Feedback Systems for Linear Colliders

Feedback systems are essential for stable operation of a linear collider, providing a cost-effective method for relaxing tight tolerances. In the Stanford Linear Collider (SLC), feedback controls beam parameters such as trajectory, energy, and intensity throughout the accelerator. A novel dithering optimization system which adjusts final focus parameters to maximize luminosity contributed to achieving record performance in the 1997-98 run. Performance limitations of the steering feedback have been investigated, and improvements have been made. For the Next Linear Collider (NLC), extensive feedback systems are planned as an intregal part of the design. Feedback requiremetns for JLC (the Japanese Linear Collider) are essentially identical to NLC; some of the TESLA requirements are similar but there are significant differences. For NLC, algorithms which incorporate improvements upon the SLC implementation are being prototyped. Specialized systems for the damping rings, rf and interaction point will operate at high bandwidth and fast response. To correct for the motion of individual bunches within a train, both feedforward and feedback systems are planned. SLC experience has shown that feedback systems are an invaluable operational tool for decoupling systems, allowing precision tuning, and providing pulse-to-pulse diagnostics. Feedback systems for the NLC will incorporate the key SLC features and the benefits of advancing technologies.Comment: Invited talk presented at IEEE Particle Accelerator Conference (PAC99

Crystallinity Effects in Sequentially Processed and Blend-Cast Bulk-Heterojunction Polymer/Fullerene Photovoltaics

Although most polymer/fullerene-based solar cells are cast from a blend of the components in solution, it is also possible to sequentially process the polymer and fullerene layers from quasi-orthogonal solvents. Sequential processing (SqP) not only produces photovoltaic devices with efficiencies comparable to the more traditional bulk heterojunction (BHJ) solar cells produced by blend casting (BC) but also offers the advantage that the polymer and fullerene layers can be optimized separately. In this paper, we explore the morphology produced when sequentially processing polymer/fullerene solar cells and compare it to the BC morphology. We find that increasing polymer regioregularity leads to the opposite effect in SqP and BC BHJ solar cells. We start by constructing a series of SqP and BC solar cells using different types of poly(3-hexylthiophene) (P3HT) that vary in regioregulary and polydispersity combined with [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM). We use grazing incidence wide-angle X-ray scattering to demonstrate how strongly changes in the P3HT and PCBM crystallinity upon thermal annealing of SqP and BC BHJ films depend on polymer regioregularity. For SqP devices, low regioregularity P3HT films that possess more amorphous regions allow for more PCBM crystallite growth and thus show better photovoltaic device efficiency. On the other hand, highly regioregular P3HT leads to a more favorable morphology and better device efficiency for BC BHJ films. Comparing the photovoltaic performance and structural characterization indicates that the mechanisms controlling morphology in the active layers are fundamentally different for BHJs formed via SqP and BC. Most importantly, we find that nanoscale morphology in both SqP and BC BHJs can be systematically controlled by tuning the amorphous fraction of polymer in the active layer. © 2014 American Chemical Society

P3HT-Based Solar Cells: Structural Properties and Photovoltaic Performance

Each year we are bombarded with B.Sc. and Ph.D. applications from students that want to improve the world. They have learned that their future depends on changing the type of fuel we use and that solar energy is our future. The hope and energy of these young people will transform future energy technologies, but it will not happen quickly. Organic photovoltaic devices are easy to sketch, but the materials, processing steps, and ways of measuring the properties of the materials are very complicated. It is not trivial to make a systematic measurement that will change the way other research groups think or practice. In approaching this chapter, we thought about what a new researcher would need to know about organic photovoltaic devices and materials in order to have a good start in the subject. Then, we simplified that to focus on what a new researcher would need to know about poly-3-hexylthiophene:phenyl-C61-butyric acid methyl ester blends (P3HT: PCBM) to make research progress with these materials. This chapter is by no means authoritative or a compendium of all things on P3HT:PCBM. We have selected to explain how the sample fabrication techniques lead to control of morphology and structural features and how these morphological features have specific optical and electronic consequences for organic photovoltaic device applications

The Paleolithic of the Iranian Plateau: hominin occupation history and implications for human dispersals across southern Asia

The biological and cultural evolution of hominins in Asia is a central topic of paleoanthropology. Yet, the Paleolithic archaeology of key regions of Asia, including the Iranian plateau, have not been integrated into human evolutionary studies. Here, we examine the prehistory of the Iranian plateau with a focus on Iran, one of the largest and archaeologically best-known countries in the region. After approximately eight decades of professional fieldwork on the Paleolithic in Iran, a broad outline of the occupation history of the region has been achieved, though significant gaps remain in understanding the evolution and behavior of hominins in the region. Here we examine the history of Paleolithic investigations, synthesizing key archaeological information from the Lower Paleolithic to the EpiPaleolithic, placing emphasis on archaeological sites with stratified deposits and dated finds. We collect and summarize information on site locations, chronologies, rare hominin fossils, the more common lithic assemblages, and scarce worked items and symbolic objects. Our study documents considerable chronological and archaeological gaps in the Lower Paleolithic record, although Acheulean sites with characteristic lithics are present signaling the early colonization of the region by early hominin ancestors. The early Middle Paleolithic is poorly known owing to dating lacunae, although more abundant evidence is available from younger sites after 50,000 years ago (ka), spanning the late Middle Paleolithic, the Upper Paleolithic and the EpiPaleolithic. The fossil and archaeological evidence indicates the presence of Neanderthals in the Iranian plateau and later, Homo sapiens. The distribution of Lower to EpiPaleolithic sites are examined here, indicating both overlaps and divergences in the use of geographic areas, while pointing to large-scale research gaps in archaeological coverage. Key dispersal models are summarized, illustrating alternative views on the routes of human expansions in the Late Pleistocene, and how the Iranian plateau situates relative to the Levant, Arabia and Central Asia.1. Introduction 2. Research history and background 3. Geography and environment 4. The Pleistocene archaeological record 4.1. Lower Paleolithic 4.2. Middle Paleolithic 4.3. Upper Paleolithic 4.4. EpiPaleolithic 5. Discussion 5.1. Chronological gaps in the record and their meaning 5.2. The hominin fossil record 5.3. Patterns and trends in occupation history 5.4. Dispersal patterns within and across the Iranian plateau 6. Conclusion