Design and implementation of fractional order pole placement controller to control the magnetic flux in Damavand tokamak.

In this paper, a routine algorithm is presented to design a fractional order controller for tracking the reference model. Using this algorithm, a pole placement controller can be designed by assigning the desired integer and fractional order closed loop transfer functions. Considering the desired time response and using the generalized characteristic ratio assignment (CRA) method for fractional order systems and coefficient diagram method (CDM) for integer order systems, the desired closed loop system can be achieved. For various practical experiments, having the desired time responses is vital for magnetic flux in Damavand tokamak. To approach this, at first, the desired reference models are obtained based on CRA and CDM methods. After that, a fractional order pole placement controller is designed and simulated by this algorithm. At last, this controller is implemented on a digital signal processor to control the vertical magnetic flux of Damavand tokamak plant. The practical results show the satisfactory performance of the controller.

Study of runaway electrons using dosimetry of hard x-ray radiations in Damavand tokamak.

In this work several studies have been conducted on hard x-ray emissions of Damavand tokamak based on radiation dosimetry using the Thermoluminescence method. The goal was to understand interactions of runaway electrons with plasma particles, vessel wall, and plasma facing components. Total of 354 GR-200 (LiF:Mg,Cu,P) thermoluminescence dosimeter (TLD) crystals have been placed on 118 points--three TLDs per point--to map hard x-ray radiation doses on the exterior of the vacuum vessel. Results show two distinctive levels of x-ray radiations doses on the exterior of the vessel. The low-dose area on which measured dose is about 0.5 mSv/shot. In the low-dose area there is no particular component inside the vessel. On the contrary, on high-dose area of the vessel, x-ray radiations dose exceeds 30 mSv/shot. The high-dose area coincides with the position of limiters, magnetic probe ducts, and vacuum vessel intersections. Among the high-dose areas, the highest level of dose is measured in the position of the limiter, which could be due to its direct contact with the plasma column and with runaway electrons. Direct collisions of runaway electrons with the vessel wall and plasma facing components make a major contribution for production of hard x-ray photons in Damavand tokamak.

Design of set-point weighting PIλ + Dµ controller for vertical magnetic flux controller in Damavand tokamak.

In this paper, a simple method is presented for tuning weighted PI(λ) + D(µ) controller parameters based on the pole placement controller of pseudo-second-order fractional systems. One of the advantages of this controller is capability of reducing the disturbance effects and improving response to input, simultaneously. In the following sections, the performance of this controller is evaluated experimentally to control the vertical magnetic flux in Damavand tokamak. For this work, at first a fractional order model is identified using output-error technique in time domain. For various practical experiments, having desired time responses for magnetic flux in Damavand tokamak, is vital. To approach this, at first the desired closed loop reference models are obtained based on generalized characteristic ratio assignment method in fractional order systems. After that, for the identified model, a set-point weighting PI(λ) + D(µ) controller is designed and simulated. Finally, this controller is implemented on digital signal processor control system of the plant to fast/slow control of magnetic flux. The practical results show appropriate performance of this controller.

Identification and control of plasma vertical position using neural network in Damavand tokamak.

In this work, a nonlinear model is introduced to determine the vertical position of the plasma column in Damavand tokamak. Using this model as a simulator, a nonlinear neural network controller has been designed. In the first stage, the electronic drive and sensory circuits of Damavand tokamak are modified. These circuits can control the vertical position of the plasma column inside the vacuum vessel. Since the vertical position of plasma is an unstable parameter, a direct closed loop system identification algorithm is performed. In the second stage, a nonlinear model is identified for plasma vertical position, based on the multilayer perceptron (MLP) neural network (NN) structure. Estimation of simulator parameters has been performed by back-propagation error algorithm using Levenberg-Marquardt gradient descent optimization technique. The model is verified through simulation of the whole closed loop system using both simulator and actual plant in similar conditions. As the final stage, a MLP neural network controller is designed for simulator model. In the last step, online training is performed to tune the controller parameters. Simulation results justify using of the NN controller for the actual plant.

Runaway electron energy measurement using hard x-ray spectroscopy in "Damavand" tokamak.

Set of experiments has been developed to study existing runaway electrons in "Damavand" tokamak plasma upon characteristics of hard x-ray emissions produced by collision of the runaway electrons with the plasma particles and limiters. As a first step, spatial distribution of hard x-ray emissions on the equatorial plane of the torus was considered. Obtained spectra of hard x-ray emissions for different alignments of shielded detector indicate isotropic emissivity in the equatorial plane. This is in agreement with wide angle cone of bremsstrahlung radiations, deduced from the mean value of energy of the runaway electrons. The mean energy was calculated from the slope of the energy spectrum of hard x-ray photons. In the second stage in order to investigate time evolution of energy of the runaway electrons, similar technique were applied to obtain hard x-ray energy in every 3 ms intervals, from the beginning to the end of plasma. The mean energy of the runaway electrons increases during the ramp up phase and reaches its maximum between 3 and 9 ms after plasma formation. Also considering the time dependence of the counted photons in each energy range shows that energetic photons are emitted during the ramp up phase of the plasma current in Damavand tokamak.

Spontaneous kidney allograft rupture.

Spontaneous renal allograft rupture is one of the most dangerous complications of kidney transplantation, which can result in graft loss. This condition needs immediate surgical intervention. Conservative management has dismal results. Its prevalence varies from 0.3% to 3%. Rupture occurs in first few weeks after transplantation. Predisposing factors for graft rupture are acute rejection, acute tubular necrosis, and renal vein thrombosis. There are growing reports about successful results of repairing these ruptured kidneys. In this study, we reviewed the medical records of 1682 patients who received kidney allografts from living donors from 1986 through 2003. There were six (0.35%) cases of renal allograft rupture. All were preceded by acute graft rejection. They were treated with antirejection medications. In first three cases, the kidney allografts were removed because the procedure of choice in this situation is graft nephrectomy; but in three next cases we repaired the ruptured grafts with good results in two of them. In conclusion, the procedure of choice for kidney allograft rupture is graft repair.

Modified phacotrabeculectomy with Crozafon punch.

We retrospectively evaluated the results of combined phacoemulsification and trabeculectomy by analyzing 22 consecutive operations. A "Crozafon punch" was used to perform the trabeculectomy through the sclerocorneal tunnel. The mean follow-up period was 6 months. Visual acuity of 0.5 or better was achieved in 18 eyes (82%). Intraocular pressure control was achieved in 18 eyes without medication, 4 eyes required a beta-blocking agent. The complication rate was low.