Here's the inside of a radiation treatment machine I repaired. It's what I've been doing for the last 30+ years to make a living, but will not be doing any longer. I'm going to be quiting now.
This section of the machine is called the modulator. It stores a lot of energy in a large bank of capacitors which gets discharged into a klystron amplifier tube. The klystron makes microwaves that accelerate electrons into a target to produce the x-rays that are used to treat many types of cancers.
Cool
Amazing!
They need frequent repair/adjustment to keep working. A linear accelerator is a very complicated piece of machinery. They have an approximately 6 ft. long accelerator waveguide where the electrons get accelerated to very close to the speed of light. There is a complicated series of steering magnets needed to keep them going down the accelerator properly. As we learned from Einstein, E=MC squared. So we are increasing the mass of the electrons to a range of 6-20 MEV before they are converted to photons (x-rays). We also use the electrons themselves to treat cancers that are more superficial since the range of electrons (beta particles) is much shorter. I have to work with radiation physicists to insure the beam charateristics are correct so I have to know some radiation physics myself. Very interesting and challenging stuff. Some of the problems are incredibly difficult to figure out, but that makes it even more interesting.
A "Linac" does have some similarities to the old tube-type televisions. The old TVs also work by accelerating electrons into a phosphor to make photons, but those photons are much lower energy, in the visible light spectrum. So old TVs are accelerators too.
Cool, I used to have a reel-to-reel machine too. They were better than cassettes, but the problem with magnetic tape was always the limited dynamic range. Recording technology has come so far since those days.
Wow what a machine. I could do with one of those at home to treat the nodes they wouldn’t do! 😂
You'd just need some 6 foot thick concrete walls on your house for shielding. 
A big thank you to those who design, build and maintain these machines
What we have to do with the radiation beam is measure the profile of it in what's called a "water phantom" which is basically a tank of water with motor driven ionization chambers that can run across the treatment field and also up and down in depth. We measure radiation by its ability to ionize gas. Ionization can be measured electronically. So we submerge the probe into this water phantom and run it across the treatment field at a certain depth, typically 10cm. The beam intensity basically needs to be same across the field. We want to make sure the beam profile is flat and symmetrical which is a function of how the electron beam hits the target. We adjust the steering magnets according to what we see in the beam profile scans. If the symmetry is off for example, we would adjust either the position steering or the angle steering depending on what we are seeing. Once that's accomplished, we adjust an automated feedback loop that keeps it wherever we set it as the machine rotates around. All of this is done with adjustments outside of the treatment room. No lead suit you could wear would be thick enough to protect you. Besides that, high energy x-rays would produce neutron radiation when they hit your lead suit. You need to be behind 6 feet of concrete or more to be safe. We also measure the beam's energy by running the ionization chamber down through the water doing what's called a "depth of ionization" scan. Depending on the energy, the beam intensity follows a specific curve as you go down in depth. The intensity goes up until it reaches a maximum point called the "Dmax" (depth of maximum ionization). Then it drops from there. This enables the doctors to deliver less radiation to the surface and more radiation where the tumors are. The higher the beam's energy, the deeper the Dmax is. Electron's are also used to treat more superficial cancers. They have a very shallow Dmax and a finite range of travel in body tissue or water.
Troubleshooting these machines is a step by step logical process. Before I became disabled with this cancer, I was also doing classes, teaching people how to do it. It starts by learning how the machine works then applying that knowledge to troubleshooting.
Now that I'm not working any more, I'm already missing doing this. I have a great reputation in this field.
Klystron; it has been a while since I have heard that word. I used to work in broadcast television as an engineer. The klystron was used as the final stage of amplification in the transmitter to bring the television signal up to 55,000 watts. From there, the energy was delivered to the antenna through about 1,000 feet of transmission line.
So now, I might be on the receiving end of a klystron if I need more radiation; interesting.
The klystron or a magnetron is used to make the microwave power that accelerates electrons. A conventional transformer can put out enough voltage to accelerate up to around 300-400 KeV, but to go into the MeV energy range, you need a linear accelerator. A linear accelerator uses microwave power to accelerate electrons. The electrons ride on the microwaves like a surfer rides on the ocean waves. The ones I work on run around 5.5 megawatts peak, 65KW average power so it's a similar power to what you were using. The magnetron is a simpler device, an amplifier and an oscillator. The klystron is an amplifier only so it requires an RF source.
Wow, looks like the insides of my self winding watch.
Maybe that's why I'm never on time.
Good Luck and Good Health.
j-o-h-n Tuesday 01/30/2018 11:54 AM (guessing) EST
Thank you for your very informative post about the linear accelerator. I've had a lifetime experience as a radiologic technologist and I understand and appreciate the hard work and extreme dedication of service engineers such as yourself. I spent 38 years as a department director and I've seen those people spend tireless hours troubleshooting various machines in my departments and always felt those men were totally underappreciated for what they could do. Believe me, there is nothing worse than having a patient that is in dire need of examination and the feeling when you press the button and nothing happens. What's next? call the serviceman. No doctor can do anything if the diagnosis can't be made and treatment can't be given without working equipment, and that, my friend, takes a skilled and experienced person such as yourself. And that can't be taught in any college, no bachelors degree or masters degree or even PHD can repair something like those machines without the experience and training you have and can give. I want to thank you and all those like you for your lifetime dedication and service.
Thanks. It's a very demanding job. Long hours, stressful, on call 24-7 and like you say, not much appreciation. It was always interesting and challenging though so I liked it. Eventually, when I got good at it, the company I worked for ran me into the ground until I finally quit. Once it started to affect my health I had to give up working for them. Then I started my own company doing the same thing.
I've often wondered if the stress repair people and IT guys work under attributes to PC. I think mine does. I carry a good deal of misplaced frustration on my back and frustration that I can't get people to buy better equipment in a timely fashion. I even got into an argument 6 months before my diagnosis where I exclaimed to another employee that I was "taking it in the shorts" every day. 6 months later, PSA of 49.
EricE: Reading your old post here. I would say emotional stress is a big factor in developing cancer. 1 year after selling my professional business to a “ business partner”, this was a non bank earnout agreement, I developed Pca. Why? I was full of anger after realizing my new business partner was stealing me blind. There’s a greatness book out here entitled: Feelings buried alive never die by: Karol K. Truman. I think you can get it cheap on Kendal. Great read for this subject, Take care, Stan
Had a similar experience with my business. Partners are for dancing.
Very well said. Yes, foolhardy idealism, as in fools rush in, spawn “ partnerships”. The word belongs in a con artists bag of tricks. I’ve learned my lesson well. Thx Gregg57. I graduated from the same school— hard knock high, moving on now. My only partner in life is my wife. Enough said.
Cool! I repair servers so it looks kind of familiar. Mostly I'm an admin but I do get my hands dirty occasionally. I'm sorry you are giving it up. For a long retirement, I hope. It must be fulfilling to keep these things going. Thanks for your service.
I once got called to a medical imaging place because all the hard drives in their computers were failing. We replaced them all but they seemed uncomfortably close to their imaging machine. I always wondered if that was the problem.
WOW!!!!! So Amazing Gregg! I hope you'll enjoy your future endeavors ☺. Thank you for all of your years of helping to keep people alive.
Most sincere,
Jackie
Mine too. I wish they would get bigger and cheaper but that's happening already.
I spent many years at the Lawrence Berkeley Laboratory working on particle beam accelerators. One of my assignments was to design the power electronics to drive the steering magnets. 1000 amps was needed on one magnet. Another required 250 amps but had to be reversed in direction in less than 100 milliseconds. This was easier than it sounds as huge diodes would allow dumping the energy in to a capacitor bank and then turning on the transistor actuators on the other side would put the current back in the reverse direction. Fun days of my youth. One of my fraternity brothers has a family business repairing these machine here in Florida.
Do you think that the radiation from machines caused any cancer, from improper shielding. I had a 300/100 machine. Lead shielding around room.
today is the second radiation treatment (out of 25) for what my new radiologist is calling Oligomatastic* stage 4 prostate cancer.
Radiation a second time? Recurrent PC 
Meeting with a radiation oncologist for the first time this Thursday. 
Time to radiation treatment
