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RFQ Input Acceptance Studies

RFQ Input Acceptance Studies. Simon Jolly 27 th June 2012. RFQ Input Acceptance. At the last FETS meeting there was a lot of discussion about how hard the beam should be focussed into the RFQ entrance. Anecdotal evidence suggests a HARD focus is needed (~100 mrad at 2.5 mm).

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RFQ Input Acceptance Studies

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  1. RFQ Input Acceptance Studies Simon Jolly 27th June 2012

  2. RFQ Input Acceptance • At the last FETS meeting there was a lot of discussion about how hard the beam should be focussed into the RFQ entrance. • Anecdotal evidence suggests a HARD focus is needed (~100 mrad at 2.5 mm). • 2 parts to optimise input beam: • Run many simulations with larger emittance to determine acceptance. • Match slit-slit measurements to this input emittance. • I have given Christoph a beam distribution for part 2 based on Alan’s 0.25 pi mm mradwaterbag distribution but drifted to slit-slit scanner position. • I am now running simulations for part 1 … Simon Jolly, University College London

  3. RFQ Input Acceptance Simulations • Finding input acceptance is tricky! As soon as you include space charge, iteration becomes virtually impossible… • Use zero current to find 100% ellipse then check with 60 mA. • Ran simulations for 4 different emittances using same input alpha/beta: • 0.25 pi, 1 pi, 4 pi and 16 pi mm mrad. • Zero beam current. • Waterbag distribution. • Finely grained loss map and manufactured RFQ field map. Simon Jolly, University College London

  4. 0.25 pi mm mrad Transmission Simon Jolly, University College London

  5. 1 pi mm mrad Transmission Simon Jolly, University College London

  6. 4 pi mm mrad Transmission Simon Jolly, University College London

  7. 16 pi mm mrad Transmission Simon Jolly, University College London

  8. Results • Definite plateau in acceptance around 1 pi mm mrad. • Hard limits around ±4 mm and ±150 mrad. • Interestingly, beam does NOT need to be square! • Clear elliptical boundary to emittance though. Simon Jolly, University College London

  9. Conclusions • Whichever way we look at it, we need small, highly convergent beams. • We can’t realistically transmit more than 1 pi mm mrad (and most certainly much less with full space charge). • We might be able to get away with “cutting out” a less convergent beam from the 1 pi emittance as necessary, but this will need to be tested with full space charge. • The last LEBT drift DEFINITELY needs to be short… Simon Jolly, University College London

  10. Paper 1: RFQ Integrated Design • Paper will cover modelling background for our integrated RFQ design method. • This is mainly RFQSIM -> Inventor -> Comsol -> GPT -> Matlab, but also includes sections on bulk CAD design and electromagnetic/thermal simulations. • Half written: just waiting for other people to fill in some sections: • Introduction • *Vane Modulation Parameter Generation (APL – RFQSIM) • *RFQ Mechanical Design (PJS) • Vane Tip Modulation CAD Design (SJ) • *Electromagnetic Cavity Simulations (SL) • *Thermal Modelling (SL) • Beam Dynamics Simulations (SJ) • Field Mapping (SJ - Comsol) • Particle Tracking in GPT (SJ) • Conclusions (SJ) Simon Jolly, University College London

  11. Paper 2: FETS RFQ Design • Paper will cover all steps we went through to design FETS RFQ. • Will refer to previous integrated design paper, so no need to describe methods again, but needs to include all information showing how much work we’ve done on the various aspects of the design. • I will take as much as I can from the conference papers, but will need help filling in gaps as there are several things that have been presented at FETS meetings I couldn’t find in PAC/EPAC papers. • Outline will be similar: • Initial parameter generation and design limitations (APL + RF/klystron) • Basic CAD design (PJS) • Cold model construction and bead pull (SJ/PJS) • Electromagnetic cavity simulations (SL) • Thermal simulations and squirt nozzle/cooling design (SL/PJS) • Vane tip CAD modelling (SJ) • Beam dynamics simulations, inc RFQSIM/CAD modelling comparison (SJ) • Final CAD design, including tuner design, RF feedthroughs etc and final RFQ parameter comparison (SJ/PJS/APL) • Anything else… • As Juergen suggested, this paper should include everything but also refer to conference papers… Simon Jolly, University College London

  12. Paper 3: Fringe Fields/Tolerances • Paper will cover all the “edge effects” that have come largely from the CAD modelling. • Try to show how really starts to interfere on some of the “optimised” areas of the RFQ design. • Juergen’s work on the effect on the beam energy spread from the matching section fringe field: I will run some simulations (suggestions please…). • All the simulations I’ve done recently checking the alignment and machining tolerances. Simon Jolly, University College London

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