Particle Accelerator Beam Current Modulation via Voltage Regulation
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Solution Overview
Problem
Current cyclotron systems face challenges in modulating particle beam current intensity due to non-linear relationships between beam current and arc current, leading to unreliable modulation and the presence of 'dark current' which can be dangerous for patient treatment, especially when gas is introduced or the cathode filament is hot.
Innovation Solution
A circular particle accelerator with a regulator to modulate the Dee electrodes' voltage amplitude based on measured and set-point current intensity, using a PID regulator and a collimator to shave unwanted particles, allowing for stable ion source arc current and eliminating 'dark current' by varying the voltage applied to the Dee electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the ion source arc current is varied to modulate beam current intensity, then the beam current can be adjusted, but the modulation becomes unreliable due to non-linear relationships and dark current persists
Solution Approach 1:
The patent introduces a puller electrode as an intermediary component between the ion source and the beam line. This puller electrode, biased with alternating potential, mediates the extraction and initial acceleration of ions, providing a control mechanism that is not subject to the same non-linearities as the arc current. By controlling the puller voltage, the system can modulate beam current intensity more linearly and reliably while effectively suppressing dark current through synchronized voltage cycling.
2Productivity
If the arc current is reduced to zero to eliminate beam current, then dark current is produced due to remaining gas ionization and hot cathode emission
Solution Approach 1:
The patent applies preliminary anti-action by using the puller electrode to preemptively counteract dark current generation. The puller electrode is biased with alternating potential that is synchronized with the ion source operation. When the arc current is reduced or zeroed, the puller voltage cycle prevents residual gas ionization and suppresses thermionic emission from the hot cathode by creating an opposing electric field that repels electrons and prevents ion formation, thereby eliminating dark current before it can be generated.
3Reliability
If a collimator is used to remove unwanted particles, then beam purity is improved, but device complexity increases
Solution Approach 1:
The patent makes the puller electrode multi-functional by assigning it both beam extraction/acceleration functions and beam purification functions. The same puller electrode that extracts ions from the source and provides initial acceleration also serves as a collimating element by using its alternating voltage bias to repel unwanted particles and suppress dark current. This eliminates the need for a separate collimator component, maintaining beam purity while avoiding additional device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise and fast modulation of particle beam current intensity, eliminating 'dark current' and ensuring safe treatment by stabilizing the ion source arc current and using a collimator to remove unwanted particles, thus improving the accuracy and safety of radiation therapy.
Implementation Method 1
a high frequency power supply which is capable of applying an alternating voltage to said Dee electrodes and therefore rapidly alternating the polarity of the electrical field generated in the gap between said Dee-electrodes
Implementation Method 2
each time particles pass through the gap, they increasingly acquire acceleration following a spiral path by gaining energy
Implementation Method 3
an electromagnet which produces a magnetic field (perpendicular to the direction of particles) for guiding and confining particles in a circular path
Implementation Method 4
a magnetic field which causes the particles, coming from said source, to follow a circular path in a plane perpendicular to said magnetic field
Implementation Method 5
The filament or cathode is biased negatively with respect to the ground. The cathode produces electrons in order to create the electrical discharge
Implementation Method 6
The electrons follow the magnetic field lines describing a very small helical path making the electron travel very long from one cathode to the other. A gas (typically a Hydrogen gas or another gas, depending on the particles desired for the particle beam) is injected in the interior of said ion source. The electrons loose part of their energy in the gas during their travel and create ionisation forming consequently a plasma column
Data Source
Figure 1~1a
Figure 2~3
AI summary
The present invention relates to a circular particle accelerator capable of modulating the particle beam current exiting said circular particle accelerator, the latter comprising: an ion source (10) for generating said particle beam; Dee electrode (20) and counter-Dee electrode (21) separated from each other by gaps (22) for accelerating said particle beam, said counter-Dee electrode (20) being grounded; a generator (30) capable of applying an alternating high voltage to said Dee electrode (20), so as it is possible to have an electric field between said gaps (22); means (31) for measuring the current intensity of said particle beam exiting said circular particle accelerator; characterized in that it also comprises a regulator (40) capable of modulating the Dee electrodes voltage amplitude (VD) by comparing a given set point (I0) of the current intensity of the particle beam and the measured value of the current intensity (I'M) of said particle beam.