Upgrade of SARAF fast beam chopper and its applications in Phase I and Phase II of SARAF linac

Abstract

A fast chopper system has been developed for single-bunch selection for Phase I of the Soreq Applied Research Accelerator Facility (SARAF) in Israel. Further upgrade of the fast chopper system has improved its performance by enabling single-bunch selection for protons and deuterons at a repetition rate up to 220 kHz, with bunch transmission of up to 65% and with neighboring bunch contamination of less than 15%. The upgrade included (1) the redesign of the chopper deflection plates to minimize the electric-field asymmetry and provide more effective single-bunch selection, (2) a new trigger system with better trigger time resolution and better control capabilities, (3) an upgrade of the chopper electronics to increase the repetition rate, (4) the design of the chopper machine protection system, and (5) a general upgrade of the chopper concept to allow for operation in fast and slow modes. The implemented upgrades and the performance of the upgraded system are described. In addition, examples of the first experiments using the neutron time-of-flight (TOF) technique are presented. A fast neutron TOF facility, based on the upgraded fast chopper, is planned for SARAF Phase II. The high neutron flux at SARAF Phase II combined with the upgraded fast chopper system will make SARAF competitive with other advanced neutron research facilities.

Beam commissioning of the SARAF Injector and MEBT (protons)

“…3. New chopper electrodes and new electronics hardware [8], enabling chopper operation in both slow and fast modes.…”

“…The switching of polarity must be synchronized with the RF field. The concept of the fast chopper was demonstrated at Phase I, and allowed us to perform the first neutron TOF experiments [8].…”

Opportunities for high-energy neutron- and deuteron-induced measurements for fusion technology at the Soreq applied research accelerator facility (SARAF)

“…To avoid overlap of slow neutrons from successive bunches (down to ~0.1 MeV), the SARAF bunch rate should be reduced to below ~250 kHz. This will be achieved by a fast beam chopper that acts as a single bunch selector, which has been demonstrated recently [17]. The highest singlebunch selection frequency achieved so far is 220 kHz [17], accelerating one out of 800 ion bunches.…”

“…This will be achieved by a fast beam chopper that acts as a single bunch selector, which has been demonstrated recently [17]. The highest singlebunch selection frequency achieved so far is 220 kHz [17], accelerating one out of 800 ion bunches. The achieved time resolution for the SARAF single-bunch selector is 0.75 ns FWHM [17].…”

“…The highest singlebunch selection frequency achieved so far is 220 kHz [17], accelerating one out of 800 ion bunches. The achieved time resolution for the SARAF single-bunch selector is 0.75 ns FWHM [17]. Together with an estimated flight path uncertainty of 2-3 cm, the expected neutron energy resolution after an 18-m flight path is slightly above 0.2 MeV FWHM for 30 MeV neutrons.…”