• Y. Lee, P.-A. Duperrex, V. Gandel, D.C. Kiselev, U. Müller
  PSI, Villigen

A new cur­rent mon­i­tor (MHC5) based on a re-en­trant cav­i­ty tuned at the 2nd RF har­mon­ic (101.26 MHz) has been in op­er­a­tion since April 2009 at PSI. It mon­i­tors the cur­rent of the high in­ten­si­ty 590 MeV pro­ton beam at 8 m down­stream of the graphite meson pro­duc­tion tar­get (TgE). The scat­tered par­ti­cles and their sec­on­daries from TgE in­tro­duce a heavy ther­mal load ap­prox­i­mate­ly of 230 W on MHC5 at 2 mA beam in­ten­si­ty, which is car­ried away by ac­tive water cool­ing. The in­ho­mo­ge­neous tem­per­a­ture pro­file in MHC5 re­sults in ther­mo­me­chan­i­cal de­for­ma­tions which leads to a change in its HF elec­tro­mag­net­ic char­ac­ter­is­tics. In­deed, an anoma­lous RF drifts were ob­served dur­ing ini­tial op­er­a­tions, which had to be com­pen­sat­ed for, to ob­tain cor­rect beam cur­rent mon­i­tor­ing. In this paper, the physics of the ob­served RF drift is an­a­lyzed by using ad­vanced mul­ti­physics sim­u­la­tion tech­nolo­gies.

• P.-A. Duperrex, V. Gandel, D.C. Kiselev, Y. Lee, U. Müller
  PSI, Villigen

For high in­ten­si­ty beam op­er­a­tion (3mA, 1.8MW) in the PSI cy­clotron, a new cur­rent mon­i­tor for pro­ton beams has been in­stalled dur­ing the 2009 main­te­nance pe­ri­od. This cur­rent mon­i­tor is an ac­tive­ly cooled re-en­trant cav­i­ty with its res­o­nance tuned at the 2nd RF har­mon­ic (101 MHz). Op­er­at­ing this sys­tem pre­sents sev­er­al chal­lenges due to the heavy show­er of en­er­get­ic par­ti­cles, the res­onator being placed 8 m be­hind a graphite tar­get. The res­onator is ac­tive­ly cooled with water, its ex­ter­nal sur­face was black­ened to im­prove the ra­di­a­tion cool­ing and its me­chan­i­cal struc­ture was op­ti­mized for good heat con­duc­tion. The res­o­nance char­ac­ter­is­tics are ex­treme­ly sen­si­tive to struc­tural changes of the res­onator. Be­cause of non-uni­form tem­per­a­ture dis­tri­bu­tion and dy­nam­i­cal changes the ob­served gain drift dur­ing op­er­a­tion is of the order of 10%. To cor­rect these drifts 2 tests sig­nals 50 kHz off the RF fre­quen­cy are mea­sured on-line dur­ing beam op­er­a­tion. They pro­vide an in­no­va­tive mean to es­ti­mate and to cor­rect on-line the res­onator gain. This paper will pre­sent the mea­sure­ment method and the achieved per­for­mances.

• Y. Lee, V. Gandel, D.C. Kiselev, D. Reggiani, M. Seidel, S. Teichmann
  PSI, Villigen

A sim­u­la­tion based op­ti­miza­tion of a col­li­ma­tor sys­tem at the 590 MeV PSI pro­ton ac­cel­er­a­tor is pre­sent­ed, for the on­go­ing beam power up­grade from the cur­rent 1.2 MW [2 mA] to­wards 1.8 MW [3 mA]. The col­li­ma­tors are lo­cat­ed down­stream of the 4 cm thick graphite meson pro­duc­tion tar­get. These are de­signed to shape the op­ti­mal beam pro­file for low-loss beam trans­port to the neu­tron spal­la­tion source SINQ. The op­ti­mized col­li­ma­tors are pre­dict­ed to with­stand the beam in­ten­si­ty up to 3 mA, with­out sac­ri­fic­ing in­tend­ed func­tion­al­i­ties. The col­li­ma­tor sys­tem is under the heavy ther­mal load gen­er­at­ed by a pro­ton beam power de­po­si­tion ap­prox­i­mate­ly of 240 kW at 3 mA, and it needs an ac­tive water cool­ing sys­tem. Ad­vanced mul­ti­physics sim­u­la­tions are per­formed for a set of ge­o­met­ric and ma­te­ri­al pa­ram­e­ters, for the ther­mo­me­chan­i­cal op­ti­miza­tion of the col­li­ma­tor sys­tem. In par­tic­u­lar, a FOR­TRAN sub­rou­tine is in­te­grat­ed into CFD-ACE+, for cal­cu­lat­ing local beam stop­ping power in the col­li­ma­tor sys­tem. Se­lect­ed re­sults are then com­pared with those of full MCNPX sim­u­la­tions.