Fig 1.
Concept of the preclinical proton minibeam irradiation facility.
A 16 MeV proton beam provided by a tandem is accelerated to 70 MeV by a radio-frequency linac system and subsequently focused to 0.1 x 0.1 mm2 by a quadrupole triplet. The 6-dimensional phase space of the tandem beam is matched to the accepted phase space of the linac by a buncher unit and a quadrupole quartet.
Fig 2.
Longitudinal phase space between the tandem and linac.
a) longitudinal phase space at z1 (see Fig 1) coming from the tandem (Ekin = 16 MeV, ΔEkin = 0.01%) [18] b) longitudinal phase space in front of the linac at z2 (see Fig 1) (colored dots) and accepted phase space of the linac (grey dots). The red curves along the x- and y-axes are projections of the particle distributions.
Fig 3.
Proton transmission into an area of 0.1 x 0.1 mm2 at the focus (see Fig 1) as a function of buncher amplitude Ub.
Fig 4.
Cavity concept 1 (4-gap): Three drift tubes are attached by stems.
Pickup loop, excitation loop and copper tuner have access to the cavity through ports. Red line: proton beam.
Fig 5.
Cavity concept 2 (5-gap): Four drift tubes are attached by stems with implemented cooling channels.
Pickup loop, excitation loop, fixed copper tuner and variabe tuner are depicted. Red line: proton beam.
Table 1.
Parameter list of basic buncher cavities.
Fig 6.
Mounted on a CF-100 flange, the cavity can be installed directly in the beam tube. The vacuum pot provides pickup loop, excitation loop and variable tuner access to the cavity.
Fig 7.
Connection to the beam pipe via CF-16 flanges. CF-16 flanges also provide access to the cavity for pickup loop, variable tuner and fixed copper tuner. The excitation loop is mounted on a CF-63 flange.
Fig 8.
Schematic representation of frequency tuning- and RF system of the two buncher units.
Fig 9.
Signal characteristics of the RF system.
Schematic: gate generator signal and amplifier bias. The time offset between amplified signal and generator signal is corrected for illustration purposes.
Fig 10.
Measurement setup for performance evaluation using a tandem accelerator and a Q3D magnetic spectrograph.
Fig 11.
Input power stability measurement.
Measuring time: 32 h.
Table 2.
Simulated and measured unloaded quality factor Q0 for the expected (exp.) tuner position to reach fR and for the maximum (max.) extended tuning rod of both buncher units.
Fig 12.
Energy distribution of the bunched protons recorded with the Q3D magnetic spectrograph setup (Pin = 778 W, 4-gap buncher).
Fig 13.
Performance of the two buncher concepts.
Black and pink: Measurement series of the accelerator voltage Ub as a function of the input power Pin, performed on the Q3D. Green and Red: “Best Case” scenario simulations. Light blue and dark blue: reduced measured quality Q0.
Fig 14.
Pick-up signal measurement of the 4-gap concept with 800W (8 μs at 200 Hz) input power.
Black line: Mean of the pick-up signal, red line: maximum pick-up signal and blue line minimum pick-up signal. Dashed lines: 95% coefficient interval of maximum and minimum pick-up signal.