A compact linear accelerator based on a scalable microelectromechanical-system RF-structure

Abstract

A new approach for a compact radio-frequency (RF) accelerator structure is presented. The new accelerator architecture is based on the Multiple Electrostatic Quadrupole Array Linear Accelerator (MEQALAC) structure that was first developed in the 1980s. The MEQALAC utilized RF resonators producing the accelerating fields and providing for higher beam currents through parallel beamlets focused using arrays of electrostatic quadrupoles (ESQs). While the early work obtained ESQs with lateral dimensions on the order of a few centimeters, using a printed circuit board (PCB), we reduce the characteristic dimension to the millimeter regime, while massively scaling up the potential number of parallel beamlets. Using Microelectromechanical systems scalable fabrication approaches, we are working on further reducing the characteristic dimension to the sub-millimeter regime. The technology is based on RF-acceleration components and ESQs implemented in the PCB or silicon wafers where each beamlet passes through beam apertures in the wafer. The complete accelerator is then assembled by stacking these wafers. This approach has the potential for fast and inexpensive batch fabrication of the components and flexibility in system design for application specific beam energies and currents. For prototyping the accelerator architecture, the components have been fabricated using the PCB. In this paper, we present proof of concept results of the principal components using the PCB: RF acceleration and ESQ focusing. Ongoing developments on implementing components in silicon and scaling of the accelerator technology to high currents and beam energies are discussed.

Multi-beam RF Accelerators for Ion Implantation

“…The maximum energy gain was 10.2 keV equivalent to an applied voltage of 2.56 keV per acceleration gap. The signal agrees well with our expectation from a 1d model [5].…”

“…The beam energy was measured using the same setup and method as described previously [5]. Ions were produced using a filament-driven ion source operated with argon at a pressure of 1 Pa (7.5 mTorr).…”

“…Multi-beam RF-linacs can boost the total current for applications where beams of mass analyzed single species are required. We have recently reported on the development of multi-beam RF accelerators that we assemble from stacks of low cost wafers [5], [6]. We form RF-acceleration structures and electrostatic quadrupole (ESQ) focusing elements on printed circuit board and silicon wafers with 10-cm diameter using standard microfabrication techniques [7].…”

“…After several stages of acceleration the RF frequency can be increased to compensate for increasing ion velocities and to keep drift distances small. In our first proofof-concept of this approach of multi-beam ion acceleration we used an external LC-tank circuit to generate RF acceleration voltages of 600 V/gap [5]. We have now implemented compact GaN based RF sources [8] that are placed near the acceleration wafers inside the vacuum chamber.…”

Retrospective of the ARPA-E ALPHA Fusion Program

“…The team was able to demonstrate proof of concept for the MEMS accelerator with a prototype compact accelerator fabricated from PCB board. The prototype demonstrated injection and transport of a 5-10 uA beam in a 3x3 beam array, and achieved ion acceleration of 0.5 kV/gap, for a gradient of about 0.3 MV/m [70], [71]. Building on these results, the team has used a compact, near-board RF driver to achieve up to 2.6 kV per gap [72].…”