’s public transport for free (I live a 10 minute walk from the train station, so winning!)
  • There are two gyms on campus, one of which has a climbing wall (yay for free stuff)
  • I get free tickets to some Stanford football games (yay?)
  • I can do language courses for free
  • Stanford pays me $360 a year just for riding my bike to work

Now, SLAC…

The Stanford Linear Accelerator was built in the 1970s as a particle collider. The 2 mile long accelerator runs underneath one of the Bay’s major highways. At the end of the accelerator is the SPEAR (Stanford Positron Electron Accelerating Ring) which is 80m in diameter. This is the building that I work in. The linear part of the accelerator would get particles up to great speed (almost speed of light) and then they’d be “stored” in the SPEAR until such a time the particles could be collided and their behaviours observed.

The facility was used in this capacity until the 1990s when it was re-purposed for synchrotron radiation research. Don’t worry, “synchrotron radiation” is just a fancy phrase for x-rays. This was because facilities such as the Large Hadron collider in Switzerland had overtaken Stanford’s abilities as a particle collider, building on what SLAC invented to produce a more sophisticated version of the 20-year old technology. Generating Synchrotron Radiation doesn’t require as much energy as particle collision so SPEAR was separated from the LINAC (linear accelerator) and a new ring was built right next to SPEAR. This “booster” ring became the new source of energy for SPEAR with only a 10 meter long LINAC, instead of the 2-mile long version, which was re-purposed to power other facilities within SLAC.

Stay with me…. SSRL stands for Stanford Synchrotron Radiation Lightsource, which is exactly what you see pictured above: the booster ring, the SPEAR and the beamlines coming off SPEAR (those small arrows). You see, some very clever person discovered that when an electron turns, it emits x-rays. So…

  1. The booster ring generates an electron beam and gets it up to speed
  2. The electron beam is then delivered into SPEAR where it will go round and round, getting top-ups from the booster ring when needed
  3. The turning electron beam generates x-rays that travel down the beamlines
  4. At the end of each beamline is an experimental “hutch” which is a small room (about van-sized) where the cool stuff happens. The hutch walls are lined with lead to stop nasty x-rays hitting people

But what good are x-rays anyway? Here’s where I’m a bit out of my depth, but I’ll give this a shot…

  • The x-rays at SSRL are not so very different from the x-rays you have done on your body, except that they are much, much more powerful (and therefore harmful to humans)
  • We know how these x-rays behave in a vacuum, so if we hit a sample with an x-ray beam and measure the x-ray left on the other side, we can figure out what the sample is made of, on an atomic level (i.e. the really, really small stuff that you can’t see with your eyes)

Here’s a good example. You have a single AA battery. While it’s being used, it’s losing charge, but you can’t see that. Using x-rays, you can take “pictures” of the chemical structure of the battery while it’s discharging. SSRL beamlines can take a “picture” every millionth of a second, so you end up with a movie showing what the chemicals inside a battery are doing while it’s in use. With this information, you can determine where you’re losing efficiency and improve the battery’s design. Maybe something Apple should investigate…

Don’t stress about all this radiation talk, I will not be growing a third ear! I’m required to wear a device called a dosimeter at all times which monitors the amount of radiation I am exposed to over the course of the year.

  • SLAC requires that I am exposed to no more than 100 mrem/year
  • The average human is exposed to 620 mrem/year (step away from that microwave!)



I hope most of that makes sense! As I learn more, I’ll post more!

Disclaimer: This piece was written with the intention of giving friends and family a general gist of what I do, based on what I have learned so far. This does not in any way represent the views/opinions of Stanford, SLAC, the Department of Energy or any of its affiliates.

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