Phase Jump Method for Efficiency Enhancement in Free-Electron Lasers

The efficiency of a free-electron laser can be enhanced by sustaining the growth of the radiation power beyond the initial saturation. One notable method is undulator tapering, which involves the variation of the gap height and/or the period along the undulator. Another method is the introduction of phase jumps, using phase-shifting chicanes in the drift sections separating the undulator segments. In this article, we develop a physics model of this phase jump method, and verify it with numerical simulations. The model elucidates the energy extraction process in the longitudinal phase space. The main ingredient is the microbunch deceleration cycle, which enables the microbunched electron beam to decelerate and radiate coherently beyond the initial saturation. The ponderomotive bucket is stationary, and energy can even be extracted from electrons outside the bucket. The model addresses the selection criteria for the phase jump values, and the requirement on the undulator segment length. It also describes the mechanism of the final saturation. In addition, we discuss the similarities and differences between the phase jump method and undulator tapering, by comparing our phase jump model to the classic Kroll-Morton-Rosenbluth model

Journal Staff

Additive manufacturing is a growing manufacturing technology that has lately transcended from mostly being used in prototype manufacturing to be used in conventional production. The transition has occurred with, among other technologies, Fused Deposit Modelling (FDM), developed by Stratasys for plastic manufacturing. The interest in replacing conventional methods (which for plastic is injection moulding) is increasing in Sweden and at the same time the demand for a more sustainable production increases. We have in this thesis managed to adapt a general framework for sustainability analysis with 31 indicators to a framework, for the analysis of the transition from injection moulding to FDM, with only 8 relevant indicators. This process was conduced through first establishing what sustainability is and mapped both production processes. Afterwards was the differences in the production processes analysed in regards to the general framework for sustainability analysis and a new framework, was created. Finally we analysed how firm management views frameworks for sustainability analysis, how they use them and how our framework complements the wrongful use that sometimes occur today.Adderande tillverkning är en stadigt växande tillverkningsteknik som på senare tid övergått från att huvudsakligen användas till prototyptillverkning till att användas för traditionell produktion. Övergången har bland annat skett med metoden Fused Deposit Modelling (FDM) som utvecklades av Stratasys och producerar i plast. Intresset för att ersätta traditionella metoder (vilket för plast är, bland annat, formsprutning) ökar i Sverige samtidigt som efterfrågan för en hållbar produktion ökar. Vi har i rapporten lyckats anpassa ett generellt ramverk för hållbarhetsanalys med 31 indikatorer till ett ramverk, för att analysera hållbarheten vid en övergång från formsprutning till FDM, med enbart 8 relevanta indikatorer. Denna process genomfördes genom att först etablera vad hållbarhet är och kartlagt de båda tillverkningsprocesserna. Därefter analyserades skillnaderna hos tillverkningssprocesserna utifrån de generella indikatorer för hållbarhetanalys och ett nytt ramverk skapades. Slutligen analyserades hur företagsledningar ser på ramverk för hållbarhetsanalys, hur de använder ramverken och hur vårt ramverk kompletterar det felaktiga användandet som ofta existerar idag

Single-shot transverse coherence in seeded and unseeded free-electron lasers: A comparison

The advent of x-ray free-electron lasers (FELs) drastically enhanced the capabilities of several analytical techniques, for which the degree of transverse (spatial) coherence of the source is essential. FELs can be operated in self-amplified spontaneous emission (SASE) or seeded configurations, which rely on a qualitatively different initialization of the amplification process leading to light emission. The degree of transverse coherence of SASE and seeded FELs has been characterized in the past, both experimentally and theoretically. However, a direct experimental comparison between the two regimes in similar operating conditions is missing, as well as an accurate study of the sensitivity of transverse coherence to key working parameters. In this paper, we carry out such a comparison, focusing in particular on the evolution of coherence during the light amplification process

Helikoptern som sjuktransport : Hur har utvecklingen av MEDEVAC (sjuktransport) sett ut i den moderna krigföringen och i militärteorin med exemplen Vietnam och dagens Afghanistan

Helikoptern som sjuktransport är ett väl beprövat system. Dess förmåga att landa och starta på nästintill vilka platser som helts gör den mycket lämplig för denna typ av arbete. Även om förmågan funnits i nästan 50 år är teoribildningen kring MEDEVAC bristande. I arbetet kommer helikopterns användande som MEDEVAC-­‐resurs under Vietnamkriget och Afghanistankriget att analyseras. I båda dessa fall analyseras även de doktriner som styr användandet av MEDEVAC. Brister i teoribildning kring MEDEVAC är centralt för detta arbete, då syftet är att belysa de brister i utveckling som det kan ha inneburit. De slutsatser som dras av dessa analyser är att den taktiska och doktrinära utvecklingen inte utvecklats i någon större utsträckning under denna period. De framsteg som har gjorts har framför allt varit teknisk utveckling samt att resursen värderas mer och används på ett försiktigare sätt.The helicopter is regularly used for performing evacuation of sick and wounded. Its ability to take off and land almost anywhere makes it especially useful for these kinds of missions. Even though the ability to do this has been around for nearly 50 years, theories concerning MEDEVAC are lacking. This essay will examine the helicopters role as a MEDEVAC resource during the Vietnam war and the war in Afghanistan. The respective doctrines and Field Manuals that guide the usage of MEDEVAC helicopters will also be examined. The lack of theories in this field will be central in this essay, since the goal is to point out if any shortcomings in the evolution of the MEDEVAC helicopter could be a result of this

Use of a Multiplexer to get Multiple Streams Through a Limited Interface : Encapsulation of digital video broadcasting streams

In digital video broadcasting, sometimes many sources are used. When handling this broadcast a problem is a limited interface that has a fixed number to input channels but overcapacity in data transfer rate. To be able to connect more inputs to the interface a protocol that lets the user send more than one channel on a connection is needed. The important part for the protocol is that it keeps the input equal to the output both in timing and in what data is sent. These are done by encapsulating the data and use a header containing information for recreating the input. To solve the timing constraint dynamic buffer are used that makes all data evenly delayed. To validate the functionality of the protocol a test designed is implemented in VHDL and simulated