The Project
1.Functional Description:
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The increasing requirements of CERN experiments make essential the upgrade of beam instrumentation in general, and high accuracy beam profile monitors in particular. The CERN Beam Instrumentation Group has been working during the last years on the Wire Scanners upgrade
A beam wire scan is an interceptive method for transverse beam profile measurements. The working principle of wire scanners consists on the passage of a very thin carbon wire (~30um) through the particle beam. The secondary particle shower generated by the beam/wire interaction, during the wire passage, is detected outside of the beam pipe and transformed into an electrical current proportional to the loss intensity. The beam profile is reconstructed by plotting the losses intensity versus the wire position (figure 1. left). Using the measurements of these devices the beam emittance, and therefore the accelerator luminosity are calculated
Currently at the CERN complex, 32 beam wire systems are located along the injector chain and in the Large Hadron Collider (LHC). These devices are used on a regular basis by the accelerators operators to assess the characteristics of the beams produced by the injector chain before reaching the LHC. |  |
2.Challenges on the Upgraded system:
The development of a new scanner type is motivated by the need to measure smaller beam sizes at higher beam intensities. The basic concept is to combine the high velocity of the rotating fast scanners at 20ms-1, to avoid wire damage, with an accurate and direct wire position determination without bellows. The expected beam profile measurement accuracy is set to 2μm. For reaching such specifications and overcome previous systems limitations, a new mechanical design (compatible for PS, SPS and LHC), where all the mobile parts are located inside the vacuum chamber and share the same shaft, has been adopted (see figure bellow). The upgraded secondary shower acquisition system aims to use polycrystalline chemical vapour deposition (pCVD) diamond detector. New electronics and mechanics are therefore needed to cover high dynamic range without tuneable parameters, providing very low noise measurements for beam Gaussian tails determination or halo visualization. The design of such system must be compatible with any CERN accelerator and beam wire scanner location.
SPS Prototype
PSB Prototype
3. Specifications
| Upgraded System Specifications |
| Scan Angular movement |
180º |
| Nominal Wire Scan Speed |
20 ms-1 |
| Wire Position Resolution |
500 +- 25 uRad |
| Ultra High Vacuum Level |
2x10-11 Pa.m3.s-1 |
| Materials Outgassing |
< 10-9 Pa.m3.s-1 |
| Bakeout Temperature |
Cycles of 200ºC during 24h |
| Environmental Radiation (TID) |
20 kGy over 20 years |
Specification Documents:
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