Instrumentation in small, low energy machines

1. Instrumentation in small, low energy machines Ulrich Raich CERN AB-BDI Ulrich Raich CERN AB/BDI

2. LHC SPS Dump line LHC Duo Plasmatron Proton source PS PSB RFQ Proton Linac Proton source Ion Linac RFQ LEIR Cyclotron resonance Ion source The LHC • The LHC is CERN’s flagship projectbut … it is not exactly a small, low energymachine! • why start with the LHC? Ulrich Raich CERN AB/BDI

3. Luminosity • Quality factor of a collider: luminosity • Depends on kb: number of bunches • N: number of particles per bunch • εn: emittance • LEP was limited in energy by synchroton radiation • In LEP, due to Landau damping, the biggest machine was largely responsible for beam quality. • In LHC the injectors determine beam quality Ulrich Raich CERN AB/BDI

4. Peculiarities of small machines • Particles have small magnetic rigidity Bρ • Particles are easy to bend • Beam spot and angles are large (adiabatic damping)physical emittance shrinksfactor 1500 from 50MeV – 450 GeV • They need tight mesh of focusing magnets (leaves little space for instrumentation) • Space charge • Energy deposition inintercepting matter is high • Few instruments but large variety • Particle speed changes with acceleration Photo GSI Darmstatt Ulrich Raich CERN AB/BDI

5. Uses of small machines • Small machines: • Injectors for bigger machines • Test stands • Medical machines • Accelerators for industrial use (ion implantation, material tests)even the Louvre has an accelerator • Accelerators at Universities or small research institutes Ulrich Raich CERN AB/BDI

6. Intensity measurementsFaraday Cup • Electrode: 1 mm stainless steel • Only low energy particles can be measured • Very low intensities (down to 1 pA) can be measured • Creation of secondary electrons of low energy (below 20 eV) • Repelling electrode with some 100 V polarisation voltage pushes secondary electrons back onto the electrode Ulrich Raich CERN AB/BDI Contributed by G. Molinari and V. Prieto

7. Repelling secondary electrons • With increasing repelling voltage the electrons do not escape the Faraday Cup any more and the current measured stays stable. • At 40V and above no decrease in the Cup current is observed any more Ulrich Raich CERN AB/BDI

8. Measurements of ion charge-state distribution Faraday Cup slit Spectrometer magnets Ulrich Raich CERN AB/BDI

9. Current transformers • Often very close to pulsing magnetic elements • Needs good shielding • Long beam pulses from ion sources (typical 100μs) • Digitization of raw signal with digital integration is possible Ulrich Raich CERN AB/BDI

10. Magnetic shielding • Shield should extend along the vacuum chamber length > diameter of opening • Shield should be symmetrical to the beam axis • Air gaps must be avoided especially along the beam axis • Shield should have highest μ possible but should not saturate monitor Permalloy (μ3) Transformer steel (μ2) Soft iron (μ1) Ulrich Raich CERN AB/BDI

11. Calibration of AC current transformers • The transformer is calibrated with a very precise current source • The calibration signal is injected into a separate calibration winding • A calibration procedure executed before the running period • A calibration pulse before the beam pulse measured with the beam signal Ulrich Raich CERN AB/BDI Trace contributed by F. Lenardon

12. Interaction of particles with intercepting matter • with the following constants: NA: Avogadro’s number me and re: electron rest mass and classical electron radius c: speed of light • the following target material properties: ρ: material density AT and ZT: the atomic mass and nuclear charge • and the particle properties: Zp: particle charge β: the particles velocity and Dependance on Ulrich Raich CERN AB/BDI

13. Screen Tests • Penetration depth of ions at 4 MeV/u: <10µm • Particle energy is deposited in very small volume • Heat load and electric charging becomes a problem • Several screen materials tested Ulrich Raich CERN AB/BDI T. Lefevre, this conference

14. Test for resistance against heat-shock Use as reference Better for electrical conductivity (>400ºC) Better for thermal properties (higher conductivity, higher heat capacity) Ulrich Raich CERN AB/BDI question

15. Wire Scanners A thin wire is quickly moved across the beam Secondary particle shower is detected outside the vacuum chamber on a scintillator/photo-multiplier assembly Position and photo-multiplier signal are recorded simultaneously Ulrich Raich CERN AB/BDI

16. Problems at low energy • Secondary particle shower intensity in dependence of primary beam energy Ulrich Raich CERN AB/BDI

17. Wire scanners and partially stripped ions Partially stripped ions loose electrons when interacting with the wire The beam is lost Can measure amplitude distribution however Ulrich Raich CERN AB/BDI

18. Influence of a drift space x’ x’ x x slit Transforming angular distribution to profile • A slit produces a vertical slice in transverse phase space • Moving the slit scans the phase space • When moving through a drift space the angles don’t change (horizontal move in phase space) • When moving through a quadrupole the position does not change but the angle does (vertical move in phase space) slit Influence of a quadrupole x’ slit x Ulrich Raich CERN AB/BDI

19. The Slit Method Ulrich Raich CERN AB/BDI 3d plot from P. Forck

20. Single pulse emittance measurement Every 100 ns a new profile slit Kickers SEMgrid Ulrich Raich CERN AB/BDI

21. Result of single pulse emittance measurement Ulrich Raich CERN AB/BDI

22. Multi-slit measurement • Needs high resolution profile detector • Must make surethat profilesdont overlap beam Scintillator + TV + frame grabber often used as profile detector Very old idea, was used with photographic plates Ulrich Raich CERN AB/BDI

23. Pepperpot Uses small holes instead of slits Measures horizontal and vertical emittance in a single shot Ulrich Raich CERN AB/BDI Photo P. Forck

24. E • Spectrometer transforms energies into positions • Buncher transforms time into Energy kicker φ Spectrometer magnet SEMgrid buncher slit kicker Spectrometer magnet Longitudinal emittance Ulrich Raich CERN AB/BDI

25. The End • Thanks for your attention Ulrich Raich CERN AB/BDI