20 research outputs found
An observation of a transverse to longitudinal emittance exchange at the Fermilab A0 photoinjector:
No full textAn experimental program to perform a proof of principle of transverse to longitudinal emittance exchange has been developed at the Fermilab A0 Photoinjector. A new beamline, including two magnetic dogleg channels and a TM110 deflecting mode radio frequency cavity, were constructed for the emittance exchange experiment.
The first priority was a measurement of the Emittance Exchange beamline transport matrix. The method of difference orbits was used to measure the transport matrix. Through varying individual beam input vector elements, such as input x, x', y, y', z, or momentum and measuring the changes in all of the beam output vector's elements, output x, x', y, y', z, and momentum the full 6X6 transport matrix was measured. The measured emittance exchange transport matrix was in overall good agreement with our calculated transport matrix.
A direct observation of an emittance exchange was performed by measuring the electron beam's characteristics before and after the emittance exchange beamline. Operating with a 14.3 MeV, 250 pC electron bunch, longitudinal input emittance of 21.1+/-1.5 mm.mrad was observed to be exchanged with output horizontal emittance of 20.8+/-2.00 mm.mrad. Diagnostic limitations in the longitudinal output emittance measurement did not account for an energy-time correlation, thus potentially returning values larger than the actual longitudinal emittance. The horizontal input emittance of 4.67+/-0.22 mm.mrad was observed to be exchanged with the longitudinal output emittance of 7.06+/-0.43 mm.mrad. The apparent longitudinal output emittance growth is consistent with calculated values in which the correlation term is neglected.Ph.D.Includes bibliographical references (p. 160-164)by Timothy W. Koet
Undergraduate Education with the Rutgers 12-Inch Cyclotron
No full textAbstractThe Rutgers 12-Inch Cyclotron is a research grade accelerator dedicated to undergraduate education. From its inception, it has been intended for instruction and has been designed to demonstrate classic beam physics phenomena and provides students hands on experience with accelerator technology. The cyclotron is easily reconfigured, allowing experiments to be designed and performed within one academic semester. Our cyclotron offers students the opportunity to operate an accelerator and directly observe many fundamental beam physics concepts, including axial and radial betatron motion, destructive resonances, weak and azimuthally varying field (AVF) focusing schemes, RF and DEE voltage effects, diagnostic techniques, and perform low energy nuclear reactions. This paper emphasizes the unique beam physics measurements and beam manipulations capable at the Rutgers 12-Inch Cyclotron
SPACE CHARGE LIMITED DIELECTRIC BREAKDOWN, OR: HOW I LEARNED TO STOP WORRYING AND LOVE APPROXIMATIONS
No full textSpace charge induced dielectric breakdown in spacecraft components exposed to energetic cosmogenic radiation has remained poorly understood despite decades of research. In this work, breakdown in electron irradiated polymethyl methacrylate is described by a new 1D space charge limited front (SCLF) model that reconceives breakdown as a propagating front rather than a diffuse event. To quantify embedded charge distributions and validate model predictions of breakdown charge transport, charge distributions produced in bulk PMMA by electron irradiation were mapped using custom designed pulsed electroacoustic systems. These measurements both supported the SCLF model of breakdown charge transport and revealed unexpected positive charge accumulation at high electron deposition within PMMA. To capture the real time dynamics of the breakdown front, high speed direct and streak imaging were employed, and a sharply localized front was observed whose velocity increased with embedded charge density, in agreement with SCLF predictions. To characterize the difficult to probe environment through which the breakdown current is transported, varied resistance loading was used to measure the time dependence of breakdown source impedance. These measurements demonstrated a transition from a capacitive, high impedance regime during front propagation to a resistive, low impedance state after breakdown, thereby highlighting the differing current transport environments at and behind the breakdown front. Limitations of the 1D SCLF arising from multi sign charge configurations, three dimensional effects, and transient breakdown pathways were identified, and the necessity for multidimensional numerical simulations to extend and refine the SCLF framework for spacecraft relevant geometries was outlined. Together, these results establish a unified experimental and theoretical foundation for understanding space charge induced breakdown in PMMA and outline a clear path for future quantitative empirical validation and model development
Cryogenic Design and Thermal Analysis of the CURIE CryoTrap
No full textThe decay rates of electron capture (EC) radioisotopes, such as 7Be, are demonstrativelysusceptible to alteration with change to the electron orbital structure [1] [2] [3] [4]. The Cryogenic
Ultra-high vacuum Radioactive Isotope Experiment (CURIE) Project aims to isolate the various
charge states of the low-Z radioisotope 7Be stably to perform novel half-life measurements. To
achieve this, the system must be cooled to 4K to reach extreme high vacuum (XHV) conditions
in excess of 10E−15 mbar and to ensure single ion resolution detection. The cryogenic design
which achieves this is presented here. The design consists of the actively cooled 45K radiation
shield, and the 4K stage which houses the Penning trap. The 4K stage is brought to XHV
and maintained at these pressures through the design of a rotary “cryovalve”. This thesis details
the entire apparatus, the heat loads incident on both stages through simulation, and outlines an
experimental method for testing the “cryovalve”
Insulating Materials for an Extreme Environment in a Supersonically Rotating Fusion Plasma
No full textFusion energy has long been sought as the “holy grail” of energy sources. One of the most critical remaining challenges in fusion is that of plasma-facing materials, even denoted by the National Academies of Science. The materials challenge is particularly acute for centrifugal mirrors, an alternative concept to the industry-standard tokamak that may offer a more efficient scheme with a faster path to development.
The centrifugal mirror incorporates supersonic rotation into a conventional magnetic mirror scheme, providing three primary benefits: (1) increased confinement, (2) suppression of instabilities, and (3) plasma heating through shear flow. However, this rotation, which is driven by an axial magnetic field and a radial electric field, requires the magnetic field lines to terminate on electrically insulating surfaces to avoid “shorting” the plasma. This unique requirement presents a novel materials challenge: the insulator must not only resist irradiation and thermal damage, but also be an excellent electrical insulator and thermal conductor that can be actively cooled.
To address this materials challenge, the Centrifugal Mirror Fusion Experiment (CMFX) was developed at the University of Maryland. CMFX serves as a test bed for electrically insulating materials in a fusion environment, as well as a proof-of-concept for the centrifugal mirror scheme. To guide the design of future power plants and better understand the neutronand ion flux on the insulators, a zero-dimensional (0-D) scoping tool, called MCTrans++, was developed. This software, discussed in Chapter 2, demonstrates the ability to rapidly model experimental parameter sets in CMFX and predict the scaling to larger devices, informing material selection and design. Assuming the engineering challenges have been met, the centrifugal mirror has been demonstrated as a promising scheme for electricity production via fusion energy.
One of the key aspects to the operation of CMFX is the high voltage system. This system, discussed in Chapter 3, was developed in incremental stages, beginning with a 20 kV, then 50 kV pulsed power configuration, and finally culminating in a 100 kV direct current power supply to drive rotation at much higher voltages, creating an extreme environment for materials testing.
This work identified hexagonal boron nitride (hBN) as a promising insulator material. Computational modeling (Chapter 4) demonstrated hBN’s superior resistance to ion-irradiation damage compared to other plasma-facing materials.
Additionally, fusion neutrons are crucial for assessing both material damage and power output. Chapter 5 details the neutronics for CMFX, including 3He proportional counters, which have been installed on CMFX to measure neutron production. In parallel, Monte Carlo computational methods were used to predict neutron transport and material damage in the experiment.
Ultimately, a materials test stand was installed on CMFX to expose electrically insulating materials to high energy fusion plasmas (Chapter 6). Comparative analysis of hBN and silicon carbide after exposure revealed superior performance of hBN as a plasma-facing material. Two primary erosion mechanisms were identified by surface morphology and roughness measurements: grain ejection and sputtering, both more pronounced in silicon carbide.
This work advances our understanding of insulating material behavior in fusion environments and paves the way for the development of the next-generation centrifugal mirror fusion reactors. Chapter 7 discusses conclusions and proposes future work. In particular this section suggests some changes that may allow CMFX to operate at much higher voltages, unlocking higher plasma density and temperature regimes for further material testing
Novel Emittance Measurement Through Experimental Study of Envelope Mode Resonance in a High-Intensity Particle Beam
No full textOn-line monitoring of beam quality for high-intensity particle beams requires non-invasive transverse phase space diagnostics. Such diagnostics are in high demand for use in heavy ion accelerators and free-electron lasers (FELs). A technique to measure emittance using multi-turn resonant excitation of the quadrupole envelope mode has been demonstrated at the University of Maryland Electron Ring (UMER).
The rms Kapchinsky-Vladimirsky (KV) equations predict the time-evolution of particle beam envelopes. Linear perturbations to the matched envelope solution of these equations excite normal modes at space-charge-dependent natural frequencies. This experiment employs periodic, impulsed perturbations to drive resonant excitations of these modes. Steady state resonance structure in the form of a lattice is predicted using analytic solutions of a delta-kicked simple harmonic oscillator (SHO). Numerical simulations of this SHO along with simulations from the WARP envelope solver and particle-in-cell (PIC) codes are documented.
This dissertation presents the first proof-of-principle experimental resonant excitation of the quadrupole envelope mode in a high-intensity particle beam. To excite the mode experimentally, an rf-driven electric quadrupole is constructed and installed in UMER. The quadrupole fields are driven by a tunable resonant tank circuit designed and built for this experiment. After resonant excitation, the knockout imaging method is used to collect 3 ns synchronized transverse time slice images of the beam. Image moments are analyzed and show good agreement with simulation. Emittance can then be inferred from the measured natural frequencies of the envelope modes utilizing a conversion obtained through simulation. A direct emittance measurement is performed using a conventional pinhole scan at injection as an experimental validation of the envelope resonance method
Demonstration of the First 4H-SiC EUV Detector with Large Detection Area
No full textUltraviolet (UV) and Extreme Ultraviolet (EUV) detectors are very attractive in astronomy, photolithography and biochemical applications. For EUV applications, most of the semiconductor detectors based on PN or PIN structures suffer from the very short penetration depth. Most of the carries are absorbed at the surface and recombined there due to the high surface recombination before reach the depletion region, resulting very low quantum efficiency. On the other hand, for Schottky structures, the active region starts from the surface and carriers generated from the surface can be efficiently collected. 4H-Sic has a bandgap of 3.26eV and is immune to visible light background noise. Also, 4H-Sic detectors usually have very good radiation hardness and very low noise, which is very important for space applications where the signal is very weak. The E W photodiodes presented in this paper are based on Schottky structures. Platinum (Pt) and Nickel (Ni) are selected as the Schottky contact metals, which have the highest electron work functions (5.65eV and 5.15eV, respectively) among all the known metals on 4H-Sic
CHARACTERIZATION OF RADIATION DAMAGE TO A NOVEL PHOTONIC CRYSTAL SENSOR
No full textNew methods of nuclear fuel and cladding characterization must be developed and implemented to enhance the safety and reliability of nuclear power plants. One class of such advanced methods is aimed at the characterization of fuel performance by performing minimally intrusive in-core, real time measurements on nuclear fuel on the nanometer scale.
Nuclear power plants depend on instrumentation and control systems for monitoring, control and protection. Traditionally, methods for fuel characterization under irradiation are performed using a “cook and look” method. These methods are very expensive and labor-intensive since they require removal, inspection and return of irradiated samples for each measurement. Such fuel cladding inspection methods investigate oxide layer thickness, wear, dimensional changes, ovality, nuclear fuel growth and nuclear fuel defect identification. These methods are also not suitable for all commercial nuclear power applications as they are not always available to the operator when needed. Additionally, such techniques often provide limited data and may exacerbate the phenomena being investigated.
This thesis investigates a novel, nanostructured sensor based on a photonic crystal design that is implemented in a nuclear reactor environment. The aim of this work is to produce an in-situ radiation-tolerant sensor capable of measuring the deformation of a nuclear material during nuclear reactor operations.
The sensor was fabricated on the surface of nuclear reactor materials (specifically, steel and zirconium based alloys). Charged-particle and mixed-field irradiations were both performed on a newly-developed “pelletron” beamline at Idaho State University's Research and Innovation in Science and Engineering (RISE) complex and at the University of Maryland's 250 kW Training Reactor (MUTR). The sensors were irradiated to 6 different fluences (ranging from 1 to 100 dpa), followed by intensive characterization using focused ion beam (FIB), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to investigate the physical deformation and microstructural changes between different fluence levels, to provide high-resolution information regarding the material performance. Computer modeling (SRIM/TRIM) was employed to simulate damage to the sensor as well as to provide significant information concerning the penetration depth of the ions into the material
Search for dark matter particles in W+ W− events with transverse momentum imbalance in proton-proton collisions at √s = 13 TeV
No full textA search for dark matter particles is performed using events with a pair of W bosons and large missing transverse momentum. Candidate events are selected by requiring one or two leptons (l = electrons or muons). The analysis is based on proton-proton collision data collected at a center-of-mass energy of 13 TeV by the CMS experiment at the LHC and corresponding to an integrated luminosity of 138 fb−1. No significant excess over the expected standard model background is observed in the lνqq and 2l2ν final states of the W+W− boson pair. Limits are set on dark matter production in the context of a simplified dark Higgs model, with a dark Higgs boson mass above the W+W− mass threshold. The dark matter phase space is probed in the mass range 100–300 GeV, extending the scope of previous searches. Current exclusion limits are improved in the range of dark Higgs masses from 160 to 250 GeV, for a dark matter mass of 200 GeV. © The Author(s) 2024
Observation of electroweak W+W− pair production in association with two jets in proton-proton collisions at √s = 13 TeV
No full textCopyright © 2022 The Author(s). An observation is reported of the electroweak production of a W+W− pair in association with two jets,
with both W bosons decaying leptonically. The data sample corresponds to an integrated luminosity of 138 fb−1 of proton-proton collisions at √s = 13 TeV, collected by the CMS detector at the CERN LHC.Events are selected by requiring exactly two opposite-sign leptons (electrons or muons) and two jets with large pseudorapidity separation and high dijet invariant mass. Events are categorized based on the flavor of the final-state leptons. A signal is observed with a significance of 5.6 standard deviations (5.2 expected) with respect to the background-only hypothesis. The measured fiducial cross section is 10.2 ± 2.0 fb and this value is consistent with the standard model prediction of 9.1 ± 0.6 fb.SCOAP3
