ISIS Introduction to the accelerator and target.General information.

1. FELIX QVI POTVIT RERVM COGNOSCERE CAVSAS Introduction to ISIS accelerator and target David Findlay Accelerator Division ISIS Department Rutherford Appleton Laboratory

3. Electron source Proton source

4. Neutron source

6. Structure Atomic motions Paracetamol

8. Measurements are made on condensed matter samples on ISIS by neutron scattering Just as an object can be seen by suitably collecting scattered optical photons, so a condensed matter sample can “seen” by suitably collecting scattered neutrons Source Sample Detector neutrons

9. Neutron source is pulsed Neutron energies measured by time of flight t = 0 Source Detector time t E = ½ m (l/t)² length l

10.  =  /p (reduced de Broglie wavelength)  pc =  c/   = 1 Å   = 0.159 Å  c = 197 MeV.fm = 1970 eV.Å (e²/  c = 1/137)  pc = 12.4 keV Neutrons: p²c² = 2mc²E, m = 938 MeV  E(neutron) = 80 meV X-rays: pc = E  E(X-ray) = 12 keV Cf. dynamics: typical energies ~meV

11. ISIS is accelerator -driven neutron source 800 MeV protons, 200 µA, 160 kW on tungsten target ~2×10 16 neutrons/second (mean) from spallation Uses three cascaded particle accelerators

15. Extremes of accelerator range

19. Neutron generation on ISIS: 800 MeV protons, 200 µA, 160 kW on tungsten target ~2×10 16 neutrons/second (mean) from spallation

29. Linac (70 MeV, H – ions) 4-section (-tank) drift tube linac Acceleration by 202.5 MHz RF, not DC Each tank highly ~10 m long, ~1 m diameter. Highly resonant; Q ~50000 Hide particles inside drift tubes while sign of oscillating accelerating field wrong

36. Everything synchronised to magnetic field Biased sine wave — (660 + 400 cos (  t)) amps Megawatt resonant LC circuit

40. All beam in synchrotron extracted in one turn  = v/c = 0.84, 163 m circumference  revolution time = 0.65 µs 4 µC ÷ 0.65 µs  6 A circulating current Extracted pulse ~0.4 µs long

48. Target ~2.5×10 13 (4 µC) protons per pulse on to tungsten target (50 pps) ~15–20 neutrons / proton, ~4×10 14 neutrons / pulse Primary neutrons from spallation: evaporation spectrum (E ~1 MeV) + high energy tail

51. Moderators But want m eV, not M eV Moderation — elastic nuclear scattering — low A Three moderators: liquid hydrogen (20°K), methane (100°K), water (43°C) Reflector Moderators Primary target Protons

55. Source Sample Detector neutrons

59. DC accelerator

60. RF accelerator

67. Second Target Station 10 pps Every fifth pulse 200 kW ÷ 5 = 40 kW

70. Second Target Station (TS2) — £100M, first beam 2007 Optimised for cold neutrons Cold neutrons  low energy / slow neutrons Consistent with low pulse repetition frequency — 10 pps ( cf. 50 pps to present target) Slow neutrons  long wavelengths — sensitive to longer range structure Polymers, surfactants, colloids, proteins, viruses, pharmaceuticals, ...

71. 1 MW upgrade Add 3 / 8 GeV synchrotron Muons Neutrons

72. Further into future — 2½ and/or 5 MW upgrades