Meeting on Debuncher Cavity 24. March 2011

present: A.K. Bhattacharyya, H. Broere, C. Carli, F. Gerigk, L.M. Hein, W. Hoefle, A. Lombardi, J. Tuckmantel, M. Vretenar, R. Wegner

Power needs for the debuncher cavity (R. Wegner)

R. Wegner used the analytic formulas of J. Tuckmantel (Power Overhead in the Linac4 Debuncher Cavity, unpublished) to calculate the power needs for various modes of operation (see presentation), adding a 30% overhead, which covers:

• RF losses during RF transport,
• RF losses in circulator,
• cavity/coupler mismatch, and
• 16% overhead for LLRF.

He concludes that 40 mA operation (40 us period) is possible including a 20% margin on the voltage of the cavity, if an amplifier system of 100 kW is available.

Beam dynamics for injection into PSB (L. Hein)

L. Hein discussed the positions in the transfer line and the voltages needed to achieve a certain energy spread at the injection into the PSB. He also looks at the needed phase swing in the debuncher cavity.

In the following discussion it was concluded that 42 m after the end of the linac is a suitable position for the debuncher cavity. Here, a voltage of 0.68 MV is needed together with a phase swing of -+ 105 deg.

LLRF simulations (A.K. Bhattacharyya)

The validity of J. Tuckmantels analytical approach was confirmed.

Cost and options of amplifier system (H. Broere)

The present baseline is a 55 kW solid state amplifier. An option was discussed with the manufacturer to double the power by combining 2 such systems. This will basically double the cost and it will lead into a very challenging power regime for solid state technology.

Conclusions (all)

• The debuncher cavity will be placed 42 metres after the end of Linac4.
• The baseline amplifier (55 kW) will be used in the first years of operation, allowing the needed phase swing of -+ 105 deg at nominal voltage for operation at 20 mA peak current.
• For higher current operation one needs to either reduce the voltage in the debuncher, yielding larger energy spread at PSB injection, or one needs to reduce the energy swing (and thereby the phase swing).
• If low-current operation shows that the beam accumulation and acceleration in the PSB clearly benefits from the energy painting, one can either use a LEP klystron at 100 kW to feed the debuncher cavity, or one can upgrade the baseline amplifier.
• The analytic approach, LLRF simulations, and the low-level RF test with a buncher cavity have all predicted the same power needs, which means that we can be confident of our predictions.
• For RF transport a "heliflex" coax-cable will be installed that is suitable for 100 kW.
• The Linac4 integration (J.P. Corso) must be informed of these plans (A. Lombardi for position, H. Broere for coax cable).

-- FrankGerigk - 28-Mar-2011