2019-12-06

The fan of the power supply of the linac had a problem in the morning, solved at noon. Wire experiment was conducted in the afternoon.

A wire of 142 microns is attached to a movable probe in the main ring vertically with a frame giving an additional 10 cm after the wire for a surviving beam to be detected by the bunch monitor. The location of the wire is at nezumi in the ring. A PMT is installed near the wire on the vacuum chamber on the inner side of the ring. A Qin Bin (QB) scrapper is also installed 1/2 cell after the wire.

A first run with nominal parameters was used to find the location of the 12 MeV beam at the wire: from the table of acceleration with the nominal RF pattern, 12.105 MeV is reached 1ms after the start of the RF trigger (and 0.5 ms after injection). The wire is highly scrapping the beam, making it easy to find the location of the wire with the bunch monitor. A position of 158 mm is found on the ruler of the movable probe with wire. Since for an RF pattern of more than 50 deg, the final energy is >12.1 MeV, the position of 12.5 MeV beam has been determined (linear interpolation between the 2 neighbouring points) in the same way (1.17 ms of acceleration after RF trigger, position: 167 mm).

Bunch monitor and RF data has been taken for different RF patterns and 2 differnt amplification factors, with wire and without wire. For high synchronous phase, the beam was lost quickly due to bucket mismatch, so there was no difference of bunch monitor signal with wire and without. The different configurations are detailed in the .rtf file.

A run with nominal parameters was then used to determine the location of the QB scrapper (~2 ms after RF trigger, about 15 MeV and about 5 cm after the wire location, position 0 mm on the ruler of QB scrapper). When the wire is located at 12.1~MeV, almost no difference was observed on the bunch monitor with the QB scrapper and without, which means most of the beam is completely scrapped by the wire.

The first PMT could only detect something outside of the magnetic field region, so far away from the ring, but the signal was too weak. A second PMT (Yoshimoto PMT) was then installed instead, and signal could be detected even in the field region. An average and integral function (1Mohm) gives access to the size of the beam (half size since full scrapping?).