Intense Diagnostic Neutral Beam For Burning Plasmas

1. Intense Diagnostic Neutral Beam For Burning Plasmas Challenges for ITER and Opportunities for KSTAR Jaeyoung Park Glen Wurden and MFE team Los Alamos National Laboratory US-Korea workshop, Sad Diego, May 19, 2004 Presented at the US ITER Forum, Univ.. of Maryland, May 8, 2003

2. Why IDNB? • Upcoming burning plasma experiments (ITER or FIRE) • Intense diagnostic neutral beam (IDNB):Critical baseline diagnostics for burning plasma experiments. • CHarge Exchange Recombination Spectroscopy (CHERS): ion temperature profile, impurity and helium ash measurements and fast alpha distribution. • Motional Stark Effect (MSE): current profile (q-profile). • Current technology on diagnostic neutral beam: unlikely to work on burning plasmas due to beam penetration, increased background noise -> low S/N. • Intense (~ 100 A/cm2) pulsed beam: better S/N. • LANL has hardware, history and expertise (since 90s) and personnel for pulsed IDNB source R&D.

3. Existing IDNB Hardware at LANL

4. Conventional DNB in burning plasmas? How well will it work? • Burning plasmas: higher electron density and larger plasma dimension --> beam penetration problem • Visible background bremsstrahlung: main source of noise and increase with radius and ne2 (while CHERS signal increase with ne) • Increasing beam intensity: very costly in CW beam. • Proposed ITER heating beam: H- based at 500 keV vs. ~125 keV for optimal beam energy for CHERS (need for DNB)

5. Bremsstrahlung vs. CER signal levels for CW beam- Low S/N ratio especially in the core region From ITER data base: Te ~ 20-30 keV flat Ne ~ 1x1014 cm-3 Beam energy = 125 keV/AMU Beam current of 40 A (CW) Beam area of 20 cm x 20 cm * Full-sized ITER Calculations by Dan Thomas, 1997 Varenna Workshop

6. Pulsed Ion Diode Neutral Beam (IDNB) Dan Thomas (GA) ran a comparison of CW and Pulsed DNB systems for the original ITER (Varenna 1997 Workshop) • Since energy is fixed, consider increasing current. • Magnetically Insulated Diode (MID) technologies can be used to create intense, pulsed beams at the requisite energy. • S/N improved by : • synchronous gating on detection system. • comparable CER and VB signals require smaller dynamic range from detection system. • Assumptions:CW beam • beam diameter = .2m x .2m • initial beam intensity = 1.0 x 103 A/m2 • Assumptions: pulsed beam • beam diameter = .2m x .2m • initial beam intensity = 1.0 x 106 A/m2 • pulse length = 1 ms • gate time = 2 ms • pulses per second = 30 (300)

7. Pulsed IDNB yields much larger signals* and could work in the core region * Full-sized ITER Calculations by Dan Thomas, 1997 Varenna Workshop

8. LANL IDNB Proposal • Technical approach • Intense ion beam source: Magnetically Insulated Diode (MID) • beam extraction over Child-Langmuir (CL) limit (~ 100 times) • Plasma anode: clean beam with long lifetime • Repetitive pulse operation: short pulses (1-2 ms) with high rep-rate (~ 30 Hz) • - improve S/N ratio with low cost. • Optimal beam energy: @ 125 keV/amu for CHERS. Independent from neutral heating beam. • Potential show stoppers • Beam divergence: 1˚ or less divergence required. Not yet proven with MID with plasma anode at high beam extraction. • Lifetime issue: 10,000 shots or more. May not be compatible with high beam extraction (~ 100 times CL limit), high power (~ 4 GW peak power), low beam divergence, etc. • Repetition rate: gas handling and cooling requirement.

9. B Magnetically insulated diode (MID) basic Electron sheath • Transverse magnetic fields in A-K gap • provide insulation and charge neutralization • Critical magnetic field (B*): required B-field for electron sheath = A-K gap • B* ~ 1.3 kG for 1.5 cm gap @ 250 kV. • If B >>B* or B <<B*: jion limited by space charge • jion ~ 2A/ cm2 for D0 ion. • When B ~ B*: ion current enhancement over CL limit • required current density: > 100A/ cm2 for D0 ion. • enhancement factor of ~ 100 was obtained (by Ueda et al. in 1993) for H0 ion beam. • Beam extraction will be done in the cathode opening Electrons Ions Cathode Anode Plasma

10. IDNB ITER- relevant parameters Critical issue  Critical issue 

11. Opportunities for KSTAR • In relation to ITER • Beam divergence, gas handling and repetition rate, lifetime and reliability - all critical issues for IDNB performance • KSTAR is a logical choice for IDNB demonstration and deployment • Successful operation of IDNB ensures the critical diagnostic capability for ITER • Specific to KSTAR • High S/N ratio and excellent spatial resolution • Diagnostic flexibility (independent of NBI) • Low power consumption (100 kW@ 30 Hz) and small footprint

12. Project scope and expected schedule • IDNB R&D (2-3 years) - LANL lead • FY 06 funding requested • MID operation and performance optimization • - High beam extraction (~ 100 x CL limit) • - Low beam divergence (5-10 mrad) • - Lifetime (~ 100,000 shots) • - Optimize the repetition rate (10 - 100 Hz) • Design tool for MID system • - 2D fluid + PIC simulation • Deployment and Demonstration (2-3 years) - KSTAR lead • Prototype construction and installation • - Beam neutralization (gas handling and pumping requirement) specific to KSTAR • DNB capability to KSTAR • IDNB performance demonstration for ITER

13. Proposal Title:Intense Diagnostic Neutral Beam For Burning Plasmas Pulsed Ion Source - Magnetically Insulated Diode • Proposal Objective: • FESAC panel on “A Burning Plasma Program Strategy to Advance Fusion Energy”: 2nd highest priority “ to develop enabling technology that supports the burning plasma research and positions the US to more effectively pursue burning plasma research” • The highest priority for US contributions to the ITER project: “baseline diagnostics, plasma control, remote research tools, etc.” • Intense diagnostic neutral bea (IDNB): Critical baseline diagnostics for CHERS and MSE - ion temperature profile, impurity and helium ash measurements, fast alpha distribution., and q profile. • Intense (~ 50 A/cm2), pulsed beam: better S/N and cost efficient. • LANL has hardware, history & expertise (since 90s) and personnel for pulsed IDNB source R&D. Expected Cost and Schedule: Task 1: 24 month effort headed up by LANL - P24 (outside collaboration on modeling) ~$1.2 M/yr Task 2: 24 month effort headed up by LANL - P24 (collaboration with major fusion facility) ~ $1.2M/yr Total: $4.8M over 48 months Deliverables: Task 1&2: Technical reports on bulleted items and a numerical design tool for IDNB MID. Task 2: Prototype intense diagnostic neutral beam for deployment. Contact Information: • Proposed Technical Approach: • Intense ion beam source: magnetically insulated diode (MID) with anode plasma for clean, intense (~ 50 A/cm2) neutral beam • Repetitive pulse operation: short pulses (1-2 ms) with high rep-rate (~ 30 Hz) to improve S/N ratio with low cost. • Optimal beam energy of 125 keV/amu for CHERS and MSE. • Low beam divergence: 1˚ divergence with modified electrodes and additional electric quadrupole beam shaping. • Task 1: Characterization and optimization of MID • Operation MID facility (CHAMP) at LANL • High beam extraction (50-100 times Child-Langmuir limit) • Modeling of MID (two-fluid and PIC simulation). • Task 2: Deployment of prototype diagnostic beam • Parallel beam extraction with electrode modification. • Efficient neutralization and high rep-rate • Deployment ready at major fusion facility in 4 years Dr. Jaeyoung Park and Dr. Glen Wurden Plasma Physics Group (P-24), MS E-526 Los Alamos National Laboratory, Los Alamos, NM 87545 Tel) 505-667-8013, e-mail) jypark@lanl.gov and wurden@lanl.gov