Abstract:The first time-resolved x-ray/optical pump-probe experiments at the SLAC Linac Coherent Light Source (LCLS) used a combination of feedback methods and post-analysis binning techniques to synchronize an ultrafast optical laser to the linac-based x-ray laser. Transient molecular nitrogen alignment revival features were resolved in time-dependent x-rayinduced fragmentation spectra. These alignment features were used to find the temporal overlap of the pump and probe pulses. The strong-field dissociation of x-ray generated quasi-bound molecular dications was used to establish the residual timing jitter. This analysis shows that the relative arrival time of the Ti:Sapphire laser and the x-ray pulses had a distribution with a standard deviation of approximately 120 fs. The largest contribution to the jitter noise spectrum was the locking of the laser oscillator to the reference RF of the accelerator, which suggests that simple technical improvements could reduce the jitter to better than 50 fs. ©2010 Optical Society of America

We demonstrate distribution of a 2850 MHz rf signal over stabilized optical fiber links. For a 2.2 km link we measure an rms drift of 19.4 fs over 60 h, and for a 200 m link an rms drift of 8.4 fs over 20 h. The rf signals are transmitted as amplitude modulation on a continuous optical carrier. Variations in the delay length are sensed using heterodyne interferometry and used to correct the rf phase. The system uses standard fiber telecommunications components.

The Advanced Photoinjector Experiment (APEX) at the Lawrence Berkeley National Laboratory is dedicated to the development of a high-brightness high-repetition rate (MHz-class) electron injector for x-ray free-electron laser (FEL) and other applications where high repetition rates and high brightness are simultaneously required. The injector is based on a new concept rf gun utilizing a normal-conducting (NC) cavity resonating in the VHF band at 186 MHz, and operating in continuous wave (cw) mode in conjunction with high quantum efficiency photocathodes capable of delivering the required charge at MHz repetition rates with available laser technology. The APEX activities are staged in three phases. In phase 0, the NC cw gun is built and tested to demonstrate the major milestones to validate the gun design and performance. Also, starting in phase 0 and continuing in phase I, different photocathodes are tested at the gun energy and at full repetition rate for validating candidate materials to operate in a high-repetition rate FEL. In phase II, a room-temperature pulsed linac is added for accelerating the beam at several tens of MeV to reduce space charge effects and allow the measurement of the brightness of the beam from the gun when integrated in an injector scheme. The installation of the phase 0 beam line and the commissioning of the VHF gun are completed, phase I components are under fabrication, and initial design and specification of components and layout for phase II are under way. This paper presents the phase 0 commissioning results with emphasis on the experimental milestones that have successfully demonstrated the APEX gun capability of operating at the required performance.

Low levels of life satisfaction have been linked to low self-esteem and loneliness, but this association has never been tested directly in LGB (lesbian/gay/bisexual) populations. We compared 275 Chinese LGB adults to 275 demographic-matched Chinese heterosexual controls on life satisfaction, self-esteem, and loneliness. LGB adults reported lower levels of self-esteem and higher levels of loneliness than heterosexuals, but similar levels of overall life satisfaction. Self-esteem partially mediated (but did not moderate) the relationship between loneliness and life satisfaction in both groups. Hierarchical regressions indicated that demographic variables, loneliness, and self-esteem can predict life satisfaction in both LGB and heterosexual adults, but explained more variance of life satisfaction in the LGB group. Thus self-esteem and loneliness play a more important role in life satisfaction for LGB rather than heterosexual Chinese adults.

An x-ray streak camera with high resolution in both temporal and spatial dimensions has been developed. It is achieved by using extraction-mesh acceleration and a large opening aperture magnetic solenoid lens design. High resolutions in the temporal and spatial dimensions can be retained in a wide 53ps time window. A temporal resolution of 233fs and a spatial resolution of 10μm have been demonstrated using a Au photocathode.

Accumulating evidence suggests that sexual minorities experience elevated levels of depressive symptoms compared to heterosexuals in Western countries. Still, little is known about whether there is any difference in depressive symptoms between sexual minority men and heterosexual men in China. This study investigated the differences in depressive symptoms and social support between 302 Chinese sexual minority men and 249 heterosexual men. The association between depressive symptoms, social support and sexual orientation was also explored. Our results indicated that Chinese sexual minority men have more depressive symptoms and perceived lower social support than heterosexual men. Overall, sexual orientation and social support both predicted depressive symptoms. Different from previous Western studies, in our results, social support fully mediates but does not moderate the relationship between sexual orientation and depressive symptoms in Chinese men. The current findings suggest that social support has a significant impact on depressive symptoms among Chinese sexual minority men, highlighting the unique role of social support in understanding depressive symptoms among Chinese sexual minority men. Providing more social support, as well as promoting accepting and positive environments, may lead to better adjustment in this population in China.

We demonstrate a new method for controlling diffractive, high power beam combination, sensing phase errors by analyzing the intensity pattern of uncombined side beams at the output. A square array of eight beams is combined with <0.3% stability and 84.6% efficiency. As channel count is increased, so does the usable information, enabling scaling to large channel counts without significant slowing of control loop response time, an advantage over single-input algorithms.

Phase sequence exchanging technology (PSET) is a recently developed emergency control technology for out-of-step power systems. The PSET system does not satisfy the condition of synchronization however, and will produce impulse current and impact torque. In this paper, the impulse current and impact torque produced by PSET are calculated. Taking the three-phase short circuit at the generator outlet as a reference, the impulse current generated by PSET is determined to be less than half of the threephase short circuit at the generator outlet, which is within the system's endurable range. When the system connection reactance is 0.543 times larger than generator direct axis sub-transient reactance, it can endure the impact torque produced by PSET. To reduce the impact and improve the practicability of PSET, a splitphase switching control method is proposed in this paper. The characteristics of fast breaking are utilized to turn off the solid-state circuit breaker separately when the three-phase current is at zero-crossing, and after exchanging the phase sequence, it is turned-on separately when two sides of the three-phase voltage are equal. An example is provided to verify that the impact of PSET can be dramatically reduced by using the proposed control method instead of the traditional simultaneous switching control method. INDEX TERMS Phase sequence exchange technology, impulse current, impact torque, split-phase switching control method.