### Minutes of the Booster Commissioning Working Group held on 18th of November 2010

**Present:**

**Agenda:**

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

#### 1. Communications

The last minutes have been approved.

#### 2. Follow-up of open actions

#### 3. Alternative for Linac4 Beam Energy Measurement

Presently it is planned to upgrade the LBS line (about 50 m upstream of the PS Booster injection) for the Linac4 beam according to the already known concept. This uses 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 the this original concept is by no means ruled out, T. Hermanns presented an alternative for Linac4 beam energy measurement. The proposed concept is based on the BNL Linac (200 MeV Hminus ion, 30 mA beam current) energy measurement. Hminus ions interact with atoms of the rest gas and strip off electrons. These are deflected into an analysis line which is perpendicular to the beam line. In this analysis line a variable voltage slows down/stops them and only those electrons, which escape from this field region, are measured by a Faraday cup. The integrated electron current is sampled as a function of the retarding voltage. Differentiating the signal allows for determining the mean energy and the energy spread of the electron distribution, which is correlated to the energy distribution 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 plotted versus different voltage steps. It can be observed that 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 step, 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.

#### 4. AOB

-- ThomasHermanns - 18-Nov-2010