A new type of compact induction accelerator is under development at the Lawrence Livermore National Laboratory that promises to increase the average accelerating gradient by at least an order of magnitude over that of existing induction machines. The machine is based on the use of high gradient vacuum insulators, advanced dielectric materials and switches and is stimulated by the desire for compact flash x-ray radiography sources. Research describing an extreme variant of this technology aimed at proton therapy for cancer will be described. Progress in applying this technology to several applications will be reviewed.
The dielectric wall accelerator (DWA) is a compact pulsed power device where the pulse forming lines, switching, and vacuum wall are integrated into a single compact geometry. For this effort, we initiated a extensive compact pulsed power development program and have pursued the study of switching (gas, oil, laser induced surface flashover and photoconductive), dielectrics (ceramics and nanoparticle composites), pulse forming line topologies (asymmetric and symmetric Blumleins and zero integral pulse forming lines), and multilayered vacuum insulator (HGI) technology. Finally, we fabricated an accelerator cell for test on ETA-II (a 5.5 MeV, 2 kA, 70 ns pulsewidth electron beam accelerator). We review our past results and report on the progress of accelerator cell testing.
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During normal DARHT II I operation , the beam exiting the accelerator will he wcll characterized by its nominal de sign parameters of 20-MeV, 2000-Amperes, 2-psee pulse length , and 3 em-1m llllnornlaiized emitlance. Normal operation will have the heam delivered to a hcam dump via several DC magnets. A 2-way kicker magnet is used to deflect portions of the beam into the straight ahead beHmline leading to either a diagnostic heamline or to the converter target beamline. During start up and or beam development periods , the he am exiling the accelerator may have parameters outside the acceptable range of values for normal operation. The Enge beam line must accommodate this range of unacceptablc beam parameters, delivering the entire 80 Kilojoule of heam to the dump even though the energy, emittance, and/or match is outside the nominal design range.
THE UEAMLINEThe beamline system co nsi sts of four operationally distinct beam lines: I) the Bilge beamline, 2) the main dump beamline, 3) the diagnostic heal11linc, ami 4) the target beamline. These lines share some components and floor space within the DARHT huilding. The heamline considered here extends from the exit of the accelcrator , SOlllC 12 metcrs beforc the beginning of the shielding wall. Depending on the magnet settings, the heam from the accelerator is transported to the "Enge clump," a "tuning dump," kicked into a "diagnostic line," or kicked into the "transport line" with eventual delivery to the x ray converter target outside the shiel ding wall. The two dump beamlines and diagnostic bcamline arc constrained to lie within thc DARHT shielding wall. The be amlin e to the converter target penetrates the shielding wall and extends some 5.9 meters from the exit of that wall to the converter target. When ready to produce a radiograph we usc the 2�way kicker Lo cancel the DC rield or the kicker bias dipole allowing a scction of the beam to pass undefleeted into the target beamline. We repeat this up to four times during the 2-�lsec-beaTll duration, producing up -----------_. to four beam pulses separated by 600 ns. The x-rays are produced when the electrons arc tightl y focused by the final focusing lens to the earrect position on a Bremsstrahlung target.
2.TH]�REAMThe beam delivered hy the DARI-IT accelerator consists of a 2-�lsec-beal11 body of 20-McV electrons, This is preceded by the "heam head ," a O.4-Jlscc dribble of electrons X-20 MeV with current i ncreasing from .1 ta 2 kA. If a beam head cleanup section is used
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