Graphite Probe Research Articles

Striations in a radio frequency hydrogen discharge tube: Optical emission plasma diagnostics and Raman analysis of in situ graphite probes

Striations in a radio frequency hydrogen discharge tube: Optical emission plasma diagnostics and Raman analysis of <i>in situ</i> graphite probes

The influence of mercury vapor on the electrical resistance of chalcogenide amorphous films

Using the planar structures "Ni layer - chalcogenide amorphous film - Ni layer" and "graphite probe - chalcogenide amorphous film graphite probe" samples, the influence of mercury vapor on the electrical resistance of amorphous films of the Se-Te, Se-Sb and Se-As systems was investigated. It was established that exposure of samples in mercury vapor leads to a decrease in their electrical resistance by 4-7 orders of magnitude. As the temperature and mercury concentration increase, the transition time from a high-resistance state to a low-resistance state decreases. When introducing Te, Sb, and As into amorphous selenium and increasing their concentration in the composition of the films, the transition time increases, and the value of the change in resistance decreases. It was established that the change in resistance is mainly determined by the change in surface conductivity of chalcogenide films. A decrease in the electrical resistance of selenium-containing amorphous films modified with mercury is caused by the formation of HgSe crystalline inclusions in their matrix.

Design and first result of combined Langmuir-magnetic probe on J-TEXT tokamak

In order to measure boundary electrostatic and magnetic fluctuations simultaneously, a combined Langmuir-magnetic probe (CLMP) has been designed and built on joint-Texas experimental tokamak. The probe consists of 8 graphite probe pins and a 3D magnetic probe, driven by a mechanical pneumatic device. By means of simulation, the shielding effect of the graphite sleeve on the magnetic fluctuation signal is explored, and the influence of the eddy current was reduced by cutting the graphite sleeve. In the experiment, it has been verified that the mutual inductance of electromagnetic signals can be ignored, and a 70–90 kHz electromagnetic mode is observed around the last closed magnetic surface. The establishment of CLMP provides data for the exploration of the coupling of electrostatic and magnetic fluctuations.

Thermo-mechanical limits of a magnetically driven fast-ion loss detector in the ASDEX Upgrade tokamak

A real-time control system is being developed for a magnetically driven Fast-Ion Loss Detector (FILD) at the ASDEX Upgrade tokamak. The insertion of the diagnostic head will be adjusted in real-time to react to changes in the graphite head temperature, plasma position and appearance of MHD instabilities. The graphite probe head of the detector is exposed to an intense heat flux (located ∼3–5 cm from separatrix). The control algorithm performance is constrained by: the graphite head sublimation temperature, the ultimate stress limit, the reaction time of the controller and the retraction time. In this work, the temperature and thermal induced stress distribution on the probe head are assessed to determine what temperature-related magnitude is the limiting factor. The heat flux at the probe head has been estimated using the time-averaged parallel heat flux measured at the divertor target via infrared thermography. A field line tracing algorithm determines which regions of the probe head receives a weighted heat flux due to shadowing (self-induced or from other structures) and the incidence angle of the field lines. A finite element model is used to simulate the temporal evolution of the graphite head temperature and to obtain the induced thermal stress. The temperature spatial distribution at the probe head is validated against measurements of the probe head for different FILD systems showing a good agreement. These measurements have been obtained from visible cameras with an infrared filter. The model concludes that the maximum stress (∼100 MPa) does not overcome the graphite mechanical limit (170 MPa) and that the probe head is not affected by fatigue. Therefore, the graphite sublimation temperature (2000 °C) is set as the limiting factor of the new control system.

Error analysis and cazlibration of Langmuir probes embedded in ITER-like tungsten divertor on EAST

• The measuring error of divertor Langmuir probes is huge due to the ablation on EAST. • A model is proposed to fit the effective collection area of the probe-tip. • The new method is suitable for calibration of the Div-LPs data in most discharges. The divertor Langmuir probes (Div-LPs) system is a key diagnostic for measuring divertor plasma parameters in tokamaks. The accuracy of the measurement is the basis of physical researches. However, the excessive heat load on the target plates may lead to serious ablation of graphite probe tips, especially during long-pulse operation or unmitigated disruptions. In order to evaluate the data uncertainty caused by ablation, a statistical study has been made based on the Ohmic discharges in the EAST (Experimental Advanced Superconducting Tokamak) 2018 experiment campaign. The results show that for the discharges with the same plasma parameters, the peak particle flux of upper outer divertor measured by Div-LPs becomes several times smaller as the discharge progresses in a long experimental campaign, which is mainly due to that the effective collection area of the ablated probe tip becomes smaller and smaller. To quantitatively calculate the decrease of the effective area of the probe tip, the physical quantity of accumulated injection energy is introduced. A simple model is proposed and used to characterize the relationship between the effective collection area and the total accumulated injection energy. In addition, arbitrary H-mode discharges are selected to verify the model. By comparing the calibrated data of Div-LPs with other diagnostics, it is found that the model is also suitable for H-mode discharges with the strike point near the frequently-used-SP, and thereby the uncertainty after calibration is significantly reduced. In the future, the method will be employed for Div-LPs data processing near the strike point on EAST, which will facilitate further researches on divertor physics.

Dissolution and Online Monitoring of Nd and Pr Oxides in NdF3–PrF3–LiF Electrolytes

Concentrations of dissolved rare earth metal oxides, Nd2O3, and Pr2O3 or their mixtures in different fluoride electrolytes composed of NdF3, PrF3, and LiF at ca. 1040 °C were monitored using a graphite probe inserted into the electrolyte during the dissolution process. Fast voltage sweeps of 100 V/s were applied to the graphite probe, and the current response was measured. As the oxide concentration in the diffusion layer towards the electrode depletes, a passive layer is, at a certain point, formed on the probe, resulting in a current drop. The magnitude of the peak current attained before the formation of the passive layer reflects the concentration of the dissolved oxide and, thus, is applied to determine the oxide concentration. The oxide concentration in the electrolyte samples determined using the inert gas fusion technique showed a good correlation to the peak current determined by the probe.

Diamond-Coated Plasma Probes for Hot and Hazardous Plasmas.

Plasma probes are simple and inexpensive diagnostic tools for fast measurements of relevant plasma parameters. While in earlier times being employed mainly in relatively cold laboratory plasmas, plasma probes are now routinely used even in toroidal magnetic fusion experiments, albeit only in the edge region, i.e., the so-called scrape-off layer (SOL), where temperature and density of the plasma are lower. To further avoid overheating and other damages, in medium-size tokamak (MST) probes are inserted only momentarily by probe manipulators, with usually no more than a 0.1 s per insertion during an average MST discharge of a few seconds. However, in such hot and high-density plasmas, their usage is limited due to the strong particle fluxes onto the probes and their casing which can damage the probes by sputtering and heating and by possible chemical reactions between plasma particles and the probe material. In an attempt to make probes more resilient against these detrimental effects, we tested two graphite probe heads (i.e., probe casings with probes inserted) coated with a layer of electrically isolating ultra-nano-crystalline diamond (UNCD) in the edge plasma region of the Experimental Advanced Superconducting Tokamak (EAST) in Hefei, People’s Republic of China. The probe heads, equipped with various graphite probe pins, were inserted frequently even into the deep SOL up to a distance of 15 mm inside the last closed flux surface (LCFS) in low- and high-confinement regimes (L-mode and H-mode). Here, we concentrate on results most relevant for the ability to protect the graphite probe casings by UNCD against harmful effects from the plasma. We found that the UNCD coating also prevented almost completely the sputtering of graphite from the probe casings and thereby the subsequent risk of re-deposition on the boron nitride isolations between probe pins and probe casings by a layer of conductive graphite. After numerous insertions into the SOL, first signs of detachment of the UNCD layer were noticed.

Cadmium separation in human biological samples based on captopril-ionic liquid paste on graphite rod before determination by electrothermal atomic absorption spectrometry

A mixture of captopril nanoparticles (CAP-NPs) and ionic liquid (IL, [HMIM] [PF6]) paste on micro graphite rod (CAP-IL-MGR) and was used for separation cadmium in human serum and urine samples by micro solid phase extraction (μ-SPE). 0.01 g of CAP-NPs and 0.1 g of [HMIM] [PF6] mixed with 1 mL of acetone and mixture passed physically on micro graphite rod (MGR) at 55oC. Then, the graphite probe placed on 10 mL of human biological samples with 5 min of sonication, then cadmium ions complexed by thiol group of captopril (CAP-SH) at pH=5.5. The cadmium ions on micro probe were back extracted with 0.25 mL of nitric acid (0.5 M) which was diluted with DW up to 0.5 mL and finally, the cadmium concentration determined by ET-AAS. By optimizing of amount of captopril, the absorption capacity and recovery were obtained 132.4 mg g-1 and more than 96%, respectively.

Density effects of silica aerogel insulation on the performance of a graphite probe calorimeter.

With the introduction of a novel graphite probe calorimeter, called the Aerrow, various thermal insulating materials are being explored to further improve the device. Silica-based aerogels are proving to be an optimal material due to their low densities, small thermal conductivities, rigidity, and machinability. The aim of this work is to determine how various silica aerogel densities affect the Aerrow's performance. Performance concerns three areas: heat transfer from the core, the Aerrow's beam quality dependence, and the effects of an applied magnetic field on its measurement of absorbed dose to water. A numerical heat transfer study was done to determine heat transfer time constants. The EGSnrc radiation transport toolkit was used to determine absorbed dose conversion factors which are used to quantify the Aerrow's beam quality dependence. Dose conversion factors for Cobalt-60 and two clinical photon beams (6 and 10MV) were determined. Magnetic field perturbation factors are used to characterize the Aerrow's performance under an applied magnetic field. EGSnrc with the magnetic field transport algorithm was used to determine these perturbations for a 1.5T MR-linac. Several aerogel densities (0.01-0.55g ) were examined for each performance area. Heat transfer time constants were found to vary from 52±2 to 117.4±0.4s. The time constants decreased with increasing aerogel density. The Aerrow's beam quality dependence varied between 0.5% and 1%, decreasing with increasing aerogel density. Beam quality dependence was determined in the range of Co to 10MV (58.4% ≤ ≤73.5%). Under an applied magnetic field, perturbations were smallest when the Aerrow was parallel to the field. Perturbations varied more so when the Aerrow was perpendicular to the magnetic field and increased with increasing aerogel density. In all cases, perturbations were less than 0.6% from unity with a relative uncertainty of 0.1%. Silica-based aerogels demonstrate an improved performance over thermal insulation used in previous iterations of the Aerrow. With it, the Aerrow has shown to be robust in several areas. If heat transfer can be properly corrected for in the dose determination and the parallel orientation is used under a magnetic field, then the high density aerogel is possibly more preferable.

Cuprous oxide/cadmium stannate heterojunction diodes obtained by dip-coating method

The fabrication of p-n heterojunction diodes using semiconducting metal-oxides obtained from a solution-based method was investigated. Initially, n-type transparent cadmium stannate (Cd2SnO4) conducting films were deposited by the dip-coating method on glass substrates. The films were sintered in air for 1 h at 550 °C and annealed in vacuum for 10 min at 550 °C. A low resistivity value was obtained (ρ ≈ 2 × 10−3 Ω-cm) for films with average thickness of ∼ 380 nm. For the p-type layer, cupric oxide (CuO) was deposited using the dip-coating method over the transparent conductive oxide. Several layers were deposited and a drying process in air was applied at 250 °C for each coating. CuO thickness (τ) was in the 49–270 nm range as the number of coats varied from 5 to 14. After that, the samples were subjected to a rapid thermal annealing treatment (RTA) in vacuum during 10 min at a temperature TA, within the 300 °C ≤ TA ≤ 450 °C range, depending on τ, to reduce the CuO phase into the cuprous oxide (Cu2O) phase. Cu2O has shown a better crystalline quality and lower resistivity than CuO, obtaining a more efficient charge transport. From the X-ray diffraction patterns obtained from the heterojunction, the presence of Cd2SnO4 is confirmed. The CuO layer after RTA treatment shows three different types of films, depending on both TA and τ: i) CuO (amorphous)+Cu2O, ii) Cu2O and iii) Cu2O + Cu. Specular reflectance measurements were performed to show the presence of amorphous CuO and to confirm the full transformation from CuO to Cu2O. Current-voltage measurements were performed using silver paste on Cd2SnO4 and a graphite probe on the copper oxide layer, as ohmic contacts. All heterojunctions with a copper oxide layer of ∼ 49 nm, show an ohmic behavior. For higher τ, independent of the type of copper oxide film, a rectifying behavior is shown, which improves as τ increases and only the Cu2O phase is obtained. Best rectification is achieved in samples with ∼ 270 nm of Cu2O at TA = 425 °C. In this work, as far as we know, for first time Cu2O/Cd2SnO4 diodes were fabricated using the dip-coating method. The electrical parameters for the best rectification were: ideality factor (n = 4.8), saturation current density (J0 = 3.20 × 10−5 A/cm2) and turn-on voltage (Vto = 1.1 V).

Recurrence quantification analysis to estimating surface roughness in finish turning processes

Surface roughness is one of the important factors in all areas of tribology and in evaluation of the quality of machining operations such as turning, milling, or grinding. This paper describes a method for in-process estimation of workpiece surface roughness in a turning process from acoustic emission signals generated by the sliding friction between a graphite probe and the workpiece. Acoustic emission signals are first transformed into recurrence plots and from these plots computed are a set of recurrence statistics using the recurrence quantification analysis. The surface roughness parameters are estimated using an artificial neural network, taking the recurrence statistics of the acoustic emission signals as inputs. This method is verified by conducting an extensive set of experiments on AISI 1054 steel workpiece and K420 grade uncoated carbide inserts. Three surface roughness parameters, namely arithmetic mean (Ra), maximum peak-to-valley roughness (Rmax), and mean roughness depth (Rz) are estimated. The estimation accuracy of the proposed method is in the range of 90.13 to 91.26 %. The merit of the proposed method lies in its ability to circumvent the limitations of the existing optical and induction-based techniques which are hampered by the rotation of the workpiece, presence of coolants, and interference of chips. Furthermore, these accurate results indicate that the proposed surface roughness estimation method is very effective and amenable for practical implementation.

WE-AB-BRB-01: Development of a Probe-Format Graphite Calorimeter for Practical Clinical Dosimetry: Numerical Design Optimization, Prototyping, and Experimental Proof-Of-Concept

Purpose: In this work, the feasibility of performing absolute dose to water measurements using a constant temperature graphite probe calorimeter (GPC) in a clinical environment is established. Methods: A numerical design optimization study was conducted by simulating the heat transfer in the GPC resulting from irradiation using a finite element method software package. The choice of device shape, dimensions, and materials was made to minimize the heat loss in the sensitive volume of the GPC. The resulting design, which incorporates a novel aerogel-based thermal insulator, and 15 temperature sensitive resistors capable of both Joule heating and measuring temperature, was constructed in house. A software based process controller was developed to stabilize the temperatures of the GPC’s constituent graphite components to within a few 10’s of µK. This control system enables the GPC to operate in either the quasi-adiabatic or isothermal mode, two well-known, and independent calorimetry techniques. Absorbed dose to water measurements were made using these two methods under standard conditions in a 6 MV 1000 MU/min photon beam and subsequently compared against TG-51 derived values. Results: Compared to an expected dose to water of 76.9 cGy/100 MU, the average GPC-measured doses were 76.5 ± 0.5 and 76.9 ± 0.5 cGy/100 MU for the adiabatic and isothermal modes, respectively. The Monte Carlo calculated graphite to water dose conversion was 1.013, and the adiabatic heat loss correction was 1.003. With an overall uncertainty of about 1%, the most significant contributions were the specific heat capacity (type B, 0.8%) and the repeatability (type A, 0.6%). Conclusion: While the quasi-adiabatic mode of operation had been validated in previous work, this is the first time that the GPC has been successfully used isothermally. This proof-of-concept will serve as the basis for further study into the GPC’s application to small fields and MRI-linac dosimetry. This work has been supported in part by the CREATE Medical Physics Research Training Network of the Natural Sciences and Engineering Research Council (NSERC) grant 432290, NSERC grants RGPIN 298191 & 435608-13, Canadian Institutes of Health Research doctoral scholarship GSD-121793. This work has also been supported by Sun Nuclear Corporation.

TH-C-19A-02: Characterization of An Actively Controlled Graphite Probe Calorimeter

Purpose: To construct and experimentally evaluate the performance of a miniature probe-format graphite calorimeter (GPC) with built-in active control. The GPC is the first ever calorimeter designed specifically for routine clinical use. Methods: The original GPC design, developed as part of our previous work, was modified to accommodate a micro-thin, resistive heating element and sensing thermistors embedded in the outermost graphite layer. A software-based process control loop was written to maintain a predefined set point temperature throughout the detector by precisely modulating the current flowing through the resistive element. Continuous feedback is provided to the controller by the additional thermistors. A functioning prototype was constructed in-house and operated in adiabatic mode in a 6 MV photon beam. Ten sets of measurements of varying duration (10 to 60 seconds) and repetition rate (200 to 600 MU/min) were analyzed. Reproducibility, linearity and dose rate dependence were assessed. Results: A total of 47 individual measurements were performed using the active GPC. The reproducibility, defined here as the sample standard deviation weighted across all 10 measurement sets, was found to be 0.37%. Similarly, the standard error (type A uncertainty) was 0.17%. Linearity was quantified by plotting signal as a function of monitor units delivered at 600 MU/min. The adjusted R-square of the resulting linear fit was 0.9996. Dose rate dependence, evaluated as the change in normalized response (signal/MU) as a function of repetition rate, was found to be statistically insignificant. Conclusions: The incorporation of active control has resulted in a marked improvement in the GPC's reproducibility and it allows the user to now perform measurements within minutes of setup. With this refinement, it is estimated that the overall standard uncertainty in the absolute determination of dose to water is 1%, making the GPC comparable to a calibrated ionization chamber. This research has received financial support from Sun Nuclear Corporation.

Ultra‐Trace Silver Determination in Biological and Water Samples by Electrothermal Atomic Absorption Spectrometry after Electrodeposition on a Graphite Probe

AbstractA rapid and simple procedure was developed for selective and sensitive determination of ultra‐trace silver in biological and environmental samples using the electrodeposition on a graphite probe modified with palladium followed by electrothermal atomic absorption spectrometry. Several experimental parameters for the electrodeposition, such as deposition potential, electrolyte concentration, pH of solution and deposition time were optimized. The calibration graph after preconcentration was linear in the range of 10‐250 ngL−1 with correlation coefficient of 0.9989 under the optimum conditions for procedure. The limits of detection (LOD) and quantification (LOQ) base on (3σ) and (10σ) were 2.8 ngL−1 and 9.4 ngL−1 respectively. Related standard deviation (RSD) for eight replicate measurements of 100 ngL−1 silver was 4.3%. Samples were digested completely in a closed microwave digestion system using only perchloric acid, and interference owing to various cations was also investigated. The proposed procedure was successfully applied to determine silver in blood, urine and some environmental samples with satisfactory analytical results.

Development of a graphite probe calorimeter for absolute clinical dosimetry

The aim of this work is to present the numerical design optimization, construction, and experimental proof of concept of a graphite probe calorimeter (GPC) conceived for dose measurement in the clinical environment (U.S. provisional patent 61∕652,540). A finite element method (FEM) based numerical heat transfer study was conducted using a commercial software package to explore the feasibility of the GPC and to optimize the shape, dimensions, and materials used in its design. A functioning prototype was constructed inhouse and used to perform dose to water measurements under a 6 MV photon beam at 400 and 1000 MU∕min, in a thermally insulated water phantom. Heat loss correction factors were determined using FEM analysis while the radiation field perturbation and the graphite to water absorbed dose conversion factors were calculated using Monte Carlo simulations. The difference in the average measured dose to water for the 400 and 1000 MU∕min runs using the TG-51 protocol and the GPC was 0.2% and 1.2%, respectively. Heat loss correction factors ranged from 1.001 to 1.002, while the product of the perturbation and dose conversion factors was calculated to be 1.130. The combined relative uncertainty was estimated to be 1.4%, with the largest contributors being the specific heat capacity of the graphite (type B, 0.8%) and the reproducibility, defined as the standard deviation of the mean measured dose (type A, 0.6%). By establishing the feasibility of using the GPC as a practical clinical absolute photon dosimeter, this work lays the foundation for further device enhancements, including the development of an isothermal mode of operation and an overall miniaturization, making it potentially suitable for use in small and composite radiation fields. It is anticipated that, through the incorporation of isothermal stabilization provided by temperature controllers, a subpercent overall uncertainty will be achieved.

Sci-Thur PM: YIS - 09: Development of a graphite probe calorimeter for absolute clinical dosimetry: Numerical design optimization, prototyping and experimental proof-of-concept.

In this work, the feasibility of absolute dose to water measurements using a small-scale graphite probe calorimeter (GPC) in a clinical environment is established. A numerical design optimization study was conducted by simulating the heat transfer in the GPC resulting from irradiation using a finite element method software package. The choice of device shape, dimensions and materials was made to minimize the heat loss in the sensitive volume of the GPC. The resulting design, which incorporates a novel aerogel-based thermal insulator, was built in-house. Absorbed dose to water measurements were made under standard conditions in a 6 MV 1000 MU/min photon beam and subsequently compared against TG-51 derived values. The average measured dose to water was 95.7 ±1.4 cGy/100 MU, as compared to an expected value of 96.6 cGy/100 MU. The Monte Carlo-calculated graphite to water dose conversion factor was 1.099, while the derived heat loss correction factors varied between 1.005 and 1.013. The most significant sources of uncertainty were the repeatability (type A, 1.4%) and thermistor calibration (type B, 2.1%). The contribution of these factors to the overall uncertainty is expected to decrease significantly upon the implementation of active thermal stabilization provided by a temperature controller and direct electrical calibration, respectively. This work demonstrates the feasibility of using the GPC as a practical clinical absolute photon dosimeter and will serve as the basis for a miniaturized version applicable to small and composite fields.

Electrothermal atomic absorption spectrometry with two-step probe atomization and primary absorption signal feedback

A method is proposed to reduce the relative detection limits for elements in an atomic absorption spectrometer with a graphite furnace and two-step probe atomization, based on using feedback between the absorption impulse of primary sample atomization and probe fixation in the position for vapor fractionation. Deposition of sample fractions on the probe, which interferes with measuring the analytical signal, is reduced. The relative limits of the direct detection of Pb, Cd, and Tl in NaCl and K2SO4 are lowered by more than one order of magnitude in comparison to the atomization of such salts under the conditions of a temperature-stabilized furnace with a platform. The detection limits are 10−7 to 10−8 wt %. The relative standard deviation of the analytical signals does not exceed 5%, which is appropriate for the measurement of concentration.

TH-E-BRB-07: Developing a Graphite Probe Calorimeter for Accurate Clinical Dosimetry

Purpose: To optimally design, construct and validate an innovative graphite probe calorimeter (GPC), comparable in size to a 0.6 cm3 cylindrical ionization chamber, for use as an absolute clinical dosimeter. Methods: A numerical finite element method (FEM) based heat transfer study was conducted using COMSOL Multiphysics® to explore the feasibility of the GPC and to optimize its design in terms of shape, dimensions and materials. Through the use of a novel aerogel-based material as the thermal insulation between the graphite bodies, the portability and robustness of the GPC design is made suitable for routine clinical use. A functioning prototype was constructed in-house and used to perform dose to water measurements under a 6 MV stereotactic radiosurgery (1000 MU/min) photon beam from a Novalis Tx, under reference conditions. Heat loss correction factors were determined using FEM analysis and graphite to water absorbed dose conversion factors were calculated using Monte Carlo techniques. Results: The dose to water measurements agreed well with the TG-51 derived values, with an average measured dose output of 95.7 (s = 1.4) cGy/100 MU, compared to an expected output of 96.6 cGy/100 MU. Heat loss correction factors ranged between 1.005 and 1.013, while the graphite to water dose conversion factor was 1.099. The combined relative uncertainty was estimated at 2.7%, with the largest contributions being the repeatability (type A, 1.4%) and thermistor calibration (type B, 2.1%). Conclusions: This proof of concept demonstrates the feasibility of using the GPC as a practical clinical absolute photon dosimeter and lays the foundation for a miniaturized version suitable for small and composite field dosimetry. It is expected that through active thermal stabilization provided by a temperature controller and electrical calibration, the uncertainty due to repeatability and calibration will be decreased, such that the overall uncertainty is better than 1%. This work has been supported in part by Grant RGPIN 298191 of the Natual Sciences and Engineering Research Council of Canada (NSERC). J.R. is a recipient of a NSERC M.Sc. scholarship.

Development of hollow anode penning ion source for laboratory application

The research work presented here focuses for the development of miniature penning type ion source. One hollow anode penning type ion source was developed in our laboratory. The size of the ion source is 38 mm diameter and 55 mm length. The ion source consists of two cathodes, a hollow anode and one piece of rare earth permanent magnet. The plasma was created in the plasma region between cathodes and the hollow anode. The J × B force in the region helps for efficient ionization of the gas even in the high vacuum region∼1×10 −5 Torr. The ions were extracted in the axial direction with help of the potential difference between the electrodes and the geometry of the extraction angle. The effect of the extraction electrode geometry for efficient extraction of the ions from the plasma region was examined. This ion source is a self extracted ion source. The self extracted phenomena reduce the cost and the size of the ion source. The extracted ion current was measured by a graphite probe. An ion current of more than 200 μA was observed at the probe placed 70 mm apart from the extraction electrode. In this paper, the structure of the ion source, effect of operating pressure, potential difference and the magnetic field on the extracted ion current is reported.

Li collection experiments on T-11M and T-10 in framework of Li closed loop concept

The concept of a steady state tokamak with plasma facing components (PFC) on the basis of liquid lithium circulation demands the decision of three tasks: lithium injection to the plasma, lithium ions collection before their deposition on the vacuum vessel and lithium returning to the injection zone. Main subject of paper is the investigations of Li collection by different types of limiters intersected the scrape-of-layer (SOL) in T-10 and T-11M tokamaks. For finding solution for this problem in T-11M and T-10, experiments have been applied with Li-, C-rail limiters and ring SS R-limiter-collector (T-11M). The efficiency of Li collection by limiters in T-11M and T-10 tokamaks was investigated by post mortem sample–witness analysis and (T-11M) by the use of the mobile graphite probe (limiter) as a recombination target in the stream of lithium ions. The characteristic depth of lithium penetration in the SOL area of T-11M is about 2cm and 4cm in SOL of T-10. The quantitative analysis of the sample–witnesses located on T-11M limiters showed that 60±20% of the lithium injected during plasma operating of T-11M had been collected by limiters. It confirms an opportunity of the lithium ions collection by limiters in tokamak SOL.