SPARK PURIFICATION SYSTEM

1. SPARK PURIFICATION SYSTEM Kemar James Mechanical Engineering Department, Vanderbilt University Case Western Reserve University REU Summer Program 2010 Cleveland , Ohio 44106-4901 Faculty Advisors: Dr. Thomas Shutt , Dr. Dan Akerib, Dr Carmen Carmona Abstract This experiment was conducted in order to fabricate and optimize a spark purification system in addition to observing the titanium dust particle size and how it correlates to the purification of noble gas. This experiment was performed using a tube and titanium electrode to generate sparks that abrade the getter material from the electrode that interacts with the noble gas impurities. From the data obtained, it is evident that electrode geometry affects the sparks and particle size produced. Spark rate is proportional to the voltage, current and pressure. Knowing how these variables affect the particle size and the amount of dust produced per spark will give an insight of how to implement this system inside a noble gas detector for direct search of WIMP particles. Introduction The existence and the formation of the universe has intrigued and stimulated the scientific community to explore the very essence of its existence. Throughout the years astrophysical observations have clearly indicated that there exists a non-luminous and invisible matter called “dark matter.” This has lead to the postulation of several dark matter candidates such as axion and WIMP that hold the key towards a more extensive interpretation of our universe. Experimental groups such as the LUX collaboration attempts the “direct detection” [1] of the WIMP particle via dual phase Xe detector. However an inevitable problem of using such detectors is getting the impurity levels in the fluid on an order of 0.1 ppb to allow longer electron drift paths on the order of a few meters [2]. This allows the charge to be read by the PMT located near the liquid surface of the detector after scintillation. The spark purification system plays an imperative role in the purification of the noble gas detector. The localized sparks are generated between both the electrodes, grazing small dust particles (getter material) from the titanium electrode which interact with the noble gas reducing its impurity level within each cycle. The more purified the noble gas/liquid is the longer the electron drift paths are which allow the Ionization charge to be detected. This ionization charge along with the scintillation photons allow us to detect the nuclei recoil due to a WIMP interaction. Figure 3: The Spark Purification System showing the continuous circulation of the noble gas /liquid through the getter material ( titanium dust particles). Conclusion Experimental Setup • Figure 4, 5 and 6 show the experimental setup • The inside electrode was either a titanium threaded rod or strip • Experimental set up of fig. 4 was repeated using 2”,1” and 0.5” OD tube. • The materials used for the tubes were stainless steel and copper • Figure 6 used the same concept except the tube was replaced with a titanium sheet and a titanium strip was used for the other electrode. • The breakdown voltage required to generate sparks depends on the electrodes’ geometry, thus we use a voltage output in the range 1-10kV. Overall the experiment was quite successful in generating the sparks necessary to produce getter material (Titanium dust particles) for various electrodes geometries. Also from the observations, it is explicit that the curvature of the titanium electrode is proportional to the breakdown voltage and the particle size. The spark box without a doubt is superior, since sparks are generated at a lower voltage with the same separation between the electrodes as in the sparks tube. Also alignment issues of the electrodes like in the spark tube are avoided, thus making it easier for implementation in the existing model of LUX detector. Figure 5: The experimental setup of the spark tube with 0.5” OD and a strip titanium electrode Figure 4: The experimental setup of the 1” OD spark tube and a threaded titanium rod electrode Acknowledgement This work was supported the NSF grant numbers DMR-0850037. I would also like to acknowledge the program coordinators Kathleen Kash and Edith Gaffney. Finally I would also like to thank my advisors Dr. Thomas Shutt , Dr. Dan Akerib, and Carmen Carmona for the tremendous work they have done to equip and guide me along this wonderful experience. Figure 6: The experimental setup of the spark box with titanium electrodes Results and Discussion Figure 1: The interior design of the LUX 1.0 detector References Figure 2: The experimental set up of LUX 0.1 detector at CWRU Gaitskell, R. J., Direct detection of dark matter, Ann . Rev. Nucl. Part. Sci. 54(2004) 315-359. Sorensen, P. F., “A Position-Sensitive Liquid Xenon Time-Projection Chamber for Direct detection of Dark Matter”. Ph.D. thesis (2008). Griffiths, D. J., Introduction to Electrodynamics, Third Edition. Upper Saddle River, New Jersey: Prentice Hall , 1999. Ramsey, B., Bolotnikov A., "Purification techniques and purity and density measurements of high-pressure Xe." Nucl. Inst. Meth. A 383 (1996): 619-623. Table 1: The breakdown voltage required to initialized sparks with a titanium electrode of various geometries and sizes In table 1 a trend is apparent; as the size of the electrode decreases in width or radius the breakdown voltage increases. This variation in the breakdown voltage is primarily due to the separation between the electrodes and the concentration of the electric field lines. This basically concurs with a fundamental equation in electrostatics seen below. V =-Ed [1] Table 3: The of breakdown voltage required to generate sparks with the various separation between electrodes. The data in table 3 is in concordance with equation 1, as the distance increases the breakdown voltage required to generate sparks increases and vice versa. This data also indicates that using a spark box is even more effective than using the spark tubes; since sparks are produced at about 1.6 kV lower on average with approximately the same separation between electrodes. Table 2: Illustrates how the sparks’ rate vary as the current increases. In table 2 it is evident that the current is proportional to the spark rate which is also true for voltage, thus playing an imperative role in generating dust. Despite this there is an optimal current range that is necessary to produce dust and having a current that exceeds this range will lead to arcing. The arc effect doesn’t effectively graze the electrode instead it produces a similar phenomenon to an arc lamp.