Explaining Cold-Pulse Dynamics in Tokamak Plasmas Using Local Turbulent Transport Models.

A long-standing enigma in plasma transport has been resolved by modeling of cold-pulse experiments conducted on the Alcator C-Mod tokamak. Controlled edge cooling of fusion plasmas triggers core electron heating on time scales faster than an energy confinement time, which has long been interpreted as strong evidence of nonlocal transport. This Letter shows that the steady-state profiles, the cold-pulse rise time, and disappearance at higher density as measured in these experiments are successfully captured by a recent local quasilinear turbulent transport model, demonstrating that the existence of nonlocal transport phenomena is not necessary for explaining the behavior and time scales of cold-pulse experiments in tokamak plasmas.

Efficient design and verification of diagnostics for impurity transport experiments.

Recent attempts to measure impurity transport in Alcator C-Mod using an x-ray imaging crystal spectrometer and laser blow-off impurity injector have failed to yield unique reconstructions of the transport coefficient profiles. This paper presents a fast, linearized model which was constructed to estimate diagnostic requirements for impurity transport experiments. The analysis shows that the spectroscopic diagnostics on Alcator C-Mod should be capable of inferring simple profiles of impurity diffusion DZ and convection VZ accurate to better than ±10% uncertainty, suggesting that the failure to infer unique DZ and VZ from experimental data is attributable to an inadequate analysis procedure rather than the result of insufficient diagnostics. Furthermore, the analysis reveals that even a modest spatial resolution can overcome a low time resolution. This approach can be adapted to design and verify diagnostics for transport experiments on any magnetic confinement device.

Effects of magnetic shear on toroidal rotation in tokamak plasmas with lower hybrid current drive.

Application of lower hybrid (LH) current drive in tokamak plasmas can induce both co- and countercurrent directed changes in toroidal rotation, depending on the core q profile. For discharges with q(0) <1, rotation increments in the countercurrent direction are observed. If the LH-driven current is sufficient to suppress sawteeth and increase q(0) above unity, the core toroidal rotation change is in the cocurrent direction. This change in sign of the rotation increment is consistent with a change in sign of the residual stress (the divergence of which constitutes an intrinsic torque that drives the flow) through its dependence on magnetic shear.

Edge temperature gradient as intrinsic rotation drive in Alcator C-Mod tokamak plasmas.

Intrinsic rotation has been observed in I-mode plasmas from the C-Mod tokamak, and is found to be similar to that in H mode, both in its edge origin and in the scaling with global pressure. Since both plasmas have similar edge ∇T, but completely different edge ∇n, it may be concluded that the drive of the intrinsic rotation is the edge ∇T rather than ∇P. Evidence suggests that the connection between gradients and rotation is the residual stress, and a scaling for the rotation from conversion of free energy to macroscopic flow is calculated.

Rotation reversal bifurcation and energy confinement saturation in tokamak Ohmic L-mode plasmas.

Direction reversals of intrinsic toroidal rotation have been observed in diverted Alcator C-Mod Ohmic L-mode plasmas following electron density ramps. For low density discharges, the core rotation is directed cocurrent, and reverses to countercurrent following an increase in the density above a certain threshold. Such reversals occur together with a decrease in density fluctuations with 2 cm(-1)≤k(θ)≤11 cm(-1) and frequencies above 70 kHz. There is a strong correlation between the reversal density and the density at which the Ohmic L-mode energy confinement changes from the linear to the saturated regime.

Operation Request Gatekeeper: a software system for remote access control of diagnostic instruments in fusion experiments.

Tokamak diagnostic settings are repeatedly modified to meet the changing needs of each experiment. Enabling the remote diagnostic control has significant challenges due to security and efficiency requirements. The Operation Request Gatekeeper (ORG) is a software system that addresses the challenges of remotely but securely submitting modification requests. The ORG provides a framework for screening all the requests before they enter the secure machine zone and are executed by performing user authentication and authorization, grammar validation, and validity checks. A prototype ORG was developed for the ITER CODAC that satisfies their initial requirements for remote request submission and has been tested with remote control of the KSTAR Plasma Control System. This paper describes the software design principles and implementation of ORG as well as worldwide test results.

Observation of ion-cyclotron-frequency mode-conversion flow drive in tokamak plasmas.

Strong toroidal flow (Vphi) and poloidal flow (Vtheta) have been observed in D-3He plasmas with ion cyclotron range of frequencies (ICRF) mode-conversion (MC) heating on the Alcator C-Mod tokamak. The toroidal flow scales with the rf power Prf (up to 30 km/s per MW), and is significantly larger than that in ICRF minority heated plasmas at the same rf power or stored energy. The central Vphi responds to Prf faster than the outer regions, and the Vphi(r) profile is broadly peaked for r/a < or =0.5. Localized (0.3 < or = r/a < or =0.5) Vtheta appears when Prf > or =1.5 MW and increases with power (up to 0.7 km/s per MW). The experimental evidence together with numerical wave modeling suggests a local flow drive source due to the interaction between the MC ion cyclotron wave and 3He ions.

Observation of anomalous momentum transport in tokamak plasmas with no momentum input.

Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas through analysis of the time evolution of core impurity toroidal rotation velocity profiles. Following the L-mode to EDA (enhanced D(alpha)) H-mode transition, the ensuing cocurrent toroidal rotation velocity, which is generated in the absence of any external momentum source, is observed to propagate in from the edge plasma to the core. The steady state toroidal rotation velocity profiles are relatively flat and the momentum transport can be simulated with a simple diffusion model. Velocity profiles during edge localized mode free (ELM-free) H-modes are centrally peaked, which suggests the addition of inward momentum convection. In all operating regimes the observed momentum diffusivities are much larger than the neoclassical values.

Mucolipidosis IV in an African American patient with new findings on electron microscopy.

PURPOSE: We report an unusual case of mucolipidosis IV in a patient of African ancestry, with intracytoplasmic inclusions of the corneal endothelium found on electron microscopy. METHOD: Clinical description with light and electron microscopy. RESULTS: We describe a case of mucolipidosis IV diagnosed in a patient of African ancestry after penetrating keratoplasty. Electron microscopic evaluation revealed intracytoplasmic inclusions in both the corneal epithelium and endothelium. CONCLUSION: The diagnosis of mucolipidosis in a patient of African ancestry is unusual, as this genetic disorder is found predominantly in individuals of Jewish descent. Corneal endothelial involvement in mucolipidosis IV has not previously been reported.

In-the-bag secondary intraocular lens implantation in children.

BACKGROUND: Surgery for congenital cataracts in early infancy usually includes a primary posterior capsulectomy and an anterior vitrectomy. Initially, most of these infants have aphakia after surgery. Over time, remaining equatorial lens epithelial cells produce new cortical fibers, resulting in a ring of cortex trapped between the lens equator and the fused anterior and posterior capsulectomy edges. A potential space is maintained between the anterior and posterior capsular leaflets. We describe a technique for placing a secondary intraocular lens (IOL) within the capsular bag. PATIENTS AND METHODS: Eight children, ranging in age from 11 months to 14 years, who originally had aphakia after cataract extraction were operated on with the intent to reopen the capsular bag and place an IOL in the bag. RESULTS: Secondary in-the-bag IOL implantation was successfully completed in 7 of 8 children. This was accomplished by reopening the capsular bag 360 degrees at the edge of the fused anterior and posterior capsulectomy remnants, using the previously published vitrectorhexis technique. Residual cortical material was aspirated, and an IOL was placed within the capsular bag. In 1 child, aged 14 years, the capsular bag was reopened, but the lens was placed in the ciliary sulcus because the new anterior capsule edge could not be visualized for 360 degrees . CONCLUSION: Placement of secondary IOLs within the capsular bag can be accomplished successfully for selected patients in the pediatric population. Surgeons operating on infantile cataracts without primary IOL placement can facilitate capsular IOL sequestration later by limiting the anterior and posterior capsulectomy to 4 to 5 mm and performing a generous anterior vitrectomy to help prevent secondary closure of the smaller capsulectomy.

Hypobaric ocular trauma from a Popper.

We have observed 3 cases of ocular trauma in children that were caused by an atypical, hypobaric mechanism induced by a toy called a Popper. When we initially notified the United States Consumer Product Safety Commission in 1990, Poppers disappeared from store shelves. We are concerned that this potentially harmful toy is making a comeback in 1998 (Smilemakers Inc, Spartanburg, SC; June-July 1998 catalog, p. 57). In 1990, packaged poppers cautioned against applying to face or skin; we are not sure that such warnings accompany current Poppers.

Iridocorneal adhesions in patients with the Marfan syndrome.

Marfan syndrome is an autosomal dominant connective tissue disorder characterized by skeletal, cardiovascular, and ocular anomalies. Ectopia lentis is the most common ocular manifestation. We report an ocular sign not previously described in Marfan syndrome, iridocorneal adhesions secondary to anterior lens subluxation. Three patients with the Marfan syndrome had iridocorneal adhesions on slit-lamp examination. One patient developed adhesions following treatment with pilocarpine. She underwent pars plana vitrectomy and lensectomy in both eyes due to progression of the iridocorneal adhesions. Treatment with miotics rotates the lens-iris diaphragm anteriorly and may contribute to the formation of such adhesions. The two other patients remained stable and did not received lensectomy or vitrectomy. Careful slit-lamp examination of the anterior segment should be conducted in patients with dislocated lenses.

Visual outcomes after surgery for unilateral cataract in children more than two years old: posterior chamber intraocular lens implantation versus contact lens correction of aphakia.

PURPOSE: We sought to determine whether posterior chamber intraocular lens implantation yields better visual acuity and binocular vision than does conventional contact lens correction of aphakia in similar groups of pediatric cataract patients. METHODS: We reviewed the medical records of children aged 2 to 16 years who had unilateral cataract surgery by a single pediatric ophthalmologist between 1986 and 1996. Before 1992 all patients underwent standard lensectomy with vitrectomy. Beginning in 1992 posterior chamber intraocular lens (IOL) implantation was offered as a choice to families and was performed on most patients. RESULTS: Monocular vision outcomes were not significantly different in 20 IOL and 31 lensectomy-vitrectomy patients, with 85% of the IOL group and 77% of the lensectomy-vitrectomy group showing better than 20/100 final acuity. Binocularity, however, was much better in the IOL group, with 90% demonstrating at least 400 seconds of arc stereopsis, as opposed to 39% in the lensectomy-vitrectomy group (p = 0.003). Subgroups of patients with traumatic or nontraumatic cataract origin, age at surgery less than 7 years, and preoperative visual acuity less than 20/100 compared very similarly. CONCLUSION: Posterior chamber IOL implantation appears to provide significantly better binocular function than conventional management of unilateral cataract in childhood but does not substantially improve visual acuity results.

Treatment of intraocular retinoblastoma with carboplatin and etoposide chemotherapy.

PURPOSE: Management of intraocular retinoblastoma was initiated with 2-drug chemotherapy in an effort to improve the rate of vision preservation and ocular salvage and to avoid or delay the use of external beam radiation treatment. METHODS: Six patients with intraocular retinoblastoma (five bilateral; one unilateral, 1 month old) received 6 to 7 monthly cycles of intravenously administered carboplatin and etoposide (VP-16) as primary treatment. No eyes were enucleated primarily. Twelve of the 33 discrete tumors in the 11 study eyes received prophylactic supplemental treatment with cryotherapy or laser hyperthermia. Response was documented with frequent eye examinations with the patient under general anesthesia and with repeated fundus photography. RESULTS: All eight larger tumors (> 10-mm diameter) underwent dramatic regression after treatment with chemotherapy alone, and six of these tumors ultimately became fully calcific. One larger tumor and two smaller tumors showed post-treatment growth, each within 2 months after completion of chemotherapy. Six larger tumors were observed without growth or further treatment for 7 to 21 months after completion of chemotherapy. Subretinal fluid resorbed completely in four of four eyes with extensive retinal detachment, and vitreous seeding diminished considerably in four of four eyes. In five eyes, intraocular disease recurrence at a distance from any initially observed tumor eventually required treatment with external beam radiation (three eyes) or enucleation (three eyes). Eight of 11 involved eyes were salvaged, including 5 of 8 with larger tumors and 4 of 4 with vitreous seeding; 4 retained eyes received no radiation exposure, including 3 with larger tumors and 1 with vitreous seeding. Good vision was preserved in six eyes, two of which were markedly improved after occlusion therapy for amblyopia. There was no extraocular disease recurrence and no serious harm from treatment during observation ranging from 12 to 40 months after diagnosis. CONCLUSION: Chemotherapy with carboplatin and etoposide shows promise as initial treatment for intraocular retinoblastoma. Further study is indicated to define its proper role in the management of this disease.

Principles and paradigms of pediatric cataract management.

Propensity for increased postoperative inflammation and capsular opacification, a refractive state that is constantly in a state of flux due to growth of the eye, difficulty in documenting anatomic and refractive changes due to poor compliance, and a tendency to develop amblyopia, makes management of cataract in the child different from that in the adult. The recent past has unraveled several caveats of pediatric cataract management-the importance of atraumatic surgery and complete removal of lens matter, benefits of in-the-bag intraocular lens (IOL) implantation, role of titrating IOL power to counter refractive changes due to growth of the eye, prudery of continuously following these eyes for early detection of aphakic glaucoma and benefits of some surgical innovations. Although these promise to significantly improve our management of pediatric cataract, their long-term benefits are yet to be determined. We will also have to harness newer techniques, especially in the areas of wound construction and capsule management, and will have to develop effective strategies for the refractive management of infantile aphakia.

Ocular abnormalities associated with unilateral coronal synostosis.

Forty-five patients with premature fusion of one coronal suture were treated between June 1985 and June 1991. Thirty-three patients were evaluated with pre- and postoperative photographs, computed tomographic scans, and serial radiographs and were assessed by the ophthalmological and plastic surgical services before and after surgery. The patients' mean age was 11.5 +/- 3.2 months at the time of surgery. Two patients (6%) were noted to have facial abnormalities preoperatively. Seventeen patients (52%) exhibited a disorder of extraocular muscle function preoperatively. After craniofacial repair, 21% of patients exhibited a distinct change from their preoperative ocular examination. A substantial majority of patients with premature fusion of the unilateral coronal suture (72%) will present with an abnormal examination postoperatively. In addition, a significant percentage of these patients will exhibit a change in ophthalmological status after craniofacial surgery; therefore, surgery on the extraocular musculature should, in general, be deferred until after bony repositioning.