Trapped ion magnetic resonance: concepts and designs

A novel spectroscopy of trapped ions is proposed which will bring single-ion detection sensitivity to the observation of magnetic resonance spectra. The approaches developed here are aimed at resolving one of the fundamental problems of molecular spectroscopy, the apparent incompatibility in existing techniques between high information content (and therefore good species discrimination) and high sensitivity. Methods for studying both electron spin resonance (ESR) and nuclear magnetic resonance (NMR) are designed. They assume established methods for trapping ions in high magnetic field and observing the trapping frequencies with high resolution (<1 Hz) and sensitivity (single ion) by electrical means. The introduction of a magnetic bottle field gradient couples the spin and spatial motions together and leads to a small spin-dependent force on the ion, which has been exploited by Dehmelt to observe directly the perturbation of the ground-state electron's axial frequency by its spin magnetic moment.

A series of fundamental innovations is described m order to extend magnetic resonance to the higher masses of molecular ions (100 amu = 2x 10^5 electron masses) and smaller magnetic moments (nuclear moments = 10^(-3) of the electron moment). First, it is demonstrated how time-domain trapping frequency observations before and after magnetic resonance can be used to make cooling of the particle to its ground state unnecessary. Second, adiabatic cycling of the magnetic bottle off between detection periods is shown to be practical and to allow high-resolution magnetic resonance to be encoded pointwise as the presence or absence of trapping frequency shifts. Third, methods of inducing spindependent work on the ion orbits with magnetic field gradients and Larmor frequency irradiation are proposed which greatly amplify the attainable shifts in trapping frequency.

The dissertation explores the basic concepts behind ion trapping, adopting a variety of classical, semiclassical, numerical, and quantum mechanical approaches to derive spin-dependent effects, design experimental sequences, and corroborate results from one approach with those from another. The first proposal presented builds on Dehmelt's experiment by combining a "before and after" detection sequence with novel signal processing to reveal ESR spectra. A more powerful technique for ESR is then designed which uses axially synchronized spin transitions to perform spin-dependent work in the presence of a magnetic bottle, which also converts axial amplitude changes into cyclotron frequency shifts. A third use of the magnetic bottle is to selectively trap ions with small initial kinetic energy. A dechirping algorithm corrects for undesired frequency shifts associated with damping by the measurement process.

The most general approach presented is spin-locked internally resonant ion cyclotron excitation, a true continuous Stern-Gerlach effect. A magnetic field gradient modulated at both the Larmor and cyclotron frequencies is devised which leads to cyclotron acceleration proportional to the transverse magnetic moment of a coherent state of the particle and radiation field. A preferred method of using this to observe NMR as an axial frequency shift is described in detail. In the course of this derivation, a new quantum mechanical description of ion cyclotron resonance is presented which is easily combined with spin degrees of freedom to provide a full description of the proposals.

Practical, technical, and experimental issues surrounding the feasibility of the proposals are addressed throughout the dissertation. Numerical ion trajectory simulations and analytical models are used to predict the effectiveness of the new designs as well as their sensitivity and resolution. These checks on the methods proposed provide convincing evidence of their promise in extending the wealth of magnetic resonance information to the study of collisionless ions via single-ion spectroscopy.

Generating monoenergetic heavy-ion bunches with laser-induced electrostatic shocks

A method for efficient laser acceleration of heavy ions by electrostatic shock is investigated using particle-in-cell (PIC) simulation and analytical modeling. When a small number of heavy ions are mixed with light ions, the heavy ions can be accelerated to the same velocity as the light ions so that they gain much higher energy because of their large mass. Accordingly, a sandwich target design with a thin compound ion layer between two light-ion layers and a micro-structured target design are proposed for obtaining monoenergetic heavy-ion beams.

Experiments and modification on electron cyclotron resonance ion sources at the Institute of Modern Physics

Uranium ion beams were produced from electron cyclotron resonance (ECR) ion sources by sputtering method this year at the Institute of Modern Physics. At first, we chose the Lanzhou ECR No. 3 ion source to implement the production experiment of U ion beams. Finally, 11 e mu A of U28+, 5 e mu A of U32+, and 1.5 e mu A of U35+ were obtained. A U26+ ion beam produced by the LECR2 ion source was accelerated successfully by the cyclotron. This means that the Heavy Ion Research Facility in Lanzhou (HIRFL) has accomplished the acceleration of the ion beam of the heaviest element according to the designed parameters. The Lanzhou ECR ion source No. 2 (LECR2), which was built in 1997, has served the HIRFL for eight years and needed to be upgraded to provide more intense high charge state ion beams for HIRFL cooling storage ring. We started the upgrading project of LECR2 last year, and the modified design just has been finished. (c) 2006 American Institute of Physics.

Development of the lanzhou heavy ion linac

The heavy ion linac in Lanzhou is designed as a future injector for the Cooling Storage Ring (CSR). In order to keep the total machine within 40 meters, the IH (Interdigital H-type) structure is adopted for its higher acceleration gradient compared with the traditional DTL structure. The designed minimum charge over mass ratio is 1/6, the output energy is 16MeV/u and the beam current is 1A.mu A. The RFQ and the first DTL tank will work at 100MHz, and the other DTL tanks will work at the double frequency. The design criteria, main parameters and the detailed beam dynamic design are introduced in this paper.

Preliminary study of a niobium quarter-wave prototype cavity for a heavy-ion superconducting linac

Superconducting quarter-wave resonators, due to their compactness and their convenient shape for tuning and coupling, are very attractive for low-beta beam acceleration. In this paper, two types of cavities with different geometry have been numerically simulated: the first type with larger capacitive load in the beam line and the second type of lollipop-shape for 100 MHz, beta=0.06 beams; then the relative electromagnetic parameters and geometric sizes have been compared. It is found that the second type, whose structural design is optimized with the conical stem and shaping drift-tube, can support the better accelerating performance. At the end of the paper, some structural deformation effects on frequency shifts and appropriate solutions have been discussed.

Ultrahigh compression of water using intense heavy ion beams: laboratory planetary physics

Intense heavy ion beams offer a unique tool for generating samples of high energy density matter with extreme conditions of density and pressure that are believed to exist in the interiors of giant planets. An international accelerator facility named FAIR (Facility for Antiprotons and Ion Research) is being constructed at Darmstadt, which will be completed around the year 2015. It is expected that this accelerator facility will deliver a bunched uranium beam with an intensity of 5x10(11) ions per spill with a bunch length of 50-100 ns. An experiment named LAPLAS (Laboratory Planetary Sciences) has been proposed to achieve a low-entropy compression of a sample material like hydrogen or water (which are believed to be abundant in giant planets) that is imploded in a multi-layered target by the ion beam. Detailed numerical simulations have shown that using parameters of the heavy ion beam that will be available at FAIR, one can generate physical conditions that have been predicted to exist in the interior of giant planets. In the present paper, we report simulations of compression of water that show that one can generate a plasma phase as well as a superionic phase of water in the LAPLAS experiments.

Hybrid simulation of ion cyclotron resonance in the solar wind: evolution of velocity distribution functions

Li, Xing; Habbal, S.R., (2005) 'Hybrid simulation of ion cyclotron resonance in the solar wind: evolution of velocity distribution functions', Journal of Geophysical Research 110(A10) pp.A10109 RAE2008

Shock creation and particle acceleration driven by plasma expansion into a rarefied medium

The expansion of a dense plasma through a more rarefied ionized medium is a phenomenon of interest in various physics environments ranging from astrophysics to high energy density laser-matter laboratory experiments. Here this situation is modeled via a one-dimensional particle-in-cell simulation; a jump in the plasma density of a factor of 100 is introduced in the middle of an otherwise equally dense electron-proton plasma with an uniform proton and electron temperature of 10 eV and 1 keV, respectively. The diffusion of the dense plasma, through the rarefied one, triggers the onset of different nonlinear phenomena such as a strong ion-acoustic shock wave and a rarefaction wave. Secondary structures are detected, some of which are driven by a drift instability of the rarefaction wave. Efficient proton acceleration occurs ahead of the shock, bringing the maximum proton velocity up to 60 times the initial ion thermal speed. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3469762]

Modulational instability of dust acoustic waves in dusty plasmas: Modulation obliqueness, background ion nonthermality, and dust charging effects

The oblique modulational instability of dust acoustic (DA) waves in an unmagnetized warm dusty plasma with nonthermal ions, taking into account dust grain charge variation (charging), is investigated. A nonlinear Schrodinger-type equation governing the slow modulation of the wave amplitude is derived. The effects of dust temperature, dust charge variation, ion deviation from Maxwellian equilibrium (nonthermality) and constituent species' concentration on the modulational instability of DA waves are examined. It is found that these parameters modify significantly the oblique modulational instability domain in the k-theta plane. Explicit expressions for the instability rate and threshold have been obtained in terms of the dispersion laws of the system. The possibility and conditions for the existence of different types of localized excitations are also discussed. The findings of this investigation may be useful in understanding the stable electrostatic wave packet acceleration mechanisms close to the Moon, and also enhances our knowledge on the occurrence of instability associated to pickup ions around unmagnetized bodies, such as comets, Mars, and Venus.

Radiation pressure acceleration of thin foils with circularly polarized laser pulses

A new regime is described for radiation pressure acceleration of a thin foil by an intense laser beam of above 10(20) W cm(-2). Highly monoenergetic proton beams extending to giga-electron-volt energies can be produced with very high efficiency using circularly polarized light. The proton beams have a very small divergence angle (< 4 degrees). This new method allows the construction of ultra-compact proton and ion accelerators with ultra-short particle bursts.

Monoenergetic Ion Beam Generation by Driving Ion Solitary Waves with Circularly Polarized Laser Light

Experimental data from the Trident Laser facility is presented showing quasimonoenergetic carbon ions from nm-scaled foil targets with an energy spread of as low as 15% at 35 MeV. These results and high resolution kinetic simulations show laser acceleration of quasimonoenergetic ion beams by the generation of ion solitons with circularly polarized laser pulses (500 fs, ¼ 1054 nm). The conversion ef?ciency into monoenergetic ions is increased by an order of magnitude compared with previous experimental results, representing an important step towards applications such as ion fast ignition.

Laser-ion accelerators: State-of-the-art and scaling laws

A significant amount of experimental work has been devoted over the last decade to the development and optimization of proton acceleration based on the so-called Target Normal Sheath acceleration mechanism. Several studies have been dedicated to the determination of scaling laws for the maximum energy of the protons as a function of the parameters of the irradiating pulses, studies based on experimental results and on models of the acceleration process. We briefly summarize the state of the art in this area, and review some of the scaling studies presented in the literature. We also discuss some recent results, and projected scalings, related to a different acceleration mechanism for ions, based on the Radiation Pressure of an ultraintense laser pulse.

Instrumentation for diagnostics and control of laser-accelerated proton (ion) beams

Suitable instrumentation for laser-accelerated proton (ion) beams is critical for development of integrated, laser-driven ion accelerator systems. Instrumentation aimed at beam diagnostics and control must be applied to the driving laser pulse, the laser-plasma that forms at the target and the emergent proton (ion) bunch in a correlated way to develop these novel accelerators. This report is a brief overview of established diagnostic techniques and new developments based on material presented at the first workshop on 'Instrumentation for Diagnostics and Control of Laser-accelerated Proton (Ion) Beams' in Abingdon, UK. It includes radiochromic film (RCF), image plates (IP), micro-channel plates (MCP), Thomson spectrometers, prompt inline scintillators, time and space-resolved interferometry (TASRI) and nuclear activation schemes. Repetition-rated instrumentation requirements for target metrology are also addressed. (C) 2013 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

High-energy monoenergetic proton beams from two stage acceleration with a slow laser pulse

We present a new regime to generate high-energy quasimonoenergetic proton beams in a "slow-pulse" regime, where the laser group velocity vg<c is reduced by an extended near-critical density plasma. In this regime, for properly matched laser intensity and group velocity, ions initially accelerated by the light sail (LS) mode can be further trapped and reflected by the snowplough potential generated by the laser in the near-critical density plasma. These two acceleration stages are connected by the onset of Rayleigh-Taylor-like (RT) instability. The usual ion energy spectrum broadening by RT instability is controlled and high quality proton beams can be generated. It is shown by multidimensional particle-in-cell simulation that quasimonoenergetic proton beams with energy up to hundreds of MeV can be generated at laser intensities of 1021W/cm².