The recently commissioned Linac Coherent Light Source is an X-ray free-electron laser at the SLAC National Accelerator Laboratory. It produces coherent soft and hard X-rays with peak brightness ...nearly ten orders of magnitude beyond conventional synchrotron sources and a range of pulse durations from 500 to <10 fs (10-15 s). With these beam characteristics this light source is capable of imaging the structure and dynamics of matter at atomic size and timescales. The facility is now operating at X-ray wavelengths from 22 to 1.2 A and is presently delivering this high-brilliance beam to a growing array of scientific researchers. We describe the operation and performance of this new 'fourth-generation light source'.
The very bright electron beam required for an x-ray free-electron laser (FEL), such as the linac coherent light source (LCLS), is susceptible to a microbunching instability in the magnetic bunch ...compressors, prior to the FEL undulator. The uncorrelated electron energy spread in the LCLS can be increased by an order of magnitude to provide strong Landau damping against the instability without degrading the FEL performance. To this end, a “laser-heater” system has been installed in the LCLS injector, which modulates the energy of a 135-MeV electron bunch with an IR-laser beam in a short undulator, enclosed within a four-dipole chicane. In this paper, we report detailed measurements of laser-heater-induced energy spread, including the unexpected self-heating phenomenon when the laser energy is very low. We discuss the suppression of the microbunching instability with the laser heater and its impact on the x-ray FEL performance. We also present the analysis of these experimental results and develop a three-dimensional longitudinal space charge model to explain the self-heating effect.
The Linac Coherent Light Source is a SASE x-ray free-electron laser (FEL) project presently under construction at SLAC J. Arthur et al., SLAC-R-593, 2002.. The injector section, from drive laser and ...rf photocathode gun through first bunch compressor chicane, was installed in the fall of 2006. The initial system commissioning with an electron beam was completed in August of 2007, with the goal of a 1.2-micron emittance in a 1-nC bunch demonstrated. The second phase of commissioning, including second bunch compressor and full linac, is planned for 2008, with FEL commissioning in 2009. We report experimental results and experience gained in the first phase of commissioning, including the photocathode drive laser, rf gun, photocathode, S-band and X-band rf systems, first bunch compressor, and the various beam diagnostics.
The recently commissioned Linac Coherent Light Source is an X-ray free-electron laser at the SLAC National Accelerator Laboratory. It produces coherent soft and hard X-rays with peak brightness ...nearly ten orders of magnitude beyond conventional synchrotron sources and a range of pulse durations from 500 to <10fs (10 super(-15)s). With these beam characteristics this light source is capable of imaging the structure and dynamics of matter at atomic size and timescales. The facility is now operating at X-ray wavelengths from 22 to 1.2Aa and is presently delivering this high-brilliance beam to a growing array of scientific researchers. We describe the operation and performance of this new 'fourth-generation light source'.
The linac coherent light source (LCLS) is a SASE X- ray free-electron laser (FEL) project presently under construction at SLAC 1. The injector section, from drive-laser and RF photocathode gun ...through first bunch compressor chicane, was installed in fall 2006. Initial system commissioning with an electron beam is taking place during the spring and summer of 2007. The second phase of construction, including second bunch compressor and full linac, will begin later, in the fall of 2007. We report here on experience gained during the first phase of machine commissioning, including RF photocathode gun, linac booster section, S-band and X-band RF systems, first bunch compressor, and the various beam diagnostics.
Commissioning the LCLS Injector Akre, R; Dowell, D; Emma, P ...
Physical review special topics. PRST-AB. Accelerators and beams,
11/2007
Journal Article
Odprti dostop
The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project presently under construction at SLAC. The injector section, from drive laser and RF photocathode gun through ...first bunch compressor chicane, was installed in fall 2006. Initial system commissioning with an electron beam was completed in August 2007, with the goal of a 1.2-micron emittance in a 1-nC bunch clearly demonstrated. The second phase of commissioning, including second bunch compressor and full linac, is planned for 2008, with FEL commissioning in 2009. We report experimental results and experience gained in the first phase of commissioning, including the photo-cathode drive laser, RF gun, photocathode, S-band and X-band RF systems, first bunch compressor, and the various beam diagnostics.
Mutations in the Parkin gene (PARK2) are the most commonly identified cause of recessively inherited early-onset Parkinson disease (EOPD) but account for only a portion of cases. DJ-1 (PARK7) was ...recently reported as a second gene associated with recessively inherited PD with a homozygous exon deletion and a homozygous point mutation in two families.
To investigate the frequency of DJ-1 mutations, the authors performed mutational analysis of all six coding exons of DJ-1 in 100 EOPD patients. For the detection of exon rearrangements, the authors developed a quantitative duplex PCR assay. Denaturing high performance liquid chromatography analysis was used to screen for point mutations and small deletions. Further, Parkin analysis was performed as previously described.
The authors identified two carriers of single heterozygous loss-of-function DJ-1 mutations, including a heterozygous deletion of exons 5 to 7 and an 11-base pair deletion, removing the invariant donor splice site in intron 5. Interestingly, both DJ-1 mutations identified in this study were found in the heterozygous state only. The authors also detected a polymorphism (R98Q) in 1.5% of the chromosomes in both the patient and control group. In the same patient sample, 17 cases were detected with mutations in the Parkin gene.
Mutations in DJ-1 are less frequent than mutations in Parkin in EOPD patients but should be considered as a possible cause of EOPD. The effect of single heterozygous mutations in DJ-1 on the nigrostriatal system, as described for heterozygous changes in Parkin and PARK6, remains to be elucidated.
A relative humidity‐moderated differential mobility optical particle size spectrometer (RH‐DMOPSS) was developed to measure particle size distributions at different humidity conditions in the 0.1‐ to ...1.1‐μm size range. The system has a high‐flow differential mobility analyzer followed by an optical counter and condensation particle counter in parallel. An aerosol dryer or humidity conditioner can be placed in line ahead of the mobility analyzer. A second dryer ahead of the optical counter permits measurements of the decrease in particle size when particles classified at high relative humidity were dried. The RH‐DMOPSS data set includes (1) optical counter response to monodisperse ambient aerosols, (2) accumulation mode particle size distributions for dry and humid conditions, (3) selected hygroscopic growth factors for humid diameters of 0.2 to 1.1 μm, (4) inferred volatile particle water volume, and (5) inferred refractive index for dried particles. The RH‐DMOPSS was operated in Smoky Mountains National Park as part of the Southeastern Aerosol and Visibility Study and compared with other collocated size and aerosol growth measurements. For dried ambient particles, size distribution parameters were correlated with those from impactor measurements, but volume median diameters were 12% smaller, on average. Growth factors for particles below 0.5‐μm diameter were in the same range as those measured by a tandem differential mobility analyzer and, for all sizes, were consistent with the measured differences between dried and humidified particle size distributions. The mean ambient particle real refractive index inferred from the RH‐DMOPSS dry‐particle calibration data was 1.48, equal to that measured by a multiangle light‐scattering instrument.
The hypervariable tetranucleotide STR polymorphism DXS10011 is a powerful marker for forensic purposes. Investigation of this STR led to an allele nomenclature which is in consensus with the ISFG ...recommendations. DXS10011 is located at Xq28 and genetically closely linked to DXS7423 and DXS8377 but is unlinked to HPRTB and more distant X-chromosomal STRs. DXS10011 is a very complex marker exhibiting some structural variants within alleles of identical length. Two types of repeat structure (regular and inter-alleles) are known and described as types A and B. Two SNPs which are in strong linkage disequilibrium to the different sequence types were found in the repeat flanking region. The type A sequence consists of a long stretch of uninterrupted homogenous repeats which is highly susceptible to slippage mutation during male meiosis.
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