Alexander Mikhailichenko

The role of polarized positrons and electrons in revealing fundamental interactions at the Linear Collider

The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.

On the physical limitations to the lowest emittance (toward colliding electron-positron crystalline beams)

In this paper we explore the conditions under which a relativistic beam of electrons or positrons, treated as a Fermi gas, becomes degenerate. The quantum effects give an absolute limit to the emittance of the beam. We discuss here some methods for preparing this ultra-cold electron-positron gas in a framework of colliding beams at high energy.

Injector for a laser linear collider

The injector for 2×1 km long laser driven linac considered. Basically injector is a race track with long straight sections. These sections squeezed together for a compact size (a Kayak-Paddle like ring). In straight section the short period wigglers and RF cavities installed in series one by one for keeping the energy along the straight section practically constant. This injector is able to provide the invariant emittances of the order 5 10−8 cm rad and 2 10−9 cm rad for horizontal and vertical directions correspondingly. Bunch population required below 107 reduces the IBS effects.

Enhanced optical cooling system test in an electron storage ring

We are proposing to test experimentally the idea of Enhanced Optical Cooling (EOC) in an electron storage ring, to confirm new fundamental processes in beam physics and to open important applications of EOC in elementary particle physics and in Light Sources (LS).

Collection optics for ILC positron target

We are considering the implementation of a Lithium lens and SC solenoidal lens for collection of positrons in ILC undulator-based source. Such a lens installed right after the thin target, which is illuminated by gamma quants from helical undulator.

Self-stimulated emission of undulator radiation

We attract attention that interaction of particle in downstream undulator with its own wavelet emitted in upstream undulator could be as strong as with the frictional field in undulator itself. This phenomenon could be used for enhancement of signal from pickup undulators in optical stochastic cooling methods as well as for increase of damping. Particle passed an undulator emits undulator radiation wavelet (URW) which length is 1  M where M is the number of undulator periods, 1  – is the wavelength of first harmonic. In system of N identical undulators located along straight line the particle radiates train of wavelets with separation l; both l and 1  defined by Doppler effect, by angle  between instant velocity and direction to observer, by distance between undulators 0 l , by period of undulator u  and by relativistic factor 1   . In straight forward direction 0   they are 2 0 / 2 l l   , 2 1 / 2 u     . Energy radiated by particle in system of N undulators is N times bigger than the one radiated in just one undulator. Spectrum of radiation emitted in arbitrary direction also changes: appears line-type spectrum. Integrated spectrum changes not much, see [1]. In this publication we suggest to increase the loss rate in system of N undulators by introduction of controlled delays in motion of particles relative to the URW between undulators, Fig.1. Figure 1: Scheme of installation. Delays chosen so that particle enters the following undulator together with the front edge of URW emitted in anterior undulators in decelerating phase. In this case the particle will experience deceleration in its self field generated by its instant motion in a field of undulator (friction force generated by spontantenous incoherent radiation) as well as in the field of URW from anterior undulators (induced radiation in field of co-propagating electromagnetic wave). Under such condition occurs superposition of wavelets which yield the electric field grows ~N so the energy emitted grows ~N 2 . To be effective and optimal, this system must use appropriate focusing elements such as lenses and/or focusing mirrors, see the scheme of installation on Figs. 1, 2. Mirrors and lenses must form crossover with the Rayleigh length of the order of the length of undulator 2 / u R M Z   [2]. Figure 2: Equivalent optical scheme. The scheme of installation suggested could be used effectively in different methods of optical cooling (OC) of particles in damping rings [2]-[5]. So this installation can serve as effective pick-up undulator. According to OC principle the optical parametric amplifier(s), controllable screens [2] and kicker undulators could be located in the subsequent straight sections. We would like to remind here that for any method of Optical Stochastic Cooling it is important to inject in spectral bandwidth / ~1/ 2M    and in angles ~ 1 / M    as many photons as possible. This number does not depend on the length of undulator [2]. So usage of three pickup undulators is 3 times more effective in the emitted field strengths and 9 times more effective in the emitted energy, than just single pickup undulator and so on. It means that usage of three pickup undulators and singe kicker one in the schemes of OSC is 3 times more effective for damping time, than just single pickup and single kicker undulator. Usage of three pickup undulators and three kicker undulator is 9 times more effective, than just single pickup and single kicker undulator and so on. So the effectiveness of the pickup and kicker systems consisting of N undulators each is proportional to N 2 . We considered here the case when optical delays tuned so that wavelets emitted by particle are congruent and particle always stays in decelerating phase. To be so the beam delay system must be isochronous for all particles in the beam. There is a possibility for another scheme with self-stimulated undulator radiation. This scheme uses isochronous storage ring with undulator installed in one straight section. Mirrors installed at both sides of undulator set an optical cavity so that period of oscillation of wavelet in optical cavity coincides with period of revolution of particles in storage ring. In that case the wavelets will be accumulated in optical cavity superimposed one by another with the accuracy   1 . This scheme is typical for FEL, but the difference is that the storage ring is isochronous and that the motion of the wavelet and the bunch are synchronized one with another. In this case there is no coherence in radiation among different particles in the bunch (as the particles are not grouped in microbunches with longitudinal dimensions      separated by distances which are integer of 1  ), but stimulated processes are going in their own fields of URWs emitted in undulator in earlier times. All properties of spontantenous incoherent radiation emitted by particles in this case are not changed, except intensity, which becomes higher now in Q times, where Q is the quality factor of optical cavity. If however, conditions of synchronicity are broken weakly so the wavelets emitted at each pass through undulator are shifted by 1 1 ~ M    , then properties of radiation might be different now (intensity will drop, but monochromaticity will be enhanced). If isochronicity satisfied for particles in some narrow diapason of angles and energy, then this will narrow angular divergence and spectrum of undulator radiation at the exit of optical cavity. Strong dependence of intensity of undulator radiation on energy may change the cooling rate of particles in storage ring [6]. This phenomenon of self-stimulated emission in undulator can be used for tuning optical system of any optical stochastic cooling schemes. This correspond operation of system with optical amplifier turned off and the optical delay shifted by 2 / ~  with respect to the optimal cooling phase. So some tuning could be done without optical amplifier at all, if someone just registering intensity of forward radiation after kicker undulator. Then just by shifting optical delay back by half wavelength and tuning on optical amplifier, the system will be set to optimal phasing. We would like to mention that in parametric FEL with mirrors [7], [8] (stimulated superradiant emission in pre-bunched Free-Electron Laser) the process of radiation is similar to described in our paper. However there new portions of particles, bunched into small-size, passing through undulator with the same periodicity. This work was supported in part by RFBR under Grant No 09-02-00638a. References [1] E.G.Bessonov, “Undulators, Undulator Radiation, Free-Electron Lasers”, Proc. Lebedev Phys. Inst., Ser.214, 1993, p.3-119, Chief ed. N.G.Basov, Editor-in-chief P.A.Cherenkov; “Peculiarities of harmonic generation in a system of identical undulators”, Nucl. Instr. Meth. A 341 (1994), ABS 87 (http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TJM-470F3WY-J01&_cdi=5314&_user=492137&_pii=0168900294904596&_orig=search&_coverDate=03 %2F01%2F1994&_sk=996589998&view=c&wchp=dGLbVzzzSkzV&md5=8309b9f8f17e8b2ad6263367db281526&ie=/sdarticle.pdf ). [2] E.G. Bessonov, M.V. Gorbunkov, A.A. Mikhailichenko, “Enhanced Optical Cooling System Test in a Muon Storage Ring”. Phys. Rev. ST Accel. Beams 11, 011302 (2008). [3] A.A. Mikhailichenko, M.S. Zolotorev,” Optical Stochastic Cooling”, Phys. Rev. Lett.71: 4146-4149, 1993. [4] A.A. Zholents, M.S. Zolotorev, W. Wan “Optical Stochastic Cooling of Muons”, Phys. Rev. ST Accel. Beams 4, 031001, (2001). [5] W.A. Franklin, “ Optical Stochastic Cooling Proof-of-Principle Experiment”, Proceedings of PAC07, p.1904-1906, 2007. [6] E.G. Bessonov, “The Evolution of the Phase Space Density of Particle Beams in External Felds”, Proceedings of COOL 2009, Lanzhou, China http://cool09.impcas.ac.cn/JACoW/papers/tua2mcio02.pdf, see also: arXiv:0808.2342v1; http://lanl.arxiv.org/abs/0808.2342; http://arxiv.org/ftp/arxiv/papers/0808/0808.2342.pdf . [7] V.I. Alexeev, E.G.Bessonov et al., “A Parametric Free-Electron Laser Based on the Microtron”, Nucl. Instr. Meth., 1989, A282, p.436-438; Brief reports on Physicas No 12 (1987), p. 43. [8] M.Arbel, A.Abramovich, A.L.Eichenbaum, A.Gover, H.Kleinman, Y.Pinhasi, I.M.Yakover Superradiant and Stimulated Superradiant Emission in Prebunched Free-Electron Maser”, PRL, v.86, No 12, 2001, p. 2561-2564.We raise attention to the fact that a particle in a downstream undulator interacting with its own wavelet emitted from an upstream undulator can be as strong as its direct interaction with the frictional field of undulator itself. This phenomenon could be used for the enhancement of the signal from pickup undulators in optical stochastic cooling as well as to decrease of the damping time of particles in storage rings.

Enhanced Optical Cooling of Particle Beams in Storage Rings

An enhanced optical cooling method (EOC) based on external selectivity of interaction between particles and theirs amplified undulator radiation wavelets (URW) is discussed. The selectivity arranged by a moving screen located on the image plane of optical system projecting URW there. A non-exponential damping time in this scheme of cooling is not limited by any restriction like Robinson’s damping criterion.

Fast Sweeping Device for Laser Bunch

An electro-optical laser sweeping device directs the head and the tail of a laser bunch into different frontal directions, so at some distance, the laser bunch becomes tilted with respect to forward direction. For sweeping of a laser bunch having 300 ps duration up to 10 mrad, the voltage drop along the laser bunch must be ∼ 10kV. The repetition rate desirable for this type of device used in laser acceleration or generation secondary back-scattered electrons is up to 1 MHz. Details of this scheme are described here.

The concept of a Linac driven by a Traveling Laser Focus

Here we describe a Linac, driven by a Traveling Laser Focus (TLF), arranged with the help of a special deflecting device. This Linac has an accelerating structure, which is open from one side. The laser radiation is focused from this side onto a spot with minimal transverse dimensions. This spot is moved by a fast deflecting device synchronous with the instantaneous position of the charged particles, thereby providing an accelerating field mostly in the region where the accelerating particles are located. The method described allows a reduction of the power required to create the accelerating gradient, which should be proportional to the number of resolved spots of the deflecting device (typically a hundred). The same number shortens the illumination time for any point on the structure. All this allows for a gradient of up to 100 GeV/m with present day techniques. The systems for the laser beam sweeping, the emittance requirements, the electrofocusing system, the accelerating structure, the final focusing...

A laser linear collider design

A conceptual design of crucial elements of 2×1 km long linac is considered. This linac is driven by a laser radiation distributed within open accelerating structures with special sweeping devices. These devices deflect the laser radiation to the structures in accordance with instant position of accelerated particles. The power reduction and shortening the illumination time for every point on the structure equates to the number of resolved spots, associated with this sweeping device. A 300 J total, 100-ps laser flash could provide the final energy 30 TeV for λ≡1 μm and 3 TeV for λ≡10 μm on 1 km with the method described. This total power required could be generated with amplifiers distributed along the linac. For repetition rate 160 Hz the luminosity associated with colliding beams could reach L≈1033 cm−2 s−1 per bunch with population 107. Wall plug power required for operation of LLC is ∼2 MW.