Low energy operation of the DIAMOND light source

Abstract Within the last decade storage ring free-electron lasers (SRFELs) have reached UV output wavelengths and beyond: several facilities have achieved down to 250nm and quite recently below 200nm. The design of DIAMOND, the third-generation replacement for the existing SRS light source at Daresbury Laboratory, has been optimised at 3 GeV to provide high quality output for the scientific community, mainly from a range of insertion devices. In this paper we propose an additional DIAMOND regime at 1-1.5 GeV in an attempt also to include an SRFEL which would be of major benefit to users needing high quality, high brightness UV/VUV radiation. Such variable ring operating energy will have significant implications, not least in achieving acceptable beam lifetimes. In addition, enhanced beam coherent instabilities (notably microwave) at low energy will affect the single bunch length (peak current) and energy spread which will in turn limit the achievable FEL gain. All these factors will have to be assessed in the detailed design stages of DIAMOND. DIAMOND LIGHT SOURCE The recent successful demonstration of an SRFEL on the ELETTRA light source [1], together with earlier experience at LURE (Super-ACO) and elsewhere, has encouraged interest in the incorporation of such advanced facilities in all leading light sources. The normal operating mode of DIAMOND at 3GeV is described in detail elsewhere FEL OPERATING MODE When operating in optimised FEL mode, the storage ring will be populated with bunches spaced apart in time by twice the round trip time in the FEL cavity, ensuring energy transfer occurs as frequently as possible; the cavity length is always chosen to be a sub-harmonic of the storage ring circumference, whilst satisfying other, practical constraints. The final circumference of the DIAMOND storage ring has not yet been fixed but may be finalised at 528 m (an increase on the present 489 m layout [2] to budget for additional elements), giving a harmonic number of 880 at 500 MHz RF frequency. With 8 equally spaced bunches this leads to a required cavity length of 33 m, which is reasonable (cf. the ELETTRA device which has a cavity length of 32.4 m [1]). Since a very small vertical emittance is not necessary for FEL operation, a conservative coupling value of 3% has been assumed for these calculations, which should both be readily achievable and provide a satisfactory Touschek lifetime; both greater coupling and larger emittance could be selected if necessary. The momentum acceptance will be the primary limit on the beam lifetime at low energies, via Touschek scattering and quantum lifetime; the 4% dynamic and physical acceptance limit specified for 3 GeV operation BUNCH MODELLING To provide peak currents of tens of Amperes, as will be needed for useful FEL gains, bunch currents of several milliamperes are required. At these currents the effects of bunch lengthening from potential well distortion (PWD) and from the microwave instability (MI) are large, but are beneficial in that they provide low enough number densities within the bunches to give an acceptable Touschek lifetime; however the issue is whether sufficient peak current can then be maintained, together with acceptable energy spread. The ZAP code [3] was used to predict the effect on bunch parameters of PWD and MI (details are given in [4]); however, the implementation of Brück's approximatio

Degeneracy measures for the algebraic classification of numerical spacetimes

We study the issue of algebraic classification of the Weyl curvature tensor, with a particular focus on numerical relativity simulations. The spacetimes of interest in this context, binary black hole mergers, and the ringdowns that follow them, present subtleties in that they are generically, strictly speaking, Type I, but in many regions approximately, in some sense, Type D. To provide meaning to any claims of "approximate" Petrov class, one must define a measure of degeneracy on the space of null rays at a point. We will investigate such a measure, used recently to argue that certain binary black hole merger simulations ring down to the Kerr geometry, after hanging up for some time in Petrov Type II. In particular, we argue that this hangup in Petrov Type II is an artefact of the particular measure being used, and that a geometrically better-motivated measure shows a black hole merger produced by our group settling directly to Petrov Type D.Comment: 14 pages, 7 figures. Version 2 adds two references

Radio and X-ray properties of submillimeter galaxies in the A2125 field

We present the radio and X-ray properties of 1.2 mm MAMBO source candidates in a 1600 sq. arcmin field centered on the Abell 2125 galaxy cluster at z=0.247. The brightest, non-synchrotron mm source candidate in the field has a photometric redshift, z = 3.93^+1.11_-0.80, and is not detected in a 31 ks Chandra X-ray exposure. These findings are consistent with this object being an extremely dusty and luminous starburst galaxy at high-redshift, possibly the most luminous yet identified in any blank-field mm survey. The deep 1.4 GHz VLA imaging identifies counterparts for 83% of the 29 mm source candidates identified at >=4-sigma S(1.2mm) = 2.7 - 52.1 mJy, implying that the majority of these objects are likely to lie at z <~ 3.5. The median mm-to-radio wavelength photometric redshift of this radio-detected sample is z~2.2 (first and third quartiles of 1.7 and 3.0), consistent with the median redshift derived from optical spectroscopic surveys of the radio-detected subsample of bright submm galaxies (S(850um) > 5 mJy). Three mm-selected quasars are confirmed to be X-ray luminous in the high resolution Chandra imaging, while another mm source candidate with potential multiple radio counterparts is also detected in the X-ray regime. Both of these radio counterparts are positionally consistent with the mm source candidate. One counterpart is associated with an elliptical galaxy at z = 0.2425, but we believe that a second counterpart associated with a fainter optical source likely gives rise to the mm emission at z~1.Comment: Accepted for publication in Ap

Plant pathogens as biological agents for the control of weeds

Weed control is by far the most pervasive and costly need in agriculture, both in underdevel­ oped as well as in technologically advanced production systems. In 1994, losses due to weeds in U.S. agriculture—including herbi­ cide costs and yield losses—amounted to over $ 15 billion, and about 96% of the more than 21 million acres of row crops grown in Iowa received at least one chemical herbicide appli­ cation. Pesticide use statistics reveal that more herbicides are used than any other class of pesticide. Despite the extensive use of herbi­ cides, certain weed species continue to cause problems in agriculture, and current control strategies for some of these are inadequate. Among these weeds are johnsongrass (Sor­ ghum halapense), the morning glorys (Ipomoea spp.), nutsedges (Cyperus esculentus), shattercane (Sorghum bicolor), and velvetleaf (Abutillon theophrasti)

Start to end simulations of the ERL prototype at Daresbury Laboratory

Daresbury Laboratory is currently building an Energy Recovery Linac Prototype (ERLP) that will serve as a research and development facility for the study of beam dynamics and accelerator technology important to the design and construction of the proposed 4th Generation Light Source (4GLS) project. Two major objectives of the ERLP are the demonstration of energy recovery and of energy recovery from a beam disrupted by an FEL interaction as supplied by an infrared oscillator system. In this paper we present start-to-end simulations of the ERLP including such an FEL interaction. The beam dynamics in the highbrightness injector, which consists of a DC photocathode Gun and a superconducting booster, have been modelled using the particle tracking code ASTRA. After the booster the particles have been tracked with the code elegant. The 3D code GENESIS 1.3 was used to model the FEL interaction with the electron beam at 35 MeV. A brief summary of impedance and wakefield calculations for the whole machine is also given