ILC: why do scientists need the second Big Collider?

a) Anticipating some workers' cries of excessive simplifications in this article: if your knowledge allows you to understand what is described more deeply, you are unlikely to be interested in this article at all. Let's discuss all your questions in the LAN.
b) I apologize for the large number of references to foreign articles, the translation of all these articles will take me too long.

A month has passed since the place where the construction of the International Linear Collider was finally chosen by a special committee. ILC will be built next to the Kitakami mountain range in the vicinity of the eponymous city of Iwate Prefecture. By the way, this prefecture is adjacent to the prefecture of Miyagi, in which in 2011 there was a strong earthquake . However, there is no need to worry about the choice of location: during 2013, the committee met 60 times, which corresponds to more than 300 hours of discussions. 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 was considered a potential candidate for a site for the construction of ILC several years ago, but was rejected later.
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To my surprise, I discovered that there is not enough information in RuNet describing this grandiose project. Certainly, the press will take up the discussion of the “Second Collider That Will Be sure to Cast the Black Hole That Will Become Absorb the Earth” ( actually not ), but only closer to the beginning (and, probably, to the end) of its construction. In the meantime, let's see what the collider is, why scientists need it, and why the existing Large Hadron Collider does not suit them.

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

What are the benefits of such a solution?

• Collisions of electrons and positrons are clearer. 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 makes it possible to study in more detail the processes occurring during their collision, without suffering from the sifting noise (noise is the main thing that detectors at the LHC register).
• Despite the lower particle energy on the ILC and the lower collision energy (and, consequently, the lower probability of the Higgs boson nucleation), each event 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 on the LHC (on which, I repeat, the useful signal is very noisy). That is why the lower energy of particles at the International Linear Collider (about 500 GeV) compared to the Large Hadron Collider (about 14000 GeV) is not so important.
• From the school course of physics it is known that with an uneven motion of charged particles they become a source of electromagnetic radiation. Therefore, during the acceleration of electrons 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 language - the efficiency of a cyclic accelerator will be less than a linear one.
• When particles are accelerated in a linear collider, complex systems are not provided for stabilizing the beams and there is no need to re-focus the non-colliding particles (in other words, it is not necessary to “keep” the beams after the collision in a steady state). This makes it possible to somewhat simplify the design of the linear collider in comparison with the ring one and more precisely focus the beams before the collision (by the way, focusing the beams before the collision is a very difficult task).
• Well, and finally, after many years of research, a highly efficient method of particle acceleration 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 in the hundreds, but tens of kilometers).

Why it is impossible to manage the existing LHC collider? As already mentioned, beams of heavy protons collide at the LHC. The resulting "junk" collisions significantly interfere with the processing of results. The Higgs boson discovered a year ago forces scientists to come to grips with the study of this particle, and here the Large Hadron Collider is powerless. Not only is the birth of the Higgs boson a very rare event, so at the LHC it also needs to be separated from the background noise of “junk” collisions. The International Linear Collider is planned to be used as a tool for experimentally studying the properties of the Higgs boson.

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

• The electron gun is an electron gun with a photocathode inside. The photocathode will be irradiated by pulses of intense laser radiation.
• The source of positrons is an undulator , through which a part of the electron beam is passed, where they periodically accelerate and slow down, emit X-rays. These rays are directed to a titanium target and knock electron-positron pairs out of it.
• Electronic and positron damping rings with a length of 3.2 km will be located in a common tunnel. These rings are necessary to “calm” the beam received from the source and accumulate the necessary 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 to tens of nanometers in height and width. These compressors are essentially gigantic magnetic "lenses" focusing the 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 in length. Their action is based on the radio-frequency principle of acceleration of charged particles , which has been developed by great efforts in recent decades. The main element of these linacs is niobium resonators, cooled to a temperature of 1.8 K in huge cryogenic "covers" - cryomodules . Passing an alternating electric current through the resonators (for ILC - 1.3 GHz frequency), it is possible to create in the internal cavity of the resonators such an electric field configuration that would allow charged particles to be accelerated along the entire length of the resonator.

The current ILC configuration provides two scenarios for further upgrading the accelerator after its construction: an increase in luminosity (particle collision intensity) by increasing the number of “bunches” of particles in each beam, or an increase in the collision energy of particles. Each of the development scenarios has its advantages and disadvantages, which of them will be selected 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/