5 research outputs found
RF surface resistance study of non-evaporable Getter coatings
In many particle accelerators the beam parameters could be affected by the beam pipe wakefield impedance. It is vital to understand how the wakefield impedance might vary due to various coatings on the surface of the vacuum chamber, and this can be derived from surface resistance measurements. The bulk conductivity of two types of NEG films (dense and columnar) is determined. This is achieved by measuring the surface resistance of NEG-coated samples using an RF test cavity and fitting the experimental data to a standard theoretical model. The conductivity values obtained are then used to compare resistive wall wakefield effects in beam pipes coated with either of the two types of film
Nonlinear waves and coherent structures in the quantum single-wave model
Starting from the von Neumann-Maxwell equations for the Wigner
quasi-probability distribution and for the self-consistent electric field, the
quantum analog of the classical single-wave model has been derived. The linear
stability of the quantum single-wave model has been studied, and periodic in
time patterns have been found both analytically and numerically. In addition,
some features of quantum chaos have been detected in the unstable region in
parameter space. Further, a class of standing-wave solutions of the quantum
single-wave model has also been found, which have been observed to behave as
stable solitary-wave structures. The analytical results have been finally
compared to the exact system dynamics obtained by solving the corresponding
equations in Schrodinger representation numerically.Comment: 10 pages, 9 figure
Nonlinear density waves in the single-wave model
The single-wave model equations are transformed to an exact hydrodynamic
closure by using a class of solutions to the Vlasov equation corresponding to
the waterbag model. The warm fluid dynamic equations are then manipulated by
means of the renormalization group method. As a result, amplitude equations for
the slowly varying wave amplitudes are derived. Since the characteristic
equation for waves has in general three roots, two cases are examined. If all
three roots of the characteristic equation are real, the amplitude equations
for the eigenmodes represent a system of three coupled nonlinear equations. In
the case, where the dispersion equation possesses one real and two complex
conjugate roots, the amplitude equations take the form of two coupled equations
with complex coefficients. The analytical results are then compared to the
exact system dynamics obtained by solving the hydrodynamic equations
numerically.Comment: 7 pages, To appear in the Physics of Plasmas, Volume 18, Issue
The Black Sea Symposium for Young Scientists in Biomedicine 20-23 September 2012, Varna
ΠΠ°ΡΠ½Π΅Π½ΡΠΊΠΈ ΠΌΠ΅Π΄ΠΈΡΠΈΠ½ΡΠΊΠΈ ΡΠΎΡΡΠΌ (Varna Medical Forum) V. 1, No 2 (2012