We discuss the new layout of a cavity chain (superstructure) allowing, we hope, significant cost reduction of the RF system of both linacs of the TESLA linear collider. The proposed scheme increases the fill factor and thus makes an effective gradient of an accelerator higher. We present mainly computations we have performed up to now and which encouraged us to order the copper model of the sch...

RF breakdown in high-frequency accelerators appears to limit the maximum achievable gradient as well as the reliability of such devices. Experimental results from high power tests, obtained mostly in the framework of the NLC/GLC project at 11 GHz and from the CLIC study at 30 GHz, will be used to illustrate the important issues. The dependence of the breakdown phenomena on rf pulse length, oper...

Recent work at CERN and SLAC has opened the possibility of the development of concrete designs for electron positron linear colliders that have a center of mass energy substantially above 1 TeV [1,2]. These designs are based on high gradient, normal conducting acceleration with the power provided by an auxiliary beam that is efficiently accelerated in a fully loaded, low frequency linac. This t...

Single-shot STEAM MRI [1] is insensitive to off-resonance effects because it is based on RF refocused echoes but suffers from a inherently low signal-to-noise ratio (SNR). Recently, gradient and stimulated echo (GRASTE) imaging [2] has been shown to ameliorate the limitations of single-shot STEAM by improving the SNR efficiency. Here, an extension of 2D GRASTE is presented that is capable of ac...

Fig. 1: General scheme for spin echo based SER-EPI sequence: The standard SER-scheme is extended not only by the refocusing 180 RF-pulse but also by a gradient pulse in phase-encoding direction. This gradient prephasing pulse aligns the gradient echo with the spin echo of the first excitation pulse s1. Fig.2: k-space data of spin-echo based SER-EPI sequence: Phase-encode direction is top to bot...

We present a modulated gradient spin-echo method (MGSE), which uses a train of sinusoidally shaped gradient pulses separated by 180-degree RF pulses. The RF pulses efficiently refocus chemical shifts and de-phasing due to susceptibility differences, resulting in undistorted, high-resolution diffusion weighted spectra. This allows for simultaneous spectral characterization of diffusion of severa...

J-Y. Park, M. Garwood Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, United States Synopsis: Frequency-swept pulses, like the hyperbolic secant (HS1) pulse, are not typically employed for excitation in MRI. When used for excitation in gradient-echo imaging, the HS1 pulse does not produce a proper echo because the magnetization phase...

We present a design of acoustic metasurfaces yielding asymmetric transmission within a certain frequency band. The design consists of a layer of gradient-index metasurface and a layer of low refractive index metasurface. Incident waves are controlled in a wave vector dependent manner to create strong asymmetric transmission. Numerical simulations show that the approach provides high transmissio...

This paper considers reconstructing a spectrally sparse signal from a small number of randomly observed time-domain samples. The signal of interest is a linear combination of complex sinusoids at R distinct frequencies. The frequencies can assume any continuous values in the normalized frequency domain [0, 1). After converting the spectrally sparse signal recovery into a low rank structured mat...

We present a Modulated Gradient Spin Echo pulse sequence that enables diffusion measurements with chemical shift resolution in the obtained spectra at higher modulation frequencies (1600 Hz) than previously obtained. The modulation is generated using a CarrPurcell-Meiboom-Gill train of radiofrequency pulses in a constant gradient. To avoid distortions from eddy currents, a longitudinal eddy cur...