The ALOHA project

ALOHA (A Linear Open-Hardware Accelerator) is our principal project: a family of tabletop electron machines, built in stages. ALOHA started in 2026. Each machine is a complete instrument that can be built, tested and documented on its own.

Design requirements

Three requirements apply to every machine.

• Affordable. It has to be within reach of a teaching laboratory or another student team.
• Modular. Subsystems meet at defined interfaces, so that one can be replaced or improved without redesigning the rest.
• Customisable. Whoever builds the machine next will have a different budget, different goals and different parts. The design has to accommodate them.

The machines

The machines are numbered in the order they were proposed. While we build ALOHA-0, we design ALOHA-1. If the conservators who would use ALOHA-2 give the go, we then design and build it around ALOHA-0. ALOHA-1 waits for a host before it is built, so ALOHA-2 may be built first.

ALOHA-0, the electron source. A thermionic source in telefocus configuration: a tungsten hairpin cathode at −20 kV, with a Wehnelt electrode biased slightly below it, faces a grounded anode, and the beam ends on a graphite collector inside a closed vacuum chamber. Its design point is 20 keV and below 1 mA. We build it once, to the beam requirements of ALOHA-2, and a second unit of the same design is the injector of ALOHA-1.

ALOHA-1, the accelerator. An electron linear accelerator of up to 1 MeV. We design it now, without beam: accelerating cavities and their cold tests. We build it only once a university laboratory commits to using it, supervising it and housing it in a shielded room. Direction reviews that decision every September, with the Tutor’s agreement.

ALOHA-2, the instrument. We aim to make ALOHA-0 the source of an X-ray fluorescence instrument for the analysis of paintings. It adds a target that converts the beam into X-rays, an exit window that lets only X-rays out towards the painting, an energy-dispersive detector, shielding and a scanning stage. At 20 keV it is designed to read the core of a conservator’s palette: calcium, iron, copper, arsenic, mercury and lead. Its design starts from a meeting with its future users that fixes their requirements. The first decision there is the target, whose own emission lines must not hide the pigments conservators care about. Once the instrument is handed over, its users decide every measurement and we maintain it.

Model-0, the demonstrator. A glow-discharge demonstrator in which the discharge makes the path of an electron beam visible. It runs at 10 kV, at a pressure of 1.7 Torr measured with a Pirani gauge. We use it for outreach. It brought us our first sponsor, Edwards Vacuum.

The machine parameters and the record of design decisions are published in the ALOHA design documentation.