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This is the working site for members of the Front End Test Stand (FETS) project.

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FETS Project Overview

High power short-pulse proton drivers are required for a wide range of applications including neutron spallation sources, neutrino factories, muon colliders, ADSRs and nuclear waste transmutation. In order to generate high power beams, proton drivers typically require multi-turn charge-exchange injection of H⁻ ions into an accumulator ring. The overall deliverable power and quality of the beam is largely determined by the initial accelerating stage of the machine: the 'Front End'. Creating a front end to meet the demands of modern proton drivers is an ongoing challenge in accelerator technology.

For hands-on maintenance of high power proton drivers, the beam-loss-induced radio-activation of components must be kept to a minimum. One of the major sources of beam loss is the trapping of particles in the ring RF buckets. By pre-chopping the H⁻ beam in the linac, trapping losses are considerably reduced. Chopping should be performed at low energy, in the front end, to ease the dumping of up to 40% of the beam. Chopping should also be as quick as possible so there are no partially chopped bunches leaving the linac. A sufficiently quick 'perfect' chopper has yet to be demonstrated world-wide.

The Front End Test Stand (FETS) is an experiment based in building R8 at the Rutherford Appleton Laboratory (RAL). It is a collaboration between ISIS, ASTeC, Imperial College, University of Warwick, University College London and Royal Holloway. This project will design, build and test the first stages necessary to produce a very high quality, perfectly chopped H⁻ ion beam as required for high power proton drivers. The beam parameters are 3 MeV energy and 60 mA beam current at 50 Hz repetition rate and up to 2ms pulse duration. The major components and contact details are detailed below.

Ion Source

Penning ion source

• Caesium-enhanced Penning surface plasma H⁻ ion source
• 60 mA pulsed beam current at 50 Hz repetition rate and up to 2 ms pulse length
• 0.25 π mm mrad transverse emittance

Contacts:

LEBT

LEBT

• Three-solenoid magnetic low energy beam transport
• Space-charge neutralised
• 95% transmission

Contacts:

RFQ

RFQ machining

• 324 MHz, 4 metre, 3 MeV radio frequency quadrupole
• Vane-type resonating cavity
• Bolted construction

Contacts:

MEBT

MEBT

• Electromagnetic quadrupole and re-bunching cavity medium energy beam transport
• Transport beam through chopper to diagnostics line or rest of accelerator
• Low beam loss and emittance growth

Contacts:

Chopper

Electrostatic chopper

• Novel separated 'fast-slow' electrostatic deflectors
• Fast chopper rise time <3 ns (between RFQ microbunches): no partially chopped bunches
• Slow chopper pulse rises in gap made by fast chopper

Contacts:

Diagnostics

Principle of laser photodetachment emittance measurement

• Non-interceptive
• Beam current transformers & beam position monitors
• Laser photo-detachment emittance scanning

Contacts:

Controls/DAQ

Block diagram of BPM DAQ

• Labview PXI-based
• EPICS distribution
• Fast sampling and calculation

Contacts: