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Is an RFQ a good candidate for a next- generation underground accelerator?

Is an RFQ a good candidate for a next- generation underground accelerator?. Underground Accelerator for Nuclear Astrophysics Workshop October 27-28, 2003 Tucson, AZ Tom Wangler LANL. In any accelerator design there will be tradeoffs and choices must be made.

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Is an RFQ a good candidate for a next- generation underground accelerator?

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  1. Is an RFQ a good candidate for a next- generation underground accelerator? Underground Accelerator for Nuclear Astrophysics Workshop October 27-28, 2003 Tucson, AZ Tom Wangler LANL

  2. In any accelerator design there will be tradeoffs and choices must be made. • How much physics remains to be studied by low-voltage(<1 MV), low-current DC accelerators by the time this facility will be built?Will higher current accelerators be needed? • Although DE/E=10-4 is most desirable, would an accelerator that produced DE/E=10-3 be useful if it delivered more current? • Is size an issue? What are practical space requirements? • Is AC power an issue? What are practical power requirements? • How much beam current is desirable, and how much can you tolerate in the target and detectors?

  3. The RFQ • The RFQ provides rf longitudinal electric field for acceleration and transverse rf electric quadrupole field for focusing -ideal for acceleration of low-velocity high-current ion beams.

  4. Status of RFQ Technology • Normal-conducting RFQ technology is very mature. • LEDA RFQ at Los Alamos has operated at 100-mA CW, accelerating proton beam from 75 keV to 6.7 MeV. • Superconducting RFQs have been built and will soon operate at the Legnaro heavy-ion facility. Should follow their progress. • A normal-conducting 57.5-MHz 4-m-long RFQ is the front-end accelerator for RIA design, accelerating ions up to uranium from 12 keV/u to 200 keV/u. • An RFQ can probably provide DE/E=10-3, which may be acceptable for this application. Need a design study to confirm this. • Energy variability has not been a requirement for most RFQs built so far. This topic was discussed at this workshop and a good concept was proposed.

  5. What about energy variability in an RFQ? • It should be straightforward to provide variable output energy in discrete steps. • Separate the RFQ into independent sections, each with independent amplitude adjustment. • Each RFQ section delivers beam at fixed design value when vane voltage is above threshold to form longitudinal bucket. • Acceleration in downstream RFQ sections can be turned off by lowering their vane voltages below longitudinal bucket threshold. These sections still provide focusing.

  6. Suggestion at this workshop: Continuous energy variability can be provided by installing the sectioned RFQ on a DC HV platform. By providing a variable HV platform voltage with a maximum value that exceeds the voltage gain of the individual RFQ sections, it should be possible to dial up any output energy by: • turning off appropriate number of downsteam RFQ sections • adjusting the platform HV.

  7. Example • Consider 6 RFQ sections for acceleration of q/A ≥1/2 ions from 30 keV/u to 330 keV/u, e.g. H+, D+, 3He++, 4He++ beams. • Energy gain per section = 50 keV/u. • 4He++ would be accelerated from 120 keV to 1.32 MeV with energy gain per section of 200 keV. • Continuous output energies would require a HV platform voltage specification of ≥ 100 kV with q=2 for 4He++ .

  8. Conclusions • The RFQ may be a very good candidate for achieving higher currents with 10s of mA possible for a next generation underground accelerator. • A concept for providing continuous output-energy variability consists of independent RFQ sections installed on a HV platform. • An RFQ design study should be carried out to answer questions such as current limits, energy spread, energy variability, size, and AC power for normal-conducting and superconducting options.

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