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Muon Beam Studies in the H4 beam line and the Gamma Irradiation Facility (GIF++)Work Technical ReportRachel MargrafNon-Member States Summer Student Program & University of Michigan/CERN REUSupervisor: Nikolaos Charitonidis, CERN EN/EAAugust 11, 2017SummaryIn this report, I summarize my work of detailed study and optimization of the muon beam configuration of H4 beam line in SPS North Area. Using Monte-Carlo simulations, I studied the properties and behavior of the muon beam in combination with the field of the large, spectrometer “ GOLIATH” magnet at -1.5, -1.0, 0, 1.0 and 1.5 Tesla, which is shown to affect the central x position of the muon beam that is delivered to the Gamma Irradiation Facility (GIF++). I also studied the muon beam for different configurations of the two XTDV beam dumps upstream of GIF++ in the H4 beam line. I will also discuss my role in mapping the magnetic field of the GOLIATH magnet in the H4 beam line. IntroductionThe H4 beam line, located in CERN’s North Area, is a multi-purpose beam line capable of delivering secondary particle beams with a very wide momentum range, from 10 GeV/c to 400 GeV/c [1]. It delivers particles to three experimental areas, H4-PPE134, GIF++ (H4-PPE154), and CMS (PPE164). The H4-PPE134 area is an experimental zone used to test beam stands and perform R&D of detectors or detector components [2]. Moreover, it hosts the GOLIATH magnet, a large dipole magnet with maximum design strength of 1.5T, used to examine the detector’s response in strong magnetic fields simultaneously with the particle beams. As with every electromagnet, GOLIATH’s polarity can be also be reversed to produce a field in the opposite direction. The GIF++ facility is located downstream PPE134 [2], and offers the possibility to test equipment under exposed simultaneously to gamma photons (produced by a strong Cs source) and charged particle beams. A muon beam can be produced in the H4 beam line by incidence of a pion-rich beam on a many interaction length material, located upstream of the GOLIATH magnet. The muon beam can be utilized by users in both the H4-PPE134 and GIF++ areas simultaneously, however when the GOLIATH magnet is on, the muon beam trajectory that reaches GIF++ is deflected from its normal center. In order for users in both areas to coexist, GIF++ users must know the precise location of the deflected muon beam. The goal of my project was to simulate and analyze the trajectory of muons in the H4 beam line in order to advise GIF++ users where to position their equipment to receive muons. To provide a through description of different operating conditions utilized in the H4 beam area, I studied several configurations of the beam line, including different GOLIATH magnetic field strengths and configurations of the two beam dumps upstream GIF++, and analyzed their effects on beam quality.SimulationsSimulations were performed using the simulation software G4Beamline [3]. I modeled in detail the shielding of the H4 beam line (Figure 1A) and implemented it into an existing H4 beam line G4beamline model [4]. I studied an incident beam with momentum 150 GeV/c composed of 70% positively charged pions, 25% protons, and 5% positively charged kaons. This beam was incident on collimators 9/10 in the “Closed Horizontally” configuration (Figure 1B). The collimators serve as a dump for the pions, allowing the muons to continue towards PPE134 and GIF++. For the preliminary results discussed below, the GOLIATH magnet was modeled as a 2.5 m long generic bending magnet with a uniform vertical magnetic field. This model is the orange magnet shown in Figure 1A. This length is shorter than the diameter of the coils of GOLIATH, and was chosen because preliminary magnetic field mapping data from GOLIATH showed that the magnet’s field fell sharply after the 2m diameter yoke of the magnet. The final results of these simulations, however, will instead use the magnetic field map of GOLIATH in combination with the more accurate yoke and coils modeled in red and green in Figure 1A. Figure 1: G4beamline simulation of H4 beam line between Collimators 9 and 10, and GIF++. (A): Overview of beam elements. (B): Possible configurations of Collimators 9 and 10. The collimators’ aperture width can be set between 1mm and 90mm. Captions indicate the width of the aperture in X (horizontal) and Y (vertical). In the closed conformations, the center of the beam is shifted to hit the center of the lower right collimator jaw. Figure depicts a positive pion of p=150GeV incident on the collimators. This study produced muons with beam incident on collimators in the “Closed Horizontally” conformation. (C): Open and closed dump conformations. Dump XTDV 022.520 is depicted.Figure 2: Z Positions of interest. Z positions are given from the start of the H4 beam line to the center of each element. Detectors are “zntuple” detectors in G4beamline, which record all particles that cross the defined Z position. The “Upstream GOLIATH” and “Downstream GOLIATH” detectors are placed 3.4m apart, which is the diameter of the coils of GOLIATH. The “Downstream Collimator” detector is placed 5mm downstream of the collimator.There are 3 beam dumps present in this simulation, labeled XTDV Dumps 022.520, 022.610, and 022.628, which are located as shown in Figure 1 and 2. These are XTDV dumps consisting of 3.22m of iron that can be placed in the path of the beam. While high-energy muons are not affected by the iron, all hadrons are absorbed by the dumps. Thus, these beam dumps affect the level of residual pions that reach GIF++. The muon beam was studied for the four different possible combinations of opening/closing the two dumps (022.520 & 022.610) upstream of GIF++.Simulated data was collected at eight z locations described in Figure 2. Our coordinate system defines z along the beam, y vertically upward, and x to the left if viewing the beam from upstream. Particles were analyzed in y for particles in the 4 meter space above the hall floor (-2.06m below the beam, and 1.94m above the beam). Cuts in x were made to display the usable beam between the walls of each location, the x positions of which are also indicated in Figure 2.GOLIATH Field MappingI worked as a member of a team to map the magnetic field of GOLIATH, which will benefit this and future simulations. The first mapping attempt, July 4th-July 6th, did not produce a complete field map due to problems with powering GOLIATH. The second mapping attempt, August 2nd-4th and August 9th-10th, will produce two extensive field maps, at the -1.5T and -1.0T design strength of GOLIATH, which can then be linearly extrapolated to lower strengths if needed.The top and bottom coils of GOLIATH are not identical, and thus must be powered differently. The upper coil is made of 216 turns of copper, and is 442mm thick vertically. The lower coil is made of 128 turns of aluminum, and is 300mm vertically [5]. The David power supply supplies additional current to the lower coils to produce a more uniform magnetic field.GOLIATH was powered with +3600A on the GOLIATH power supply and +1750A on the David power supply to produce the -1.5T design strength field of the magnet. GOLIATH was then powered with +2400A on the GOLIATH power supply and +1166.6A on the David power supply to produce the -1.0T design strength field of the magnet.I developed ROOT [6] macros to plot our field measurements, and utilized Mayavi [7] and Matplotlib [8] Python packages to produce vector plots of our field map. While it is too early to include these plots in this work project report, these scripts will allow the magnetic field map, when completed, to be readily represented for future publication. An extensive ATS note of this work that I will co-author is currently under preparation. Simulation Results/ConclusionFigure 3: x vs y muon (μ- and μ+) position plots for locations in the GIF hall. Detector locations are defined in Figure 2. Plots were created for 1*106 particles (70% π+, 25% p, and 5% K+) incident on the collimator. (A): 1.5T Magnet strength with both Dump 022.520 and Dump 022.610 closed. Here, we see in the front and center of the GIF++ hall, the muon beam passes through the “right” wall of the GIF++ enclosure, and is inaccessible to users. However, the beam is still useable along the back wall of GIF++, and in a small nook in the right wall. (B): -1.5T Magnet strength with both Dump 022.520 and Dump 022.610 closed. Here, the beam is much more accessible to users at all four points in GIF++.Using ROOT, I constructed 12 sets of plots for each of the 20 beam line configurations (4 combinations of open/closed dumps x 5 GOLIATH magnet strength settings). These plots include 1D histograms of the x, y, and p (momentum) distribution of particles in the beam, and 2D histograms of x vs p, y vs p, and x vs y. These plots were constructed for all eight z positions of interest indicated in Figure 2. Separate plots were made to describe muon content (μ+ and μ-) and pion contamination (π+ and π-). For brevity, I display only muon plots of the x vs y beam position for the four z positions of interest within GIF++ with both dumps closed at the -1.5T and 1.5T GOLIATH field strength (Figure 3). Figure 4: Equipment placement regions to receive muon and gamma photon flux. Geometrical analysis of gamma ray source, using the gamma source collimator half-angle of 37° is shown. The gamma ray source can be moved laterally in x from 0.65m to 2.15m from the beam. Here it is analyzed in its 0.65m position in order to achieve maximum overlap with the muon beam for the 1.5T setting. Equipment may be placed near the back wall of GIF++, the “Downstream Location,” or in the nook of the right wall, the “Upstream Location” for the respective magnet strength.These results show that the 1.5T magnet strength deflects the muon beam approximately 1m in the –x direction, directing the beam into the “right” wall of GIF++. The 1.5T magnet strength similarly deflects the beam approximately 1m in the +x direction. Using these results, and the precise location of the muon beam determined in the simulations, we can advise users on the appropriate location to place their equipment in order to receive muon beam in addition to gamma photon flux from the 137Cs source. Figure 4 shows the approximate regions upstream and downstream of the gamma radiation source where users could place their equipment. It is readily apparent from these simulations that the -1.5T GOLIATH strength provides more usable beam within GIF++ than the 1.5T GOLIATH strength. In the 1.5T case, the muon beam is directed into the right wall of GIF++, leaving accessible beam only near the back wall of GIF++ and in a small nook in the right wall. The -1.5T setting, on the other hand, has much larger regions upstream and downstream of the gamma source in which to place equipment.The final simulation results of this project will give users the precise location and rate of the muon beam delivered to GIF++. This will allow H4-134 and GIF++ users to share the muon beam effectively, optimizing their beam time.Acknowledgements:I would like to thank my supervisor, Nikolaos Charitonidis, for his incredible support and guidance throughout this project. I would also like to thank Marcel Rosenthal for his advice on G4Beamline and his creation of a Python script that was used to interpolate the GOLIATH field map data. I would like to thank Yiota Chatzidaki for her help in obtaining magnetic field map measurements of GOLIATH. Additionally, the GOLIATH field mapping I worked on was performed in collaboration with the EP/DT magnet group (Felix Bergsma & Pierre-Ange Giudici?), Henric Wilkens and the kind support of RD51 Collaboration (Eraldo Oliveri & Yorgos Tsipolitis) and GIF++.References: BIBLIOGRAPHY [1] Brianti, G. “SPS North Experimental Area – General Layout”, CERN/LAB II/EA/Note 73-4, 12-09-1973[2]"Introduction to the use of the H4 beam." CERN/EN/SBA. 19-05-2010.[3] Muons, Inc., “G4Beamline, v3.01.” Available: .[4] Charitonidis, N. et al., "Beam Performance and instrumentation studies for ProtoDUNE-DP experiment of CENF", CERN-ACC-NOTE-2016-0052[5]Flegel, W. "GOLIATH Magnet." CERN/EP 8-10-1998.[6]Rene Brun and Fons Rademakers, ROOT - An Object Oriented Data Analysis Framework, Proceedings AIHENP'96 Workshop, Lausanne, Sep. 1996, Nucl. Inst. & Meth. in Phys. Res. A 389 (1997) 81-86. See also . Version used: 5.34/34.[7] Ramachandran, P. and Varoquaux, G., "Mayavi: 3D Visualization of Scientific Data" IEEE Computing in Science & Engineering, 13 (2), pp. 40-51 (2011)[8] Hunter, J.D. "Matplotlib: A 2D graphics environment." Computing In Science & Engineering. 9 (3) pp. 90-95. IEEE Computer Society (2007). doi: 10.1109/MCSE.2007.55 ................
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