Summary on Discussion on Screens for the Linac4 Dump Line and LBE Line

Present: E. Bravin, T. Hermanns, B. Mikulec, U. Raich

1. Base Line

The aim of this discussion has been to continue the communication between the beam dynamics simulation and the beam instrumentation parts on the requirements and constraints for the screens, which shall in future measure the beam sizes as input for the emittance measurments in the Linac4 dump line and in the LBE line. For each line three screens are required. Two out of these six must provide a resolution of 50um, while the remaining four screens need a resolution of 200um. Readout cameras must be selected accordingly.

2. Screens and Readout System

In order to meet the required specifications standard chrome-oxide screens can be selected. As the signals from these screens are emitted isotropically, a mirror system can be installed to allow for a convenient positioning of the readout cameras. For the latter it is planned to buy commercial equipment coping with the required resolutions. Given the parameters for resolution, radiation-hard objects can be chosen to avoid too frequent interventions.

Concerning information on the level of radiation and back-scattered particles at the positions where the screens and cameras are planned to be installed, simulations studies are on-going in the beam intercepting devices group. R. Chamizo should be contacted for details.

3. In/Out Mechanism

During the beam sizes measurement only one monitor may be placed in the beam at the same time. Therefore, each screen must be retractable. Any operating time between 1s and 10 s for moving the screen into or out of the beam can be achieved. However, any very fast system creates vibrations on fragile material like bellows etc. which make cause them to break, so that ppm-operation could have the draw-back of less reliability and might require more interventions.

For standard operating conditions a fast system is not needed, while for the commissioning phase a system with an operating time of a few seconds (significantly less than 10s) is appreciated. A ppm-system does not seem to be required, but the beam dynamics group should be consulted to finally answer this question. In the end the time for the movement of the screens, i.e. the deadtime for measurements, should be reported to adapt the interlock-system accordingly.

It was also noted that the beam instrumentation in the transfer line between Linac4 and the PS Booster is also not capable of ppm-operation. Therefore, similar information for the interlock-system (dead-time, maximum pulse length) should be provided as well.

4. Design and Installation

A typical array for a single monitor consits of 300x300 pixels, which is sufficiently large for the for all beam sizes to be measured. However, for the mid-position the direction which is not actually measured might become a problem.

5. Support Structure

The support structure will be designed and fabricated by the BI-team as well. This allows to build a decent system respecting all kind of requirements like cables for signal routing between screen and camera, shielding of equipment etc.

6. Time-Line

The design of the a system (screen, camera and support structure) is estimated to take about six months, while for all fabrication also six months should be reserved (conservative assumption.)

-- ThomasHermanns - 19-Apr-2010

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Topic revision: r5 - 2010-04-22 - ThomasHermanns
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