Hyunsun Han

Laparoscopic Hepatectomy for a Modified Right Graft in Adult-to-Adult Living Donor Liver Transplantation

BACKGROUND We performed a modified right hepatectomy completely by laparoscopic techniques preserving the middle hepatic vein (MHV) branches in adult-to-adult living donor liver transplantation (LDLT). PATIENTS AND METHODS Two young women (24 and 25 years old) volunteered to be live donors for their parents who had hepatocellular carcinomas. As the donors expressed concerns about scarring, we performed a laparoscopic procedure using a hand port device. Mobilization of the right liver and the hepatic parenchymal transection were performed under pneumoperitoneum. Parenchymal transection was performed using a laparoscopic ultrasonic aspirator without the Pringle maneuver. During parenchymal transection, major MHV branches >5 mm were preserved using Hem-o-lock clips. The graft was extracted through the hand port site. On the back table, the 3 MHV branches were reconstructed using an artificial vascular graft. The livers were transplanted without complications. RESULTS The operative times for the donors were 765 and 898 minutes. The donors did not require transfusions or reoperation; they were discharged on postoperative days 10 and 14 with normal liver functions. CONCLUSION A hepatectomy performed completely by laparoscopic techniques for a right graft with preservation of the MHV branches was technically feasible.

Numerical simulation on edge localized mode control capability of resonant magnetic perturbation in the KSTAR tokamak

Numerical simulations are carried out to investigate the applicability of resonant magnetic perturbation (RMP) to KSTAR plasmas for a possible control of edge localized mode (ELM) to suppress or mitigate its damages to divertor materials. For the verification of the feasibility of RMP application, magnetic island configurations, resonant normal fields, magnetic island widths and Chirikov parameters are calculated for two types of KSTAR operation scenarios: steady state and hybrid. Field error correction (FEC) coils in KSTAR are considered to produce externally perturbed magnetic fields for RMP, and the directions of coil currents determine the toroidal mode n and the parity (even or odd). The RMP configurations are described by vacuum superposition of the equilibrium magnetic fields and the perturbed ones induced by FEC coils. The numerical simulations for n = 2 toroidal mode in both operation scenarios show that when the pitches of the equilibrium and perturbed magnetic fields are well aligned, magnetic islands are formed for a series of m poloidal modes and the adjacent islands are overlapped to generate a stochastic layer in the edge region. Even parity turns out to be more effective in making the magnetic islands overlapped to become stochastic field lines in the steady-state operation, while odd parity in the hybrid operation. The formation of the stochastic layer is verified by the calculated Chirikov parameters, which also give basic information on the current requirement of FEC coils. Additionally, lobe structures of stochastic field lines are found in the edge region extended to the divertor plate in the hybrid scenario. Based on the standard vacuum criteria for RMP, the simulation results indicate that the FEC coils will be feasible for control of ELMs and mitigation of divertor heat load by RMP in both steady-state and hybrid operation scenarios.

Predictive modeling of pedestal structure in KSTAR using EPED model

A predictive calculation is given for the structure of edge pedestal in the H-mode plasma of the KSTAR (Korea Superconducting Tokamak Advanced Research) device using the EPED model. Particularly, the dependence of pedestal width and height on various plasma parameters is studied in detail. The two codes, ELITE and HELENA, are utilized for the stability analysis of the peeling-ballooning and kinetic ballooning modes, respectively. Summarizing the main results, the pedestal slope and height have a strong dependence on plasma current, rapidly increasing with it, while the pedestal width is almost independent of it. The plasma density or collisionality gives initially a mild stabilization, increasing the pedestal slope and height, but above some threshold value its effect turns to a destabilization, reducing the pedestal width and height. Among several plasma shape parameters, the triangularity gives the most dominant effect, rapidly increasing the pedestal width and height, while the effect of elongation and squareness appears to be relatively weak. Implication of these edge results, particularly in relation to the global plasma performance, is discussed.

Supersonic molecular beam injection effects on tokamak plasma applied non-axisymmetric magnetic perturbation

The change of tokamak plasma behavior by supersonic molecular beam injection (SMBI) was investigated by applying a three-dimensional magnetic perturbation that could suppress edge localized modes (ELMs). From the time trace of decreasing electron temperature and with increasing plasma density keeping the total confined energy constant, the SMBI seems to act as a cold pulse on the plasma. However, the ELM behaviors were changed drastically (i.e., the symptom of ELM suppression has disappeared). The plasma collisionality in the edge-pedestal region could play a role in the change of the ELM behaviors.

Numerical Simulation of Pure Argon Plasma Transport in a Linear Divertor Simulator

Abstract A two-dimensional numerical modeling is carried out to simulate argon plasma-neutral transport in a linear divertor simulator with an axisymmetric cylindrical geometry. A pure argon plasma flow is introduced from the source region into the transport region, and pumped out near the target plate. This numerical modeling is based on a time-dependent Braginskii’s fluid formulation for plasma transport and a simple diffusion model for neutral transport. The Bohm diffusion model is adopted for calculation of radial diffusion coefficients across the parallel magnetic field in the simulator. Using the design and operation parameters of the Multi-Purpose Plasma (MP2) facility at the National Fusion Research Institute (NFRI) in Korea, argon plasma properties such as density and temperature distributions are calculated, and the formation of ionization front is found in the transport region. Plasma equilibrium profiles along the near axis turn out to be actually unaffected by the pumping positions along the cylindrical wall. Moreover, a gas target divertor concept is numerically simulated to find out puffing effects as well as pumping roles. As increasing the puffing rate at the target plate, not only the ionization front in the plasma density profile is gradually moving toward the entrance region, but also plasma density and electron temperature at the target are dramatically reduced. Two relatively peaked poles in the neutral density profile are resulted from puffing and recycling neutrals, respectively.