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Title: Experimental Study of Pellet Delivery to the ITER Inner Wall through a Curved Guide Tube at Steady-State Pressure

Abstract

Injection of solid hydrogen pellets from the magnetic high-field side will be the primary technique for depositing fuel particles into the core of International Thermonuclear Experimental Reactor (ITER) burning plasmas. This injection scheme will require the use of a curved guide tube to route the pellets from the acceleration device, under the divertor, and to the inside wall launch location. In an initial series of pellet tests in support of ITER, single 5.3-mm-diam cylindrical D2 pellets were shot through a mock-up of the planned ITER curved guide tube. Those data showed that the pellet speed had to be limited to ≈300 m/s for reliable delivery of intact pellets. Also, microwave cavity mass detectors located upstream and downstream of the test tube indicated that ≈10% of the pellet mass was lost in the guide tube at 300 m/s. The tube base pressure for that test series was ≈10-4 torr. However, for steady-state pellet fueling on ITER, the guide tube will operate at an elevated pressure due to the pellet erosion in the tube. Assuming the present design values for ITER pellet fueling rates/vacuum pumping and a 10% pellet mass loss during flight in the tube, calculations suggest a steadystate operating pressuremore » in the range of 10-20 torr. Thus, experiments to ascertain the pellet integrity and mass loss under these conditions have been carried out. Also, some limited test data were collected at a tube pressure of ≈100 torr. No significant detrimental effects have been observed at the higher tube pressures. The new test results are presented and compared to the baseline data previously reported.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [2];  [1];  [1]
  1. ORNL
  2. ITER International Team, Garching, Germany
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
930822
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: 21st IEEE/NPSS Symposium on Fusion Engineering, Knoxville, TN, USA, 20050926, 20050929
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; ACCELERATION; DESIGN; EXPERIMENTAL REACTORS; FUEL PARTICLES; GUIDE TUBES; HYDROGEN; PELLETS; PUMPING

Citation Formats

Combs, Stephen Kirk, Baylor, Larry R, Caughman, John B, Fehling, Dan T, Foust, Charles R, Maruyama, S., McGill, James M, and Rasmussen, David A. Experimental Study of Pellet Delivery to the ITER Inner Wall through a Curved Guide Tube at Steady-State Pressure. United States: N. p., 2006. Web.
Combs, Stephen Kirk, Baylor, Larry R, Caughman, John B, Fehling, Dan T, Foust, Charles R, Maruyama, S., McGill, James M, & Rasmussen, David A. Experimental Study of Pellet Delivery to the ITER Inner Wall through a Curved Guide Tube at Steady-State Pressure. United States.
Combs, Stephen Kirk, Baylor, Larry R, Caughman, John B, Fehling, Dan T, Foust, Charles R, Maruyama, S., McGill, James M, and Rasmussen, David A. Sun . "Experimental Study of Pellet Delivery to the ITER Inner Wall through a Curved Guide Tube at Steady-State Pressure". United States. doi:.
@article{osti_930822,
title = {Experimental Study of Pellet Delivery to the ITER Inner Wall through a Curved Guide Tube at Steady-State Pressure},
author = {Combs, Stephen Kirk and Baylor, Larry R and Caughman, John B and Fehling, Dan T and Foust, Charles R and Maruyama, S. and McGill, James M and Rasmussen, David A},
abstractNote = {Injection of solid hydrogen pellets from the magnetic high-field side will be the primary technique for depositing fuel particles into the core of International Thermonuclear Experimental Reactor (ITER) burning plasmas. This injection scheme will require the use of a curved guide tube to route the pellets from the acceleration device, under the divertor, and to the inside wall launch location. In an initial series of pellet tests in support of ITER, single 5.3-mm-diam cylindrical D2 pellets were shot through a mock-up of the planned ITER curved guide tube. Those data showed that the pellet speed had to be limited to ≈300 m/s for reliable delivery of intact pellets. Also, microwave cavity mass detectors located upstream and downstream of the test tube indicated that ≈10% of the pellet mass was lost in the guide tube at 300 m/s. The tube base pressure for that test series was ≈10-4 torr. However, for steady-state pellet fueling on ITER, the guide tube will operate at an elevated pressure due to the pellet erosion in the tube. Assuming the present design values for ITER pellet fueling rates/vacuum pumping and a 10% pellet mass loss during flight in the tube, calculations suggest a steadystate operating pressure in the range of 10-20 torr. Thus, experiments to ascertain the pellet integrity and mass loss under these conditions have been carried out. Also, some limited test data were collected at a tube pressure of ≈100 torr. No significant detrimental effects have been observed at the higher tube pressures. The new test results are presented and compared to the baseline data previously reported.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}

Conference:
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  • Two microwave cavity mass detectors have been used to measure the mass loss of deuterium (D{sub 2}) pellets transported through a curved guide tube. The test tube was a mock-up of the pellet injection guide tube for the proposed ITER experiment, which will be used to transport pellets, including deuterium-tritium (D-T), from the pellet acceleration device to the inner wall (or magnetic high-field side) of the large tokamak for pellet injection and core fueling of plasmas. An accurate estimate of the mass loss is particularly important for D-T injection, because the inventory of the radioactive isotope (T) for ITER ismore » limited and accountability and recycling will be crucial issues. In the laboratory, frozen cylindrical D{sub 2} pellets of nominal 5.3-mm diameter were shot through the stainless steel test tube ({approx_equal}10 m in length and 10-mm inside diameter), with each end equipped with a microwave cavity. As the pellet passes through each tuned microwave cavity, the peak output signal from the electronics is directly proportional to the pellet mass. An absolute calibration of the cavities, which can be problematic, is not needed for the nondestructive technique described here. Instead, a cross calibration of the two cavities with pellets of varying masses provides the relationship to determine mass loss more precisely than any other technique previously reported. In addition, the individual output signals from the cavities can be used to identify intact pellets (a single signal peak) or broken pellets (multiple signal peaks). For the pellet speed range tested in this study (100-500 m/s), the mass loss for intact pellets was directly dependent on the pellet speed, with {approx_equal}10% mass loss at 300 m/s. The microwave cavities and the associated electronics, as well as some basic theory, are described; calibration and experimental data are presented and discussed.« less
  • The use of curved guide tubes for transporting frozen hydrogen pellets offers great flexibility for pellet injection into plasma devices. While this technique has been previously employed, an increased interest in its applicability has been generated with the recent ASDEX Upgrade experimental data for magnetic high-field side (HFS) pellet injection. In these innovative experiments, the pellet penetration appeared to be significantly deeper than for the standard magnetic low-field side injection scheme, along with corresponding greater fueling efficiencies. Thus, some of the major experimental fusion devices are planning experiments with HFS pellet injection. Because of the complex geometries of experimental fusionmore » devices, installations with multiple curved guide tube sections will be required for HFS pellet injection. To more thoroughly understand and document the capability of curved guide tubes, an experimental study is under way at the Oak Ridge National Laboratory (ORNL). In particular, configurations and pellet parameters applicable for the DIII-D tokamak and the International Thermonuclear Experimental Reactor (ITER) were simulated in laboratory experiments. Initial test results with nominal 2.7- and 10-mm-diam deuterium pellets are presented and discussed.« less
  • Operational scenarios for the International Thermonuclear Experimental Reactor (ITER) steady-state and technology testing phases are identified by trade-offs among wall load, burn time, and divertor heat loads. Steady-state operation with Q {ge} 5 is limited to wall loads {ge}0.5 MW/m{sup 2} and injection powers {ge} 100 MW. Even at steady-state wall loads of 0.5 MW/m{sup 2}, the divertor heat loads are higher than predicted for the physics phase. For technology testing, hybrid operation (with simultaneous inductive and noninductive current drive) results in a wall load of 0.8 MW/m{sup 2}, with injection power of about 100 MW, and a burn timemore » of about 1200 s, with a divertor heat load similar to that of the physics phase. Significant uncertainty exists in our present understanding of the divertor conditions. Should conditions prove to be more favorable than assumed here, the operational windows would open considerably. For factor of {approx}3 reductions in predicted divertor loads, we show potential steady-state cases at wall loads of 0.8 MW/m{sup 2}, injection powers of about 130 MW, and Q near 7. With factors of {approx}1.5--2.5 reduction in the predicted divertor loads, hybrid technology testing could be accomplished with wall loads of 0.8 MW/m{sup 2} burn times of 1--3 h, and injection powers of 100--150 MW. 5 refs., 3 figs., 2 tabs.« less
  • High-pressure gas injection has been shown to be an effective disruption mitigation technique in the DIII-D tokamak, offering dramatic reductions in localized power deposition and forces to the internal components due to halo currents. To date, the gas (Ar, Ne, He, or H2) has been injected from the magnetic low-field side of the machine through closecoupled stainless steel tubes, with relatively high gas load per shot (up to 4000 torr-L in 10 ms). Another option for high-pressure gas injection in DIII-D is to utilize curved guide tubes similar to those presently used for magnetic high-field side pellet injection with exitmore » ports on the inner wall. To demonstrate the feasibility of this option, an experimental study with different tube diameters and configurations has been carried out in the laboratory. The test results indicate that sufficiently high gas flows can be delivered through the curved guide tubes as long as the tube bore is not too restrictive ( 7.5-mm diam). The experimental results are presented and discussed relative to the disruption mitigation experiments in DIII-D.« less