Magnetic field Peter Gttlicher DESYFEB January 29 th

Magnetic field Peter Göttlicher, DESY-FEB, January 29 th 2009 • Estimation of forces approach as “worst case” scenarios • PMT issues ---- reminder from December 2008 PMT handles magnetic field optimized angle to beam axis radiation hardness Only magnetic component : Tungsten µr > 1. 05 B-field measured 0. 1 T, 0. 16 T 1

Magnetic forces, basic for estimation Peter Göttlicher, DESY-FEB, January 29 th 2009 CASTOR is weak-magnetic material in an external defined B-field Assumption: Changes of B-field by moving CASTOR negligible Iron of Collar, rotational shield CASTOR 2

Magnetic forces, Force from field-energy Peter Göttlicher, DESY-FEB, January 29 th 2009 Only change by moving Castor by dz: That volume changes µr : 1 to Tungsten 3

Peter Göttlicher, DESY-FEB, January 29 th 2009 Magnetic forces, Force from field-energy 4

Peter Göttlicher, DESY-FEB, January 29 th 2009 Magnetic forces, Numbers Only magnetic material: Tungsten µr > 1. 05 (data sheet) measure = 1. 025 neglected: some volume is Quartz Area: outer circle of Tungsten 18. 3 cm B=0. 1 T measurement from Oct. 2008 20 N pulling CASTOR forward 5

Peter Göttlicher, DESY-FEB, January 29 th 2009 Magnetic forces, side wards Moving CASTOR side wards … same mathematics Handwaving: end of field not well… CASTOR as whole: compensating halves alone: Same order as pulling along axis neglected field at center, “worst case” 6

Peter Göttlicher, DESY-FEB, January 29 th 2009 Torque moment to tungsten plate Replacing vector-product by product of absolute values For B=0. 16 T (the higher value of the two measurements X =0. 16 Nm/plate Summing over all plates, ignoring the vector-sum X<< 83 Nm even that is very low 7

Peter Göttlicher, DESY-FEB, January 29 th 2009 Summary on forces Estimation/ guesses/ hand waving Forces and torque-moments are on the level generated by a few “kg” Is transversal force critical? Does it turn CASTOR? Being conservative, Mechanical locking to each other 8

Peter Göttlicher, DESY-FEB, January 29 th 2009 PMT‘s in magnetic field Hamamatsu Data sheet only 0 and 30 degree Measurement: Single PMT at nominal voltage 2 k. V Measurement: Good for <45 degree Feel safe: If < 35 degree 9

PMT‘s in magnetic field -2 Pulse height Peter Göttlicher, DESY-FEB, January 29 th 2009 Variation of HV with light at center, zero degree B_to-PMT 0 T Magnetic field 1 T As expected: Distance between different HV’s is just a constant factor 10

Comparison to CMS-field -3 Peter Göttlicher, DESY-FEB, January 29 th 2009 PMT-axis ? IP For the two measurement, existing design is OK. Modification for getting safety margin ? !? 11

Peter Göttlicher, DESY-FEB, January 29 th 2009 Orientation of PMT’s New strategy: Keep EM section with 45 degree to beam pipe: expected field is pointing outwards Turn HAD to 30 degree: Mechanical compromise, tolerates slightly negative theta gap: Collar-rotational shield Example of field line 300 tolerated 12

Summarizing PMT Appropriate PMT found for fields up to 1 T. Peter Göttlicher, DESY-FEB, January 29 th 2009 Safety margin added to tolerate wide range of stray field directions We have shown, that the PMT’s can be operated in high field and radiation environment as expected in CMS-CASTOR volume. 13