Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Electromagnetic shielding plays a significant role in the protection of electronic equipment. Its application is essential for mitigating radio-frequency interference for the Karoo Array Telescope (MeerKAT) project in the Karoo region of the Northern Cape. In this context, time-domain (TD) methodology for small enclosure shielding effectiveness (SE) is developed using a reverberated environment technique. Interest revolves around measurement time speed-up and an extended SE response which covers the under-moded condition of small enclosures. Recommended IEC standard 61000-4-21 [1] e ciency of 0.75, for log-periodic dipole array (LPDA) antenna, is also validated from a reverberation chamber (RC) characterisation of a printed circuit-board (PCB) LPDA e ciency. A built-in pulse generator and the Square Kilometre Array (SKA) receiver RATTY form the main elements of the TD metrology. For validation purpose, a reference coaxial airline is built. The cable is characterised with computational codes (CST and FEKO) and is also modelled with Vance and Kley's analytical expressions. The results are compared with TD transfer impedance (Zt) measurement within the RC. The study shows that the cable fixture within an RC shapes the cable under-test (CUT) Zt. The airline itself is also introducing an oscillating component within Zt. The resonance is proportional to the CUT length and it is visible within the measurement data and the simulations. It is not, however, taken into account by the theoretical models. The consequence of an incorrect antenna efficiency on RC applications is also addressed using a PCB LPDA antenna efficiency investigation. The unknown LPDA is simulated with CST for the study. The result is compared to an RC measurement validating the IEC 61000-4-21 standard efficiency recommendation of 0.75 [1]. This methodology characterised the unknown antenna parameter from a reference dipole antenna efficiency we investigated with FEKO. Simulated Wheeler-cap techniques permitted the reference antenna validation. We found that an inaccurate LPDA efficiency has little effect at higher frequency if the IEC efficiency is adopted. However, a difference of more than 7 dB can arise at low frequency if the real efficiency differs by more than 0.3 with respect to the IEC value. The study highlights the importance of a correct antenna efficiency for accurate RC applications. The nested-enclosure technique is regarded as the conventional method of investigating small enclosures SE [2]. The technique is in general time-consuming and works for a frequency range higher than three times the enclosure under test (EUT) lowest cut-o value. Our TD metrology covers a frequency band up to 1.4 GHz which coincides with our enclosure under-moded region. The SE characterisation is not well-documented within this particular region. The dissertation contributes to this field using a non-stirred nested-enclosure configuration. In contrast to the conventional use of the nested-enclosure methodology [2], the source is placed here within the EUT and the enclosure is treated as a normal radiator. The SE definition according to the IEEE standard in [2] is followed and the enclosure total transferred-power is computed from the port's reflection coeficient. The approach does not require a stirrer for the EUT. Our measurement shows an SE agreement between the modfied and the appropriate nested-enclosure technique from 390 MHz up to 4 GHz. The investigation is faster, but in addition the TD spectrum gives a more detailed SE response than the FD approach. / AFRIKAANSE OPSOMMING: Elektromagnetiese skerming speel n belangrike rol in die beskerming van elektroniese komponente. Die toepassing daarvan is noodsaaklik vir die versagting van radiofrekwensie steurings in die Karoo Array Telescope (MeerKAT) projek wat tans ontwikkel word in die Karoo omgewing van die Noord-Kaap. In hierdie konteks is daar op n tydsgebied metode vir klein-omhulsel beskermingse ektiwiteit (BE) gefokus, deur gebruik te maak van n weerkatingsomgewing tegniek. Die belangstelling handel om metingstye te verkort en n uitgebreide BE reaksie wat die lae-modus toestand van klein omhulsels dek. Aanbeveelde International Electrotechnical Commission (IEC) standaard 61000-4-21 [2] e ektiwiteit van 0.75, vir log-periodiese dipool-skikking (LPDA) antennas, is ook bekragtig deur n weerkaatsingskamer karakterisering van n gedrukte-stroombaanbord (PCB) LPDS antenna e ektiwiteit. n Ingeboude impulsgenerator en die Square kilometre Array (SKA) ontvanger, RATTY, vorm deel van die hoof elemente van die tydsgebiedmetings. Vir bekragtigings doeleindes is n koaksiale lugtransmissielyn gebou. Hierdie kabel is gekarakteriseer deur numeriese sagteware (CST en FEKO) en is ook gemoduleer met behulp van Vance en Kley se analitiese uitdrukkings. Die resultate is vergelyk met tydsgebied-oordragsimpedansie (Zt) metings, wat in die weerkaatsingskamer gedoen is. Die studie wys dat kabel posisie binne in die weerkaatsingskamer die Zt van die kabel-onder-toets vervorm. Die lugstreep voeg ook n ossillerende component by tot die gemete Zt. Die resonansie is eweredig aan die lengte van die kabel en is duidelik sigbaar binne die meting- en simulasiedata. Dit is egter nie in-berekening gebring in die analitiese modelle nie. Die gevolge van n verkeerde antenna e ektiwiteit in die weerkaatsingskamer toepassing is ook aangespreek deur ondersoek na die e ektiwiteit van n PCB LPDA. Die onbekende LPDA is gesimuleer met CST vir hierdie studie. Die resultate is vergelyk met n weerkaatsingskamer meting, wat die IEC 61000-4-21 standaard e ektiwiteit van 0.75 [1] bekragtig. Die metode karakteriseer die onbekende antenna veranderlike deur n verwysings dipool antenna e ektiwiteit wat ge-ondersoek is in FEKO. Gesimuleerde Wheeler-cap tegnieke het die veri kasie van die verwysings antenna resultate toegelaat. Daar is gevind dat n onakkurate LPDA e ektiwiteit n klein e ek op die ho er frekwensies het, as die IEC e ektiwiteit aangeneem is. Daar kan egter n verskil van 7dB voorkom by laer frekwensies, as die werklike e ektiwiteit met meer as 0.3 van die IEC waarde verskil. Hierdie studie lig die belangrikheid van n korrekte antenna e ektiwiteit uit vir akkurate weerkaatsingskamer toepassings. Die geneste-omhulsel tegniek word beskou as die konvensionele metode vir die bestudering van beskermingse ektiwiteit vir klein omhulsels. Die tegniek is gewoontlik tyd-rowend en werk net vir frekwensies wat drie maal ho er is as die af-sny waarde van die omhulselonder- toets. Ons tydgebiedmeting dek net n frekwensieband tot 1.4GHz, wat ooreenstem met ons omhulsel lae-modus gebied. Die beskermingse ektiwiteit karakterisering, in hierdie spesi eke veld, is nie goed gedokumenteer nie. Hierdie verhandeling dra by tot hierdie veld deur gebruik te maak van n onversteurde geneste-omhulsel kon gurasie. In teenstelling met die konvensionele gebruik van die geneste-omhulsel metode, is die bron geplaas binne die omhulsel-onder-toets en word dit gebruik as n gewone uitstraler. Die de nisie van beskermingse ektiwiteit volgens die IEEE standaard in [2], is gevolg en die totale oordragskrag van die omhulsel is bereken deur gebruik te maak van n poort se re eksie ko e si ent. Die benadering benodig nie n steurder vir die omhulsel-onder-toets nie. Ons metings se beskermingse ektiwiteit het ooreengestem met die veranderde - en die geskikte geneste-omhulsel tegniek, van 390MHz tot 4GHz in die spektrum. Hierdie ondersoek is vinniger en lewer n meer gedetailleerde beskermingse ektiwiteit reaksie as die frekwensiegebied benadering.

Doctor of Philosophy / Department of Physics / Brian R. Washburn / Optical frequency combs produced by mode-locked fiber lasers are useful tools for high precision frequency metrology and molecular spectroscopy in a robust and portable format. We have specifically investigated erbium doped fiber mode-locked lasers that use single-walled carbon nanotubes as a saturable absorber. We have, for the first time, developed and phase- stabilized a carbon nanotube fiber laser (CNFL) frequency comb. The carbon nanotube saturable absorber, which was fabricated using an optically driven deposition method, permits a high repetition frequency (>150 MHz) since an optical nonlinearity of fibers is not used for mode-locking. The CNFL comb combined with a parabolic pulse erbium doped fiber amplifier (EDFA) has shown a compact, robust, and cost-effective supercontinuum source. The amplified pulse from the parabolic pulse EDFA was compressed with a hollow-core photonic bandgap fiber, which produced a wave-breaking-free pulse with an all-fiber set-up. The stabilized comb has demonstrated a fractional instability of 1.2 ×10[superscript]-11 at 1 sec averaging time, the reference-limited instability. We have performed optical frequency metrology with the CNFL comb and have measured an optical frequency, P(13) which is a molecular overtone transition of C2H2. The measured frequency has shown a good agreement with the known value within an uncertainty of 10 kHz. In order to extend the application of the CNFL comb such as multi-heterodyne dual comb spectroscopy, we have investigated the noise of the CNFL comb and particularly, the broad carrier envelope offset frequency (f[subscript]0) linewidth of the CNFL comb. The primary noise source is shown to be white amplitude noise on the oscillator pump laser combined with the sensitivity of the mode-locked laser to pump power fluctuations. The control bandwidth of f[subscipt]0 was limited by the response dynamics of the CNFL comb. The significant reduction of comb noise has been observed by implementing a phase-lead compensation to extend control bandwidth of the comb and by reducing the pump relative intensity noise simultaneously. Therefore the f[subscipt]0 linewidth has been narrower from 850 kHz to 220 kHz. The integrated phase noise for the f[subscipt]0 lock is 1.6 radians from 100 Hz to 102 kHz.

Optical frequency combs have resulted in significant advances in optical frequency metrology and found wide application to precise physical measurements and molecular fingerprinting. A direct analogue of frequency combs in the phononic or acoustic domain has not been reported to date. This thesis describes a series of results to provide the first clear evidence for the generation of phononic frequency combs in the domain of micromechanical resonators. These results are supported by a theoretical framework which was originally developed to predict the existence of such features of combs in physical systems described by Fermi-Pasta-Ulam dynamics. The phononic frequency combs is mediated by nonlinear coupling between a primary driven mode and one or more parametrically excited internal modes. We provide experimental evidence for the formation of such phononic frequency combs in systems comprising of 2 or more coupled modes, with results qualitatively consistent with previous numerical studies based on Fermi-Pasta-Ulam dynamics. Additionally, externally pumped comb processes are also reported. Through systematic experiments at different drive frequencies and amplitudes, we portray the well-connected processes of phononic frequency comb formation and define attributes to control their concomitant features. Further, the interplay between these new nonlinear resonances and the well-established Duffing phenomenon is also discussed. While the experimental verification of the existence of phononic frequency combs is of scientific interest, several potential engineering applications exist including the unique capability to track resonant frequency of a micromechanical resonator without the requirement for an external feedback loop to sustain oscillations at the resonant frequency. The initial experimental results also demonstrate that good short-term frequency stability may be obtained for such micromechanical resonators operated under ambient conditions.

Due to the recent success, in terms of accuracy and precision, of a number of strontium optical lattice optical frequency standards, and the classification of the 5s² ¹S₀ to 5s5p ³P₀ transition in neutral strontium as a secondary definition of the SI unit of the second, many new strontium lattice clocks are under development. The strontium optical lattice clock (Sr OLC) at the National Physical Laboratory (NPL) is one such project. This thesis describes the design and build of the NPL Sr OLC, discussing the considerations behind the design. Details of the first cooling stage are given, which includes the characterisation of a novel permanent-magnet Zeeman slower by measurements of the longitudinal velocity distributions and loading of the MOT at 461 nm. Development of a narrow linewidth laser system at 689 nm is described, which is used for initial spectroscopy of the second-stage cooling transition. In particular, this work describes progress towards two independent ultra-narrow linewidth clock lasers. The new generation of strontium lattice clock experiments have focused on characterising the systematic frequency shifts and reducing their associated fractional frequency uncertainties, as well as reducing the fractional frequency instability of the measurement. One focus of the Sr OLC at NPL is to help characterise the frequency shift of the clock transition due to black-body radiation (BBR), which is currently the largest contributor to the uncertainty budget of the measured clock frequency. Our approach, discussed here, is to make a direct, differential measurement of the shift with the atoms housed alternately in environments of differing temperatures. Better characterisation and control of the BBR frequency shift of the strontium clock transition is crucial for the future of the Sr OLC as a leading frequency standard.

Esta dissertação propõe o projeto e a implementação de um sintetizador de sinal pertencente à banda X, com frequência de 9.192 GHz, para promover a transição atômica do átomo de césio durante o ciclo de operação do padrão atômico de frequência do CePOF/IFSC. Diferente do sintetizador em uso, este provê duas fontes de sinais, a fim de realizar a alimentação simétrica da cavidade de micro-ondas. A alimentação simétrica apresenta uma melhoria em relação à montagem experimental atual e visa atenuar os efeitos de gradiente de potência ao quais os átomos estão expostos enquanto cruzam a cavidade de interrogação. O sintetizador também apresenta um controle de fase em um dos sinais, para que seja possível um ajuste de fase entre eles, permitindo que ambos cheguem à cavidade de interrogação em fase. O método utilizado para a síntese dos sinais é o indireto, onde o sinal de interesse é obtido por meio de osciladores e componentes que possibilitam a manipulação algébrica das frequências, aliados aos circuitos de travamento para controle dos osciladores / This text considers the design and implementation of an X-band signal synthesizer, with a 9.192 GHz frequency, to promote the atomic transition of cesium during the operation process of the CePOF/IFSCs atomic frequency standard. Unlike the current synthesizer, the present one provides two sources of signal, in order to perform the symmetrical feed of the microwave cavity. The symmetrical feed is an improvement compared to the current experimental set up and aims at reducing the power gradient effects to which the atoms are exposed when travelling throughout the interrogation cavity. The synthesizer also has a phase control in one of the signals, in order to ensure that both signals will get into the interrogation cavity in phase. The synthesis method used is the indirect one; the desired signal is formed by means of oscillators and devices that allow the algebraic manipulation of frequencies, combined with lock circuits to control the oscillators

Tendo por objetivo principal a implementação de um laboratório de pesquisa em tempo e freqüência, tomamos como primeiro alvo a ser alcançado a realização da definição primária do segundo, conforme estabelecido pelo BIPM, baseado no átomo de 133CS. Seguindo os passos nessa linha de pesquisa, o laboratório construiu um primeiro padrão baseado em feixe efusivo e operado opticamente. Atualmente, os sistemas com maior capacidade de determinação do segundo são os padrões de átomos frios, denominados chafarizes, dado o seu esquema de funcionamento. O objetivo principal desse trabalho foi o desenvolvimento de um padrão de tempo e freqüência baseado em um sistema de átomos frios, passando por todas as fases de sua implementação. Tais fases dizem respeito à construção de sistemas de controle de lasers de diodo, síntese de freqüências, avaliação de sinais de tempo e freqüência e controle e aquisição dos sinais de interrogação atômica. Adicionada a isso a necessidade de estabelecer um ambiente próprio ao desenvolvimento de tal experimento. Os resultados observados até aqui permitem que sejam estabelecidas novas metas, em busca do refinamento desse padrão. Além disso, os tipos de sistemas abordados são passíveis de utilização no desenvolvimento de outros padrões, tanto primários como secundários, sendo requisitos fundamentais no estabelecimento de metrologia científica de tempo e freqüência. / Having as a main goal the implementation of a research laboratory in time and frequency, we set the first target to be reached the realization of the primary definition of the second, as stated by BIPM, based on the 133CS atom. Following the steps in this research line our laboratory constructed a first standard based on an effusive beam optically operated. Nowadays, the most capable systems in the determination of the second are the cold atoms standards, called fountains, due to their operation mode. The main subject of this thesis is the development of a time and frequency standard based in cold atoms doing all the steps to implement it. These steps concern to the construction of diode lasers control systems, frequency synthesis, time and frequency signal characterization and atomic interrogation signal acquisition, added the need to the establishment of an appropriate environment to develop such experiment. The observed results until now allowed the determination of the new goals in the search of the standard refinement. Moreover, the kind of systems described here can be used in the development of other standards, either primary or secondary, being fundamental requisites in the establishment of time and frequency scientific metrology.

Esta dissertação propõe o projeto e a implementação de um sintetizador de sinal pertencente à banda X, com frequência de 9.192 GHz, para promover a transição atômica do átomo de césio durante o ciclo de operação do padrão atômico de frequência do CePOF/IFSC. Diferente do sintetizador em uso, este provê duas fontes de sinais, a fim de realizar a alimentação simétrica da cavidade de micro-ondas. A alimentação simétrica apresenta uma melhoria em relação à montagem experimental atual e visa atenuar os efeitos de gradiente de potência ao quais os átomos estão expostos enquanto cruzam a cavidade de interrogação. O sintetizador também apresenta um controle de fase em um dos sinais, para que seja possível um ajuste de fase entre eles, permitindo que ambos cheguem à cavidade de interrogação em fase. O método utilizado para a síntese dos sinais é o indireto, onde o sinal de interesse é obtido por meio de osciladores e componentes que possibilitam a manipulação algébrica das frequências, aliados aos circuitos de travamento para controle dos osciladores / This text considers the design and implementation of an X-band signal synthesizer, with a 9.192 GHz frequency, to promote the atomic transition of cesium during the operation process of the CePOF/IFSCs atomic frequency standard. Unlike the current synthesizer, the present one provides two sources of signal, in order to perform the symmetrical feed of the microwave cavity. The symmetrical feed is an improvement compared to the current experimental set up and aims at reducing the power gradient effects to which the atoms are exposed when travelling throughout the interrogation cavity. The synthesizer also has a phase control in one of the signals, in order to ensure that both signals will get into the interrogation cavity in phase. The synthesis method used is the indirect one; the desired signal is formed by means of oscillators and devices that allow the algebraic manipulation of frequencies, combined with lock circuits to control the oscillators

Tendo por objetivo principal a implementação de um laboratório de pesquisa em tempo e freqüência, tomamos como primeiro alvo a ser alcançado a realização da definição primária do segundo, conforme estabelecido pelo BIPM, baseado no átomo de 133CS. Seguindo os passos nessa linha de pesquisa, o laboratório construiu um primeiro padrão baseado em feixe efusivo e operado opticamente. Atualmente, os sistemas com maior capacidade de determinação do segundo são os padrões de átomos frios, denominados chafarizes, dado o seu esquema de funcionamento. O objetivo principal desse trabalho foi o desenvolvimento de um padrão de tempo e freqüência baseado em um sistema de átomos frios, passando por todas as fases de sua implementação. Tais fases dizem respeito à construção de sistemas de controle de lasers de diodo, síntese de freqüências, avaliação de sinais de tempo e freqüência e controle e aquisição dos sinais de interrogação atômica. Adicionada a isso a necessidade de estabelecer um ambiente próprio ao desenvolvimento de tal experimento. Os resultados observados até aqui permitem que sejam estabelecidas novas metas, em busca do refinamento desse padrão. Além disso, os tipos de sistemas abordados são passíveis de utilização no desenvolvimento de outros padrões, tanto primários como secundários, sendo requisitos fundamentais no estabelecimento de metrologia científica de tempo e freqüência. / Having as a main goal the implementation of a research laboratory in time and frequency, we set the first target to be reached the realization of the primary definition of the second, as stated by BIPM, based on the 133CS atom. Following the steps in this research line our laboratory constructed a first standard based on an effusive beam optically operated. Nowadays, the most capable systems in the determination of the second are the cold atoms standards, called fountains, due to their operation mode. The main subject of this thesis is the development of a time and frequency standard based in cold atoms doing all the steps to implement it. These steps concern to the construction of diode lasers control systems, frequency synthesis, time and frequency signal characterization and atomic interrogation signal acquisition, added the need to the establishment of an appropriate environment to develop such experiment. The observed results until now allowed the determination of the new goals in the search of the standard refinement. Moreover, the kind of systems described here can be used in the development of other standards, either primary or secondary, being fundamental requisites in the establishment of time and frequency scientific metrology.

Les horloges à réseau optique montrent des performances impressionnantes et sont en train de soulever la question de la redéfinition de la seconde. Dans ces systèmes, un laser ultra-stable est utilisé en tant qu’oscillateur local pour sonder des transitions optiques très étroites d’atomes neutres piégés dans un réseau optique. La stabilité ultime de ces dispositifs, déterminée par le nombre d’atomes interrogés à chaque cycle et évaluée à quelques 10−17/sqrt(tau) (où tau est le temps d’intégration), n’est actuellement pas atteinte et est limitée à quelques 10−16/sqrt(tau) par les fluctuations de phase du laser sonde. Si l’amélioration des cavités ultra-stables sur lesquels sont stabilisés les lasers sonde est largement étudiée, le LNE-SYRTE a opté pour une approche plus récente, dans laquelle la référence de fréquence utilisée est un trou brûlé spectral creusé dans un cristal dopé terres rares refroidi à température cryogénique (environ 4 K). Une stabilité court terme de quelques 10−18 pourrait alors être atteinte. Cette thèse décrit la construction de l’expérience et montre ensuite les résultats d’une étude spectroscopique à haute résolution sur des trous brûlés spectraux étroits (FWHM = 3.3 kHz) creusés dans le cristal Eu3+ : Y2SiO5. L’influence du cryostat à cycle fermé sur la stabilité des trous brûlés spectraux est notamment mise en évidence et diminuée. Enfin, une méthode d’asservissement originale basée sur une détection hétérodyne d’un trou brûlé spectral et un asservissement numérique via un FPGA qui permet de verrouiller le laser sur le sommet du trou brûlé spectral étroit est décrit et montre une stabilité court terme de quelques 10−14, ce qui est un premier résultat encourageant pour la suite du projet. / Optical lattice clocks show impressive performances and are begining to raise the question of the redefinition of the SI second. In these systems, an ultra-stable laser is used as local oscillator to probe very narrow optical transitions of neutral atoms trapped in an optical lattice. The ultime stability of these systems, determined by the number of atoms interrogated at each clock cycle, evaluated at a few 10−17/sqrt(tau) (where tau is the integration time), is currently not reached and is limited to a few 10−16/sqrt(tau) by the phase fluctuations of the probe laser. If the enhancement of the ultra-stable cavities, on which are currently stabilized the probe lasers, is widely studied, LNE-SYRTE has adopted a more recent approach where the frequency reference is a spectral hole burned in rare earth doped crystal cooled down at cryogenic temperature (around 4 K). A short term stability of a few 10−18 could be achieved. This thesis describes the construction of the experiment and present the results of a high resolution spectroscopy of narrow spectral holes (FWHM = 3.3 kHz) burned in the crystal Eu3+ : Y2SiO5. The influence of the closed cycle cryostat on the behaviour of the spectral holes is hightlighted and reduced. Finally, an original locking scheme based on a heterodyne detection of a spectral hole and a numerical lock program using FPGA in order to stabilize the laser frequency on the top of the narrow spectral hole is described and shows a short term stability of a few 10−14, which is a first promising result for the future of the project.

Cette thèse a été effectuée dans le cadre d'un projet qui vise à explorer les facteurs limitants des performances d'une horloge à ions dans le domaine des fréquences micro-onde. Ce travail repose sur l'observation et la manipulation d'un grand nuage d'ions dans des potentiels de géométries différentes. Le but est l'analyse et le transport d'un grand nuage pouvant dépasser 10^6 ions dans un piège radio-fréquence linéaire à plusieurs zones. Notre groupe à construit un piège à trois zones destiné au piégeage d'ions calcium: deux parties quadrupolaires et une partie octupolaire montées en ligne. Les ions sont créés dans la première partie quadrupolaire et refroidis par laser le long de l'axe du piège. Nous avons d'abord étudié la création d'un grand nuage. La limite actuelle des paramètres du système permet de confiner et détecter des nuages de taille maximale 1,2.10^5 ions. Ensuite, grâce à un protocole de transport rapide et optimisé, ces ions sont transportés dans le deuxième et troisième piège avec une efficacité pouvant atteindre 100%. Les résultats en fonction de la durée de transport montrent une asymétrie entre les deux sens de transport que nous exploitons pour ajouter des ions dans le deuxième piège sans perte du nuage initialement présent. Cette technique d'accumulation a permis de piégér 2,5.10^5 ions dans le deuxième et troisième piège. Ce nombre semble limité par les refroidissement. Enfin, dans l'octupole, les observations montrent que, contrairement aux structures creuses attendues par les modèles, les ions froids s'organisent dans trois minima locaux de potentiels. La cause de cette différence est un petit défaut dans la symétrie octupolaire des barreaux. / This thesis is part of a project aiming to explore the performance limiting factors of a microwave ion clock. This work is based on the observation and manipulation of a large ion cloud in potentials with different geometries. The purpose is to analyze and transport a large cloud of more than 10^6 ions in a linear radio-frequency trap with several zones. Our group has build a three-zone trap for calcium ion trapping: two quadrupole parts and an octupole part mounted inline. Ions are created in the first quadrupole part and cooled by lasers along the trap symmetry axis. We study the creation of a large ion cloud. The current trapping and cooling parameters limit the maximum size of the cloud to 1,2.10^5 ions. with a rapid and optimized transport protocol, these ions are transfered in the second part of the trap and then in the octupole trap with an efficiency of up to 100%. The result as function of the transport duration shows an asymmetry between the two transport directions. We exploit this feature to add ions in the second or third trap without loss of the already trapped ions. This accumulation technique has allowed to trap 2,5.10^5 ions in the second and third trap. The cooling laser power seems to be the major limiting factor of this number. Finally the observation of the ions in the octupole shows that the cold ions are localised in three different potential wells. This is in contradiction with the hollow structure predicted by the analytical fluid model and molecular dynamics simulations. The cause of this difference is a tiny defect in the octupole symmetry of the RF-electrodes which leads to local minima in the multipole potential.