Observation of E8 Particles in an Ising Chain Antiferromagnet

Near the transverse-field induced quantum critical point of the Ising chain, an exotic dynamic spectrum consisting of exactly eight particles was predicted, which is uniquely described by an emergent quantum integrable field theory with the symmetry of the $E_8$ Lie algebra, but rarely explored experimentally. Here we use high-resolution terahertz spectroscopy to resolve quantum spin dynamics of the quasi-one-dimensional Ising antiferromagnet BaCo$_2$V$_2$O$_8$ in an applied transverse field. By comparing to an analytical calculation of the dynamical spin correlations, we identify $E_8$ particles as well as their two-particle excitations.Comment: 6 pages, 3 figures, plus supplementary material

Analysis of ICRH of H and He-3 minorities in D and D-T plasmas in JET

Kärnfusion är en i praktiken outtömlig energikälla och en av kandidaterna till att ersätta fossila bränslen. Det är en ren energikälla som kan hjälpa oss att minska CO2 utsläpp utan att skapa långlivat radioaktivt avfall. Den mest lovande fusionsreaktionen är mellan deuterium och tritium som producerar en heliumkärna och en mycket energetisk neutron. Dock är tritium komplicerat att producera och hantera. I nuläget finns bara mycket små mängder tritium på jorden. Av denna anledning har endast ett litet antal experiment utförts med deuterium och tritium plasman. Därför är det viktigt att studera fysik hos deuterium-tritium plasma teoretiskt för att kunna göra prognoser för de kommande experiment. RF uppvärmning är en metod som används i plasmauppvärmning. Denna metod kommer att också finnas på ITER. Detta arbete behandlar uppvärmning av deuterium-tritium plasman med jon-cyklotron resonans på ett minoritetsjonslag som t.ex. väte eller helium-3 . I arbetet används en analytisk modell för jon-cyklotron uppvärmning baserad på tidigare forskning. Resultaten från den analytiska modellen har jämförts med resultaten från numeriska simuleringar som utförts med SELFO-koden för att utvärdera giltigheten av analytiska modellen. Framförallt kan den användas för att uppskatta hur vågenergin fördelas mellan de olika jonslagen, och volymsintegrerade fördelningsfunktionerna av snabba partiklar och deras energiinnehåll. Energiöverföringen från snabba minoritetsjoner till elektroner och termiska joner via Coulomb-kollisioner kan uppskattas till viss del. För fallet med helium-3 minoritet så finns det stora avvikelser mellan den analysiska och numeriska modellen för energiöverföringen. Båda modellerna visar att den bästa jon-uppvärmningen erhålls vid absorption på helium-3 joner. Slutsatsen av jämförelsen är att analytiska modellen kan användas för att återskapa flera viktiga resultat från simuleringarna.Nuclear fusion is potentially a source of practically endless energy. It is one of the candidates to replace fossil fuels in the future. Fusion is also a source of clean energy, which should make a positive environmental impact. It can decrease the CO2 emission without creating any long-lived radioactive waste. The most promising fusion reaction is between deuterium and tritium that produces a helium atom and a highly energetic neutron. However, tritium is complicated to manufacture and handle, so its supply on Earth is currently limited. For this reason, only a small number of deuterium-tritium plasma experiments have been performed. Therefore, it is important to study the physics of the deuterium-tritium plasma to be able to make predictions for the future experiments. The topic addressed in this project is radio frequency heating, which is one of the main plasma heating methods. This method will also be applied in the future ITER experiment. The goal is to study how ion cyclotron resonance heating of hydrogen and helium-3 minorities performs in deuterium-tritium plasma. An analytical model based on previous research is presented in the report. The results from this analytical model are compared with the results from the numerical simulations performed using SELFO code to evaluate the validity of the analytical model. It is shown that the approximate analytical model provides viable estimations for power partition, fast ion population and their energy content. Collisional power transfer from minority to bulk plasma ions and electrons can be estimated to a certain extent, although a deviation from the numerical simulations are found when heating the helium-3 minority. Nevertheless, helium-3 minority fundamental resonance heating is shown to result in the strongest bulk plasma heating. The conclusion is that the analytical model can be used to recreate several important results of the simulations

Study of Nb-Cu 1.3 GHz SRF cavity resonators for future particle accelerators

Niobium-coated superconducting radio-frequency cavities have a number of advantages over cavities made from bulk niobium. Cavities coated with high-power impulse magnetron sputtering are tested at CERN in order to optimize the coating and study the Q-slope that limits the performance. To accurately measure the quality factor as a function of accelerating field, it is important to have good matching between an input antenna and a cavity impedance. To improve the matching, a variable coupler that changes the length of the antenna can be used. We have shown that the Q-factor of the input antenna can be changed between $10^7-10^{11}$ by moving the antenna, which should allow to achieve critical coupling with a cavity. This technology could be used in future measurements, so that reflections are always minimized

Experimental observation of quantum many-body excitations of E-8 symmetry in the Ising chain ferromagnet CoNb2O6

Close to the quantum critical point of the transverse-field Ising spin-chain model, an exotic dynamic spectrum was predicted to emerge upon a perturbative longitudinal field. The dynamic spectrum consists of eight particles and is governed by the symmetry of the E-8 Lie algebra. Here we report on high-resolution terahertz spectroscopy of quantum spin dynamics in the ferromagnetic Ising-chain material CoNb2O6. At 0.25 K in the magnetically ordered phase we identify characteristics of the first six E-8 particles, m(1) to m(6), and the two-particle (m(1) + m(2)) continuum in an applied transverse magnetic field of B-c(1D) = 4.75 T, before the three-dimensional magnetic order is suppressed above B-c(3T )approximate to( )5.3 T. The observation of the higher-energy particles (m(3) to m(6)) above the low-energy two-particle continua features quantum many-body effects in the exotic dynamic spectrum

Quantum spin dynamics of quasi-one-dimensional Heisenberg-Ising magnets in a transverse field: confined spinons, E-8 spectrum, and quantum phase transitions

We report on high-resolution terahertz spectroscopic studies of quantum spin dynamics in the quasi-one-dimensional Ising-like ferromagnet CoNb2O6 and antiferromagnet BaCo2V2O8 as a function of an applied transverse magnetic field. In the ordered phases stabilized by inter-chain couplings, we reveal characteristics for confined spinon excitations, E-8 dynamical spectrum, and field-induced quantum phase transitions. The connections between these characteristic dynamical features are found in the field-dependent evolution of the excitation spectra

Broadband magnetic resonance spectroscopy in MnSc 2_2 2 S 4_4 4

Abstract Recent neutron scattering experiments suggested that frustrated magnetic interactions give rise to antiferromagnetic spiral and fractional skyrmion lattice phases in MnSc $$_2$$ 2 S $$_4$$ 4  . Here, to trace the signatures of these modulated phases, we studied the spin excitations of MnSc $$_2$$ 2 S $$_4$$ 4  by THz spectroscopy at 300 mK and in magnetic fields up to 12 T and by broadband microwave spectroscopy at various temperatures up to 50 GHz. We found a single magnetic resonance with frequency linearly increasing in field. The small deviation of the Mn $$^{2+}$$ 2 + ion g-factor from 2, g = 1.96, and the absence of other resonances imply very weak anisotropies and negligible contribution of higher harmonics to the spiral state. The significant difference between the dc magnetic susceptibility and the lowest-frequency ac susceptibility in our experiment implies the existence of mode(s) outside of the measured frequency windows. The combination of THz and microwave experiments suggests a spin gap opening below the ordering temperature between 50 GHz and 100 GHz