Proposal for the continuation of the Front End Test Stand

Accelerator peer review panelAugust 2011

Alan LetchfordSTFC, Rutherford Appleton Lab.

On behalf of the FETS collaboration

• Introduction• Motivation for FETS• FETS work packages• Schedule and costs• Conclusions

Outline

The Front End Test Stand (FETS) aims to demonstrate key technologies for the front end of the next generation of high power pulsed proton accelerators. FETS is the only dedicated high power proton accelerator hardware R&D in the UK. Applications include:

• ISIS upgrades• Neutrino Factory• Future Spallation Neutron Sources• Accelerator Driven Systems• Waste Transmutation etc

The key components of FETS are:• High intensity, high duty factor, H- ion source• Magnetic Low Energy Beam Transport (LEBT)• 324 MHz 4-vane Radio Frequency Quadrupole (RFQ)• Medium Energy Beam Transport (MEBT)• Very high speed beam chopper• Comprehensive diagnostics

FETS is a collaboration between ISIS, ASTeC, Imperial College London, Warwick University, the ESS Bilbao consortium and Royal Holloway University of London. Huddersfield and UCL will join on success of this proposal.

Introduction

Considerable progress has already been made on the ground at RAL.

Introduction

FETS was conceived to demonstrate perfect beam chopping but is a generic test stand not a single experiment.

FETS is educational – much of the team were complete new-comers to the field a few short years ago. Now producing world class work.

FETS is collaborative – our facility means people can move from computer studies to real world experiments. Having hardware improves our international credibility.

Motivation for FETS

FETS is well aligned with STFC strategy which recognises the importance of accelerator technology. FETS is currently the only large scale, hardware based, proton accelerator R&D activity within STFC.

Completing FETS in a timely manner allows us to achieve the narrow goal of demonstrating an intense, high quality, perfectly chopped H- beam.

FETS is a significant resource allowing our academic collaborators to ‘get their hands dirty’ with high power accelerator hardware.

FETS has great potential utility beyond the current phase of work. In the future the test stand could:

– Remain a test stand to develop novel structures, RF techniques, diagnostics etc.– Be incorporated into a new facility or upgrade of an existing facility.– Become the focus of a Proton Centre at RAL.– Be developed into a low energy beam facility.– …

Motivation for continuing FETS

The work completed and planned for FETS is recognised internationally. Our demonstrated expertise has attracted interest from institutions including

– CERN– ESS Bilbao– ESS Lund– SNS Oakridge– FermiLab– J-Parc– CSNS

A relatively modest allocation over 3 years will see FETS become a world class facility producing internationally significant results.

International context

The FETS ion source delivers world class performance and has been the subject of an intensive development programme.

The FETS specification is for a 60mA beam in 2ms pulses with low emittance at 50Hz. All of the specification has been met although not quite yet simultaneously.

WP1: Ion Source and LEBT optimisation

60 mA H- beam current demonstrated

Low measured emittance at high current in the FETS LEBT

In the period of the proposal the tasks to be completed in WP1 are:

– Increase the extraction voltage to 25 kV– Further investigate extraction geometry– Determine source lifetime– Measure the plasma parameters– Model the plasma in detail and develop codes based on measurements– Design and construct a 2X scaled source– Evaluate the scaled source– Investigate the space charge neutralisation process for negative ions in a magnetic LEBT

Requested resources:– £642k staff– £90k hardware

WP1: Ion Source and LEBT optimisation

Following extensive modelling and experimentation the design of the FETS 3 MeV, 324 MHz, 4-vane RFQ is complete. Machining of the 16 segments of the 4m long structure is about to commence.A novel approach to RFQ design has resulted in high performance whilst overcoming some of the shortcomings associated with previous designs.

WP2: RFQ commissioning

RFQ engineering model

RFQ cold model

‘Weld test’ models under investigation at I.C.

A huge computational effort has been put into perfecting the design. Electromagnetic, thermal, fluid and mechanical.

WP2: RFQ commissioning

WP2: RFQ commissioning

An novel integrated engineering and physics modelling method developed by FETS gives the most accurate beam dynamics simulations of an RFQ.

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In the period of the proposal the tasks to be completed in WP2 are:

– Assemble and install RFQ– Manufacture RF couplers– Complete RF power distribution installation– Low power tests and tuning of RFQ structure– High power conditioning– Low level RF system evaluation– Cooling system evaluation– Beam tests– Comparison of RF and beam performance measurements with design

Requested resources:– £764k staff– £278k hardware

WP2: RFQ commissioning

At low energies electrostatic and RFQ accelerators perform well.

At higher energies side coupled or elliptical SC cavities deliver high RF efficiency.

For intermediate energies the drift tube linac has traditionally been used. Although a mature and well understood technology, DTLs suffer from low shunt impedance compared to alternatives such as CH, IH or spoke resonators.

With a view to future linac facilities or further development of FETS to higher energies, the beam dynamics and RF characteristics of a room temperature CH linac will be investigated.

WP3: Design of a CH linac

In the period of the proposal the tasks to be completed in WP3 are:

– Detailed RF modelling of 324 MHz CH resonators– Full particle tracking simulations of a CH linac to ~20 MeV– Construction of a CH cold model for low power RF tests

WP3: Design of a CH linac

Chopping is an essential aspect of all high power proton accelerators that use rings.

The FETS project has developed a state-of-the-art two stage chopping scheme to achieve perfect bunch-by-bunch chopping of the 3 MeV RFQ beam. A compact, low loss, low emittance growth medium energy beam transport to contain the choppers and match the beam downstream has been highly optimised.

The European Spallation Source project has identified the FETS MEBT as the most promising design on which to base their own.

WP4: MEBT

MEBT layout and beam envelopes

Prototyping of the two types of high bandwidth chopper deflector is currently underway.

Prototyping of the rebunching cavities is about to start with our partners at ESS Bilbao. These studies are relevant to a wide range of applications.

WP4: MEBT

Helical prototype Planar prototype

In the period of the proposal the tasks to be completed in WP4 are:

– Prototype complete chopper assemblies– Produce a fully engineered design of the complete MEBT– Manufacture the choppers, cavities and quadrupoles– Procure the remaining MEBT components (vacuum, RF, PSUs etc)– Complete installation of the MEBT– Commission all the MEBT equipment– Achieve a MEBT beam– Demonstrate chopping

Requested resources:– £656k staff– £922k hardware

WP4: MEBT

In addition to conventional beam diagnostics and measurements, non destructive techniques based on laser photo-detachment is an important aspect of FETS.

Diagnostics already developed and in use on FETS include– Current transformers– Faraday cup– Slit and cup scanners for time resolved 2D emittance– Scintillators for beam profiles– Pepper-pot for 4D phase space

Sophisticated software for data analysis has also been developed.

Non destructive diagnostics will be an essential aspect of any future high power accelerator, allowing on-line full power measurements with minimal beam loss and activation.

WP5: Diagnostics

First proof of principle tests of laser photo detachment are being carried out on the ion source beam upstream of the LEBT.

WP5: Diagnostics

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Tests of the emittance reconstruction technique have been completed on a low power beam using slits in place of the laser.

The Maximum Entropy Method of reconstruction is being evaluated against more traditional techniques

WP5: Diagnostics

In the period of the proposal the tasks to be completed in WP5 are:

– Design beam current measurement system for MEBT– Design beam profile (wire scanner/scintillator) system for MEBT– Design strip line beam position system for MEBT– Install and commission MEBT diagnostics– Demonstrate 1D laser profile measurement– Demonstrate 2D laser profile measurement and reconstruction– Commission operational laser emittance system in MEBT

Requested resources:– £659k staff– £139k hardware

WP5: Diagnostics

This work package will investigate the way in which the investment in the FETS infrastructure could best be put to use for the accelerator community.

FETS offers, after commissioning, a unique facility producing a low-energy high-power proton beam which could be interesting for a series of experiments and applications.

The aim of this work package will be to describe in detail the different options for FETS as an injector facility and nucleus for a possible Proton Accelerator Centre at RAL.

The work package will also define the desired upgrade plan and evaluate the cost for the different options proposed. So far 5 different subjects for study have been identified, but it is intended to keep the work package open for other ideas and partners.

WP6: Future of FETS and development into a proton centre

In the period of the proposal the areas to be investigated in WP6 include:

– Test of novel RF power systems (eg Siemens solid state klystron) on FETS

– High-power beam test of a CH cavity linac module reusing the available RF and delivering a 5-6 MeV beam

– High power target tests for Boron Neutron Capture Therapy, isotope and slow neutron production (at 5-6 MeV)

– Extension of FETS to a 20 MeV linac and injection into a low energy proton FFAG to investigate injection and acceleration of space charge dominated proton beams as required for ADSR and other applications

– Extension of FETS to 70 MeV (or above) as a replacement for the ISIS linac

Requested resources for WPs 3 & 6:– £311k staff

WP6: Future of FETS

The proposal for continuation of FETS covers the three year period 2012-2015

Schedule

The costs identified for the 3 year programme to continue FETS are £1.5M for equipment and £3.1 M for staff, a total of £4.6 M.The costs are flat for the first two years, reducing in the third.

Costs

FETS is well aligned with STFC strategy which recognises the importance of accelerator technology.

A modest investment over 3 years will allow us to complete FETS which is currently the only large scale, hardware based, proton accelerator R&D activity within STFC.

Completing FETS in a timely manner allows us to achieve the narrow goal of demonstrating an intense, high quality, perfectly chopped H- beam.

Completing FETS allows us to achieve the wider goal of demonstrating competence and engaging convincingly with international collaborators.

FETS is a significant resource allowing non-laboratory accelerator institutes access to high power proton accelerator hardware.

FETS has great potential utility beyond the current phase of work.

Conclusions