Inversion methods for fast-ion diagnostics in fusion plasmas

The present dissertation presents my Ph.D. research on inversion methods for fast-ion diagnostics in fusion plasmas. This work is part of a collaboration between the Technical University of Denmark and École Polytechnique Fédérale de Lausanne. My research focused on developing mathematical methods for solving ill-posed inverse problems in velocity-space tomography applied to synthetic and experimental data from projections of fast-ion velocities, ion cyclotron emission, and fast-ion loss detectors. A main objective in diagnostics of fusion plasmas is to determine the fast-ion velocityspace distribution function. As part of my research, a technique called “slowing-down physics regularization” was developed to determine the fast-ion velocity-space distribution function throughout the fusion plasma from projections of velocities of the fast ions. This technique was applied to synthetic data from the TCV tokamak and the W7-X stellarator. Extensive modelling of the physical systems is required to determine the fast-ion velocity-space distribution function. In fast-ion parlance, such models are built into a “weight function matrix”. For point-wise determination of the velocities of the fast ions emitting ion cyclotron emission, 2D weight functions and reconstruction techniques using them were developed. The ill-posed inverse problem can be solved using regularization methods. Tikhonov regularization has been the standard regularization method in velocity-space tomography for the past decade. Other regularization techniques were investigated and evaluated. In particular, algebraic iterative reconstruction techniques were applied to synthetic and experimental measurements from fast-ion loss detectors and compared with Tikhonov regularization. When diagnosing fusion plasmas, simulations are performed to model the physical processes. Measurements from fast-ion loss detectors are simulated using a code called “FILDSIM”. A raised cosine model was proposed as an alternative to the standard Gaussian model. The resulting improvements in weight functions and reconstructions were obtained for the TCV tokamak. A model based on these improvements achieves higher precision and faster calculations, making it possible to compute reconstructions of measurements from fast-ion loss detectors between repeated experiments. In addition, neural networks were used to perform velocity-space tomography. Neural networks were trained to suggest an optimal value of the regularization parameter for Tikhonov regularization and to compute reconstructions directly from synthetic and experimental measurements from fast-ion loss detectors. The neural networks provide instantaneous reconstructions of the fast-ion velocity-space distribution function, which can supplement reconstruction methods for diagnostics of fast ions in fusion plasmas and contribute to improved control of fusion plasmas.</div

Steroid Response after Trabeculectomy&mdash;A Randomized Controlled Trial Comparing Dexamethasone to Diclofenac Eye Drops

This prospective randomized controlled trial aimed to compare changes in intraocular pressure in three different anti-inflammatory regimens following trabeculectomy. Sixty-nine patients were randomized to receive either postoperative prophylaxis with topical preservative-free dexamethasone (DEX), diclofenac (DICLO), or their combination (DEX+DICLO). Our main outcome measure was an intraocular pressure (IOP) change of a minimum 4 mmHg following the withdrawal of anti-inflammatory prophylaxis 9 weeks after trabeculectomy. We found that the IOP decreased &ge; 4 mmHg in 18.6% of eyes after cessation of the topical steroid DEX (n = 3/22) and DEX+DICLO (n = 5/21), whereas a decrease in IOP was not observed in the DICLO group. In conclusion, IOP decreased in nearly 1/5 of patients after cessation of topical steroidal anti-inflammatory prophylaxis after trabeculectomy. This points toward a steroid-induced increase in IOP even after trabeculectomy. Thus, increased postoperative IOP may be related to steroid use, and the success or failure of a trabeculectomy cannot be fully evaluated before anti-inflammatory prophylaxis with steroids is stopped or changed to non-steroidal eye drops

Early Inflammation Control After Trabeculectomy by Steroid and Non-steroidal Eye Drops:A Randomized Controlled Trial

Introduction: To compare the effect of three different anti-inflammatory regimens consisting of preservative-free dexamethasone (DEX), diclofenac (DICLO) eye drops, and their combination (DEX + DICLO) following trabeculectomy on early postoperative inflammation. Methods: A prospective randomized controlled trial. Sixty-nine patients undergoing trabeculectomy were randomized to receive either postoperative treatment with topical DEX (n = 23), topical DICLO (n = 23), or a combination of topical DEX and topical DICLO (n = 23) after trabeculectomy. The primary outcome was the anterior chamber flare measurement in the first 3 months postoperatively. Secondary outcomes included intraocular pressure, central corneal thickness, conjunctival injection, and number of cells in the anterior chamber from baseline to 3 months postoperatively. Results: Anterior chamber flare reached a maximum 1 day after trabeculectomy with an increase of 55% (95% CI 37–73%) for DEX, 64% (95% CI 47–82%) for DICLO, and 57% (95% CI 39–75%) for DEX + DICLO and returned to near pre-operative values 6 weeks after surgery. There were no significant differences in anterior chamber flare [effect size for DICLO: 0.16 (95% CI − 4.3 to 4.6), effect size for DEX + DICLO: 0.09 (95% CI − 4.1 to 4.3)], intraocular pressure, central corneal thickness, conjunctival injection, or number of cells in the anterior chamber between DEX, DICLO, or DEX + DICLO groups. Conclusion: We found that topical diclofenac was not statistically different from topical dexamethasone in controlling early postoperative inflammation after trabeculectomy, while combining diclofenac and dexamethasone offered no added anti-inflammatory control compared to dexamethasone alone. Trial Registration: www.clinicaltrials.gov (NCT04054830).</p

Steroids and/or Non-Steroidal Anti-Inflammatory Drugs as Postoperative Treatment after Trabeculectomy—12-Month Results of a Randomized Controlled Trial

This prospective randomized controlled trial aimed to compare the efficacy and safety of topical preservative-free diclofenac (DICLO) to dexamethasone (DEX) eyedrops, and their combination (DEX+DICLO) after trabeculectomy. Sixty-nine patients with medically uncontrolled glaucoma were randomized to receive topical postoperative treatment with DICLO (n = 23), DEX (n = 23), or a combination of DEX and DICLO (n = 23). The primary outcome was the intraocular pressure (IOP) 12 months postoperatively. Secondary outcomes included surgical success, failure, visual field, and visual acuity from baseline to 12 months postoperatively. IOP reached the lowest point one day after trabeculectomy. At 12 months, IOP was 10.0 mmHg (95% CI, 8.4–11.6 mmHg) for DICLO, 10.9 mmHg (95% CI, 9.4–12.3 mmHg) for DEX, and 11.2 mmHg (95% CI, 9.1–13.3 mmHg) for DEX+DICLO. There were no significant differences in IOP, surgical success, failure, visual field, or visual acuity between the DICLO, DEX, or DEX+DICLO groups. We found that topical diclofenac was not statistically different from topical dexamethasone in controlling IOP 12 months after trabeculectomy. Combining diclofenac and dexamethasone offered no added IOP control compared to dexamethasone alone.</p