The SPES 50 kW Beam Dump Test Report for BEST 70p Cyclotron Commissioning at INFN Legnaro Labs

J. Esposito, P. Antonini, D. Benini, M. Calderolla, A. Calore, D. Campo, L. De Ruvo A. Lombardi, M. Maggiore, L. Pranovi,

INFN, Laboratori Nazionali di Legnaro, Legnaro (Padova), Italy.

INTRODUCTION

In 2016 the SPES (Selective Production of Exotic Species) project [1] entered the planned cyclotron commissioning program at the INFN Legnaro National labs (LNL), comprising the successful repetition of the Factory acceptance Tests (FAT), first, followed by the first stage of Site Acceptance Tests (SAT) operations afterwards. The availability of the new 70p cyclotron, supplied by Best Cyclotron System Inc (BCSI) company [2], with the related beam transport lines foreseen by the SPES Radioactive Ion Beams (RIBs) nuclear research program, has soon been taken into consideration as the proper tool to establish a new, interesting nuclear science and technology research center as well, dedicated to both nuclear medicine and material science/applied physics. LARAMED (LAboratory for RAdionuclides of MEDical interest) is indeed the LNL proposal for an international-class level and well-established research center, which main goal is the study and development of new, and/or more efficient methods, for existing/novel radionuclides production routes, having potential medical interest. A general view of the SPES/LARAMED beamlines final layout foreseen is shown in Figure 1.

Fig. 1. Overall final layout configuration for the SPES/LARAMED facility beamlines. The beamline L1 to transport the beam to the ISOL bunker A6 is currently under commissioning, with a BD system installed at the end of it. Bunkers RI#1, 2, 3 are dedicated to high intensity beams for both research and production of new/innovative radioisotopes (LARAMED project).

The accelerator main feature is to deliver a proton beam between 35-70 MeV energy range and 750μA current maximum (i.e. ~52 kW max), shared into two exit ports. The

new facility design has been expanded and upgraded for taking advantage of the dual simultaneous cyclotron beam extraction, in order to provide a multipurpose high intensity irradiation facility. At the final beamlines configuration layout, up to 10 experimental stations are foreseen to be irradiated by proton beams and three of those are put into heavily shielded bunkers for receiving high power beams (up to 50 kW).

HIGH POWER BEAM DUMPER

In order to assess the 70p cyclotron full power capability (i.e. 750μA, 70MeV), a dedicated Beam Dumper (BD) system has been at the purpose designed and constructed at LNL, which further description may be found in [3]. It basically comprises two cooled-down copper plates, tilted by 10° angle, in order to split and spread out the beam hitting area, thus reducing the power density to a few hundred W/cm2 on the hot spots. The two copper plates are bolted on an aluminum frame and an indium sealing in-between allows for the vacuum seal. In order to limit somehow the residual activation of A6 bunkers' walls, thus allowing for a fast removing operation of the device, once the cyclotron commissioning is completed and next installation of SPES ISOL target, in a safe environment, a series of lead shielding (50 mm thick) and high density polyethylene layers (350 mm full width) have been assembled around the beam stopper structure. A picture showing the final BD installation inside the A6 bunker is shown in Figure 2.

Fig. 2. The 3.4 tons SPES BD installed in A6 bunker, once completed the in-line positioning with the laser tracking tool procedure and connected to both the cooling and beam instrumentation/control and safety systems.

Fig. 3. (Left) MCNPX v2.7e Ambient Equivalent Dose Rate (AEDR) calculation map expected by neutron prompt radiation during beam-on stage at the maximum cyclotron performance (70 MeV, 52.5 kW) on BD located inside A6 bunker. (Right) AEDR distribution of residual decay radiation 4 weeks after EOB in nominal conditions (70 MeV, 52.5 kW) and 5 days of continuous beam-on operation.

The heat power on the SPES BD is removed by a dedicated cooling system, thus avoiding the activated water mixing with water used for cooling other apparatuses. A series of detectors serve as BD instrumentation to monitor the operational status of the whole BD system by the PILZ control and safety system tool.

BEAM COMMISSIONING REPORT

BCSI started the commissioning of the 70p cyclotron and beamline on March 2016, to be planned in different phases: starting from acceleration at 1 MeV, up to beam extraction and transport at full power capability. Between late August, early September 2016, the proton beam was indeed extracted and delivered along the beamline 1 (BL1 in Fig. 1) on the BD system. After exploring beamline operation at 100 μA, the current was gradually increased and sustained at every 100 μA increment, to confirm stable, problem-free operation at each level, before the next increase. Figure 4 shows all the BD instrumentation parameters history acquired by the PILZ control/safety system (i.e. vacuum level, 12 temperatures sensors, and main cooling fluid data) that recorded this ramp up to 400 μA (i.e. 28 kW), followed the day after by a ramp up to 500 μA (35 kW). At that time the BD experienced a vacuum leak and the operation was stopped. After careful investigation and test with low current beams, it was soon plain that such an issue could be managed without problems, so that the scheduled program, at the SPES-required beam level, could be operated prior the final tests at the maximum beam power (i.e. 52.5 kW). Commissioning was however interrupted on late November, almost at the end of a one-week long-run test, due to the ion source isolation transformer failure. The radiation dose level map expected at the maximum performance, during both beam-on and beam-off stages (30 days after EOB) are shown in Figure 3. On mid-march 2017, 130 µSv/h dose-

rate level has been measured in cyclotron room, at beam pipe entrance in the wall duct, thus basically confirming MCNPX calculations (dose plateau region).

Fig. 4. SPES BD instrumentation parameters events history time-window, recorded by the PILZ control/safety system, from Sept. 1st at h 12.00, up to Sept. 2nd at h 12.38. The maximum cyclotron beam performance has been achieved so far (i.e. ~400 and 500 µA respectively) corresponding to ~28 and 35 kW beam extracted and delivered on BD.

[1] G. Prete et al. “The SPES project: a second generation ISOL facility”, Physics Procedia, vol.52, (2012), 274-283. [2] Best Cyclotron Systems, Inc., www.bestcyclotron.com [3] E. Boratto et. al. INFN-LNL Annual Report (2015).