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

2. 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

3. 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

4. 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 )
This programme a benefit to front end test stand programme

5. Ion Source Development Rig at RAL

6. 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

7. 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

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

9. 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!

10. 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

11. 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

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

13. 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

14. Front end test stand at RAL — costs
SY £k (hardware incl. VAT +
contingency)
Overall design + infrastructure
Ion source
LEBT
RFQ
Chopper
4355 hardware
185 travel
staff
9035 total

15. Front end test stand at RAL — time scales

16. 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