CERN Accelerating science

Schematics of the tuning concept. The left side shows the cavity in the closed position with no gap and at its highest resonant frequency. On the right side, a gap was introduced between the two cavity halves, tuning the cavity to a lower frequency depending on the gap size.

Electric field pattern for the five electromagnetic modes of the cavity. Red colour refers to a maximum and blue colour to a minimum in the electric field. Taken from \cite{RADES_paper1}.

Left: Mode pattern with symmetry plane. The fabrication is done in two halves defined by this symmetry plane. 3D model housing of the vertical cut inductive irises cavity to be manufactured (right). This piece is one of the two symmetrical halves, which must be parallel. SMA coaxial ports are situated at the $\varnothing4.1$ holes. Dimensions given in Table~\ref{tab:VC_dimensions}.

Left: Mode pattern with symmetry plane. The fabrication is done in two halves defined by this symmetry plane. 3D model housing of the vertical cut inductive irises cavity to be manufactured (right). This piece is one of the two symmetrical halves, which must be parallel. SMA coaxial ports are situated at the $\varnothing4.1$ holes. Dimensions given in Table~\ref{tab:VC_dimensions}.

Results from CST simulations for the vertical cut tuning study applied in the haloscope depicted in Figure~\ref{fig:5Iris_vs_tuning} (right): frequency and tuning versus gap (left), unloaded quality and form factors versus gap (centre), and volume and figure of merit ($Q_0V^2C^2$) versus gap (right).

Results from CST simulations for the vertical cut tuning study applied in the haloscope depicted in Figure~\ref{fig:5Iris_vs_tuning} (right): frequency and tuning versus gap (left), unloaded quality and form factors versus gap (centre), and volume and figure of merit ($Q_0V^2C^2$) versus gap (right).

Results from CST simulations for the vertical cut tuning study applied in the haloscope depicted in Figure~\ref{fig:5Iris_vs_tuning} (right): frequency and tuning versus gap (left), unloaded quality and form factors versus gap (centre), and volume and figure of merit ($Q_0V^2C^2$) versus gap (right).

Misalignment effect in the vertical cut haloscope for three scenarios: angular $y-$axis (top left), angular $z-$axis (top right), and lineal $y-$axis (bottom).

Misalignment effect in the vertical cut haloscope for three scenarios: angular $y-$axis (top left), angular $z-$axis (top right), and lineal $y-$axis (bottom).

Misalignment effect in the vertical cut haloscope for three scenarios: angular $y-$axis (top left), angular $z-$axis (top right), and lineal $y-$axis (bottom).

Results obtained in the simulation of the misalignment study in the angular $y-$axis (first column), in the angular $z-$axis (second column), and in the lineal $y-$axis (third column). The first row of graphs shows the variation of the quality and form factors versus the variation of the misalignment variable. The second row plots the variation in frequency and figure of merit $Q_0V^2C^2$ versus misalignment. The quality factor and figure of merit parameters are given in terms of the percentage change from the aligned scenarios ($\theta_y = \theta_z = g_y = 0$).

Results obtained in the simulation of the misalignment study in the angular $y-$axis (first column), in the angular $z-$axis (second column), and in the lineal $y-$axis (third column). The first row of graphs shows the variation of the quality and form factors versus the variation of the misalignment variable. The second row plots the variation in frequency and figure of merit $Q_0V^2C^2$ versus misalignment. The quality factor and figure of merit parameters are given in terms of the percentage change from the aligned scenarios ($\theta_y = \theta_z = g_y = 0$).

Results obtained in the simulation of the misalignment study in the angular $y-$axis (first column), in the angular $z-$axis (second column), and in the lineal $y-$axis (third column). The first row of graphs shows the variation of the quality and form factors versus the variation of the misalignment variable. The second row plots the variation in frequency and figure of merit $Q_0V^2C^2$ versus misalignment. The quality factor and figure of merit parameters are given in terms of the percentage change from the aligned scenarios ($\theta_y = \theta_z = g_y = 0$).

Results obtained in the simulation of the misalignment study in the angular $y-$axis (first column), in the angular $z-$axis (second column), and in the lineal $y-$axis (third column). The first row of graphs shows the variation of the quality and form factors versus the variation of the misalignment variable. The second row plots the variation in frequency and figure of merit $Q_0V^2C^2$ versus misalignment. The quality factor and figure of merit parameters are given in terms of the percentage change from the aligned scenarios ($\theta_y = \theta_z = g_y = 0$).

Results obtained in the simulation of the misalignment study in the angular $y-$axis (first column), in the angular $z-$axis (second column), and in the lineal $y-$axis (third column). The first row of graphs shows the variation of the quality and form factors versus the variation of the misalignment variable. The second row plots the variation in frequency and figure of merit $Q_0V^2C^2$ versus misalignment. The quality factor and figure of merit parameters are given in terms of the percentage change from the aligned scenarios ($\theta_y = \theta_z = g_y = 0$).

Results obtained in the simulation of the misalignment study in the angular $y-$axis (first column), in the angular $z-$axis (second column), and in the lineal $y-$axis (third column). The first row of graphs shows the variation of the quality and form factors versus the variation of the misalignment variable. The second row plots the variation in frequency and figure of merit $Q_0V^2C^2$ versus misalignment. The quality factor and figure of merit parameters are given in terms of the percentage change from the aligned scenarios ($\theta_y = \theta_z = g_y = 0$).

Photograph of the vertical cut haloscope coated with copper before assembly and brass spacers (top) and after assembly with a gap between the two halves introduced with stainless steel washer spacer (bottom). Note that for the characterisation both ports were attached to one cavity half unlike shown on the picture in which each port is attached to another cavity half.

Unloaded quality factor $Q_0$ and resonant frequency for different gap sizes which were generated by spacers from washers (left) and $Q_0$ of the cavity between $7$ and $300$~K for gap sizes of $0$ (red) and $1.25$~mm (blue) using brass spacers (right).

Comparison of measurement with uncertainty (blue) and simulation (black) of the unloaded quality factor $Q_0$ (left) and the resonant frequency (right) for different gap openings. For the simulations a copper conductivity at room temperature of $5.8\times10^7$~$S/m$ was assumed.

Unloaded quality factor $Q_0$ and resonant frequency for different gap sizes which were generated by spacers from washers (left) and $Q_0$ of the cavity between $7$ and $300$~K for gap sizes of $0$ (red) and $1.25$~mm (blue) using brass spacers (right).

Comparison of measurement with uncertainty (blue) and simulation (black) of the unloaded quality factor $Q_0$ (left) and the resonant frequency (right) for different gap openings. For the simulations a copper conductivity at room temperature of $5.8\times10^7$~$S/m$ was assumed.

Cavity tuning test stand in the CERN Central Cryogenic laboratory with adjusting screw and rod (red), RF cables (green), temperature sensor (yellow), and the cavity (grey).

Photographs of the cavity halves installed in the tuning holding structure with gears. Top view with RF ports (left) and bottom view (right). The bottom view displays the gear mechanism that moves the cavity halves to each other.

Drawings of the cavity support structure with (a) holding piece for the cavity halves, (b) the sliding structure for alignment, (c) the assembly of the sliding structure, and (d) the complete assembly with the gear system.

Drawings of the cavity support structure with (a) holding piece for the cavity halves, (b) the sliding structure for alignment, (c) the assembly of the sliding structure, and (d) the complete assembly with the gear system.

Tuning range measured with the cavity embedded in the sliding structure at ambient conditions (left) and in liquid nitrogen (right) with a maximum gap size of $2.5$~mm (blue) and no gap (red). At $77$~K disturbances of the spectra due to the boiling of liquid nitrogen are visible, most clearly for the second cavity peak in the spectra of the cavity with a $2.5$~mm gap.

Tuning range measured with the cavity embedded in the sliding structure at ambient conditions (left) and in liquid nitrogen (right) with a maximum gap size of $2.5$~mm (blue) and no gap (red). At $77$~K disturbances of the spectra due to the boiling of liquid nitrogen are visible, most clearly for the second cavity peak in the spectra of the cavity with a $2.5$~mm gap.

Tuning range measured with the cavity embedded in the sliding structure at $20$~K with maximum gap size (blue) and without gap (red) (left). Zoom in on the first cavity peak (axion mode) for a selected set of cavity openings, demonstrating the minimum step size achieved for this measurement.

Tuning range measured with the cavity embedded in the sliding structure at $20$~K with maximum gap size (blue) and without gap (red) (left). Zoom in on the first cavity peak (axion mode) for a selected set of cavity openings, demonstrating the minimum step size achieved for this measurement.

Unloaded quality factor ($Q_0$) of the cavity for different gap sizes generated by the tuning mechanism (yellow) and by spacers (blue) measured at cryogenic temperatures below $20$~K.

Unloaded quality factor ($Q_0$) of the cavity for different gap sizes generated by the tuning mechanism (yellow), by spacers (blue) and without tuning (red) measured at cryogenic temperatures below $20$~K.

(Left) 3D model of the vertical cut structure with gap$ = 2$~mm applying symmetry with the coaxial ports laying in the middle of the gap (centred at gap$/2 = 1$~mm), and (Right) quality factor results from CST simulations for this structure without (blue solid line) and with (red dashed line) centring the coaxial ports.

(Left) 3D model of the vertical cut structure with gap$ = 2$~mm applying symmetry with the coaxial ports laying in the middle of the gap (centred at gap$/2 = 1$~mm), and (Right) quality factor results from CST simulations for this structure without (blue solid line) and with (red dashed line) centring the coaxial ports.