Upgrade of vacuum ultraviolet spectroscopy system on J-TEXT tokamak

The vacuum ultraviolet (VUV) spectroscopy system on the Joint Texas Experimental Tokamak has been upgraded to achieve fast acquisition for the study of impurity transport in transient modulated experiments. In this upgrade, the previous high-energy charge-coupled device detector was replaced by a microchannel plate with a CsI-coated photocathode and P43 phosphor to transform the VUV light to visible light, which is then acquired by a high-speed electron-multiplying charge-coupled device. Two-stage focusing was achieved using a reference slit plate illuminated successively by a green light source and the Lyman series hydrogen spectral lines from the vacuum-conditioning plasma. The spatial resolution was evaluated as ∼4 mm based on the level of image blurring from the alignment plate. A response time of ∼2 ms was obtained with the ten-vertical-track setup.

Measurement of the toroidal radiation asymmetry during massive gas injection triggered disruptions on J-TEXT

Disruptions have the potential to cause severe damage to large tokamaks like ITER. The mitigation of disruption damage is one of the essential issues for the tokamak. Massive gas injection (MGI) is a technique in which large amounts of a noble gas are injected into the plasma in order to safely radiate the plasma energy evenly over the entire plasma-facing wall. However, the radiated energy during the disruption triggered by massive gas injection is found to be toroidally asymmetric. In order to investigate the spatial and temporal structures of the radiation asymmetry, the radiated power diagnostics for the J-TEXT tokamak have been upgraded. The multi-channel arrays of absolute extreme ultraviolet photodiodes have been upgraded at four different toroidal positions to investigate the radiation asymmetries during massive gas injection. It is found that the toroidal asymmetry is associated with plasma properties and MGI induced MHD activities.

Measurement of diagnostic neutral beam parameters on J-TEXT

A Doppler frequency shift spectrum (DFSS) system composed of two spectrometers has been developed for the joint Texas experimental tokamak to measure diagnostic neutral beam parameters including the beam energy fractions, intensity distributions, and divergences. The beam energy fractions are derived from measurements of H-alpha (Hα) emission using collisional excitation cross sections. The beam intensity distributions are obtained using an 11-channel measurement with a reconstruction technique. The beam divergences are obtained from spectrum broadening and geometric calculations. The results of preliminary investigations indicate that the DFSS system works well and can be used to obtain all of these parameters simultaneously. According to the preliminary experiment, the one-third energy fraction has the largest proportion (about 45%) of the beam energy and the full energy fraction is about 10%. The beam diameter is about 8.1 cm at a distance of 2.04 m from the accelerator. The beam divergence angle is about 3.3°. The current beam parameters are insufficient for charge-exchange measurements.

Design of charge exchange recombination spectroscopy for the joint Texas experimental tokamak

The old diagnostic neutral beam injector first operated at the University of Texas at Austin is ready for rejoining the joint Texas experimental tokamak (J-TEXT). A new set of high voltage power supplies has been equipped and there is no limitation for beam modulation or beam pulse duration henceforth. Based on the spectra of fully striped impurity ions induced by the diagnostic beam the design work for toroidal charge exchange recombination spectroscopy (CXRS) system is presented. The 529 nm carbon VI (n = 8 - 7 transition) line seems to be the best choice for ion temperature and plasma rotation measurements and the considered hardware is listed. The design work of the toroidal CXRS system is guided by essential simulation of expected spectral results under the J-TEXT tokamak operation conditions.

Edge impurity rotation profile measurement by using high-resolution ultraviolet/visible spectrometer on J-TEXT

An upgrade of the edge rotation diagnostic system is achieved by increasing the number of viewing channels to 17 on J-TEXT tokamak. With the upgrade, the spatial resolution reaches 1 cm. The bulk plasma is used as the calibration light source. And the toroidal velocity profile of C V (carbon V) at edge region is obtained by using a spatial deconvolution technique. The valid measurement region is at ρ = 0.6-0.9, corresponding to the emitting region of C V. The preliminary experimental results express that the velocity of plasma may have a zero point near ρ = 0.85.

Improvement of the edge rotation diagnostic spectrum analysis via simulation

The edge rotation diagnostic (ERD) system has been developed on the Joint Texas Experimental Tokamak to measure the edge toroidal rotation velocity by observing the shifted wavelength of carbon V (C V 227.09 nm). Since the measured spectrum is an integrated result along the viewing line from the plasma core to the edge, a method via simulation has been developed to analyze the ERD spectrum. With the necessary parameters such as C V radiation profile and the ion temperature profile, a local rotation profile at the normalized minor radius of 0.5-1 is obtained.

Upgrade of absolute extreme ultraviolet diagnostic on J-TEXT

The absolute extreme ultraviolet (AXUV) diagnostic system is used for radiation observation on J-TEXT tokamak [J. Zhang, G. Zhuang, Z. J. Wang, Y. H. Ding, X. Q. Zhang, and Y. J. Tang, Rev. Sci. Instrum. 81, 073509 (2010)]. The upgrade of the AXUV system is aimed to improve the spatial resolution and provide a three-dimensional image on J-TEXT. The new system consists of 12 AXUV arrays (4 AXUV16ELG arrays, 8 AXUV20ELG arrays). The spatial resolution in the cross-section is 21 mm for the AXUV16ELG arrays and 17 mm for the AXUV20ELG arrays. The pre-amplifier is also upgraded for a higher signal to noise ratio. By upgrading the AXUV imaging system, a more accurate observation on the radiation information is obtained.

Measurement of the edge plasma rotation on J-TEXT tokamak

A multi-channel high resolution spectrometer was developed for the measurement of the edge plasma rotation on J-TEXT tokamak. With the design of two opposite viewing directions, the poloidal and toroidal rotations can be measured simultaneously, and velocity accuracy is up to 1 km∕s. The photon flux was enhanced by utilizing combined optical fiber. With this design, the time resolution reaches 3 ms. An assistant software "Spectra Assist" was developed for implementing the spectrometer control and data analysis automatically. A multi-channel monochromatic analyzer is designed to get the location of chosen ions simultaneously through the inversion analysis. Some preliminary experimental results about influence of plasma density, different magnetohydrodynamics behaviors, and applying of biased electrode are presented.

The vacB gene required for virulence in Shigella flexneri and Escherichia coli encodes the exoribonuclease RNase R

vacB, a gene previously shown to be required for expression of virulence in Shigella and enteroinvasive Escherichia coli, has been found to encode the 3'-5' exoribonuclease, RNase R. Thus, cloning of E. coli vacB led to overexpression of RNase R activity, and partial deletion or interruption of the cloned gene abolished this overexpression. Interruption of the chromosomal copy of vacB eliminated endogenous RNase R activity; however, the absence of RNase R by itself had no effect on cell growth. In contrast, cells lacking both RNase R and polynucleotide phosphorylase were found to be inviable. These data indicate that RNase R participates in an essential cell function in addition to its role in virulence. The identification of the vacB gene product as RNase R should aid in understanding how the virulence phenotype in enterobacteria is expressed and regulated. On the basis of this information we propose that vacB be renamed rnr.

Involvement of medullary tail-flick related neurons in descending facilitation evoked by chemical stimulation of rat lateral habenular nucleus

AIM

To study effects of sodium L-glutamate microinjection into lateral habenular nucleus (LHN) of rats on the firing of medullary tail-flick related neurons and tail-flick reflex (TF).

METHODS

Using synchronous recording of unitary neuronal discharges and TF induced by noxious heat.

RESULTS

Chemical stimulation of LHN induced an excitement of the on-cell spontaneous activity, an inhibition of the off-cell spontaneous activity with an enhancement of their TF related responses. The spontaneous firing rate of on-cells increased from 5.8 +/- 2.2 Hz to 10.9 +/- 3.4 Hz while the spontaneous firing rate of off-cells decreased from 11.8 +/- 2.2 Hz to 6.1 +/- 2.2 Hz. Meanwhile the TFL was shortened from 4.04 +/- 0.17 s to 2.97 +/- 0.13 s.

CONCLUSION

The chemical stimulation of LHN produced a facilitating action on nociceptive spinal defensive reflex. This effect is brought out by the cooperation of on- and off-cells.

[The application of artificial neural network method in diagnose and classify research on functional disease of the esophagus]

This paper applied a typical artificial neural network model, that is Back-Propagation Model, to the diagnose and classify research on functional disease of the esophagus, and achieved good results in clinical practice.

[Involvement of medullary tail-flick related neurons in the descending facilitating effects evoked by stimulation of lateral habenular nucleus]

In lightly anesthetized rats 3 classes of neurons in the rostral ventromedial medulla (RVM) were in relation to tail-flick reflex (TF) recorded, i. e. the TF triggired on-cells, the TF triggered off-cells and the non-responsive or neutral cells. When lateral habenular nucleus (LHb) was stimulated the on-cells were excited, the off-cells inhibited while the neutral cells unaffected. The fact that stimulation of LHb facilitated tail-flick reflex appears to be quite well explained by its enhancement effect on the tail-flick related response of both the on- and the off-cells. These results indicate that the facilitating action of LHb on spinal defensive reflex is probably brought out by participation of the medullary tail-flick related cell activity.

[Effects of lateral habenular stimulation on nociceptive response of neurons in rat spinal dorsal horn]

Ipsilateral stimulation of the LHb produced a significant attenuation of nociceptive response of wide dynamic range (WDR) neurons in the rat spinal dorsal horn. The inhibitory effect produced by LHb stimulation was partially blocked by systemic cyproheptadine and phentolamine but not naloxone. No significant change was observed in the activity of WDR neurons after ipsilateral electrolytical lesions of the LHb. These results suggest that the LHb participates in the supraspinal descending control on nociceptive response of WDR neurons in the spinal dorsal horn. However, tonic inhibitory mechanism seems not to be involved.

[The action of medullary tail-flick related neurons in electroacupuncture analgesia]

Three types of cells, i.e., off-neurons, on-neurons and neutral neurons, could be recorded in the rostral ventromedial medulla (RVM) in light anesthetized rats. Just prior to the occurrence of tail flick elicited by noxious heat, the on-cells showed a burst of activity while the off-cells exhibited a cessation of discharge. No change of neutral cell activity related to tail flick was observed. Electroacupuncture at two "Ci Liao" points which resulted in inhibition of tail-flick reflex affected the spontaneous activity of off- and on-cells in a different way, i.e, the discharge of most off-cells was significantly increased (P < 0.001), while that of on-cells showed no obvious change (P > 0.05). Tail-flick related responses of the both cells were inhibited. These results provide the evidence that the off-cells may be the main efferent neurons in RVM involving in electroacupuncture analgesia.

[Descending cord dorsum potentials evoked by stimulation at "Yong Quan" acupoint]

Segmental spinal cord potential (Y-sCDP) evoked by stimulation at "Yong Quan" acupoint of Sprague-Dawley rat vanished gradually when the recording electrode was moved rostrally along the dorsal surface of the spinal cord. When the recording electrode was placed more rostrally, for example at C6, another positive slow potential, Y-dCDP, could be recorded. Y-dCDP disappeared completely when the spinal cord had been sectioned at a higher cervical level. Electrolytic lesions of ventral periaqueductal gray (PAG) could also decrease remarkably the amplitude of Y-dCDP. This facet suggests that the PAG, an analgesia related nucleus, is involved in the generation of Y-dCDP induced by stimulation at "Yong Quan" acupoint.

[Field potentials evoked by stimulation of DLF in the rat spinal cord]

When stimulation of DLF at cervical cord, a train of evoked potentials are recorded with a microelectrode at lumber level in rat. The longer slow positive potential wave, latency 7.22 +/- 1.41 ms, peak time 15 +/ 12 +/- 5.58 ms, duration 93 +/ 92 +/- 9.06 ms, is called DLF-FP. The negative center of the isopotential map of DLF-FP is located at 1.0-1.3 mm below the dorsal surface nearly in coincidence with that of the P1-FP evoked by the sural nerve stimulation. The amplitude of DLF-FP was decreased by picrotoxin and increased by strychnine. Both summation and inhibition can be observed between the potentials evoked by stimulation of the sural nerve and DLF. The results mentioned above show that DLF-FP is the reflection of primary afferent depolarization probably by the same spinal circuit underlying P1-FP.

2450 MHz oesophagus applicator with multi-temperature sensors and its temperature-control equipment

A 2450 MHz microwave applicator for heating the oesophagus, complete with temperature monitoring and controlling equipment, is described. The geometrical parameters and performance in both animal experiments and clinical applications are discussed.

[Dorsal root potential evoked by stimulation of periaqueductal gray and its efferent pathway analysis in rats]

When periaqueductal gray (PAG) was stimulated with concentric electrodes, a steady negative potential called PAG-DRP was recorded from L5 dorsal root. PAG-DRP with properties of spatial and temporal summation propagates decrementally along the dorsal root and is inhibited by picrotoxin. Lesions of NRM had no effect on the PAG-DRP evoked by stimulation of dorsal PAG, but showed obvious reduction up to about 40% on the PAG-DRP evoked by stimulation of ventral PAG. It is suggested that the descending inhibition of PAG includes some presynaptic inhibition and that the ventral PAG-DRP is relayed partly via NRM while the dorsal PAG-DRP is not associated with NRM.

Evidence for two classes of nociceptive modulating neurons in the periaqueductal gray

The midbrain periaqueductal gray (PAG) and the rostral ventromedial medulla (RVM) are important links in a neuronal network that modulates nociceptive transmission. In the RVM, 2 classes of cells have been identified that show changes in activity at the time of the tail-flick response (TF) elicited by noxious heat (Fields et al., 1983a). We now report that neurons in the PAG region also show changes in activity related to TF. Extracellular recordings were made from the PAG and the ventrally adjacent tegmentum at sites from which it was possible to inhibit TF using stimulating currents of 10 microA or less. Cell activity, time of TF occurrence, and tail temperature were recorded during 5 repetitions of the heat stimulus. Periresponse and peristimulus histograms were plotted with reference to the TF and tail temperature, respectively. A significant number of neurons in the PAG region showed changes in activity that preceded the TF. "Midbrain On-cells" (13.6% of the sample) displayed an abrupt increase in firing just prior to the TF. "Midbrain Off-cells" (4.4%) paused just prior to the TF. The remaining neurons (241 of 294, or 82%) did not exhibit changes in firing prior to the TF. Thus, cells with changes in activity related to the TF are present in the PAG region as well as in the RVM. The PAG has a large projection to the RVM, and microinjection of morphine in the PAG increases activity of RVM Off-cells and decreases that of RVM On-cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphine microinjected into the periaqueductal gray has differential effects on 3 classes of medullary neurons

The effects of microinjection of 5-10 micrograms of morphine into the midbrain periaqueductal gray (PAG) on the activity of neurons in the rostral ventral medulla (RVM) were studied in lightly anesthetized rats. Based on the relationship between changes in neuronal activity and the occurrence of the tail-flick reflex (TF), RVM neurons were divided into 3 groups: off-cells, on-cells and neutral cells. The off-cells exhibited an abrupt pause and the on-cells an acceleration beginning just prior to the occurrence of the TF. Neutral cell firing did not change at the time of the TF. Microinjections of morphine into the PAG which inhibited the TF had differential effects on the spontaneous activity of the 3 groups of neurons in RVM. Off-cells showed an increase and on-cells a decrease in spontaneous activity which preceded the inhibition of the TF. These microinjections also reduced the TF-related responses of off- and on-cells. The effects on cell activity were reversed by systemically administered naloxone and were not seen following microinjections which failed to block the TF. Neutral cell activity was unchanged following microinjection of morphine into the PAG. These results support the hypothesis that off- and on-cells in the RVM mediate the effects of microinjection of morphine into the PAG on spinal nociceptive reflexes.