PREPARATION AND CHARACTERIZATION OF CNTS Structures and Synthesis of Carbon Nanotubes Preparation of Carbon Nanotube (CNT) Emitters FIELD EMISSION FROM CNTS Field Emission Theory Field Emission Properties of CNTs Field Emission Microscopy (FEM) of Multiwall Carbon Nanotubes In-situ TEM (Transmission Electron Microscopy) of CNT Emitters Field Emission from Single-Wall Carbon Nanotubes Field Emission from Patterned Arrays Surface Treatments of CNT Emitters FIELD EMISSION FROM OTHER NANOMATERIALS Graphite Nanoflakes and Diamond Carbon Nanowalls Si Nanowire and ZnO Nanowire APPLICATIONS OF CNT EMITTERS Field Emission Display Electron Sources in Electron Microscopes Field Emission X-Ray Sources Microwave Amplifier Parallel Electron-Beam Lithography

Carbon nanotube and related field emitters : fundamentals and applications

Electronic devices are exposed to high dose radiation in the Hi-Lumi LHC [1] and space environment. Radiation exposure to these devices affects their performance and the reliability so they must be tested. In the scope of METU-DBL (Defocusing Beam Line) project, a beamline has been constructed at Turkish Atomic Energy Authority (TAEA)’s proton accelerator facility’s (PAF) R&D room. The schematic design of the proton accelerator facility is given in Fig. 1, where a central cyclotron provides proton beams to two simultaneous irradiation rooms. METU-DBL’s goal is to study single event effects (SEEs), are caused by single, energetic particles, namely protons. In the space environment, protons which are trapped in radiation belts around the Earth, or solar flares, can cause both direct ionization and indirect ionization SEEs in sensitive electronic devices [2].

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Metu-Defocusing Beamline : A 15-30 Mev Proton Irradiation Facility and Beam Measurement System

Next generation linear colliders such as the Compact Linear Collider (CLIC) or the International Linear Collider (ILC) will accelerate particle beams with extremely small emittance. The high current and small size of the beam (micron-scale) due to such a small emittance require non-invasive, high-resolution techniques for beam diagnostics. Diffraction Radiation (DR), a polarization radiation that appears when a charged particle moves in the vicinity of a medium, is a promising candidate as it is non-invasive. Despite these advantages DR is used less than other techniques mainly due to a challenging target fabrication (micrometer scale slits production) and data extraction. The aim of this thesis is devoted to study the feasibility of an instrument based on DR and the limitation of this technique applied to high energy linear accelerators. Since DR is sensitive to beam parameters other than the transverse profile (e.g. its divergence and position), preparatory simulations have been performed with realistic beam parameters. A new dedicated instrument has been designed, installed and commissioned in the KEK Accelerator Test Facility (ATF2) beam line. At present DR has been observed in the visible wavelength range and in the ultraviolet (down to 250 nm) to optimize sensitivity to small beam sizes. Presented here are the latest results of these DR beam size measurements and simulations showing that this technique allows beams as small as a few microns to be measured.

Development of a combined transition and diffraction radiation station for non-invasive beam size monitoring on linear accelerators

Characterizing the phase space distribution of particle beams in accelerators is a central part of understanding beam dynamics and improving accelerator performance. However, conventional analysis methods either use simplifying assumptions or require specialized diagnostics to infer high-dimensional (>2D) beam properties. In this Letter, we introduce a general-purpose algorithm that combines neural networks with differentiable particle tracking to efficiently reconstruct high-dimensional phase space distributions without using specialized beam diagnostics or beam manipulations. We demonstrate that our algorithm accurately reconstructs detailed 4D phase space distributions with corresponding confidence intervals in both simulation and experiment using a limited number of measurements from a single focusing quadrupole and diagnostic screen. This technique allows for the measurement of multiple correlated phase spaces simultaneously, which will enable simplified 6D phase space distribution reconstructions in the future.

Phase Space Reconstruction from Accelerator Beam Measurements Using Neural Networks and Differentiable Simulations.

Towards ultra-high gradient particle acceleration in carbon nanotubes

Transverse emittance measurements based on the quadrupole scan technique have been widely used to characterize the beam phase space parameters in linear accelerators. This paper discusses the implementation of the technique at the Advanced Superconducting Test Accelerator (ASTA) at Fermilab. We plan on deploying a flexible implementation that permits an operator to select a quadrupole with associated analyzing screen to measure the beam emittance. Our implementation utilizes Python scripts combined with Fermilab’s control system ACNet and ELEGANT tracking code. We also discuss the applicability of the quadrupole scan method at 20.3 MeV at an operating charge of 250 pC at ASTA. Some preliminary measurements will also be presented. INTRODUCTION The Advanced Superconducting Test Accelerator (ASTA) has been constructed and commissioned in Fermilab and it is currently scheduled to build a high energy beamline (150 – 300 MeV) by adding a cryomodule with construction plan of the Integrable Optics Test Accelerator (IOTA) ring by 2016. Most recently, 20 MeV of electron beam energy was successfully demonstrated in the ASTA injector beamline and it is planned to increase the beam energy up to 50 MeV with the schedule to add a capture cavity downstream of the photoinjector. Along with the timeline of the construction/commissioning schedules, it is necessary to assure a beam monitoring technique for a full scale transverse and longitudinal phase-space characterization of a commissioned beam, which enables to precisely operate the machine. Instantaneous monitoring of beam parameters is highly required for preserving the beam emittance along the beamline. We have been working on the idea of developing a real-time emittance monitoring system based on a quadruple-scan technique [1,2]. Our plan is to design a Python script programmed with a quad-scan algorithm and to implement it in the ASTA beamline control system (ACNet console). We expect that successful development of a designed system will allow a beamline operator to trace temporal profiles of transverse beam parameters and also to systematically control the dynamics using quadrupoles installed in the ASTA beamline. BEAM DYNAMICS Emittance is an important property of charged particle beams, allowing for a description of beam quality and the comparison of beams. Generally, emittance can be described in six-dimensional phase space as the spread of density of particles in the beam. In many cases, the transverse emittance is of particular interest and the six-dimensional phase space is split into subspaces comprised of and [1]. The area occupied by the particles of interest may be considered as being bound by an ellipse and can mathematically be described by the following beam matrix:

Implementation of Quadrupole-scan Emittance Measurement at Fermilab's Advanced Superconducting Test Accelerator (ASTA)

We have been constructing an S-band RF-injector system for field-emission tests of a CNT-tip cathode. A pulsed S-band klystron is installed and fully commissioned with 5.5 MW peak power in a 2.5 microsecond pulse length and 1 Hz repetition rate. A single-cell RF-gun is designed to produce 0.5 – 1 pC electron bunches in a photo-emission mode with duration 3 ps at 0.5 – 1 MeV. The measured RF system jitters are within 1% in magnitude and 0.2 degree in phase, which would induce 3.4 keV and 0.25 keV of energy jitters, corresponding to 80 fs and 5 fs of temporal jitters, respectively. Our PIC simulations indicate that the designed bunch compressor reduces the time-of-arrival (TOA) jitter by about an order of magnitude. Emission current and beam brightness of the field-emitted beam are improved by implanting CNT tips on the cathode surface, since they reduce the emission area, while providing high current emission. Once the system is commissioned in field-emission mode, the CNT-tip cathode will be tested in terms of klystron-power levels to map out its currentvoltage (I-V) characteristics in pulse emission mode.

http://inspirehep.net/record/1636485/files/wepoa40.pdf

Construction Status of a RF-Injector with a CNT-Tip Cathode for High Brightness Field-Emission Tests

This paper describes simulation analyses on beam and laser (X-ray)-driven accelerations in effective nanotube models obtained from Vsim and EPOCH codes. Experimental setups to detect wakefields are also outlined with accelerator facilities at Fermilab and NIU. In the FAST facility, the electron beamline was successfully commissioned at 50 MeV and it is being upgraded toward higher energies for electron accelerator R&D. The 50 MeV injector beamline of the facility is used for X-ray crystal-channeling radiation with a diamond target. It has been proposed to utilize the same diamond crystal for a channeling acceleration POC test. Another POC experiment is also designed for the NIU accelerator lab with time-resolved electron diffraction. Recently, a stable generation of single-cycle laser pulses with tens of Petawatt power based on thin film compression (TFC) technique has been investigated for target normal sheath acceleration (TNSA) and radiation pressure acceleration (RPA). The experimental plan with a nanometer foil is discussed with an available test facility such as Extreme Light Infrastructure - Nuclear Physics (ELI-NP).

Ultra-High Gradient Channeling Acceleration in Nanostructures: Design/Progress of Proof-of-Concept (POC) Experiments

Electron beams emitted from a cold cathode are thermally stable and mono-energetic with a small phasespace volume. We have been developing a field-emission type RF-gun system for high brightness electron source applications, including electron scattering/diffraction and tunable coherent X-ray/THz generation. The system consists of a single-gap gun-cavity and an S-band klystron/modulator capable of powering the gun with up to 5.5 MW peak (PRR = 1 Hz, duration = 2.5 s). The designed gun built with the symmetrised side-couplers has surface field on the cathode ranging 50 – 100 MV/m with 1.3 – 1.7 MW klystron-power and 1.2 field ratio (HFSS). ASTRA simulations also indicate that the gun produces the beam with transverse emittances of less than 1 mm-mrad with 10 – 20 pC bunch charge at 500 keV beam energy. Under the gun operating condition, particle tracking/PIC simulations (CST) show that a single-tip CNT field-emitter produces short pulsed bunches (~ 1/10 RF-cycle) with small emittance ( 0.01 mm-mrad) and high peak current density ( 10,000 kA/cm). After the gun is fully installed and commissioned, a CNT-tip cathode will be tested with RF-field emission.

Development of a Field-Emission Type S-band RF-Gun System for High Brightness Electron Source Applications

A short bunch of relativistic particles, or a short-pulse laser, perturb the density state of conduction electrons in a solid crystal and excite wakefields along atomic lattices in a crystal. Under a coupling condition between a driver and plasma, the wakes, if excited, can accelerate channeling particles with TeV/m acceleration gradients [1], in principle, since the density of charge carriers (conduction electrons) in solids n0 = ~ 1020 – 1023 cm−3 is significantly higher than what was considered above in gaseous plasma. Nanostructures have some advantages over crystals for channeling applications of high power beams. The de-channeling rate can be reduced and the beam acceptance increased by the large size of the channels. For beam-driven acceleration, a bunch length with a sufficient charge density would need to be in the range of the plasma wavelength to properly excite plasma wakefields, and channeled particle acceleration with the wakefields must occur before the ions in the lattices move beyond the ...

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Andrew Green

Papers

Implementation of Quadrupole-scan Emittance Measurement at Fermilab's Advanced Superconducting Test Accelerator (ASTA)

Construction Status of a RF-Injector with a CNT-Tip Cathode for High Brightness Field-Emission Tests

Ultra-High Gradient Channeling Acceleration in Nanostructures: Design/Progress of Proof-of-Concept (POC) Experiments

Development of a Field-Emission Type S-band RF-Gun System for High Brightness Electron Source Applications

Ultra-High Gradient Channeling Acceleration in Nanostructures: Design/Progress of Proof-of-Concept (POC) Experiments