# Presentation: 365154

## Heating Systems Issues, Status, and Plans*

- David Swain
-  Oak Ridge National Laboratory, Oak Ridge, TN, USA
- FIRE Engineering Meeting
- PPPL
- June 24, 2003

- * This research was sponsored by the Office of Fusion Energy, U. S. Department of Energy, under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory managed by UT-Battelle.

## Summary of status and work to do (from Nov. Eng. mtg)  with comments on status at this meeting

- Ion cyclotron:
- Reasonable shape for heating
- Current drive *marginally *OK – need to revise requirements, obtain self-consistent solutions, do design study with 4 straps/port* *
*Still have requirements issues (see next VGs)*
*Looked at 4 straps/port  but it doesn’t look very attractive if antenna is contained in the confines of in the port*
*However, 4-strap “keyhole” antenna looks promising (discussion later)*
- Lower hybrid:
- Reasonable shape for heating and current drive
- Need to check scenarios for consistency, review CD calculations, compare with more detailed computations
*I think we’re in good shape here; primarily a physics issue - Kessel?*

## Summary and comments (cont.)

- Electron cyclotron (for NTM stabilization)
- May be large problem in source availability for high frequency (≥ 170 GHz)
- How aggressive do we want to be in our assumptions?
- Need definition of requirements, operating scenarios
- Determine frequency (operating range in B0, r/a), power required
*Chose 170 GHz *
*Power requirement is still a question.  - Need to be realistic (170 GHz system will be mucho dinero per watt)*
- Begin conceptual design
*Very pre-conceptual design, invoking launcher designs for ITER, putting in same port as LH launchers*
- Need to do thermal and stress analysis (mainly IC and LH)
- Need Prad, Pfusion for different operating scenarios
- Need** B**(t) and heat loads for disruption scenarios
- Manpower and funding are limiting factors
*No thermal or stress analysis has been done.*
- Reassess port allocations *vis a vis* H & CD system needs.
*Port allocation (Ken Young 1/2003) shows 4 ports for ICRF (in a row), two more ports for LH/EC. Looks OK to me. *

## Issues from Meade outline

- ICRH
- 	Frequency range (*my addition*)
- 	FWCD 4 strap option concept – (future work?)
- 	Generic port design ?
- LHCD –
- 	Availability of sources
- 	Launcher feasibility
- ECCD
- 	Frequency, source availability
- 	Launcher geometry
- Engineering and Physics Issues are tied together

## ICRH Frequency Wish List is not compatible with present antenna

- Desired frequencies and modes of operation –
- Heat ions
- 10 T –> 100 MHz 2nd Harmonic T
- 6.5 - 7 T  –> ≈ 100 MHz 2nd harmonic D (with maybe H minority)
- Drive current
- 10 T –> 115 MHz just below 2nd harmonic D resonance, hits 2nd harm T at r ≈ -a/2. Get some absorption by T, but CD requirement (< 300 kA) met
- 6.5 T –> 75 MHz same scenario as above
- 7.0 T –>  80 MHz
- ITB Formation (minority ion CD at r/a ≈ 0.5, both high and low-field side)
- 10 T –> 115 MHz and 88 MHz  He3 or 2T resonance
- 6.5 T –> 75 MHz (He3 or 2T resonance) and 88 MHz (H resonance)
- 7.0 T –> 80 MHz (He3 or 2T resonance) and 94 MHz (H resonance)
- Bottom line: Need 75 to 115 MHz frequency range to cover all bases.

## Present antenna design is simple, reliable but has a limited tuning range

- Antenna characteristics:
- Two current straps
- Straps grounded at each end (“violin” antenna)
-  good mechanical strength
- Each strap fed by 2 coax feeders
- Driven out of phase
- Optimized for ~100 MHz
- Low-voltage operation near optimal frequency
- Limited frequency range

- Antenna seen from plasma

- Side cut

## Can’t fulfill all the desirables with present antenna design

- Extending frequency range will require different antenna design
- Can we operate with less frequency range?
- Do we need 115 MHz operation?
- Can we use 7.0 T instead of 6.5 T?

- Resonances (R) for 6.5 and 10 T

- Antenna power for 35 kV max vs. freq.

- Max. V on rf system vs. freq

## ICRF status for PVR

- We need to EITHER
- Reduce requirements
- Forget about 115 MHz CD OR
- Operate at 7 T instead of 6.5 T for AT modes
- OR start on new antenna design.
- Will do some quick looks at different electrical configurations with broader frequency response between now and PVR.
- Aside from that, electrical operating characteristics are fairly well-defined and should meet the mission.
- Disruption effects not analyzed
- No disruption analysis done, and none likely before PVR with limited resources
- However, antenna with current straps grounded at each end is intrinsically strong.
- Earlier analyses for high-field machines (CIT, BPX) indicated that antennas could be built to withstand disruptions, so we’ll rely on existence proof at PVR.

## Lower-frequency range option

- Giving up 115 MHz operation will allow operation at 75 MHz
- For this case, can deliver 20 MW over 72 to 100 MHz frequency range, *assuming* that everything in rf system can handle 35 kV

- Antenna power for 35 kV max vs. freq.

- Max. V on rf system vs. freq

## Capacitor-tuned option

- Wider frequency band, tunable over 75-115 MHz
- Capacitors in vacuum will require tuning remotely between shots - how?
- End of current strap is free, transmits disruption forces to capacitor - can it stand it?
- More real estate taken up by HV rf in vacuum, more chance for breakdown
- Less shielding
- Cost more

- Bottom line: About the *only *advantage is it will operate over wider freq. range

## For the future (FY04?)...

- Look at 4-strap “keyhole” antenna?
- More power per port
- Factor of 2 better CD efficiency
- Requires recess in vessel
- Mechanical design (vacuum seal, installation) may be difficult
- Look at broadband antenna in more detail?

## 30 MW lower hybrid system

- ~ 5 GHz needed to drive current in AT modes (must keep f > 2 fLH).

- Waveguide array for 5 GHz–
- Choose RF power flux ≈ 53 MW/m2,
- Need ≈ 0.57 m2 of WG area for 30 MW
-  Each waveguide opening is 5.7 cm high x 0.65 cm toroidally
- Need ≈ 1500 waveguides

*Thanks for help from Stefano Bernabei*

## LH launchers in two ports deliver 30 MW

- For each port, put array as shown.
- 96 toroidally x 8 poloidally.
- LH launcher contour must conform very closely to the plasma contour for good coupling. The taller the coupler, the greater the constraint on the plasma outer separatrix shape.
- Geometry flexibility precludes filling entire port with LH launcher, so need 2 ports for LH system.
- Good news:
- Can put EC launchers above and below LH antenna

## Source availability at 5 GHz is an issue, but solvable

- Is a 1 MW, long-pulse, source available at 5 GHz?
*Not exactly**. *
*But: *A 3.7 GHz, 750 kW, 1000 s klystron (TH2103 C) is presently available from Thales Electron Devices (in EU; was Thomson-CSF)
- Thales did a cost estimate for ITER in 1998:
- 64 to 72 klystrons at 5 GHz, 1 MW CW
- 16 to 18 High-voltage power supplies, each 80 kV/100A
- 64 to 72 RF amplifiers
- The result was an estimate of 1.15 €/W, *for the sources and HV supplies only. *(I don’t know if any R&D costs would have to be added).
- Requested info from CPI (US vendor), but no response so far.

## Electron cyclotron system

- Needs to be absorbed at particular r/a to stabilize NTMs
- Assume midplane launcher with steerable optics to aim launched power at particular location on (almost) vertical resonance surface
- r/a range that can be reached depends on location of resonance surface

- Need steerable launcher that can change direction in vertical and toroidal direction – launch waves so ≈ toroidal when reaching resonance region *if* good CD is needed.

## EC launcher – off-midplane, use similar to ITER upper launcher?

- ITER upper launcher
- Steerable mirrors. Beams reflected by four mirrors through a vertical slot at the front shield.
- Poloidal RF beam steering capability (± 5°)
- Accurate focussing of the RF power on the m = 2 and m = 3/2 plasma flux rational surfaces is obtained

- ITER midplane EC launcher

- ITER upper EC launcher

## Frequency of EC sources is significant issue

- Requirement:
-  Be able to reach r/a ≥ 0.6 to stabilize NTMs at rational q-surface locations
- Questions:
- How much power is needed?
- How much current must be driven?
- For what magnetic fields will NTM stabilization be needed?
- As B0 increases, required operating frequency increases.

- Gyrotron availability:
- US and Russian tubes at ≈ 1 MW level for f = 120 GHz
*Proposed* development of 170 GHz tubes for ITER (JA, US, RU)
- will require significant R&D effort
- 200+ GHz? Fuggedaboutit! (major development effort would be needed)

**NTM **
**control **
**range**

## Proposal for EC system design frequency (fm. Nov. mtg).

- Pick f = 170 GHz for design study
- Allows penetration to  r/a ≈ 0.6 at B0 = 7 T
- Allows penetration to r/a ≈ 0.25 at B0 = 6.5 T
- Compatible with ongoing EC source development work (we get it for free)
- Consider higher-frequency operation (and consequent development of higher-frequency source) as an upgrade that could be done
- after initial operation with 170 GHz
- or if it becomes evident it will be needed

## ECH power requirements and cost

- Cost info from ITER cost estimate:
- US has just completed a cost estimate for the ITER EC system
- 170 GHz
- 20 MW
- Long-pulse/CW system
- Cost estimate for sources + HV supplies is > $***x***/W (not counting R&D)
- Cost estimate for launchers, transmission lines, etc. is ≈ $(0.6 ***x***)/W
- (I could tell you what ***x*** is, but then I’d have to kill you)
- (But it’s a lot.)
- Issue: What is a realistic power?
- How much do we *need* to stabilize NTMs?
- How much can we *afford*?

## Stress and thermal analysis – needed by PVR?(from November Engineering Meeting)

- We need information to do the analyses:
- Normal operation scenarios:
- Prad(t) - radiated power (UV, soft x-rays) to midplane port
- Pfusion(t) - neutron flux at outer midplane
- Pulse length
- Disruptions:
**B**(t) in front of midplane port
- Power to wall from disruption
- Time is of the essence:
- We have funding and manpower limitations
- If we want serious engineering analysesby the PVR, then input needed by Jan.(?)
- Probably don’t have the resources(i.e., funding) to do much; will need to prioritize.