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Emittance measurement for ISIS LINAC operation

Emittance measurement for ISIS LINAC operation. Alan Letchford ISIS Injector Group RAL. The Short Version. We do not routinely measure the emittance in the Linac as part of ISIS operations. The End. The Long Version. The Injector Linac delivers a 70MeV H - beam to the ISIS synchrotron.

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Emittance measurement for ISIS LINAC operation

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  1. Emittance measurement for ISIS LINAC operation Alan Letchford ISIS Injector Group RAL ABI Workshop on tranverse and longitudinal emittance measurement Castle Kauzenburg, 10-12 December 2008

  2. The Short Version. We do not routinely measure the emittance in the Linac as part of ISIS operations. The End ABI Emittance Workshop

  3. The Long Version. The Injector Linac delivers a 70MeV H- beam to the ISIS synchrotron. The 800 MeV proton beam is sent to 2 neutron production targets ABI Emittance Workshop

  4. Linac Systems • H- Ion Source • 3 Solenoid Low Energy Beam Transport (LEBT) • 4-rod Radio Frequency Quadrupole (RFQ) • 4 Alvarez type Drift Tube Linac (DTL) tanks to 10, 30, 50 & 70 MeV • 70 MeV High Energy Drift Space (HEDS) • Debuncher Cavity ABI Emittance Workshop

  5. CT Wire profile scanner Emittance scanner ABI Emittance Workshop

  6. Drift Tube Linac ABI Emittance Workshop

  7. The RFQ Pre-Injector Emittance scanners ABI Emittance Workshop

  8. Slit-slit Scanner A pair of slit-slit scanners measure the horizontal and vertical phase spaces at 35keV. Originally designed to measure before and after the RFQ on the test stand. Beam Faraday Cup Slit 1 Slit 2 ABI Emittance Workshop

  9. The Emittance Scanners • The original specification called for very compact devices to be fitted on a single flange. • The separation between slits is only 20mm • Slit 1 height = 0.25mm • Slit 2 height = 0.1mm (5 mrad) • Stepper motors drive the slits with a resolution of 800 steps/mm • A charge amplifier measures the Faraday cup signal • A high speed DAQ system allows time resolved measurements • The original software was in NI LabView which was far from optimal. Recently rewritten in C++ (later talk) ABI Emittance Workshop

  10. Advantages • Only requires a single current amplifier • Less susceptible to secondaries • Can be very compact and high resolution • Can ‘overscan’ for v. high resolution or ‘underscan’ for quick low resolution Disadvantages • High resolution scans can be slow (beam stabilty) • Expensive (?) • Heavy ABI Emittance Workshop

  11. The Emittance Scanners ABI Emittance Workshop

  12. The Front Slit Tungsten Carbide knife edges Water cooled front slit Up to 600W average power ABI Emittance Workshop

  13. Side View Bellows Faraday Cup Slit 2 Slit 1 Beam Feedthroughs ABI Emittance Workshop

  14. Emittance Measurement Screen shot Post processed data SCUBEEx is used for noise removal during post processing ABI Emittance Workshop

  15. RFQ Output Previously the same system was used to measure emittance downstream of the RFQ at 665keV. This is not possible on the linac. ABI Emittance Workshop

  16. Beam Dynamics in the LEBT The beam dynamics in the LEBT are dominated by strong collimation in the first solenoid. Because of this and because the solenoid fields for an RFQ match are well known, routine emittance measurement rarely tells us anything useful or interesting. ABI Emittance Workshop

  17. Beam Dynamics in the LEBT Some limited experimental work has been done to investigate different operational parameters for the LEBT. Lower loss can be achieved by tuning for a strong waist in the LEBT but it gives a poorer match into the RFQ. ABI Emittance Workshop

  18. Anomalous Results When tuned for a waist in the LEBT the small beam size gives rise to small measured emittances. These emittance values are hard to believe. The effect was not investigated in detail as it isn’t relevant to ISIS operation. Effects such as these can be investigated further on The Front End Test Stand LEBT under construction at RAL ABI Emittance Workshop

  19. Emittance measurement in the ISIS linac • The only beam diagnostics between 665keV and 70 MeV are current transformers and beam loss monitors. • The emittance could be determined from beam profiles in the transport line but this isn’t done routinely. • The linac is set-up empirically for maximum transmission and minimum loss. • Emittance scanners are installed in the LEBT at 35keV. • The system was designed for use on the pre-injector test stand and then transferred to the linac. • Due to the nature of the beam dynamics in the LEBT measurement of the emittance is of limited value. ABI Emittance Workshop

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