The Soreq Applied Research Accelerator Facility (SARAF) is under construction in the Soreq Nuclear Research Center at Yavne, Israel. When completed at the beginning of the next decade, SARAF will be a user facility for basic and applied nuclear physics, based on a 40 MeV, 5 mA CW proton/deuteron superconducting linear accelerator. Phase I of SARAF (SARAF-I, 4 MeV, 2mA CW protons, 5 MeV 1mA CW deuterons) is already in operation, generating scientific results in several fields of interest. The main ongoing program at SARAF-I is the production of 30 keV neutrons and measurement of Maxwellian Averaged Cross Sections (MACS), important for the astrophysical s-process. The world leading Maxwellian epithermal neutron yield at SARAF-I (5×10 10 epithermal neutrons/sec), generated by a novel Liquid-Lithium Target (LiLiT), enables improved precision of known MACSs, and new measurements of lowabundance and radioactive isotopes. Research plans for SARAF-II span several disciplines: Precision studies of beyond-Standard-Model effects by trapping light exotic radioisotopes, such as 6 He, 8 Li and 18,19,23 Ne, in unprecedented amounts (including meaningful studies already at SARAF-I); extended nuclear astrophysics research with higher energy neutrons, including generation and studies of exotic neutron-rich isotopes relevant to the rapid (r-) process; nuclear structure of exotic isotopes; high energy neutron cross sections for basic nuclear physics and material science research, including neutron induced radiation damage; neutron based imaging and therapy; and novel radiopharmaceuticals development and production.
Phase I of the SARAF superconducting RF linac is under operation at the Soreq Nuclear Research Center. The present status of Phase I main components is reported, as well as, the beam operation experience accumulated in 2013-2014. The latter include acceleration of a 2 mA and 1.6 mA CW proton beams at energies of 2 MeV and 3.9 MeV correspondingly and 1 mA pulsed, duty cycle of few %, deuteron beams up to 5.6 MeV. The recent experiments include operation of intense CW proton beams on the liquid lithium target.
The front end of any modern ion accelerator includes a radio frequency quadrupole (RFQ). While many pulsed ion linacs successfully operate RFQs, several ion accelerators worldwide have significant difficulties operating continuous wave (CW) RFQs to design specifications. In this paper we describe the development and results of the beam commissioning of a CW RFQ designed and built for the National User Facility: Argonne Tandem Linac Accelerator System (ATLAS). Several innovative ideas were implemented in this CW RFQ. By selecting a multisegment split-coaxial structure, we reached moderate transverse dimensions for a 60.625-MHz resonator and provided a highly stabilized electromagnetic field distribution. The accelerating section of the RFQ occupies approximately 50% of the total length and is based on a trapezoidal vane tip modulation that increased the resonator shunt impedance by 60% in this section as compared to conventional sinusoidal modulation. To form an axially symmetric beam exiting the RFQ, a very short output radial matcher with a length of 0:75 was developed. The RFQ is designed as a 100% oxygen-free electronic (OFE) copper structure and fabricated with a two-step furnace brazing process. The radio frequency (rf) measurements show excellent rf properties for the resonator, with a measured intrinsic Q equal to 94% of the simulated value for OFE copper. An O 5þ ion beam extracted from an electron cyclotron resonance ion source was used for the RFQ commissioning. In off-line beam testing, we found excellent coincidence of the measured beam parameters with the results of beam dynamics simulations performed using the beam dynamics code TRACK, which was developed at Argonne. These results demonstrate the great success of the RFQ design and fabrication technology developed here, which can be applied to future CW RFQs.
A fast chopper system has been developed and tested for single bunch selection with the radio-frequency quadrupole (RFQ) accelerating element of the Soreq Applied Research Accelerator Facility (SARAF). The fast chopper consists of a high voltage (HV) deflector just before the RFQ, providing both positive and negative HV deflections and fast HV switching between polarities to enable momentary transmission of a single prebunch to the RFQ. Presently, the system enables single bunch selection for protons and deuterons at a repetition rate as determined by the user of up to 200 kHz, with bunch transmission of up to 50%, and with neighboring bunch contamination of less than 15%. Single bunch selection provides SARAF with fast neutron time-of-flight (TOF) capabilities. Measurements performed with liquid scintillation detectors show clear gamma and neutrons peaks, with TOF resolution of about 1 nanosecond FWHM. Beam dynamics simulations suggest possibilities for further improvements of the fast chopper and single bunch selection characteristics, with a significant lowering or elimination of the neighboring bunches, enhanced TOF resolution, and increased repetition rate to above 200 kHz. Fast neutron TOF capabilities, especially at phase II of SARAF, will provide exceptional opportunities for neutron induced reaction measurements for nuclear technology and fundamental research.
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