1. Optimisation of the FETS RFQ
Simon Jolly
Imperial College
16th September 2008

2. Simon Jolly, Imperial College
FETS RFQ Optimisation
RFQ development progressing on a number of fronts.
Bead-pull and resonance measurements of cold model.
Beam dynamics simulations in General Particle Tracer (GPT).
New integrated design method using Autodesk, Microwave Studio and GPT.
16/9/08
Simon Jolly, Imperial College

3. Bead-Pull Field Flatness Measurements
Ø6mm dielectric bead
EPAC’08
THPP024
16/9/08
Simon Jolly, Imperial College

4. Cold Model End Flange Inserts
2 new types of end flange were designed to alter the inductance and capacitance of the RFQ end regions: a cone-shaped flange insert and a flat insert with 4 removable fingers (copper or iron).
GUIDE
CONE
HUB
FINGER HUB
SPACER
FINGERS
16/9/08
Simon Jolly, Imperial College

5. Cold Model Frequency and Q-value
Frequency (MHz)
Q-value
CST Simulation
319.7
9306
Brazed RFQ
±0.1
5616±50
Flat end plates
±0.1
7773±30
EPAC’08
THPP024
16/9/08
Simon Jolly, Imperial College

6. Simon Jolly, Imperial College
GPT RFQ Simulations
General Particle Tracer is a particle tracking package: sophisticated particle tracking but only simple beamline components.
Need to model RFQ as time-varying E and B field map: track particles through field map and measure beam properties.
Field map produced using RFQ optimisation code (Alan) for full 4m FETS:
11 x 11 x 3110 mesh points.
x/y: -3.5 to 3.5mm (fixed mesh).
z: 0 to 4.1m (variable mesh).
Includes transverse and longitudinal field modulations.
Input conditions:
Input beam: 60mA, 65keV, x/y = 2mm, x’/y’ = 100mrad, ex/ey = 0.2p mm mrad, beam converging.
10,000 particles, 0.3ns timestep (freq/10), 100% 3Dtree space charge.
Single bunch at injection with 3D space charge.
Measure beam transmission, bunching and energy.
16/9/08
Simon Jolly, Imperial College

7. RFQ Transverse Field Map
16/9/08
Simon Jolly, Imperial College

8. Simon Jolly, Imperial College
RFQ On-Axis Ez Field
16/9/08
Simon Jolly, Imperial College

9. RFQ Parameters (from TUP066, LINAC06)
16/9/08
Simon Jolly, Imperial College

10. Initial Conditions: Z-Y, 5 bunches
16/9/08
Simon Jolly, Imperial College

11. Full FETS Simulation: Z-Y, 5 bunches
16/9/08
Simon Jolly, Imperial College

12. Initial Conditions: Z-E, full beam
16/9/08
Simon Jolly, Imperial College

13. Full FETS Simulation: Z-E, full beam
16/9/08
Simon Jolly, Imperial College

14. Simon Jolly, Imperial College
Final Beam Energy (60mA)
16/9/08
Simon Jolly, Imperial College

15. Simon Jolly, Imperial College
RFQ Beam Transmission
16/9/08
Simon Jolly, Imperial College

16. RFQ Transmitted Current
16/9/08
Simon Jolly, Imperial College

17. Simon Jolly, Imperial College
RFQ Integrated Design
RFQ parameterised by ‘a’ and ‘m’ parameters for modulations and ‘L’ for cell length.
These parameters generated using optimisation code, then handed to Frankfurt for RFQ manufacture.
Would like to have a method of designing RFQ where all steps are integrated:
Engineering design.
EM modelling.
Beam dynamics simulations. L a
r0 (mm) ma
L/2
rod axis
beam axis
16/9/08
Simon Jolly, Imperial College

18. RFQ Integrated Design: Step 1
Most FETS CAD modelling done using Autodesk Inventor, including the cold model.
Possible to draw vane modulations using spline interpolation.
Parameters read out from Excel spreadsheet: can change modulations “on the fly”...
16/9/08
Simon Jolly, Imperial College

19. RFQ Integrated Design: Step 2
EM modelling already carried out for cold model using CST Microwave Studio.
Export “.sat” file to MWS from Autodesk of 3D vane model: only central 1cm x 1cm section.
Cut into 4 sections:
Mirrors real assembly.
Easier for MWS meshing.
Output as E & B field map.
16/9/08
Simon Jolly, Imperial College

20. RFQ Integrated Design: Step 3
Import field map of central field region into GPT for particle tracking.
Optimise design based on RFQ transmission and feed back into engineering design.
We now have a method of producing a field map and carrying out simulations for the thing we’re going to build!
16/9/08
Simon Jolly, Imperial College

21. Simon Jolly, Imperial College
Conclusions
Incremental progress on field flatness and resonant properties – see EPAC’08 paper THPP024, S. Jolly et al.
RFQ beam dynamics simulations in GPT very promising: see bunching, acceleration, current-dependent transmission.
>90% transmission for ideal beam, only ~50% for “real” parameters.
Can (almost) run end-to-end simulations in GPT using pepperpot measurements from ion source, optimised LEBT parameters and field map for RFQ.
Integrating Autodesk, MWS and GPT design steps will reduce bifurcation of design.
Need to ensure CAM systems will understand our CAD models so we can manufacture what we’re designing (this is the point...).
16/9/08
Simon Jolly, Imperial College