Abstract

A high degree of beam stability is essential for the smooth operation of an active scanning system as applied by the Heidelberg Ion Beam Therapy Centre (HIT). Amongst other parameters such as particle intensity and beam width, the feedback controlled beam position at the isocentre is particularly crucial as it has to meet a very tight tolerance band of ±1.0 mm. Due to this fact we pay special attention to beam position fluctuations along the beamline by running daily procedures. The results are stored in CSV-files and visualised by python scripts using the matplotlib plotting library. Our investigation comprises the beam positions as a function of time in the accelerator sections MEBT (middle energy beam transport), synchrotron and HEBT (high energy beam transport). These sections are successively equipped with profile grids, beam position monitors (BPM) or multi wire proportional chambers (MWPC). The aim is to find correlations between the beam position and external factors like e.g. temperature conditions of the surroundings or the cooling water. We also look for seasonal dependencies and interactions with the power load of the facility.

Accelerator Reliability Workshop | October 15-20, 2017| Versailles, France

Long Term Investigation of Beam Parameters Based on Beam Diagnostics Data Exports

R. Cee*, M. Galonska, T. Haberer, K. Höppner, J. Mosthaf, A. Peters, S. Scheloske, C. Schömers, J. Schreiner, T. Winkelmann Heidelberg Ion Beam Therapy Centre, 69120 Heidelberg, Germany

Beam Position

*Corresp. author: Dr. rer. nat. Rainer Cee, e-mail: rainer.cee@med.uni-heidelberg.de

Beam Width

Beam Position average over beam energy

Beam Width average over beam energy

Characteristics No. of wires (hor. / ver.) 64 / 64

No. of channels (hor. / ver.) 32 / 32

Wire center spacing 1.2 mm

Wire thickness 0.1 mm

Wire material WRe-alloy

Active area 80x80 mm²

Absorption ~15 %

Characteristics No. of wires (hor. / ver.) 64 / 64

No. of channels (hor. / ver.) 32 / 32

Wire center spacing 1.1 mm

Wire thickness 50 µm

Wire material WRe-alloy, gold plated

Active area 75x75 mm²

Detector gas 80 % Ar / 20 % CO2

Characteristics Type Shoe box

Frame material Stainless steel

Plate material Ceramics, Al2O3 coated

Aperture 180 x 70 mm²

Impedance (out) 50 Ω

Legend for all plots

Synchrotron BPM measurement

Date Event Ion MEBT SYNC / HEBT 2017 with influence on beam properties C p Position Width Position Width Feb 26 MEBT-steerer set value changed Hor. Hor. Ver.

Apr 14 new stripper foil Hor. / Ver.

Mai 05 BPM cable replugged Hor.

Jun 20 IH-DTL set value changed Ver. Ver.

Jul 09 IH-DTL new preamplifier tube Hor. / Ver. Hor. / Ver. Ver.

Jul 11 RFQ, IH-DTL + inflector set value changed Hor. / Ver. Hor. / Ver. Ver.

Jul 19 IH-DTL set value changed Hor. / Ver. Ver. Hor. Ver.

Jul 25 IH-DTL new main amplifier tube Ver.

Aug 25 RFQ calibration + debuncher set value changed Hor. / Ver. Hor. / Ver. Ver.

C-Beam @ extraction phase

p-Beam @ extraction phase

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Profile Grids (M1DG1, M1DG4/5)

MWPC (H1DG1G)

BPMs (S#DX#)

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Gantry

Treatment Rooms

HEBT

Synchrotron

Ion Sources

MEBT

LINAC

MEBT Profile Grid measurement

HIT Facility with relevant beam diagnostics

Conclusion The long term logging of beam properties along the beam line is very useful in daily operation of a medical accelerator. Measured values outside the usual band are quickly detected and corrective measures can be triggered in time. On the basis of the diagnostic data the influence of parameter modifications or other beam affecting actions can be studied. This allows predictions on the beam response for certain activities at the machine. We have observed correlations between the cooling water temperatures and beam properties for abrupt variations of the cooling power consumption, e.g. by switching off and on the LINAC-RF, but under typical operations conditions the infrastructure runs very stable and does not contribute to the beam fluctuations. Correlations between the outside temperature / humidity have been investigated but no clear proof could be found.

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HEBT MWPC measurement

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