Neutron-Induced Signal Measurements in Coaxial Cables on OMEGA

Transcription

1 Neutron-Induced Signal Measurements in Coaxial Cables on OMEGA RG-8 (CH) Y n = cm from target RG-142 (teflon) LMR-400 (CH foam) SHF-8M (teflon) 0.10 V. Yu. Glebov University of Rochester Laboratory for Laser Energetics Time (ns) 49th Annual Meeting of the American Physical Society Division of Plasma Physics Orlando, FL November 2007

2 Summary Neutron induced signals in coaxial cables will be one of the harsh environment challenges on the NIF and LMJ Neutron interactions create an electrical signal in a coaxial cable. Neutron-induced signals vary substantially by cable type CH dielectric (Heliax, LMR) produces higher signals Teflon dielectric produces lower signals Signals are much higher in cables under high voltage. Careful cable selection and routing is needed for the NIF and LMJ. A new model of neutron-induced signals is under development. E16245

3 Collaborators T. C. Sangster, C. Stoeckl, S. Roberts, and W. Bittle University of Rochester Laboratory for Laser Energetics J. L. Bourgade and J. L. Leray CEA/DIF Bruyères-le-Châtel R.A. Lerche Lawrence Livermore National Laboratory

4 The neutron-induced signal in coaxial cables was measured using high-yield implosions on OMEGA Cables Cables Coaxial cables on OMEGA Target Chamber at 165 cm from TCC Coaxial cables in re-entrant tube at 42 cm from TCC Cables: 60 ft long Input: Open circuit with EMP cover Output: 50 X, 1 GHz, 5 GS/s Tektronix 684 scope E15921a

5 Neutron-induced signals in coaxial cable with CH dielectric vary substantially by cable type 5 Shot 46827, DT, Y = , at 42 cm from TCC LMR-400 Heliax 1/2 in. LMR-600 Heliax 3/8 in. E15922a Time (ns)

6 Neutron-induced signals in LMR cables are proportional to the neutron yield Signals on Target Chamber Signals on Reentrant Tube Signal amplitude (mv) LMR 600 LMR Signal amplitude (mv) LMR 600 LMR DT neutron yield ( ) DT neutron yield ( ) Similar yield dependence was measured for Heliax cables E16306

7 The neutron-induced signal varies substantially for different kinds of coaxial cable RG-8 (CH) Y n = cm from target RG-142 (teflon) LMR-400 (CH foam) SHF-8M (teflon) E Time (ns) A new model is needed to explain the neutron-induced signal.

8 The neutron-induced signal is much higher in coaxial cable with HV applied Shot 47539, Y = RG kv Without high voltage Shot 47540, Y = RG kv 0.2 Without high voltage LMR kv LMR kv Time (ns) Time (ns) CVD diamond detectors require cables with HV applied E15925a

9 It is important to maximize the average distance between n source and cables Shot 36948, DT, Y = n in cable Direct Shot 37602, DT, Y = mm CVD diamond at 2.5 m from TCC Reflected n in CVD n in CVD Time (ns) Floor Floor Neutron-induced background n LMR-400 Scope Neutron-induced background n LMR-400 Scope E15919a Do not route cables along target chamber wall!

10 The CEA scientists are working on a model to explain neutron-induced signals 15 mm Main package 0.4 Dielectric under test Bottom plate connected to inner conductor of the cable Cap connected to outer conductor of the cable 23 mm Polyethylene d = 28.8 cm Shot yield (neutron/r4)( ) Polyethylene d = 40 cm Teflon d = 28.8 cm No dielectric (vacuum) Since coaxial cables are difficult to model, CEA uses a simple test platform to study* neutron-induced signals. E16307 *J. L. Leray et al., submitted to IEEE Transactions on Nuclear Science

11 All mitigation techniques will be implemented in the NIF ntof diagnostic for the ignition campaign E13962d

12 Cables to high-yield detectors will be located outside of neutron beam NIF multichannel ntof prototype with CVD diamond detectors CVD diamond detectors Example of CVD diamond detector RG-142 cable E15923a Best solution 2 m of concrete shielding

13 Summary/Conclusions Neutron induced signals in coaxial cables will be one of the harsh environment challenges on the NIF and LMJ Neutron interactions create an electrical signal in a coaxial cable. Neutron-induced signals vary substantially by cable type CH dielectric (Heliax, LMR) produces higher signals Teflon dielectric produces lower signals Signals are much higher in cables under high voltage. Careful cable selection and routing is needed for the NIF and LMJ. A new model of neutron-induced signals is under development. E16245