Observation of the second harmonic in Thomson scattering from relativistic electrons.

A free relativistic electron in an electromagnetic field is a pure case of a light-matter interaction. In the laboratory environment, this interaction can be realized by colliding laser pulses with electron beams produced from particle accelerators. The process of single photon absorption and reemission by the electron, so-called linear Thomson scattering, results in radiation that is Doppler shifted into the x-ray and gamma-ray regions. At elevated laser intensity, nonlinear effects should come into play when the transverse motion of the electrons induced by the laser beam is relativistic. In the present experiment, we achieved this condition and characterized the second harmonic of Thomson x-ray scattering using the counterpropagation of a 60 MeV electron beam and a subterawatt CO2 laser beam.

Heating rate of hadron beams during crystallization.

A theory concerning the relation between the heating rate and temperature of hadron beams is formulated from a quantum point of view. This theory predicts that the heating rate can be reduced by increasing the lattice periodicity of the accelerator with its fixed tunes and circumference. This prediction is quite consistent with simulation results.

Resistive wall impedance and tune shift for a chamber with a finite thickness.

Since the resistive wall impedance for a beam pipe of a nonround cross section depends on the coordinates of a witness particle, the witness particle receives an incoherent tune shift. When the expression for the impedance of an infinitely thick chamber is applied to the calculation of this tune shift, it becomes infinite. We have derived the resistive wall impedance for a chamber with a finite thickness and calculated the tune shift. There is no ambiguity in this expression for the tune shift, because it is automatically finite.