Transcript Is an RFQ a good candidate for a next

Is an RFQ a good candidate for a nextgeneration 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.
• 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?
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.
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.
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.
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.
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++ .
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.