Waterfall Target

The waterfall target system provides a target for experiments on ¹⁶O (see figure 2.3.3.1). The hydrogen is used for calibration purposes.

The conceptual design of the waterfall target system for Hall A is very similar to the one used at Saclay (  mg/cm² one-foil, stable in time within 1%, and insensitive to beam current up to at least 20 mA[1]. Notice that itŐs possible to modulate, slightly, the thickness of the waterfall target, by changing the pump speed; this adds flexibility to the system and allowes the user to choose the best value according to the wanted resolution and luminosity.

Elastic scattering from the hydrogen in the target was used to measure the target thickness. For continuous monitoring of the target thickness, one `calibrates' the raw counting rate of the hadron spectrometer by the elastic peak measurements; thus it is possible to convert the proton rate seen during the measurement to an average target thickness.

The waterfall target can be single foil or multi-foils according to the needs of the particular experiment. In fact, a modified version of this target has been built and used for experiments at NIKHEF (a mg/cm² single-foil) and a three-foil one ( mg/cm²). The target built for the two commissioning experiments on ¹⁶O (PR- 89- 003 and PR...) is a three-foils one ( mg/cm²).

The main components of the target system are:

a

) the waterfall target container, the target and the solid target ladder

b

) the hydraulic system

c

) the gas system

d

) the movement system

e

) the slow-control system

The slow control of the waterfall target system can be done by using a personal computer which is in the HallA, or directly from the Counting Room, by using another computer connected to the first one. The layout is as in the figure 2.3.3.2.