The RFQ uses oscillating radio-frequency (RF) fields to impart energy to the charged particles. It's designed to work at very low energies, where conventional acceleration methods are less effective. Instead of relying solely on magnetic lenses for beam focusing, the RFQ generates strong electric quadrupole fields. These fields provide both transverse focusing (keeping the beam confined) and longitudinal bunching (compressing the beam in time). As the beam is accelerated, the RFQ structure manipulates the phase of the particles relative to the RF field. This causes particles that are out of phase to be re-bunched, improving beam quality and stability for subsequent acceleration stages.
Components
A Radio Frequency Quadrupole (RFQ) is a complex device with several key components that work together to bunch, focus, and accelerate charged particles. Below is the summary:
1. Electrodes (Vanes)
The RFQ typically has four parallel electrodes arranged in a quadrupole configuration around the beam axis, and these electrodes generate the oscillating electric fields necessary for focusing and accelerating the particles. The electrodes are alternately charged with positive and negative RF voltages.
2. RF Power Supply
A high-frequency RF power source, usually in the range of tens to hundreds of MHz, it provides the oscillating voltage to the electrodes, creating the necessary electric fields for particle acceleration and focusing.
3. Resonant Cavity
It is a structure that houses the electrodes and supports the RF fields, and the cavity is designed to resonate at the frequency of the RF power supply, ensuring efficient transfer of energy to the particles.
4. Beam Pipe
A vacuum tube that runs through the center of the RFQ, and it provides a path for the particle beam, maintaining a high vacuum to minimize interactions with residual gas molecules.
5. Cooling System
This system of water or other coolant channels integrated into the RFQ structure, and it removes heat generated by the RF power and particle interactions, preventing thermal deformation and damage to the components.
6. Support Structure
It's a mechanical framework that holds the electrodes and other components in precise alignment, and it ensures the stability and alignment of the RFQ components, which is critical for maintaining the quality of the particle beam.
7. Tuning Mechanism
These are adjustable components, such as tuning screws or plungers, and they allow fine-tuning of the resonant frequency of the cavity to match the RF power supply frequency, optimizing the performance of the RFQ.
8. Vacuum System
The pumps and seals that maintain a high vacuum inside the beam pipe and resonant cavity, it reduces the presence of gas molecules that could scatter or absorb the particles, ensuring efficient beam transport.
9. Diagnostics
The instruments such as beam position monitors and current transformers, and they reassure various parameters of the particle beam, such as position, intensity, and energy, allowing for monitoring and optimization of the RFQ performance.
10. Control System
It includes electronic control units and software, and it manages the operation of the RF power supply, cooling system, vacuum system, and diagnostics, ensuring coordinated and stable operation of the RFQ.
The components of an RFQ work together to create the necessary electric fields for bunching, focusing, and accelerating charged particles. Each component plays a critical role in ensuring the efficient and stable operation of the RFQ, making it a vital part of many particle acceleration systems. It combines electric fields oscillating at radio frequencies with a specially shaped electrode structure to manipulate the particle beams. RFQs are often used as the initial stage in larger accelerator systems because they are very efficient at controlling and accelerating low-energy ion beams.
How does it work?
A Radio Frequency Quadrupole is a type of linear accelerator used to efficiently bunch, focus, and accelerate low-energy charged particles (such as ions or protons) at the initial stages of a particle accelerator. It operates using oscillating radio frequency (RF) electric fields to achieve these functions, and it works in certain way as indicated below:
√ Structure
The RFQ consists of four parallel electrodes (vanes) arranged in a quadrupole configuration around the beam axis.
These electrodes are alternately charged with positive and negative RF voltages, creating an oscillating electric field.
√ Electric Fields
The RFQ generates two types of electric fields: transverse (radial) field & longitudinal (axial) field. The quadrupole field focuses the particles radially, preventing them from spreading out due to space charge effects or other forces while the alternating polarity of the electrodes creates a focusing force that keeps the beam tightly confined. The oscillating RF field provides a series of accelerating "buckets" that push the particles forward along the beam axis. The field is timed so that particles arriving at the correct phase of the RF cycle are accelerated, while those arriving at the wrong phase are decelerated.
√ Particle Bunching
When particles enter the RFQ, they are initially spread out in time and space, and the oscillating RF field groups the particles into bunches by accelerating those that arrive at the right phase and decelerating those that arrive at the wrong phase. This process ensures that the particles are synchronized and tightly bunched.
√ Acceleration
The longitudinal electric field accelerates the bunched particles along the beam axis, and the energy of the particles keeps increasing as they move through the structure. The energy gained per unit length is relatively low, but the RFQ is highly efficient for accelerating particles from very low energies (a few keV) to several MeV.
√ Focusing
The transverse quadrupole field continuously focuses the particles, keeping the beam tightly confined and preventing it from diverging, and this focusing is crucial for maintaining beam quality and ensuring efficient acceleration.
√ Phasing and Synchronization
The RFQ operates at a specific frequency, typically in the range of tens to hundreds of MHz. The particles must be injected into the RFQ at the correct phase of the RF cycle to ensure efficient acceleration and bunching while maintaining synchronization.
Model Nr.: FAB325-25
- √ 325MHz
- √ Linear four-wing RFQ, pulsed beam,
- √ Extraction energy: 2.5MeV
- √ Chamber: CW008A(C10200) ≥99.97%
- √ Electrode accuracy ±0.05mm,
- √ Chamber vacuum leak rate ≤1×10-10mbar･L/s
- √ Chamber Size L2,185mm, W300mm, H300mm
- √ Number of sections: 2
- √ Weight 1.5 tons
Model Nr.: FAB805-165
- √ FRIB rare isotope 80.5MHz four-wing RFQ
- √ Frequency (MHz): 80.5
- √ Injection/output energy (keV/u): 12 / 500
- √ Design charge-to-mass ratio: 1/7 - 1/3
- √ Accelerating voltage ramp (U, kV): 60-120
- √ Surface electric field (Kilpatrick): 1.6
- √ Q factor: 16500
- √ Operating RF power (kW, O-U): 15–100
- √ Dipole mode (closest, MHz): 78.3 / 83.2
- √ Cavity size 5,040 x 1000 x 1000mm
- √ Nr. of sections: 5
- √ Total weight 30 tons
Model Nr.: FAB165-20-5
- √ Continuous wave beam, injecti
- √ 165MHz boron neutron RFQ, on energy 50KeV
- √ Current 20mA
- √ Chamber material, CW009A/C10100 Cu≥99.99%
- √ Electrode accuracy ±0.05mm
- √ Cavity vacuum leak rate <1.0×10-9 Pa·L/s
- √ Cavity dimension 5,600 x 341 x 341
- √ Cavity dimension tolerance (±0.03mm)
- √ 5 segmented beams
Custom Fabrication Service
Fabmann specialize in precision-engineered solutions for advanced particle accelerator systems, including custom-designed Radio Frequency Quadrupoles (RFQs). Our engineering team is committed to develop RFQs tailored to your specific frequency, energy, and beam dynamics requirements. While our advanced manufacturing facility & skills such as CNC machining, high-vacuum brazing, and surface finishing techniques to meet exacting tolerances. Our RFQs are manufactured to micron-level precision, ensuring minimal field distortion and maximal energy transfer for stable beam acceleration. We partner closely with our clients to understand your technical challenges, offering flexible solutions for highly sophisticated RFQ, and our team provides ongoing support, including RF tuning, multipacting analysis, and cryogenic compatibility testing.
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