Thomas Spickermann

Status of the experimental studies of the electron cloud at the Los Alamos proton storage ring

The electron cloud (EC) at the Los Alamos Proton Storage Ring (PSR) has been studied extensively for the past several years with an overall aim to identify and measure its important characteristics, the factors that influence these characteristics, and to relate these to the two-stream (e-p) transverse instability long observed at PSR. Some new results since PAC2001 are presented

Stripper foil temperatures and electron emission at the Los Alamos proton storage ring

We have modeled the heating process of the PSR stripper foil and compared our results to observations that depend on the foil temperature. The foil is heated by the energy deposited by injected H - ions and stored protons passing through the foil. Secondary emission of electrons due to these foil hits results in a measurable current that we can use to benchmark our model. At higher beam intensities, thermionic emission of electrons dominates the foil current. Due to the extreme temperature dependence of the thermionic current this is a very sensitive indicator of the foil temperature and will be used to safeguard against overheating the foil in extreme beam conditions. We will present our best estimates of the foil temperature for different beam intensities

Halo measurements of the extracted beam at the Los Alamos Proton Storage Ring

The spatial beam density distribution beyond 2.5 to 3 standard deviations of the beam center is an important property for understanding the relatively small fractional losses of high intensity beams at the Los Alamos Proton Storage Ring (PSR) and transport lines to the neutron production target. This part of the distribution (sometimes referred to as beam halo) is not well determined by the LANSCE-standard wire scanner system nor is it yet reliably predicted by the simulation codes. To significantly improve the experimental determination of the beam halo, an improved wire scanner has been developed, tested and installed in the extraction line. To enhance the signal-to-noise ratio, an amplifier consisting of a wide dynamic-range, integrating amplifier, sample-and-hold circuit, log amplifier and line driver is located near the beam line. Offset errors at the input of the amplifiers are actively cancelled and timing gates are derived from a single input pulse. We will describe the prototype instrument, discuss our encouraging test results and report our experience with the instrument in the PSR extraction line.

Beam Loss Measurements at the Los Alamos Proton Storage Ring

During normal operation the Los Alamos Proton Storage Ring (PSR) accumulates up to 4⋅1013 protons over 625μs with a repetition rate of 20 Hz, corresponding to a current of 125μA to the Lujan Neutron Science Center. Beam losses in the ring as well as in the extraction beam line and the subsequent activation of material are a limiting factor at these currents. Careful tuning of injection, ring and extraction line is paramount to limiting losses to acceptable levels. Losses are typically not uniform around the ring, but occur in significantly higher levels in certain “hot spots”. Here I will report on losses related to the stripper foil which are the dominant source of losses in the ring. First results of a comparison with simulations will also be presented.

An experimental study of microwave stability near transition in the PSR

We have undertaken a study of microwave stability in the PSR storage ring under a variety of beam conditions near transition, including variable intensity and machine impedance, which can be independently controlled in the PSR. Results indicate that the general features of a linear stability model are valid, namely that the instability threshold becomes very small sufficiently close to transition. In addition, many nonlinear features are apparent and the results suggest an extended operating regime is possible with saturated, but otherwise benign, longitudinal fluctuations. Details of the linear model experimental results and corresponding simulations will be presented