MATCHING A RESONANT FREQUENCY OF A RESONANT CAVITY TO A FREQUENCY OF AN INPUT VOLTAGE

• US 20090140671A1
• Filed: 11/30/2007
• Published: 06/04/2009
• Est. Priority Date: 11/30/2007
• Status: Active Grant

• Current Assignee: Mevion Medical Systems Incorporated
• Original Assignee: Mevion Medical Systems Incorporated
• Inventors: Vincent, John J., O'Neal, Charles D. III, Molzahn, Adam C.
• Granted Patent: US 8,933,650 B2
• Time in Patent Office: Days
• US Class Current: 315/502
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation
• CPC Class Codes: H05H 13/02 Synchrocyclotrons, i.e. frequency modulated cyclotrons

Abstract

A synchrocyclotron includes magnetic structures that define a resonant cavity, a source to provide particles to the resonant cavity, a voltage source to provide radio frequency (RF) voltage to the resonant cavity, a phase detector to detect a difference in phase between the RF voltage and a resonant frequency of the resonant cavity that changes over time, and a control circuit, responsive to the difference in phase, to control the voltage source so that a frequency of the RF voltage substantially matches the resonant frequency of the resonant cavity.

Claims

1. A synchrocyclotron comprising:

magnetic yokes that define a resonant cavity;

a source to provide input voltage to the resonant cavity; and

feedback circuitry to control the source so that a frequency of the input voltage substantially matches a resonant frequency of the resonant cavity.

2. The synchrocyclotron of claim 1, wherein the source comprises a voltage controlled oscillator (VCO);

and

wherein the feedback circuitry comprises;

a phase detector to detect a phase difference between the frequency of the input voltage and the resonant frequency;

wherein the VCO is configured to change the frequency of the input voltage when the phase difference deviates from a predetermined value.

3. The synchrocyclotron of claim 2, further comprising circuitry to present the phase detector with substantially constant frequencies over a swept frequency range, the substantially constant frequencies being derived from a frequency of the input voltage and the resonant frequency.

4. The synchrocyclotron of claim 2, further comprising:

an integrator to receive an output of the phase detector; and

a filter to generate a control signal for the VCO based on the output of the phase detector, the control signal for causing the VCO to change the frequency of the input voltage when the phase difference deviates from the predetermined value.

5. The synchrocyclotron of claim 4, wherein the filter comprises a low-pass filter having a cutoff frequency that is inversely proportional to a sweep time of the resonant frequency.

6. The synchrocyclotron of claim 2, wherein the phase detector is configured to detect the phase difference by comparing the frequency of the input voltage to a resonant frequency of a voltage in the resonant cavity.

7. The synchrocyclotron of claim 2, wherein the phase detector is configured to detect the phase difference by comparing the frequency of the input voltage to a resonant frequency of a current in the resonant cavity.

8. The synchrocyclotron of claim 1, wherein the resonant frequency sweeps between about 30 megahertz (MHz) and about 300 MHz in about 1 millisecond (ms).

9. The synchrocyclotron of claim 8, further comprising:

a tuning circuit to change the resonant frequency of the resonant cavity.

wherein the tuning circuit comprises;

a variable capacitive circuit that is rotatable;

or

a variable inductive circuit.

10. The synchrocyclotron of claim 1, further comprising:

an ion source to provide particles to the resonant cavity,

wherein the input voltage comprises a radio frequency (RF) voltage to draw particles from the resonant cavity; and

wherein a combination of the RF voltage and a magnetic field caused by the magnetic yokes causes particles drawn from the resonant cavity to accelerate.

11. An apparatus comprising:

magnetic structures that define a resonant cavity;

a source to provide particles to the resonant cavity;

a voltage source to provide radio frequency (RF) voltage to the resonant cavity;

a phase detector to detect a difference in phase between the RF voltage and a resonant frequency of the resonant cavity that changes over time; and

a control circuit, responsive to the difference in phase, to control the voltage source so that a frequency of the RF voltage substantially matches the resonant frequency of the resonant cavity.

12. The apparatus of claim 11, wherein the control circuit comprises:

an integrator to generate a current control signal in response to the phase difference; and

a low-pass filter to generate, in response to the current signal, a voltage control signal for the voltage source.

13. The apparatus of claim 11, wherein the resonant cavity comprises:

a first dee to receive the RF voltage; and

a second dee that is electrically connected to ground;

wherein a space between the first dee and the second dee forms a gap; and

wherein the first dee and the second dee define a tunable resonant circuit configured to create an oscillating electric field across the gap in response to the RF voltage.

14. The apparatus of claim 11, further comprising

a voltage pickup element associated with the resonant cavity, the voltage pickup element for obtaining a voltage of the resonant cavity and for providing the voltage to the phase detector, the voltage corresponding to the resonant frequency.

15. Circuitry to substantially match a resonant frequency of a resonant cavity to a frequency of an input voltage to the resonant cavity, where the resonant frequency changes over time, the circuitry comprising:

a phase detector to detect a difference in phase between the resonant frequency and the input voltage, the phase detector outputting a first signal that corresponds to the difference;

an integrator and filter circuit to generate a control signal in response to the first signal; and

a voltage controlled oscillator to regulate the input voltage in response to the control signal.

16. The circuitry of claim 15, wherein the phase detector is configured to obtain the resonance frequency from one of a voltage of the resonant cavity and a current of the resonant cavity.

17. The circuitry of claim 15, wherein the resonant frequency sweeps over a frequency range of about 30 megahertz (MHz) and about 300 MHz in about a predefined time;

and

wherein the integrator and filter circuit comprises a low-pass filter having a cutoff frequency that is inversely proportional to the predefined time.

18. The circuitry of claim 15, wherein the resonant cavity is part of a synchrocyclotron that is configured to accelerate protons from the resonant cavity.

19. The circuitry of claim 15, further comprising:

a pickup element associated with the resonant cavity, the pickup element for obtaining a signal corresponding to the resonant frequency, the phase detector for receiving the signal from the pickup element.

20. The circuitry of claim 15, wherein the pickup element is capacitive and the signal comprises a voltage signal;

or

wherein the pickup element is inductive and the signal comprises a current signal.

21. A method of matching a resonant frequency of a resonant cavity to a frequency of an input voltage to the resonant cavity, where the resonant frequency changes over time, the method comprising:

detecting a difference in phase between the resonant frequency and the input voltage, a first signal corresponding to the difference;

generating a control signal in response to the first signal; and

regulating the input voltage in response to the control signal.

22. The method of claim 21, wherein detecting the difference in phase comprises obtaining the resonance frequency from one of a voltage of the resonant cavity and a current of the resonant cavity.

23. The method of claim 21, wherein the resonant frequency sweeps over a frequency range of about 30 megahertz (MHz) and about 300 MHz in about a predefined time;

and

wherein the control signal is low-pass filter circuit that has a cutoff frequency that is inversely proportional to the predefined time.

24. The method of claim 21, wherein the resonant cavity is part of a synchrocyclotron that is configured to accelerate protons from the resonant cavity.

25. The method of claim 21, further comprising:

obtaining a signal corresponding to the resonant frequency, the difference in phase between the resonant frequency and the input voltage being determined based on the signal corresponding to the resonant frequency.