Beam losses on ISIS and induced radioactivity from MICE David Findlay Head, Accelerator Division ISIS Department Rutherford Appleton Laboratory / STFC MICE target review, RAL, 17 September 2010

70 MeV H – linac 800 MeV proton synchrotron TS-1

Collector straight MICE target

4 Operating ISIS Beam losses Concentrated at one place — on collectors Imperative to keep beam losses low (~1 W/m) ISIS: ~1 kW lost, 163 m circumference, ~6 W/m — activity would be worse at higher energies ISIS only ~0.2 MW, but ×2 beam losses would make life impossible (3 mSv annual dose limit) UK legal limit: 20 mSv/year RAL formal investigation level: 6 mSv/year ISIS limit: 3 mSv/year

BLMs in grey trunking

~0 V-ms 1.6 V-ms R8BLM1 (V-ms) 2.8 V-ms5 V-ms

Without MICE, sum BLMs = 1.6 V-ms At 1 target dip per second for R8BLM1 = 5 V-ms Average sum BLMs = (49 × ) ÷ 50 = 2.7 V-ms 69% greater — not tolerable R8BLM1 Sum BLMs 0 V-ms 1.6 V-ms 1.6 V-ms 20.3 V-ms 2.8 V-ms 30.6 V-ms 5.0 V-ms 57.0 V-ms

Typical contact dose rates around synchrotron — average ~2 mSv/h (On average, dose rates proportional to (days cooling) –0.25 ) Straight 1 — too active for routine measurement

“Activation runs” ~12 hours continuous running Measure dose rates around Straight 7 before and after Example:

10 R8BLM1After ÷ before around Straight 7 (excluding target itself) Mean St. dev.St. error 1 V-ms12 & 13 Sep V-ms10 & 11 Feb V-ms19 & 20 Jun (these surveys done at the beginnings of cycles) Does rates around Straight 7 measured 16 Aug 10, ~1–2 days after end of Cycle 2010/02 with more intense MICE running régime 16 Aug 10 ÷ 20 Jun But 16 Aug and 20 Jun not really comparable — after and before cycle respectively

Pattern of induced activity after end of Cycle 2010/02 with more intense MICE running régime cf. previous cycles? No obvious MICE-induced activity yet But long way to go with muon rates — Cycle 2010/02 ~1 dip every 15 s, and R8BLM1 at only ~2 V ~0.0 V R8BLM1 2.8 V

12 Way(s) forward ? [from Dec target review] Dean’s bump Create vertical bump (R0VD1, R5VD1, R7VD1, R9VD1) Ramp up over 8–9 ms, maintain over 9–10 ms 6 mm achieved so far 10 mm vertical bump at MICE target should be possible with new trim quad. PSUs (higher currents and higher slew rates) Different target configurations and/or materials E.g. pion production cf. multiple scattering Beam dynamics modelling ?

13

15 Synchrotron:800 MeV proton, 50 Hz 5 µC each acceleration cycle Targets:W (Ta coated) Protons: 2 × ~100 ns pulses, ~300 ns apart Moderators:TS-1: 2 × H 2 O, 1 × liq. CH 4, 1 × liq. H 2 TS-2: 1 × liq. H 2 / solid CH 4, 1 × solid CH 4 Instruments:TS-1: 20TS-2: 7 ~330 permanent staff, ~£35M/year budget ~750 experiments, ~1500 users, ~5000 user-visits per year World-leading

Superperiods 9, 0 and 1 of the ISIS 800 MeV synchrotron

Long mechanical drives to reduce need to work close to high-radiation locations (e.g. when changing motor drives for beam collectors)

Vertical and horizontal collectors in Straight 1, looking downstreamand upstream