Talk:Particle accelerator

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Contents 1 Possible vandalism 2 Frequently Ask Questions About Accelerators 3 Is this really still a stub? 4 Removed from article 5 Organization 6 Typos 7 Sources 8 Safety Concerns? 9 == Spam? == 10 Micro black hole hazard 11 Discussion of Large Hadron Collider risks

[edit] Possible vandalism

There have been a lot of major deletions in the particle accelerator article since 18 November 2007, with no discussion on the talk page. I expanded the article by about 35% on 25-26 October 2007, and the current version seems to have lost all that work. There was no comment or criticism that I know of since that period, only some minor corrections.

I am a newbie to Wikipedia editing, so I may have missed something important, but the deletions since 18 Nov by anonymous editors (especially 169.204.228.210, who has been the main offender, as far as a quick look tells me), with no discussion or justification, seem like vandalism to me.

Without careful study, it seems to me that the versions of the 3 Nov to 19 Nov interval, up to the one by Cloudguitar, are probably the last best ones to go back to.

I had been thinking about working on the organization of the article some more, and described my ideas on the talk page under the "Organization" and "Safety concerns?" sections. I guess I will hold off on this project until the current flurry is resolved. It may be that my additions were massively inappropriate, as they were somewhat unreferenced and based on my experience and general knowledge as a particle physicist grad student and professional physicist and (gamma-ray) astronomer. I do think I know a lot of stuff that is correct, interesting, and useful, and hoped the needed references could be filled in later, maybe partly by others.

Most of this has been reported to ClueBot, w/r its 21:42 Nov 21 revert, which seems about the same length as before the attack, but the current article looks pretty much like it did before 25 October.

I do have the qualification of 40+ years experience, a PhD in physics, and I am a staff astronomer at Caltech. (None of this necessarily means anything, of course!!) But let me know if I am off base in my approach, and thanks. Wwheaton (talk) 20:16, 21 November 2007 (UTC)

[edit] Frequently Ask Questions About Accelerators

1. Q : What do different particle accelerators sound like when in operation?

A : Basically, you cannot hear the motion of the particles nor the sound produced by the collision with the target. The walls of the vacuum chambers are about one inch thick of solid metal, so they are great accoustic isolators. However, to operate an accelerator facility, a lot of electronics is needed. Just imagine a room full of computers and you will be close...

Umm... All of our particle accelerators at work are composed mainly of 1mm thick stainless tubing, nowhere near one inch thick. Many smaller and midsized electrostatic accelerators have moving charging belts or chains and actually are quite loud when in operation. Martyman 10:43, 16 Mar 2005 (UTC)

speaking as a former SLAC employee, i can tell you that most (all?) RF accelerators are either cooled by water (for room-temperature cavities) or by cryogenics (for superconducting cavities). the various pumps that run these cooling systems, along with the pulsed switch tubes in the klystrons usually generate one hell of a racket while the accelerator is operational.

Natelipkowitz 00:46, 6 December 2005 (UTC)

A tandem Van de Graaf makes a bang when there is a ten million volt spark, but they had to have a sound system for us to be able to hear it in the control room.

A Synchrotrons repeatedly cycle their bending magnetic field B up to keep the radius of the particle orbits closely constant as the beam momentum increases during acceleration. At the end of each cycle (typically a few seconds), the B field has to be turned down in preparation for the next cycle. Because the energy density in the B field is proportional to B², the total energy stored in the field for a large synchrotron can be very large; for the Large Hadron Collider at CERN, with 7 TeV beams in a 27 km long tunnel, the stored magnetic energy at the peak of each cycle is about 10 GJ, roughly the equivalent of the energy in 2.5 tons of TNT. It is not economic to simply draw this much energy out of the power grid and dump it at the end of each cycle. Hence historically a system was provided for large synchrotrons to store this energy, after the accelerating cycle. I am not sure about the machinery to do this energy storage nowadays, but for the first large synchrotrons --the Cosmotron, Bevatron, and AGS, a large set of flywheels was provided, along with a powerful motor-generator system, so that energy stored in the rotating flywheels was converted into electrical power during the B field ramp up, and then during the latent part of the cycle the stored magnetic induction energy was converted back into electrical energy, and used to spin up the flywheel for the next cycle. As a result, those synchrotrons had a characteristic whine that could be heard all over the site, with the pitch dropping as the MG set slowed down on acceleration, and rising again as the magnets were turned down. I suspect this must still be the case for the Tevatron and LHC, though probably the cyclic undulating whine is not audible everywhere. —Preceding unsigned comment added by Wwheaton (talk • contribs) 00:52, 25 October 2007 (UTC)

2. Q : Do particle accelerators have any characteristic oder or visual effect?

A : Yes in Ion implantation toxic odor when opened to atmosphere. Visual effects?

3. Q : Why do physicists create particle accelerators?

A : Particle accelerators are developed by physicists who want to get a better understanding of the fundamental laws of nature. When particles collide in a particle accelerator, physicists can see attributes of subatomic particles by using a bubble chamber (modern) or a cloud chamber (less modern, less expensive). The chamber will allow scientists to collect the path of particles after the collision. These paths tell physicists a lot.

Particle accelerators are used for much more than high end nuclear physics research. They are used in the fabrication of semiconductors, the treatment and diagnosis of cancer and production of medical radioisotopes to name a few uses. These more mundane everyday accelerators greatly outnumber the giant super colliders of sub atomic physics. Even a cathode ray tube in a television or computer screen is a very low energy particle accelerator. Martyman 10:43, 16 Mar 2005 (UTC)

4. Q : Can you cook food with a particle accelerator, like a microwave?

A : surely this is a joke. i'm sure physicists don't spend millions of dollars, and even more valuable technology, in building a particle accelerator, just to heat up their hot pockets...

Actually, I recall that one physicist stuck a glass of beer in the beamline of the bevatron to test the theory that cosmic rays where what caused bubbles to nucleate in it. It got him a brief write-up in "Discover" magazine (and the answer was "no, something else causes nucleation"). --Christopher Thomas 01:37, 22 June 2006 (UTC)

5. Q: What is the purpose of building extreamly large circular accelerators - like the one in Texas? Is the information that could be learned really worth the billions these devices cost? Themepark

Circular accelerators are built because particles pass through any given set of RF cavities many times, being boosted each time, unlike a linear accelerator, where they make only one pass through. This allows higher energy for a given size of accelerator. However, forcing particles to follow a curved path causes losses due to synchrotron radiation, which places an upper limit to the energy that can be attained by any given circular accelerator. Linear accelerators are used for lighter particles like electrons and positrons (which have more severe synchrotron losses in curved accelerators), and ring-shaped accelerators are used for proton/antiproton experiments and experiments that collide heavy atomic nuclei.

Whether or not these devices are worth the money depends on what goals are considered important when judging "worth". They are unlikely to produce data that has practical application, but they are the only way to test many aspects of our theories of how the universe works. In other words, they are "pure research" devices. --Christopher Thomas 17:48, 12 March 2007 (UTC)

"Someday you'll tax it", as I believe Faraday responded to a similar question posed to him by an MP. The period of development before uses are found and applications developed is likely to be very long and unpredictable, in my opinion, so in the short term the value may really be cultural: helping us to learn about the universe that is the context of all our human stage, wherein we move and do and have our being. I personally believe these vast machines are our equivalent of medieval cathedrals, monuments to our deep curiosity and our striving to understand where and who we are. Wwheaton (talk) 22:21, 18 November 2007 (UTC)

6. Q: Is the amount of energy created when the collision occurs equal to the amount of energy put in to the process of acceleration? 83.146.14.113 17:04, 12 March 2007 (UTC)B Briggs

No. There are inefficiencies in the acceleration mechanisms (energy put into the RF cavities doesn't all end up in the accelerated particles, by a long shot; most of it probably ends up as heat). There are also losses due to synchrotron radiation in ring-shaped accelerators that cause energy to be drained from the accelerated particles (lost as x-rays). When particles collide, not all of the energy goes into producing new particles, and the vast majority of particles produced aren't the ones any given experiment is interested in (high-energy accelerators are built to produce heavy, exotic particles, but it's much easier for lighter particles to be produced, so many more are). --Christopher Thomas 17:48, 12 March 2007 (UTC)

[edit] Is this really still a stub?

This seems to me like a pretty complete layman's treatment of the subject. Shall we remove the stub template? It could perhaps use some additional wikifying, but it sure doesn't seem stubby to me. --Kgf0 18:03, 11 October 2005 (UTC)

Feel free to add....Scott 18:30, 11 October 2005 (UTC)

honestly, in my opinion this article is rather incomplete, very poorly organized (separate sections on synchrotron light and synchrotron radiation, for instance) and in need of attention. i will do it when i can find the time! Natelipkowitz 00:48, 6 December 2005 (UTC)

[edit] Removed from article

I have just removed teh following text from the article. I couldn't find anything online that backed it up. If anyone knows anything about it feel free to re-add it. --Martyman-(talk) 05:49, 26 November 2005 (UTC)

There is also a new larger accelerator being built in Sweden crossing over the border
into Switzerland. It will span in an underground tunnel under the border over 3 km and
has two different acceleration magnets at each end to help in extensive study of different
things done with the accelerator.

Well, Swededen and Switzerland don't border each other, so a 3km linac wouldn't help much. Looks like somebody was confused and/or writing a silly hoax. -- SCZenz 16:40, 26 November 2005 (UTC)

You know the thought that Sweden and Switzerland wheren't anywhere close to each other did cross my mind, but strangely it didn't click as evidence that this was a hoax. ;-) The big CERN accelerator is in a ring that crosses the Switzerland-France border, but this is not what they are talking about (not a linear accelerator 3km long). --Martyman-(talk) 21:06, 26 November 2005 (UTC)

[edit] Organization

It seems to me, on first looking back on this article to need help. High and low energy are related to how the energy is applied to the particles, but that is not the way to start the article. We should say something about the scale and use of high and low energy accelerators, describe some technology and then say what techniques have proven most useful for what types of accelerators.

I agree the article does need a good going over. There is also the problems of a confused terms in the article. I am under the understanding that a linear accelerator is any accelerator that does not follow a curved path, this would include large linacs, smaller electrostatic accelerators and could even be stretched to cathode ray tubes, etc. The term "linac" obviously a shortening of linear accelerator seems to be solely applied to large superconducting RF type accelerators, though is used interchangably in this article. --Martyman-(talk) 05:07, 20 January 2006 (UTC)

I think "linac" includes all straight-line accelerators that use radio frequency fields to accelerate the particles, at leas if they have high enough energy to induce nuclear reactions. I can't remember for sure, but I think the professors I worked with when I did my thesis used the temp to apply to the Luis Alvarez proton linear accelerator. I also believe the term was used to describe the second injector stage of the CERN PS. David R. Ingham 19:54, 22 January 2006 (UTC)

I reorganized and expanded the section on circular & cyclic accelerators a bit last month. I also added the lead-in section on the "Uses..." of accelerators. Now I am thinking of moving most of the present subsections on high and low energy machines to the linear accelerator section, as appropriate, and incorporating most of the rest of those subsections into the present section on "Uses...". I think I would organize the "Linear..." section roughly by energy, which would also pretty much follow the historical sequence. Does this sound sensible? I am also thinking of retitling the sub-section on "Black hole..." to a section on "Safety issues" or maybe "Hazards", and expanding it with some of the material in my comments here in the discussion yesterday, even though I cannot reference most of that very thoroughly or very quickly, most of it being based on my experience as a particle grad student in the late 1960s, and as an interested bystander since. I hope others might step in to rescue the useful and winnow out the rest. Anyhow, comments are solicited. Wwheaton (talk) 21:56, 18 November 2007 (UTC)

[edit] Typos

The last sentence of the first paragraph of Astrophysics is broken, too broken for me to figure out what it is meant to say.

Removed "Black Hole production". Not relevant to discussion of particle accelerators, per se. This should instead go into an article on exotic physics at colliders.--131.225.233.132 16:21, 11 September 2006 (UTC)

[edit] Sources

While the "Black hole production" section provides details of interesting theories, it contained limited and useful references to the source of these theories. There was a reference to an issue of Scientific American in May 2006 in parenthesis, which violated the Wikipedia standards for citing sources. I marked it as an NOR until the specific article can be referenced.

[edit] Safety Concerns?

Should there be a section on some of the possible safety concerns? The article on the Large Hadron Collider contains a section that might be a good starting point.GreenGourd 18:10, 3 November 2007 (UTC)

I'd agree. I've always wondered what would happen if one stuck his or her head in one. My best guess is that it would break, but how can I be sure? I'm interested in any theories Lancensis 13:18, 5 November 2007 (UTC)

With modern large synchrotrons like the LHC, with high intensity beams, you would receive a fatal radiation dose in a few seconds or less (ignoring the problem of the vacuum, of course). The simple beam electrical power, current times voltage (voltage being the particle energy, 1 volt per eV, so typically many billions of volts), was 30 GeV X 20 microampere (average) at SLAC in its earliest operation, ie, 600 kilowatts in a beam about mm in diameter. A real Death Ray, in other words. On a more modest scale, I remember at the old Bevatron, one of the first (1950s) accelerators to extract particle beams from the main ring for experimental use, there were places where one could walk through the beam-lines (which sometimes passed through air for short distances), and these reportedly featured signs saying "Walk Fast Through Here", or advising one to time ones' passage to avoid the pulse of particles, coming every five seconds or so, marked by a bell and the audible cyclic whine of the motor-generator units.Wwheaton (talk) 02:47, 18 November 2007 (UTC)

Whether you agree with them or not, there are scientists and others who warn about dangers. This is an encyclopedia, not a pro- or con-pamphlet, and we should provide balanced coverage. GreenGourd 03:03, 10 November 2007 (UTC)

The primary safety protection is of course that very large, very high energy machines have been invariably buried in deep tunnels since about the mid-1960s, so that shielding of the order of 10 m of earth is automatically provided. The tunnels themselves are generally accessible by unprotected workers when the machine is off, but regions downstream of targets may receive very high doses of scattered high-energy particles, and can become significantly radioactive. Managing these hazards is rather like safety in laboratory or medical contexts where radio-isotopes are handled, or around nuclear reactors, except that there is no danger of runaway fission or meltdown as with nuclear fission situations. Since beams are now routinely stored for times of hours in storage rings, the technology of confinement for millions of cycles with very low particle loss has necessarily come quite far. Also, considerable care is taken nowadays, when beam intensities are much higher than formerly, to avoid allowing the beam to leak stray particles and to avoid accidental "beam dumps" (loss of particle bunches from the nominal orbit) because of the danger of cumulative radiation damage to nearby structures (like superconducting magnets), and also the desire to avoid producing secondary induced radioactive materials, which would contaminate the tunnel and complicate access for normal maintenance. I can add some words about these issues to the article, but references and documentation would require more time than I have available now. Wwheaton (talk) 02:47, 18 November 2007 (UTC)

[edit] == Spam? ==

A recent reversion of the external link to a pdf for free download of a textbook [Stanley Humphries (1999) Principles of Charged Particle Acceleration ] seems like a needless loss to me. The web page is indeed by the author, a professor emeritus at the University of New Mexico, but the work seems to be scholarly, fairly recent, and useful, with a lot of material covered. It seems to me that the purpose of the link is to make the text widely available for personal use, not to promote it commercially, although the latter motive cannot be excluded. The web site does have links to other services and tools provided by the author's company, so it seems a borderline case.

Also, the contributor of the Wiki reference, (User:Comparat, no information on user or talk pages; the edit in question was on 4 March 2007), has made only a few edits to Wikipedia, which seem to be technical improvements, and I see no evidence of systematic spamming. It would be useful for someone to download the .pdf and study the book carefully, but based on the table of contents it appears to be valuable.

All things considered, I suggest reconsideration of the deletion of this link, as the book appears to be a useful source for deeper study of material on particle accelerators that would be beyond the reasonable for direct inclusion in an encyclopedia. Wwheaton (talk) 19:52, 4 January 2008 (UTC)

I've reinserted the link.--Hu12 (talk) 20:41, 4 January 2008 (UTC)

[edit] Micro black hole hazard

The wording User:84.56.237.95 deleted in the article was indeed so poor as to be incorrect. I have attempted to fix it. The subject has been discussed extensively (and mostly ignorantly, I think) on the LHC talk page and elsewhere. I personally think the risk is negligible (note that it cannot possibly be zero, since we do not know everything ), but deserved careful scrutiny by experts, which I hope (& trust) it has already received. Wwheaton (talk) 13:55, 21 May 2008 (UTC)

[edit] Discussion of Large Hadron Collider risks

This subject has been knocking around several talk pages: here, LHC itself, Hawking radiation, and Black holes, in particular. I have just proposed to separate the subject into a separate article; see the Talk:Large Hadron Collider page if you are interested. I think it could help to keep some of these other articles on-topic. Cheers, Wwheaton (talk) 19:47, 4 June 2008 (UTC)