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**Present:** T. Zickler, J. Borburgh, F. Regis, L. Hein, G. Bellodi, A. Newborough, D. Nisbet, C. Carli, U. Raich, A. Lombardi, K. Hanke, T. Hermanns and B. Mikulec.

**Agenda:**

- Communications
- Follow-up of open actions
- Alternative for Linac4 Beam Energy Measurement (T. Hermanns)
- AOB

The last minutes have been approved.

B. Mikulec informs that the list of open actions has been cleaned up. Some of the open actions overlap with actions of the Linac4 BCC. Please consult the open actions twiki page to follow up the remaining points.

This work is a follow up of a discussion at the Linac10 conference, where D. Raparia from BNL suggested that their beam energy measurement principle (see TUPSM011_BNL.pdf) could also be applied to Linac4.

At the moment it is planned to upgrade the LBS line (about 50 m upstream of the PS Booster injection) for operation with the Linac4 beam according to the present concept for Linac2 operation. This foresees to use a slit to select a beam slice, which is then analysed by a spectrometer magnet, recorded by a SEM grid and finally dumped in an installation inside the concrete ceiling of the experimental area. While a concept to install a beam dump at ceiling height is already available, first discussions on a new slit show that its production could become more complex than expected (refer to slide 3 of the presentation for details).

Therefore, even if this original proposal is by no means ruled out, T. Hermanns presented an alternative for Linac4 beam energy measurement. This is based on the BNL Linac energy measurement, which is expected to be applicable for Linac4 energy measurements because the BNL beam parameters resemble those of Linac4 (200 MeV Hminus ions, 30 mA beam current):

When Hminus ions interact with atoms of the rest gas inside the vacuum pipe and they strip off their electrons. Due to the kinematics of this reaction - initially electrons and Hminus ions have the same velocity - there exists a correlation between Hminus and electron energy. Hence, a bending magnet deflects the electrons into an analysis line being perpendicular to the beam line. In this analysis line a variable voltage slows down/stops them and only those, which escape from this field region, are measured by a Faraday cup. Over several Linac4 pulses the integrated electron current is sampled as a function of the retarding voltage. Finally, one differentiates the resulting curve to determine the mean energy and the energy spread of the electron distribution and so of the Hminus ions.

As the precision of the measurement depends on the step width, with which the voltage is varied, the reconstructed values for mean energy and energy spread are compared with their input values as a function of different voltage steps. A range from 50 V to 300 V has been tested. In general the reconstruction is better the finer the voltage steps are. While for the mean energy the absolute deviation is still acceptable (below 1%) even for the greatest voltage steps, it is indispensable to sample the electron energy distribution with steps at the order of half the energy spread to obtain

sensible deviations that are sufficiently low for the energy spread measurements.

No AOB.

-- ThomasHermanns - 18-Nov-2010

- TUPSM011_BNL.pdf: Paper on beam energy and laser beam profile monitor at the BNL Linac

- 1011_L4Commissioning_ThHermanns.pdf: Alternative for L4 Energy Measurement via Electron Spectrum

I | Attachment | History | Action | Size | Date | Who | Comment |
---|---|---|---|---|---|---|---|

1011_L4Commissioning_ThHermanns.pdf | r1 | manage | 5236.5 K | 2010-11-24 - 09:18 | ThomasHermanns | Alternative for L4 Energy Measurement via Electron Spectrum | |

TUPSM011_BNL.pdf | r1 | manage | 2115.3 K | 2010-11-19 - 11:14 | BettinaMikulec | Paper on beam energy and laser beam profile monitor at the BNL Linac |

Topic revision: r4 - 2010-11-24 - ThomasHermanns