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Gyrotrons are essential for electron cyclotron resonance heating in fusion reactors, making efficient operation crucial for advancing fusion energy. Past experiments revealed instability issues due to trapped electrons in the magnetron injection gun (MIG) region, causing undesired currents and operational failures. To address this, tight manufacturing tolerances are required for the MIG geometry [Pagonakis et al., Phys. Plasmas 23, 023105 (2016)]. We present the initial findings of the trapped electrons experiment developed at the Swiss Plasma Center, designed to understand the physics of electron clouds in gyrotron MIGs. T-REX replicates MIG geometries, as well as their typical electric and magnetic fields, and it is supported by 2D particle-in-cell simulations with the FENNECS code [Le Bars et al., Phys. Plasmas 29, 082105 (2022); Le Bars, Ph.D. thesis, EPFL, Lausanne, 2023]. The setup includes two coaxial electrodes in a vacuum chamber atop a superconducting magnet, with a central electrode biased to negative DC voltages and an outer one at the ground, creating a radial electric field (1-2 MV/m) and an axial magnetic field (B < 0.4 T). This setup mimics Penning-Malmberg traps. We present the experimental device and first findings on current distribution and also a qualitative comparison with FENNECS simulations [Le Bars et al., Comput. Phys. Commun. 303, 109268 (2024)]. Planned diagnostics include optical emission spectroscopy, phosphor screen imaging, streak camera imaging, and potentially electric field distribution via the Stark effect. This research aims to enhance gyrotron performance and reliability in fusion energy systems., (© 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International (CC BY-NC-ND) license (https://creativecommons.org/licenses/by-nc-nd/4.0/).)

An experimental study of a nanosecond pulsed regime in a THz gyrotron oscillator operating in a self-consistent Q-switch regime has been carried out. The gyrotron is operated in the TE(7,2) transverse mode radiating at a frequency of 260.5 GHz. The 5 W nanosecond pulses are obtained in a self-consistent Q-switch regime in which the cavity diffraction quality factor dynamically varies by nearly 2 orders of magnitude on a subnanosecond time scale via the nonlinear interaction of different mode-locked frequency-equidistant sidebands. The experimental results are in good agreement with numerical simulations performed with the TWANG code based on a slow time scale formulation of the self-consistent time-dependent nonlinear wave particle interaction equations.

We demonstrate the construction of corrugated waveguides using stacked rings to propagate terahertz frequencies. The waveguide allows propagation of the same fundamental mode as an optical-fiber, namely, the HE(11) mode. This simple concept opens the way for corrugated wave-guides up to several terahertz, maintaining beam characteristics as for terahertz applications., (© 2011 American Institute of Physics)

Stereotactic core needle biopsy (SCNB) of the breast is a cost-effective alternative to needle localization biopsy for the diagnosis of mammographic calcifications. We questioned whether an exhaustive search for calcium in the small samples obtained in SCNB yields more diagnostic information than that obtained with examination of a standard number of sections. We retrospectively reviewed 168 specimens from 123 patients with mammographic calcifications, including cases in which radiographic suspicion ranged from low to high. Microcalcifications were identified on three initial levels in 112 specimens. Additional sections were examined in 50 specimens. The final diagnosis differed from the diagnosis based on three levels in 11/50 cases (22%). In 6/50 (12%), complete sectioning yielded a specific diagnosis. The increase in technical cost associated with the additional levels was 414% per case. We conclude that exhaustive searching for microcalcifications in SCNB yields a small increase in specific diagnostic information and a high technical cost. In individual cases, the additional information may be critical for appropriate patient management.

Unusual lesions of the breast can present a diagnostic challenge. These lesions include systemic diseases, benign tumors, and primary and metastatic malignancies. Lymphadenopathy is the most common mammographic finding associated with collagen vascular disease. Wegener granulomatosis may manifest as an irregular, high-density mass simulating breast cancer. Diabetic fibrous mastopathy manifests at mammography as very dense breast tissue and at ultrasonography (US) as an irregular, hypoechoic mass with striking posterior acoustic shadowing simulating malignancy. Fibromatosis simulates malignancy at mammography as an irregularly shaped, uncalcified, high-density mass and at US as an irregular, hypoechoic mass with posterior acoustic shadowing. At US, granular cell tumor may manifest as a solid, poorly marginated mass with marked posterior acoustic shadowing or may appear more benign. At mammography, hamartomas are typically well-circumscribed, round to oval masses with a thin, radiopaque pseudocapsule; at US, they manifest as a sharply defined, heterogeneous oval mass or as normal glandular tissue. Phyllodes tumor manifests at mammography as a large, well-circumscribed oval or lobulated mass; at US, it usually manifests as an inhomogeneous, solid-appearing mass. At mammography, primary breast lymphoma manifests as a relatively circumscribed mass or a solitary, indistinctly marginated, uncalcified mass. Metastatic lesions may manifest mammographically as single or multiple masses or as diffuse skin thickening; at US, they tend to have circumscribed margins with low-level internal echoes. Radiologists should be familiar with the characteristic mammographic appearances of these lesions and should consider benign and systemic causes in the differential diagnosis when malignant-appearing findings are encountered.

Autologous myocutaneous flaps (AMFs) are used increasingly as a method of breast reconstruction after mastectomy for breast cancer. Autogenous breast reconstruction may be performed with a rectus abdominis, latissimus dorsi, or gluteus maximus myocutaneous flap. Mammographic imaging of AMFs is controversial but has been recommended by some authors because mammographic detection of nonpalpable local recurrences in AMFs continues to be reported. At mammography, AMFs have a predominantly fatty appearance with variable density due to the muscle component and postoperative scarring. Normal mammographic findings include the vascular pedicle, surgical clips, and surgical scars, which produce radiopaque lines in predictable locations. Abnormal mammographic findings include fat necrosis appearing as a spiculated mass, noncalcified or calcified lipid cysts, calcifications, lymph nodes, epidermal inclusion cysts, and locally recurrent carcinoma.

Detection and management of breast abnormalities that develop during pregnancy and lactation is difficult for both the clinician and the radiologist. This article reviews the hormonal and physiologic effects on the breast during pregnancy and lactation. Breast masses that occur in pregnant or lactating patients, including pregnancy-associated breast cancer, are discussed and the corresponding ultrasound and mammographic findings are presented. Finally, a rationale for the imaging evaluation and management of the pregnant or lactating patient with a breast mass are presented.

Evaluation of mammograms for artifacts is essential for mammographic quality assurance. A variety of mammographic artifacts (i.e., variations in mammographic density not caused by true attenuation differences) can occur and can create pseudolesions or mask true abnormalities. Many artifacts are readily identified, whereas others present a true diagnostic challenge. Factors that create artifacts may be related to the processor (eg, static, dirt or excessive developer buildup on the rollers, excessive roller pressure, damp film, scrapes and scratches, incomplete fixing, power failure, contaminated developer), the technologist (eg, improper film handling and loading, improper use of the mammography unit and related equipment, positioning and darkroom errors), the mammography unit (eg, failure of the collimation mirror to rotate, grid inhomogeneity, failure of the reciprocating grid to move, material in the tube housing, compression failure, improper alignment of the compression paddle with the Bucky tray, defective compression paddle), or the patient (e.g., motion, superimposed objects or substances [jewelry, body parts, clothing, hair, implanted medical devices, foreign bodies, substances on the skin]). Familiarity with the broad range of artifacts and the measures required to eliminate them is vital. Careful attention to darkroom cleanliness, care in film handling, regularly scheduled processor maintenance and chemical replenishment, daily quality assurance activities, and careful attention to detail during patient positioning and mammography can reduce or eliminate most mammographic artifacts.

Digital mammography using storage phosphor CR is still in the investigational stage. It is the only digital mammography system that has been tested in preliminary clinical trials with promising early results. Further clinical studies are needed to assess the impact of the limited spatial resolution of storage phosphor technology on its application as a digital screening mammography system. Further studies also are needed to determine the optimum image processing parameters needed in digital mammography.

Digital mammography is a rapidly developing technology that has great potential to improve upon and ultimately replace conventional film-screen mammography for the early detection of breast cancer. This article reviews current progress in digital mammographic systems, computer-aided diagnostic programs, and artificial neural networks. Digital mammographic systems are currently in an investigational phase only. Large-scale clinical trials are needed in all areas of digital mammography before this exciting new technology can be implemented outside of research centers.

Fat necrosis of the breast is a benign condition that most commonly occurs as the result of minor breast trauma. The radiographic and clinical significance of fat necrosis of the breast is that it may mimic a breast malignancy, requiring biopsy for diagnosis. The mammographic appearance of fat necrosis ranges from a lipid cyst to findings suspicious for malignancy, including clustered microcalcifications, a spiculated area of increased opacity, or a focal mass. The changes of fat necrosis may be seen following blunt trauma, cyst aspiration, biopsy, lumpectomy, radiation therapy, reduction mammoplasty, breast reconstruction with a transverse rectus abdominis myocutaneous (TRAM) flap, implant removal, and anticoagulant therapy, as well as in patients without a relevant history. Fat necrosis may also be detected mammographically as an incidental finding in benign lipomas. It is important to recognize the mammographic spectrum of appearances of fat necrosis to avoid unnecessary biopsy and to avoid overlooking breast cancer.