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ACC-OTHERS-07 GSI SCIENTIFIC REPORT 2009 Status report on the Frankfurt 200 mA proton source A remarkable progress on the 200 mA 120 keV high current proton source source for FRANZ (Frankfurt Neutron Source Source at the Stern Gerlach Centre) was achieved till end of 2009. Figure 1 1 shows a technical cross-section of the source. Principally, Principally, the source is composed of the Frankfurt Volume Volume Source Source plasma generator and equipped with a new pentode pentode extraction system. The plasma generator has a maximum input power power of 8 8 kW with a total total arc current of 100 A and an arc voltage voltage of 80 V. V. The plasma confinement is achieved by a solenoidal magnetic field with with a maximum flux density of 40 mT. Also included in the design is a filter magnet which generates generates a a transversal magnetic field field in front of emission aperture. aperture. Figure 1: Cross-section of the 200 mA proton source. The first measurements were performed for testing source characteristics and to evaluate the total beam current and the relative fraction of protons. An exemplary measurement can be seen in Figure 2. Figure 2: Measured beam fraction at a 25 mA total beam current. 166 GSITemplate2007 J. Sun 1 , W. Schweizer 1 , K. Volk 1 J. Sun 1 , W. Schweizer 1 , K. Volk 1 1 IAP, Frankfurt, Germany A pentode extraction system has been designed for the FRANZ project with a single hole aperture of 5 mm radius. The application of a pentode extraction system enables not only decoupling of beam parameters from the beam energy but also allows a pulsed operation mode. With an optic fibre controlled high voltage switcher it is possible to adjust and optimize the repetition rate and pulse length to aim for a higher field strength resulting in higher peak current and less sparking between plasma and puller electrode. Furthermore, the pulsed operation mode relaxes the thermal loading for the whole extraction system and beam transport section. The operation time can be consequently extended. The very first pulsed beam is displayed in figure 3. voltage drop of 1 st stage [V] pulsed beam with thyristor stack 10Hz 4500 4000 3500 3000 2500 2000 1500 1000 500 0 -0,05 -0,3 -0,2 -0,1 0 0,1 0,2 0,3 t [s] UEX 4,4kV 2,2 mA Figure 3: Beam pulse from Frankfurt volume source in pulsed extraction operation mode. A reliable switch system has been interdisciplinary developed and successfully tested. Current beam sensor using parallel flux gating principle is chosen for comprehensive investigation on the pulsed beam. Intensive investigation on soft magnetic material for flux gate sensors has been accompanied. This helps for optimized operation parameters for detecting beam pulse [1] with sufficient resolution under current operation environment. Pulsed pentode extraction system opens new perspective in terms of operation mode extraction system, it brings also further topic with itself, which are relevant for a study of dynamic behaviour of plasma meniscus, sparking from Hz till kHz range, beam noise. All these topics associated with pulsed extraction mode will sustain more innovative development of extraction system. [1] B-J. Lee et al.: “Properties of magnetic materials at very high magnetization rates”. 0,3 0,25 0,2 0,15 0,1 0,05 0
GSI SCIENTIFIC REPORT 2009 ACC-OTHERS-08 GSITemplate2007 Neutron streaming though the RF waveguide ducts of SPL* E. Kozlova 1 , T. Radon 1 , T. Otto 2 , and G. Fehrenbacher 1 1 GSI, Darmstadt, Germany; 2 CERN, Geneva, Switzerland Introduction Presently a new accelerator complex is being planned at CERN, which will replaced the ageing Proton Synchrotron (PS). A high-power160 MeV H - linac (Linac 4) will replace the present 50 MeV proton linac injector [1], a 5 GeV Superconducting Proton Linac (SPL) will replace the 1.4 GeV PS Booster (PSB) [2] and a 50 GeV synchrotron (PS 2) will replace the 26 GeV PS [3]. A tentative layout of the planned accelerators, integrated into the CERN accelerator complex, is shown in Fig. 1. Figure 1: Layout of the LHC injectors at present and in the future. In this paper some radiological aspects are discussed concerning the propagation of neutrons through the waveguide ducts from the SPL tunnel to the surface. Injected 160 MeV H - ions from the Linac 4 into the SPL will be accelerated up to 4-5 GeV. The SPL tunnel will be situated in the earth at a depth between 20 and 30 meters. The expected uncontrolled losses are 1 W/m at each section of the SPL. Thus the radiobiological study has been started with the estimation of the dose rate level at the surface at the exit of the waveguide, coursed by uncontrolled losses in the SPL. Prompt dose calculations The calculations of the prompt dose rate were performed by using the Monte Carlo code FLUKA. The first calculation was done for a proton beam energy of 5 GeV. The total length of the SPL is 550 meters, for the calculation 100 meters were taken. Along 100 meters three waveguide ducts (shaft) will be situated. The target in which the beam is lost was assumed by a 0.02 × 0.02 × 100 m 3 iron block placed at the beam height. The dose rate was calculated from the superposition of 11 sources, which were equally distributed all over the target. In Fig. 2 the radiation streaming in the SPL tunnel and in one of the shafts is presented. The most conservative case is for * Work supported by FP7 under the Grant Agreement No. 212114 (SLHC-PP). the shaft number 3 which is shown in the lower part of Fig. 2. Without implementing any waveguides in the calculations the dose rate on ground level is less than 50 µSv/h. The inclusion of the waveguides in the ducts will further reduce the dose rate at the surface. This will be one of the future radiation protection studies for the SPL. The same calculations were performed for the beam energy of 1 GeV. Assuming in this case also the beam losses of 1 W/m it was found out that the dose rate at ground level is by a factor of 3 higher than for the beam energy of 5 GeV. This lower energy is overcompensated by the higher intensity. Figure 2: Neutron streaming through three waveguide ducts of SPL. Uncontrolled losses are assumed to be 1 W/m. The primary beam energy is 5 GeV. The importance biasing technique was used to improve the transport of the neutrons. The beam transport in the soil was switched off. References [1] E. Mauro and M. Silari, “Radiation protection studies for a high-power 160 MeV proton linac”, Nucl. Instrum. Methods Phys. Res. A, 605, 2008, p. 249. [2] https://twiki.cern.ch/twiki/bin/view/SPL/SplWeb. [3] https://paf-ps2.web.cern.ch/paf-ps2. [4] www.fluka.org. 167
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