Instrumentation & Commissioning
In the next years, bERLinPro will be build at the HZB campus's site in Berlin Adlershof.
Because of the missing of specific know-how and expertise, which has to be developed, and a limited manpower, the construction and the commissioning the accelerator will be separated in individual blocks/stages in which sub parts are going to be tested and defined milestones should be fulfilled. This partition is also flexible enough allowing to implement modified designs at later time.
Three stages are planned, see top figure:
1. The low-energy section of bERLinPro will be installed as a whole. This implies a change of the Drive Laser System and the GUN-1 cyro module which both will be extensively tested in the GunLab first. Further components are the Booster module (checked in HoBiCaT without beam), the merger chicane, the splitter chicane and the main dump. The setup ought to achieved cw beam currents of more than 1 mA at 6.5 MeV kinetic energy.
2. The next expansion will be the replacement of the GUN-1 module by an new one, GUN-2, which is capable to accelerated the full current of 100 mA providing a maximum power of 650 kW. Milestones for this stage is a current more than 10 mA.
3. The last step is the implementation of the three cavity LINAC module and the closing of the recirculator transfer line. The electron bunches will then accelerated up to 50 MeV, guided back in the loop into the merger chicane, decelerated down to the start energy and finally terminated in the main dump.
After finishing the whole installation after approx. four years, the physics program is going to start. Goal is a beam current of 100 mA at 50 MeV kinetic energy and excellent electron bunch properties in the six dimensional phase space simultaneously.
For achievement of the ambitious goals parameters of bERLinPro, it is necessary to develop specific commissioning strategies for each construction stage. It means: What kinds of monitors with a demanded resolution and dynamic range are needed to setup the accelerator properly?
The question does not only cover the measurement of the intrinsic properties of the electron beam like energy, emittance, current, etc. but also how to determine the relative and absolute alignment between the electron beam and a certain device like a bending magnet or cavity, and furthermore to correct an identified malposition.
In case of high current ERLs, special emphasis is put on the scope:
1. Electron bunch pulse patterns with various frequencies and with scaling beam currents from about nanoampere's (10-9) for the machine startup to few tenth of milliampere's (10-1) for the norminal operation mode. This span of eight orders of magnitudes ought to be measured (interceptive and non-invasive) and controlled.
2. At high beam currents or beam power, harmful beam loss can arise on very short time scales (microseconds) and destroy permanently the accelerator structure. Causes can be for example beam HALO formation (relative intensity level of 10-5), collective instabilities ( like beam breakup) or system failures. A sophisticated machine protection and inhibit system is goging to be developed.
3. For excellent energy recovery the path length of the recirculator has to be adjusted to the right phase advance of 180 deg in the LINAC. Also the collinearity of the high- and low-energy beam by a simultaneously position measurement has to be ensured.