ILC: Why do scientists need a second Big Collider?

a) Anticipating some of the workers' exclamations about excessive simplifications in this article: if your knowledge allows you to understand what is described more deeply, this article is hardly interesting to you at all. Let's discuss all your questions in the PM.
b) I apologize for the large number of references to foreign articles, the translation of all these articles will take me too much time.

A month has passed since the special committee finally chose the place for the construction of the International Linear Collider. ILC will be built next to the Kitakami ridge in the vicinity of the eponymous city of Iwate Prefecture. By the way, this prefecture is adjacent to Miyagi prefecture, in which a strong earthquake occurred in 2011. However, one should not worry about choosing a place: during 2013, the committee met 60 times, which corresponds to more than 300 hours of discussion. The press release also briefly describes the reasons for this choice.
In addition, it is worth mentioning that the Joint Institute for Nuclear Research in Dubna a few years ago was considered as a potential candidate for the site for the construction of ILC, but was rejected later.

To my surprise, I found that in RuNet there is not enough information describing this grandiose project. Of course, the press will take up the discussion of the “Second Collider, Which will surely spew the Black Hole, which will surely swallow the earth” ( in fact , no), but only closer to the beginning (and, probably, the end) of its construction. In the meantime, let's figure out what kind of collider it is, why scientists need it, and why they are not happy with the existing Large Hadron Collider.

So, the International Linear Collider is the largest particle accelerator project, comparable in scale to the Large Hadron Collider. Unlike the LHC, the new collider will not be circular, but linear. In addition, electrons and positrons will be accelerated particles, unlike LHC, which is a proton-proton collider. ILC also has many times lower energy of colliding particles.

What are the benefits of this solution?

• Collisions of electrons and positrons are more “pure”. Recall that protons are much more massive than electrons, therefore, when they collide, a lot of side particles are formed. Electrons and positrons, unlike protons, are much smaller, which allows a more detailed study of the processes occurring during their collision, without suffering from the elimination of noise (noise is the main thing that detectors register at the LHC).
• Despite the lower particle energy on the ILC and lower collision energy (and, accordingly, the lower probability of the Higgs boson nucleation), each event of the creation and decay of the Higgs boson on the ILC will be reliably recorded, and the scientific value of such data will be higher than the data obtained at the LHC (on which, I repeat, the useful signal is very noisy). That is why the lower particle energy at the International Linear Collider (about 500 GeV) compared to the Large Hadron Collider (about 14,000 GeV) is not so important.
• From the school course of physics it is known that with the uneven movement of charged particles they become a source of electromagnetic radiation. Therefore, when electrons are accelerated by a cyclic accelerator at high energies, circular motion will cause huge energy losses in the form of hard electromagnetic radiation (the so-called synchrotron radiation). In simpler terms, the efficiency of a cyclic accelerator will be less than linear.
• When particles are accelerated, the linear collider does not provide for complex systems to stabilize the beams and there is no need to re-focus non-colliding particles (in other words, it is not necessary to “keep” the beams after a collision in a stable state). This allows us to somewhat simplify the design of the linear collider compared to the annular one and to more accurately focus the beams before the collision (by the way, focusing the beams before the collision is a very difficult task).
• Well, finally, after many years of research, a highly efficient particle acceleration technique based on the principle of radio frequency acceleration has been well developed . This allows you to achieve a high accelerating gradient (and build an accelerator not tens of kilometers long, but tens of kilometers).

Why can not do with the existing LHC collider? As already mentioned, beams of heavy protons collide at the LHC. The resulting “garbage” collisions significantly impede the process of processing the results. The Higgs boson discovered a year ago forces scientists to closely study this particle, and here the Large Hadron Collider is powerless. Not only is the birth of the Higgs boson a very rare event, but at the LHC it still needs to be separated from the background noise of “garbage” collisions. It is planned to use the International Linear Collider as a tool for experimental study of the Higgs boson properties.

Next, let's briefly go over the general principle of operation and the main elements of the new collider project. The first volume of the ILC technical specification will help us with this .

• An electron gun with a photocathode inside acts as a source of electrons . The photocathode will be irradiated by pulses of intense laser radiation.
• The source of positrons is an undulator , through which part of the electron beam is passed, where they periodically accelerate and decelerate, emit x-rays. These rays are directed to a titanium target and electron-positron pairs are knocked out of it.
• 3.2 km electronic and positron damping rings will be located in a common tunnel. These rings are necessary to “calm” the beam received from the source and to accumulate the required number of particles to start their collisions.
• Two-stage compressors of electron and positron beams are designed to compress electron and positron beams from 6 mm to 0.15 mm in length, and up to tens of nanometers in height and width. These compressors are essentially giant magnetic “lenses” that focus an electron beam in the same way that optical lenses focus light rays.
• Well, finally, the heart of the ILC is two linacs (from "linac" = "linear accelerator") 11 km long. Their action is based on the radio-frequency principle of acceleration of charged particles , a huge effort developed in recent decades. The main element of these lines is niobium resonators, cooled to a temperature of 1.8 K in huge cryogenic “covers” - cryomodules . By passing an alternating electric current through the resonators (for ILC - a frequency of 1.3 GHz), it is possible to create in the internal cavity of the resonators such a configuration of the electric field that would allow charged particles to accelerate along the entire length of the resonator.

The current ILC configuration provides two scenarios for further upgrading of the accelerator after its construction: an increase in luminosity (particle collision intensity) by increasing the number of “clumps” of particles in each beam, or an increase in the energy of colliding particles. Each of the development scenarios has its advantages and disadvantages, which one will be chosen so far is unclear.

Sources:
http://www.linearcollider.org/ILC/What-is-the-ILC/Facts-and-figures
http://ilc-str.jp/topics/2013/08281826/
http: //www.quantumdiaries .org / 2013/08/23 / ilc-more-than-just-a-higgs-factory /
http://arxiv.org/ftp/arxiv/papers/1306/1306.6327.pdf
http://thescience.ru/ 2013/09/23 / why-the-scientists-need-the-second-large-collider /