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Why not build a particle accelerator on ground level? What is the shallowest feasible depth to build one?
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Assume you wanted to build a particle accelerator in a non-commerical/non-residential area. It costs more money the deeper you want to build it, therefore you want to build it as close to ground level as possible.
Why aren't particle accelerators built on ground level? What is the shallowest depth at which particle accelerators can be feasibly built, and what are the equations such as synchrotron radiation or luminosity interference (or, at least, the phenomena, and not necessarily the equations behind them) that determine this?
My speculation:
Some situation (forgot where and when) in which a stray particle from an accelerator hit someone ended in them from the effects of being by a high-energy (hadron?). Also, a Fermilab researcher who taught one of my classes told us about one of the times in which some loose particles found their way out of the accelerator and shot an inches-wide hole through a steel beam in a fraction of a fraction of a second.
Now, I doubt the particle-accelerator engineers sat down in a conference and said 'we must build them below ground or else particles beams could tear through people' but this is the only drawback I know of that comes with a ground-level accelerator; it can accidentally release fairly high-energy particles that can hit things.
Also, solar radiation must have some effect on the experiments, but I do not know one thing about those.
particle-physics experimental-physics particle-accelerators
asked 55 mins ago
nine-hundred
835
add a comment |Â
up vote
2
down vote
favorite
Assume you wanted to build a particle accelerator in a non-commerical/non-residential area. It costs more money the deeper you want to build it, therefore you want to build it as close to ground level as possible.
Why aren't particle accelerators built on ground level? What is the shallowest depth at which particle accelerators can be feasibly built, and what are the equations such as synchrotron radiation or luminosity interference (or, at least, the phenomena, and not necessarily the equations behind them) that determine this?
My speculation:
Some situation (forgot where and when) in which a stray particle from an accelerator hit someone ended in them from the effects of being by a high-energy (hadron?). Also, a Fermilab researcher who taught one of my classes told us about one of the times in which some loose particles found their way out of the accelerator and shot an inches-wide hole through a steel beam in a fraction of a fraction of a second.
Now, I doubt the particle-accelerator engineers sat down in a conference and said 'we must build them below ground or else particles beams could tear through people' but this is the only drawback I know of that comes with a ground-level accelerator; it can accidentally release fairly high-energy particles that can hit things.
Also, solar radiation must have some effect on the experiments, but I do not know one thing about those.
particle-physics experimental-physics particle-accelerators
asked 55 mins ago
nine-hundred
835
3
Well, obviously, it's because... uh... huh. I can't believe I've never asked that. This is a great question, and I have no idea what the answer is. Perhaps it has to do with cooling the magnets efficiently? Radiation shielding?
– knzhou
51 mins ago
1
@knzhou I would say that cooling the magnets efficiently would also be less expensive in an above-ground accelerator. I was thinking radiation shielding is the main reason; it could directly affect the studies done in the accelerator, but I asked because I'm sure someone must have a specific answer.
– nine-hundred
49 mins ago
I'm thinking you probably need X meters of concrete to shield out cosmic rays, but I am very interested to know if that is correct or not.
– Time4Tea
47 mins ago
@Time4Tea But why is that even a problem? Sure, the detector itself must be shielded, but then why not just encase just the detector in a building with thick walls?
– knzhou
44 mins ago
@knzhou Dirt is a very cost-effective material for constructing thick walls.
– rob♦
5 mins ago
add a comment |Â
up vote
2
down vote
favorite
up vote
2
down vote
favorite
Assume you wanted to build a particle accelerator in a non-commerical/non-residential area. It costs more money the deeper you want to build it, therefore you want to build it as close to ground level as possible.
Why aren't particle accelerators built on ground level? What is the shallowest depth at which particle accelerators can be feasibly built, and what are the equations such as synchrotron radiation or luminosity interference (or, at least, the phenomena, and not necessarily the equations behind them) that determine this?
My speculation:
Some situation (forgot where and when) in which a stray particle from an accelerator hit someone ended in them from the effects of being by a high-energy (hadron?). Also, a Fermilab researcher who taught one of my classes told us about one of the times in which some loose particles found their way out of the accelerator and shot an inches-wide hole through a steel beam in a fraction of a fraction of a second.
Now, I doubt the particle-accelerator engineers sat down in a conference and said 'we must build them below ground or else particles beams could tear through people' but this is the only drawback I know of that comes with a ground-level accelerator; it can accidentally release fairly high-energy particles that can hit things.
Also, solar radiation must have some effect on the experiments, but I do not know one thing about those.
particle-physics experimental-physics particle-accelerators
asked 55 mins ago
nine-hundred
835
Assume you wanted to build a particle accelerator in a non-commerical/non-residential area. It costs more money the deeper you want to build it, therefore you want to build it as close to ground level as possible.
Why aren't particle accelerators built on ground level? What is the shallowest depth at which particle accelerators can be feasibly built, and what are the equations such as synchrotron radiation or luminosity interference (or, at least, the phenomena, and not necessarily the equations behind them) that determine this?
My speculation:
Some situation (forgot where and when) in which a stray particle from an accelerator hit someone ended in them from the effects of being by a high-energy (hadron?). Also, a Fermilab researcher who taught one of my classes told us about one of the times in which some loose particles found their way out of the accelerator and shot an inches-wide hole through a steel beam in a fraction of a fraction of a second.
Now, I doubt the particle-accelerator engineers sat down in a conference and said 'we must build them below ground or else particles beams could tear through people' but this is the only drawback I know of that comes with a ground-level accelerator; it can accidentally release fairly high-energy particles that can hit things.
Also, solar radiation must have some effect on the experiments, but I do not know one thing about those.
particle-physics experimental-physics particle-accelerators
particle-physics experimental-physics particle-accelerators
asked 55 mins ago
nine-hundred
835
asked 55 mins ago
nine-hundred
835
edited 38 mins ago
asked 55 mins ago
nine-hundred
835
asked 55 mins ago
nine-hundred
835
asked 55 mins ago
nine-hundred
835
835
3
Well, obviously, it's because... uh... huh. I can't believe I've never asked that. This is a great question, and I have no idea what the answer is. Perhaps it has to do with cooling the magnets efficiently? Radiation shielding?
– knzhou
51 mins ago
1
@knzhou I would say that cooling the magnets efficiently would also be less expensive in an above-ground accelerator. I was thinking radiation shielding is the main reason; it could directly affect the studies done in the accelerator, but I asked because I'm sure someone must have a specific answer.
– nine-hundred
49 mins ago
I'm thinking you probably need X meters of concrete to shield out cosmic rays, but I am very interested to know if that is correct or not.
– Time4Tea
47 mins ago
@Time4Tea But why is that even a problem? Sure, the detector itself must be shielded, but then why not just encase just the detector in a building with thick walls?
– knzhou
44 mins ago
@knzhou Dirt is a very cost-effective material for constructing thick walls.
– rob♦
5 mins ago
add a comment |Â
3
Well, obviously, it's because... uh... huh. I can't believe I've never asked that. This is a great question, and I have no idea what the answer is. Perhaps it has to do with cooling the magnets efficiently? Radiation shielding?
– knzhou
51 mins ago
1
@knzhou I would say that cooling the magnets efficiently would also be less expensive in an above-ground accelerator. I was thinking radiation shielding is the main reason; it could directly affect the studies done in the accelerator, but I asked because I'm sure someone must have a specific answer.
– nine-hundred
49 mins ago
I'm thinking you probably need X meters of concrete to shield out cosmic rays, but I am very interested to know if that is correct or not.
– Time4Tea
47 mins ago
@Time4Tea But why is that even a problem? Sure, the detector itself must be shielded, but then why not just encase just the detector in a building with thick walls?
– knzhou
44 mins ago
@knzhou Dirt is a very cost-effective material for constructing thick walls.
– rob♦
5 mins ago
3
3
Well, obviously, it's because... uh... huh. I can't believe I've never asked that. This is a great question, and I have no idea what the answer is. Perhaps it has to do with cooling the magnets efficiently? Radiation shielding?
– knzhou
51 mins ago
Well, obviously, it's because... uh... huh. I can't believe I've never asked that. This is a great question, and I have no idea what the answer is. Perhaps it has to do with cooling the magnets efficiently? Radiation shielding?
– knzhou
51 mins ago
1
1
@knzhou I would say that cooling the magnets efficiently would also be less expensive in an above-ground accelerator. I was thinking radiation shielding is the main reason; it could directly affect the studies done in the accelerator, but I asked because I'm sure someone must have a specific answer.
– nine-hundred
49 mins ago
@knzhou I would say that cooling the magnets efficiently would also be less expensive in an above-ground accelerator. I was thinking radiation shielding is the main reason; it could directly affect the studies done in the accelerator, but I asked because I'm sure someone must have a specific answer.
– nine-hundred
49 mins ago
I'm thinking you probably need X meters of concrete to shield out cosmic rays, but I am very interested to know if that is correct or not.
– Time4Tea
47 mins ago
I'm thinking you probably need X meters of concrete to shield out cosmic rays, but I am very interested to know if that is correct or not.
– Time4Tea
47 mins ago
@Time4Tea But why is that even a problem? Sure, the detector itself must be shielded, but then why not just encase just the detector in a building with thick walls?
– knzhou
44 mins ago
@Time4Tea But why is that even a problem? Sure, the detector itself must be shielded, but then why not just encase just the detector in a building with thick walls?
– knzhou
44 mins ago
@knzhou Dirt is a very cost-effective material for constructing thick walls.
– rob♦
5 mins ago
@knzhou Dirt is a very cost-effective material for constructing thick walls.
– rob♦
5 mins ago
add a comment |Â
3 Answers
3
active
oldest
votes
up vote
2
down vote
accepted
The main reason for going underground is that the earth above provides some radiation shielding. An accelerator where everything is working properly is (outside the beam pipe) a relatively low-radiation environment. However if you have a steering or focusing magnet malfunction, so that the beam spills out of the pipe, you can briefly generate lots of prompt radiation.
The amount of shielding that you need depends on the energy of the accelerator. For example,
The 12 GeV electron accelerator at JLab is seven or eight meters underground --- just a couple of flights of stairs.
The 1 GeV proton machine at the Spallation Neutron Source is actually at ground level, but there's an earthen berm above it.
The (shuttered) 25 MV tandem accelerator at ORNL actually did most of its acceleration in a tower aboveground, and the various beam pathways are in a single above-ground building.
The lower the energy of your accelerator is, the less you need earthen shielding for safety reasons.
Another answer points out that background-limited experiments go underground to reduce cosmic ray backgrounds. This is a reason to put your detectors underground, but not necessarily a reason to put your accelerator underground.
answered 30 mins ago
rob♦
37.8k970158
So accelerators are built underground because the possibility that beams could malfunction and end up 'shooting' out the pipe is a danger to the integrity of the rest of the structure, and a danger to those around it?
– nine-hundred
23 mins ago
Nicely stated. If I'd seen this before I started typing I might not have bothered.
– dmckee♦
10 mins ago
@nine-hundred Not a possibility, but a practical reality. For example, as part of the recent 12-GeV upgrade at JLab, one of the upgraded acceleration modules was installed on the beam during the 6 GeV running. The accelerator folks had all sorts of trouble getting that prototype module to behave nicely; it would frequently fail, take the linac offline, and no one could walk up to it to repair it for a couple of hours due to neutron activation. Structural integrity issues general come long after radiation issues, though.
– rob♦
9 mins ago
add a comment |Â
up vote
2
down vote
It's because of shielding against cosmic rays, (from the official CERN website), and also shielding the outside world from radiation generated by the device.
Also because building such large ring-shaped devices underground is actually often cheaper than building on the surface, since you do not need to acquire a huge amount of land.
answered 39 mins ago
Al Nejati
1,028111
The source you link doesn't mention cosmic rays. They're not really a concern for collider experiments (very easy to filter out things that don't come from the collision point), and they're even used for calibration.
– dukwon
10 mins ago
add a comment |Â
up vote
1
down vote
Particle accelerator facilities are complicated beasts and they have several parts. Two subsets of thee systems have different reasons for being underground.
The beam generation, acceleration, steering and focusing mechanisms generate ionizing radiation (by bremsstrahlung and beam scraping mostly). Some parts of some system generate a lot of radiation. These parts need shielding to protect people and a pile of dirt is a cheap way to get that shielding.
The civil construction costs are usually lowest if you dig a shallow tunnel and then pile the dirt so obtained back over the top, and this is a common pattern for accelerators build in areas with relatively low population density.
Currently running example: CEBAF at Jefferson Lab in Newport News, Virginia, USA.
The detector system used to do science with the beams detect all kinds of radiation and large detectors get many signals from cosmic rays. These detector systems can benefit from being put underground where the overburden reduces the cosmic ray background, though this is mostly of interest in neutrino physics where even with intense beams the rate at the detector is quite low.
Unfortunately the cosmic rays consist largely of muons (because the atmosphere is enough shielding to reduce the contribution of less penetrating components) and have a spectrum that goes up to very high energies, so it takes a lot of overburden to significantly reduce the background.
Currently running example: LHC at CERN in Geneva, Switzerland.
As a matter of universal policy facilities with beam intense enough to cut through the vacuum components of the accelerator if badly mis-steered (which has happened—briefly because the machine doesn't operate when the vacuum is compromised—at more than one lab) don't run the machine with people in the enclosure. This isn't really from worry that people will actually get hit by the beam, but because the radiation generated by the running apparatus represents a severe threat to human health.
answered 13 mins ago
dmckee♦
72.6k6128260
add a comment |Â
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
accepted
The main reason for going underground is that the earth above provides some radiation shielding. An accelerator where everything is working properly is (outside the beam pipe) a relatively low-radiation environment. However if you have a steering or focusing magnet malfunction, so that the beam spills out of the pipe, you can briefly generate lots of prompt radiation.
The amount of shielding that you need depends on the energy of the accelerator. For example,
The 12 GeV electron accelerator at JLab is seven or eight meters underground --- just a couple of flights of stairs.
The 1 GeV proton machine at the Spallation Neutron Source is actually at ground level, but there's an earthen berm above it.
The (shuttered) 25 MV tandem accelerator at ORNL actually did most of its acceleration in a tower aboveground, and the various beam pathways are in a single above-ground building.
The lower the energy of your accelerator is, the less you need earthen shielding for safety reasons.
Another answer points out that background-limited experiments go underground to reduce cosmic ray backgrounds. This is a reason to put your detectors underground, but not necessarily a reason to put your accelerator underground.
answered 30 mins ago
rob♦
37.8k970158
So accelerators are built underground because the possibility that beams could malfunction and end up 'shooting' out the pipe is a danger to the integrity of the rest of the structure, and a danger to those around it?
– nine-hundred
23 mins ago
Nicely stated. If I'd seen this before I started typing I might not have bothered.
– dmckee♦
10 mins ago
@nine-hundred Not a possibility, but a practical reality. For example, as part of the recent 12-GeV upgrade at JLab, one of the upgraded acceleration modules was installed on the beam during the 6 GeV running. The accelerator folks had all sorts of trouble getting that prototype module to behave nicely; it would frequently fail, take the linac offline, and no one could walk up to it to repair it for a couple of hours due to neutron activation. Structural integrity issues general come long after radiation issues, though.
– rob♦
9 mins ago
add a comment |Â
up vote
2
down vote
accepted
The main reason for going underground is that the earth above provides some radiation shielding. An accelerator where everything is working properly is (outside the beam pipe) a relatively low-radiation environment. However if you have a steering or focusing magnet malfunction, so that the beam spills out of the pipe, you can briefly generate lots of prompt radiation.
The amount of shielding that you need depends on the energy of the accelerator. For example,
The 12 GeV electron accelerator at JLab is seven or eight meters underground --- just a couple of flights of stairs.
The 1 GeV proton machine at the Spallation Neutron Source is actually at ground level, but there's an earthen berm above it.
The (shuttered) 25 MV tandem accelerator at ORNL actually did most of its acceleration in a tower aboveground, and the various beam pathways are in a single above-ground building.
The lower the energy of your accelerator is, the less you need earthen shielding for safety reasons.
Another answer points out that background-limited experiments go underground to reduce cosmic ray backgrounds. This is a reason to put your detectors underground, but not necessarily a reason to put your accelerator underground.
answered 30 mins ago
rob♦
37.8k970158
So accelerators are built underground because the possibility that beams could malfunction and end up 'shooting' out the pipe is a danger to the integrity of the rest of the structure, and a danger to those around it?
– nine-hundred
23 mins ago
Nicely stated. If I'd seen this before I started typing I might not have bothered.
– dmckee♦
10 mins ago
@nine-hundred Not a possibility, but a practical reality. For example, as part of the recent 12-GeV upgrade at JLab, one of the upgraded acceleration modules was installed on the beam during the 6 GeV running. The accelerator folks had all sorts of trouble getting that prototype module to behave nicely; it would frequently fail, take the linac offline, and no one could walk up to it to repair it for a couple of hours due to neutron activation. Structural integrity issues general come long after radiation issues, though.
– rob♦
9 mins ago
add a comment |Â
up vote
2
down vote
accepted
up vote
2
down vote
accepted
The main reason for going underground is that the earth above provides some radiation shielding. An accelerator where everything is working properly is (outside the beam pipe) a relatively low-radiation environment. However if you have a steering or focusing magnet malfunction, so that the beam spills out of the pipe, you can briefly generate lots of prompt radiation.
The amount of shielding that you need depends on the energy of the accelerator. For example,
The 12 GeV electron accelerator at JLab is seven or eight meters underground --- just a couple of flights of stairs.
The 1 GeV proton machine at the Spallation Neutron Source is actually at ground level, but there's an earthen berm above it.
The (shuttered) 25 MV tandem accelerator at ORNL actually did most of its acceleration in a tower aboveground, and the various beam pathways are in a single above-ground building.
The lower the energy of your accelerator is, the less you need earthen shielding for safety reasons.
Another answer points out that background-limited experiments go underground to reduce cosmic ray backgrounds. This is a reason to put your detectors underground, but not necessarily a reason to put your accelerator underground.
answered 30 mins ago
rob♦
37.8k970158
The main reason for going underground is that the earth above provides some radiation shielding. An accelerator where everything is working properly is (outside the beam pipe) a relatively low-radiation environment. However if you have a steering or focusing magnet malfunction, so that the beam spills out of the pipe, you can briefly generate lots of prompt radiation.
The amount of shielding that you need depends on the energy of the accelerator. For example,
The 12 GeV electron accelerator at JLab is seven or eight meters underground --- just a couple of flights of stairs.
The 1 GeV proton machine at the Spallation Neutron Source is actually at ground level, but there's an earthen berm above it.
The (shuttered) 25 MV tandem accelerator at ORNL actually did most of its acceleration in a tower aboveground, and the various beam pathways are in a single above-ground building.
The lower the energy of your accelerator is, the less you need earthen shielding for safety reasons.
Another answer points out that background-limited experiments go underground to reduce cosmic ray backgrounds. This is a reason to put your detectors underground, but not necessarily a reason to put your accelerator underground.
answered 30 mins ago
rob♦
37.8k970158
answered 30 mins ago
rob♦
37.8k970158
answered 30 mins ago
rob♦
37.8k970158
answered 30 mins ago
rob♦
37.8k970158
37.8k970158
So accelerators are built underground because the possibility that beams could malfunction and end up 'shooting' out the pipe is a danger to the integrity of the rest of the structure, and a danger to those around it?
– nine-hundred
23 mins ago
Nicely stated. If I'd seen this before I started typing I might not have bothered.
– dmckee♦
10 mins ago
@nine-hundred Not a possibility, but a practical reality. For example, as part of the recent 12-GeV upgrade at JLab, one of the upgraded acceleration modules was installed on the beam during the 6 GeV running. The accelerator folks had all sorts of trouble getting that prototype module to behave nicely; it would frequently fail, take the linac offline, and no one could walk up to it to repair it for a couple of hours due to neutron activation. Structural integrity issues general come long after radiation issues, though.
– rob♦
9 mins ago
add a comment |Â
So accelerators are built underground because the possibility that beams could malfunction and end up 'shooting' out the pipe is a danger to the integrity of the rest of the structure, and a danger to those around it?
– nine-hundred
23 mins ago
Nicely stated. If I'd seen this before I started typing I might not have bothered.
– dmckee♦
10 mins ago
@nine-hundred Not a possibility, but a practical reality. For example, as part of the recent 12-GeV upgrade at JLab, one of the upgraded acceleration modules was installed on the beam during the 6 GeV running. The accelerator folks had all sorts of trouble getting that prototype module to behave nicely; it would frequently fail, take the linac offline, and no one could walk up to it to repair it for a couple of hours due to neutron activation. Structural integrity issues general come long after radiation issues, though.
– rob♦
9 mins ago
So accelerators are built underground because the possibility that beams could malfunction and end up 'shooting' out the pipe is a danger to the integrity of the rest of the structure, and a danger to those around it?
– nine-hundred
23 mins ago
So accelerators are built underground because the possibility that beams could malfunction and end up 'shooting' out the pipe is a danger to the integrity of the rest of the structure, and a danger to those around it?
– nine-hundred
23 mins ago
Nicely stated. If I'd seen this before I started typing I might not have bothered.
– dmckee♦
10 mins ago
Nicely stated. If I'd seen this before I started typing I might not have bothered.
– dmckee♦
10 mins ago
@nine-hundred Not a possibility, but a practical reality. For example, as part of the recent 12-GeV upgrade at JLab, one of the upgraded acceleration modules was installed on the beam during the 6 GeV running. The accelerator folks had all sorts of trouble getting that prototype module to behave nicely; it would frequently fail, take the linac offline, and no one could walk up to it to repair it for a couple of hours due to neutron activation. Structural integrity issues general come long after radiation issues, though.
– rob♦
9 mins ago
@nine-hundred Not a possibility, but a practical reality. For example, as part of the recent 12-GeV upgrade at JLab, one of the upgraded acceleration modules was installed on the beam during the 6 GeV running. The accelerator folks had all sorts of trouble getting that prototype module to behave nicely; it would frequently fail, take the linac offline, and no one could walk up to it to repair it for a couple of hours due to neutron activation. Structural integrity issues general come long after radiation issues, though.
– rob♦
9 mins ago
add a comment |Â
up vote
2
down vote
It's because of shielding against cosmic rays, (from the official CERN website), and also shielding the outside world from radiation generated by the device.
Also because building such large ring-shaped devices underground is actually often cheaper than building on the surface, since you do not need to acquire a huge amount of land.
answered 39 mins ago
Al Nejati
1,028111
The source you link doesn't mention cosmic rays. They're not really a concern for collider experiments (very easy to filter out things that don't come from the collision point), and they're even used for calibration.
– dukwon
10 mins ago
add a comment |Â
up vote
2
down vote
It's because of shielding against cosmic rays, (from the official CERN website), and also shielding the outside world from radiation generated by the device.
Also because building such large ring-shaped devices underground is actually often cheaper than building on the surface, since you do not need to acquire a huge amount of land.
answered 39 mins ago
Al Nejati
1,028111
The source you link doesn't mention cosmic rays. They're not really a concern for collider experiments (very easy to filter out things that don't come from the collision point), and they're even used for calibration.
– dukwon
10 mins ago
add a comment |Â
up vote
2
down vote
up vote
2
down vote
It's because of shielding against cosmic rays, (from the official CERN website), and also shielding the outside world from radiation generated by the device.
Also because building such large ring-shaped devices underground is actually often cheaper than building on the surface, since you do not need to acquire a huge amount of land.
answered 39 mins ago
Al Nejati
1,028111
It's because of shielding against cosmic rays, (from the official CERN website), and also shielding the outside world from radiation generated by the device.
Also because building such large ring-shaped devices underground is actually often cheaper than building on the surface, since you do not need to acquire a huge amount of land.
answered 39 mins ago
Al Nejati
1,028111
edited 29 mins ago
answered 39 mins ago
Al Nejati
1,028111
answered 39 mins ago
Al Nejati
1,028111
answered 39 mins ago
Al Nejati
1,028111
1,028111
The source you link doesn't mention cosmic rays. They're not really a concern for collider experiments (very easy to filter out things that don't come from the collision point), and they're even used for calibration.
– dukwon
10 mins ago
add a comment |Â
The source you link doesn't mention cosmic rays. They're not really a concern for collider experiments (very easy to filter out things that don't come from the collision point), and they're even used for calibration.
– dukwon
10 mins ago
The source you link doesn't mention cosmic rays. They're not really a concern for collider experiments (very easy to filter out things that don't come from the collision point), and they're even used for calibration.
– dukwon
10 mins ago
The source you link doesn't mention cosmic rays. They're not really a concern for collider experiments (very easy to filter out things that don't come from the collision point), and they're even used for calibration.
– dukwon
10 mins ago
add a comment |Â
up vote
1
down vote
Particle accelerator facilities are complicated beasts and they have several parts. Two subsets of thee systems have different reasons for being underground.
The beam generation, acceleration, steering and focusing mechanisms generate ionizing radiation (by bremsstrahlung and beam scraping mostly). Some parts of some system generate a lot of radiation. These parts need shielding to protect people and a pile of dirt is a cheap way to get that shielding.
The civil construction costs are usually lowest if you dig a shallow tunnel and then pile the dirt so obtained back over the top, and this is a common pattern for accelerators build in areas with relatively low population density.
Currently running example: CEBAF at Jefferson Lab in Newport News, Virginia, USA.
The detector system used to do science with the beams detect all kinds of radiation and large detectors get many signals from cosmic rays. These detector systems can benefit from being put underground where the overburden reduces the cosmic ray background, though this is mostly of interest in neutrino physics where even with intense beams the rate at the detector is quite low.
Unfortunately the cosmic rays consist largely of muons (because the atmosphere is enough shielding to reduce the contribution of less penetrating components) and have a spectrum that goes up to very high energies, so it takes a lot of overburden to significantly reduce the background.
Currently running example: LHC at CERN in Geneva, Switzerland.
As a matter of universal policy facilities with beam intense enough to cut through the vacuum components of the accelerator if badly mis-steered (which has happened—briefly because the machine doesn't operate when the vacuum is compromised—at more than one lab) don't run the machine with people in the enclosure. This isn't really from worry that people will actually get hit by the beam, but because the radiation generated by the running apparatus represents a severe threat to human health.
answered 13 mins ago
dmckee♦
72.6k6128260
add a comment |Â
up vote
1
down vote
Particle accelerator facilities are complicated beasts and they have several parts. Two subsets of thee systems have different reasons for being underground.
The beam generation, acceleration, steering and focusing mechanisms generate ionizing radiation (by bremsstrahlung and beam scraping mostly). Some parts of some system generate a lot of radiation. These parts need shielding to protect people and a pile of dirt is a cheap way to get that shielding.
The civil construction costs are usually lowest if you dig a shallow tunnel and then pile the dirt so obtained back over the top, and this is a common pattern for accelerators build in areas with relatively low population density.
Currently running example: CEBAF at Jefferson Lab in Newport News, Virginia, USA.
The detector system used to do science with the beams detect all kinds of radiation and large detectors get many signals from cosmic rays. These detector systems can benefit from being put underground where the overburden reduces the cosmic ray background, though this is mostly of interest in neutrino physics where even with intense beams the rate at the detector is quite low.
Unfortunately the cosmic rays consist largely of muons (because the atmosphere is enough shielding to reduce the contribution of less penetrating components) and have a spectrum that goes up to very high energies, so it takes a lot of overburden to significantly reduce the background.
Currently running example: LHC at CERN in Geneva, Switzerland.
As a matter of universal policy facilities with beam intense enough to cut through the vacuum components of the accelerator if badly mis-steered (which has happened—briefly because the machine doesn't operate when the vacuum is compromised—at more than one lab) don't run the machine with people in the enclosure. This isn't really from worry that people will actually get hit by the beam, but because the radiation generated by the running apparatus represents a severe threat to human health.
answered 13 mins ago
dmckee♦
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Particle accelerator facilities are complicated beasts and they have several parts. Two subsets of thee systems have different reasons for being underground.
The beam generation, acceleration, steering and focusing mechanisms generate ionizing radiation (by bremsstrahlung and beam scraping mostly). Some parts of some system generate a lot of radiation. These parts need shielding to protect people and a pile of dirt is a cheap way to get that shielding.
The civil construction costs are usually lowest if you dig a shallow tunnel and then pile the dirt so obtained back over the top, and this is a common pattern for accelerators build in areas with relatively low population density.
Currently running example: CEBAF at Jefferson Lab in Newport News, Virginia, USA.
The detector system used to do science with the beams detect all kinds of radiation and large detectors get many signals from cosmic rays. These detector systems can benefit from being put underground where the overburden reduces the cosmic ray background, though this is mostly of interest in neutrino physics where even with intense beams the rate at the detector is quite low.
Unfortunately the cosmic rays consist largely of muons (because the atmosphere is enough shielding to reduce the contribution of less penetrating components) and have a spectrum that goes up to very high energies, so it takes a lot of overburden to significantly reduce the background.
Currently running example: LHC at CERN in Geneva, Switzerland.
As a matter of universal policy facilities with beam intense enough to cut through the vacuum components of the accelerator if badly mis-steered (which has happened—briefly because the machine doesn't operate when the vacuum is compromised—at more than one lab) don't run the machine with people in the enclosure. This isn't really from worry that people will actually get hit by the beam, but because the radiation generated by the running apparatus represents a severe threat to human health.
answered 13 mins ago
dmckee♦
72.6k6128260
Particle accelerator facilities are complicated beasts and they have several parts. Two subsets of thee systems have different reasons for being underground.
The beam generation, acceleration, steering and focusing mechanisms generate ionizing radiation (by bremsstrahlung and beam scraping mostly). Some parts of some system generate a lot of radiation. These parts need shielding to protect people and a pile of dirt is a cheap way to get that shielding.
The civil construction costs are usually lowest if you dig a shallow tunnel and then pile the dirt so obtained back over the top, and this is a common pattern for accelerators build in areas with relatively low population density.
Currently running example: CEBAF at Jefferson Lab in Newport News, Virginia, USA.
The detector system used to do science with the beams detect all kinds of radiation and large detectors get many signals from cosmic rays. These detector systems can benefit from being put underground where the overburden reduces the cosmic ray background, though this is mostly of interest in neutrino physics where even with intense beams the rate at the detector is quite low.
Unfortunately the cosmic rays consist largely of muons (because the atmosphere is enough shielding to reduce the contribution of less penetrating components) and have a spectrum that goes up to very high energies, so it takes a lot of overburden to significantly reduce the background.
Currently running example: LHC at CERN in Geneva, Switzerland.
As a matter of universal policy facilities with beam intense enough to cut through the vacuum components of the accelerator if badly mis-steered (which has happened—briefly because the machine doesn't operate when the vacuum is compromised—at more than one lab) don't run the machine with people in the enclosure. This isn't really from worry that people will actually get hit by the beam, but because the radiation generated by the running apparatus represents a severe threat to human health.
answered 13 mins ago
dmckee♦
72.6k6128260
edited 8 mins ago
answered 13 mins ago
dmckee♦
72.6k6128260
answered 13 mins ago
dmckee♦
72.6k6128260
answered 13 mins ago
dmckee♦
72.6k6128260
72.6k6128260
add a comment |Â
add a comment |Â
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3
Well, obviously, it's because... uh... huh. I can't believe I've never asked that. This is a great question, and I have no idea what the answer is. Perhaps it has to do with cooling the magnets efficiently? Radiation shielding?
– knzhou
51 mins ago
1
@knzhou I would say that cooling the magnets efficiently would also be less expensive in an above-ground accelerator. I was thinking radiation shielding is the main reason; it could directly affect the studies done in the accelerator, but I asked because I'm sure someone must have a specific answer.
– nine-hundred
49 mins ago
I'm thinking you probably need X meters of concrete to shield out cosmic rays, but I am very interested to know if that is correct or not.
– Time4Tea
47 mins ago
@Time4Tea But why is that even a problem? Sure, the detector itself must be shielded, but then why not just encase just the detector in a building with thick walls?
– knzhou
44 mins ago
@knzhou Dirt is a very cost-effective material for constructing thick walls.
– rob♦
5 mins ago