The Lissajour pattern target raster system has been used for about 8 years since 1994. The operation is based on power resonance loop. Lissajous pattern is generated from two independent sinusoidal current signals. Its simplicity makes the system very reliable. No major maintenance was performed during past 8 years.
The major problem of Lissajous raster is the uniformity of the raster pattern. Along the boundaries of raster pattern, there is density enhancement produced by slowdown behavior of sinusoidal waveform at turning point. This large increase in deposited beam energy in these areas eventually causes overheating of the target material. By experimental measurements - a luminosity scan with HMS, we found the luminosity decreases gradually by increase of beam curent. That indicates that local overheating effect near the boundaries and the corners of Lissajous pattern contributes an uncertainty in the target length which, in turn, effects the acuracy of the experimental data.
Therefore, besides upgrade target circulation system - increase stream velocity, generation of uniform raster density is the first requirement of new raster system design.