Elements of Ion Linear Accelerators, Calm in The Resonances, Other_Tales

The main part of this book, Elements of Linear Accelerators, outlines in Part 1 a framework for non-relativistic linear accelerator focusing and accelerating channel design, simulation, optimization and analysis where space charge is an important factor. Part 1 is the most important part of the book; grasping the framework is essential to fully understand and appreciate the elements within it, and the myriad application details of the following Parts. The treatment concentrates on all linacs, large or small, intended for high-intensity, very low beam loss, factory-type application. The Radio-Frequency-Quadrupole (RFQ) is especially developed as a representative and the most complicated linac form (from dc to bunched and accelerated beam), extending to practical design of long, high energy linacs, including space charge resonances and beam halo formation, and some challenges for future work. Also a practical method is presented for designing Alternating-Phase- Focused (APF) linacs with long sequences and high energy gain. Full open-source software is available. The following part, Calm in the Resonances and Other Tales, contains eyewitness accounts of nearly 60 years of participation in accelerator technology. (September 2023) The LINACS codes are released at no cost and, as always,with fully open-source coding. (p.2 & Ch 19.10)Comment: 652 pages. Some hundreds of figures - all images, there is no data in the figures. (September 2023) The LINACS codes are released at no cost and, as always,with fully open-source coding. (p.2 & Ch 19.10

IFMIF, the European–Japanese efforts under the Broader Approach agreement towards a Li(d,xn) neutron source: Current status and future options

The necessity of a neutron source for fusion materials research was identified already in the 70s. Though neutrons induced degradation present similarities on a mechanistic approach, thresholds energies for crucial transmutations are typically above fission neutrons spectrum. The generation of He via 56Fe (n,α) 53Cr in future fusion reactors with around 12 appm/dpa will lead to swelling and structural materials embrittlement. Existing neutron sources, namely fission reactors or spallation sources lead to different degradation, attempts for extrapolation are unsuccessful given the absence of experimental observations in the operational ranges of a fusion reactor. Neutrons with a broad peak at 14 MeV can be generated with Li(d,xn) reactions; the technological efforts that started with FMIT in the early 80s have finally matured with the success of IFMIF/EVEDA under the Broader Approach Agreement. The status today of five technological challenges, perceived in the past as most critical, are addressed. These are: 1. the feasibility of IFMIF accelerators, 2. the long term stability of lithium flow at IFMIF nominal conditions, 3. the potential instabilities in the lithium screen induced by the 2 × 5 MW impacting deuteron beam, 4. the uniformity of temperature in the specimens during irradiation, and 5. the validity of data provided with small specimens. Other ideas for fusion material testing have been considered, but they possibly are either not technologically feasible if fixed targets are considered or would require the results of a Li(d,xn) facility to be reliably designed. In addition, today we know beyond reasonable doubt that the cost of IFMIF, consistently estimated throughout decades, is marginal compared with the cost of a fusion reactor. The less ambitious DEMO reactor performance being considered correlates with a lower need of fusion neutrons flux; thus IFMIF with its two accelerators is possibly not needed since with only one accelerator as the European DONES or the Japanese A-FNS propose, the present needs > 10 dpa/fpy would be fulfilled. World fusion roadmaps stipulate a fusion relevant neutron source by the middle of next decade, the success of IFMIF/EVEDA phase is materializing this four decades old dream

Design and analysis of a RFQ resonant cavity for the IFMIF project

The IFMIF RFQ is designed with very challenging specifications to accelerate a 125mA deuterons beam from 0.1 MeV to 5 MeV at a frequency of 175 MHz, consists of 18 modules with length of ~550 mm each. The total lenght is 9.78 m. During the three years of PhD the candidate was involved on different aspects, from the mechanical design to the quality control on the production process. Chapter 1 presents a general overview of the IFMIF project and the scientific context. On chapter 2 the design of the cooling system of the modules of the accelerator will be described, with the development of thermal-structural and fluid-thermal-structural numerical analyses. Chapters 3 and 4 will describe the development of an in-house technology for the vertical brazing and the fixation tooling, by means a strict collaboration of the section of Padova of INFN and the LNL. The developments of 1D and 3D FE analyses for the prediction of the thermal brazing cycle will be described. Moreover, the improvements on the control (visual and ultrasonic inspection) of the brazed joints and the feedbacks to the mechanical design will be presented. Chapter 5 will describe the various phases of the production of the modules of the RFQ with the most important mechanical design aspects. The production of the IFMIF EVEDA RFQ accelerator is a quite challenging task due to the narrow tolerance of the pieces that should be guarantee also after some thermal treatments for the brazing. The focus will be in particular to the quality control of the single elements and the entire modules during the production: -The dimensional quality control, prevalently by CMM with active scanning probe. -The quality assurance of the brazed joints by visual and the ultrasonic inspection. Their influence for the design choices and the solution of eventual problem will be described

Development and Manufacturing of the IFMIF/EVEDA RFQ Modules

The IFMIF (International Fusion Material Irradiation Facility) project aim is to build a facility for the mechanical characterization of material that will constitute the wall of the nuclear reactor for DEMO (DEMOnstration power plant). The complexity of this facility, containing numerous components with peculiar specifications, requires the development of a preliminary stage for the engineeristic evaluation that will led to outline the framework of the activities, the so called EVEDA (Engineering Validation Engineering Design Activities) phase, including the LIPAc prototype construction that involve many research institutes around the world each one has in charge the realization of a line components. The description of the IFMIF project and also each contribution of the participating research institutes are briefly reported on chapter 1. Such facility require the realization of a RFQ four-vane particle accelerator, composed of 18 modules, whose part of mechanical design and construction has been entrusted respectively to mechanical design office and workshop of the I.N.F.N. Padova Unit (Istituto Nazionale di Fisica Nucleare). Since the mechanical design of the accelerator ha almost completed, we faced on the production covering over all metrological quality control phases. Metrologic control and qualification stages are strictly related to the cavity behaviour therefore we focus our attention to its working principle. Thus, in the second chapter it has been summarised the basics to understand the basic working principles of such machines, the main parameter affecting their performances and finally the main geometrical parameter of the accelerator concerned. The most critical issues arise from the production concerning the brazing process which does not permit adjustment except with re-brazing causing a strong deterioration of the mechanical properties of the copper components. It should be mentioned that brazing turned out to be an uncertainty source for the quality of the pieces , therefore, part of the activities have been carried out on the resolution of such problems. The possible causes of defect on brazed geometries have been found and one-dimensional considerations about thermal expansion as well as 3d thermo-structural simulation confirm all the statements. Such problematics has been reported on third chapter which, moreover, consists on their resolutions: the design of a new brazing cycle with an intermediate plateau. All the remaining modules are then brazed with this new cycle that permitted the disappearance of the brazing distortion. This confirms the reliability of the production phases and methods for the obtainments of modules respecting the project specifications. The quality control of the modules include: vacuum tightening test of the cavity, the coolant circuits seal test, Ultrasonic Test (UT) of the brazed joints, dimensional inspection using a CMM (Coordinate Measuring Machine) and Radio-Frequency (RF) test that identifies the electromagnetic behaviour of the single modules. These two last quality controls are strictly correlated each other in such a way that the deviations from the nominal dimensions could be used to predict the electromagnetic ones. Therefore in the last chapter, along with descriptions of the production phases and their metrological controls, it exposes a method for predicting the frequency deviation based on the deviations of measurements. The method validation is done thank to the comparison between metrological control results and those of the RF test. To sum up, the first chapter talks about the IFMIF project, its purpose and its main components; the second summarizes the principle of operation of the four-vane RFQ and describes the main parameters of the one used for the project IFMIF / EVEDA; the third introduces the basic concepts of the brazing process, the identification of defects and determining causes by means of a thermal-structural simulation and finally outlines a new brazing cycle; the last chapter describes the main stages of production, the metrological control between them, culminating in an metrological characterization method to predict the electromagnetic behaviour of the cavity

Linac design for intense hadron beams

Energy and environment are two major concerns in the 21st century. At present, the energy required for the daily life still mainly relies on the traditional fossil fuel resources, but the caused air pollution problem and greenhouse effect have seriously threatened the sustainable development of mankind. Another adopted energy source which can provide a large fraction of electricity for the world is the nuclear fission reaction. However, the increasing high-radioactive spent nuclear fuels, which half-lives are usually >1 million years, are becoming the hidden perils to the earth. A great advance in accelerator physics and technology opens an opportunity to solve this dilemma between man and nature, because powerful accelerator-based neutron sources can play important roles for clean nuclear power production, for example: - The Accelerator-Driven System (ADS) can serve as an easy control of a sub-critical fission reactor so that the nuclear fuels will be burnt more completely and safely. - The EUROTRANS project launched by EU is investigating another application of the ADS technology to reduce the radiotoxicity and the volume of the existing nuclear waste greatly and quickly in a transmutation way. - The developing international IFMIF plant will be used to test and qualify reactor materials for future fusion power stations, which can produce much cleaner nuclear electricity more efficiently than the fission ones. Therefore, the R&D of high-power driver linacs (HPDL) is of a worldwide importance. As the proverb said, "everything is hard at the beginning", the front end is the most difficult part for realizing an HPDL machine. Based on the RFQ and H-type DTL structures, this dissertation is dedicated to study the beam dynamics in the presence of significantly strong space-charge effects while accelerating intense hardon beams in the low- and medium-beta-region. Besides the 5mA/30mA, 17MeV proton injector (RFQ+DTL) and the 125mA, 40MeV deuteron DTL of the above-mentioned EUROTRANS and IFMIF facilities, a 200mA, 700keV proton RFQ has been also intensively studied for a small-scale but ultra-intense neutron source FRANZ planned at Frankfurt University. The most remarkable properties of the FRANZ RFQ and the IFMIF DTL are the design beam intensities, 200mA and 125mA, which are the record values for the proton and deuteron linacs, respectively. Though the design intensities for the two development stages, XT-ADS (5mA) and EFIT (30mA), of the EUROTRANS injector are well within the capability of the modern RF linac technology, the special design concept for an easy upgrade from XT-ADS to EFIT brings unusual challenges to realize a linac layout which allows flexible operation with different beam intensities. To design the 200mA FRANZ RFQ and the two-intensity EUROTRANS RFQ, the classic LANL (Los Alamos National Laboratory) Four-Section Procedure, which was developed by neglecting the space-charge forces, is not sufficient anymore. Abandoning the unreasonable constant- B (constant-transverse-focusing-strength) law and the resulting inefficient evolution manners of dynamics parameters adopted by the LANL method, a new design approach so-called "BABBLE", which can provide a "Balanced and Accelerated Beam Bunching at Low Energy", has been developed for intense beams. Being consistent with the beam-development process including space-charge effects, the main features of the "BABBLE" strategy (see Pages 55-58) are: 1) At the entrance, the synchronous phase is kept at = phi s = -90° while a gradual increase in the electrode modulation is started so that the input beam can firstly get a symmetrical and soft bunching within a full-360° phase acceptance. 2) In the following main bunching section, B is increasing to balance the stronger and stronger transverse defocusing effects induced by the decreasing bunch size so that the bunching speed can be fast and safely increased. 3) When the real acceleration starts, the quickly increased beam velocity will naturally weaken the transverse defocusing effects, so B is accordingly falling down to avoid longitudinal emittance growths and to allow larger bore apertures. Taking advantage of the gentle initial bunching and the accelerated main bunching under balanced forces enabled by the "BABBLE" strategy, a 2m-long RFQ with beam transmission in excess of 98% and low emittance growths has been designed for FRANZ, and a 4.3m-long RFQ with almost no beam losses and flat emittance evolutions at both 5mA and 30mA has been designed for EUROTRANS. All design results have proven that the "BABBLE" strategy is a general design approach leading to an efficient and robust RFQ with good beam quality in a wide intensity-range from 0mA to 200mA (even higher). To design the IFMIF DTL and the injector DTL part of the EUROTRANS driver linac, which have been foreseen as the first real applications of the novel superconducting CH-DTL structure, intensive attempts have been made to fulfill the design goals under the new conditions, e.g. long drift spaces, SC transverse focusing elements and high accelerating gradients. For the IFMIF DTL, the preliminary IAP design has been considerably improved with respect to the linac layout as well as the beam dynamics. By reserving sufficient drift spaces for the cryosystem, diagnostic devices, tuner and steerer, introducing SC solenoid lenses and adjusting the Linac Design for Intense Hadron Beams accelerating gradients and accordingly other configurations of the cavities (see Pages 78-80), a more realistic, reliable and efficient linac system has been designed. On the other hand, the specifications and positions of the transverse focusing elements (see Pages 81-82) as well as the phase- and energy-differences between the bunch-center particle and the synchronous particle at the beginning of the phi s=0° sections have been totally redesigned (see Pages 83-84) resulting in good beam performances in both radial and longitudinal planes. For the EUROTRANS injector DTL, in addition to the above-mentioned procedures, extra optimization concepts to coordinate the beam dynamics between two intensities, such as employing short adjustable rebunching cavities with phi s = -90° (see Page 116), have been applied. ...Energie und Umwelt sind zwei Hauptthemen im 21. Jahrhundert. Zurzeit wird der für das tägliche Leben benötigte Energiebedarf hauptsächlich aus fossilen Quellen abgedeckt, doch die dadurch verursachte Luftverschmutzung und der Treibhauseffekt bedrohen ernsthaft die Weiterentwicklung der Menschheit. Eine weitere Energiequelle, welche einen Großteil der Elektrizität für den Weltverbrauch liefert, ist die Kernspaltung. Jedoch stellen die ständig anwachsenden Mengen von radioaktivem Müll mit Halbwertszeiten von über eine Million Jahre ein wachsendes Problem dar. Die Beschleunigerphysik und -technologie eröffnet eine Lösungsmöglichkeit dieses Problems, weil beschleunigergestützte intensive Neutronenquellen eine wichtige Rolle für eine saubere nukleare Energieerzeugung übernehmen können: - Beschleunigergetriebene unterkritische Reaktorsysteme (englisch: "Accelerator Driven Systems", ADS) ermöglichen eine leichte Kontrolle des Reaktorbetriebes, so dass die Kernbrennstoffe vollständiger und sicherer verbraucht werden. - Das von der Europäischen Union geförderte Forschungsprogramm für die Transmutation von hoch radioaktiven Abfällen EUROTRANS wendet die ADS-Technologie an mit dem Ziel, die Radiotoxizität und Menge des radioaktiven Abfalls stark zu mindern. - Die "International Fusion Material Irradiation Facility" (IFMIF) wird geeignete Materialien für Fusionsreaktoren wie ITER durch Beschuss mit Neutronen untersuchen und so einen langfristigen Beitrag für eine sauberere und effizientere Erzeugung von Kernenergie durch Fusionsreaktionen leisten. Deshalb ist die Forschung und Entwicklung von Hochleistungs-Treiber-Linearbeschleuniger (Linacs) von weltweiter Bedeutung. Wie das Sprichwort (auch in China) sagt: "Aller Anfang ist schwer", so ist der Nieder- und Mittelenergiebereich gewöhnlich der anspruchsvollste Teil eines Beschleunigers. In der vorliegenden Dissertation wurden Strahldynamikuntersuchungen bei starkem Einfluss der Raumladungseffekte durchgeführt, wobei intensive Hadronenstrahlen im niedrigen und mittleren Energiebereich durch Hochfrequenz-Quadrupol- (englisch: "RFQ") und H-Mode Driftröhrenstrukturen (DTL) beschleunigt werden. Neben dem 5 bzw. 30mA, 17MeV Protoneninjektor (RFQ und DTL) für EUROTRANS und dem 125mA, 40MeV Deuteronen - DTL für IFMIF, wurde auch die strahldynamische Auslegung eines 200mA, 700keV Protonen-RFQs für die intensive Neutronenquelle FRANZ an der Goethe-Universität Frankfurt untersucht. Die markantesten Eigenschaften des FRANZ-RFQs sowie des IFMIF-DTLs sind die Strahlintensitäten von 200mA respektive 125mA, welche jeweils Rekordwerte für Protonen- und Deuteronen- Linacs darstellen. Obgleich die geplanten Intensitäten der beiden Entwicklungsstufen XT-ADS (5mA) und EFIT (30mA) des EUROTRANS-Projektes sich im Rahmen der technologischen Möglichkeiten moderner Beschleuniger befinden, stellte in diesem Fall die Option einer leichten Ausbaumöglichkeit des XT-ADS Entwurfes für EFIT wegen der unterschiedlichen Teilchenströme eine besondere Herausforderung dar. Die am Los Alamos National Laboratory (LANL) unter Vernachlässigung der Raumladungskräfte entwickelte Vier-Sektionen-Prozedur für den RFQ-Entwurf war im Falle des 200mA FRANZ-RFQs sowie des EUROTRANS-RFQs nicht geeignet. Unter Aufgabe des von LANL entwickelten konstantes B-Kriteriums (konstante transversale Fokussierstärke), welches in den vorliegenden Fällen zu ineffizienten Parametersätzen geführt hätte, wurde ein neues Designkonzept für intensive Teilchenstrahlen mit der Bezeichnung "Balanced and Accelerated Beam Bunching at Low Energy" (BABBLE, siehe Seiten 55-58) ausgearbeitet. Dieses ist im Einklang mit dem Prozess der Strahlformierung unter Berücksichtigung der Raumladungseffekte und hat folgende Hauptmerkmale: 1) Die Synchronphase wird am Eingang konstant bei phi s=-90° gehalten, während die Modulation der Elektroden langsam erhöht wird. Dadurch erfährt der Strahl eine symmetrische und gemäßigte Fokussierung innerhalb der gesamten 360° Phasenakzeptanz. 2) In der nachfolgenden Hauptfokussierungs-Sektion wird B erhöht um die immer größer werdende ransversale Defokussierung zu kompensieren, wodurch auch die Geschwindigkeit und Stabilität des Fokussierungsprozesses erhöht wird. 3) Zu Beginn der Hauptbeschleunigung kommt es durch die schnell anwachsende Teilchengeschwindigkeit zu einer natürlichen Reduktion der transversalen Defokussierung, so dass auch B entsprechend reduziert wird, um das longitudinale Emittanzwachstum zu vermeiden und um größere Aperturen zu ermöglichen. Unter Ausnutzung der Vorteile der mäßigen anfänglichen Fokussierung sowie der daran anschließenden schnellen Fokussierung im Kräftegleichgewicht gemäß der "BABBLE"-Strategie, konnten ein 2m langer RFQ für FRANZ mit 98% Transmission und geringem Emittanzwachstum sowie ein 4.3m langer RFQ für EUROTRANS mit sehr geringen Teilchenverlusten und flachem Emittanzverlauf sowohl für 5mA wie auch für 30mA entworfen werden. Diese Ergebnisse bestätigen die "BABBLE"-Strategie als allgemeinen Design-Ansatz, welcher effiziente RFQs mit guter Strahlqualität in einem weiten Bereich der Strahlintensitäten (0mA bis 200mA und höher) ermöglicht. Beim Entwurf des IFMIF DTLs sowie des Injektor DTLs für EUROTRANS, welche als erste Anwendungen der neuartigen, supraleitenden CH-Driftröhrenstruktur dienen könnten, wurden mit großer Sorgfalt versucht, die Designkriterien bei neuen Randbedingungen wie längere Driftstrecken, supraleitende transversale Fokussierelemente und hohe Beschleunigungsgradienten möglichst gut zu erfüllen. Im Falle des IFMIF-DTL wurde das ursprüngliche IAP-Design wesentlich verbessert, sowohl im Hinblick auf den Aufbau des Beschleunigers wie auch strahldynamisch. Es wurden ausreichend Driftstrecken für die Kryoelemente, Diagnosekomponenten, Tuner und Steeringmagnete vorgesehen, ferner wurden supraleitende Solenoidlinsen eingesetzt und die Beschleunigungsgradienten angepasst (siehe Seiten 78-80). Daraus resultierte ein realistischerer, zuverlässiger und effizienter Entwurf. Darüber hinaus wurden die Spezifikationen und Lagen der transversal fokussierenden Elemente (siehe Seiten 81-82), sowie die Phasen- und Energieablagen zwischen Schwerpunkt der Teilchenverteilung und Sollteilchen am Eingang der phi s=0° Sektionen neu bestimmt (siehe Seiten 83-84), wodurch verbesserte Ergebnisse in allen Raumebenen erzielt wurden. Im Falle des EUROTRANS Injektor-DTLs, wurden zusätzlich zu den obengenannten Maßnahmen Konzepte zur Anpassung der Strahldynamik für zwei verschiedene Strahlintensitäten entwickelt, wie zum Beispiel der Einsatz kurzer, abstimmbarer Rebunching- Kavitäten mit phi s = -90° (siehe Seite 116) ..