This paper focuses on a new rectangular waveguide grating Slow-Wave Structure (SWS) with cosine-shaped grooves and studies the propagation characteristics of the wave in the SWS. By using the approximate field-matchin...This paper focuses on a new rectangular waveguide grating Slow-Wave Structure (SWS) with cosine-shaped grooves and studies the propagation characteristics of the wave in the SWS. By using the approximate field-matching conditions,the dispersion equation and the coupling impedance of this circuit are obtained. The dispersion curves and coupling impedances of the fundamental wave are calculated and the influences of the various geometrical dimensions are discussed. The results show that the bandwidth of the cosine-shaped groove SWS is much wider than that of rectangular-shaped groove one. And reducing the groove width can broaden the frequency-band and decrease the phase-velocity,while increment of the groove-depth can also decrease phase-velocity. For above cases,the coupling impedance is more than 16Ω. The present analysis will be helpful on further study and design of the RF systems used in millimeter wave Traveling Wave Tube (TWT).展开更多
Purpose To reduce the beam coupling impedance of the vacuum chamber made of poorly conducting material,a layer of high-conductivity metal,such as copper,is often coated on its inner surface.As the natural bunch length...Purpose To reduce the beam coupling impedance of the vacuum chamber made of poorly conducting material,a layer of high-conductivity metal,such as copper,is often coated on its inner surface.As the natural bunch length of modern accelerators is about several millimeters,its beam spectrum can reach tens of GHz.In this case,the skin depth of copper is of the same order of magnitude as its surface roughness,and its electrical properties can be different from that in DC,which will influence the beam coupling impedance.Therefore,the electrical property of copper coating at high frequency needs to be investigated.Methods In this paper,the method of resonant cavity is adopted to measure the coating conductivity,which is based on the relation between the quality factor of the cavity and material conductivity.Results Three different resonant modes are tested in the measurement,among which the H011 mode shows the best performance.The results also indicate that surface roughness of copper can have an influence on its effective conductivity at high frequency.Conclusion The H011 mode is suitable for measuring high-conductivity materials.When the skin depth of copper is comparable to or larger than its surface roughness,its effective conductivity will be significantly reduced.展开更多
BBU(Beam breakup)instability once appeared in the early stage of 'Dragon-Ⅰ' LIA,which was excited by TM_(110)mode stimulated when the eccentric beam passed through the multi-functional cavity(MFC).The radio f...BBU(Beam breakup)instability once appeared in the early stage of 'Dragon-Ⅰ' LIA,which was excited by TM_(110)mode stimulated when the eccentric beam passed through the multi-functional cavity(MFC).The radio frequency characteristics of MFC were analyzed with three methods such as analytic calculation,numerical computation,and measurement.The frequency of the TM_(110)mode from these methods agreed with the experimental results,while the transverse coupling impedance was different from the experimental results by some times.The main BBU exciter was the big transverse coupling impedance of the MFC which could be concluded.A grid was designed to shield the gap of the MFC.The experiments show that the BBU was compressed and the high frequency oscillation disappeared.展开更多
文摘This paper focuses on a new rectangular waveguide grating Slow-Wave Structure (SWS) with cosine-shaped grooves and studies the propagation characteristics of the wave in the SWS. By using the approximate field-matching conditions,the dispersion equation and the coupling impedance of this circuit are obtained. The dispersion curves and coupling impedances of the fundamental wave are calculated and the influences of the various geometrical dimensions are discussed. The results show that the bandwidth of the cosine-shaped groove SWS is much wider than that of rectangular-shaped groove one. And reducing the groove width can broaden the frequency-band and decrease the phase-velocity,while increment of the groove-depth can also decrease phase-velocity. For above cases,the coupling impedance is more than 16Ω. The present analysis will be helpful on further study and design of the RF systems used in millimeter wave Traveling Wave Tube (TWT).
基金supported by the National Natural Science Foundation of China(No.11775239).
文摘Purpose To reduce the beam coupling impedance of the vacuum chamber made of poorly conducting material,a layer of high-conductivity metal,such as copper,is often coated on its inner surface.As the natural bunch length of modern accelerators is about several millimeters,its beam spectrum can reach tens of GHz.In this case,the skin depth of copper is of the same order of magnitude as its surface roughness,and its electrical properties can be different from that in DC,which will influence the beam coupling impedance.Therefore,the electrical property of copper coating at high frequency needs to be investigated.Methods In this paper,the method of resonant cavity is adopted to measure the coating conductivity,which is based on the relation between the quality factor of the cavity and material conductivity.Results Three different resonant modes are tested in the measurement,among which the H011 mode shows the best performance.The results also indicate that surface roughness of copper can have an influence on its effective conductivity at high frequency.Conclusion The H011 mode is suitable for measuring high-conductivity materials.When the skin depth of copper is comparable to or larger than its surface roughness,its effective conductivity will be significantly reduced.
文摘BBU(Beam breakup)instability once appeared in the early stage of 'Dragon-Ⅰ' LIA,which was excited by TM_(110)mode stimulated when the eccentric beam passed through the multi-functional cavity(MFC).The radio frequency characteristics of MFC were analyzed with three methods such as analytic calculation,numerical computation,and measurement.The frequency of the TM_(110)mode from these methods agreed with the experimental results,while the transverse coupling impedance was different from the experimental results by some times.The main BBU exciter was the big transverse coupling impedance of the MFC which could be concluded.A grid was designed to shield the gap of the MFC.The experiments show that the BBU was compressed and the high frequency oscillation disappeared.
