A Compact 1 MeV Electron Electron Accelerator

Transcription

1 A Compact 1 MeV Electron Electron Accelerator Chris Westerfeldt Duke University & Triangle UniversiAes Nuclear Laboratory Durham, NC USA Supported by the United States Department of Energy, Office of High Energy and Nuclear Physics, under: Grant: DE- FG02-97ER41033, DE- FG02-97ER41042, & DE- FG02-97ER41041

2 Who? Lead: Dr. Albert Young, NCSU Professor & LANL collaborator Myself technical oversight and design Kenneth Jutz NCSU undergraduate Physics Student, preliminary design and assembly Andrei Makhanov High Point University undergraduate Physics Student, preliminary design and primary pair of hands Brian Walsh TUNL Technical Staff

3 What? This accelerator is being constructed using Lucite to support the charging system and grading resistors. A 1 MV JN tube (obtained surplus) will be supported from the pressure vessel baseplate A Pelletron charging system will be used Some Pelletron components were obtained surplus, others are spares or used parts from our FN tandem The column resistors are spares from our FN.

4 What? ConAnued The machine will first be tested in air hopefully to 100 kv. The enare accelerator will be inside a weak magneac guide field A stainless steel tank will be custom fabricated to enclose the accelerator. SF 6 will be used as the dielectric (80 psig?)

5 Where? Triangle UniversiAes Nuclear Lab on Duke University Campus Space was provided in Dr. Young s mini- proton accelerator lab in the Duke Physics Building.

6 When? This began as a summer 2013 REU project at TUNL The basic design was developed by the undergraduates using Autodesk Inventor Low voltage tests are planned for Q Ion Source and Laser system design planned for Q Q Ordering of pressure vessel : Q1 2014

7 When? - ConAnued Ordering of terminal spinning Q Final assembly and full voltage tests Q Shipment to LANL Summer 2014

8 Why? A source of well collimated energeac electrons is needed for an experiment at LANL. The electrons will be pulsed, at energies up to 1 MeV. The electron current should be very small ~ fa. The accelerator must be compact and able to be moved while in operaaon to probe the experiment at mulaple locaaons.

9 How? The electrons will be pulsed, at energies up to 1 MeV. A laser will be pulsed at ~100 Hz, striking a photo- cathode at the end of the accelerator tube. We haven t decided whether this will be done from inside the tube or via a window in the tank and terminal spinning. The electron current should be very small ~ fa.

10 Autodesk Views - Preliminary

11 Autodesk Views - Preliminary

12 Autodesk Views - Preliminary

13 Simple Column Design Supports only Pelletron and Resistors 18.50" 12.00" 30" 1" Lucite 54.00"

14 Charging System SCHEMATIC OF THE! CHARGING SYSTEM 0-50 KV I3 P2 P3 P4 DRIVE! SHEAVE P1 Charging! I4 Current KV ~1m R col = 23 GΩ" "! Icol MV

15 Lucite Column and AcceleraAon Tube

16 Column, Tube, Pelletron Mockup

17 Column Resistor String For iniaal TesAng we are using spare FN Tandem column resistors: EBG SSX- 154, 500 MΩ Rated o C, 48 kv ConAnuous On order, EBG SSX- 154, 1 GΩ 30 Resistors, maximum 33 kv each in operation

18 Beginnings of Resistor String Assembly

19 Resistor String ConnecAons To Tube

20 Latest Status Photo

21 Charging System Challenges Must eliminate the electric motor minimal magneac materials allowed inside the tank, no stray magneac fields. The electric motor is too large it would require a large diameter tank We are proposing to use a Hydraulic Motor, Variable Speed up to ~900 RPM. The motor needs to move, to maintain chain tension.

22 Other Details There will be no acave voltage control Pelletron stability is typically 1 x 10-4 Voltage readout will use the column current We have the capability to cross check at 200 kv using a commercial power supply A solenoidal field will be put in place by an external magnet coil surrounding the tank which will be stainless steel.

23 Thank You! QuesAons??

24 Neutron β- decay β (electron) spectrum from 0 to 782 kev (b) n p e - ν e 0 (UCNA experiment)

25 Energy Reconstruction In beta-decay experiments, beta energy calibration is critical element of the error budget! Typically established with conversion sources UCNA: Source port (conversion sources placed here) Beta particle s detected here and energy measured Neutron decay volume

26 Calibration Accomplished at present with conversion line sources: mg/cm 2 mylar foils - Inserted in source port - K capture lines: Cd: Ce: m In: kev (& β w/endpt 1989 kev) 113 Sn: Sr: Bi: 481.7, Bi 139 Ce Red: data; Blue: MC (<% agreement)

27 Problems Calibration points not distributed evenly over beta energy spectrum Foil backing produces perturbations of electron spectrum Solution: use external, tunable electron beam (very low rate, ~100 Hz), coupled by magnetic field to experiment

28 An external electron beam Magnetic fields in spectrometer: 1 T Guiding fields for electron gun:.05 to 0.01 T electron gun: 50 kev to 1 MeV 10 4 electrons/s pulsed (few ns width), 10 khz rate We expect electrons to spiral around magnetic field, and increasing field will create a range of pitch angles Use arrival time to determine pitch angle!