Session E2: Undergraduate Research/SPS III

Investigating the Neutral-Gas Manometers in the Wendelstein 7-X Experimental Fusion Reactor

The neutral-gas manometer is a powerful diagnostic tool used in the Wendelstein 7-X stellarator, a magnetized fusion experiment located in Germany. The Wendelstein, produced at a cost of 1.2 billion euros, and 20 years in the making, had its first experimental results in Winter 2016. Initial findings exceeded expectations but further study is still necessary. The particular instrument we examined was a hot-cathode ionization gauge, critical for attaining a quality in-vessel environment and a stable plasma. However, after the winter operation of Wendelstein, we found that some of the gauges had failed the six-second (maximum) plasma runs. Wendelstein is on track for 30-minute operations within three years, so it has become of utmost importance to scrutinize gauge design claims. We therefore subjected the devices to high magnetic field, input current, and temperature, as well as to long operational periods. Our results confirmed that the manometer cannot survive a 30-minute run. Though our findings did motivate promising recommendations for design improvement and for further experimentation so that the gauge can be ready for upcoming operations in Summer 2017 and eventual installment in ITER, the International Thermonuclear Experimental Reactor, currently under construction.   

Pion Charge Exchange Cross Section on Liquid Argon

The observation of neutrino oscillations allows charge parity violation to be probed in the neutrino sector. Detectors with high calorimetric energy resolution and high spatial resolution will provide precise measurements of neutrino oscillations. By measuring small $\pi^\pm$ cross sections for individual interaction channels, specifically charge exchange, we will make a measurement in the first of its kind on liquid Argon and demonstrate the physics capabilities of a relatively new detector technology: the Liquid Argon Time Projection Chamber (LAr TPC). This analysis will report on the thin slab cross section measurement technique and the Monte Carlo cross section measurements in the energy range of 0.2 - 1.0 GeV. This analysis is the first iteration in classifying charge exchange events from a sample of incident pions, and it aims to identify events in which a $\pi^0$ was produced without any charged pions leaving the interaction vertex. We will also report on the methodology and efficiency of this algorithm in identifying particles and their interactions in liquid argon. This analysis will inform a future measurement of the $\pi^\pm$ charge exchange cross section on liquid argon.   

Development of compact particle detectors for space based instruments

The Silicon Photomultipliers (SiPMs) are new photon-detectors which have been increasingly used in particle physics. Their small size, good single photon resolution, simple readout, and immunity to magnetic fields offers benefits compared to traditional photomultipliers. LYSO and CeBr3 crystals are relatively new scintillators with high stopping power, very good light yield and fast decay time. The response of these detectors to low energy gamma rays will be presented.   

Scintillating Bolometer Monte Carlo for Rare Particle Event Searches

This study uses the Geant4 physics simulation toolkit to characterize various scintillating bolometer constructions for potential experimental commissioning. Emphasis is placed on detector sensitivity to neutrinoless double-beta decay. Constructions minimally include a scintillating source material for the decay and an absorber material. Tellurium, Selenium, Germanium and other candidate isotopes are studied as source materials. Various background discrimination techniques are analyzed including reflective housings and anti-reflective coatings upon the source material. Different geometric optimizations are considered. Ability to discriminate incident alpha and beta radiation, as well as photon detection efficiency for each construction is presented.   

Development of an Inductively Coupled Thermometer for a Cryogenic Half-Wave Plate

The current state of Cosmic Microwave Background (CMB) research has focused much attention on the measurement of polarization. In an effort to modulate the CMB polarization while also minimizing photon noise due to thermal emission, we are developing a sapphire half-wave plate (HWP) cooled to 50 K rotating at 2 Hz on a superconducting magnetic levitating bearing. In order to measure the temperature of the rotor without making physical contact, we designed an inductively coupled cryogenic thermometer. The complex impedance of the circuit has a resonant peak when driven around 1 MHz. The width of this resonance is dependent on the value of the resistor, which varies with temperature and functions as a thermometer once calibrated. In this talk, we will present results from stationary measurements of this impedance and discuss the temperature accuracy of this thermometer, as well as a preliminary circuit design to measure this impedance during the HWP rotation.   

Quantum Tunneling and Complex Trajectories

In general, the semiclassical approximation of quantum mechanical tunneling fails to treat tunneling through barriers if real initial conditions and trajectories are used. By analytically continuing classical dynamics to the complex plane the problems encountered in the approximation can be resolved. While, the complex methods discussed here have been previously explored, no one has exhibited an analytically solvable case. The essential features of the complex method will be discussed in the context of a novel, analytically solvable problem. These methods could be useful in quantum gravity, with applications to the tunneling of spacetime geometries.   

The Atmospheric Muon Lifetime, with the Lead Absorption Potential for Muons and References to the Standard Model of Particle Physics

Muon is one of twelve fundamental particles and has the longest free-particle lifetime. It decays into three leptons through an exchange of weak vector bosons W$+$/W-. Muons are present in atmospheric secondary cosmic rays and reach the sea level. By detecting the time delay between arrival of muons and appearance of decay electrons in a scintillation detector, we will measure muon's lifetime at rest. From the lifetime we can find the ratio g$_{\mathrm{w}}$~/M$_{\mathrm{W}}$~of the weak coupling constant g$_{\mathrm{w}}$~(a weak analog of the electric charge) to mass of the W-boson M$_{\mathrm{W}}$. Vacuum expectation value v of the Higgs field, which determines masses Standard Model (SM) particles, can be calculated as v$=$2M$_{\mathrm{W}}$c$^{\mathrm{2}}$/g$_{\mathrm{w}}$~$=(\tau $m$_{\mathrm{\mu }}$c$^{\mathrm{2}}$/6$\pi ^{\mathrm{3}}$\^{h})$^{\mathrm{1/4}}$m$_{\mathrm{\mu }}$c$^{\mathrm{2}}$~regarding muon mass m$_{\mathrm{\mu }}$~and muon lifetime $\tau $ only. Using the experimental value for~M$_{\mathrm{W}}$c$^{\mathrm{2}}$~$=$ 80.4 GeV,~we will find weak coupling constant g$_{\mathrm{w}}$.~With the SM relation e$=$g$_{\mathrm{w}}$sin$\theta \surd $hc$\varepsilon_{\mathrm{0}}$~and experimental value of the Z$_{\mathrm{0}}$-photon weak mixing angle~$\theta =$29$^{\mathrm{o}}$~we use our muon lifetime to find the elementary electric charge e value. In this experiment we will also determine the sea level fluxes of low-energy (\textless 160 MeV) and high-energy cosmic muons, then will shield the detector with varying thicknesses of lead plates and from the new values of fluxes find the energy-dependent muon stopping power in lead.   

Atmospheric Muon Lifetime, Standard Model of Particles and the Lead Stopping Power for Muons

The muon is a fundamental particles of matter. It decays into three other leptons through an exchange of the weak vector bosons W$+$/W-. Muons are present in the atmosphere from cosmic ray showers. By detecting the time delay between arrival of the muon and an appearance of the decay electron in our detector, we'll measure muon's lifetime at rest. From the lifetime we should be able to find the ratio gw /MW of the weak coupling constant gw (a weak analog of the electric charge) to the mass of the W-boson MW. Vacuum expectation value v of the Higg's field, which determines the masses of all particles of the Standard Model (SM), could be then calculated from our muon experiment as v$=$2MWc2/gw $=(\tau $m$\mu $c2/6$\pi $3\^{h})1/4m$\mu $c2 in terms of muon mass m\textmu and muon lifetime $\tau $ only. Using known experimental value for MWc2 $=$ 80.4 GeV we'll find the weak coupling constant gw. Using the SM relation e$=$gwsin$\theta \surd $hc$\varepsilon $0 with the experimental value of the Z0-photon weak mixing angle $\theta =$29o we could find from our muon lifetime the value of the elementary electric charge e. We'll determine the sea-level fluxes of low-energy and high-energy cosmic muons, then we'll shield the detector with varying thicknesses of lead plates and find the energy-dependent muon stopping power in lead.   

Determining Linac Beam Energy from C-11/O-15 Activity Ratios in Polymers

A method for precisely measuring the beam energy of 20-25 MeV electron linear accelerator was developed. Polyoxymethylene (Delrin) and poly(methyl methacrylate) (acrylic) samples were irradiated with an electron linac at several energy settings of the accelerator simultaneously producing C-11 and O-15 via photonuclear reactions within each of the polymers. Using gamma-ray spectroscopy the activity ratios of C-11/O-15 were measured by analyzing the decay of activity vs. time. The C-11/O-15 ratio exhibits an energy dependence due to differences in the production cross section vs. energy. The observed dependence can be matched to predictions of the activity ratio vs. energy, developed from GEANT4 Monte Carlo models of an electromagnetic shower and knowledge of the cross sections, in order to determine the energy of the beam at a sub-MeV level of precision.