Radio-Frequency design of a Lower Hybrid Slotted Waveguide Antenna

Helou, W.; Goniche, M.; Hillairet, J.; Žáček, F.; Achard, J.; Adámek, Jiřı́; Bogar, O.; Mollard, P.; Pascal, J.-Y.; Poli, S.; Šesták, D.; Volpé, Robert; Zaja̧c, J.

doi:10.1016/j.fusengdes.2017.04.011

Cited by 7 publications

(3 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The antenna design for the FNSF combines a poloidal resonant slotted waveguide antenna, similar in concept to those employed on the Alcator C-Mod 18 and COMPASS (Ref. 21), with a toroidal multijunction. The LHRF antenna under construction for the DIII-D (Ref.…”

Section: Radiofrequency Designmentioning

confidence: 99%

Multiphysics Simulations of a Steady-State Lower Hybrid Current Drive Antenna for the FSNF

Wallace

Bohm

Kessel

2021

Fusion Science and Technology

View full text Add to dashboard Cite

The Fusion Nuclear Science Facility (FNSF) is a proposed tokamak reactor with the mission to investigate operation of a fusion reactor in a nuclear environment. The high neutron fluence component of the FNSF mission requires steady-state operation for extremely long pulses (t pulse , months) at full power. Plasma sustainment and current drive will be critical components of a successful FNSF. COMSOL Multiphysics® software is used for combined radiofrequency (RF) and thermal simulations of the lower hybrid current drive antenna system. These simulations consider the resistive RF losses in the antenna including realistic surface roughness and a range of potential materials. The thermal analysis adds volumetric nuclear heating, plasma heat flux on leading edges, and electromagnetic radiation from the plasma to the RF heating calculated by COMSOL. Additional neutronics calculations have been performed to determine the impact of these antenna designs on activated waste disposal for the materials considered. The simulations show that it is technically feasible to implement a fully active multijunction (FAM) rather than a passive-active multijunction (PAM) style of antenna if the septum between adjacent waveguides is sufficiently wide and the thermal conductivity of the structural material is sufficiently high. The FAM has the benefit of higher achievable power density with respect to the PAM, which results in a more compact antenna with potentially lower impact on neutron shielding and tritium breeding. These considerations point to tungsten rather than steel as the preferred structural material in constructing the antenna.

show abstract

Section: Radiofrequency Designmentioning

confidence: 99%

Multiphysics Simulations of a Steady-State Lower Hybrid Current Drive Antenna for the FSNF

Wallace

Bohm

Kessel

2021

Fusion Science and Technology

View full text Add to dashboard Cite

show abstract

“…Figure 16 shows a multi-junction antenna design at 4.6 GHz oriented for use on the HFS of the proposed ADX Device [31] where radial space is limited. The feed waveguide has been reoriented from radial to vertical, with the poloidal splitting between rows achieved through use of a series of slotted waveguide apertures [20]. A difference between the HFS multi-junction concept presented here and a conventional LFS multi-junction is that the poloidal splitting follows the toroidal multi-junction rather than preceding it.…”

Section: Implementation Of Hfs Launchmentioning

confidence: 99%

High field side lower hybrid wave launch for steady state plasma sustainment

Bonoli¹,

Wallace²,

Shiraiwa³

et al. 2018

Nucl. Fusion

View full text Add to dashboard Cite

This paper explores how the use of waves in the lower hybrid range of frequencies (LHRF) alleviates many unresolved current drive issues when launched from the high field side (HFS) of a tokamak. Efficient, robust, reliable, steady-state current drive is a requirement for a viable tokamak fusion reactor. Launching LHRF waves from the HFS opens the ‘accessibility window’, allowing for use of a lower parallel refractive index, , for a given plasma density and on-axis magnetic field. The lower waves damp in a region of higher temperature, resulting in increased current drive efficiency and a damping profile shifted closer to the mid-radius as compared to low field side launch. Moving the LHRF antenna to the quiescent scrape off layer on the HFS reduces the likelihood of detrimental wave scattering from density fluctuations, as well as ameliorating the plasma-material-interaction and wave coupling challenges. Additional benefits with respect to fast particle and neutron fluxes can be realized by moving to the HFS. An engineering assessment of HFS launch shows that it is feasible to implement an HFS LHRF system on existing tokamaks, with fewer hurdles anticipated for future tokamaks built with HFS antenna systems integrated in the design from the start.

show abstract

“…A standing wave pattern coupling to a series of H-plane apertures set λ/2 apart is established by a shorted tuning stub. A λ/4 stub[31] promotes better toroidal power splitting per arm, however it excites a poorly coupled eigenmode resulting in high electric fields in the vacuum section, figure8(a). A λ/2 stub minimizes return loss and circulating power by exciting the proper eigenmode in H-plane tee, figure 8(b).…”

mentioning

confidence: 99%

A high field side multijunction launcher with aperture impedance matching for lower hybrid current drive in DIII-D advanced tokamak plasmas

et al. 2019

View full text Add to dashboard Cite

A high field side (HFS) lower hybrid current drive launch scenario improves wave accessibility, has single pass damping at r/a ~ 0.6–0.8 and good current drive efficiency in DIII-D advanced tokamak discharges. The DIII-D experiment is an opportunity to validate HFS wave propagation, absorption and scrape-off layer benefits. A HFS multi-junction launcher is designed and simulated in COMSOL over a range of plasma edge conditions to evaluate n|| spectrum, directivity, and return loss. The COMSOL model utilizes a lossy anisotropic dielectric modeled with the cold plasma dispersion relation cross validated against ALOHA and Petra-M codes. The COMSOL model seamlessly includes a realistic plasma model and coupler that allows for rapid optimization of a single launcher module, while Petra-M allows more complex simulation of an eight-module array including curvature, and warm plasma effects. The resulting design utilizes a traveling wave poloidal power divider to minimize peak electric fields in the vacuum region of the coupler, and an internal aperture matching structure provides an impedance match to the plasma over a wide range of plasma density and density gradient edge conditions.

show abstract

Radio-Frequency design of a Lower Hybrid Slotted Waveguide Antenna

Cited by 7 publications

References 17 publications

Multiphysics Simulations of a Steady-State Lower Hybrid Current Drive Antenna for the FSNF

Multiphysics Simulations of a Steady-State Lower Hybrid Current Drive Antenna for the FSNF

High field side lower hybrid wave launch for steady state plasma sustainment

A high field side multijunction launcher with aperture impedance matching for lower hybrid current drive in DIII-D advanced tokamak plasmas

Contact Info

Product

Resources

About