User name X. Zheng
Log entry time 03:27:16 on January22,2003
Entry number 92930
Followups:
keyword=Halo testFrom 12:20 to 1:20am we have performed a halo test to test the effect of beam halo on the data quality (backgroundf from the cell walls).
We took 20 min data with empty reference cell and the following conditions:
- Hall C pre-buncher OFF;
- Increase injector current, use narrow slit such that only 5 uA goes to Hall A;
- Decrease raster size to 0.5 mm diameter in both X and Y, or as small as possible. We finally got about 1.2x0.8 mm (XxY).
These conditions are supposed to give the ideal beam spot (least halo).
Below please find react_z spectrum from this run, compared with runs under three different conditions:
- top left: From 4 pass, and good Compton tuning. Black: empty ref cell, Magenta: pol3He cell;
- top right: 5 pass (01/21), bad tuning and larger raster size (6x6mm), empty ref cell;
- bottom left: 5 pass (01/22), good tuning and 4x4 raster, empty ref cell;
- bottom right: 5 pass(01/22), halo test (this test), empty ref cell.
The number in each plot gives the ratio of events coming from one side of the window (-0.2
Current conclusion: From the two plots in the bottom, did not find significant difference between "Prebuncher off" and "4x4 raster (prebuncher on)".
FIGURE 1
