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life:what_s_an_accelerator [2025/06/24 22:19] – created ryanslife:what_s_an_accelerator [2025/08/07 01:53] (current) – ryans
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 ====What's an Accelerator?==== ====What's an Accelerator?====
 +{{tag>needs_review}}
   * Welcome! If you haven't already please check out [[What is an Operator?]] for a better idea of what your role as a new Operator here is. I also introduce some of the basics of the machine there and will reference those portions.   * Welcome! If you haven't already please check out [[What is an Operator?]] for a better idea of what your role as a new Operator here is. I also introduce some of the basics of the machine there and will reference those portions.
   * Operators come from a wide variety of backgrounds, some of us have Master's in Physics and some have Bachelor's in totally different fields. All this is to say that nobody joined as an expert in accelerators and even those who had some foreknowledge had to become accustomed to our particular lab. These are pretty complicated machines and by their nature are hard to understand in their totality, a lot of concepts intersect, overlap, and interact is some confusing ways.    * Operators come from a wide variety of backgrounds, some of us have Master's in Physics and some have Bachelor's in totally different fields. All this is to say that nobody joined as an expert in accelerators and even those who had some foreknowledge had to become accustomed to our particular lab. These are pretty complicated machines and by their nature are hard to understand in their totality, a lot of concepts intersect, overlap, and interact is some confusing ways. 
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   * Another kind of magnet is the __Quadrupole__, which is like a combination of two dipoles. Quadrupoles exist to focus the beam and should not redirect it, though they can if the beam isn't centered. You'll find both horizontal and vertical quadrupoles, these work in tandem to first smush the beam in one direction, then the other. Their field is a bit more complex to imagine, but the configuration is the elementary consequence of having four magnets in each corner of a square, alternating polarity so the bottom left and top right magnets are both North and the top left and bottom right are both South.   * Another kind of magnet is the __Quadrupole__, which is like a combination of two dipoles. Quadrupoles exist to focus the beam and should not redirect it, though they can if the beam isn't centered. You'll find both horizontal and vertical quadrupoles, these work in tandem to first smush the beam in one direction, then the other. Their field is a bit more complex to imagine, but the configuration is the elementary consequence of having four magnets in each corner of a square, alternating polarity so the bottom left and top right magnets are both North and the top left and bottom right are both South.
   * After SCS1 and 2 join together we get our **ULEBT**, or **U**pper **L**ow **E**nergy **B**eam **T**ransport. Remember, we've created a plasma but haven't really accelerated it so this is very low energy. The "Upper" refers to the architectural location of this portion, it is literally above the rest of LEBT. The first major thing here is the __Chopper__, which is probably the most familiar bit of the machine for you at this point. It's crucial that the __Chopper__ is in LEBT as the lower energy beam is much easier to redirect.   * After SCS1 and 2 join together we get our **ULEBT**, or **U**pper **L**ow **E**nergy **B**eam **T**ransport. Remember, we've created a plasma but haven't really accelerated it so this is very low energy. The "Upper" refers to the architectural location of this portion, it is literally above the rest of LEBT. The first major thing here is the __Chopper__, which is probably the most familiar bit of the machine for you at this point. It's crucial that the __Chopper__ is in LEBT as the lower energy beam is much easier to redirect.
 +
 +====Chopper Break====
 +  * The __Chopper__ is great, but has more utility than I've previously let on. This comes from the __Repetition Rate__ and __Pulse Width__ Parameters. __Pulse Width__ tells the Chopper to spend this much time allowing beam to continue down the beamline. So if the __Pulse Width__ is 100us it will stay off for that period of time and then turn on until it repeats the cycle. How long the cycle lasts is determined by the __Rep Rate__, which tells the __Chopper__ how many cycles there should be every second. You can then find the period of the cycle by finding inverse of the __Rep Rate__.
 +  * So let's return to our example, let's say we have  a __Pulse Width__ of 100us and a __Rep Rate__ of 100Hz. We can say the period of each cycle is then 1/100 s just as it would be 1/50 s if the __Rep Rate__ were 50. Let's convert 1/100s into microseconds to match the units of our __Pulse Width__ and we get a cycle period of 10,000us. So the Chopper will allow beam to pass by for 100us, then stop beam from the remaining 9,900us. A little more math reveals that we're only allowing beam to pass by 1% of the time. This is an important calculation that we refer to as the __Duty Factor__.
 +  * By Default, we like to send __CW Beam__, or __Constant Wave__. This means a __Rep Rate__ of 100Hz and a __Pulse Width__ of 9950us. You might have realized that those numbers don't give us a 100% __Duty Factor__, and you'd be right! We use the 50us gap to help with machine timing, so it's our best approximation of allowing 100% of beam to pass through. We don't change these values too often, but they are helpful for __Beam Development__.
 +
 +
 +====More Front End====
 +
 +
   * From here we have our most famous Dipoles, those being the __E-Bends__. E-Bends are very important to our __PPS__ System. With the E-Bends powered off there is no way for beam to go into the LINAC, note that beam should be stopped on the __Chopper__ or ideally a source cup before turning off the E-Bends. There are 4 E-Bends in total I DON'T ACTUALLY KNOW WHY and they first divert the beam into traveling downwards through **VLEBT** or **V**ertical **L**ow **E**nergy **B**eam **T**ransport for obvious reasons, then it redirects them into moving horizontally through the **LLEBT** or **L**ower **L**ow **E**nergy **B**eam **T**ransport.   * From here we have our most famous Dipoles, those being the __E-Bends__. E-Bends are very important to our __PPS__ System. With the E-Bends powered off there is no way for beam to go into the LINAC, note that beam should be stopped on the __Chopper__ or ideally a source cup before turning off the E-Bends. There are 4 E-Bends in total I DON'T ACTUALLY KNOW WHY and they first divert the beam into traveling downwards through **VLEBT** or **V**ertical **L**ow **E**nergy **B**eam **T**ransport for obvious reasons, then it redirects them into moving horizontally through the **LLEBT** or **L**ower **L**ow **E**nergy **B**eam **T**ransport.
   * Getting Bored? That's alright, don't forget to bother the other Operators about what's going on and also we're on to a new kind of device!   * Getting Bored? That's alright, don't forget to bother the other Operators about what's going on and also we're on to a new kind of device!
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   * The others are different, but we'll use this one as an example. If both drives are not extended, then there is no part of the attenuator that is in the path of the beam. If the first drive is extended then the 2x attenuator enters the path of the beam, blocking about half of it though attenuators are notoriously inaccurate and weird. NEVER trust what the attenuator says. Only extending the second drive would make the 5x attenuator enter the path of the beam, leaving you with about 20% of whatever it was initially. Extending both inserts the 100x attenuator. You'll notice if you try changing the attenuator configuration that it will shoot up sometimes or return odd numbers at others. This is a consequence of this drive system. You can see the Attenuation Factor on one of the TV Displays in teh Control Room, ask one of the other Operators where it is.    * The others are different, but we'll use this one as an example. If both drives are not extended, then there is no part of the attenuator that is in the path of the beam. If the first drive is extended then the 2x attenuator enters the path of the beam, blocking about half of it though attenuators are notoriously inaccurate and weird. NEVER trust what the attenuator says. Only extending the second drive would make the 5x attenuator enter the path of the beam, leaving you with about 20% of whatever it was initially. Extending both inserts the 100x attenuator. You'll notice if you try changing the attenuator configuration that it will shoot up sometimes or return odd numbers at others. This is a consequence of this drive system. You can see the Attenuation Factor on one of the TV Displays in teh Control Room, ask one of the other Operators where it is. 
   * Generally because of how they work, the different attenuators will interact in pretty weird ways that normally kills any beam output you were hoping to get through. Best practice is to skip one attenuator when possible, so should you need to use 2 attenuators it is better to use the first and third than the first and second. Attenuation also muddies up the beam in an odd way, which mostly isn't a big deal, but the Accelerator Physics sometimes wish to not use them for this reason.   * Generally because of how they work, the different attenuators will interact in pretty weird ways that normally kills any beam output you were hoping to get through. Best practice is to skip one attenuator when possible, so should you need to use 2 attenuators it is better to use the first and third than the first and second. Attenuation also muddies up the beam in an odd way, which mostly isn't a big deal, but the Accelerator Physics sometimes wish to not use them for this reason.
 +
 +====RFQ====
 +  * I call it the __RFQ__ mostly because you'll almost never hear the full name of the __Radio Frequency Quadrupole__, I like the RFQ because it's the first time we really accelerate beam in the direction of the beamline and also it is normally pretty well behaved. CAN"T RESEARCH IT ON THIS MACHINE HAHAHA
 +
 +====MEBT====
 +  * The **MEBT** or **M**edium **E**nergy **B**eam **T**ransport gets its name from the slight boost to energy that we see after the __RFQ__. Before we get to the cavities and everything, I'd like to shout out __Faraday Cup__ D1102. This is a particular Cup that is designated by it's "D Number", this is the number of decimeters from some point, this changes at points through the beamline so for simplicity's sake just remember that that number INCREASES as you go down the beamline. So if we compare Faraday Cups D0998 and D1102, you can tell that D1102 comes after D0998. This is very important for __Faraday Cups__ as if you have both D0998 and D1102 inserted it's important that you know where the beam is stopping.
 +  * D1102 is a very important __Faraday Cup__. It is used often when working with Physicists or checking beam before sending it along. Good sources for this are the pages for [[task:pdt|Primary Beam Development (PDT)]], [[task:sdt|Secondary Beam Development (SDT)]], and [[task:power|Beam Power]].
 +
 +====Cavities and Cryomodules==== 
 +  * This is the meat of the accelerator. There are 45 __cryomodules__ and inside each there are generally 8 __cavities__. These __cryomodules__ are split up into different groupings to help clarity when dealing with such a large number. The vaguest distinction we can make is where the __cryomodule__ is in LS1, LS2, or LS3. 
 +  * These are "Linear Segments" of the beamline. The beam first enters LS1, which is the middle of any paperclip-esque diagram you'll see of the accelerator, then it will be turned 180 degrees by __dipoles__ through the first "Folding Segment" until it enters LS2. The same process occurs through FS2 (Folding Segment 2) and the beam then goes through LS3. 
 +  * From here, the __cryomodules__ are further divided based on their name. __Cryomodules__ aren't referred to by their D Numbers like Faraday Cups are, you can imagine they're quite a bit bigger so it's a less useful designation. Instead They're referred to as "C-XYZ" where X is a letter, and YZ is a number. If YZ is less than 10, Y will be 0. For example, the first __cryomodule__ is CA01, the next is CA02, then CA03, then CB01. Notice how we changed the lagging number back to "01". There are more CB cryomodules than CA cryomodules. Last thing of note is that cryomodule CC12 is called as such, so if the number is greater than 10, the 0 disappears. THIS IS EXPLAINED BADLY
 +  * The cavities within the cryomodules do have D numbers, but this can be a confusing topic. Operators will almost always refer to cavities by their D number, you'll hear of "cavity 1195", "1372", and "1711" quite a bit and those names are just their D number (with the D excluded for brevity). However, many physicists and cavity experts will refer to them by their cryomodule. Here, the aforementioned cavities would be "CA03 cavity 1", "the third cavity in CB03", or "the third from last cavity in CB08".
 +  * So what ARE the cryomodules and cavities? Cryomodules are collections of cavities that rely on the same cryogenics system for cooling, cavities within the same cryomodule can affect each other but it's much more rare for cavities from different cryomodules to affect each other as each cryomodule is a big metal box.
 +  * Cavities create electric fields that quickly vary their strength sinusoidal, or like a sine wave. The idea being that any electrical force is conservative, you can't gain energy by approaching and then going away from an electric force. Let's say the force is repulsive, you would lose the same energy approaching the cavity as you would moving away from it, so if you're only considering this electric force, you haven't accelerated at all.
 +  * Cavities then diminish the field as ions approach so as to not repel them and then ramp up as the ions fly away. The process is a bit more complicated, but know this was well considered enough to get a large portion of beam up to one consistent energy. 
 +  * The period of this ramping sine wave is not something to worry about, two measurements that are worth understanding are the "Amplitude" and "Phase", You can probably guess, but the amplitude is a way of measuring the vertical span of the sine wave which is tied to the electric field strength we want the cavity to output. The phase is the offset of this sine wave in comparison to other cavities.
 +  * We talked __MPS Faults__ before, and cavities are a main perpetrator of these. There are two main kinds, first is a __Phase Wobble__, this was a brief instability in the phase that fell out of tolerance. The cavity itself doesn't shut off and MPS sees it as being good to go, but the __Interlock__ still exists and needs to be acknowledged. __Cavity Trips__ are some error that "turned off the cavity". These need to be investigated and the cavity restarted.
 +  * The scare quotes in the last sentence are probably worrying, but there's two modes of "off" for a cavity. There is the __Low Level Radio Frequency__ and the __Amplifier__. I don't fully understand these so I'll spare you from my hypotheses, though I do have a hunch. With a __Cavity Trip__ the LLRF is most likely what turned off and the Amplifier is on. In general, anything that causes an amplifier to turn off is a pretty big deal and scary.
 +  * Speaking of scary, remember that these cavities are all cooled within the cryomodules, that means one of the measurements we take is the __Fast Thermometry__ of the cavities, which is normally just the variance in temperature compared to what we think it should be. I say this is scary because any cryo related thing scares me, but realistically this is more often a sign of beam loss.
 +
 +====Lithium Stripper====
 +  * I'll start off by saying that I really like everyone who works on the Lithium Stripper. They're smart and friendly people that I have a lot of respect for, that being said the Lithium Stripper is a challenging piece of machinery. The Stripper gets its name from stripping the incoming beam of even more electrons, it does this by sustaining a thin film of liquid lithium that travels super fast. With such a dynamic process it should follow that there are occasional instabilities that can change what kind of ions come out of it.
 +  * One frequent example are minute holes rapidly appearing and disappearing in the film. This will trip MPS and stop beam, though it is very easy to clear. Even within stability it can change though, there are a few different stable configurations that the film can swap between irregularly. Some of these configurations trip MPS more than others, but any change can cause excess energy loss that, you guessed it, trips MPS.
 +  * We use the __Lithium Stripper Stage Feedback Tool__ in order to counteract this, the stripper stage eludes me somewhat admittedly, but a summary of how we interact with it can be found __here__.
 +
 +**Notes**
 +  * Maybe add in a pic of the graphs from the litium stripper feedback and explain what is going on/how to identify trips and when it levels out. 
 +  * Could add in details about the viewers here or start a subsection here about the viewers since you can view the lithium stripper from them.
 +====Sensors and More Alarms====
 +
 +  * I talked quite a bit about tripping MPS there, as far as the __Lithium Stripper__ goes this will likely be because of the __Beam Current Monitors__ or BCMs. They measure the amount of beam at one point in the beamline and gives units of uA. The ones that trip MPS the most are the __Differential Beam Current Monitors__, which are just two BCMs that compare readings. If a significant amount of beam is lost somehow between those two points then beam trips off. We have poked holes in the beamline from "losing" beam on a bellow so it's something we need to be very careful about. This is covered under MPS as this beam loss really only endangers the machine.
 +  * Different Differential BCMs are normally named after the region they're monitoring. LS1TRANS is the transmission through LS1, once you're comfortable with the LINAC and its components most of them will make sense, the only exception possibly being the LINACTGT, which measures from the start of the LINAC to the target.
 +  * This isn't the only way to detect beam loss, we also have __Neutron Detectors__ which are our go-to's anytime we're worried about beam-born radiation leaking out. These look like big white tupperware cylinders that you can see if you ever walk by N4. Tunnel __Neutron Monitors__ are connected to MPS because if there's a person down in the __Tunnel__, the area where the LINAC is, while beam is running then there's bigger issues. 
 +  * We also have __X-Ray Monitors__ in the __Tunnel__, but these are to monitor __cavities__, you might remember that cavities within the same cryomodule can "interact" with each other, a lot of this comes down to x-rays. Errant X-rays can prevent cavities from turning on (read more __here__), and aside from that they can tell experts things about the health of the cavities.
 +
 +====Folding Segment 1====
 +
 +  * I would say there's three interesting concepts within FS1. If you look at a diagram of it you'll notice 2 (or 3) arms coming off of it. The first of these is the __FRIB Single Event Experiment__ beamline, or the FSEE Beamline for short. You'll notice a __dipole__ that if powered on would continue the beam through the rest of the LINAC, if turned off the beam will continue into the FSEE Beamline.
 +  * From here is a second __dipole__, this choice is a bit more complicated however. If the __dipole__ is off then beam will continue into a __Beam Dump__, or often a "BD" for short. __Beam Dumps__ are exactly what they sound like, places to dump beam and not worry too much about it. These are big receptacles made to take beam without irradiating too much outside of it. 
 +  * If the __dipole__ is on, then the beam gets sent towards the FSEE Experiment. This is a topic with a lot of depth to it, but in short we use this for some outside entities that would like to test how their stuff works when experiencing low level radiation like this. Often mimicking the increased radiation present in space or high atmosphere. Read more about it __here__.
 +  * Lastly for FS1, if the first __dipole__ is on and the __FSEE Beamline__ is avoided, there is a second beam dump, or if all four of the dipoles are on, the charge selector.
 +  * I don't know anything about the charge selector
 +  * You may remember that we have a cocktail of different isotopes present in the source and that the horizontal source slits help reduce the unwanted isotopes, but here is another filter that I'll explain in more depth. 
 +  * The ions that make up the beam are all charged by definition, so are subject to forces brought about by a magnetic field. As you can imagine, the more charge something has, the more affected it is by magnetic fields. The acceleration experienced by an ion is inversely proportional to it's mass as well, so we have two factors that impact the turning of beam. Mathematically the acceleration is proportional to the charge divided the mass, or q/m. For reasons beyond me we refer to this invertedly as "m/q". I guess it sounds less awkward to say. 
 +  * We can separate differently ionized isotopes based on how much they'll turn when going through one of these dipoles. If it has too much charge, then it will be more effected by the magnetic field and will overturn, if it has too little charge then it will be less effected by the magnetic field and will underturn. The issue comes in when we can have multiple isotopes, as many have nearly overlapping m/q values. GIVE EXAMPLE TOO LAZY NOW
 +  * Recall however, that the source slits and charge selector have many things between them, notably the __Lithium Stripper__. This would mean that for an unwanted isotope to get past the charge selector, it would have to have 2 ionizations that overlap with the desired isotope at the desired ionization. Many ions are also fully stripped by this point, after the __Lithium Stripper__, making it all the more unlikely that these m/q's line up.
 +
 +
 +====Vacuums====
 +  *The whole beamline is kept under a pretty extreme vacuum, this is generally anywhere between e-8 Torr to e-12 Torr! There are many devices that we use to accomplish this, but here are a few of the main ones. Note also that a lot of them only work for a specific range of pressures.
 +    - **Gate Valves**: Gate Valves are beamline devices that can portion off segments of the beamline any other space we intend to pump down on. Their primary responsibility is to contain any fluctuations in the vacuum pressure and stop them from propagating. There are also **Turbo** Gate Valves, which are distinct in their ability to close very quickly and rather violently, this can be greatly helpful to prevent total vacuum excursions in the case of a leak, but due to their extreme nature have a short shelf life and should be actuated as infrequently as possible. 
 +    - **Pirani Gauge**: These are measurement devices that work best for higher pressure spaces, you'll often see these reading nominal values of e-4 Torr. Their primary uses are for **roughing**, or pumping down on atmospheric or near atmospheric regions, or for the higher pressure **Insulating Vacuums**, which I'll cover next.
 +    - **Roughing Pumps**: Scroll Pumps, Ion Pumps, Roughing Pumps, I'm sure I'm forgetting one, but generically these are pumps that are used for higher pressures, there are differences between them, but I'm no expert and it's all a bit more info than is really necessary for our role. Andy knows a lot about vacuums, feel free to ask him if things are quiet! These pumps reduce pressure, either to a desired point, or to a point where more powerful pumps can take over and further reduce pressure. I believe they stay on even after more powerful pumps are activated.
 +    - **Cold Cathode Gauges**: CCG's are like Pirani Gauges, but work for much lower pressures, like those e-12 Torr areas I mentioned earlier. They do tend to turn themselves off when exposed to higher pressures so they don't break, so every now and again one will "trip off" due to those higher pressures despite being a diagnostic, or measurement, device.
 +    - **Turbo Pumps**: What CCG's are to Pirani Gauges, Turbo Pumps are to Roughing Pumps. Once the PG's and Roughing Pumps give us a lower pressure environment, the CCG's and Turbo Pumps work to further reduce pressure from ~e-4 to something like e-10. They also can be harmed if they try to operate when pressure is too high, also an interesting thing to note is that for these lower pressures you don't get the outward flow of gas like you'd envision for atmospheric systems. Here the random travel of molecules within the vacuum matters greatly and the pump can't do much until one of them happens to cross its path. Like a cellular pump or a venus fly trap, it becomes a game of waiting, even if not for long.
 +
 +  * **Insulating Vacuums** are not vacuums we intend to send beam through, they're as the name suggests, a vacuum to limit the transfer of heat into some protected device. Air is a decent insulator, but an even better insulator is nothing, given that a vacuum is just an attempt at nothing the intent here becomes clear. These are not as great of vacuums as you'd find in the beamline, the marginal increase in insulation does not make up for the increase in complexity and power necessary to run a full turbopump set up, so they mostly stay in the e-4 Torr range. What kind of devices do they insulate? Great Question! Often these are our **Super Conducting Magnets** or **SCMs**. What are they? Well...
 +
 +====SCM vs Room Temp Magnets====
 +  * **SCMs** not sure I know enough about this, where do i find more imll research
 +  * Not all magnets are Super Conducting, a phenomenon that occurs when you make the magnet really really cold, if your professor ever made a cold magnet run around a track like f zero then this is the same concept. This requires cryogenic support to super cool and has a different department to work on. The only time we really need to care about if a magnet is super conducting or not is if something happens to it, then the alarm should tell you if it's superconducting or room temperature.
 +====Rest of LINAC====
 +honestly very boring after that.
 +
 +====Target====
 +  *We made it! The target is made out of something and at higher beam powers we need to spin it to prevent overheating. You may also recognize it from the display, where it should look rainbowy, very cool!
 +  *Of the two tasks the involve the target, the easier one is working with Matthias Steiner to measure the thickness of the Target. You can read more about that __here__, as the more interesting aspects are purely documentation and safety.
 +  *We can also start or stop the target, nominally it runs at 500 rpm. It must be stopped on occasion, such as when the remote handling group needs to do their work. That process is explained __here__.
 +
 +====The End(?)====
 +  * I really wish it was, but this isn't even the end of the ftc network. This is a long page and it covers a lot of information, really most of what you need to know regarding the devices in the beamline upto the target. However there is more, which can be found in __What is an Accelerator II__. See you there when you're ready.
 +
 +OTHER IDEAS
 +   *wedges
 +   *dccts
 +   *target and ARIS specifics
 +   *idk shane 2 add stuff
  
  
life/what_s_an_accelerator.1750817947.txt.gz · Last modified: 2025/06/24 22:19 by ryans
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