Simon Jolly UKNFIC Meeting 25th April 2008 RFQ Simulations in GPT Simon Jolly UKNFIC Meeting 25th April 2008

Simon Jolly, Imperial College RFQ Optimisation Need to optimise RFQ: beam transmission, energy, bunching etc. This is not easy! Requires fine modifications to vane modulations. Need to model RFQ beam properties and measure beam properties at RFQ exit. Start with simple RFQ model and work our way up... 25/4/08 Simon Jolly, Imperial College

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. Start with RFQ cold model (simple case with simple field) and work up to full 4m FETS RFQ channel. 25/4/08 Simon Jolly, Imperial College

Cold Model Simulation in GPT Cold model field map produced by CST (Ajit). Large, coarse and simple (no vane modulations): 100x100x100 mesh points. z: -50 to 450mm with 5mm spacing. x/y: -162 to 162mm with 3.3mm spacing. Simulate with standard FETS parameters: Input beam: 60mA, 65keV, x/y = 2mm, x’/y’ = 100mrad, ex/ey = 0.2p mm mrad, beam converging. 5000 particles, 0.2ns timestep, 100% 2Dtree space charge. How much beam is transmitted? Where do losses occur? Use Matlab to analyse data, colour-code losses, construct movie. 25/4/08 Simon Jolly, Imperial College

Cold Model Simulation: Initial Conditions 25/4/08 Simon Jolly, Imperial College

Cold Model Simulation: Trajectories 25/4/08 Simon Jolly, Imperial College

Transmitted Particles: Phase Dependence 25/4/08 Simon Jolly, Imperial College

Simon Jolly, Imperial College FETS Layout Ion Source Beam Diagnostics Laserwire Tank LEBT RFQ MEBT/ Chopper 25/4/08 Simon Jolly, Imperial College

From Cold Model to Full Simulation Field map for full 4m FETS simulation created by Alan Letchford: 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. Vary current from 0-240mA. Measure beam transmission, bunching and energy. 25/4/08 Simon Jolly, Imperial College

RFQ Transverse Field Map 25/4/08 Simon Jolly, Imperial College

Simon Jolly, Imperial College RFQ On-Axis Ez Field 25/4/08 Simon Jolly, Imperial College

RFQ On-Axis Ez Field (0-0.5m) 25/4/08 Simon Jolly, Imperial College

Full FETS Simulation: Initial Conditions 25/4/08 Simon Jolly, Imperial College

Full FETS Simulation: Z-Y 25/4/08 Simon Jolly, Imperial College

Simon Jolly, Imperial College Final Beam Energy (60mA) 25/4/08 Simon Jolly, Imperial College

Simon Jolly, Imperial College RFQ Beam Transmission 25/4/08 Simon Jolly, Imperial College

RFQ Transmitted Current 25/4/08 Simon Jolly, Imperial College

Simon Jolly, Imperial College Conclusions RFQ simulations extremely promising: we can see bunching, acceleration and losses. RFQ design is almost optimal! Already transmitting ~85% of beam within 10% of target energy (3MeV). Need to measure acceptance of RFQ: input very large beam and see what survives. Also measure beam transmission with measured beam parameters from FETS ion source, tracked through LEBT. Optimise RFQ field and layout. 25/4/08 Simon Jolly, Imperial College