Search Results (5 total)

A method for producing short electron bunches in an electron storage ring using pulsed phase modulation has been demonstrated. A simple theoretical model was validated using the particle tracking code elegant, and the bunch compression process was observed experimentally in the Advanced Photon Source storage ring using a visible light streak camera. Compression to 54% of the initial bunch length was achieved.

Experimental evidence for self-amplified spontaneous emission (SASE) at 530 nm is reported. The measurements were made at the low-energy undulator test line facility at the Advanced Photon Source, Argonne National Laboratory. The experimental setup and details of the experimental results are presented, as well as preliminary analysis. This experiment extends to shorter wavelengths the operational knowledge of a linac-based SASE free-electron laser and explicitly shows the predicted exponential growth in intensity of the optical pulse as a function of length along the undulator.

A method is described that provides a solution to the long-standing problem of stray radiation-induced signals on photoemission-based x-ray beam position monitors (BPMs) located on insertion device x-ray beam lines. The method involves the introduction of a chicane into the accelerator lattice that directs unwanted x radiation away from the photosensitive x-ray BPM blades. This technique has been implemented at the Advanced Photon Source, and experimental confirmation of the technique is provided.

The problem of cumulative beam break-up for a coasting beam in a linac with periodically placed acceleration cavities and transverse focusing units is treated using a general technique. The equations of motion for a series of equally spaced pointlike bunches are reduced to a single Hill’s-type differential equation, from which a transfer matrix for a single period is derived. The technique is applied to the special case of a single resonance impedance, yielding a result which is in agreement with that derived elsewhere. The case of two nearly degenerate resonances is investigated using saddle-point integration, in the limit of strong focusing.

The characteristic whistler structure of oblique hydromagnetic shocks is observed experimentally to suffer from a rapidly growing short-wavelength instability, which is tentatively identified as the decay instability first predicted by Galeev and Karpman. It is suggested that this instability is responsible for the turbulent whistler shock structure observed when a super-Alfvénic plasma stream encounters a magnetic obstacle.