The neutron source FRANZ (Frankfurter Neutronenquelle am

Stern-Gerlach-Zentrum), which is currently under construction, will be the neutron source with the highest intensity in the nuclear-astrophysically relevant energy

region. The TraceWin code was used to design the High-Energy Beam-Transport section with regard to the experimental requirements at different target positions

Arda, C.

Claessens, C.

Fiebiger, S.

Hinrichs, O.

Meusel, O.

Noll, D.

Reich, M.

Reifarth, R.

Schmidt, S.

Schwarz, M.

Sonnabend, K.

Thomas, B.

English

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2015-15191-1Colloquia: UCANS-VIL NUOVO CIMENTO 38 C (2015) 191Simulations of the High-Energy Beam-Transport (HEBT) sectionat FRANZO. Hinrichs, C. Arda, C. Claessens, S. Fiebiger, O. Meusel, D. Noll,M. Reich, R. Reifarth, S. Schmidt, M. Schwarz, K. Sonnabendand B. ThomasInstitut fu¨r Angewandte Physik, Goethe University - Frankfurt a. M., Germanyreceived 22 February 2016Summary. — The neutron source FRANZ (Frankfurter Neutronenquelle amStern-Gerlach-Zentrum), which is currently under construction, will be the neu-tron source with the highest intensity in the nuclear-astrophysically relevant energyregion. The TraceWin code was used to design the High-Energy Beam-Transportsection with regard to the experimental requirements at different target positions.PACS 26 – Nuclear astrophysics.PACS 29.27.Eg – Beam handling; beam transport.PACS 41.85.Lc – Particle beam focusing and bending magnets and quadrupoles.1. – FRANZThe accelerator driven neutron source FRANZ is currently under construction at theGoethe University Frankfurt, Germany [1]. The first stage of construction will consist ofthe sections illustrated in fig. 1.The high-intensity proton beam is extracted from the volume-type ion-source, whichis arc-discharge-driven [2]. Then, the beam is transported in the so called Low-EnergyBeam-Transport section (LEBT). The LEBT consists of four solenoid magnets and achopper. It fits the extracted beam into the acceptance of the following radio-frequencyquadrupole (RFQ) accelerator. In addition, undesired H+2 and H+3 hydrogen fractions areremoved [3]. The chopper is able to divide the continuous beam into macro-bunches. Ithas a Wien filter-type E×B configuration to combine advantages of magnetic and electricdeflection [4].In the following LINAC section, the proton beam is accelerated up to an energy of700 keV by the four-rod RFQ of 1.7m length. Then, the Interdigital H-type drift tubelinac (IH-DTL), which is equipped with an internal quadrupole triplet, increases thebeam energy up to 2MeV. The frequency of the coupled accelerators is 175MHz [5].Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 O. HINRICHS et al.Fig. 1. – Schematic overview of the FRANZ facility in its first stage of construction.In the Medium-Energy Beam-Transport section (MEBT), a crossbar H-mode (CH)rebuncher cavity is surrounded by two quadrupole triplets. It will be used to vary the finalenergy between 1.8MeV to 2.2MeV allowing to adapt the neutron energy spectrum [6].The final section is the High-Energy Beam-Transport section (HEBT). Here, a dipolemagnet serves different beamlines. The so called In-beam beamline includes two targetstations. The neutron production target is at position 1. Inside a 4π-BaF2 calorime-ter, the target for neutron- or proton-induced reactions is installed (position 2). Theactivation target at position 3 has a separate beamline. This paper shows the resultsof simulations of the In-beam beamline including the dipole magnet, the quadrupoledoublet and the target positions 1 and 2.Two different operation modes are foreseen for FRANZ: A bunched mode to performtime-of-flight experiments with neutrons and a CW mode for proton-induced and acti-vation experiments. For the time-of-flight experiments a fast calorimeter will be used. Itconsists of 41 BaF2 crystals with a total efficiency of 90% and 50% full-energy peak effi-ciency. The data acquisition system is supported via six CAEN V1751 digitizer moduleswith eight channels, 10 bit and 1 gigasample-per-second [7].At its final stage, FRANZ will have the highest proton beam current at an energy of2MeV worldwide. Hence, the production of p-nuclei via proton-induced reactions canbe studied. Furthermore, neutron capture reactions for the s- and r-processes can beinvestigated.2. – Neutron productionAt FRANZ, the neutrons will be produced via the reaction 7Li(p,n)7Be. If the protonenergy is about 1.91MeV, the resulting energy distribution of the neutrons is similar toa thermal distribution at kT = 25 keV, which is a typical temperature in s-process nu-cleosynthesis [8]. Because the proton energy is close to the neutron production thresholdthe neutrons are kinematically collimated in the forward direction.The neutron production target has a copper backing and two cooling cycles to dissi-pate the high power deposition of 4 kW of a 2MeV proton beam with 2mA of intensity [7].3. – HEBT simulationsTo obtain the general conditions of the magnetic parameters, beam-dynamics sim-ulations with hard edge models were performed. In cooperation with the companySIMULATIONS OF THE HIGH-ENERGY BEAM-TRANSPORT (HEBT) SECTION AT FRANZ 3Danfysik, three-dimensional CAD models based on these parameters were developed.Magnetic field simulations with these models were performed via CST EM Studio [9].The extracted magnetic fields were used as an input for more precise beam-dynamicssimulations, which were performed using the software TraceWin [10]. Multi-particle sim-ulations in a space charge regime were performed due the high beam current at FRANZ.100000 particles were tracked with a beam current of 2mA, which will be the currentfor the first stage of FRANZ. The energy was set to 2MeV and the bunch frequency to175MHz.The simulations of the HEBT section used calculations of the MEBT section as aninput. Thus, the sections were treated independently. A dipole gap of 40mm anda quadrupole aperture radius of 52.5mm fulfill the requirements on the magnetic pa-rameters and fit into the setup of the beamline. The influence of the magnets canclearly be seen in the envelopes (see fig. 2). The final quadrupole doublet can focusFig. 2. – Transverse beam envelopes (99%) towards the neutron production target (upper plots,compare fig. 1 position 1) and the target for proton-induced reactions (lower plots, comparefig. 1 position 2).4 O. HINRICHS et al.Fig. 3. – Output distribution at the neutron production target (left, compare fig. 1 position 1)and at the target for proton-induced reactions (right, compare fig. 1 position 2).the beam onto both target positions. The highest particle density is found along thebeam axis.The aim is to have as many protons on the targets as possible, but some losses alongthe beamline, mainly from off-momentum particles in the dipole, are unavoidable. Thetotal losses in the HEBT section are below 1%, which keeps activation and damage ofthe beam pipe at a minimum. Behind the dipole, a collimating slit is planned to absorbthe off-momentum particles safely.Figure 3 shows the beam distribution at the first two target positions. The beam spotis circular, matching the geometry of the targets, and the one-dimensional distributionin green has a Gaussian shape. The minimum beam radii are 3.5mm at target position 1(left plot) and 6.4mm at target position 2 (right plot), respectively.As beam diagnostics elements, Beam Induced Fluorescence (BIF) Monitors areforeseen.4. – ConclusionsThe neutron source FRANZ and its HEBT design has been described. The experi-mental requirements at the different target positions can be reached with the specifiedsystem of a dipole switching magnet and a doublet of focussing quadrupole magnets.∗ ∗ ∗This project is supported by DFG (SO907/2-1) and HIC for FAIR.REFERENCES[1] Reifarth R. et al., Publ. Astron. Soc. Aust., 26 (2009) 255.[2] Schweizer W. et al., Rev. Sci. Instrum., 85 (2014) 02A743.[3] Schneider P. et al., LEBT Dynamics and RFQ Injection , in IPAC’15, Richmond, USA,THPF024 (2015).[4] Wiesner C. et al., Chopping High-Intensity Ion Beams at FRANZ, in LINAC’14, Geneva,Switzerland, WEIOB01 (2014).SIMULATIONS OF THE HIGH-ENERGY BEAM-TRANSPORT (HEBT) SECTION AT FRANZ 5[5] Heilmann M. et al., Preparation of the Coupled RFQ-IH-Cavity for FRANZ, in IPAC’14,Dresden, Germany, THPME059 (2014).[6] Schwarz M. et al., A Rebunching CH Cavity for Intense Proton Beams, in LINAC’14,Geneva, Switzerland, TUPP062 (2014).[7] Schmidt S., Neutrons at FRANZ: Production and Data Acquisition Systems, PhD thesis,Goethe University Frankfurt, Germany (2015).[8] Reifarth R., Lederer C. and Ka¨ppeler F., J. Phys. G: Nucl. Particle Phys., 41 (2014)053101.[9] CST GmbH, CST EM-Studio, Darmstadt, Germany (2015), www.cst.de.[10] Duperrier R., Pichoff N. and Uriot D., CEA Saclay Codes Review for High IntensitiesLinacs Computations, in ICCS, Amsterdam, The Netherlands (2002).

Simulations of the High-Energy Beam-Transport (HEBT) section

at FRANZ

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Simulations of the High-Energy Beam-Transport (HEBT) section at FRANZ

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