Half-wave coaxial RF cavity for K500 superconducting cyclotron at VECC.
Schematic block diagram for the RF system of K500 superconducting cyclotron.
Electrical equivalent circuit of a cavity, where L, R, and C represent equivalent inductance, resistance, and capacitance of the cavity, respectively. β represents the inductive coupling coefficient.
(a) Cross-section of computer model of single half-wave resonant cavity with sliding short, Dee stem, and Dee at the operating frequency of 19 MHz and (b) electric field lines in Dee-liner region of the cavity (simulated in CST Microwave Studio®).
Step response of (a) Gaa(s)/Gpp(s) at 19 MHz, for Δf = 0, 1 kHz, 2.5 kHz, 5kHz; (b) Gpa(s)/Gap(s) at 19 MHz, for Δf = 0, 1 kHz, 2.5 kHz, 5 kHz; and (c) Gaa(s)/Gpp(s) at 9 MHz, 13 MHz, 19 MHz, 23 MHz, and 27 MHz.
Phase detector response. The output voltage with respect to phase change increases from θ = 0° to 180° but decreases from 180° to 360° forming an “inverted V” shape.
Phase detector dynamic response centred at 90°.
In-phase/Quadrature (I/Q) modulator as phase shifter.
Output phase variation with control voltage at different frequency. The phase deviation reduces with frequency at a fixed input voltage.
Algorithm to examine phase controller output.
The equivalent baseband model of the control system.
Root locus plot of the control system, where “G” is the gain cross-over point.
Step response of phase loop MATLAB/Simulink (simulated) for different time constant (RC).
Step response of phase loop captured in oscilloscope (experimental), where “red” plot shows output phase and “blue” plot shows the control signal to I/Q modulator.
Step response of phase loop captured in oscilloscope and simulation (compared).
The phase stability (bottom plot) for 30 min where AB phase loop was CLOSED, AC loop was OPEN. Although, a deliberate change in AB phase (blue) was made, it remained stable. However, AC phase (green) is not stable as the loop is OPEN. Amplitude variation in three cavities with respect to time is shown in top plot.
The phase stability (bottom plot) for 30 min where both AB loop and AC loop were CLOSED. In spite of deliberate changes made, AB phase remained stable. Also AC phase is stable as it CLOSED. The glitch found in phase deviation plot (blue) is due to analogue phase loop saturation. Amplitude variation in three cavities with respect to time is shown in top plot.
Measured RF pick up at 19 MHz in the spectrum analyzer with no residual phase modulation.
RF parameter chart for different frequencies.
Article metrics loading...
Full text loading...