G. V. Sotnikov

Auto-oscillation system based on dielectric resonator with “Whispering gallery” modes

A new method of microwave generation in a system with high-Q quasi-optical cylindrical dielectric resonator (CDR) excited by an azimuthal-periodic electron beam current is proposed. Characteristic parameters of a cylindrical fluoroplastic CDR have been determined. Data on microwave generation in a system based on a CDR with whispering-gallery eigenmodes excited by a relativistic azimuthal-periodic electron beam current are presented. Electromagnetic radiation of this system was measured using a detector for the 8-mm wavelength range.

Analysis of a Symmetric Terahertz Dielectric‐Lined Rectangular Structure for High Gradient Acceleration

We study, using computational methods based on analytic theory as well as a PIC code, the wakefields set up in a seven‐zone symmetric rectangular THZ structure, and find that for overall transverse x/y dimensions 2.121 mm×0.6 mm, two 5‐GeV drive bunches (3 nC, with x/y/z dimensions 0.3/0.3/0.12 mm3 as available at SLAC) will set up an axial wakefield ∼350 MV/m in the witness channel, with a transformer ratio ∼18–20. The symmetry of the structure ensures not only that small transverse forces are imposed on the witness bunch, but also that the two components of transverse force are equal and opposite at the bunch location so as to enable dynamical stabilization in an accelerator comprising many modules. Transverse forces on the drive bunch tails may allow bunches to move ∼0.5–1 m without suffering excessive erosion.

Accelerated Bunch Stability in a Coaxial Dielectric Wakefield Structure When its Symmetry is Broken

The influence of symmetry‐breaking for a coaxial dielectric structure or its associated drive bunch on bunch stability in a coaxial dielectric wake field accelerator is investigated. Studies have been carried out for a 18.8 GHz structure with alumina dielectric tubes, and for a 1 THz structure with diamond dielectric tubes.

A THz Coaxial Two‐Channel Dielectric Wakefield Structure for High Gradient Acceleration

A coaxial two‐channel dielectric wakefield structure is examined for use as a high gradient accelerator. A THz design, having radius ∼1 mm, is shown to provide GeV/m—level acceleration gradient, high transformer ratio, and stable accelerated bunch motion when excited by a stable‐moving 5‐GeV 6‐nC annular drive bunch.

3D Analysis of Wake Field Excitation in a Dielectric Loaded Rectangular Resonator

The results of a three‐dimensional analysis of wake field excitation in a slab‐symmetric dielectric‐loaded resonator by rigid electron bunches are presented. The complete set of solutions, including the solenoidal and potential parts of the electromagnetic field, consists of LSM and LSE modes. Each of the LSM and LSE modes contains odd and even waves. A numerical analysis of wake field excitation by symmetric electron bunches is carried out. The three‐dimensional spatial structure of the longitudinal electric field is investigated. The influence of the drift vacuum channel on the wake field amplitude and on the coherent summation of wakefields for a regular sequence of bunches is studied.

Broadband emission from a relativistic electron bunch in a semi-infinite waveguide

A study is made of the excitation of a transition radiation pulse during the injection of a charged particle bunch through the end metal wall into a semi-infinite cylindrical waveguide. Exact analytic expressions for the fields of a thin ring-shaped bunch are obtained in terms of the Lommel functions of two variables. The energy efficiency, power, and spectrum of radiation emitted from a finite-size charged bunch in a vacuum waveguide are calculated numerically with allowance for the multimode nature of the excited field. It is shown that, under certain conditions, the bunch can generate a short, high-intensity electromagnetic pulse with a broad frequency spectrum. The effect of various parameters of the charged bunch-waveguide system (such as the bunch current, bunch duration, and waveguide radius) on the generation efficiency of a transition radiation pulse is investigated.

Charged particles accelerated by wake fields in a dielectric resonator with exciting electron bunch channel

We have studied the acceleration of electrons by wake fields excited in a resonator by a train of electron bunches. The resonator comprised a cylindrical metal waveguide section, containing a dielectric sleeve with a vacuum channel and ends closed by metal walls. Expressions describing the wake field excited by uniformly moving exciting electron bunches have been derived. The self-consistent process of resonator excitation by a train of charged bunches and the particle acceleration in the excited wake field has been numerically simulated.

Two‐Channel Rectangular Dielectric Wake Field Accelerator Structure Experiment

A design is presented for a two‐channel 30‐GHz rectangular dielectric wake field accelerator structure being built for experimental tests at Argonne National Laboratory (ANL). This structure allows for a transformer ratio T much greater than two, and permits continuous coupling of energy from drive bunches to accelerated bunches. It consists of three planar slabs of cordierite ceramic (e = 4.7) supported within a rectangular copper block, forming a drive channel 12 mm×6 mm, and an accelerator channel 2 mm×6 mm. When driven by a 50 nC, 14 MeV single bunch available at ANL, theory predicts an acceleration field of 6 MeV/m, and T = 12.6. Inherent transverse wake forces introduce deflections and some distortion of bunch profiles during transit through the structure that are estimated to be tolerable. Additionally, a cylindrical two‐channel DWFA is introduced which shares many advantages of the rectangular structure including high T, and the added virtue of axisymmetry that eliminates lowest‐order transverse d...

Amplitudes and Spectra of Wake Fields in a Planar Dielectric Resonator with Finite Q‐Factor

The influence of dielectric losses upon the amplitude and spectrum of the wake fields excited by a train of electron bunches in a planar dielectric resonator is investigated. Analytical expressions for the wakefields in a planar dielectric resonator with finite value of Q‐factor are obtained. Numerical calculations using various values of the dielectric resonator Q‐factor are carried out.

Wakefield Excitation by a Sequence of Electron Bunches in a Rectangular Waveguide Lined with Dielectric Slabs

A rectangular dielectric‐lined metallic structure was studied that has an advantage over a cylindrical structure from the possibility of exciting by a sequence of bunches many equally‐spaced modes, thereby building up a larger mode‐locked wakefield. A rectangular vacuum copper waveguide was lined with two dielectric slabs, the size of which was calculated to provide resonant excitation of the fundamental LSM mode by a sequence of bunches with repetition frequency f0=2805 MHz, produced by linear resonant electron accelerator (4.5 MeV, number of bunches 6.103, diameter 1cm, duration 60 ps each, distance between bunches 300 ps, number of electrons in each bunch 109). The waveguide has cross section 85 mm × 180 mm, and Teflon (e = 2.1) plates were placed along the smaller sides of the waveguide, their thickness from the calculation being 22 mm. In experiments, the length of the resonator was 535mm. We found that the total wakefield is three times larger than the fundamental mode; thus a greater number of exci...