Ring Accelerator Physics at ISIS
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Improved understanding of loss-driving phenomena is fundamental to ISIS improvements and upgrades.
The mechanisms potentially driving loss, and thus limiting the intensity of the ISIS proton ring are not fully understood. The principle mechanisms, traditionally labelled "Space Charge" and "Instabilities", are significant areas of R&D in their own right. The ISIS Ring is one of the few machines world wide where some of these important loss mechanisms can be studied experimentally, thereby benchmarking Computer Codes, Theoretical Models, and ensuring future machine designs are based on sound assumptions. In addition, improved understanding of these phenomena is fundamental to ISIS improvements and upgrades.
Below is an outline of our current projects and plans. Links give more detail on the various topics, more will be added as progress is made.
(1) Transverse Space Charge and Associated Loss Mechanisms
Transverse space charge is thought to be a main loss mechanism on the ring, though the exact mechanisms of growth are not fully understood. Initially studies are purely 2D, with no momentum spread or dispersion. The main topics are:
Envelope and Half Integer Errors: Related Coherent Modes
Higher Order, Non Linear Modes
Extension to beams with momentum spread and longitudinal motion
Experimental trials with ISIS in Storage Ring Mode
Studies will include: a review and application of relevant theory, numerical calculations, simulations and modelling work, experimental tests and trials.
(2) Injection Studies
The injection painting process on the ISIS ring is critical in determining beam distributions, loss levels and therefore operational intensity. This is a potentially fruitful area for machine improvement, both for present operational optimisation, and the possibility of an upgraded injection system. Eventually a fully 3D study is planned, but initially work will concentrate on 2D transverse models. Key steps and topics are:
Modelling 2D painting with space charge using tracking codes
Identify and assess effect of the important loss/growth mechanisms
Explore optimal painting schemes for minimised loss
Experimental tests of basic painting calculations and simulations
Experimental trials exploring different and optimal painting schemes
(3) Beam Diagnostics Studies for High Intensity R&D
Experimental studies of the beam all depend on the availability of suitable diagnostics. A detailed understanding of the devices used, and their limitations is essential. Main topics are:
Ring Residual Gas Profile Monitors
Ring Position and Envelope Monitors
R&D for Strip-line Monitors
R&D for new Diagnostic Beam Exciters
Instabilities do not presently limit ISIS running intensity, but they are a potential problem for most upgrade proposals. The appearance and behaviour of instabilities on the ISIS ring are of also of particular interest to help confirm and improve current theories. There has been significant work on these topics on the ring in the past, and it is now planned to revisit these topics, exploiting latest codes. Main topics and areas of work are
Review ISIS Instabilities and Predictions
Estimate Impedances, Build up computer models
Longitudinal Instability Studies
Transverse Instability Studies
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