Front end test stand — WP2 Lead author: David Findlay Accelerator Division ISIS Department Rutherford Appleton Laboratory Michael Clarke-Gayther Alan Letchford John Thomason

Why interest in front end? Front end of machine is where currents and duty cycles are set for whole machine beam quality is set for whole machine UKNF: 5 MW — Front end must be good! Multi-megawatt proton accelerators are new Neutrino factories Neutron sources, transmutation, tritium, energy, etc. 1 W/m loss max., ~10—7 loss per metre Strong overlap

Neutrino factory proton driver: Ion source (65 mA) LEBT (low energy beam transport) RFQ (75 keV  2.5 MeV, 280 MHz) Chopper (typically ~30% chopped out) DTL (2.5 MeV  180 MeV, 280 MHz) Achromat Synchrotrons Need a front end test stand! Front end

Ion source: H—, 65 mA, 400 µs 2 × 2 × world’s leading H— source — ISIS Existing negative ion source development programme at RAL for HPPAs in general ASTeC EU (network HPRI-CT-2001-50021) This programme a benefit to front end test stand programme

Ion Source Development Rig at RAL

LEBT and RFQ Low energy beam transport Matches 65 mA from ion source to RFQ RFQ 4-rod, 75 keV  2.5 MeV, 280 MHz These less of a problem Can base on experience of LEBT and RFQ for ISIS More a matter of implementation than R&D But ~1–1½ MW RF driver required for RFQ

Also to minimise RF transients and control beam intensity Why chopper? Ion source Linac Ring Beam loss >10 × ISIS Bunching Also to minimise RF transients and control beam intensity

With chopper — gaps in beam Ion source Linac Ring No beam loss Bunching

Chopper performance required DC accelerator RF accelerator ns – µs spacing UKNF: 280 MHz, bunch spacing 3.57 ns Switch between bunches Good On Off Bad Partially chopped bunches a problem! Tune shifts!

Choppers across the world: SNS 402 MHz, slow — only chopper built CERN 352 MHz, power dissipation? RAL 280 MHz, fast, rugged, “UK” LEBT MEBT SNS, 2½ ns per bunch

Slow transmission line RAL aspiration: switch in 2 ns and dissipate ~3–4 kW (when “off”) 2-stage process Slow transmission line 1 Lumped line — thermally hardened 2 ns 8 ns

RAL beam chopper — outline scheme Need to build and test with bunched beam

Build test stand Ion source (R&D already under way) LEBT RFQ (bunches beam) Chopper Diagnostics Experience of building test stands at RAL — ISIS RFQ test stand

Front end test stand at RAL — costs SY £k (hardware incl. VAT + contingency) Overall design + infrastructure 8 398 Ion source 7 347 LEBT 5 231 RFQ 14 1388 Chopper 48 1990 4355 hardware 185 travel 82 4495 staff 9035 total

Front end test stand at RAL — time scales

Front end test stand at RAL Six-year programme to build Costed on basis of test stand already built and working ~£4½M equipment ~80 staff-years RAL + university staff Physics and engineering of real accelerator facility