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The proton beam of CERN's Super Proton Synchrotron (SPS) is extracted towards the fixed-target experiments of the North Area in multi-turn slow-extraction mode. This extraction mode delivers a constant flux of protons over many seconds (typically 3·1013 protons over 4.8 seconds, i.e. while the beam circulates 200000 times in the ring). The extraction device - an electrostatic septum - utilizes a long array of thin stretched wires which separate a high-electric-field and no-electric-field region. The beam is excited using a third order resonance. While particles have small betatron oscillation amplitudes, they remain in the field-free region and keep circulating unperturbed. When they gain large enough amplitudes, they enter the high-field region and get deflected out from the ring. Particles hitting the wires of the device are lost and produce a high radiation load of the device and the environment. This makes the maintenance of this delicate device also difficult.

In order to reduce beam loss and radiation, a short wire array will be placed upstream of the electrostatic septum, very precisely aligned with the plane of the wires of this latter. This is a simple mechanical device which functions as a diffuser: particles which would otherwise hit the wires of the electrostatic septum, receive a small transverse momentum spread due to multiple scattering in the wires of the diffuser, thereby creating a dip in the particle density distribution at the position of the electrostatic septum wires - this is practically the "shadow" of the diffuser's wires.

In the framework of a collaboration with CERN, our group made the full design and construction of this device with a very tight schedule, in collaboration with Engious Ltd. The device was installed into the SPS at the beginning of February, and performed according to the expectations, reducing the losses by about 15%.


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