Beam Loss Monitors at LINAC 4 Bernd Dehning

Beam Loss Monitors at LINAC 4 Bernd Dehning 9 May 2007 Bernd Dehning 1

Specifications n Main design parameters considered for BLMs n n n Beam energy Beam Intensity Question to be answered: n n n n Dynamic range (low and high limit) (SNS max loss 1 E-4 of beam intensity) Response time (SNS 40 us) Sampling rate (LHC 40 us) Beam permit signal (use of threshold) to protect against damage of equipment due to beam induced heating Logging rate (Linac 4 2 Hz) Location of detectors Triggered acquisition 9 May 2007 Bernd Dehning 2

LINAC 4 and Beam Loss Parameters 9 May 2007 Bernd Dehning 3

Ionisation chamber SNS n n n 9 May 2007 Bernd Dehning Stainless steal Coaxial design, 3 cylinder (outside for shielding) Low pass filter at the HV input Ar, N 2 gas filling at 100 mbar over pressure Outer inner electrode diameter 1. 9 / 1. 3 cm n Length 40 cm n Sensitive volume 0. 1 l n Voltage 2 k V n Ion collection time 72 us 4

Ionisation chamber LHC n n Bernd Dehning Parallel electrodes separated by 0. 5 cm n Al electrodes n Low pass filter at the HV input n 9 May 2007 Stainless steal cylinder N 2 gas filling at 100 mbar over pressure n Diameter 8. 9 cm n Length 60 cm n Sensitive volume 1. 5 l n Voltage 1. 5 k. V n Ion collection time 85 us 5

ACEM n Regular photomultiplier, with an aluminum foil as cathode (secondary electron emitter when irradiated). n n n 10 dynodes High voltage: 0. 5 -1. 5 k. V Max. current: 20 m. A for short pulses Electron transit time: 40 ns Cathode surface area: 7 cm 2 Gain variation 1 E 3 U = 1000 V U = 600 V M. Palm AB-ATB-EA 9 May 2007 Bernd Dehning 6

Comparison of ACEM and Ionisation Chamber J. Bosser, G. Ferioli • ACEM 3 orders of magnitude more sensitive • ACEM disadvantage: gain depending on environmental B field 9 May 2007 Bernd Dehning 7

LHC acquisition board n n n 9 May 2007 Bernd Dehning Current to Frequency Converters (CFCs) Analogue to Digital Converters (ADCs) Tunnel FPGAs: Actel’s 54 SX/A radiation tolerant. Communication links: Gigabit Optical Links. Surface FPGAs: Altera’s Stratix EP 1 S 40 with 780 pin. n Current between 5 p. A to 1 m. A n Minimum integration time 40 us 8

Summary n n n Beam loss and shower simulation are needed to make the choice for the detector and the locations Definition of machine protection procedure needs to be done Detector type: ionisation chamber or ACEM LHC type electronics: main feature appropriate Definition of post mortem and logging, specifications are needed 9 May 2007 Bernd Dehning 9

Gain Variation of SPS Chambers Test with Cs 137 n n n 30 years of operation Measurements done with installed electronic Relative accuracy n n Total received dose: ring 0. 1 to 1 k. Gy/year extr 0. 1 to 10 MGy/year 9 May 2007 Bernd Dehning Ds/s < 0. 01 (for ring BLMs) Ds/s < 0. 05 (for Extr. , inj. BLMs) Gain variation only observed in high radiation areas Consequences for LHC: n No gain variation expected in the straight section and ARC of LHC n Variation of gain in collimation possible for ionisation chambers 10

SNS 9 May 2007 Bernd Dehning 11

Ionisation chamber currents (1 litre, LHC) 450 Ge. V, quench levels (min) 100 s 12. 5 n. A 7 Te. V, 100 s 2 n. A quench levels (min) Required 25 % rel. accuracy, error small against 25% => 5% 450 Ge. V, dynamic range min. , used for tuning 7 Te. V, dynamic range min. 9 May 2007 100 p. A 10 s 10 p. A 100 s 2. 5 p. A 10 s 160 p. A 100 s 80 p. A Bernd Dehning 12