Between 7th to 21st March modifications were made to the top of the CIRCE target chamber.

These modifications address the three key issues highlighted during the February shifts

1. The central S2 detector did not fit, because its connector pins came into contact with the chamber lid

Additional machining was performed on the central chamber lid, allowing the pins to fit

2. Mounting the iris hooks was non-trivial, resulting in the inability to open and close the irises whilst the lids were mounted on the chamber

Peter designed a guide rod allowing the hook to be connected to the iris arm before mounting the lid onto the chamber. Now the only difficult part is ensuring the actuator arms hook connects to this guide rod.

I checked the position settings needed for both actuators when mounting or removing the chamber lids, these are:

Central actuator setting = 85.5mm

Downstream actuator setting = 82.5mm

The actuator positions for a fully opened iris still need to be checked in CIRCE.

When mounting the lids the guide rods will be arranged such that the irises are in the mostly-closed position (~16mm diameter). This reduces chance of damage made to the S2's during installation and removal, and also means the iris is already setup ready for beam tuning.

See attached pictures for the downstream and central lids.

A sample S2 in Edinburgh was used to check the connectors fit with the lid and other parts. When mounting the lids onto the chamber collar it was decided to leave the S2s off the iris mount. This was to avoid the risk of damaging the S2 from slippage of the parts - note in CIRCE the collar will be on top of the target section with threaded rods and so the conditions are more stable than on tabletop. During lid mounting, the metal mask was used in place of the S2 to simulate its size.

Marks "CE" and "DW" were made respectively on the central and downstream lids and guide rods.

3. The pin diode angle was not reproducible

A mounting block has been machined in Edinburgh, it has an angled slant of 39.0 +/- 0.5 degrees for setting the angle of the plastic block used to support the diode. We noticed in the CAD drawing that mounting the diode at the closest distance to the target would mean the target frame is likely to cause scatter from the backscattered beam, therefore we chose to mount the diode in its central position. The angled block has a width 22.0 +/- 0.1mm for setting the distance between the back of the diode mount and the upstream side of the central chamber lid.

An excel spreadsheet was used to calculate the diode angle, see attached "DIODE_ANGLE_CALCULATION.xlsx"

The chamber parts were shipped back to CIRCE and arrived on 26/03/18, the mounting block and PB-5 Pulse Generator were also sent in the same shipment.