Design of a 10 MeV, 1000 kW average power electron-beam accelerator for wastewater treatment applications

We present the technical and engineering design of a medium energy (10 MeV) and high average power (1000 kW) electron-beam accelerator intended for irradiation treatment of high-volume industrial and municipal wastewater. The accelerator uses a ${\mathrm{Nb}}_3\mathrm{Sn}$ superconducting radio-frequency (SRF) cavity for producing the high average beam power with $>90\%$ rf to beam efficiency. The design of the accelerator is tailored for industrial settings by adopting the cryocooler conduction-cooling technique for the SRF cavity instead of a conventional liquid helium bath cryosystem. The technical design is supplemented with a detailed analysis of capital and operating cost of the accelerator. The designed accelerator can treat up to 12 million gallons per day of wastewater, requires capital of $\sim \$8\mathrm{M}$ for construction, and has $\sim 13.5¢/\mathrm{ton}/\mathrm{kGy}$ in material processing cost.

Figure 1

$e$-beam accelerator components and layout. The overall size is $\sim 4\mathrm{m}$ long (end to end), $\sim 2\mathrm{m}$ wide, and $\sim 2\mathrm{m}$ tall.

Figure 2

The rf gun design parameters (left) and components (right).

Figure 3

Injector cavity design and operating parameters.

Figure 4

Beam distribution at the time of emission from the cathode and $\beta \gamma$ beam distribution in the middle of the injector gap.

Figure 5

Beam characteristics at the exit of the injector cavity. Top three plots: charge distribution vs energy and phase and current vs radius. Bottom three plots: phase vs energy, $x^{\prime }-x$ phase-space distribution, and $x-y$ plot at the injector exit.

Figure 6

Surface magnetic field produced by the solenoid (dimensions in meters).

Figure 7

Geometrical dimensions of the five-cell cavity rf volume. All dimensions are in millimeters.

Figure 8

Axial electric and surface magnetic field for the five-cell cavity at 10 MV voltage gain.

Figure 9

Five-cell cavity coupler-side end-group (a) enlarged view of coupler antenna tip, (b) dimensions of power coupler port and antenna position, and (c) electric field distribution in the cavity end group.

Figure 10

The three sets of EM fields used for michelle simulation of beam transport through the accelerator.

Figure 11

Beam transport through the five-cell SRF cavity: cell-by-cell bunch energy gain (left) and output beam parameters (right).

Figure 12

Beam characteristics and particle distributions at the exit of the five-cell cavity. Top plots: charge distribution vs energy and phase and current vs radius; bottom plots: phase vs energy, $x^{\prime }-x$ phase-space distribution, and $x-y$ beam spot size.

Figure 13

Impedances of (a) monopole HOMs and (b) dipole HOMs as a function of the mode frequency.

Figure 14

(a) Monopole HOM voltage and (b) dipole HOM voltage for the five-cell 650 MHz cavity.

Figure 15

Configuration and dimensions of the coupler ceramic window.

Figure 16

Cut view of configuration of 650 MHz, 500 kW, cw coupler.

Figure 17

Thermal analysis of the fundamental power coupler at 500 kW forward propagation (a) geometry and material properties and (b) steady-state temperature map.

Figure 18

(a) Vacuum side coupler sections analyzed for multipacting and (b) representative observation of multipacting and mitigation by applying dc bias. A similar plot is obtained for each section but not shown here to avoid clutter.

Figure 19

Cross-section view of the SRF cryomodule assembly. The end-to-end length is 1.95 m.

Figure 20

(a) Rendering of the five-cell cavity with $e$-beam welded cooling rings and (b) thermal links attached to the five-cell cavity by bolting.

Figure 21

Steady-state cavity temperature profile for 10 MeV, 100 mA operation (a) surface temperature map and (b) line graph along the cavity wall profile.

Figure 22

(a) Thermal shield exploded view showing how the shield panels and components are assembled. (b) Thermal shield temperature distribution during steady-state operation of the accelerator.

Figure 23

(a) The exploded view of the magnetic shield shows that it is composed of two halves, a top lid, and a bottom tub which are attached at a small interface flange during assembly. Chimneys are attached around each feedthrough to improve shielding. (b) Magnetic flux density displayed along the surface of the SRF cavity, in the case where the beam line is oriented toward North.

Figure 24

(a) CAD view of the cryostat vacuum vessel made of a large tub and a lid that are sealed together. (b) Distribution of von Mises stresses due to vacuum loading (displacements exaggerated 130-fold). (c) The von Mises stresses in the vacuum vessel when the first buckling failure mode occurs on one side of the lid. The loading required for this mode of failure is approximately 64 times larger than under normal loading.

Figure 25

CAD views of (a) the beam line assembly prior to installation in the cryocooler and (b) the beam line assembly suspended on the lid of the vacuum vessel.

Figure 26

Cryomodule assembly sequence. (a) Installation of the beam line assembly and cryocoolers on the vacuum vessel lid. (b) Installation of the thermal shield. (c) Installation of the bottom half of the magnetic shield inside the vacuum vessel tub and (d) fully assembled cryomodule.

Figure 27

Power flow diagram for the 10 MeV, 1 MW SRF accelerator.

Figure 28

Cost breakdown of the SRF cryomodule assembly.