Recent Developments in Toroid Cavity Autoclave Engineering

A toroid cavity autoclave (TCA) is a metal pressure vessel that simultaneously functions as an NMR resonator. Since the introduction of the TCA concept, many adaptations and optimizations were put together to suit particular applications such as catalysis in supercritical fluids, rotating-frame imaging of materials, and evaluation of transport phenomena. In this article, we present recent achievements in TCA engineering that were carried out for both major fields of research with TCAs, i.e., high-pressure and imaging studies. A new modular TCA design is introduced that makes it possible to easily access all individual parts of the autoclave for maintenance and replacement. The TCA is double tuned to a high frequency for 1H and 19F resonances and a low frequency for hetero nuclei. It withstands pressures up to 400 bar at room temperature and 300 bar at temperatures up to 100°C. The autoclave sample volume is electrically separated into two compartments with only the lower compartment NMR sensitive. With the two-compartment TCA, it is possible to monitor multiple-phase systems or gas/liquid reactions in situ without sacrificing high-resolution qualities of the probe. In addition, special features are presented, such as the utilization of a second pressure line for injecting key reagents that initiate a chemical reaction or for vigorously mixing gases with a reactive solution. A newly designed resistive heater that does not introduce stray magnetic fields is also described

Material consumption and crosstalk characteristics of different holographic storage concepts

Holographic data storage is considered to be one of the most promising technologies for high-capacity data storage. Several holographic concepts have been suggested and investigated in detail by many companies. The concepts differ in the method of superposing object and reference beams inside the holographic medium. At present, the most relevant concepts are the plane wave concept, the collinear concept, and a concept with counterpropagating beams. We compare all three concepts, with regard to their beam overlap, efficiency of material consumption, diffraction efficiency, and crosstalk characteristics. The investigation is performed by numerical simulations, which offer well-defined conditions in all setups and are independent of experimental uncertainties such as the nonlinear behavior of medium sensitivity and the effects of light scattering or reflection

Two-dimensional modulation for holographic data storage systems

Page-oriented holographic data storage systems (HDSSs) generally use spatial light modulators (SLMs) to generate two-dimensional (2D) digital patterns, so-called data pages. These data pages are stored via interference patterns of the object and reference beam in the holographic medium and are retrieved from the medium by exposing it to the reference beam. The reconstructed data pages are then detected by a matrix detector. One important challenge in designing an HDSS is to develop a suitable modulation, which takes into account the specific characteristics of the transfer channel and enables high data capacity, high data transfer rate and low symbol error rate (SER). In this paper, we present a new method for modulating data in an HDSS. The main idea is to adapt the general concept of 2D run-length limited modulation (RLL) to a numerically more efficient implementation usable for HDSS. We demonstrate that this 2D block coding method with a constant weight and a sparse code increases the amount of user data per data page, while the SER remains low compared with standard sparse modulation coding. This results in a higher data rate and higher data density

RIDE\u27n RIPT -- Ring Down Elimination in Rapid Imaging Pulse Trains

A new pulse sequence is introduced for compensation of acoustic ringing effects, which occur in rotating-frame images obtained with the rapid imaging pulse trains (RIPT). The new sequence (RIDE\u27n RIPT) combines features of ring down elimination (RIDE), the most common difference-spectroscopy sequence for acoustic-ringing compensation, with the advantages of RIPT for fast acquisition of magnetization profiles in B1 field gradients. For even greater time efficiency in many experiments, the two transients of RIDE\u27n RIPT are combined to a single transient in which data for the difference spectroscopy are collected sequentially. RIDE\u27n RIPT was used to record one-dimensional profiles of the proton magnetization in supercritical fluid samples of methane in carbon dioxide. The profiles showed substantial improvements over profiles obtained from standard RIPT. To withstand the high pressures required for the supercritical carbon dioxide mixtures, a toroid cavity autoclave (TCA) was used as the NMR resonator and pressure vessel. The well-defined, strong, and nonuniform B1 field of the TCA was used to resolve distances along the radial dimension

The Toroid Cavity Autoclave for High-Pressure and Variable-Temperature in situ Nuclear Magnetic Resonance Studies

The toroid cavity autoclave (TCA) is a coaxial nuclear magnetic resonance (NMR) resonator and high-pressure autoclave for in situNMR studies, which combines the advantages of a toroid NMR detector with the features of a cylindrical metal pressure vessel. It is designed to fit within the limited space of a standard NMR narrow-bore cryomagnet and allows for recording high resolution NMR spectra during chemical reactions under high pressure. Compounds that, for example, initiate a reaction can be injected into the reactor through a nonreturn valve even if the TCA is already pressurized. The TCA is heated by a resistive, coaxial heating arrangement that does not generate any stray magnetic field in the sample volume. Current pressure and temperature capabilities are 0–300 bar and room temperature to 150?°C, respectively. With standard 200 MHz 1H NMR experiments, signal resolution of 0.55 Hz and signal-to-noise ratios comparable to those of standard NMR probes were achieved. In a further development, the TCA is optimized for gas/liquid reactions in which gaseous components are vigorously mixed with the liquid to obtain maximum reaction rates. Applications to parahydrogen induced polarization are shown, in which the nuclear spin polarization patterns show pairwise addition of hydrogen in both liquid organic solvents and in supercritical CO2

Shift selectivity in common-aperture holography

Common-aperture holography is presented as an alternative shift multiplexing concept. We measured the shift selectivity of holograms recorded with this novel concept. The experimental results are discussed and compared to theoretical predictions calculated with the beam propagation method

Special phase mask and related data format for page-based holographic data storage systems

Random phase masks in object and reference beam of page-based holographic storage systems suppress the DC-peak and improve the overlap of both beams inside the storage material. Furthermore, they allow for a narrow shift-selectivity. In a holographic setup the phase mask has to be introduced at a conjugate image plane of the spatial light modulator (SLM), if it is not fixed directly on the SLM itself. A binary phase mask with cells generating 0 and π phase shifts has to be aligned very accurately with respect to the SLM pixels, otherwise image artifacts disturb the received data page. We present a phase mask, where the phase cells have the size of a data block which consists of a rectangular set of SLM pixels. Additionally, the corresponding data page has no data at the position of phase jumps and thus relaxes the alignment tolerance significantly