Install a 20 MW ICRF system in the first operational phase (AFP) on ITER

Dear colleagues,

Below you find in plain text the petition on the ICRF system in the first operational phase (AFP) for ITER.
A formatted pdf version can be found here: https://shorturl.at/ghoVX 

If you support this petition, may we kindly ask you to perform the following steps:

- Click on the "Sign" or the "Show the sign form" button (on the right-hand side of this petition page) and enter your name, city, country and email address;
- Please add the affiliation (including city and country) of your Laboratory/Institute/Company in the corresponding field;
- Your signature will be explicity treated as a personal one, i.e. it does not necessarily represent the opinion of the direction of your laboratory.
For this reason, please add "Yes" in the field "I confirm that I sign in my personal name (Yes)";
- (Optional) You can still add further personal comments in the field "I'm signing because...";
- If you do not want your signature to be visibile online, then click on the radiobutton "No";
- Choose "Yes" or "No" for the next radiobutton, depending on your wish to receive updates;
- Choose "Yes" to confirm that you are at least sixteen years old and accept the privacy policy.

As a final step, please confirm your signature in the email that you will receive shortly afterwards. This will ensure that the list of signatures is verified.

=== Start of the petition text ===

September 6, 2023

The international community of ICRF experts and fusion researchers is drawing the attention of the IO and the other ITER organisations on the following aspects:

[I].   The importance of ICRF heating in D-T operation has been experimentally validated on both JET and TFTR [1-6]. A powerful ICRF system will contribute to the successful realization of the main goal of ITER, i.e. demonstrating Q = 10 at 500 MW fusion power. It adds operational flexibility and enlarges the parameter space to reach the necessary high ion temperatures in the ramp-up phase and to provide early alpha particles in the high performance flat top phase. It also offers the possibility to generate fast particles to control the core microturbulence and to improve confinement [7, 8]. We emphasize that experiments in medium size machines have shown that it is difficult to reach high central ion temperatures with dominant electron heating alone [9]. 

[II].  There are also numerous technical advantages for the ITER program in implementing a 20 MW ICRF system already in the Augmented First Plasma (AFP) phase. To mention only a few:               

• i.   A 20 MW ICRF system is a much better guarantee to properly assess and reduce to negligible  levels the ICRF-specific tungsten (W) sputtering than a 5 MW system;             
• ii.   A 20 MW ICRF power will enable commissioning of the ITER ICRF system at full voltages   and currents in the ITER tokamak environment under relevant conditions in AFP;            
• iii.   It will enable early preparations for high power D-T scenarios;            
• iv.   It will allow exploring MHD activities triggered and/or controlled by ICRF generated fast ions;             
• v.   It will allow to study (and to further optimise) energetic particle diagnostics in the AFP, as recommended by the ITPA-EP group [10]. 

[III].  A delayed installation of 20 MW ICRF power post AFP is likely to trigger a series of difficulties for the use of 20 MW ICRF in ITER’s high power D-T phase. There is no guarantee that industry will maintain the specialised competences and associated technological know-how between the AFP and D-T phases on ITER, in particular to produce the high power continuous-wave end-stage tubes required for the ITER ICRF system. Consequently, long delays can be anticipated to re-establish the lost technological expertise post AFP, if a 20 MW ICRF system is not implemented already in the AFP. Moreover, it could well be a challenging task to install additional transmission lines and RF sources in later phases of the ITER project, due to the extra complexities of integrating new elements once the construction of a nuclear facility is concluded. 

[IV]. ICRF has made continuous progress in increasing coupling, while at the same time minimizing impurity release. In particular, the compatibility of ICRF for plasma heating in presence of a full-W wall has been convincingly demonstrated experimentally on ASDEX Upgrade (AUG) in recent years, both by recent developments in antenna design and by optimizing the antenna electrical settings [11, 12]. These important achievements are further supported by the successful ICRF operation on the Alcator C-Mod tokamak with a molybdenum first wall [13, 14]. The experimental results have been extensively validated by state-of-the-art modelling of underlying processes such as the role of near electric fields, RF sheaths, local gas injection, etc. thereby allowing to extrapolate to future experiments, including ITER. We stress that the ITER ICRF system will benefit from an unprecedented capability for suppressing impurity generating fields due its design with four toroidal columns of straps and its electrical settings flexibility [11, 12, 15, 16]. Modelling confirms that with proper electrical settings low sputtering can be realized by the ITER ICRF system at full 20 MW power by virtue of the versatility of its design [16].  Furthermore, recent studies show that coupling of up to 20 MW of ICRF power is possible with one antenna in a broad range of relevant plasma conditions [16]. This is in particular owing to the ICRF local midplane gas injection system that is now included in the ITER baseline [17].

Conclusion:

Delaying the decision to install a 20 MW ICRF system at ITER until after AFP poses great risks to its availability in the high power D-T phase of ITER and thus to the success of the main goal of the ITER project demonstrating Q = 10 at 500 MW fusion power. It also seriously limits testing of all relevant heating systems for next step fusion reactors, in particular the new ICRF antenna design reducing ICRF-specific impurity generation to negligible levels. We emphasize that the ITER project is shared between several international partners relying on the development and use of a powerful ICRF system in ITER to provide input to their national reactor-oriented programmes.

For all the reasons mentioned above, the international community of ICRF experts and fusion researchers undersigned below strongly recommends to the ITER organizations the installation of a full power 20 MW ICRF system already in the ITER AFP phase.

References:

[1]    J. Jacquinot, et al., "Deuterium-tritium operation in magnetic confinement experiments: results and underlying physics", Plasma Phys. Control. Fusion 41 (1999) A13; https://doi.org/10.1088/0741-3335/41/3A/002

[2]    D. F. H. Start et al., "D-T Fusion with Ion Cyclotron Resonance Heating in the JET Tokamak", Phys. Rev. Lett. 80 (1998) 4681; https://doi.org/10.1103/PhysRevLett.80.4681

[3]    D. F. H. Start et al., "ICRF results in D-T plasmas in JET and TFTR and implications for ITER", Plasma Phys. Control. Fusion 40 (1998) A87; https://doi.org/10.1088/0741-3335/40/8A/008

[4]    P. Jacquet, et al., "ICRH operations and experiments during the JET-ILW tritium and DTE2 campaigns", AIP Conference Proceedings 2984 (2023) 030003; https://doi.org/10.1063/5.0162645

[5]    E. Lerche, et al., “Fundamental ICRF heating of deuterium ions in JET-DTE2”, AIP Conference Proceedings 2984 (2023) 030005; https://doi.org/10.1063/5.0162554

[6]    Ye.O. Kazakov, J. Ongena et al., "Progress with applications of three-ion ICRF scenarios for fusion research: a review", AIP Conference Proceedings 2984 (2023) 020001; https://doi.org/10.1063/5.0162571

[7]    J. Citrin and P. Mantica, "Overview of tokamak turbulence stabilization by fast ions", Plasma Phys. Control. Fusion 65 (2023) 033001; https://doi.org/10.1088/1361-6587/acab2b

[8]    S. Mazzi, et al., "Enhanced performance in fusion plasmas through turbulence suppression by megaelectronvolt ions", Nature Physics 18 (2022) 776; https://doi.org/10.1038/s41567-022-01626-8

[9]    M.N.A. Beurskens, et al., "Confinement in electron heated plasmas in Wendelstein 7-X and ASDEX Upgrade; the necessity to control turbulent transport", Nucl. Fusion 62 (2022) 016015; https://doi.org/10.1088/1741-4326/ac36f1

[10]  ITPA-EP Group, "Recommendations of the ITPA-EP group on the proposed ITER re-baselining", 29th Meeting of ITPA Topical Group on Energetic Particle Physics, 23-25 May 2023, ORNL, https://indico.iter.org/event/65/contributions/1524/attachments/844/1445/Salewski2023ITPAep29decisionsactions.pptx

[11]   V. Bobkov, et al., "First results with 3-strap ICRF antennas in ASDEX Upgrade", Nucl. Fusion 56 (2016) 084001; https://doi.org/10.1088/0029-5515/56/8/084001

[12]   V. Bobkov, et al., "Impact of ICRF on the scrape-off layer and on plasma wall interactions: From present experiments to fusion reactor", Nuclear Materials and Energy 18 (2019) 131; https://doi.org/10.1016/j.nme.2018.11.017

[13]   Y. Lin, et al, "Physics basis for the ICRF system of the SPARC tokamak", J. Plasma Phys. 86 (2020) 865860506; https://doi.org/10.1017/S0022377820001269

[14]   R. Diab, et al., "Characterization of RF-enhanced potentials with varying antenna power ratio on Alcator C-Mod", 64th Meeting of the APS Division of Plasma Physics, Spokane, Washington, USA (2022), https://meetings.aps.org/Meeting/DPP22/Session/UO03.7

[15]   A. Messiaen and V. Maquet, "Coaxial and surface mode excitation by an ICRF antenna in large machines like DEMO and ITER", Nucl. Fusion 60 (2020) 076014; https://doi.org/10.1088/1741-4326/ab8d05

[16]   ITER Organization, Ion Cyclotron Section, "Coupling studies for the ITER ICRF system and its compatibility with high power operation under high-Z environment", ITER_D_9FHA67; https://user.iter.org/default.aspx?uid=9FHA67

[17]  W. Zhang, et al., “Parametric study of midplane gas puffing to maximize ICRF power coupling in ITER”, Nucl. Fusion 63 (2023) 036008; https://doi.org/10.1088/1741-4326/acb4ad 

Bertrand Beaumont, Volodymyr Bobkov, Yevgen Kazakov, Jef Ongena    Contact the author of the petition